TIRE WITH A RETRACTABLE TREAD

Abstract

The invention relates to a tire (1) that can be regrooved at least once and whose tread comprises at least one regroovable cut (3) made of material to be regrooved in at least one regrooving step, the height (HR) of said at least one regrooved cut (3) being greater than or equal to 70% of the cut height (HN) of said at least one regroovable cut (3) of the tire in its new condition. According to the invention, the regrooving material consists of at least one first layer of an elastomeric compound added to the bottom of the cut after curing the tire, and said at least one first layer being bonded to the cured tire over its entire surface in contact with the bottom and walls of said at least one cut. Figure for the abstract: Fig 1

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 cutout of longitudinal or circumferential orientation is a cutout of 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 cutout of longitudinal orientation 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] Combined with this need to improve grip performance by the presence of edges formed by the transverse cutouts, 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 tread thickness that can be worn before having to change the tire, in particular for regulatory reasons.

[0018] Heavy goods vehicle treads can be regrooved (an operation by which new grooves can be regrooved), and tyres with such treads carry 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 tyre and, on the other hand, to significantly increase mileage.

[0019] 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 (European Tires and Rim Technical Organization) and AFNOR (French Association for Standardization) with the NFR12714 standard. For this operation, manufacturers are required to provide regrooving diagrams that are binding on the technicians in charge of this regrooving.

[0020] The groove heights on new tires are measurable and the groove heights after regrooving can be deduced from these regrooving diagrams.

[0021] As known per se, the regrooving of a groove can be carried out using a blade 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.

[0022] Regrooving allows sharp edges to be restored and is usually intended to restore a tread height corresponding to that of a mid-wear heavy goods vehicle tyre. The usual recommendations aim for a height after regrooving of 4 to 6 mm composed of a regrooving of 2 to 4 mm and 2 mm of remaining height; in practice, regrooving is often carried out at the initiative of the tyre user 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.

[0023] 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.

[0024] 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.

[0025] Furthermore, document WO 2022 / 180325 has already described tires having rolling resistance performance that is further improved throughout their running by combining one or more regrooving steps with particularly low tire tread heights when new.

[0026] The demand for such tires conforming to the teaching of document WO 2022 / 180325 could become very significant, and consideration is being given to making it possible to offer a choice of tires conforming to this teaching and others according to a more usual design, that is to say without the possibility of regrooving, for the same dimension without requiring the multiplication of manufacturing tools and in particular baking molds.

[0027] The inventors set themselves the task of proposing tires in accordance with the teaching of document WO 2022 / 180325 which do not require the production of new molds for their baking.

[0028] This object has been achieved according to the invention by a tire, regroovable at least once, comprising a crown reinforcement, itself radially capped with a tread, consisting of at least a first elastomeric mixture forming at least the tread surface, joined to two beads by means of two sidewalls, said tread comprising at least one regroovable cutout forming at least one tread element constituting the tread of the tire, having a cut-out height when the tire is new and consisting of material to be regrooved in at least one regrooving step, the height of said at least one regrooved cut-out being greater than or equal to 70% of the height of said at least one regroovable cut-out of the tire in the new condition, said material to be regrooved of said at least one cut-out consisting of at least a first layer of an elastomeric mixture added to the bottom of the cut-out after curing of the tire and said at least one first layer being bonded to the cured tire over its entire surface in contact with the bottom and the walls of said at least one cut-out.

[0029] For the purposes of the invention, the height of a cutout 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 bottom of the cutout, said distance being measured in a direction normal to the radially outer surface of the tread. The bottoms of the cutouts are the radially innermost points of said cutouts, 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.

[0030] For the purposes of the invention, the height of material to be regrooved is measured between the bottom of said at least one cutout in the new state and the bottom of said cutout after the last regrooving. It can be determined from the regrooving plans associated with the tire.

[0031] A tire thus produced according to the invention does not require the investment of a new mold, at least part of the material to be regrooved being added after curing the tire. According to the invention, it is actually possible to produce the tire according to the invention from a commercial tire. This in fact involves modifying the tire to make it conform to the teaching of document WO 2022 / 180325.

[0032] The inventors were able to demonstrate that the simple addition of an elastomeric layer not bonded to the cured tire over its entire surface in contact with the bottom and the walls of said at least one groove does not make it possible to achieve the performance in terms of rolling resistance promised according to the teaching of document WO 2022 / 180325.

