Tire with Improved End-of-Life Grip on Wet Ground

Abstract

The present invention provides a method for manufacturing a hose with at least one legal wear indicator (46) that defines a legal wear threshold and a complex dynamic shear modulus G * a tread layer (52) having an elastomeric tread material exhibiting a complex dynamic shear modulus G * _2 and tanD0_2≧0.37×tanD0_1 and G * _2≧0.90×G * and a backing layer (54) for the tread layer (52) comprising an elastomeric backing material exhibiting a dynamic loss tan D0_2 such that the tread layer (52) is _1.

Description

Technical Field

[0001] The present invention relates to a tire for a passenger car.

Background Art

[0002] Tires sold under the trade name MICHELIN Primacy 4, which are substantially annular around an axis of rotation substantially coinciding with the axis of rotation of the tire, are known from the prior art. This tire comprises a crown, two sidewalls, and two beads, each sidewall connecting each bead to the crown. The tire also comprises a carcass reinforcement fixed within each bead and extending within each sidewall and further radially inside the crown. The crown comprises a tread and a crown reinforcement arranged radially inside the tread.

[0003] The tread comprises cuts separating the tread pattern blocks from one another. The cuts comprise in particular grooves and sipes. The grooves comprise circumferential grooves, at the bottom of which wear indicators are arranged. Such wear indicators are imposed, for example, by United Nations regulations R30 and R54, US standard FMVSS139, or Chinese standard GB97743, and are intended in particular to inform the user of the tire of a legal tire wear threshold beyond which driving is dangerous, especially on wet ground. These wear indicators are thus called legal wear indicators. Each legal wear indicator is formed by a protrusion extending radially outwards from the bottom of the circumferential groove, in particular from the bottom of the deepest circumferential groove, over a radial height substantially equal to 1.6 mm. This radial height makes it possible to define the wear potential of the tire, in this case 5.4 mm, as the radial height between the radially outermost point of the legal wear indicator when the tire is new and its projection onto the ground when the tire is in motion. In other words, the wear potential is equal to the difference between the tread pattern depth of the new tire, which is equal to 7.0 mm in this case, and the radial height of the legal wear indicator, which is equal to 1.6 mm in this case.

[0004] The tread of the tire comprises a tread layer intended to be in contact with the ground when the tire is running through the tread surface, and a backing layer for the tread layer arranged radially inside the tread layer. The tread layer comprises an elastomeric tread material, and the backing layer comprises an elastomeric backing material different from the elastomeric tread material. That is, the tread layer and the backing layer are adjacent through an interface representing an interface track in the meridian plane of the tire.

[0005] The backing layer is intended not to be in contact with the ground unless it has reached at least the legal wear threshold when the tire is running. In other words, by defining a legal wear track in the meridian plane that is parallel to the tread surface of the new tire and passes through the radially outermost point of the legal wear indicator, the interface track located radially below the tread pattern block is arranged radially inside the legal wear track in the meridian plane.

[0006] The above-mentioned MICHELIN Primacy 4 tire exhibits particularly very low rolling resistance. The reason is that each elastomeric tread and backing material, respectively denoted as tanDMAX23_1 and tanDMAX23_2, shows relatively small dynamic losses measured according to the standard ASTM D-5992-96 at a temperature of 23 °C and a frequency of 10 Hz, and is equal to 0.38 and 0.15 respectively.

[0007] The search for relatively small dynamic loss values tanDMAX23_1 and tanDMAX23_2 for obtaining very low rolling resistance has resulted in the braking performance on wet ground being inhibited compared to new tires when the wear potential exceeds half.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] The subject of the present invention is a tire that exhibits improved braking performance on a wet ground compared to prior art tires when more than half of its wear potential has been reached.

