TIRE WITH A RETRACTABLE TREAD

Abstract

The invention relates to a tire (1) that can be regrooved at least once and whose tread has at least one regroovable groove (3). According to the invention, after regrooving, the height (HR) of said at least one regrooved groove (3) is greater than or equal to 70% of the groove height (HN3) of said at least one regroovable groove of the tire in its new condition, the elastomeric compound forming the outer surface of the tread having an amount of plasticizer(s) less than 15 parts per cubic centimeter and the linearity ratio of the complex dynamic shear modulus G* of said elastomeric compound being greater than 0.55. Figure for the abstract: Fig 4

Description

Title of the invention: TYRE COMPRISING A RECROUGABLE TREAD

[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-duty tires, the carcass reinforcement is anchored on both sides in the bead area and is radially surmounted 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 in the area of ​​the crown of the tire are subjected.

[0003] Cables are said to be inextensible when said cables exhibit, under a tensile force equal to 10% of the breaking force, 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 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 that contains the axis of rotation of the tire.

[0008] 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 inside, respectively axially outside" 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 during rolling and to wear during rolling, with a sculpture formed of raised elements delimited by cutouts such as grooves, whether they are circumferential, transverse or oblique in orientation. The objective of such a sculpture is to give the tread good performance when rolling on dry roads and on water-covered roads, particularly in wet weather.

[0013] To improve the performance of the 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, during rolling, at least partial contact between the facing walls delimiting these incisions and in particular during the passage into contact with the ground, which could not 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 in which the 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 medium plane as just described.

[0015] For the purposes of the invention, a transversely oriented cutout is a cutout whose mean plane of at least a portion 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 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 may be oriented in one direction or the other relative to said radial plane. An obliquely oriented cutout may also 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 appears. 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 a fining of the elastomeric materials which is not controlled 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 performance of the tire in terms of wear and in particular regularity of wear, the thickness of the mixture to be used 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 crown reinforcement of the tire.

[0019] In recent years, new elastomeric compounds 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. These elastomeric mixtures, on the other hand, have decohesion properties before vulcanization. They are thus characterized by high risks of tearing when they are subjected to certain stresses. This decohesive character can be observed in particular at the outlet of the extruder, 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 with edges and therefore appear particularly at the level of the grooves preformed during extrusion as described above.

[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 examiners were able to demonstrate that in certain cases of use of the tires, in cases of demanding uses, unusual wear of the tread 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 is understood to mean 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, in particular for regulatory reasons.

[0023] The grooves generally include 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 which must legally remain on the tread in use. The treads for heavy goods vehicles can be regroovable (an 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 makes it possible 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 which 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 known per se, the regrooving of a groove can be carried out using a heated rounded 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 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 allows sharp edges to be restored and is usually intended to restore a tread height corresponding to that of a half-worn heavy goods vehicle tyre. 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 tyres in new condition of between 12 and 20 mm.

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

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

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

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

[0032] This aim has been achieved according to the invention by a tire, regroovable at least once, comprising a crown reinforcement, itself radially capped with a strip 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) of less than 15 pce and the linearity rate of the complex dynamic shear modulus G*, at a temperature of 23°C, 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*min 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%.

[0033] The abbreviation "pce" means parts by weight per hundred parts of elastomer (of the total elastomers if several elastomers are present).

[0034] Elastomeric mixtures having 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.

[0035] 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 zones on the tread, disregarding the presence of elements such as wear indicators, regrooving depth indicator wells or any other element whose sum of the surfaces is less than 15% of the total surface of the cutout.

[0036] 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.

[0037] Advantageously according to the invention, the height corresponding to the distance between the tread surface in the new state 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 the new state 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.

[0038] The height corresponding to the distance between the tread surface in new condition 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.

[0039] Preferably according to the invention, the linearity rate of the complex dynamic shear modulus G*, at a temperature of 23°C, of ​​said at least one elastomeric mixture forming the outer surface of the tire is greater than 0.65 and more preferably greater than 0.75.

