Tyre having a regroovable tread

Abstract

The invention relates to a tyre (1) which can be regrooved at least once and the tread of which comprises at least one regroovable groove (3). According to the invention, after regrooving, the height (HR) of the at least one regrooved groove (3) is greater than or equal to 70% of the height of the groove (HN3) of the at least one regroovable groove of the tyre when new. The elastomeric blend forming the outer surface of the tread comprises a quantity of plasticiser(s) of less than 15 phr and the degree of linearity of the complex dynamic shear modulus, G*, measured at a temperature of 23°C according to standard ASTM D 5992-96, of the elastomeric blend is greater than 0.55.

Description

TYRE COMPRISING A STRIP OF REGROWABLE BEARING

[0001] The present invention relates to a tire, with a radial carcass reinforcement and more particularly a tire intended to equip vehicles carrying heavy loads, such as, for example, trucks, tractors, trailers or road buses.

[0002] Generally speaking, in heavy goods vehicle type tires, the carcass reinforcement is anchored on both sides in the bead area and is surmounted radially by a crown reinforcement consisting of at least two layers, superimposed and formed of parallel wires or cables in each layer and crossed from one layer to the next, making angles of between 10° and 45° with the circumferential direction. Said working layers, forming the working reinforcement, may also be covered with at least one so-called protective layer and formed of advantageously metallic and extensible reinforcement elements, called elastic.It may also comprise a layer of low-extensibility metal wires or cables forming an angle of between 45° and 90° with the circumferential direction, this ply, called the triangulation ply, being radially located between the carcass reinforcement and the first crown ply, called the working ply, formed of parallel wires or cables having angles at most equal to 45° in absolute value. The triangulation ply forms with at least said working ply a triangulated reinforcement, which, under the various stresses to which it is subjected, exhibits little deformation, the triangulation ply having the essential role of absorbing the transverse compression forces to which all the reinforcing elements are subjected in the area of ​​the crown of the tire.

[0003] Cables are said to be inextensible when, under a tensile force equal to 10% of the breaking force, the said cables exhibit a relative elongation of at most 0.2%.

[0004] Cables are said to be elastic when said cables exhibit, under a tensile force equal to the breaking load, a relative elongation at least equal to 3% with a maximum tangent modulus less than 150 GPa.

[0005] The circumferential direction of the tire, or longitudinal direction, is the direction tangent to the periphery of the tire and defined by the rolling direction of the tire.

[0006] The tire's axis of rotation is the axis around which it rotates during normal use.

[0007] A radial or meridian plane is a plane that contains the tire's axis of rotation.

[0008] The circumferential median plane, or equatorial plane, is a plane perpendicular to the tire's axis of rotation and which divides the tire into two halves.

[0009] The transverse or axial direction of the tire is parallel to the tire's axis of rotation. An axial distance is measured along the axial direction. The expression "axially inner to, respectively axially outer to" means "whose axial distance measured from the equatorial plane is less than, respectively greater than".

[0010] The radial direction is a direction intersecting the axis of rotation of the tire and perpendicular to it. A radial distance is measured in the radial direction. The expression "radially inside, respectively radially outside" means "whose radial distance measured from the axis of rotation of the tire is less than, respectively greater than".

[0011] Radially outside the crown reinforcement is the tread, usually made of polymeric materials intended to come into contact with the ground in the contact area between the ground and the tire.

[0012] It is known to provide the tread, that is to say the part of the tire intended to come into contact with the ground when rolling and to wear during rolling, with a sculpture formed of raised elements delimited by cutouts such as grooves, whether circumferential, transverse or oblique in orientation. The objective of such a sculpture is to give the tread good driving performance on dry roads and on water-covered roads, particularly in wet weather.

[0013] To improve the performance of treads without, however, excessively lowering the shear rigidities of said strips, it is known to form on the rolling surface a plurality of transversely or obliquely oriented edges in order to cut the film of water on a roadway to ensure good contact between the tread and the roadway. One means of obtaining such edges consists of providing the strip with a plurality of cutouts, these cutouts having the form of grooves or the form of incisions. In the present application, incisions are distinguished from grooves in that the incisions have a width appropriate to allow at least partial contact during rolling between the facing walls delimiting these incisions and in particular during the passage into contact with the ground, which cannot be the case for grooves under normal conditions of use of the tire.

[0014] For the purposes of the invention, a longitudinally oriented cutout is a cutout whose mean plane of at least part of the walls of said cutout forms an angle with a longitudinal plane of less than 10°. This angle formed with a longitudinal plane may be oriented in one direction or the other relative to said longitudinal plane. A longitudinally oriented cutout may also be a cutout whose walls undulate or zigzag around a mean plane as just described.

[0015] For the purposes of the invention, a transversely oriented cutout is a cutout whose mean plane of at least part of the walls of said cutout forms an angle with a radial plane of less than 35°. This angle formed with a radial plane may be oriented in one direction or the other relative to said radial plane. A transversely oriented cutout may also be a cutout whose walls undulate or zigzag around a mean plane as just described.

