TYRES WITH A TREAD WITH AT LEAST ONE LAYER OF TEXTILE REINFORCEMENT ELEMENTS

Description

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

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

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

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

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

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

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

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

[0009] The transverse or axial direction of the tire is parallel to the tire's axis of rotation. An axial distance is measured along the axial direction. The expression "axially 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 inward to, respectively radially outward to" 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 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 roads covered with water, particularly in wet weather.

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

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

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

[0016] For the purposes of the invention, an obliquely oriented cutout is a cutout 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] Some current tires, called "road tires," are designed to travel at high speeds and over increasingly long distances, due to the improvement of the road network and the growth of the motorway network around the world. The set of conditions under which such a tire is called upon to travel allows for an increase in the number of kilometers traveled, with less wear on the tire.

[0018] To further increase tire life, it is common to choose polymeric tread materials with improved wear resistance properties. However, such materials are known to penalize grip properties, particularly on wet surfaces.

[0019] Document US 3,261,388 A describes a tire which may comprise a tread consisting of several layers of radially superimposed elastomeric compounds.

[0020] Document WO 02 / 90094 A1 describes a tire comprising a tread consisting of several layers of radially superimposed elastomeric compounds separated locally by interlayers to facilitate regrooving of the tread.

[0021] Document GB 167 409 A describes a tire comprising several layers of radially superimposed elastomeric compounds.

[0022] Document JP 2004 359074 A describes a tire intended to be recycled and whose tread comprises several layers of elastomeric compounds which can be separated.

[0023] Document EP 3 031 622 A1 describes a tire comprising a colored wear indicator.

[0024] The inventors set themselves the task of being able to provide tires that allow for ever-increasing rolling distances with improved wet grip properties.

[0025] This object has been achieved according to the invention by a tire, with a radial carcass reinforcement, comprising a crown reinforcement, itself radially capped with a tread joined to two beads by means of two sidewalls, said tread comprising grooves forming at least one tread element constituting the tread of the tire, having a height between the bottom of the tread and the tread surface, said tread comprising, at least locally, at least two layers of elastomeric mixtures radially superimposed on the tread height of the tread, a first layer forming the radially outer part of the tread consisting of a first elastomeric mixture, a second layer of elastomeric mixture radially more inner consisting of a second elastomeric mixture, at least one layer of textile reinforcing elements, parallel to each other,being radially in contact with two layers consisting of said first elastomeric mixture and / or said second elastomeric mixture, said at least one layer of textile reinforcing elements being arranged substantially parallel to the outer surface of the tread, at least a portion of the textile reinforcing elements being oriented in a direction making an angle of less than 30° relative to the main axis of inertia associated with the maximum moment of inertia of the surface in contact with the ground of said at least one tread element, the middle of said surface in contact with the ground, in the longitudinal direction passing through the center of gravity of said surface in contact with the ground, being located longitudinally at the center of the contact area, the tire being subjected to its nominal load and inflated to its nominal pressure on the nominal rim and, in a meridian section of the tire,the barycenter of said at least one layer of textile reinforcing elements being radially located between 30% and 70% of the tread height of the tread from the bottom of the tread.,

[0026] For the purposes of the invention, the nominal load and pressure conditions as well as the nominal rim are defined according to the ETRTO, TRA or JATMA regulations.

[0027] For the purposes of the invention, the tread height in a meridian section of the tire is the distance measured between the radially outer surface of the tread, forming the contact surface with the ground, and the parallel surface extrapolated from the tread bases, said distance being measured in a direction normal to the radially outer surface of the tread. The tread bases are the radially innermost points of the hollow areas on the tread.

[0028] The determination of the barycenter is carried out on a new tire.

[0029] According to a preferred embodiment of the invention, the first elastomeric mixture has a tan(δ)-20°C value strictly less than 0.50.

[0030] Also preferably according to the invention, the second elastomeric mixture has a tan(δ)-20°C value strictly less than 0.50.

