Tire having a regroovable tread

Abstract

The invention relates to a tire (1) that can be regrooved at least once and the tread of which forms a tread surface (7), the tread surface (7) being centered on the median plane and the width of the tread surface (7) being less than 80% of the width of the tread in the new state. According to the invention, the height (HRC) of at least one regrooved groove (3A) of the portion of the tread (6A) forming the tread surface (7) in the new state is 70% or more of the groove height (HNC) of the at least one regroovable groove (3A) of the portion of the tread (6A) forming the tread surface (7) in the new state.

Description

TYRE WITH A STRIP OF REGRESSABLE BEARING

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

[0002] In general, 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 superimposed layers formed of parallel wires or cables in each layer and crossed from one layer to the next at angles between 10° and 45° with the circumferential direction. These working layers, forming the working reinforcement, may be further covered by at least one protective layer formed of advantageously metallic and extensible reinforcing elements, known as elastic elements.It may also include a layer of low-extensibility wires or cables forming an angle of between 45° and 90° with the circumferential direction. This layer, known as the triangulation layer, is radially positioned between the carcass reinforcement and the first crown layer, known as the working layer, which is formed of parallel wires or cables having angles of no more than 45° in absolute value. The triangulation layer, together with at least the aforementioned working layer, forms a triangulated reinforcement that exhibits minimal deformation under the various stresses it is subjected to. The triangulation layer's essential role is to resist the transverse compression forces exerted on all the reinforcing elements in the crown area of ​​the tire.

[0003] Cables are said to be inextensible when, under a tensile force equal to 10% of the breaking force, said cables exhibit a relative elongation of no more than 0.2%.

[0004] Cables are said to be elastic when, under a tensile force equal to the breaking load, said cables exhibit a relative elongation of at least 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 direction of rolling 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 tire's axis of rotation. An axial distance is measured along the axial direction. The expression "axially inside to, respectively axially outside to" means "whose axial distance measured from the equatorial plane is less than, respectively greater than".

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

[0011] Radially outside the crown reinforcement, we find 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 equip the tread, that is, the part of the tire intended to come into contact with the ground while driving and to wear down during driving, with a tread pattern made up of raised elements delimited by cutouts such as grooves, whether circumferential, transverse, or oblique. The purpose of such a tread pattern is to give the tread good performance in driving on dry pavement and on water-covered pavement, particularly in rainy weather.

[0013] To improve tread performance without excessively reducing the shear stiffness of said treads, it is known to form a plurality of transversely or obliquely oriented edges on the tread surface to cut through the water film on a road surface and ensure good contact between the tread and the road. One way to obtain such edges is to provide the tread with a plurality of cutouts, these cutouts being in the form of grooves or incisions. In this application, incisions are distinguished from grooves in that the incisions have a width suitable for allowing at least partial contact between the opposing walls delimiting these incisions during rolling, particularly during contact with the ground, which would not be the case for grooves under normal tire operating conditions.

[0014] For the purposes of this invention, a longitudinally oriented cutout is a cutout in which the mean plane of at least a portion of the walls of said cutout forms an angle of less than 10° with a longitudinal plane. This angle formed with a longitudinal plane may be oriented in either direction with respect to said longitudinal plane. A longitudinally oriented cutout may also be a cutout in which the walls undulate or zigzag around a mean plane as described above.

[0015] For the purposes of this invention, a transversely oriented cutout is a cutout in which the mean plane of at least some of the walls of said cutout forms an angle of less than 35° with a radial plane. This angle formed with a radial plane may be oriented in either direction with respect to said radial plane. A transversely oriented cutout may also be a cutout in which the walls undulate or zigzag around a mean plane as described above.

[0016] For the purposes of this invention, an obliquely oriented cutout is a cutout in which the mean plane of at least a portion of the walls of said cutout forms an angle with a radial plane between 35° and 80°. This angle formed with a radial plane may be oriented in either direction with respect to said radial plane. A cutout of oblique orientation can also be a cut whose walls undulate or zigzag around a mean plane such as has just been described.

[0017] Combined with the need to improve grip performance through the presence of edges formed by transverse cuts, it is also required that the performance of a tread be sustainable, meaning that satisfactory performance is maintained even after partial wear, to varying degrees. Partial tread wear refers to a state of wear where the remaining tread thickness is no greater than the total tread thickness that can be worn before the tire needs to be replaced, particularly for regulatory reasons.