[0016] For the purposes of the invention, an obliquely oriented cutout is a cutout in which the mean plane of at least part of the walls of said cutout forms an angle with a radial plane of between 35° and 80°. This angle formed with a radial plane may be oriented in one direction or the other relative to said radial plane. A cutout of oblique orientation can still be a cutout whose walls undulate or zigzag around a mean plane as just described.

[0017] When making the grooves and more particularly when making the circumferential grooves which extend over the periphery of the tire, a phenomenon of deformation of the crown reinforcement occurs. These circumferential grooves which are obtained by molding during the curing of the tire lead to a local deformation of the crown reinforcement. The inventors interpret this deformation of the crown reinforcement as a result of uncontrolled creep of the elastomeric materials at the level of said grooves during the molding and curing of said tire. This results in a deformation in the radial direction of the constituent layers of the crown reinforcement located near said cutouts.These deformations lead, during use of the tires, to a deterioration in the tire's performance in terms of wear and in particular regularity of wear, the thickness of the mixture to be worn not being regular in the transverse direction of the tire.

[0018] To reduce or even eliminate this phenomenon, it is known to produce the semi-finished product that will constitute the surface of the tread with a prefiguration of the circumferential grooves. These semi-finished products are usually produced by extrusion, it is simple to provide a shape on which the future grooves are already partially drawn. The deformation of the material constituting these semi-finished products that occurs during molding, necessary to finalize the shape of the circumferential grooves, is then greatly reduced and it is thus possible to reduce or eliminate the risks of deforming the crown reinforcement of the tire.

[0019] In recent years, new elastomeric mixtures have been developed to provide mechanical properties, such as elongation at break or rigidity, which are particularly suitable for certain uses of tires. Such elastomeric mixtures are, for example, described in applications WO 2020094993 A1 and WO 2020212184 A1. However, these elastomeric mixtures have decohesion properties before vulcanization. They are thus characterized by high risks of tearing when subjected to certain stresses. It is possible in particular observe this decohesive character at the extruder outlet, the manufactured semi-finished product showing traces of tears causing strongly marked irregularities to appear on the surface. These irregularities are particularly marked on the areas of the semi-finished product showing edges and therefore appear particularly at the level of the grooves preformed during extrusion as described previously.

[0020] These irregularities do not usually present a problem because during the molding operation, the appearance is rectified in contact with the mold under the effect of pressure.

[0021] However, the inventors were able to demonstrate that in certain cases of use of the tires, in cases of demanding uses, unusual tread wear appears which can lead to more or less significant tearing of the tread. The inventors were able to demonstrate that these tearings are due to the presence of impurities which may have become inserted into the openings or irregularities of the tread due to the tears described above which appear at the extruder outlet. During curing of the tire these impurities may become trapped within the tread and thus be the cause of tearings during severe stresses on the tire.

[0022] It is also required that the performance of a tread be sustainable, that is to say that satisfactory performance is achieved even after more or less advanced partial wear. Partial wear of a tread means a state of wear corresponding to a tread thickness at most equal to the total thickness of the strip that can be worn before having to change the tire, particularly for regulatory reasons.

[0023] The grooves generally have wear indicators, small platforms of vulcanized rubber compound covering the bottom of these grooves over a certain circumferential length, said indicator indicating the minimum tread depth that must legally remain on the tread in use. The treads for heavy goods vehicles can be regrooved (operation by which new grooves can be regrooved), and tires having such treads bear the English wording "Regroovable" or the symbol "U" on their sidewalls. Regrooving allows on the one hand to extend the grip potential of the heavy goods vehicle tire and on the other hand to significantly increase mileage.

[0024] Regrooving heavy goods vehicle tires is a routine operation authorized for safety and the increased efficiency it brings. For example, it is explicitly authorized by the French Highway Code (Art. 4 of the decree of 24 / 10 / 94) and recommended by ETRTO and AFNOR (standard NFR12714). For this operation, manufacturers are required to provide regrooving diagrams that are binding on the technicians in charge of this regrooving.

[0025] The groove heights on new tires are measurable and the groove heights after regrooving can be deduced from these regrooving diagrams.

[0026] As is known, the regrooving of a groove can be carried out using a heated rounded blade, often still handled by an operator. Said blade, connected to a frame which rests on the tread surface, can be used manually so as to follow the path of the groove on the tread surface fairly faithfully, even in the case of a groove with a non-rectilinear path.

[0027] Regrooving restores sharp edges and is usually intended to restore a tread height corresponding to that of a mid-wear truck tire. The usual recommendations are for a post-regrooving height of 5 to 6 mm, consisting of a 3 to 4 mm regroove and 2 mm of remaining height; in practice, regrooving is often carried out earlier with remaining heights of between 4 and 5 mm, leading to a post-regrooving height of 7 to 9 mm, for tread heights of new tires of between 12 and 20 mm.

[0028] Regrooving a tire has several advantages. First, by restoring the tire's tread height, regrooving extends its life.

[0029] Furthermore, regrooving is carried out when the tread thickness is the smallest and therefore when the tire has the lowest rolling resistance, the distance traveled is extended when the rolling resistance is lowest.

[0030] It should also be noted that regrooving has no effect on potential deformation of the crown reinforcement, as it is not obtained by molding during cooking and cannot cause material creep.