Means for Solving the Problems

[0010] For the above object, the subject of the present invention is a tire for a passenger car comprising a tread having cuts and tread pattern blocks, the cuts separating the tread pattern blocks from each other, the tread being intended to be in contact with the ground when the tire is running through the tread surface, the tread comprising at least one legal wear indicator defining a legal wear threshold, and within the axial center portion of the tread having an axial width equal to at least 70% of the width of the tread surface, the tread is a tread layer carrying the tread surface, and the complex dynamic shear modulus G * _1 and the above tread layer comprising an elastomeric tread material showing the dynamic loss tanD0_1 measured according to Standard ASTM D-5992-96 at a temperature of 23°C and a frequency of 10 Hz with 10% strain, and a backing layer for the tread layer arranged radially inside the tread layer, and the complex dynamic shear modulus G *An elastomeric backing material having a tanD0_2 measured according to standard ASTM D-5992-96 at a temperature of 0 °C and a frequency of 10 Hz, and the backing layer having the elastomeric backing material, wherein the elastomeric tread material is different from the elastomeric backing material. Thus, the tread layer and the backing layer are adjacent through an interface representing an interface track in a meridian cross-sectional plane having a legal wear indicator, with tanD0_2 ≧ 0.37 × tanD0_1 and G * _2 ≧ 0.90 × G * _1, characterized in that it is parallel to the tread surface of the new tire in the meridian cross-sectional plane within the axial center portion of the tread, and by defining a legal wear track passing through the radially outermost point of the legal wear indicator, at least 75% of the length of the interface track positioned radially below the tread pattern block is arranged radially inside the legal wear track in the meridian cross-sectional plane, and at least 75% of the length of the interface track positioned radially below the tread pattern block within the axial center portion of the tread is arranged at an average radial distance less than or equal to 2.0 mm from the legal wear track.

[0011] When more than half of its wear potential has been exceeded, the tire according to the present invention exhibits significantly improved braking performance on a wet ground as shown by a comparative test described below compared to a prior art tire.

[0012] The present invention is remarkable in that it enables a backing layer, which is not intended to be in contact with the ground for most of the time when the tire is running, to improve the braking performance of the tire on a wet ground when more than half of its wear potential has been exceeded.

[0013] On the one hand, the dynamic loss tanD0 measured at 0 °C makes it possible to characterize the grip potential on a wet ground. The reason is that when the tire is running on a wet ground showing irregularities, the tread deforms to fit the upper part of the irregularities to form a press-fit body. When the tire is in a state exceeding half of its wear potential, the liner layer acts more effectively on this press-fit mechanism when the dynamic loss tanD0 of the liner layer measured at 0 °C is higher compared to the dynamic loss tanD0 of the tread layer measured at 0 °C. Therefore, by satisfying the characteristic that tanD0_2 ≧ 0.37 × tanD0_1, the grip potential of the tire on a wet ground is improved when the tire is in a state exceeding half of its wear potential.

[0014] On the other hand, the complex dynamic shear modulus G measured at 10% strain at 23 °C * characterizes the hardness of the layer and thus characterizes the function of this layer to counter the deformation of the tread under the effect of water pressure when the tire is running on a wet ground. This tread deformation mechanism is known as blistering and may cause loss of contact between a part of the contact surface and the ground, thus reducing the grip of the tire. When the tire is in a state exceeding half of its wear potential, the liner layer has a complex dynamic shear modulus G of the liner layer measured at 10% strain at 23 °C * is higher compared to the complex dynamic shear modulus G of the tread layer measured at 10% strain at 23 °C * and acts more effectively on this blistering mechanism. Therefore, by satisfying the characteristic that G * _2 ≧ 0.90 × G * _1, the hardness of the liner layer is improved, and thus the hardness of the tread is improved when the tread is in a state exceeding half of its wear potential.

[0015] It should be noted that according to the present invention, it is necessary to control the grip potential and hardness of the tread. The reason is that improving the grip potential on a wet ground is only advantageous when the tread is correctly positioned on the ground, and vice versa.