[0033] Indeed, during their tests, the inventors showed that the installation of a strip of elastomeric material at the bottom of a groove not bonded to the tire cured over its entire surface in contact with the bottom and the walls of said at least one groove leads, during rolling, to friction on the walls of the grooves of the tire. cooked having the opposite effect on performance in terms of rolling resistance, this friction inducing energy dissipation.

[0034] According to a preferred embodiment of the invention, the bond between said first layer of an elastomeric mixture and the surface of said at least one re-diggable cutout of the tire visible after curing is broken by tearing after an elongation of at least 20% of a sample according to the test as described below.

[0035] The elongation test is carried out in a direction perpendicular to the walls of the cutout on a sample taken from a tire, consisting on either side of the walls of a thickness of rubber mixture constituting the tread identical to the width of the cutout, of a height equal to the distance, not measurable on the tire, between the rolling surface in the new condition and the bottom of the cutout after the last regrooving increased by 1 mm and of a length measured in the direction of the mean plane of the walls between 40 and 60% of the distance measured between the walls of the cutout in a direction perpendicular to said walls.On a uniaxial extension machine allowing this elongation test to be carried out, the jaws grip the sample over a thickness of the rubber mixture forming the tire tread between 40 and 60% of the distance measured between the walls of the cutout in a direction perpendicular to said walls. The pressure exerted on the sample by the jaws is equal to 4 bars. The traction speed is equal to 3 mm per minute. The elongation measured and expressed as a percentage is equal to the ratio between the displacement of the jaws and the distance measured between the walls of the cutout in a direction perpendicular to said walls.

[0036] The inventors have also been able to demonstrate that from such an elongation threshold before tearing, under normal driving conditions, the connection is considered to make it possible to provide the expected rolling resistance performance according to the teaching of document WO 2022 / 180325.

[0037] Advantageously, the bond between said first layer of an elastomeric mixture and the surface of said at least one cutout of the tire visible after curing is broken by tearing after an elongation of at least 35% when particularly severe driving conditions are expected and advantageously even greater than 60%.

[0038] The bonding of a layer added after curing of the tire as described according to the invention between said at least one first layer of an elastomeric mixture added to the bottom of the groove of the cured tire can be obtained according to different types of manufacturing process of said layer.

[0039] This may be, for example, a one-step laying process consisting, using a pump, of depositing the elastomeric material at the bottom of the groove. The cord thus formed can then be cooked using “flashing” type techniques known to those skilled in the art and allows for rapid and localized action.

[0040] It may also involve printing techniques, such as additive manufacturing or 3D printing, allowing the production of a layer of an elastomeric material by successive steps of simultaneous deposition and curing. Such techniques are for example described in documents FR 3 067 281 A1 or WO 2013 / 086577.

[0041] In the case of the production of said at least one first layer by additive manufacturing, according to an advantageous embodiment of the invention, before the step of curing the tire, a thin layer, with a thickness of less than one millimeter, is deposited on the surface of the tire tread. The thin layer consists of an elastomeric mixture preferably identical to that of said at least one first layer. After curing the tire, the bottom and the walls of said at least one cutout are covered with said thin layer. The tests carried out have shown that the results obtained according to the tear-off test can be further improved with the presence of said thin layer, depending on the nature of the elastomeric mixture constituting said first layer.

[0042] According to alternative embodiments of the invention, said material to be regrooved from said at least one cutout is made up of at least two layers of elastomeric mixtures added to the bottom of the cutout after curing of the tire. According to one of these alternative embodiments comprising a first layer bonded to the cured tire over its entire surface in contact with the bottom and the walls of said at least one cutout and a second layer, said second layer is bonded to the cured tire over its entire surface in contact with the walls and indirectly to the bottom of the cutout via said first layer. In the case of three radially superimposed layers of elastomeric mixtures, the third layer is bonded to the cured tire over its entire surface in contact with the walls and to the second layer and therefore indirectly to the bottom of the cutout via the first and second layers of elastomeric mixtures.

[0043] In the case of several layers forming the material to be regrooved, these can advantageously be made up of different elastomeric mixtures.

[0044] According to a first embodiment of the invention, said at least one regroovable cutout is circumferential.

[0045] According to a second embodiment of the invention, said at least one regroovable cutout is transverse.

[0046] According to a third embodiment of the invention, said at least one regroovable cutout is oblique.

[0047] According to other embodiments of the invention, the tire has a combination of circumferential and / or transverse regroovable cutouts and / or obliques.

[0048] Whether in the same orientation or in several orientations, the invention advantageously provides that all of the cutouts of the tire are regrooved according to the invention during the same step.