[0031] The inventors set themselves the task of being able to provide tires whose tread is made of elastomeric compounds having improved mechanical properties, such as those mentioned above, without the risk of impurities appearing inserted into said compounds during manufacture, said tires also having satisfactory wear properties and in particular not having excessively pronounced wear irregularities during use.

[0032] This object has been achieved according to the invention by a tire, regroovable at least once, comprising a crown reinforcement, itself radially capped with a tread, consisting of at least one elastomeric mixture forming the outer surface of the tread of the tire, joined to two beads by means of two sidewalls, said tread comprising at least one regroovable groove forming at least one tread element constituting the tread of the tire, having a height between the bottom of said at least one groove and the tread surface when the tire is new. After regrooving, the height of said at least one regrooved groove is greater than or equal to 70% of the groove height of said at least one regroovable groove of the tire when new.According to the invention, said at least one elastomeric mixture forming the outer surface of the tread of the tire comprises a quantity of plasticizer(s) less than 15 pce and the linearity rate of the complex dynamic shear modulus G*, measured at a temperature of 23°C according to standard ASTM D 5992-96, of said at least one elastomeric mixture forming the outer surface of the tire is greater than 0.55, the linearity rate being defined by the ratio of G*. m in on G* ma x, with G*min being the minimum value of the complex dynamic shear modulus G* for a deformation of 1 to 100%, and G*max being the maximum value of the complex dynamic shear modulus G* for a deformation of 1 to 100%.

[0033] The loss factor tan(ô) is a dynamic property of the rubber compound layer. It is measured on a viscoanalyzer (Metravib VA4000), according to ASTM D 5992-96. The response of a sample of vulcanized compound (cylindrical specimen 2 mm thick and 78 mm 2 section), subjected to sinusoidal stress in alternating simple shear, at a frequency of 10 Hz, at a temperature of 60°C. A strain amplitude sweep is carried out from 0.1 to 100% (forward cycle), then from 100% to 1% (return cycle). The results used are the dynamic complex shear modulus (G*) and the loss factor tan(ô) measured on the return cycle. For the return cycle, the maximum value of tan(ô) observed is indicated, noted tan(ô)max. For the measurement of the dynamic complex shear modulus (G*) according to the invention, the sinusoidal stress in alternating simple shear, at a frequency of 10 Hz, is carried out at a temperature of 23°C.

[0034] The abbreviation "pce" means parts by weight per hundred parts of elastomer (of the total elastomers if more than one elastomer is present).

[0035] Elastomeric mixtures with a relatively high linearity rate, in particular greater than 0.55, associated with a quantity of plasticizer less than 15 pce are characterized during the manufacture of semi-finished products by extrusion by the appearance of tears forming surface irregularities, in particular at the level of the longitudinal edges formed by an extrusion profile. Such elastomeric mixtures correspond to the descriptions made previously.

[0036] For the purposes of the invention, the groove height is measured in a meridian section of the tire and corresponds to the distance measured between the radially outer surface of the tread, forming the contact surface with the ground and extrapolated to disregard the cutouts, and the surface of the tread bases, said distance being measured in a direction normal to the radially outer surface of the tread. The tread bases are the radially innermost points of the hollow areas on the tread, disregarding the presence of elements such as wear indicators, regrooving depth indicator wells or any other element whose sum of surfaces is less than 15% of the total surface area of ​​the cutout.

[0037] The groove height of said at least one regroovable groove of the tire in the new condition is thus measured on a new tire. The height of said at least one regrooved groove can in the same way be measured when the tire is regrooved; the height of said at least one regrooved groove can also be determined as explained previously from the new tire and the regrooving diagram provided by the manufacturer.

[0038] Advantageously according to the invention, the height corresponding to the distance between the tread surface in new condition and the bottom of the grooves after the last regrooving is greater than or equal to 200% of the height between the bottom of the groove and the tread surface when the tire is new. Advantageously again, the height corresponding to the distance between the tread surface in new condition and the bottom of the grooves after the last regrooving is greater than or equal to 250% of the height between the bottom of the groove and the tread surface when the tire is new.

[0039] The height corresponding to the distance between the tread surface when new and the bottom of the grooves after the last regrooving can be determined when the tire is regrooved or can also be determined as explained previously from the new tire and the regrooving diagram provided by the manufacturer.

[0040] Preferably according to the invention, the linearity rate of the complex dynamic shear modulus G*, measured at a temperature of 23°C according to standard ASTM D 5992-96, of said at least one elastomeric mixture forming the outer surface of the tire is greater than 0.65 and preferably still greater than 0.75.

[0041] The tests carried out with tires conforming to the invention have shown that in comparison with conventional regroovable tires whose tread is made with an elastomeric mixture having a relatively high linearity rate, in particular greater than 0.55, associated with a quantity of plasticizer less than 15 pce, it is possible to produce tires without the risk of impurities appearing inserted into said mixtures during manufacture, said tires also having satisfactory wear properties and in particular not having too pronounced wear irregularities during use.

[0042] Indeed, the regrooving according to the invention leads to groove heights significantly lower than those of more usual tires, in new condition, and thus allows the production of profiles of the semi-finished products intended to form the outer surface of the tread, with a surface having no groove initiations. The surface of the semi-finished product intended to constitute the outer surface of the tread is therefore almost smooth.

