WO2023222500A1

WO2023222500A1 - Tyre having a regroovable tread

Info

Publication number: WO2023222500A1
Application number: PCT/EP2023/062586
Authority: WO
Inventors: Luc Bestgen; Patrick DAYET; Stéphane HEBERT
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2022-05-18
Filing date: 2023-05-11
Publication date: 2023-11-23
Also published as: FR3135656A1

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

TIRE COMPRISING A BAND OF

RECREABLE BEARING

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-duty type tires, the carcass reinforcement is anchored on either side in the area of the bead 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 frame, can also be covered with at least one so-called protective layer and formed of advantageously metallic and extensible reinforcing elements, called elastic. It can also include a layer of low extensibility metal wires or cables making an angle of between 45° and 90° with the circumferential direction, this layer, called triangulation, being radially located between the carcass reinforcement and the first layer of so-called working summit, formed of parallel wires or cables having angles at most equal to 45° in absolute value. The triangulation sheet forms with at least said working sheet a triangulated reinforcement, which presents, under the different stresses it undergoes, few deformations, the triangulation sheet having the essential role of taking up the transverse compression forces of which is the 'object all the reinforcing elements in the area of the crown of the tire.

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

[0004] Cables are said to be elastic when said cables present, 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. 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 axis of rotation of the tire is the axis around which it rotates in normal use.

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

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

[0009] The transverse or axial direction of the tire is parallel to the axis of rotation of the tire. An axial distance is measured along the axial direction. The expression “axially interior to, respectively axially exterior to” means “whose axial distance measured from the equatorial plane is less than, respectively greater than”.

The radial direction is a direction intersecting the axis of rotation of the tire and perpendicular to it. A radial distance is measured along 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, we find the tread usually made up 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 during rolling and to wear during rolling, with a sculpture formed of elements in relief delimited by cutouts such as grooves, whether they are circumferential, transverse or oblique in orientation. The objective of such a tread pattern is to give the tread good driving performance on dry roads and on water-covered roads, particularly in rainy weather.

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

[0014] For the purposes of the invention, a longitudinally oriented cutout is a cutout whose average 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 can be oriented in one direction or the other relative to said longitudinal plane. A cutout with a longitudinal orientation can also be a cutout whose walls undulate or zigzag around a mean plane as has just been described.

[0015] For the purposes of the invention, a transversely oriented cutout is a cutout whose average 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 can be oriented in one direction or the other relative to said radial plane. A cutout with a transverse orientation can also be a cutout whose walls undulate or zigzag around a mean plane as just described.

[0016] For the purposes of the invention, a cutout of oblique orientation is a cutout whose 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 can be oriented in one direction or the other relative to said radial plane. A cutout of oblique orientation can also be a cutout whose walls undulate or zigzag around a mean plane such as it has just been 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 appears. These circumferential grooves which are obtained by molding during the baking of the tire lead to 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 baking of said tire. This results in a deformation in the radial direction of the layers constituting the crown reinforcement located near said cutouts. These deformations lead, when the tires are used, to an alteration of the performance of the tire in terms of wear and in particular of regularity of wear, the thickness of the mixture to be worn not being regular according to the transverse direction of the tire.

[0018] To reduce or even eliminate this phenomenon, it is known to produce the semi-finished product which 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 which 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 top reinforcement of the pneumatic.

[0019] In recent years, new elastomeric mixtures have been developed to confer mechanical properties, such as elongation at break or rigidity, particularly suited to certain uses of tires. Such elastomeric mixtures are for example described in applications WO 2020094993 Al and WO 2020212184 AL. These elastomeric mixtures, on the other hand, have decohesion properties before vulcanization. They are thus characterized by a high risk of tearing when they are subjected to certain stresses. We can in particular observe this decohesive character at the exit of the extruder, the manufactured semi-finished showing traces of tears revealing strongly marked irregularities on the surface. These irregularities are particularly marked on the areas of the semi-finished having 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 tires, in cases of demanding uses, there appears unusual wear of the tread which can lead to more or less significant tearing of the tires. the tread. The inventors were able to demonstrate that these tears are due to the presence of impurities which may have been inserted into the openings or irregularities of the tread due to the tears described above which appear at the exit of the extruder. When the tire is cooked, these impurities can become trapped within the tread and thus cause tearing when the tire is subjected to severe stress.