[0049] In accordance with the teaching of document WO 2022 / 180325, according to one embodiment of the invention at least one cutout can be regrooved at least twice. According to this embodiment, it may be possible to further increase the rolling resistance performance by providing further reduced cutout depths when new while still satisfying wet grip performance.

[0050] According to this embodiment and in the case of several cutouts provided in the same orientation or in several orientations, the invention advantageously provides that all of the cutouts of the tire are regrooved simultaneously during each regrooving.

[0051] Advantageously still according to the invention, the regrooved elastomeric mixture(s) are different from the elastomeric mixture constituting the tread. Advantageously still, the regrooved mixtures which are added to the cutouts after curing are elastomeric mixtures whose hysteretic properties are advantageous with regard to the rolling resistance properties.

[0052] The embodiment according to the invention advantageously makes it possible to provide elastomeric mixtures different from those constituting the tread, including in the case of transverse or oblique cutouts. Indeed, the usual technology for producing semi-finished products made up of several elastomeric mixtures is coextrusion, but this is almost impossible in the case of several mixtures forming the bottom of transverse or oblique cutouts.

[0053] Advantageously according to the invention, the height corresponding to the distance between the running surface in the new condition and the bottom of the cutouts after the last regrooving of such tires is greater than or equal to 200% of the height between the bottom of the cutout and the running surface when the tire is new.

[0054] Advantageously, the height corresponding to the distance between the tread surface in the new condition and the bottom of the cutout after the last regrooving is greater than or equal to 250% of the height between the bottom of the cutout and the tread surface when the tire is new.

[0055] The invention as just described is also particularly well suited to the regrooving of tires such as those described in patent application PCT / EP2023 / 057206 which, in addition to the description of the tire according to document WO 2022 / 180325, provides for the presence of at least one incision, flush with the tread surface when the tire is new and having a height between the bottom of said at least one incision and the tread surface when the tire is new greater than the height of a regroovable cutout of the tire in new condition and advantageously equal to the height corresponding to the distance between the rolling surface in new condition and the bottom of said at least one cutout after the last regrooving.

[0056] According to a preferred embodiment of the invention, the height of said at least one incision of the tire in the new condition is greater than 90% of the height corresponding to the distance between the rolling surface in the new condition and the bottom of said at least one cutout after the last regrooving.

[0057] More preferably, the height of said at least one incision of the tire in the new condition is equal to the height corresponding to the distance between the rolling surface in the new condition and the bottom of said at least one cutout after the last regrooving.

[0058] According to certain embodiments of the invention, the part of the tread constituting the zones capable of forming the contact surface of the tire with the ground may consist of at least two layers of radially superimposed elastomeric mixtures. Thus, according to a variant of the invention, said tread comprises, at least locally, at least two layers of radially superimposed elastomeric mixtures in the tread.

[0059] According to its embodiments of the invention, the production of the semi-finished products intended to form the tread part of the tire can be carried out according to usual methods known to those skilled in the art and in particular by co-extrusion of the mixtures during the preparation of the semi-finished product(s) intended to constitute at least part of the tread.

[0060] According to one embodiment of the invention, the crown reinforcement of the tire is formed from at least two working crown layers of inextensible reinforcing elements, crossed from one layer to the other making angles of between 10° and 45° with the circumferential direction.

[0061] According to other embodiments of the invention, the crown reinforcement further comprises at least one layer of circumferential reinforcing elements.

[0062] 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.

[0063] According to any one of the embodiments of the invention mentioned above, the crown reinforcement can also be supplemented, radially inside between the carcass reinforcement and the radially inner working layer closest to said carcass reinforcement, by a triangulation layer of reinforcement elements. inextensible steel metal reinforcements forming, 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.

[0064] 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 3 which represent: - [Fig.l], a meridian view of a diagram of a tire according to a first exemplary embodiment of the invention, - [Fig.2], a meridian view of a diagram of a tire according to a second exemplary embodiment of the invention, - [Fig.3], a force / elongation curve of a sample taken from a new tire conforming to [Fig.l].

[0065] The figures are not shown to scale to simplify understanding. Figures 1 and 2 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.

[0066] In Figures 1 and 2, the tire 1, of dimension 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 circumferential grooves 3 forming four ribs or ribs 4. The circumferential grooves 3 have a width measured in the axial direction, corresponding to the distance between the walls of said grooves measured in the direction perpendicular to said walls of said circumferential grooves, equal to 10 mm.

[0067] The lower zones and beads of the tire 1 are not shown in the figures.

[0068] In Figures 1 and 2, 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 al, - 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 a2 and crossed with the metal cables of the first working layer.