[0043] In fact, for tread thicknesses similar to those of more conventionally designed tires, the height of the grooves after regrooving greater than 70% of the height of the grooves when new means that the height of the grooves when new is reduced compared to that of more conventionally designed tires.

[0044] The low height of the grooves in the new state allows their total formation during the firing phase, the molding leading to no deformation of the crown reinforcement. Since the grooves are less deep than those usually produced, the flow of the materials generated during the molding of these grooves is not sufficient to significantly deform the crown reinforcement.

[0045] Since the surface edges of the semi-finished product are thus limited during extrusion, virtually no irregularities are formed into which impurities could become embedded. During rolling, even under severe conditions, the risks of tearing or very pronounced wear due to such impurities are greatly reduced or even non-existent.

[0046] Furthermore, the inventors have demonstrated that the rolling resistance performance is improved while maintaining similar wet grip properties and for substantially identical mileages until the tire is completely worn.

[0047] The inventors were indeed able to demonstrate that the combination of a tread thickness substantially identical to that of a tire of more usual design with reduced groove heights when new compared to those of tires of more usual design makes it possible to significantly increase performance in terms of rolling resistance.

[0048] As stated above, the regrooving provided for tires of more conventional design leads to groove heights less than half the height of the grooves in the new condition. According to the invention, for a given tread thickness, the regrooving of the tread must therefore probably be carried out more quickly, that is to say for less wear of the tread, than in the case of a tire of more conventional design.

[0049] The inventors were thus able to demonstrate that this rapid regrooving of the tread of the tire according to the invention makes it possible to significantly improve its performance in terms of rolling resistance while maintaining wear performance and wet grip performance.

[0050] According to an alternative embodiment of the invention, said at least one elastomeric mixture forming the outer surface of the tire tread comes from a semi-finished product whose axial ends do not have sharp edges.

[0051] According to this variant embodiment of the invention, the semi-finished product has substantially rounded profiles at its axial ends. These rounded profiles, like the smooth surface of the semi-finished product, are obtained by the choice of the extrusion profile; they make it possible to produce a semi-finished product by extrusion under completely usual conditions, in particular speed conditions, without the risk of irregularities appearing due to tearing usually initiated, with this type of elastomeric mixture, at the edges.

[0052] These substantially rounded profiles are found in the tire after curing. The semi-finished product intended to form the surface of the tread cannot therefore form the entire surface over a large thickness, as the radially outer part of the sidewalls cannot be rounded. The semi-finished product is then advantageously associated at each of its axial ends with two other semi-finished products, made from a different elastomeric mixture, which will form these radially outermost parts of the sides. These three semi-finished products can advantageously be co-extruded.

[0053] According to a first advantageous variant of the invention, said at least one elastomeric mixture forming the outer surface of the tread of the tire comprises a diene elastomer carrying pendant imidazole functions according to a molar content of at most 4% of the repeating units constituting the diene elastomer, which diene elastomer is a copolymer of ethylene and a 1,3-diene comprising ethylene units, the ethylene units representing at least 50% by mole of the repeating units constituting the diene elastomer, the 1,3-diene being 1,3-butadiene or isoprene.

[0054] According to a second advantageous variant of the invention, said at least one elastomeric mixture forming the outer surface of the tread of the tire comprises a diene elastomer, a reinforcing filler comprising more than 50% by mass of a silica, a crosslinking system, a modifying agent and, where appropriate, a silane coupling agent for bonding the diene elastomer to the silica, the modifying agent carrying an N-substituted imidazole function and a unit containing a group reactive with respect to the diene elastomer, the total quantity of the modifying agent and the silane coupling agent representing more than 5% by mass of the quantity of the silica, the ratio between the quantity of the modifying agent and the total quantity of the modifying agent and the silane coupling agent being greater than 0.5, the quantities being expressed in parts by weight per hundred parts of elastomer, pce.

[0055] According to a first embodiment of the invention, said at least one regroovable groove is circumferential.

[0056] According to a second embodiment of the invention, said at least one regroovable groove is transverse.

[0057] According to a third embodiment of the invention, said at least one regroovable groove is oblique.

[0058] According to other embodiments of the invention, the tire has a combination of circumferential and / or transverse and / or oblique regroovable grooves.

[0059] Whether they are in the same orientation or in several orientations, the invention advantageously provides that all of the grooves of the tire are regrooved according to the invention during the same step.

[0060] According to an advantageous variant of the invention, after regrooving, the height of said at least one regrooved groove is greater than or equal to 85% of the height of said at least one regroovable groove of the tire in the new condition and preferably still greater than 95% of the tread height of the tire in the new condition.

[0061] According to one embodiment of the invention, at least one groove can be regrooved at least twice. According to this embodiment, it is even more certain that there is no risk of deformation of the crown reinforcement during curing. It may also be possible to further increase rolling resistance performance by providing even smaller groove depths when new while still satisfying wet grip performance.

[0062] According to this embodiment and in the case of several grooves provided in the same orientation or in several orientations, the invention advantageously provides that all of the grooves of the tire are regrooved simultaneously during each regrooving.