[0031] According to an alternative embodiment of the invention, the second elastomeric mixture is identical to the first elastomeric mixture.

[0032] The dynamic property tan(δ)-20°C is measured on a viscoanalyzer (Metravib VA4000), according to the ASTM D 5992-96 standard. The response of a test piece consisting of two cylindrical pellets, each 2 mm thick and one centimeter in diameter, is recorded (the test piece is made from a tire sample taken at mid-height of the layer concerned as close as possible to the equatorial plane area in an area of sufficient thickness to constitute the test piece), subjected to a sinusoidal stress in alternating simple shear, at a frequency of 10 Hz.

[0033] For the measurement of tan(δ)-20°C, a temperature scan is carried out between -80 and +100°C, under a stress of 0.7 MPa, and the value of tan(δ) observed at -20°C is recorded. It is recalled that, in a manner well known to those skilled in the art, the value is representative of the wet grip potential: the higher the value of tan(δ)-20°C, the better the grip. An arbitrary value of 100 is given for the control composition, a result greater than 100 indicating an increase in the value of tan(δ)-20°C, corresponding to an improvement in the wet grip performance.

[0034] The grip of a tire is characterized by the force that the tire is capable of transmitting to the ground under braking stress, for example. It is particularly represented by the hysteretic losses linked to the deformations of the tread during the application of the stress. The value of tan(δ)-20°C thus corresponds to an indicator of the grip on wet ground of a tire when braking between 80km / h and 0km / h.

[0035] The various measurements are carried out on new tires, which have not yet been driven.

[0036] The inventors were first able to demonstrate that the combination of a first elastomeric mixture, forming the radially outermost part of the tread and coming into contact with the ground, of a second radially inner elastomeric mixture, possibly identical to the first elastomeric mixture and of said layer of textile reinforcing elements as described previously leads to a satisfactory compromise between the wear resistance properties and the wet grip properties of the tire.

[0037] Indeed, the first elastomeric mixture constituting the radially outer part of the tread advantageously has a rigidity giving it satisfactory wear performance.

[0038] The presence of the layer of textile reinforcing elements, its positioning and the orientation of its reinforcing elements lead to less deformation of the tire tread when the tire is crushed in the contact area. The inventors were able to demonstrate that the layer of textile reinforcing elements limits the so-called transverse deformations linked to the incompressibility of the elastomeric compounds of the first and second layers. The inventors were able to demonstrate that the deformations of the layers of elastomeric compounds that form the tire tread induce so-called parasitic forces in the contact area. These so-called parasitic forces, described in “Effect of friction on rolling tire - pavement interaction”, H. Wang, IL Al-Qadi & I. Stanciulescu, NEXTRANS Project No.049IY02, USDOT Region V Regional University Transportation Center Final Report, reduce the amount of force that can be transmitted in the contact patch before reaching the maximum force that can be transmitted, characterized by the tire sliding on the ground. In other words, these so-called parasitic forces consume part of the grip potential. The presence of the layer of textile reinforcement elements that limit the deformations of the tread thus contributes to better grip of the tire.

[0039] Preferably according to the invention, said at least one layer of textile reinforcing elements has a breaking force per unit of width greater than 20 daN / dm.

[0040] The ultimate strength per unit width of a layer of reinforcing elements is determined from measurements made on the reinforcing elements and the density of reinforcing elements in the layer, itself defined by the number of reinforcing elements per unit width.

[0041] The measurement of thread density is determined by measuring the pitch between two threads, i.e. the distance between two threads, measured in a direction perpendicular to the direction of the threads. The measurement can be carried out on a test piece extracted from the tire or by tomography.