[0040] The tests carried out with tires in accordance with 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, combined with a quantity of plasticizer of 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 excessively pronounced wear irregularities during use.

[0041] 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 beginnings of grooves. The surface of the semi-finished product intended to constitute the outer surface of the tread is therefore almost smooth.

[0042] 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 in the new condition means that the height of the grooves in new condition is reduced compared to that of tires of more usual design.

[0043] The low height of the grooves in the new state allows their total formation during the baking phase, the molding not leading to any deformation of the crown reinforcement. The grooves being less deep than those usually produced, the finishing of the materials generated during the molding of these grooves is not sufficient to significantly deform the crown reinforcement.

[0044] Since the surface edges of the semi-finished product are thus limited during extrusion, virtually no irregularities are formed into which impurities could become inserted. During rolling, including under severe conditions, the risks of tearing or very pronounced wear occurring due to such impurities are greatly reduced or even non-existent.

[0045] Furthermore, the inventors have demonstrated that the performance in terms of rolling resistance is improved while maintaining similar wet grip properties and for substantially identical mileages until the tire is completely worn.

[0046] The inventors have indeed been 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 the performance in terms of rolling resistance.

[0047] As stated previously, the regrooving provided on tires of more usual 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 usual design.

[0048] 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.

[0049] According to an alternative 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 product whose axial ends do not have sharp edges.

[0050] 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 conditions, in particular of speed, completely usual without risk of seeing irregularities appear due to tearing usually initiated, with this type of elastomeric mixture, at the edges.

[0051] 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 entirety of this surface over a large thickness, the radially outer part of the sidewalls not being able to 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 sidewalls. These three semi-finished products can advantageously be co-extruded.

[0052] 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 mol% of the repeating units constituting the diene elastomer, the 1,3-diene being 1,3-butadiene or isoprene.

[0053] 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.

[0054] According to a first embodiment of the invention, said at least one re-diggable groove is circumferential.

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

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

[0057] According to other embodiments of the invention, the tire has a combination of circumferential and / or transverse and / or oblique regroovable grooves.

[0058] Whether they are in the same orientation or in several orientations, the invention advantageously provides that all of the grooves of the tire are re-grooved according to the invention during the same step.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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 to display a color contrast when it appears at the time of the first re-grooving. Such an arrangement can in particular facilitate the re-grooving steps.

[0063] 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.

[0064] 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.

[0065] 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 radially superimposed elastomeric mixtures.

[0066] 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 making angles between 10° and 45° with the circumferential direction.

[0067] According to other embodiments of the invention, the crown reinforcement further comprises at least one layer of circumferential reinforcing elements.

[0068] 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 circumferential direction with an angle of 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.

[0069] According to any one 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 reinforcing elements made of steel 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.

[0070] 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: [Fig.l], 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, [Fig.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, [Fig.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 [Fig.2], [Fig.4], a meridian view of a diagram of a tire according to a first exemplary embodiment of the invention, [Fig.5], a meridian view of a diagram of a tire according to a second exemplary embodiment of the invention, [Fig.6], a schematic representation of the rolling resistance during wear of a reference tire and two tires according to the invention.

[0071] 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.

[0072] [Fig. 1] represents a semi-finished product U intended to form the radially outer part of the tread of the tire according to the invention. This semi-finished product 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.

[0073] [Fig. 2] illustrates a semi-finished product V according to a second variant 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 [Fig.l], 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.

[0074] 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 co-extruded, according to standard techniques, to simplify the manufacture of the tire.

[0075] Figures 3 to 6, which follow, illustrate in more detail the tire 1 and the principle of regrooving according to the invention.

[0076] 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 with a tread 6. The tread comprises three grooves 3, 23 forming four ribs or “ribs” 4 and the two ribs or “ribs” axially in the center are cut by oblique crossing grooves not shown in figures 4 and 5.

[0077] The lower zones and beads of the tire 1 are not shown in particular in Figures 3 to 5.

[0078] In Figures 3 to 5, the crown 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, - a layer of circumferential reinforcing elements 53 formed of elastic steel wire cables 21.23, with a pitch of 2 mm, and - 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.