[0018] The grooves generally include wear indicators, small platforms of vulcanized rubber compound covering a certain circumferential length of the bottom of these grooves. These indicators show the minimum tread depth that must legally remain on the tread during use. Some heavy-duty tire treads are regroovable (a process by which new grooves can be cut), and tires with such treads bear the English word "Regroovable" or the symbol "U" on their sidewalls. Regrooving allows, on the one hand, for an extension of the heavy-duty tire's grip potential and, on the other hand, for a significant increase in mileage.

[0019] Regrooving truck tires is a common and permitted operation due to its safety benefits and increased efficiency. For example, it is explicitly authorized by the French Highway Code (Article 4 of the decree of October 24, 1994) and recommended by the ETRTO and AFNOR (standard NFR12714). For this operation, manufacturers are required to provide regrooving diagrams, which are mandatory for technicians performing the regrooving.

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

[0021] As is well known, recutting a groove can be done using a heated, rounded blade, often still operated by a technician. This blade, connected to a frame which rests on the tread surface, can be used manually in such a way as to follow quite faithfully the path of the groove on the surface of the tread, even in the case of a groove with a non-straight path.

[0022] Regrooving restores sharp edges and is usually intended to bring the tread depth back to that of a truck tire at half its wear. Standard recommendations aim for a post-regrooving depth of 5 to 6 mm, consisting of 3 to 4 mm of regrooving and 2 mm of remaining depth. In practice, regrooving is often carried out earlier, with remaining depths of 4 to 5 mm, resulting in a post-regrooving depth of 7 to 9 mm, for tires with a new tread depth of between 12 and 20 mm.

[0023] Regrooving a tire offers several advantages. First, by restoring the tread depth, regrooving extends the tire's lifespan.

[0024] Furthermore, since regrooving is carried out when the tread thickness is at its lowest and therefore when the tire has the lowest rolling resistance, the distance traveled is extended when the rolling resistance is lowest.

[0025] Document WO 2022 / 180325 still proposes tires that can be regrooved at least once, whose tread depth when new is very low to allow for optimal rolling performance in terms of tire rolling resistance throughout its use.

[0026] It is also known to produce tires whose tread width is less than the width of the tread to improve wear performance without significantly penalizing the tire's endurance performance.

[0027] Document FR 2278508A1 describes such a solution to improve wear due to a particular tread profile while preserving endurance performance.

[0028] Document JP2010208505 A further describes such an arrangement to limit irregular wear and improve endurance performance by moving the bearing surface away from the ends of the top reinforcement.

[0029] Tests carried out with such tires under normal usage conditions do not highlight any notable wear performance and the endurance performance is not at the expected level with treads made in this way.

[0030] Furthermore, this type of tire design does not meet current expectations in terms of rolling resistance.

[0031] The inventors set themselves the task of being able to provide tires that offer a compromise between wear performance and improved endurance performance, while ensuring satisfactory rolling resistance performance and good wet grip properties.

[0032] This objective has been achieved according to the invention by a tire, which can be regrooved at least once, comprising a crown reinforcement, itself radially capped by a tread, made of at least one elastomeric compound, joined to two beads by means of two sidewalls, said tread forming a tread surface, centered on the median plane, the width of which is less than 80% of the width of the tread when new, the part of the tread forming the tread surface when new having at least one regroovable groove having a height HNC between the bottom of said at least one regroovable groove and the tread surface when the tire is new, two axially external parts of the tread not forming the tread surface when new,each comprising at least one regroovable groove having a height HNB between the bottom of said at least one groove and the surface of the axially outer part of the tread when the tire is new, after regrooving, the height HRC of said at least one regrooved groove of said part of the tread forming the tread surface in the new condition being greater than or equal to 70% of the height HNC, of said at least one recuttable groove of said part of the tread forming the tread surface in the new condition.

[0033] For the purposes of this invention, the groove height is measured in a meridional cross-section of the tire and corresponds to the distance measured between the radially outer surface of the tread, forming the contact patch with the ground and extrapolated to disregard any cutouts, and the surface of the tread depths, 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 grooved areas on the tread, disregarding the presence of features such as wear indicators, regrooving depth indicators, or any other feature whose combined area is less than 15% of the total cutout area.