[0016] Complex dynamic shear modulus G * is a dynamic property known to those skilled in the art and measured using specimens extracted from the tire on a Metravib VA4000 viscoanalyzer. A record of the response of the specimen exposed to a monotonic alternating sinusoidal shear stress at a frequency of 10 Hz under standard temperature conditions (23 °C in this case) is taken in accordance with ASTM D1349-99. Strain amplitude sweeps are performed from 0.1% to 100% (outward cycle) and then from 100% to 0.1% (return cycle). The specimen has a cylindrical cross-section as described in Figure X2.1 (circular version) of ASTM D5992-96 (version approved in 1996 and published in September 2006), with a diameter of 10 mm [0 to +0.04 mm] and a thickness of 2 mm [1.85 - 2.20]. Complex dynamic shear modulus G * is defined as the square root of the sum of the square of G' representing the modulus of elasticity and the square of G'' representing the viscosity coefficient. Next, measurements are obtained at 10% strain over the return cycle.

[0017] Dynamic loss tanD0 is another dynamic property known to those skilled in the art and measured using the same specimens extracted from the tire on the same Metravib VA4000 viscoanalyzer as above. To determine this property, a temperature sweep is performed at 1.5 °C per minute from a temperature Tmin lower than the glass transition temperature Tg of the material to a temperature Tmax corresponding to the rubber plateau of the elastomer material over the temperature gradient. Before starting the sweep, the sample is stabilized at temperature Tmin for 20 minutes to have a uniform temperature throughout the specimen. A record of the response of the specimen exposed to a monotonic alternating sinusoidal shear stress at a frequency of 10 Hz for each temperature value is taken until the stress representing the operating point of the elastomer material in the tire, 0.7 MPa in this case, is reached. The value of dynamic loss tanD0 is the measured value obtained at a temperature value equal to 0 °C.

[0018] The dynamic loss tanDMAX23 is another dynamic property known to those skilled in the art and is measured using the same test specimens extracted from the tire on the same Metravib VA4000 visco-analyzer as described above. A record of the response of the test specimens exposed to a monotonic alternating sinusoidal shear stress at a frequency of 10 Hz under the determination temperature conditions (23 °C in this case) in accordance with ASTM D1349-99 standard is taken. The strain amplitude sweep is carried out from 0.1% to 100% (outward cycle), and then from 100% to 0.1% (return cycle). The tangent D of the phase angle between the force applied to the sample, expressed as the dynamic loss, and the displacement of the sample is equal to the ratio G″ / G’. The maximum value tanDMAX of the tangent D of the phase angle observed in the strain return cycle is recorded.

[0019] The feature that at least 75% of the length of the interface track positioned radially downward of the tread pattern block is arranged radially inside the legal wear track in the meridian plane is characterized in that it is intended that most of the liner layer does not come into contact with the ground unless at least the legal wear threshold is reached when the tire is running. In contrast to the tires of the prior art, in the tire according to the present invention, the liner layer can be brought into contact with the ground locally, that is, over a maximum of 25% of the length of the interface track positioned radially downward of the tread pattern block. The reason is that the grip potential provided by this liner layer in the case of contact with the ground due to the relatively high value of the dynamic loss tanD0_2 of the liner layer is considered to be higher than the grip potential provided by the liner layer of the prior art tires when the liner layer of the prior art tires comes into contact with the ground. In other words, when the liner layer of the tire according to the present invention comes into contact with the ground, the grip potential is considered not to be inhibited so much.

[0020] The above features are particularly advantageous in that they make it possible to avoid discarding a tire in which a small but non-negligible portion of the liner layer has become exposed beyond the legal wear track in the radial direction. Such radial exposure is seen near the cut, in particular, because the mold shaping of the cut causes an outward axial flow of the elastomeric tread material and the elastomeric liner material located axially below the cut in the radial direction and an outward radial flow of the elastomeric tread material and the elastomeric liner material located radially close to the resulting cut.

[0021] In addition, the feature that the special tread layer and liner layer arrangements according to the invention, as well as the properties of the tread material and the liner material, are seen across the axial center portion of the tread reflects the fact that the invention requires the arrangement and properties of these materials across a significant axial portion of the tread that is intended to be in contact with the ground, in this case an axial portion equal to at least 70% of the width of the tread surface. The axial center portion comprises the meridian plane of the tire.

[0022] In a first preferred variant according to the invention, the axial center portion of the tread has an axial width equal to the axial width of the tread. In other words, the axial center portion of the tread has an axial width equal to 100% of the width of the tread surface.