[0063] Advantageously still according to this embodiment of the invention, the elastomeric mixture re-grooved during the first re-grooving is different from the elastomeric mixture re-grooved during the second re-grooving. For example, the radially innermost elastomeric mixture does not contain a black type filler for display a color contrast when it appears at the time of the first re-grooving. Such an arrangement can in particular facilitate the re-excavation stages.

[0064] According to other embodiments of the invention, the tread comprises depth indicators appearing for example in the form of wells or incisions of small non-zero width placed at the bottom of the groove either parallel to the direction of said groove, or perpendicular to said direction, or both simultaneously, the means indicating the minimum and maximum depths then being the geometric shape of the bottom of the depth-indicating incision.

[0065] Advantageously according to the invention, the regroovable elastomeric mixture is different from at least a portion of the elastomeric mixture constituting the tread. Such an embodiment can be obtained by co-extrusion of the mixtures during the preparation of the semi-finished product(s) intended to constitute at least part of the tread.

[0066] One or other of the embodiments of the invention presented previously can also be associated with the production of a complex tread, for example made up of at least two layers of radially superimposed elastomeric mixtures.

[0067] According to one embodiment of the invention, the crown reinforcement of the tire is formed from at least two working crown layers of inextensible reinforcing elements, crossed from one layer to the other making angles of between 10° and 45° with the circumferential direction.

[0068] According to other embodiments of the invention, the crown reinforcement further comprises at least one layer of circumferential reinforcing elements.

[0069] An embodiment of the invention also provides that the crown reinforcement is completed radially on the outside by at least one additional layer, called a protective layer, of so-called elastic reinforcing elements, oriented relative to the direction circumferential with an angle between 10° and 45° and in the same direction as the angle formed by the inextensible elements of the working layer which is radially adjacent to it.

[0070] According to any of the embodiments of the invention mentioned above, the crown reinforcement can also be completed, radially inside between the carcass reinforcement and the radially inner working layer closest to said carcass reinforcement, by a triangulation layer of inextensible metallic steel reinforcing elements making, with the circumferential direction, an angle greater than 60° and in the same direction as that of the angle formed by the reinforcing elements of the layer radially closest to the carcass reinforcement.

[0071] Other details and advantageous characteristics of the invention will emerge below from the description of exemplary embodiments of the invention with reference to Figures 1 to 6 which represent: - figure 1, a meridian view of a diagram of a semi-finished product intended to form the outer surface of the tire tread according to a first variant of the invention, - figure 2, a meridian view of a diagram of a semi-finished product intended to form the outer surface of the tire tread according to a second variant of the invention, - figure 3, a meridian view of a diagram of a tire incorporating the semi-finished product according to a second variant of the invention shown in figure 2, - figure 4, a meridian view of a diagram of a tire according to a first exemplary embodiment of the invention, - figure 5, a meridian view of a diagram of a tire according to a second exemplary embodiment of the invention, - figure 6, a schematic representation of the rolling resistance during wear of a reference tire and two tires according to the invention.

[0072] Figures 1 to 5 are not drawn to scale to simplify understanding. Figures 3, 4 and 5 represent only a half-view of a tire that extends symmetrically with respect to the XX' axis which represents the circumferential median plane, or equatorial plane, of a tire.

[0073] Figure 1 shows a semi-finished U intended to form the radially outer part of the tread of the tire according to the invention. This semi-finished according to the invention does not have any groove initiations on its radially outer surface. It could be produced by extrusion and the profile of the radially outer surface being almost smooth, it is possible to carry out extrusion at usual speeds without seeing any tearing or tearing appear on this radially outer surface regardless of the nature of the elastomeric mixture used.

[0074] Figure 2 illustrates a semi-finished product V according to a second embodiment of the invention consisting of a central part VI and two axially outer parts V2, V3. These axially outer parts V2, V3 are intended to form the axially outer parts of the radially outermost part of the tread and consequently the radially outermost parts of the sidewalls. These axially outer parts V2, V3 are advantageously made of an elastomeric mixture which does not present any risk of surface irregularities appearing during extrusion. The central part VI can be made of any type of elastomeric mixture including those mentioned above which may present risks of tearing or snatch leading to the appearance of surface irregularities during extrusion when the desired profile includes edges.Indeed, according to this second variant, not only does this central part VI not have any groove starters and in addition the axially outer zones are substantially rounded so that no edges are present. According to this second variant embodiment of the invention, it is thus possible to carry out extrusion at even faster speeds than in the case of the first variant of the invention, illustrated in Figure 1, without seeing any tearing or tearing appear on this semi-finished product intended to form the radially outer part of the tread, whatever the nature of the elastomeric mixture used.

[0075] According to an advantageous embodiment of this second variant embodiment of the invention, the central part VI and the axially outer parts V2 and V3 are coextruded, according to standard techniques, to simplify the manufacture of the tire.

[0076] Figures 3 to 6, which follow, illustrate in more detail the tire 1 and the principle of regrooving according to the invention.

[0077] In Figures 3 to 5, the tire 1, of size 315 / 70R22.5, comprises a radial carcass reinforcement 2 anchored in two beads, around bead wires, not shown. The carcass reinforcement 2 is formed of a single layer of metal cables. The carcass reinforcement 2 is hooped by a crown reinforcement 5, itself capped by a tread 6. The tread has three grooves 3, 23 forming four ribs 4 and the two ribs axially in the center are cut by oblique crossing grooves not shown in Figures 4 and 5.