[0034] The tread depth of at least one regroovable groove of the new tire is measured on the new tire. The depth of at least one regrooved groove can be measured in the same way when the tire is regrooved; the depth of at least one regrooved groove can also be determined, as explained previously, from the new tire and the regrooving diagram provided by the manufacturer.

[0035] In the context of the invention, the axial width of the tread is measured between two shoulder ends when the tire is mounted on its service rim and inflated to its nominal pressure.

[0036] According to the invention, a shoulder end is defined as the edge formed between the tread and the sidewall of the tire when this edge is well-defined. When this edge is not clearly marked on the tire, the shoulder end is defined, according to the invention, in the area of ​​the tire's shoulder, as the point of tangency between a straight line, forming an angle of 30° with the axial direction, and the outer surface of the tire.

[0037] For the purposes of the invention, the axial width of the tread surface is measured when the tire is mounted on its service rim and inflated to its nominal pressure and subjected to its nominal load.

[0038] During testing, the inventors demonstrated that increasing the tread thickness, limited to a portion of the tread centered on the median plane, resulted in wear reductions roughly proportional to the amount of material added, but with endurance performance that fell short of expectations. The inventors believe this result stems from the increased groove depth in the area of ​​the tread that forms the contact patch when new. While the absence of ground contact at the shoulders effectively limits heating at the ends of the apex reinforcement, deeper grooves in the central part of the tread contribute to significant overall tread heating.The axially outer parts of the tread thus reach temperatures which lead to performance below expectations due to the outer geometry of the tread.

[0039] The tests also showed that the tires according to the invention, in combination with improved wear performance, maintain satisfactory endurance performance and satisfactory rolling resistance performance.

[0040] Furthermore, the tires according to the invention allow for the maintenance of satisfactory wet grip properties throughout the life of the tire.

[0041] The inventors were thus able to demonstrate that the combination of an increased tread thickness in its central part with reduced groove heights when new compared to those of more conventional tire designs allows for the maintenance of satisfactory rolling resistance and endurance performance, while wear performance is improved.

[0042] The height of the grooves after regrooving exceeding 70% of the height of the grooves in the new condition means that the height of the grooves in the new condition is reduced compared to that of tires of more conventional design.

[0043] As previously stated, the regrooving process on more conventionally designed tires results in groove heights less than half the original groove height. According to the invention, for a given tread depth, tread regrooving should therefore likely be carried out more quickly, i.e., with less tread wear, than in the case of a more conventionally designed tire.

[0044] The inventors have thus been able to demonstrate that this accelerated regrooving of the tire tread according to the invention makes it possible to maintain satisfactory rolling resistance and endurance performance, despite an increased tread thickness in its central part for improved wear performance.

[0045] According to a preferred embodiment of the invention, the height corresponding to the distance between the tread surface in the new condition and the bottom of said at least one groove, of said part of the tread forming the tread surface in the new condition, after the last regrooving is greater than or equal to 200% of the HNC height between the bottom of said at least one groove of said part of the tread forming the tread surface in the new condition and the tread surface when the tire is new.Preferably, the height corresponding to the distance between the tread surface in its new condition and the bottom of said at least one groove, of said part of the tread forming the tread surface in its new condition, after the last regrooving is greater than or equal to 250% of the HNC height between the bottom of said at least one groove, of said part of the tread forming the tread surface in its new condition, and the tread surface when the tire is new.

[0046] The height, corresponding to the distance between the tread surface when new and the bottom of the grooves after the last regrooving, can be determined when the tire is regrooved, or it can also be determined as explained previously from the new tire and the regrooving pattern provided by the manufacturer.

[0047] According to particularly advantageous embodiments of the invention, the width of the tread surface, centered on the median plane, when new, is greater than 50% of the tread width and preferably between 60% and 75% of the tread width. Such widths of the central portion of the tread significantly improve wear performance; values ​​below 50% would be less beneficial. Above 75%, rolling resistance and durability performance could be degraded.

[0048] According to preferred embodiments of the invention, the height HNC, between the bottom of said at least one groove, of said part of the tread forming the tread surface in the new condition, and the tread surface when the tire is new, is between 6 and 8 mm.

[0049] Such deep grooves in the central part of the tread ensure satisfactory wet grip properties when new.

[0050] Preferably, according to the invention, the HFC height between the bottom of said at least one groove, of said part of the tread forming the tread surface in the new condition, and the extrapolation of the surface of the axially external parts of the tread is less than or equal to 2 mm and preferably greater than 1 mm.