[0079] The axial width L5i of the first working layer 51 is equal to 246 mm.

[0080] The axial width L52 of the second working layer 52 is equal to 228 mm.

[0081] As for the axial width L53 of the layer of circumferential reinforcing elements 53, it is equal to 200 mm.

[0082] In [Fig. 3], a part of a tire 1 incorporating a radially outermost part of its tread 6 according to the second variant illustrated in [Fig. 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 [Fig. 3] makes it possible to better visualize 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.

[0083] In [Fig. 4], in accordance with the invention, the grooves 3 are of the regroovable type. As illustrated in [Fig. 1], the grooves 3 consist of a single layer A forming the bottom of the grooves in the new state and corresponding to a single regrooving.

[0084] The height on new HN3 tire of grooves 3 is equal to 7.5 mm.

[0085] The height HR of the grooves 3 after regrooving is equal to 9.5 mm and therefore represents 127% Hn3.

[0086] 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 on [Fig.4].

[0087] The non-measurable height before this regrooving and corresponding to the distance between the rolling surface in the new state 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%.

[0088] The height HR, measured after regrooving, and the height not measurable 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.

[0089] [Fig. 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.

[0090] The height on a new HN23 tire of the grooves 23 is equal to 6 mm.

[0091] The height HRides grooves 23 after the first regrooving is equal to 7 mm and therefore represents 117% of HN23.

[0092] This height HRi 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 on [Fig.2].

[0093] The height which cannot be measured before a first regrooving and which 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.

[0094] The height HRb 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.

[0095] 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 HRb

[0096] This height HR2 corresponds to a regrooving of 4 mm when there remains a groove height of 2 mm, a value close to the generally authorized legal limit corresponding to the minimum height. This limit is symbolized by line 72 on [Fig.2],

[0097] 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%.

[0098] The height HR2, measured after the second regrooving, and the height not measurable 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.

[0099] The tire thus presented in [Fig.5] provides two regrooves at different stages of tire wear. Advantageously according to the invention the grooves are regrooved simultaneously at each regrooving stage.

[0100] According to other alternative embodiments of the invention, the regrooving of the different grooves of a tire can be arranged to be done in a time-shifted manner. According to these alternative embodiments, the tire can 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 [Fig. 1] and grooves such as those illustrated in [Fig. 2].

[0101] Tires have been produced based on the elastomeric mixtures described below as mixtures constituting the tread. ïjSalaiES 1 2 Mixture 3 «R SS sss te naves: 1R6JSS by is company ICX? and Sæ '103 22 «234 43 SS SG SteneSISS 4.3 4.S SPSS - LÏKMîpM SOTfl. 5 2 A 5 Z 2' SOÜFSë 1.5 Arcéi-érateur ftSS) D.5 2 2 sas Rate of lisant? 3.34 as &7S

[0102] The values ​​of the constituents are expressed in pce (parts by weight per hundred parts of elastomers).

[0103] Mixture 2 corresponds to mixture C8 described in patent application WO 2020212184 AL

[0104] Mixture 3 corresponds to mixture C2 described in patent application WO 2020094993 Al.

[0105] Tires of references RI, R2 and R3 similar to that of the figures are produced according to a configuration corresponding to usual regrooving embodiments. 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 tread surface in the new condition and the bottom of the grooves after regrooving is thus equal to 15 mm.

[0106] The RI tire has a tread made of the mixture 1.

[0107] The tire R2 has a tread made of the mixture 2.

[0108] The R3 tire has a tread made of the mixture 3.

[0109] Semi-finished products intended to form the tread of RI, R2 and R3 tires R3 are made by extrusion according to a profile which provides groove starters.

[0110] The R2 and R3 tires were produced from semi-finished products, themselves produced without taking precautions during extrusion, which was carried out at normal speeds. It was found that these semi-finished products contained numerous surface irregularities, and more particularly at the edges of the grooves preformed during extrusion. The inventors had previously demonstrated that producing a depth of 12 mm by molding during the curing of this tire leads to unacceptable deformation of the crown reinforcement for maintaining 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, while being comparable with a quantity that could be encountered during mass production.