[0042] For textile yarns or cables, the mechanical properties are measured on fibers that have been subjected to prior conditioning. "Preconditioning" means storing the fibers for at least 48 hours, before measurement, in a standard atmosphere according to European standard NF EN ISO 139 (temperature of 20 + / - 2°C; relative humidity of 65 + / - 4%RH). The mechanical properties in extension (force at break, elongations under load) are measured according to a specific measurement method using calibrated static traction machines from INSTRON or ZWICK. Measurements are carried out on n yarns extracted from the tire, n being between 10 and 20. The yarns are subjected to uniaxial traction at a nominal speed of 200 mm / min. The maximum value is the value retained, the other values corresponding to yarns damaged during extraction.

[0043] Advantageously according to the invention, the textile reinforcing elements are chosen from assemblies of natural fibers such as cotton, linen, hemp, bamboo, etc. Such a choice has the advantage of biodegradable reinforcing elements which will disappear when, during wear of the tire tread, they are released into nature.

[0044] According to one embodiment of the invention, the tire comprising two layers of textile reinforcing elements, the orientation of the textile reinforcing elements of the second layer is substantially perpendicular to that of the textile reinforcing elements of the first layer of textile reinforcing elements.

[0045] According to these embodiment variants, the tread is advantageously produced before curing by stacking layers of elastomeric mixtures and said at least one layer of textile reinforcing elements radially superimposed and / or axially juxtaposed according to the shapes and / or locations desired for the different mixtures.

[0046] 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.

[0047] According to other embodiments of the invention, the crown reinforcement further comprises at least one layer of circumferential reinforcing elements.

[0048] 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.

[0049] According to any of the embodiments of the invention mentioned above, the crown reinforcement can also be completed, radially inside between the carcass reinforcement and the radially inner working layer closest to said carcass reinforcement, by a triangulation layer of inextensible metallic steel reinforcing elements making, with the circumferential direction, an angle greater than 60° and in the same direction as that of the angle formed by the reinforcing elements of the layer radially closest to the carcass reinforcement.

[0050] Other details and advantageous characteristics of the invention will emerge below from the description of exemplary embodiments of the invention with reference to figures 1 to 4 which represent: figure 1 , a meridian view of a diagram of a tire according to an embodiment of the invention, figure 2, a view of a schematic representation of the contact patch of a tire, figure 3 , a partial view of a schematic representation of the contact patch of a tire illustrating the directions associated with the maximum moment of inertia and the minimum moment of inertia of a tread block of a tire, figure 4 , a partial view of a schematic representation of the contact patch of a tire illustrating the directions associated with the maximum moment of inertia and the minimum moment of inertia of a rib of a tire.

[0051] Figures are not drawn to scale to simplify understanding.

[0052] On the figure 1, the tire 1, of dimension 12 R 22.5, comprises a radial carcass reinforcement 2 anchored in two beads, around bead wires, not shown in the figures. 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 four grooves 3 forming five ribs 4.

[0053] The lower areas and beads of the tire 1 are not shown in the figures.

[0054] On the figure 1 , the crown reinforcement 5 is formed radially from the inside to the outside: of a first working layer 51 formed of inextensible metal cables 11.35 not hooped, continuous over the entire width of the sheet, oriented at an angle equal to 18°, of a second working layer 52 formed of inextensible metal cables 11.35 not hooped, continuous over the entire width of the sheet, oriented at an angle equal to 26° and crossed with the metal cables of the first working layer, of a protective layer 53 formed of elastic metal cables 6.35 not hooped, continuous over the entire width of the sheet, oriented at an angle equal to 26° in the same direction as the metal cables of the working layer 52.

[0055] According to the invention, the tread 6 consists of a first radially outer layer 61 which comes into contact with the ground and a radially inner layer 62.

[0056] Layer 61 consists of the first elastomeric mixture having a tan(δ)-20°C value equal to 0.35.

[0057] Layer 62, the radially innermost, is made of the second elastomeric mixture.

[0058] According to this embodiment, the layer 62 is made up of a second mixture identical to the first mixture.

[0059] On this figure 1 , we can still see the layer of textile reinforcing elements 63. This layer of textile reinforcing elements 63 is present in the five ribs 4.