[0069] The axial width of the first working layer 51 is equal to 246 mm.

[0070] The axial width of the second working layer 52 is equal to 228 mm.

[0071] As for the axial width of the layer of circumferential reinforcing elements 53, it is equal to 200 mm.

[0072] In [Fig.l], in accordance with the invention, the grooves 3 are of the regroovable type. As illustrated in [Fig.l], 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.

[0073] Layer A was produced in accordance with the invention after curing the tire, the groove depths of which were equal to 15 mm. Layer A is produced using additive manufacturing or 3D printing techniques.

[0074] The height on new HN3 tire of grooves 3 is equal to 7.5 mm.

[0075] The height HR of the grooves 3 after regrooving is equal to 9.5 mm.

[0076] 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.l].

[0077] The height which cannot be measured before this regrooving and which corresponds 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.

[0078] [Fig. 2] 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.

[0079] Layers B and C were produced in accordance with the invention after curing the tire, the groove depths of which were equal to 15 mm.

[0080] Layers B and C are produced using additive manufacturing or 3D printing techniques.

[0081] The height on new tire HN23 of the grooves 23 is equal to 6 mm.

[0082] The height HRides grooves 23 after the first regrooving and removal of layer B is equal to 7 mm. Layer C is then visible.

[0083] 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].

[0084] 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.

[0085] The height HR2 of the grooves 23 after the second regrooving and removal of the layer C is equal to 6 mm.

[0086] This height HR2 corresponds to a regrooving of 4 mm when a groove height of 2 mm remains, a value close to the legal limit generally authorized cor corresponding to the minimum height. This limit is symbolized by line 72 on [Fig.2],

[0087] The height which cannot be measured before the two regrooves and which corresponds to the distance between the rolling surface in the new state and the bottom of the grooves 23 after the second regroove is thus equal to 15 mm.

[0088] The tire thus presented in [Fig.2] provides two regrooves at different stages of tire wear. Advantageously according to the invention the grooves are regrooved simultaneously at each regrooving stage.

[0089] 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].

[0090] Tires I were produced in accordance with [Fig.l] on the basis of the elastomeric mixtures described below. First Mixture Second Mixture NR 80 BR 20 SIS (styrene / isoprene / styrene) 100 N234 48 15 Stearic acid '2 - 6FPQ - 1.3DIMETKÆ BUm PHENYL PARAPHENYLENE-DÎAMi NE 2.5 - ZNO 3 - Sulfur 1.5 - Accelerator (CBS) 0.9 -

[0091] The values ​​of the constituents are expressed in pce (parts by weight per hundred parts of elastomers).

[0092] The first mixture is the tread mixture.

[0093] The second mixture constitutes the A layers.

[0094] The function of the carbon black in the second mixture is in particular to confer the black color to the mixture. Variants of this mixture could include instead of carbon black an agent coloring the mixture in another color, for example to allow the different regrooving limits to be identified in the case of several superimposed layers as in the example of [Fig.2]. In addition, this second mixture can include a silica filler to provide rigidity if necessary. necessary to accompany a coloring agent.

[0095] Rolling tests were carried out with a tire I according to the invention in accordance with [Fig.l] in real conditions and on tracks at higher speeds. Following these rolling tests, the tires did not show any particular alteration relating to layer A.

[0096] Elongation tests were carried out on samples taken from new tires.

[0097] The samples are made by cutting into the tire around a groove. Each sample is made up on either side of the walls of a groove of a thickness of rubber compound, constituting the tread, identical to the width of the cutout. The height of the sample is equal to the distance, not measurable on the tire, between the tread surface in new condition and the bottom of the cutout after the last regrooving increased by 1 mm. The height is determined by the regrooving plan provided by the tire manufacturer. The length of the sample measured in the direction of the mean plane of the walls is between 40 and 60% of the distance measured between the walls of the cutout in a direction perpendicular to said walls.

[0098] The sample is then subjected to uniaxial elongation in a direction perpendicular to the walls of the cutout. On a machine marketed by the company Instron under the reference “5969”, the jaws grip the sample over a thickness of the rubber mixture forming the tread of the tire between 40 and 60% of the distance measured between the walls of the cutout in a direction perpendicular to said walls. The pressure exerted on the sample by the jaws is equal to 4 bars. The traction speed is equal to 3 mm per minute.

[0099] The elongation considered corresponds when plotting the force displacement curve to a rupture of the groove showing a horizontal plateau which indicates a rupture or tearing in the connection between layer A and the bottom and / or the walls of the groove.