[0051] For the purposes of the invention, the extrapolation of the surface of the axially outer parts of the tread is a surface, substantially parallel to the tread surface, in the new state, which connects the radially outer surfaces of said two axially outer parts of the tread.

[0052] Preferably also according to the invention, the height HNB between the bottom of said at least one groove of each of said two parts of the tread axially outer, and the surface area of ​​said at least two axially outer parts of the tread when the tire is new is equal to the HFC height between the bottom of said at least one groove, of said part of the tread forming the tread surface when new, and the extrapolation of the surface area of ​​the axially outer parts of the tread.

[0053] According to this preferred embodiment of the invention, during regrooving, all the grooves have a substantially identical depth, which can be chosen to correspond to the wear limit for allowing rolling. After this regrooving step, or just before, the width of the tread surface is substantially equal to the width of the tread band, as tire wear causes the extrapolated surface of the axially outer surfaces to coincide with the central part of the tire's tread surface.

[0054] According to a first embodiment of the invention, said at least one recuttable groove of said part of the tread forming the tread surface in the new condition and said at least one recuttable groove of each of said two parts of the tread, axially external, not forming the tread surface in the new condition are circumferential.

[0055] According to a second embodiment of the invention, said at least one recuttable groove of said part of the tread forming the tread surface in the new condition and said at least one recuttable groove of each of said two parts of the tread, axially external, not forming the tread surface in the new condition are transverse.

[0056] According to a third embodiment of the invention, said at least one recuttable groove of said part of the tread forming the tread surface in the new condition and said at least one recuttable groove of each of said two axially external parts of the tread not forming the tread surface in the new condition are 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 the grooves of the tire are recut according to the invention during the same step.

[0059] According to an advantageous embodiment of the invention, after regrooving, the HRC height of said at least one regrooved groove of said part of the tread forming the tread surface in the new condition is greater than or equal to 85% of the HNC height of said at least one regroovable groove of said part of the tread forming the tread surface in the new condition and preferably even greater than 95% of the HNC height of said at least one regroovable groove of said part of the tread forming the tread surface in the new condition.

[0060] According to one embodiment of the invention, at least one groove can be recut at least twice. According to this embodiment, it may be possible to further improve rolling resistance performance by using even shallower groove depths when new, while still meeting wet grip requirements.

[0061] Advantageously according to the invention, at least one regroovable groove of said part of the tread forming the tread surface in the new condition is regroovable at least twice and, preferably, said at least one groove of each of said two axially external parts of the tread not forming the tread surface in the new condition are regroovable at least twice.

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

[0063] Advantageously, according to this embodiment of the invention, the elastomeric compound recut during the first recut is different from the elastomeric compound recut during the second recut. For example, the innermost radially located elastomeric compound does not contain a black filler to provide color contrast when it appears during the first recut. Such an arrangement can, in particular, facilitate the recutting steps.

[0064] According to other embodiments of the invention, the tread includes depth indicators in the form, for example, 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 indicator incision.

[0065] Advantageously, according to the invention, the recuttable elastomeric compound differs from at least a portion of the elastomeric compound constituting the tread. Such an embodiment can be achieved by co-extrusion of the compounds during the preparation of the semi-finished product(s) intended to constitute at least part of the tread.

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

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

[0068] According to other embodiments of the invention, the top reinforcement also includes at least one layer of circumferential reinforcing elements.

[0069] One embodiment of the invention further provides that the top reinforcement is completed radially on the outside by at least one additional layer, called a protective layer, of so-called elastic reinforcing elements, oriented with respect to the circumferential direction 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 top reinforcement can be further completed, radially inside between the carcass reinforcement and the radially inner working layer closest to said carcass reinforcement, by a triangulation layer of inextensible metallic steel reinforcing elements making, with the circumferential direction, an angle greater than 60° and in the same direction as that of the angle formed by the reinforcing elements of the layer radially closest to the carcass reinforcement.

[0071] Other advantageous details and features of the invention will become apparent from the description of examples of embodiments of the invention with reference to the figure which represents a meridian view of a diagram of a tire according to an example of an embodiment of the invention,

[0072] The figure is not drawn to scale for ease of understanding. The figure represents only half a view of a tire that extends symmetrically with respect to the XX' axis, which represents the circumferential median plane, or equatorial plane, of a tire.