[0022] It is also required that the performance of a tread be lasting, 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 tread thickness that can be worn before having to change the tire, particularly for regulatory reasons. .

[0023] The grooves generally include wear indicators, small platforms of vulcanized rubber mixture covering the bottom of these grooves over a certain circumferential length, said indicator indicating the minimum tread depth which must legally remain on the tread in use. The tread patterns for heavy goods vehicles can be regroovable (operation by which new grooves can be regrooved), and tires having such tread patterns bear the English words “Regroovable” or the symbol “U” on their sides. Regrooving makes it possible, on the one hand, to extend the grip potential of the heavy-duty tire and, on the other hand, to significantly increase mileage efficiency.

[0024] The regrooving of heavy goods vehicle tires is a usual operation authorized for safety and the increase in efficiency that it entails. For example, it is explicitly authorized by the French Highway Code (Art. 4 of the decree of 10/24/94) and recommended by the E.T.R.T.O. and A.F.N.O.R. (NFR12714 standard). For this operation, manufacturers are required to provide regrooving diagrams which are required by 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.

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

[0027] Regrooving makes it possible to restore sharp edges and is usually intended to restore a tread height corresponding to that of a mid-wear truck tire. The usual recommendations aim for a height after regrooving of 5 to 6 mm composed of a regrooving of 3 to 4 mm 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 height after regrooving of 7 to 9 mm, for tread heights of tires in new condition of between 12 and 20 mm.

[0028] Regrooving a tire has several advantages. First of all, by restoring tread height to the tire, regrooving helps extend the life of the tire.

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

[0030] It should also be noted that regrooving has no effect on potential deformation of the crown reinforcement, this being not obtained by molding during cooking and cannot lead to creep of the materials .

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

[0032] This goal was achieved according to the invention by a tire, regroovable at least once, comprising a crown reinforcement, itself capped radially with a tread, consisting of at least one elastomeric mixture forming the outer surface of the tread of the tire, joined to two beads via two sidewalls, said tread comprising at least one regroovable groove forming at least one sculpture element constituting the sculpture of the tire, having a height between the bottom of said at least one groove and the rolling 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 in new condition. 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 phr and the rate of linearity of the complex dynamic shear module G*, measured at a temperature of 23°C according to standard ASTM D 5992-96, 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 to 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%.

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

The abbreviation "pce" means parts by weight per hundred parts of elastomer (of the total elastomers if several elastomers are present).

[0035] Elastomeric mixtures having a relatively high linearity rate, in particular greater than 0.55, associated with a quantity of plasticizer less than 15 phr are characterized during the manufacture of semi-finished products by extrusion by the appearance of tears forming irregularities surface, 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 for ignore the cutouts, and the surface of the tread pattern, said distance being measured in a direction normal to the radially outer surface of the tread. The tread depths are the radially innermost points of the recessed areas on the tread, ignoring the presence of elements such as wear indicators, regrooving depth indicator wells or any other element whose sum of the surfaces makes less than 15% of the total surface of the cut.

The groove height of said at least one regroovable groove of the tire when new is thus measured on a new tire. The height of said at least one regrooved groove can similarly 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 rolling 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 rolling surface when the tire is new. Advantageously, the height corresponding to the distance between the rolling 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 rolling surface when the tire is new.

The height corresponding to the distance between the rolling 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 rate of linearity of the complex dynamic shear module G*, measured at a temperature of 23°C according to standard ASTM D 5992-96, of said at least one elastomeric mixture forming the exterior surface of the tire is greater than 0.65 and preferably even greater than 0.75.

