Tires with a tread made of a blend of various elastomers

Abstract

The present invention relates to a tire having a radial carcass reinforcement, the tire including a crown reinforcement, the crown reinforcement itself being radially covered by a tread, the tread including at least three radially stacked layers of elastomeric compound. According to the invention, a first layer (61) forms the radial outer side of the tread and is made of a first elastomer compound, the maximum value of tan(δ) of the first elastomer compound (denoted as tan(δ)max) being strictly less than 0.150; a second layer (62) further radially inward and is made of a second elastomer compound; at least one third layer (63) is radially located between the two first layers and is made of a third elastomer compound, the Vickers hardness of which is at least 12 times greater than that of the first elastomer compound and at least 12 times greater than that of the second elastomer compound; in the meridional cross section of the tire, the ratio of the area of ​​the third elastomer compound to the sum of the areas of the at least three layers is between 10% and 30%; and the center of gravity of the third elastomer compound is radially located between 30% and 70% of the tread pattern height of the tread.

Description

Technical Field

[0001] The present invention relates to tires having radial carcass reinforcements, and more particularly to tires intended for mounting on vehicles (e.g., trucks, tractors, trailers, or buses) carrying heavy loads. Background Technology

[0002] In heavy-duty tires, the carcass reinforcement is typically anchored on both sides of the bead area and radially covered by a crown reinforcement consisting of at least two overlapping layers formed of yarns or cords. These yarns or cords are parallel in each layer and cross from one layer to the other, forming an angle between 10° and 45° with respect to the circumferential direction. The working layer forming the working reinforcement may also be covered with at least one layer called a protective layer, formed of reinforcing elements, which are advantageously metallic and stretchable, and are referred to as elastic reinforcing elements. The working layer may also include a layer of metal yarns or cords with low elongation, forming an angle between 45° and 90° with respect to the circumferential direction. This ply layer (called a triangular ply layer) is radially positioned between the carcass reinforcement and the first crown ply layer (called the working ply layer), formed of parallel yarns or cords having an angle of at most 45°. The triangular cord layer forms a triangular reinforcement with the working cord layer at least. The triangular reinforcement exhibits a small amount of deformation under various stresses it is subjected to. The triangular cord layer is mainly used to absorb the lateral compressive forces acting on all reinforcing elements in the crown region of the tire.

[0003] A cord is said to be inextensible when its relative elongation is at most 0.2% under a tensile force equal to 10% of its breaking force.

[0004] A cord is said to be elastic when its relative elongation under a tensile force equal to the breaking load is at least 3% and its maximum tangential modulus is less than 150 GPa.

[0005] The circumferential or longitudinal direction of a tire is the direction corresponding to the outer circumference of the tire and defined by the tire's direction of travel.

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

[0007] The radial plane or meridional plane is the plane that contains the axis of rotation of the tire.

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

[0009] The lateral or axial direction of the tire is parallel to the tire's axis of rotation. Axial distance is measured along the axial direction. The statement "located on the inside or outside of the axial direction" means "the axial distance measured from the equatorial plane is less than or greater than respectively."

[0010] The radial direction is the direction that intersects with and is perpendicular to the tire's axis of rotation. Radial distance is measured along the radial direction. The phrase "located on the inner side or on the outer side of the radial direction" means that "the radial distance measured from the tire's axis of rotation is less than or greater than the radial distance measured from the tire's axis of rotation."

[0011] Located radially outside the crown reinforcement is the tread, which is typically made of polymer material and is designed to make contact with the ground in the contact patch where the tire contacts the ground.

[0012] It is known to provide a tread pattern (i.e., the part of the tire intended to contact the ground during driving and intended to wear during driving) formed by raised elements defined by cuts (e.g., grooves, whether circumferentially oriented, laterally oriented, or obliquely oriented). The purpose of this tread pattern is to impart good performance properties to the tread when driving on dry roads and water-covered roads (especially when it is raining).