[0060] The reinforcing elements of the textile reinforcing element layer are 144x2 PET cables spaced two millimeters apart.

[0061] The breaking force per unit width of said at least one layer of textile reinforcing elements is equal to 80 daN / dm. It is determined by the product of the density of reinforcing elements, equal to 5 threads / dm, and the breaking force of a reinforcing element, equal to 16 daN.

[0062] The textile reinforcing elements of layer 63 are oriented in the axial direction.

[0063] The barycenter of the layer of textile reinforcement elements is positioned at 50% of the tread height.

[0064] There figure 2 schematically illustrates the contact area 21 of the surface of a tire 22 in contact with the ground, the tire being mounted on its nominal rim, inflated to its nominal pressure and subjected to its nominal load. On this surface of the tire 22, it can be seen that the sculpture is composed in the central part in an axial direction of loaves 23 between two circumferential ribs or ribs 24 on the axially external parts of the surface of the tire 22.

[0065] On this figure 2 axis 25 is also illustrated, oriented in the axial direction, longitudinally in the center of the contact area.

[0066] There figure 3schematically represents a sculpture block 23 whose middle of the surface in contact with the ground, in the longitudinal direction passing through the center of gravity of the surface in contact with the ground, is positioned longitudinally at the center of the contact area and therefore on the axis 25. The two directions associated with the maximum moment of inertia (straight 26) and the minimum moment of inertia (straight 27) of the surface of the block 23 in contact with the ground are also represented on this figure 3 . Around the direction associated with the maximum moment of inertia 26, the orientation range of the textile reinforcing elements according to the invention is represented between the two straight lines 28, 29 placed respectively at 30° on either side of the direction 26.

[0067] There figure 4schematically represents a rib or rib 24 of sculpture. The rib or rib 24 being continuous circumferentially, the middle of the surface in contact with the ground, in the longitudinal direction passing through the center of gravity of the surface in contact with the ground, is continuously positioned longitudinally at the center of the contact area and therefore on the axis 25. The two directions associated with the maximum moment of inertia (straight 36) and the minimum moment of inertia (straight 37) of the surface of the rib or rib 24 in contact with the ground are represented on this figure 4 . Around the direction associated with the maximum moment of inertia 36, the orientation range of the textile reinforcing elements according to the invention is represented between the two straight lines 38, 39 placed respectively at 30° on either side of the direction 36.

[0068] In the case of the tire according to the invention as shown in the figure 1, the textile reinforcing elements of the layer are oriented in the axial direction and therefore form a substantially zero angle with the direction associated with the maximum moment of inertia of the surface of the ribs 4 in contact with the ground.

[0069] In the case of a tire whose tread pattern is similar to that of the figure 2 , the invention may provide that the orientation of the textile reinforcing elements varies according to the axial positioning of the measurement. In other words, the orientation of the textile reinforcing elements may be provided differently depending on whether the layer of textile reinforcing elements is located in a bread 23 or in a rib 24 depending on the figure 2 .

[0070] Tires were produced based on the elastomeric mixture described below with its properties. Blend NR 80 BR 20 N234 48 6PPD - 1.3DIMETHYL BUTYL PHENYL PARAPHENYLENE-DIAMINE 3 ZNO 3 SULFUR 1.5 Accelerator (CBS) 0.9 tan(δ)-20°C 0.35

[0071] The values of the constituents are expressed in pce (parts by weight per hundred parts of elastomers).

[0072] A reference tire R produced according to a configuration corresponding to usual designs and not including a layer of textile reinforcement elements 63. The tread is produced with mixture A.

[0073] A tire T in accordance with the invention as shown in the figure 1 combines, to form the tread, the mixture A which forms the layers 61 and 62, and a layer of textile reinforcing elements 63.