[0041] The tests carried out with tires conforming to the invention have shown that in comparison with usual 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 seeing impurities inserted into said mixtures during manufacturing, said tires also exhibiting satisfactory wear properties and in particular not exhibiting irregularities. excessive wear during use.

[0042] Indeed, 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 semi-finished profiles intended to form the exterior surface of the tread, with a surface having no beginning of grooves. The surface of the semi-finished intended to constitute the exterior surface of the tread is therefore almost smooth.

[0043] Indeed, for tread thicknesses similar to those of tires of more usual design, 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 at the new condition is reduced compared to that of tires of more usual design.

[0044] The low height of the grooves when new allows them to be fully formed during the cooking phase, the molding not leading to any deformation of the crown reinforcement. The grooves being shallower than those usually made, the creep of the materials generated during the molding of these grooves is not sufficient to significantly deform the crown reinforcement.

[0045] The surface edges of the semi-finished product being thus limited during extrusion, almost no irregularities are formed into which impurities could be inserted. During driving, including in 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 performance in terms of rolling resistance is improved by maintaining similar wet grip properties and for mileages up to complete wear of the tire that are substantially identical. [0047] The inventors have actually been able to demonstrate that the combination of a tread thickness substantially identical to that of a tire of more usual design with groove heights when new reduced in comparison to those of tires of a more usual design can significantly increase performance in terms of rolling resistance.

[0048] As stated previously, the regrooving provided for tires of a more usual design leads to heights of the grooves less than half the height of the grooves when new. In accordance with 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 a more usual design.

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

According to a variant embodiment of the invention, said at least one elastomeric mixture forming the outer surface of the tread of the tire comes from a semi-finished material 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, particularly speed, without the risk of irregularities appearing due to tearing usually initiated, with this type of elastomeric mixture, at the level of the edges.

[0052] These substantially rounded profiles are found in the tire after cooking. The semi-finished intended to form the surface of the tread cannot therefore form the entirety of this surface over a large thickness, 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 in a different elastomeric mixture, which will form these radially outermost parts of the flanks. 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 in a molar content of at most 4% of the constituent repeating units of 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 constituent repeating units of the diene elastomer, 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 modification agent and where appropriate a silane coupling agent for linking the diene elastomer to the silica, the modification agent carrying an N-substituted imidazole function and a unit containing a group reactive towards -screw of the diene elastomer, the total quantity of the modification agent and the silane coupling agent representing more than 5% by mass of the quantity of silica, the ratio between the quantity of the modification agent and the total amount of the modifying agent and the silane coupling agent being greater than 0.5, the amounts being expressed in part 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 regroovable circumferential and/or transverse and/or oblique 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 when new and preferably even greater than 95% of the tread height of the tire when new.

[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 not to risk deformation of the top frame during cooking. It may also still be possible to increase rolling resistance performance by providing further reduced 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 according to this embodiment of the invention, the elastomeric mixture regrooved during the first regrooving is different from the elastomeric mixture regrooved during the second regrooving. For example, the radially innermost elastomeric blend contains no black-type filler for display a color contrast when it appears at the time of the first re-digging.

Such an arrangement can in particular facilitate the regrooving stages.

[0064] According to other embodiments of the invention, the tread comprises depth indicators in the form of, for example, wells or incisions of small, non-zero width placed at the bottom of the groove, either parallel to the direction of said groove, either 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 indicator incision.

[0065] Advantageously according to the invention, the regroovable elastomeric mixture is different from at least part of the elastomeric mixture constituting the tread. Such an achievement 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.

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

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

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

[0069] One embodiment of the invention further provides that the crown reinforcement is supplemented 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 one of the embodiments of the invention mentioned above, the crown reinforcement can still be completed, radially inside between the carcass reinforcement and the nearest radially interior working layer of 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 advantageous details and 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 tread of the tire 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 tread of the tire according to a second variant of the invention,

- Figure 3, a meridian view of a diagram of a tire incorporating the semi-finished 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 embodiment of the invention,

- Figure 5, a meridian view of a diagram of a tire according to a second 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 shown to scale to simplify understanding. Figures 3, 4 and 5 only represent a half view of a tire which extends symmetrically with respect to the axis XX' which represents the circumferential median plane, or equatorial plane, of a tire.