[0013] To improve the performance properties of the tread without excessively reducing its shear stiffness, it is known to form multiple laterally oriented or obliquely oriented edge corners on the tread surface for cutting through a water film on the road surface, thereby ensuring good contact between the tread and the road surface. One method of obtaining such edge corners involves providing multiple cuts on the tread, these cuts being in the form of grooves or sipes. In this application, the distinction between sipes and grooves is that the width of a sipe is suitable for allowing at least partial contact between the opposing walls of these sipes during driving, particularly in contact patches with the ground, whereas this does not occur with grooves under normal tire use conditions.

[0014] For the purposes of this invention, a longitudinally oriented cut is one in which the average plane of at least a portion of the cut wall forms an angle of less than 10° with the longitudinal plane. This angle with the longitudinal plane can be oriented in one direction or another relative to the longitudinal plane. A longitudinally oriented cut can also be one in which the wall undulates or zigs around the average plane as described above.

[0015] For the purposes of this invention, a laterally oriented cut is one in which the mean plane of at least a portion of the cut wall forms an angle of less than 35° with the radial plane. This angle with the radial plane can be oriented in one direction or another relative to the radial plane. A laterally oriented cut can also be one in which the wall undulates or zigs around the mean plane as described above.

[0016] For the purposes of this invention, an obliquely oriented cut is one in which the mean plane of at least a portion of the cut wall forms an angle between 35° and 80° with the radial plane. This angle with the radial plane can be oriented in one direction or another relative to the radial plane. An obliquely oriented cut can also be one in which the wall undulates or zigs around the mean plane as described above.

[0017] Due to improvements in the global road network and the growth of highway networks, some existing tires, known as "highway" tires, are designed to travel increasingly longer distances at high speeds. Because these tires wear less, the combination of driving conditions required for them is such that they can increase the distance traveled.

[0018] To further increase tire lifespan, it is common practice to select polymer materials to prepare treads with improved wear resistance properties. Since such materials often adversely affect hysteresis properties, it is also known to use a radial stack of two different materials to manufacture the tire tread, thereby achieving a satisfactory wear-hysteresis trade-off for the intended application.

[0019] Such tires are described, for example, in document US 6247512. This document describes the superposition of two material layers to form the tread, with the outer material in contact with the ground exhibiting particularly better wear performance, while the hysteretic properties of the inner material limit the temperature rise of the tire in the crown region.

[0020] Furthermore, it has been found that some tires have improved performance properties in terms of rolling resistance, but deteriorate in terms of wear properties, resulting in irregular wear, to the point that some tires may be removed from the vehicle on which they are mounted, and replaced when they cause serious discomfort to the driver. Summary of the Invention

[0021] The inventors set themselves the task of providing tires that allow for greater travel distances and have satisfactory rolling resistance properties, while also maintaining satisfactory wear properties without exhibiting irregular wear that affects the driving experience.

[0022] According to the present invention, this objective has been achieved by a tire having radial carcass reinforcements, the tire including crown reinforcements themselves radially covered by a tread, the tread being connected to two bead via two sidewalls, the tread having grooves forming a tread pattern, the grooves having a height between the bottom of the tread pattern and the tread surface, and the tread being at least partially composed of at least three elastomeric compound layers, the elastomeric compound layers being radially stacked at the tread pattern height of the tread, the first layer forming the radial outer side of the tread and being made of a first elastomeric compound, the maximum value of tan(δ) of the first elastomeric compound (denoted as tan(δ)max) being strictly less than 0.150, the second elastomeric compound layer further radially inward and being composed of... The tire is made of a second elastomer compound, and at least one third elastomer compound layer is in radial contact with two layers made of the first and second elastomer compounds, and is made of the third elastomer compound, the third elastomer compound having a Vickers hardness at least 12 times greater than that of the first elastomer compound and at least 12 times greater than that of the second elastomer compound. In the meridional section of the tire, in the defined region between the outermost axial ends of the third layer, the ratio of the area of ​​the third elastomer compound to the total area of ​​the at least three elastomer compound layers is between 10% and 30%. In the meridional section of the tire, the center of gravity of the third elastomer compound is located radially from the bottom of the tread pattern between 30% and 70% of the tread pattern height.

[0023] For the purposes of this invention, the tread height in the meridional section of the tire is the distance measured between the radially outer surface of the contact patch formed by the tread and the parallel surface extending outward from the bottom of the tread pattern, said distance being measured along a direction perpendicular to the radially outer surface of the tread. The bottom of the tread pattern is the radially innermost point of the recessed area on the tread.