[0074] Wet grip measurements were carried out on each of the tyres under identical driving conditions in accordance with ISO 15222. The measurement results are presented in the following table, with a value of 100 being assigned to tyre R. Values above 100 express superior grip performance. R pneumatic Pneumatic T 100 103

[0075] These values highlight the benefit of the presence of the layer of textile reinforcement elements to limit the deformations of the tread when passing through the contact area inducing parasitic forces in contact with the ground, and thus contribute to better grip of the tire on wet ground.

[0076] Furthermore, initial endurance tests were carried out on a test machine requiring each of the tires to run in a straight line at a speed equal to the maximum speed index prescribed for the said tire (speed index) under an initial load of 4000 kg, gradually increased to reduce the duration of the test.

[0077] Second endurance tests were carried out on a test machine cyclically imposing a transverse force and a dynamic overload on the tires. The tests were carried out for the tires according to the invention under conditions identical to those applied to the reference tires.

[0078] The tests thus carried out showed that the distances covered during each of these tests are equivalent for the T tires according to the invention and the reference tires R. It therefore appears that the tires according to the invention have performances in terms of endurance as good as those of the reference tires.

Claims

1. - Tyre (1) having a radial carcass reinforcement (2), comprising a crown reinforcement (5), itself capped radially by a tread (6) connected to two beads via two sidewalls, said tread (6) having grooves that form at least one tread pattern element constituting the tread pattern of the tyre, having a height between the bottom of the tread pattern and the tread surface, said tread having, at least locally, at least two layers of elastomeric compounds that are radially superposed over the tread pattern height of the tread, a first layer (61) forming the radially outer part of the tread being made up of a first elastomeric compound, a second layer (62) of elastomeric compound that is radially further towards the inside being made up of a second elastomeric compound, characterized in that at least one layer of textile reinforcing elements (63) is radially in contact with two layers made up of said first elastomeric compound and of said second elastomeric compound, in that said at least one layer of textile reinforcing elements (63) is disposed substantially parallel to the outer surface of the tread, in that at least a part of the textile reinforcing elements is oriented in a direction forming an angle of less than 30° with respect to the main axis of inertia associated with the maximum moment of inertia of the surface in contact with the ground of said at least one tread pattern element, the middle of said surface in contact with the ground, in the longitudinal direction passing through the centre of gravity of said surface in contact with the ground, being situated longitudinally at the centre of the contact patch, the tyre being subjected to its nominal load and inflated to its nominal pressure on the nominal rim and in that, in a meridian section of the tyre, the barycentre of said at least one layer of textile reinforcing elements is situated radially between 30% and 70% of the tread pattern height of the tread from the bottom of the tread pattern.

2. - Tyre (1) according to Claim 1, characterized in that the first elastomeric compound has a value of tan(δ)-20°C of strictly less than 0.50, the dynamic property tan(δ)-20°C being measured according to the ASTM D 5992-96 standard, with a simple alternating sinusoidal shear stress, at a frequency of 10 Hz under a stress of 0.7 MPa.

3. - Tyre according to either of Claims 1 or 2, characterized in that the second elastomeric compound has a value of tan(δ)-20°C of strictly less than 0.50.

4. - Tyre (1) according to one of Claims 1 to 3, characterized in that the second elastomeric compound is identical to the first elastomeric compound.

5. - Tyre (1) according to one of Claims 1 to 4, characterized in that the force at break per unit width of said at least one layer of textile reinforcing elements (63) is greater than 20 daN / dm.

6. - Tyre (1) according to one of Claims 1 to 5, characterized in that the textile reinforcers of said at least one layer of textile reinforcing elements (63) are chosen from assemblies of natural fibres such as cotton, linen, hemp or bamboo.

7. - Tyre (1) according to one of the preceding claims, the tyre having two layers of textile reinforcing elements, characterized in that the orientation of the textile reinforcing elements of the second layer is substantially perpendicular to that of the textile reinforcing elements of the first layer of textile reinforcing elements.