[0078] The lower areas and beads of the tire 1 are not shown in particular in figures 3 to 5.

[0079] In Figures 3 to 5, the crown reinforcement 5 is formed radially from the inside to the outside: of a first working layer 51 formed of inextensible metal cables, continuous over the entire width of the sheet, oriented at an angle of 16°, with the circumferential direction, of a layer of circumferential reinforcing elements 53 formed of elastic steel metal cables 21.23, with a pitch of 2 mm, and of a second working layer 52 formed of inextensible metal cables, continuous over the entire width of the sheet, oriented at an angle of 30°, with the circumferential direction, and crossed with the metal cables of the first working layer.

[0080] The axial width L 51 of the first working layer 51 is equal to 246 mm.

[0081] The axial width L 52 of the second working layer 52 is equal to 228 mm.

[0082] As for the axial width L 53of the layer of circumferential reinforcing elements 53, it is equal to 200 mm.

[0083] In Figure 3, a part of a tire 1 incorporating a radially outermost part of its tread 6 according to the second variant illustrated in Figure 2, is shown diagrammatically according to a meridian section. In this diagram, we see that we find parts VI and V2 after curing the tire. Also shown diagrammatically are the grooves 3 obtained integrally by molding during the curing step. This Figure 3 allows a better visualization of the destiny of each of parts VI, V2 and V3 and to note that on a cured tire, it is possible to find the initial shape of parts VI, V2 and V3; in particular with regard to part VI, the edge-free profile is preserved even if the compounds flow during molding and curing.

[0084] In Figure 4, in accordance with the invention, the grooves 3 are of the regrooving type. As illustrated in Figure 1, the grooves 3 consist of a single layer A forming the bottom of the grooves when new and corresponding to a single regrooving.

[0085] The height of grooves 3 on a new HN3 tire is 7.5 mm.

[0086] The HR height of grooves 3 after regrooving is equal to 9.5 mm and therefore represents 127% of HN3.

[0087] This HR height corresponds to a regrooving of 7.5 mm when there remains a height of the initial groove of 2 mm, a value close to the generally authorized legal limit corresponding to the minimum height and corresponding to the wear indicators. This limit is symbolized by line 7 in figure 1.

[0088] The height not measurable before this regrooving and corresponding to the distance between the rolling surface in new condition and the bottom of a groove 3 after regrooving is thus equal to 15 mm. The ratio of this non-measurable height equal to 15 mm to the height HN3 is equal to 2 and therefore much greater than or equal to 200%.

[0089] The HR height, measured after regrooving, and the non-measurable height before regrooving and corresponding to the distance between the tread surface in new condition and the bottom of a groove 3 after regrooving can also be determined on a new tire from the regrooving diagrams provided by the manufacturer as explained previously.

[0090] Figure 5 illustrates a tire whose grooves 23 can be regrooved twice. The grooves 23 are made up, when new, of two layers B and C forming the bottom of the grooves when new and corresponding to these two regrooves.

[0091] The height of grooves 23 on a new HN23 tire is 6 mm.

[0092] The HRI height of grooves 23 after the first regrooving is equal to 7 mm and therefore represents 117% of HN23.

[0093] This HRI height corresponds to a regrooving of 5 mm when there remains a height of the initial groove of 2 mm, a value close to the generally authorized legal limit corresponding to the minimum height and corresponding to the wear indicators. This limit is symbolized by line 71 in figure 2.

[0094] The height that cannot be measured before the first regrooving and corresponds to the distance between the rolling surface in new condition and the bottom of the groove after the first regrooving is thus equal to 11 mm.

[0095] The HRI height, measured after the first regrooving, and the height not measurable before a first regrooving and corresponding to the distance between the tread surface in new condition and the bottom of the groove after the first regrooving can also be determined on a new tire from the regrooving diagram provided by the manufacturer, as explained previously.

[0096] The height HR2 of grooves 23 after the second regrooving is equal to 6 mm and therefore represents 100% of HN23. And the height HR2 of grooves 23 after the second regrooving represents 86% of HRI.

[0097] This HR2 height corresponds to a regrooving of 4 mm when a groove height of 2 mm remains, a value close to the generally authorized legal limit corresponding to the minimum height. This limit is symbolized by line 72 in figure 2.

[0098] The non-measurable height before the two regrooves and corresponding to the distance between the rolling surface in new condition and the bottom of the grooves 23 after the second regroove is thus equal to 15 mm. The ratio of this non-measurable height equal to 15 mm to the height HN23 is equal to 2.5 and therefore much greater than or equal to 200%.

[0099] The HR2 height, measured after the second regrooving, and the non-measurable height before the two regroovings and corresponding to the distance between the tread surface in new condition and the bottom of the grooves after the second regrooving can also be determined on a new tire from the regrooving diagram provided by the manufacturer, as explained previously.

[0100] The tire thus presented in Figure 5 provides two regrooves at different stages of tire wear. Advantageously according to the invention, the grooves are regrooved simultaneously at each regrooving stage.