[0100] During the test, the measured elongation was 42%. This measurement is illustrated in [Fig.3] on which is represented the line 31 of the force / displacement curve. The line 32 gives us the displacement applied when the slope break described previously appears. The displacement of the jaws being then 4.2 mm, related to the width of the groove equal to 10 mm, the elongation is equal to 42%.

[0101] Other tests were carried out according to an alternative embodiment of the invention described above according to which a thin layer is produced on the surface of the tread during curing of the tire. As explained above, the thin layer is produced with the second mixture. Its thickness on the bottom of the grooves and on the walls is on average equal to 0.7 mm. The elongation measured during the elongation tests is equal to 95%.

[0102] Rolling resistance measurements were also carried out on tires I according to the invention and tires RI and R2 under identical driving conditions according to Regulation No. 117 of the United Nations Economic Commission for Europe (UNECE).

[0103] The RI tires are tires identical to the tire I according to the invention but which do not have a layer A in the grooves 23.

[0104] The R2 tires are tires identical to the tire I according to the invention, the layer A having been inserted into the grooves without being bonded to the entirety of the bottom and the walls of the grooves 23 with which it is in contact.

[0105] The measurement results are presented in the following table, with a value of 100 being assigned to the reference tire RI 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. The measurements are carried out on a new tire on each of the tires I, RI and R2. Rolling resistance Pneumatic I 94 Pneumatic Rï 100 Pneumatic R2 101

[0106] These results demonstrate that when layer A is not bonded to the cured tire over its entire surface in contact with the bottom and the walls of said at least one groove, it undergoes friction during rolling on the walls of the grooves of the cured tire having the opposite effect on the performance in terms of rolling resistance, this friction inducing energy dissipation.

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 at least the tread surface, joined to two beads by means of two sidewalls, said tread (6) comprising at least one regroovable cutout (3) forming at least one tread pattern element constituting the tread pattern of the tire, having a height (HN) of the cutout (3) when the tire is new and consisting of material to be regrooved in at least one regrooving step, the height (HR) of said at least one regrooved cutout (3) being greater than or equal to 70% of the height (HN) of said at least one regroovable cutout (3) of the tire in the new state,characterized in that said material to be regrooved from said at least one cutout (3) consists of at least a first layer of an elastomeric mixture added to the bottom of the cutout after curing of the tire and in that said at least a first layer is bonded to the cured tire, over its entire surface in contact with the bottom and the walls of said at least one cutout.,

2. Tire (1) according to claim 1, characterized in that the bond between said first layer of an elastomeric mixture and the surface of said at least one cutout of the tire visible after curing is broken by tearing after an elongation of at least 20% of a sample according to the test as described in paragraph

3. JJ. Tire (1) according to one of claims 1 or 2, characterized in that the bond between said first layer of an elastomeric mixture and the surface of said at least one cutout of the tire visible after curing is broken by tearing after an elongation of at least 35% of a sample according to the test as described in paragraph 35, preferably at least 60%.

4. Tire (1) according to one of claims 1 to 3, characterized in that said at least one regroovable cutout (3) is circumferential.

5. Tire (1) according to one of claims 1 to 3, characterized in that said at least one regroovable cutout is transverse.

6. Tire (1) according to one of claims 1 to 3, characterized in that said at least one regroovable cutout is oblique.

7. Tire (1) according to one of the preceding claims, characterized in that at least one regroovable cutout (3) can be regrooved at least twice.

8. Tire (1) according to one of the preceding claims, characterized in that the height corresponding to the distance between the rolling surface in new condition and the bottom of the cutouts (3) after the last regrooving of such tires is greater than or equal to 200% of the height (HN) between the bottom of the cutout (3) and the rolling surface when the tire is new.

9. Tire (1) according to one of the preceding claims, said tread (6) comprising at least one incision, flush with the rolling surface when the tire is new, having a height between the bottom of said at least one incision and the rolling surface when the tire is new, characterized in that the height of said at least one incision of the tire in the new state is greater than the height of said at least one regroovable cutout (3) of the tire in the new state.

10. Tyre (1) according to claim 9, characterized in that the height of said at least one incision of the tyre in the new condition is greater than 90% of the height corresponding to the distance between the running surface in the new condition and the bottom of said at least one cutout (3) after the last regrooving.

11. Tyre (1) according to claim 9 or 10, characterized in that the height of said at least one incision of the tyre in the new condition is equal to the height corresponding to the distance between the running surface in the new condition and the bottom of said at least one cutout (3) after the last regrooving.

12. 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.

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