[0024] Area measurements and center of gravity determination are performed on brand new tires.

[0025] Area measurements are performed on the meridional section of the tire in the defined region between the outermost axial ends of the third layer (i.e., in the region defined by the two radial lines that define the existence of the third layer along the axial direction).

[0026] Vickers hardness measurements were performed using a Fisherscope HM2000 microhardness measurement system equipped with a Vickers indenter (a pyramid with a square base and a 136° apex). A reference load of 25 millinewtons was applied, with a loading and unloading time of 20 seconds, a reference load holding time of 5 seconds, and a Poisson's ratio set to 0.5. The samples were taken from tires and corresponded to radially cut tread sections. The samples were coated with resin to make the profile along the tread direction represent the surface to be tested. All surfaces were mechanically polished so that the indentation depth was greater than 20 times the arithmetic surface roughness. The distance between two consecutive indentations was 100 micrometers. Vickers hardness is expressed in MPa.

[0027] According to a preferred embodiment of the invention, the third polymer compound layer is present on at least 40% of the axial width of the tread.

[0028] Preferably, according to the present invention, the Vickers hardness of the third elastomer compound is greater than 72 MPa.

[0029] Advantageously, according to the invention, the complex dynamic shear modulus G* value of the third elastomer compound measured at 5% elongation is at least 5 times greater than the complex dynamic shear modulus G* value of the first elastomer compound measured at 5% elongation, and at least 5 times greater than the complex dynamic shear modulus G* value of the second elastomer compound measured at 5% elongation.

[0030] Furthermore, according to the present invention, the complex dynamic shear modulus G* of the third elastomer compound at 5% deformation is greater than 30 MPa.

[0031] Furthermore, according to the invention, in order to limit irregular wear, the maximum value of tan(δ) of the third elastomer compound (denoted as tan(δ)max) is strictly greater than 0.150, preferably greater than 0.200.

[0032] According to one embodiment variant of the invention, the second elastomer compound is the same as the first elastomer compound.

[0033] Complex dynamic shear modulus G* and loss factor tan(δ) are dynamic properties of rubber compound layers. The complex dynamic shear modulus G* and loss factor tan(δ) were measured on a viscosity analyzer (Metravib VA4000) according to standard ASTM D 5992-96. The response of specimens made from two cylindrical pellets 2 mm thick and 1 cm in diameter (the specimens were prepared from a region of the tire as close as possible to the equatorial plane, in a region thick enough to form the specimen, at the midpoint of the height of the layer under consideration) to a simple alternating sinusoidal shear stress at a frequency of 10 Hz was recorded at 60 °C. Strain amplitude scans were performed from 0.1% to 50% peak-to-peak (outward cycle) and then from 50% to 1% peak-to-peak (backward cycle). The results used are the complex dynamic shear modulus (G*) and loss factor tan(δ). For the outward cycle, the observed maximum value of tan(δ) is indicated and denoted as tan(δ). max .

[0034] Rolling resistance is the resistance a tire experiences during driving and as temperatures rise. Therefore, rolling resistance is represented by the hysteresis loss related to the deformation of the tire during one revolution. The tan(δ) values ​​of the materials used were measured at 10 Hz between 30°C and 100°C, thus incorporating the effects of various deformation frequencies caused by tire rotation. Therefore, for the compound tested, the tan(δ) value at 60°C corresponds to an index of the tire's rolling resistance during driving.

[0035] Various measurements were taken on brand new tires that had not yet been driven at all.

[0036] The inventors have demonstrated that the combination of the first elastomer blend, the second elastomer blend, and the third elastomer blend produces a satisfactory trade-off between tire wear performance properties (particularly in terms of wear irregularity) and rolling resistance properties. The first elastomer blend has a maximum tan(δ) value (denoted as tan(δ)max) strictly less than 0.150 and forms the outermost radial portion of the tread and is in contact with the ground. The second elastomer blend is located radially inside the third elastomer blend and can be the same as the first elastomer blend. As mentioned above, the third elastomer blend has a Vickers hardness that is at least 12 times greater than that of the first elastomer blend and at least 12 times greater than that of the second elastomer blend, and preferably greater than 72 MPa.