[0101] According to other embodiments of the invention, the regrooving of the different grooves of a tire may be arranged to be done in a time-shifted manner. According to these embodiments, the tire may comprise a portion of these grooves that can be regrooved only once and other grooves that can be regrooved several times. A tire could thus comprise a combination of grooves such as those illustrated in Figure 1 and grooves such as those illustrated in Figure 2.

[0102] Tires were produced based on the elastomeric compounds described below as tread compounds.

[0103] The values ​​of the constituents are expressed in pce (parts by weight per hundred parts of elastomers).

[0104] Mixture 2 corresponds to the C8 mixture described in the patent application WO 2020212184 Al.

[0105] Mixture 3 corresponds to mixture C2 described in the patent application WO 2020094993 AL

[0106] Tires with references RI, R2 and R3 similar to those in the figures are produced according to a configuration corresponding to usual regrooving designs. It comprises a single regrooving layer at the bottom of the grooves such that the height of the grooves after regrooving is equal to 5 mm and represents 42% of the height of the grooves in the new condition, itself equal to 12 mm. This height after regrooving equal to 5 mm corresponds to a regrooving of 3 mm when a groove height of 2 mm remains, a value close to the generally authorized legal limit corresponding to the minimum height. The height not measurable before regrooving and corresponding to the distance between the rolling surface in new condition and the bottom of the grooves after regrooving is thus equal to 15 mm.

[0107] The RI tire has a tread made of compound 1.

[0108] The R2 tire has a tread made of the mixture 2.

[0109] The R3 tire has a tread made of the mixture 3.

[0110] The semi-finished products intended to form the tread of RI, R2 and R3 tires are produced by extrusion according to a profile which provides groove starters.

[0111] The R2 and R3 tires were made from semi-finished products, which were themselves made without taking precautions during extrusion, which was carried out at normal speeds. It was found that these semi-finished products contained numerous surface irregularities, particularly at the edges of the grooves preformed during extrusion. The inventors had previously demonstrated that achieving a depth of 12 mm by molding during the curing of this tire led to unacceptable deformation of the crown reinforcement to maintain regular wear during rolling. The semi-finished products were cured in a mold in which a mold release agent had been sprayed onto the inner surface in a significant quantity, although comparable with a quantity that could be encountered during mass production.

[0112] As in the case of the tires according to the invention and as explained previously, the height, measured after regrooving, and the height not measurable before regrooving and corresponding to the distance between the tread surface in the new condition and the bottom of the grooves after regrooving can also be determined on a new tire from the regrooving diagrams provided by the manufacturer.

[0113] Tires T1 to T4 are produced in accordance with the invention.

[0114] Tires T1 and T2 are as shown in Figures 2 and 5.

[0115] The tire Tl is made from a semi-finished product V whose central part VI is made from mixture 2.

[0116] The T2 tire is made from a semi-finished V whose central part VI is made from the mixture 3.

[0117] T3 and T4 tires are as shown in Figures 2 and 6.

[0118] The T3 tire is made from a semi-finished V whose central part VI is made from mixture 2.

[0119] The T4 tire is made from a semi-finished V whose central part VI is made from mixture 3.

[0120] The axially outer parts V2 and V3 of the semi-finished products used for each of the tires T1 to T4 are made of mixture 1.

[0121] Initial rolling tests were carried out along a circular trajectory with a radius of 12 meters on an aggressive asphalt concrete track for 100 laps, with the tires fitted to the two drive axles of a tractor. Each type of tire is tested according to this protocol.

[0122] After driving and analyzing the tires, it appears that 15% of R2 tires and 25% of R3 tires have at least one tear over a surface of at least 2 cm. 2and a maximum depth greater than 1 mm. The rate is zero for RI tires and tires according to the invention T1 to T4.

[0123] Furthermore, wear tests were carried out to show substantially identical performances with the T1 and T3 tires according to the invention and the reference tire RI, the T2 and T4 tires according to the invention having a 35% longer service life. Indeed, the volume of the elastomeric materials constituting the tread, to be worn during the life of the tire and the regrooving(s) is substantially identical for all tires, which leads to similar lifespans for RI, Tl and T3 tires, the tread being made in particular of natural rubber or polyisoprene. T2 and T4 tires, whose tread is made in particular of functionalized ethylene and 1,3-butadiene copolymer, have longer lifespans.

[0124] Rolling resistance measurements were also carried out on each of the tires under identical driving conditions in accordance with Regulation No. 117 of the United Nations Economic Commission for Europe (UNECE). The R2 and R3 tires were not tested again. The measurement results are shown in the following table, with a value of 100 being assigned to the RI tire in new condition. A value of 90 means that the rolling resistance coefficient is reduced by 10% and corresponds to a higher rolling resistance performance. Measurements were carried out on the new tire and on the planed tire to bring it up to the usual wear limit of approximately 2 mm on each of the RI, T1, T2, T3 and T4 tires.A measurement is again taken after regrooving on each of the RI, Tl, T2, T3 and T4 tires and another on each of the RI, Tl, T2, T3 and T4 tires planed again to bring them to the level of the usual wear limit of approximately 2 mm. The T3 and T4 tires are again measured after the second regrooving and a final measurement is taken on these T3 and T4 tires after planing to bring them to the level of the usual wear limit of approximately 2 mm.