[0023] Also in a second variant according to the invention, the tread comprises an axial lateral portion arranged axially outside the axial center portion, and the axial center portion of the tread has an axial width strictly smaller than the axial width of the tread surface such that each axial lateral portion has an axial width equal to at most 15% of the axial width of the tread. In a first configuration of this second variant, the axial lateral portion has a special arrangement different from that of the axial center portion. In a second configuration of this second variant, the axial lateral portion exhibits material properties different from those of the axial center portion.

[0024] Conventionally, the tread surface is determined on a tire mounted on a nominal rim and inflated to the nominal pressure. When there is a clear boundary between the tread surface and the remainder of the tire, the axial width of the tread surface is easily measured. When the tread surface is continuous with the outer surface of the tire sidewall, the axial limit of the tread surface is determined by the points through which a straight line passing through the point and parallel to the axial direction and the tangential direction of the tread surface at this point forms an angle equal to 30°. When there are several points in the meridian cross-sectional plane where this angle is equal to 30° in absolute value, the radially outermost point is adopted.

[0025] The interface track positioned radially below the tread pattern block is perpendicular to the tread surface when the tire is new and is axially bounded by two straight lines passing through the axial ends of each tread pattern block that is part of the tread surface.

[0026] According to the present invention, in a state where the tire has exceeded half of its wear potential, in order for the backing layer to have a significant effect on the above-described press-fitting and blistering mechanisms, it is necessary that the backing layer is not excessively separated radially from the tread surface. Therefore, a significant portion of the length of the interface track positioned radially below the tread pattern block, in this case at least 75%, is arranged at a relatively small distance from the legal wear track in the meridian cross-sectional plane, in this case a distance less than or equal to 2.0 mm. To determine the average radial distance between the interface track and the legal wear track, the average of the radial distances between the interface track and the legal wear track measured regularly along the interface track positioned radially below the tread pattern block is taken, for example, in millimeters.

[0027] The fact that the tread layer and the backing layer are adjacent is characterized in that, in particular, the tread material and the backing material are in direct contact with each other along the interface and no other material is radially sandwiched between the tread layer and the backing layer.

[0028] To determine the length of the interface track positioned radially below the tread pattern block, the measurement of the arc length of the interface track disposed radially below the tread surface is performed in the meridian plane, and this measurement implicitly excludes the lengths of the interface tracks disposed radially below various cuts that do not themselves have a surface intended to be in contact with the ground.

[0029] To determine whether the length of the interface track positioned radially below the tread pattern block is disposed on the inner or outer side of the legal wear track in the radial direction, for each point on the interface track, it is determined whether the radially projected point of the said point onto the legal wear track is positioned on the inner or outer side of the said point in the radial direction. In a similar manner, to determine the distance between the interface track positioned radially below the tread pattern block and the legal wear track, for each point on the interface track, the distance between the said point on the interface track and the radially projected point of the said point onto the legal wear track is determined.

[0030] The geometric features described in this application can be easily determined in the meridian plane of the tire.

[0031] An elastomeric material is a material that exhibits elastic behavior. Such a material is advantageously obtained by crosslinking a crosslinkable composition comprising at least one elastomer and at least one other component. Preferably, the crosslinkable composition comprising at least one elastomer and at least one other component comprises an elastomer, a crosslinking system, and a filler. The crosslinkable compositions used for the tread layer and the inner liner layer generally comprise a composition for a conventional tire tread based on a diene elastomer, a reinforcing filler such as carbon black and / or silica, a vulcanization system, and conventional additives.

[0032] In particular, in order to be able to guarantee good grip performance on a wet ground from which water is discharged, the tread of the tire according to the invention is provided with incisions. The incisions represent either wells, grooves or sipes and form spatial openings in the tread surface.