[0037] Specifically, the first elastomer blend forming the radially outer portion of the tread with a maximum tan(δ) value (denoted as tan(δ)max) strictly less than 0.150 provides satisfactory wear performance properties, but conversely, it leads to irregular wear in a known manner. It is particularly known that treads made from elastomer blends with a maximum tan(δ) value (denoted as tan(δ)max) strictly less than 0.150 result in irregular wear patterns, with the greater the number of nicks present on the tread, the more pronounced the irregular wear. This irregular wear pattern intensifies with increasing wear. They typically necessitate tire replacement because the tire becomes unusable due to the vibrations generated by the irregular wear pattern.

[0038] The inventors have demonstrated that the presence of a third elastomer compound, related to stiffness properties and location, can mitigate this irregular wear. The inventors believe this result can be explained by the action of a third layer that contacts the ground substantially when the tread is half-worn and, due to its rigidity, mitigates irregular wear until the second layer is worn down. This construction according to the invention allows for tread wear, with its irregular wear profile remaining acceptable throughout the entire service life of the tire, until the tread is completely worn, as originally intended by the tire's design.

[0039] According to a preferred variant of the invention, the ratio of the area of ​​the third elastomeric compound to the sum of the areas of the at least three elastomeric compound layers is greater than 15%, and advantageously less than 25%.

[0040] According to a first embodiment of the invention, the third layer is arranged substantially parallel to the radial outer surface of the tread.

[0041] According to another embodiment of the invention, in the meridional section of the tire, the radial position of the at least one third layer varies along the axial direction to minimize the risk of the layer forming a contact patch during the tire's life, or at least to ensure that the third compound appears only locally on the tread surface when the tread wears.

[0042] For example, since the tread pattern is composed of multiple ribs separated by circumferential grooves, the third compound according to the invention may be present only in some of the ribs. Each rib containing the third compound may include one or more layers of the third compound.

[0043] Since the tread pattern is composed of multiple ribs separated by circumferential grooves, the geometric arrangement of the at least one third elastomer compound layer can vary from one rib to another.

[0044] According to these embodiments, advantageously, the tread is produced prior to curing by stacking layers of elastomeric compounds that are radially superimposed and / or axially side-by-side, depending on the desired form and / or location of the different compounds. The profile of each stacked layer is also selected according to the desired configuration.

[0045] According to one embodiment variant of the invention, the tread includes an additional layer further radially inwardly oriented and made of a fourth elastomer compound having a maximum tan(δ) value (denoted as tan(δ)max) strictly less than 0.100. This embodiment variant is capable of further reducing the tire's hysteresis properties, and the fourth layer is advantageously designed to avoid contact with the ground.

[0046] According to one embodiment of the invention, the crown reinforcement of the tire is formed by at least two working crown layers, each working crown layer having preferably non-extendable reinforcing elements that intersect from one layer to another and are formed at an angle between 10° and 45° with respect to the circumferential direction.

[0047] According to another embodiment of the invention, the crown reinforcement further includes at least one circumferential reinforcement element layer.

[0048] One embodiment of the invention further provides that the crown reinforcement is supplemented radially outward by at least one additional layer (referred to as a protective layer), which is preferably composed of a reinforcing element called an elastic reinforcing element oriented at an angle between 10° and 45° relative to the circumferential direction, and the orientation is the same as that formed by the reinforcing element of the working layer adjacent to it radially.

[0049] According to any of the above embodiments of the present invention, the crown reinforcement may be further supplemented radially inward between the carcass reinforcement and the radially inner working layer closest to the carcass reinforcement by a triangular layer made of a non-extendable steel metal reinforcement element forming an angle greater than 60° with the circumferential direction, and the direction being the same as the direction of the angle formed by the reinforcement element along the radially closest layer to the carcass reinforcement. Attached Figure Description

[0050] In the following text, by reference Figures 1 to 3 As will become apparent from the description of exemplary embodiments of the present invention, further details and advantageous features of the invention will be apparent, wherein:

[0051] - Figure 1 A schematic meridional view of a portion of a tire according to a first embodiment of the present invention is shown.