[0073] Figure 1 represents a semi-finished U intended to form the radially outer part of the tread of the tire according to the invention. This semi-finished product in accordance with the invention does not have any grooves 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 whatever the nature of the elastomeric mixture. used.

[0074] Figure 2 illustrates a semi-finished product V according to a second alternative embodiment of the invention consisting of a central part VI and two axially external 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 exterior 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 for its part be made up of any type of elastomeric mixture including those mentioned previously which may present risks of tearing or tearing leading to the appearance of surface irregularities during extrusion when the profile desired has edges. Indeed, according to this second variant, not only does this central part VI not include the beginnings of grooves and furthermore the axially outer zones are substantially rounded so that no edges are present. According to this second alternative 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 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 alternative embodiment of the invention, the central part VI and the axially exterior parts V2 and V3 are coextruded, according to usual techniques, to make it possible 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 rods, not shown. The carcass reinforcement 2 is formed from a single layer of metal cables. The carcass reinforcement 2 is fitted by a crown reinforcement 5, itself covered with a tread 6. The tread has three grooves 3, 23 forming four ribs 4 and the two ribs axially in the center are cut out by oblique through grooves not shown in Figures 4 and 5.

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

[0079] In Figures 3 to 5, the top reinforcement 5 is formed radially from the inside to the outside: 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, at 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.

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 ₅₃ of 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 schematized in a meridian section. In this diagram, we see that we find parts VI and V2 after curing the tire. Also shown schematically are the grooves 3 obtained entirely by molding during the cooking stage. This Figure 3 allows you to better visualize the destiny of each of the parts VI, V2 and V3 and to observe that on a cooked tire, it is possible to find the initial shape of the parts VI, V2 and V3; particularly with regard to part VI, the edge-free profile is preserved even if the mixtures flow during molding and cooking.

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

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

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

[0087] This height HR 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 non-measurable height before this regrooving and corresponding to the distance between the rolling surface when new 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 height HR, measured after regrooving, and the non-measurable height before regrooving and corresponding to the distance between the rolling surface when new and the bottom of a groove 3 after regrooving can also be determined on a tire new 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 regroovings.

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

[0092] The height HRI of the 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 non-measurable height before a first regrooving and corresponding to the distance between the rolling surface when new and the bottom of the groove after the first regrooving is thus equal to 11 mm.

[0095] The height HRI, measured after the first regrooving, and the non-measurable height before a first regrooving and corresponding to the distance between the rolling surface in new condition and the bottom of the groove after the first regrooving can also be determined on new tires from the regrooving diagram provided by the manufacturer, as explained previously. [0096] The height HR2 of the grooves 23 after the second regrooving is equal to 6 mm and therefore represents 100% of HN23. And the height HR2 of the grooves 23 after the second regrooving represents 86% of HRI.

[0097] This height HR2 corresponds to a regrooving of 4 mm when there remains a height of the groove of 2 mm, 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 regroovings and corresponding to the distance between the rolling surface when new and the bottom of the grooves 23 after the second regrooving 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%.

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

[00100] The tire thus presented in Figure 5 provides for two regrooves at different stages of tire wear. Advantageously according to the invention the grooves are regrooved simultaneously at each regrooving step.

[00101] According to other alternative embodiments of the invention, the regrooving of the different grooves of a tire can be planned to take place staggered in time. According to these alternative embodiments, the tire may include a portion of these grooves which can be regrooved once and other grooves which can be regrooved several times. A tire could thus include a combination of grooves such as those illustrated in Figure 1 and grooves such as those illustrated in Figure 2.

[00102] Tires have been produced based on the elastomeric mixtures described below as mixtures constituting the tread.

[00103] The values of the constituents are expressed in pce (parts by weight per hundred parts of elastomers).

[00104] Mixture 2 corresponds to mixture C8 described in the patent application

WO 2020212184 Al.