[0033] On the tread surface, the sipes or grooves have two characteristic main dimensions, namely a width W and a length Lo which is at least equal to twice the width W. Thus, the sipes or grooves are delimited by two main side surfaces which define their length Lo, are connected by a bottom surface and are separated from each other by a non-zero distance called the width W of the incision. In a new tire, the width W of the incision is measured at the place where the radial plane coincides with the tread surface when the incision is not chamfered, and at the place where the outermost radial plane in the radial direction of the incision coincides with the innermost surface in the radial direction of the chamfer when the incision is chamfered, which is the maximum distance between two main side surfaces. On a new tire, the depth of the incision is the maximum radial distance between the bottom of the incision and the projection point of this bottom onto the ground when the tire is running. The maximum value of the depth of the incision is called the tread pattern depth.

[0034] The sipes are such that the distance between the main side surfaces allows these main side surfaces which delimit the sipes to be at least partially in contact within the contact surface, especially when the tire is new and, in particular, under normal running conditions where the tire is under nominal load and nominal pressure. Generally, the width of the sipes is less than or equal to 2 mm.

[0035] The grooves are such that the distance between the main side surfaces is such that these main side surfaces cannot be in contact with each other under normal running conditions, especially when the tire is under nominal load and nominal pressure. Generally, the width of the grooves is strictly greater than 2 mm, preferably greater than or equal to 5 mm, more preferably greater than or equal to 8 mm.

[0036] The groove can be, in particular, a circumferential groove, i.e., a groove extending in a main direction forming an angle of less than or equal to 30°, preferably less than or equal to 10° with the circumferential direction of the tire. The circumferential groove can be continuous such that its two main side surfaces determining its length are continuous over the entire circumference of the tire, i.e., not interrupted by a tread pattern block or another cut. Nevertheless, the circumferential groove can be discontinuous such that its two main side surfaces determining its length are interrupted by one or more tread pattern blocks and / or one or more other cuts, i.e., interrupted by one or more tread pattern blocks and / or one or more other cuts. Generally, the depth of the circumferential groove of a new tire is greater than or equal to 85%, preferably greater than or equal to 90% of the tread pattern depth. Very conventionally, the circumferential groove of a new tire is greater than or equal to 4.0 mm, preferably greater than or equal to 5.0 mm, more preferably greater than or equal to 5.5 mm. The cut separating the tread pattern blocks of the tire according to the present invention is very preferably a circumferential groove.

[0037] The tire according to the present invention has a substantially annular shape around a turning axis that substantially coincides with its rotation axis. This turning axis defines three directions conventionally used by those skilled in the art, namely, the axial direction, the circumferential direction, and the radial direction.

[0038] The expression "axial direction" means a direction substantially parallel to the turning axis of the tire, i.e., the rotation axis of the tire.

[0039] The expression "circumferential direction" means a direction substantially perpendicular to both the axial direction and the radius of the tire (in other words, tangent to a circle centered on the rotation axis of the tire).

[0040] The expression "radial direction" means a direction along the radius of the tire, i.e., any direction that intersects the rotation axis of the tire and is substantially perpendicular to this axis.

[0041] The meridian plane of the tire (denoted as M) is understood to be a plane that is perpendicular to the rotation axis of the tire, is located axially intermediate between the two beads, and passes through the axial center of the crown reinforcement.

[0042] The equatorial circumferential plane of the tire (denoted as E) is understood to be a meridian cross-sectional plane that passes through the equator of the tire and is perpendicular to the meridian plane and the radial direction. The equator of the tire is parallel to the rotation axis of the tire within the meridian cross-sectional plane (perpendicular to the circumferential direction and parallel to the radial direction and the axial direction), and is an axis positioned equidistantly between the radially outermost point intended to be in contact with the ground and the radially innermost point intended to be in contact with a support, such as a rim, and the distance between these two points is equal to H.

[0043] The meridian plane is understood to be a plane that is parallel to the rotation axis of the tire, contains it, and is perpendicular to the circumferential direction.

[0044] "Radially inner" and "radially outer" respectively mean "being close to the rotation axis of the tire" and "being far from the rotation axis of the tire". "Axially inner" and "axially outer" respectively mean "being close to the meridian plane of the tire" and "being far from the meridian plane of the tire".

[0045] The bead is understood to be the part of the tire intended to enable attaching the tire to a mounting support, such as a wheel equipped with a rim. Accordingly, each bead is, among other things, intended to be in contact with the flange of the rim and to be capable of being attached.