[0052] - Figure 2A schematic meridional view of a portion of a tire according to a second embodiment of the present invention is shown.

[0053] - Figure 3 A schematic meridional view of a portion of a tire according to a third embodiment of the present invention is shown.

[0054] For ease of understanding, the accompanying drawings are not shown to scale. Detailed Implementation

[0055] exist Figure 1 In this tire 1, with a size of 315 / 70R 22.5, a radial carcass reinforcement 2 is anchored in two bead lines (not shown in the figures). The carcass reinforcement 2 is formed from a single layer of metal cord. The carcass reinforcement 2 is encircled by a crown reinforcement 5, which is itself covered by a tread 6. The tread includes four grooves 3 forming five ribs 4.

[0056] The area below tire 1 and the bead are not specifically shown in the attached diagram.

[0057] exist Figure 1 In the middle, the crown reinforcement 5 is formed radially from the inside to the outside as follows:

[0058] - First working layer 51, the first working layer 51 is formed of uncovered, non-extendable 11.35 metal cords, the metal cords being continuous over the entire width of the fabric layer and oriented at an angle of 18°.

[0059] - Second working layer 52, the second working layer 52 is formed of uncovered, non-extendable 11.35 metal cords, the metal cords being continuous over the entire width of the fabric layer, oriented at an angle of 26°, and intersecting with the metal cords of the first working layer.

[0060] - Protective layer 53, which is formed of uncovered elastic 6.35 metal cords that are continuous over the entire width of the fabric layer and oriented at an angle of 26° in the same direction as the metal cords of the working layer 52.

[0061] According to the present invention, the tread 6 is composed of a radially outer first layer 61 and a radially inner layer 62, wherein the radially outer first layer 61 is in contact with the ground.

[0062] Layer 61 is made of a first elastomer compound with a Vickers hardness of 6 MPa.

[0063] The modulus G* of the first mixture at 5% deformation is 2 MPa.

[0064] The maximum value of tan(δ) for the first mixture (denoted as tan(δ)max) is 0.144.

[0065] The innermost radial layer 62 is made of a second elastomer compound.

[0066] According to this implementation scheme, layer 62 is made of a second compound, which is the same as the first compound.

[0067] In Figure 1 It can also be seen that layer 63 is made of a third compound, which has a Vickers hardness of 100 MPa.

[0068] The modulus G* of the third compound at 5% deformation is 34 MPa.

[0069] The maximum value of tan(δ) of the third mixture (denoted as tan(δ)max) is 0.260.

[0070] Of all the ribs, the area of ​​the third layer 63 is 23% of the total area of ​​the three layers 61, 62 and 63.

[0071] The areas of layers 61, 62, and 63 are measured between two straight lines d1 and d2 that form a radial straight line passing through the outermost axial end of layer 63.

[0072] The center of gravity of the third layer 63 is located at 50% of the tread height from the bottom of the tread pattern.

[0073] According to one embodiment variation of the present invention, Figure 2 Tire 21 is shown, and tire 21 is... Figure 1 Similar to other tires, but differing in the profile of the third layer 263 in the meridional plane. In each of the three central ribs 24, the third layer 263 consists of a relatively thick central portion 263a, which extends axially on both sides of its radially lower and radially upper portions by thin layers 263b, which are separated from each other by layers 264 made of a first compound. The radial position of the layers 263 can vary in different ways along the axial direction from one rib to another. The third compound is absent in the outermost axial rib 25. In some cases, this particular embodiment allows for a less adverse impact on the tire's wear profile during use.

[0074] In the three central ribs 24, the ratio of the area of ​​the third layer 263 to the sum of the areas of the three layers 261, 262 and 263 is 23%.

[0075] The areas of layers 261, 262, and 263 are measured between two straight lines d21 and d22 that form a radial straight line passing through the outermost axial end of layer 263.

[0076] The center of gravity of the third layer 263 is located at 51% of the tread pattern height.