[0111] 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 state and the bottom of the grooves after regrooving can also be determined on a new tire from the regrooving diagrams provided by the manufacturer.

[0112] Tires T1 to T4 are produced in accordance with the invention.

[0113] The tires T1 and T2 are in accordance with the representation of figures 2 and 5.

[0114] The tire T1 is produced from a semi-finished product V, the central part V1 of which is made up of the mixture 2.

[0115] The tire T2 is made from a semi-finished product V whose central part V1 is made from the mixture 3.

[0116] The T3 and T4 tires conform to the representation in Figures 2 and 6.

[0117] The T3 tire is made from a semi-finished product V, the central part V1 of which is made up of the mixture 2.

[0118] The T4 tire is made from a semi-finished product V, the central part V1 of which is made from the mixture 3.

[0119] 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.

[0120] Initial rolling tests were carried out along a circular trajectory with a radius of 12 metres on an aggressive bituminous concrete track for 100 laps, with the tyres fitted to both drive axles of a tractor. Each type of tyre is tested according to this protocol.

[0121] 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 cm2 and a maximum depth greater than 1 mm. The rate is zero for the RI tires and the tires according to the invention T1 to T4.

[0122] Furthermore, wear tests were carried out to show substantially identical performances with the tires T1 and T3 according to the invention and the reference tire RI, the tires T2 and T4 according to the invention having a service life 35% longer. Indeed, the volume of elastomeric materials constituting the tread, to be worn during the life of the tire and the regrooving(s) is substantially identical for all the tires, which leads to similar service lives for the tires RI, T1 and T3, the tread being made in particular of natural rubber or polyisoprene. The tires T2 and T4 whose tread is made in particular of functionalized ethylene and 1,3-butadiene copolymer have longer service lives.

[0123] 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 results of the measurements 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 are 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 be brought to the level. of the usual wear limit of approximately 2 mm. The T3 and T4 tires are still measured after the second regrooving and a final measurement is taken on these T3 and T4 tires after planing to bring it to the level of the usual wear limit of approximately 2 mm. W ■d-wear After a Wear limit After recreussges Gods Wear binder PssesjsîisSique .Kl IGG TA ■ Z 7g PaeutnatsqBe. 12 91 S2 iBaeums&qæe Tl §4 77 77 £5 6S 60 Paeumatiatse 14 SS $5 / .J 61

[0124] [Fig.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. [Fig.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 the 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.

[0125] The three plots appearing in this [Fig.6] correspond to each of the RI, Tl and T3 tires. The calculation of the surfaces defined by these three plots 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 RI tire and that the T3 tire allows a gain of 12% compared to the RL tire.

Claims

Claims

1. A 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 by means of two sidewalls, said tread (6) comprising at least one regroovable groove (3) forming at least one tread element constituting the tread of the tire, having a height (HN3) 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 (HN3) of said at least one regroovable groove (3) of the tire when new,in that said at least one elastomeric mixture forming the outer surface of the tread of the tire comprises a quantity of plasticizer(s) of less than 15 phr and in that the linearity rate of the complex dynamic shear modulus G*, at a temperature of 23°C, of ​​said at least one elastomeric mixture forming the outer surface of the tread of the tire is greater than 0.55, the linearity rate being defined by the ratio of G*min 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 sharp edges.

3. Tire (1) according to one of claims 1 or 2, characterized in that the linearity rate of the complex dynamic shear modulus G*, at a temperature of 23°C, of ​​said at least one elastomeric mixture forming the outer 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 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 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% 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 amount of the modifying agent and the silane coupling agent representing more than 5% by mass of the amount of the silica, the ratio between the amount of the modifying agent and the total amount of the modifying agent and the silane coupling agent being greater than 0.5, the amounts being expressed in parts by weight per cent elastomer parts, pc.

6. Tyre (1) according to one of claims 1 to 5, characterized in that the height corresponding to the distance between the running 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 running surface when the tyre 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. Tyre (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.

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