[0073] In the figure, the tire 1, size 315 / 70R22.5, comprises a radial carcass reinforcement 2 anchored in two bead ribs around beads (not shown). The carcass reinforcement 2 is formed of a single layer of steel cords. The carcass reinforcement 2 is held in place by a crown reinforcement 5, itself capped by a tread 6. The tread has four circumferential grooves 3A, 3B forming five ribs 4. The tread has a central portion 6A and two axially outer portions 6B. When new, the central portion 6A of the tread forms the tread surface 7 of the tire. The central portion 6A has two circumferential grooves 3A and Each of the axially external parts 6B of the tread has a groove 3B.

[0074] The lower areas and bulges of tire 1 are not shown in the figure.

[0075] The axial width of the tread Le is equal to 270 mm.

[0076] The axial width of the LÔA tire's tread surface is equal to 194 mm and therefore represents 72% of the axial width Le of the tread.

[0077] Each of the axially external parts has an axial width LÔB equal to 38 mm.

[0078] The figure illustrates a tire whose grooves 3A and 3B can be regrooved twice. The grooves 3A and 3B are made up, when new, of two layers I and J forming the bottom of the grooves in their new state and corresponding to these two regroovings.

[0079] The height of the 3 A grooves on a new HNC tire is equal to 8 mm.

[0080] The HFC height between the bottom of grooves 3A and line 71, represented by dashed lines in the figure, corresponding to the extrapolation of the surface of the axially external parts of the tread is equal to 2 mm.

[0081] The HRCI height of the 3 A grooves after the first re-grooving is equal to 8 mm and therefore represents 100% of HNC.

[0082] This HRCI height corresponds to a 6 mm regrooving when the remaining initial groove height is 2 mm, a value close to the generally permitted legal limit corresponding to the minimum height and the wear indicators. This limit is symbolized by line 71, shown as a dashed line in the figure, chosen to coincide with the extrapolation of the surface area of ​​the axially outer parts of the tread according to our embodiment.

[0083] The height not measurable before the first re-grooving and corresponding to the distance between the running surface in its new state and the bottom of the groove after the first re-grooving is thus equal to 14 mm.

[0084] The HRCI height, measured after the first regrooving, and the height not measurable before a first regrooving and corresponding to the distance between the tread surface in the new condition and the bottom of the groove 3 A after the first regrooving can also be determined on new tires from the regrooving diagram provided by the manufacturer, as explained previously.

[0085] The height of the 3B grooves on a new HNB tire is equal to 2 mm.

[0086] The HRBI height of the 3B grooves after the first re-grooving is equal to 8 mm.

[0087] This HRBI height corresponds to a 6 mm deep excavation.

[0088] The HRC2 height of the 3A grooves after the second recutting is 8 mm and therefore represents 100% of HNC. And the HRC2 height of the 3A grooves after the second recutting represents 100% of HRCI.

[0089] This HRC2 height corresponds to a 6 mm deep groove when the remaining groove height is 2 mm, a value close to the generally permitted legal limit corresponding to the minimum height. This limit is symbolized by line 72, shown as a dashed line, in the figure.

[0090] The unmeasurable height before the two regrooving operations, corresponding to the distance between the new running surface and the bottom of the 3A grooves after the second regrooving operation, is therefore 20 mm. The ratio of this unmeasurable height of 20 mm to the HNC height is 2.5, and therefore well above or equal to 200%.

[0091] The HRC2 height, measured after the second regrooving, and the height not measurable before the two regroovings and corresponding to the distance between the tread surface in the new condition and the bottom of the grooves after the second regrooving can also be determined on new tires from the regrooving diagram provided by the manufacturer, as explained previously.

[0092] The HRB2 height of the 3B grooves after the second re-grooving is equal to 8 mm.

[0093] This HRB2 height corresponds to a 6 mm deepening when there remains a groove height of 2 mm, a value close to the generally permitted legal limit corresponding to the minimum height.

[0094] The tire shown in the figure incorporates two regrooving operations at different stages of tire wear in grooves 3A and 3B. Advantageously, according to the invention, grooves 3B are provided with a depth of 2 mm, and grooves 3A are designed to reach the 2 mm wear limit when the tread surface widens; that is, when tire wear causes the surfaces of the axially outer portions of the tread to coincide with the tread surface. Grooves 3A and 3B can thus be regrooved in the same way and simultaneously at each regrooving stage.