[0077] Figure 3 A third embodiment variant of the invention is shown. Tire 31 and Figure 1 Similar to other tires, but differing in that they contain two layers 363a and 363b, which are radially stacked within each rib 34, 35, and 36, with the orientation of layers 363a and 363b varying from one rib 34, 35, and 36 to the other. Therefore, the two layers 363a and 363b are radially stacked between three layers 361, 362, and 364, all of which are made from a first compound. The variation in the radial position of layer 363 along the axial direction is optimized to improve grip and wear performance properties. The axially outer portion of layer 363 is omitted in the axially outermost portion of the outermost rib 36 so as not to adversely affect the wear profile of the tire shoulder during driving.

[0078] In the central rib 34, the ratio of the area of ​​the third layer 363a, 363b to the total area of ​​all layers 361, 362, 363a, 363b and 364 is 25%.

[0079] In the central rib 34, the areas of layers 361, 362, 363a, 363b and 364 are measured between two straight lines d4 and d5 that form radial straight lines passing through the outermost axial ends of layers 363a and 363b.

[0080] In the two intermediate ribs 35, the ratio of the area of ​​the third layer 363a, 363b to the total area of ​​all layers 361, 362, 363a, 363b and 364 is 20%.

[0081] In the intermediate rib 35, the areas of layers 361, 362, 363a, 363b and 364 are measured between two straight lines d6 and d7 that form radial straight lines passing through the outermost axial ends of layers 363a and 363b.

[0082] In the two outermost axial ribs 36, the ratio of the area of ​​the third layer 363a, 363b to the total area of ​​all layers 361, 362, 363a, 363b and 364 is 11%.

[0083] In the two outermost axial ribs 36, the areas of layers 361, 362, 363a, 363b and 364 are measured between two straight lines d31 and d3 that form radial straight lines passing through the outermost axial ends of layers 363a and 363b.

[0084] In all the ribs 34, 35, and 36, the ratio of the area of ​​the third layer 363a and 363b to the total area of ​​all layers 361, 362, 363a, 363b, and 364 is 16%.

[0085] In all ribs 34, 35, and 36, the area of ​​each of layers 361, 362, 363a, 363b, and 364 is measured between two straight lines d31 and d32 that form a radial straight line passing through the outermost axial ends of layers 363a and 363b.

[0086] The center of gravity of the third layer, 363a and 363b, is located at 46% of the tread height from the bottom of the tread pattern.

[0087] Tires are prepared based on two elastomer blends with certain properties described below.

[0088] Compound A Compound B NR 80 100 BR 20 - N234 48 - N326 - 75 Phenol-formaldehyde resin - 12 Hexamethylenetetramine - 8.5 6PPD-1,3-Dimethylbutylphenyl-p-phenylenediamine 3 2 stearic acid - 0.6 ZnO 3 8.5 sulfur 1.5 5.3 Accelerator (CBS) 0.9 1.05 Vickers hardness (MPa) 6 100 G*5%cc / 60℃ / 10Hz(MPa) 2 34 <![CDATA[tan(δ) max ]]> 0.144 0.260

[0089] The values ​​of the components are expressed as phr (parts by weight / parts per hundred elastomer).

[0090] The first reference tire R is produced according to the construction corresponding to the conventional embodiment excluding layer 63. The tread is produced using compound A.

[0091] According to the present invention (more particularly according to) Figure 1 In the case of the first tire T1, compound A (which forms layers 61 and 62) is combined with compound B (which forms layer 63) to form the tread.

[0092] The second tire T2 produced according to the present invention can be compared to Figure 2 The tire. The first compound corresponds to compound A, and layer 263 is made of compound B.

[0093] The third tire T3 produced according to the present invention can be compared to Figure 3 The tire. The first compound corresponds to compound A, and layer 363 is made of compound B.

[0094] Driving tests were conducted using various tires T1, T2, and T3 according to the invention, as well as a reference tire R. The tests were performed on tires mounted on the steering axle of the vehicle. Each tire was mounted on two identical vehicles driven by different drivers, so that each driver could test all tires. The tests were conducted on a track consisting of two straight sections of 1020m in length and two inclined curves with an average radius of 636m. The slopes of these curves were constructed such that, at a speed of 105km / h, at all points near the curves, the centripetal acceleration caused by gravity equals the value of the centrifugal acceleration related to the vehicle's speed, thus subjecting the vehicle to no lateral acceleration and therefore the tires to no lateral load. Therefore, 105km / h is considered the neutral speed of this track. This type of test has the ability to exacerbate irregular wear under extremely low lateral stress; therefore, irregular wear becomes visible when the tires are half-worn.