[0046] Any interval between values represented by the expression "between a and b" represents a range of values extending from greater than a to less than b (i.e., the limit values a and b are excluded), whereas any interval between values represented by the expression "from a to b" means a range of values extending from a to b (i.e., including the exact limit values a and b).

[0047] The tyre of the present invention relates to a passenger car as defined according to the 2019 standards of the European Tyre and Rim Technical Organisation (European Tyre and Rim Technical Association) or "ETRTO". Such a tyre has a cross-section in the meridian plane characterised by a section height H and a nominal section width S according to the 2019 standards of the European Tyre and Rim Technical Organisation (European Tyre and Rim Technical Association) or "ETRTO".

[0048] The tyre of the present invention preferably relates to a passenger car. Such a tyre has a cross-section in the meridian plane characterised by a nominal section width S and a section height H according to the standards described in the 2019 standard manual of the European Tyre and Rim Technical Organisation (abbreviated as "ETRTO"), and the ratio H / S expressed as a percentage is at most equal to 90, preferably at most equal to 80, more preferably at most equal to 70, and at least equal to 30, preferably at least equal to 40, the nominal section width S is at least equal to 115 mm, preferably at least equal to 155 mm, more preferably at least equal to 175 mm, and at most equal to 385 mm, preferably at most equal to 315 mm, more preferably at most equal to 285 mm, even more preferably at most equal to 255 mm. Further, the diameter D at the rim flange defining the diameter of the mounting rim of the tyre is at least equal to 12 inches, preferably at least equal to 16 inches, and at most equal to 24 inches, preferably at most equal to 20 inches.

[0049] As described above, the backing layer preferably minimizes the amount of the backing layer that can come into contact with the ground while not significantly reducing the grip potential when it comes into contact with the ground. Thus, advantageously, at least 80%, preferably at least 90% of the length of the interface track located radially below the tread pattern block is arranged radially inside the legal wear track in the meridian cross-sectional plane.

[0050] To maximize the effect of the backing layer on press fit and blistering, it will be understood that it is preferable for the largest possible amount of the backing layer to be located in a place relatively close to the legal wear track in the radial direction. Thus, advantageously, at least 80%, preferably at least 90% of the length of the interface track located radially below the tread pattern block is arranged at a radial distance less than or equal to 2.0 mm in the meridian cross-sectional plane.

[0051] Furthermore, to maximize the effect of the backing layer on press fit and blistering mechanisms, it will be understood that it is preferable for the backing layer to be located in the place closest to the legal wear track in the radial direction regardless of its amount. Thus, at least 75%, preferably at least 80%, more preferably at least 90% of the length of the interface track located radially below the tread pattern block is advantageously arranged at a radial distance less than or equal to 1.2 mm, more preferably less than or equal to 1.0 mm from the legal wear track in the meridian cross-sectional plane.

[0052] In order to improve the effect of the backing layer on the press-fitting mechanism, in an advantageous embodiment, tanD0_2 ≧ 0.5 × tanD0_1, preferably, tanD0_2 ≧ 0.75 × tanD0_1, more preferably, tanD0_2 ≧ tanD0_1, still more preferably, tanD0_2 > tanD0_1, very preferably, tanD0_2 ≧ 1.10 × tanD0_1 applies. In particular, the greater the increase in the value of tanD0_2, the more significantly the grip potential of the tire on a wet ground when the tire exceeds half of its wear potential is improved. In the more preferred and very preferred cases where tanD0_2 > tanD0_1 and tanD0_2 ≧ 1.10 × tanD0_1, when the backing layer of the tire according to the present invention is in contact with the ground, the grip potential is not only not inhibited so much, but on the contrary, it is actually improved.

[0053] To improve the effect of the backing layer on the blistering mechanism, in an advantageous embodiment, G * _2 ≧ 0.92 × G * _1, preferably, G * _2 ≧ G * _1, more preferably, G * _2 > G * _1 applies. In particular, the greater the increase in the value of G * _2, the higher the hardness of the backing layer when the tread exceeds half of its wear potential, and thus, the higher the hardness of the tread.