[0095] According to other embodiments of the invention, the regrooving of the different grooves of a tire can be staggered over time. According to these embodiments, the tire may, for example, have grooves 3B that can be regrooved only once and grooves 3A that can be regrooved multiple times.

[0096] Tyres were made based on the elastomeric compound described below as the compound constituting the tread.

[0097] The values ​​of the constituents are expressed in pce (parts by weight per hundred parts of elastomers).

[0098] A tire according to the invention thus made, and conforming to the representation in the figure, was compared to different reference tires.

[0099] A reference tire R0, with dimensions identical to the tire according to the invention, has four non-regroovable grooves with heights of 14 mm. The reference tire R0, when new, has a tread surface with a width identical to that of the tread.

[0100] A reference tire RI, similar to the reference tire R0 and therefore with a tread width identical to that of the tread when new, has four grooves that can be regrooved twice; the initial groove height on a new tire is 6 mm. After a first regrooving of 2 mm, the groove height is 4 mm, and after a second regrooving of 2 mm, the groove height is 4 mm. The regrooving steps are carried out when the groove depth is 2 mm after tire wear. The unmeasurable height on a new tire between the bottom of the grooves after the second regrooving and the tread width when new is thus 14 mm, and therefore equal to the groove height of the reference tire R0 when new.

[0101] A reference R2 tire is identical to the R0 tire with non-regroovable grooves whose heights are equal to 20 mm.

[0102] A reference R3 tire, similar to the reference R2 tire and therefore with a tread width identical to that of the tread when new, has four grooves that can be regrooved twice; the initial groove height on a new tire is 8 mm. After a first regrooving of 6 mm, the groove height is 8 mm, and after a second regrooving of 6 mm, the groove height is 8 mm. The regrooving steps are carried out when the groove depth is 2 mm after tire wear. The height not measurable on a new tire is between the bottom of the grooves after the second regrooving. regrooving and the rolling surface in the new condition is thus equal to 20 mm and therefore equal to the height of the grooves of the reference R2 tire in the new condition.

[0103] A reference R4 tire of identical dimensions to the tire according to the invention has, like the tire according to the invention, a tread area smaller than the width of the tread. The reference R4 tire has two grooves with a height of 20 mm in the portion of the tread forming the tread area when new, and one groove with a height of 14 mm in each of the axially outer portions of the tread, said axially outer portions of the tread becoming part of the tread area after 6 mm of wear on the central portion of the tread.

[0104] For each of the reference tires and for the tire according to the invention, the wear life is estimated by considering the volume of rubber material in the tread to be worn during the tire's life, including the regrooving phases for the reference tires RI and R3, and the tire according to the invention. The data are given as relative values, with a value of 100 assigned to the R0 tire. Higher values ​​indicate a greater volume to be worn.

[0105] Rolling resistance measurements were performed on each tire under identical driving conditions, in accordance with Regulation No. 117 of the United Nations Economic Commission for Europe (UNECE). The measurement results are presented in the following table, with a value of 100 assigned to the R0 tire. A value of 90 indicates a 10% reduction in rolling resistance, corresponding to superior rolling resistance performance. The measurements were taken on new tires.

[0106] To estimate the endurance of the reference tires and the tire according to the invention, the temperature at the edge of the crown of the tires is measured by inserting a thermocouple in the middle of the line connecting the ends of the cords of the working crown layers and by rolling on a handwheel of 8.56 meters of tire development at 80 km / h, with the temperature taken after 120 km of driving. The table shows the temperature difference compared to the measurement on the RO variant. The colder the temperature, the better the endurance performance.

[0107] All the values ​​are shown in the following table:

[0108] The values ​​clearly show that the tire according to the invention makes it possible to increase the volume of rubber material to be worn without increasing rolling resistance compared to the reference tire R0 and without reducing its endurance, the operating temperature remaining the same.

[0109] Wet grip tests were also carried out on each of the R0 reference tires and on tires according to the invention, under identical driving conditions in accordance with ISO 15222. The results obtained show that the wet grip properties are similar for the tire according to the invention compared to the R0 reference tire, regardless of either the state of wear of the tire, integrating the tire regrooving steps according to the invention.