[00105] Mixture 3 corresponds to mixture C2 described in the patent application

WO 2020094993 AL

[00106] Tires with references RI, R2 and R3 similar to that in the figures are produced according to a configuration corresponding to usual regrooving achievements. It has 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 when new, itself equal to 12 mm. This height after regrooving equal to 5 mm corresponds to a regrooving of 3 mm when there remains a height of the groove of 2 mm, a value close to the generally authorized legal limit corresponding to the minimum height. The unmeasurable height before re-digging and corresponding to the distance between the rolling surface when new and the bottom of the grooves after regrooving is thus equal to 15 mm.

[00107] The tire RI has a tread made of mixture 1.

[00108] The R2 tire has a tread consisting of the mixture

2.

[00109] The R3 tire has a tread consisting of the mixture

3.

[00110] The semi-finished products intended to form the tread of the RI, R2 and R3 tires are produced by extrusion according to a profile which provides the beginnings of grooves.

[00111] The R2 and R3 tires were made from semi-finished products, themselves made without taking any precautions during extrusion which is carried out at usual speeds. It was noted that these semi-finished products contained numerous irregularities on the surface, and more 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 baking of this tire led to an unacceptable deformation of the crown reinforcement to maintain regular wear during rolling. The semi-finished products were baked in a mold in which a release agent had been sprayed on the interior surface in a large quantity while being comparable to a quantity that could be encountered during large series manufacturing.

[00112] As in the case of tires according to the invention and as explained previously, the height, measured after regrooving, and the non-measurable height before regrooving and corresponding to the distance between the rolling surface in new condition and the bottom of the grooves after regrooving can also be determined on new tires from the regrooving diagrams provided by the manufacturer.

[00113] Tires Tl to T4 are produced in accordance with the invention. [00114] The tires Tl and T2 conform to the representation in Figures 2 and 5.

[00115] The tire Tl is made from a semi-finished V of which the central part VI consists of mixture 2.

[00116] The tire T2 is made from a semi-finished V, the central part VI of which is made up of mixture 3.

[00117] Tires T3 and T4 conform to the representation in Figures 2 and 6.

[00118] The tire T3 is made from a semi-finished V, the central part VI of which is made up of mixture 2.

[00119] The T4 tire is made from a semi-finished V whose central part VI is made up of mixture 3.

[00120] The axially exterior parts V2 and V3 of the semi-finished products used for each of the tires T1 to T4 are made up of mixture 1.

[00121] Initial driving tests were carried out along a circular trajectory with a radius of 12 meters on an aggressive bituminous concrete track for 100 laps, the tires equipping the two drive axles of a tractor. Each type of tire is tested according to this protocol.

[00122] After rolling, and analysis of the tires, it appears that 15% of the R2 tires and 25% of the R3 tires have at least one tear over a surface area of at least 2 cm ² and a maximum depth greater than 1 mm. The rate is zero for tires RI and tires according to the invention Tl to T4.

[00123] Furthermore, wear tests were carried out to show substantially identical performances with the Tl and T3 tires according to the invention and the reference tire RI, the T2 and T4 tires according to the invention having a duration of 35% longer life. Indeed, the volume of elastomeric materials constituting the tread, to be worn out during the life of the tire and the regrooving(s) is substantially identical for all the tires, which leads to close lifespans for the RI, Tl and T3 tires, the tread bearing being made in particular of natural rubber or polyisoprene. T2 and T4 tires whose tread is notably made of ethylene copolymer and functionalized 1,3-butadiene have longer lifespans.

[00124] Rolling resistance measurements were also carried out on each of the tires under identical rolling conditions according to Regulation No. 117 of the United Nations Economic Commission for Europe (UNECE). The R2 and R3 tires are again not tested. The measurement results are presented in the following table, 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 higher rolling resistance performance. Measurements are carried out on a new tire and on a planed tire to bring it to the level of the usual wear limit of approximately 2 mm on each of the tires RI, Tl, T2, T3 and T4. A measurement is again carried out after regrooving on each of the tires RI, Tl, T2, T3 and T4 and another on each of the tires RI, Tl, T2, T3 and T4 planed again to be brought to the level of the limit of Usual wear of approximately 2 mm. The T3 and T4 tires are again measured after the second regrooving and a final measurement is carried out on these T3 and T4 tires after planing to bring it to the level of the usual wear limit of approximately 2 mm.