[0125] Figure 6 schematically illustrates a representation of the evolution of the rolling resistance of each of the RI, Tl and T3 tires from their new condition until their end of life, that is to say during the 13 mm of wear of the tread. Figure 6 represents, on the ordinate, the measured or estimated value of the rolling resistance of the tire as a function of the worn tread height, on the abscissa, this height starting from 0 and ending at 13 mm. The 13 mm corresponds to the 15 mm of the tread planned for each of the RI, Tl and T3 tires, taking into account the 2 mm retained at the end of the tires' life, a value close to the generally authorized legal limit.

[0126] The three plots shown in Figure 6 correspond to each of the R, T1 and T3 tires. Calculating the surfaces defined by these three plots allows us to estimate the average rolling resistance during the use of each of these tires. The results showed that the T1 tire allows a gain of 8% compared to the R tire and that the T3 tire allows a gain of 12% compared to the R tire.

Claims

DEMANDS 1 - Tire (1), regroovable at least once, comprising a crown reinforcement (5), itself radially capped by a tread (6), made of at least one elastomeric compound forming the outer surface of the tire tread, joined to two beads by means of two sidewalls, said tread (6) having at least one regroovable groove (3) forming at least one tread element constituting the tread of the tire, having a height (HNS) between the bottom of said at least one groove (3) and the tread surface when the tire is new, characterized in that, after regrooving, the height (HR) of said at least one regrooved groove (3) is greater than or equal to 70% of the groove height (HNS) of said at least one regroovable groove (3) of the tire in its new condition,in that said at least one elastomeric compound forming the outer surface of the tire tread contains an amount of plasticizer(s) less than 15 parts per annum and in that the linearity ratio of the complex dynamic shear modulus G*, measured at a temperature of 23°C according to ASTM D 5992-96, of said at least one elastomeric compound forming the outer surface of the tire tread being greater than 0.55, the linearity ratio being defined by the ratio of G*, m in on G* max, with G*min being the minimum value of the complex dynamic shear modulus G* for a strain of 1 to 100%, and G*max being the maximum value of the complex dynamic shear modulus G* for a strain of 1 to 100%. 2 - Tire (1) according to claim 1, characterized in that said at least one elastomeric compound forming the outer surface of the tread of the tire is derived from a semi-finished product whose axial ends do not have sharp edges. 3 - Tire (1) according to one of claims 1 or 2, characterized in that the linearity ratio of the complex dynamic shear modulus G*, measured at a temperature of 23 °C according to ASTM D 5992-96, of said at least one elastomeric compound forming the outer surface of the tire is greater than 0.65 and preferably greater than 0.

75. 4 - Tire (1) according to any one of claims 1 to 3, characterized in that said at least one elastomeric mixture forming the outer surface of the tire tread comprises a diene elastomer bearing pendant imidazole functions in a molar content of at most 4% of the repeating units constituting the diene elastomer, which diene elastomer is a copolymer of ethylene and a 1,3-diene comprising ethylene units, the ethylene units representing at least 50% by mole of the repeating units constituting the diene elastomer, the 1,3-diene being 1,3-butadiene or isoprene. 5 - A tire (1) according to any one of claims 1 to 3, characterized in that said at least one elastomeric compound forming the outer surface of the tire tread comprises a diene elastomer, a reinforcing filler comprising more than 50% by mass of a silica, a crosslinking system, a modifying agent and optionally a silane coupling agent for linking the diene elastomer to the silica, the modifying agent bearing an N-substituted imidazole function and a motif containing a group reactive to the diene elastomer, the total quantity of the modifying agent and the silane coupling agent representing more than 5% by mass of the quantity of the silica, the ratio between the quantity of the modifying agent and the total quantity of the modifying agent and the silane coupling agent being greater than 0.5, the quantities being expressed partly by weight as a percentage. of elastomer, pc. 6 - Tire (1) according to any one of claims 1 to 5, characterized in that the height corresponding to the distance between the tread surface in the new condition and the bottom of said at least one groove (3) after the last regrooving is greater than or equal to 200% of the height between the bottom of the groove (3) and the tread surface when the tire is new. 7- Pneumatic (1) according to any one of claims 1 to 6, characterized in that said at least one re-groovable groove (3) is circumferential. 8 - Pneumatic (1) according to any one of claims 1 to 7, characterized in that said at least one re-groovable groove (3) is transverse. 9 - Pneumatic (1) according to any one of claims 1 to 8, characterized in that said at least one re-groovable groove (3) is oblique. 10 - A pneumatic tire (1) according to any one of claims 1 to 9, characterized in that at least one regroovable groove (3) is regroovable at least twice. 11 - A pneumatic tire (1) according to claim 10, characterized in that the elastomeric compound regrooved during the first regrooving is different from the elastomeric compound regrooved during the second regrooving. 12 - Pneumatic (1) according to one of the preceding claims, characterized in that the regroovable elastomeric compound is different from at least a part of the elastomeric compound constituting the tread. 13 - Pneumatic (1) according to one of the preceding claims, characterized in that said tread comprises, at least locally, at least two layers of radially superimposed elastomeric mixtures in the tread.

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