Claims

22 DEMANDS 1 - Tire (1), regroovable at least once, comprising a crown reinforcement (5), itself radially capped by a tread (6), made of at least one elastomeric compound, joined to two beads by means of two sidewalls, said tread forming a tread surface (7), centered on the median plane, the width of which is less than 80% of the width of the tread (6) when new, the portion of the tread (6A) forming the tread surface (7) when new having at least one regroovable groove (3A) having a height HNC between the bottom of said at least one regroovable groove (3A) and the tread surface (7) when the tire is new, two portions of the tread (6B), axially external,not forming the tread surface (7) in the new condition, each comprising at least one regroovable groove (3B) having a height HNB between the bottom of said at least one regroovable groove (3B) and the surface of the axially outer part of the tread when the tire is new, characterized in that, after regrooving, the height (HRC) of said at least one regrooved groove (3A) of said part of the tread (6A) forming the tread surface (7) in the new condition is greater than or equal to 70% of the groove height (HNC) of said at least one regroovable groove (3A) of said part of the tread (6A) forming the tread surface (7) in the new condition. 2 - Tire (1) according to claim 1, characterized in that the height corresponding to the distance between the tread surface (7) in the new condition and the bottom of said at least one groove (3 A) of said part of the tread (6A) forming the tread surface (7) in the new condition after the last regrooving is greater than or equal to 200% of the height (HNC) between the bottom of said at least one groove (3A) of said part of the tread (6 A) forming the tread surface (7) in the new condition and the tread surface when the tire (7) is new. 3 - Tire (1) according to one of claims 1 or 2, characterized in that the width of the tread surface (7), centered on the median plane, in the new condition is greater than 50% of the width of the tread (6) and preferably between 60 and 75% of the width of the tread (6). 4 - Tire (1) according to any one of claims 1 to 3, characterized in that the height (HNC), between the bottom of said at least one groove (3A), of said part of the tread (6A) forming the tread surface (7) in the new condition, and the tread surface (7) when the tire is new, is between 6 and 8 mm. 5 - Pneumatic (1) according to any one of claims 1 to 4, characterized in that the height (HFC) between the bottom of said at least one groove (3A), of said part of the tread (6A) forming the tread surface (7) in the new condition, and the extrapolation of the surface of the axially external parts of the tread is less than or equal to 2 mm and preferably greater than 1 mm. 6 - Tire (1) according to claim 5, characterized in that the height (HNB) between the bottom of said at least one groove (3B) of each of said two axially external parts of the tread (6B) and the surface of said at least two axially external parts of the tread (6B) when the tire is new is equal to the height (HFC) between the bottom of said at least one groove (3A) of said part of the tread (6A) forming the tread surface (7) in the new state, and the extrapolation of the surface of the axially external parts of the tread. 7 - Pneumatic (1) according to any one of the preceding claims, characterized in that said at least one regroovable groove (3 A) of said part of the tread (6A) forming the tread surface (7) in the new condition and said at least one regroovable groove (3B) of each of said two parts of the tread (6B), axially external, not forming the tread surface in the new condition are circumferential. 8 - Pneumatic (1) according to one of the preceding claims, characterized in that said at least one regroovable groove (3 A) of said part of the tread (6A) forming the tread surface (7) in the new condition and said at least one regroovable groove (3B) of each of said two parts of the tread (6B), axially external, not forming the tread surface in the new condition are transverse. 9 - Tire (1) according to any one of the preceding claims, characterized in that said at least one regroovable groove (3A) of said portion of the tread (6A) forming the tread surface (7) in the new condition and said at least one regroovable groove (3B) of each of the said two parts of the tread, axially external, not forming the tread surface in the new condition are oblique. 10 - Pneumatic (1) according to any one of the preceding claims, characterized in that at least one regroovable groove (3A) of said part of the tread (6A) forming the tread surface (7) in the new condition is regroovable at least twice and, preferably, said at least one groove (3B) of each of said two axially external parts of the tread (6B) not forming the tread surface in the new condition are regroovable at least twice. 11 - Pneumatic (1) according to claim 10, characterized in that the elastomeric mixture re-grooved during the first re-grooving is different from the elastomeric mixture re-grooved during the second re-grooving. 12 - A tire (1) according to any one of the preceding claims, characterized in that the regroovable elastomeric compound differs from at least a portion of the elastomeric compound constituting the tread. 13 - A tire (1) according to any one of the preceding claims, characterized in that said tread comprises, at least locally, at least two layers of radially superimposed elastomeric compounds within the tread.

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