[0095] Drivers gave the same rating for tire comfort. Tires T1, T2, and T3 received the highest ratings, with the tires worn down to the wear indicators. Tire T3 was considered more effective than tires T1 and T2.

[0096] Regarding the reference tires, the two drivers decided to stop the test drive at essentially the same wear level because they no longer felt safe due to discomfort and vibrations from the steering wheels.

[0097] In accordance with UNECE Regulation 117, rolling resistance was also measured for each tire under the same driving conditions. The results are shown in the table below, where a value of 100 is assigned to tire R. Values ​​below 100 indicate excellent performance properties in terms of rolling resistance.

[0098] Tire R <![CDATA[Tire T1]]> <![CDATA[Tire T2]]> <![CDATA[Tire T3]]> 100 98 99 99

[0099] These values ​​indicate that the rolling resistance performance properties of the tire according to the invention are substantially the same as, or even improved upon, those of the reference tire.

Claims

1. Tyre (1) having a radial carcass reinforcement (2), comprising a crown reinforcement (5) itself covered in the radial direction by a tread (6) connected to two beads by two sidewalls, the tread (6) having grooves forming a tread pattern, the grooves having a height between the bottom of the tread pattern and the tread surface, the tread being at least partially composed of at least three elastomeric compound layers (61, 62, 63) superimposed in the radial direction over the tread pattern height of the tread, characterized in that, A first layer (61) forms the radially outer portion of the tread and is made of a first elastomeric compound whose maximum value of tan (delta) expressed as tan (delta)max is strictly less than 0.150, a second elastomeric compound layer (62) is further radially inward and is made of a second elastomeric compound, at least one third elastomeric compound layer (63) is in radial contact with two layers made of the first elastomeric compound and / or the second elastomeric compound and is made of a third elastomeric compound whose Vickers hardness is at least 12 times greater than the Vickers hardness of the first elastomeric compound and at least 12 times greater than the Vickers hardness of the second elastomeric compound, in the meridian section of the tire, in the defined area between the axially outermost ends of the third layer, the ratio of the area of the third elastomeric compound to the sum of the areas of the at least three elastomeric compound layers is between 10% and 30% and in the meridian section of the tire, the center of gravity of the third elastomeric compound is radially located between 30% and 70% of the tread pattern height of the tread pattern from the bottom of the tread pattern, wherein tan (delta)max is measured at a temperature of 60 o C according to standard ASTM D 5992-96 at a frequency of 10 Hz.

2. Tyre (1) according to Claim 1, characterized in that, The third polymeric compound layer is present over at least 40% of the axial width of the tread.

3. Tyre (1) according to claim 1 or 2, characterized in that, The third elastomeric compound has a Vickers hardness greater than 72 MPa.

4. Tyre (1) according to claim 1, characterized in that, The third elastomeric compound has a complex dynamic shear modulus G* value measured at 5% elongation at least 5 times greater than the complex dynamic shear modulus G* value measured at 5% elongation of the first elastomeric compound and at least 5 times greater than the complex dynamic shear modulus G* value measured at 5% elongation of the second elastomeric compound.

5. Tyre (1) according to claim 1, characterized in that, The third elastomeric compound has a complex dynamic shear modulus G* value at 5% elongation greater than 30 MPa.

6. Tyre (1) according to claim 1, characterized in that, The third elastomeric compound has a maximum value of tan (delta) expressed as tan (delta)max strictly greater than 0.

150.

7. A tyre (1) according to claim 1, characterized in that, The second elastomeric compound is the same as the first elastomeric compound.

8. A tyre (1) according to claim 1, characterized in that, The ratio of the area of the third elastomeric compound to the sum of the areas of the at least three elastomeric compound layers is greater than 15%.

9. Tyre (1) according to claim 1, characterized in that, In a meridian section of the tire, the at least one third layer is arranged substantially parallel to the outer surface of the tread.

10. Tyre (1) according to claim 1, characterized in that, In a meridian section of the tire, the radial position of the at least one third layer varies along the axial direction.

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