[00125] Figure 6 schematically illustrates a representation of the evolution of the rolling resistance of each of the tires RI, Tl and T3 from their new condition until their end of life, that is to say during the 13 mm d tread wear. 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 correspond to the 15 mm of tread provided 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. [00126] The three lines appearing in this figure 6 correspond to each of the tires R, Tl and T3. Calculating the surfaces defined by these three lines makes it possible to estimate the average rolling resistance during the use of each of these tires. The results showed that the Tl 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

1 - Tire (1), regroovable at least once, comprising a crown reinforcement (5), itself radially capped with a tread (6), consisting of at least one elastomeric mixture forming the outer surface of the tread of the tire, joined to two beads via two sidewalls, said tread (6) comprising at least one regroovable groove (3) forming at least one sculpture element constituting the sculpture of the tire, having a height (HNS) between the bottom of said at least one groove (3) and the rolling surface when the tire is new, characterized in that, after regrooving, the height (HR) of said at least one groove (3) regrooved is greater than or equal to 70% of the groove height (HNS) of said at least one regroovable groove (3) of the tire in new condition, in that said at least one elastomeric mixture forming the outer surface of the strip of bearing of the tire comprises a quantity of plasticizer(s) less than 15 pce and in that the rate of linearity of the complex dynamic shear module 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 tread of the tire being greater than 0.55, the linearity rate being defined by the ratio of G* _m in to G* max, 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%.

2 - Tire (1) according to claim 1, characterized in that said at least one elastomeric mixture forming the outer surface of the tread of the tire comes from a semi-finished product whose axial ends do not have edges lively.

3 - Tire (1) according to one of claims 1 or 2, characterized in that the rate of linearity of the complex dynamic shear module G*, measured at a temperature of 23 °C according to the ASTM D 5992-96 standard, of said at least one elastomeric mixture forming the exterior surface of the tire is greater than 0.65 and preferably greater than 0.75. 4 - Tire (1) according to one of claims 1 to 3, characterized in that 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 at most 4% of the constituent repeating units of 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 constituent repeating units of the diene elastomer, the 1,3-diene being 1,3-butadiene or isoprene.

5 - Tire (1) according to one of claims 1 to 3, characterized in that 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% in mass of a silica, a crosslinking system, a modification agent and where appropriate a silane coupling agent for linking the diene elastomer to the silica, the modification agent carrying an N-substituted imidazole function and a pattern containing a group reactive with respect to the diene elastomer, the total quantity of the modification 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 part by weight per hundred parts of elastomer, pce.

6 - Tire (1) according to one of claims 1 to 5, characterized in that the height corresponding to the distance between the rolling surface in 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 rolling surface when the tire is new.

7- Tire (1) according to one of claims 1 to 6, characterized in that said at least one regroovable groove (3) is circumferential.

8 - Tire (1) according to one of claims 1 to 7, characterized in that said at least one regroovable groove (3) is transverse. 9 - Tire (1) according to one of claims 1 to 8, characterized in that said at least one regroovable groove (3) is oblique.

10 - Tire (1) according to one of claims 1 to 9, characterized in that at least one regroovable groove (3) can be regrooved at least twice. 11 - Tire (1) according to claim 10, characterized in that the elastomeric mixture regrooved during the first regrooving is different from the elastomeric mixture regrooved during the second regrooving.

12 - Tire (1) according to one of the preceding claims, characterized in that the regroovable elastomeric mixture is different from at least part of the elastomeric mixture constituting the tread.

13 - Tire (1) according to one of the preceding claims, characterized in that said tread comprises, at least locally, at least two layers of elastomeric mixtures radially superimposed in the tread.