[0054] In certain embodiments that enable maximizing the effect of the backing layer on the press-fitting and blistering mechanism, within the axial center portion of the tread, at least 75% of the length of the interface track positioned radially below the tread pattern block is parallel to the tread surface of the tire when new in the meridian cross-sectional plane and is radially disposed outside the track passing through the deepest groove or the radially innermost point of each deepest groove. In other words, the interface track is positioned on a radial plane positioned on the axial extension of the thickness of the legal wear indicator. In particular, the legal wear indicator is very preferably disposed at the bottom of the deepest groove or one of the deepest grooves.

[0055] When a plurality of grooves having the same depth are the deepest ones, the above features are verified for each deepest groove provided with a legal wear indicator.

[0056] To maximize the effect of the backing layer on the press-fitting and blistering mechanism, it will be understood that it is preferable that the largest possible amount of the backing layer is radially positioned within the axial extension of the thickness of the legal wear indicator. Thus, advantageously, at least 80%, preferably at least 90% of the length of the interface track positioned radially below the tread pattern block is parallel to the tread surface of the tire when new in the meridian cross-sectional plane and is radially disposed outside the track passing through the radially innermost point of the deepest groove or, when there are a plurality of grooves having the same depth and all of them are the deepest ones on the tread, the radially innermost point of each deepest groove.

[0057] In order to avoid the need to discard non-compliant tires due to the inner liner layer frequently and excessively penetrating through the tread layer and thus there being a possibility that an excessively large amount of the inner liner layer comes into contact with the ground, within the axial center portion of the tread, at least 75% of the length of the interface track positioned radially below the tread pattern block is arranged at an average radial distance greater than or equal to 0.4 mm from the legal wear track in the meridian cross-sectional plane, preferably also greater than or equal to 0.6 mm. Further, the volume of the elastomeric inner liner material used for a given tread thickness is reduced by increasing the radial distance between the interface track and the legal wear track.

[0058] To further widen the reduction of exposure cases and the minimization of the volume of the elastomeric inner liner material used, advantageously at least 80%, preferably at least 90% of the length of the interface track positioned radially below the tread pattern block is arranged at a radial distance greater than or equal to 0.4 mm from the legal wear track in the meridian cross-sectional plane, preferably also greater than or equal to 0.6 mm.

[0059] In a particularly advantageous embodiment where local exposure of the inner liner layer is allowed and only a small portion of the interface track is positioned radially outside the legal wear track and the tire is still avoided from being discarded as specified, within the axial center portion of the tread, at least a non-zero length of the interface track positioned radially below the tread pattern block is arranged radially outside the legal wear track in the meridian cross-sectional plane. According to the present invention, this length is equal to at most 25% of the length of the interface track positioned radially below the tread pattern block.

[0060] In an embodiment that enables optimization of the effect of the tread layer on the press-fitting mechanism, tanD0_1 ranges from 0.50 to 1.00, and more preferably from 0.50 to 0.85.

[0061] In embodiments that enable optimizing the effect of the backing layer on the press-fitting mechanism, tanD0_2 ranges from 0.60 to 1.10, and more preferably ranges from 0.60 to 1.00.

[0062] In embodiments that enable optimizing the effect of the tread layer on the blistering mechanism, G * _1 ranges from 1.30 MPa to 4.10 MPa, and preferably ranges from 1.30 MPa to 3.00 MPa.

[0063] In embodiments that enable optimizing the effect of the backing layer on the blistering mechanism, G * _2 is greater than or equal to 2.00 MPa, preferably ranges from 2.00 MPa to 4.10 MPa, and more preferably ranges from 2.15 MPa to 3.50 MPa.

[0064] Conventionally, a tire includes a crown, two sidewalls, and two beads, with each sidewall connecting each bead to the crown. Also in the conventional method, the crown includes a tread and a crown reinforcement arranged radially inside the tread. The tire further includes a carcass reinforcement fixed within each bead and extending radially inside the sidewalls and inside the crown.

[0065] Conventionally, the crown reinforcement includes at least one crown layer having reinforcement elements. These reinforcement elements are preferably textile or metallic filamentary elements.

[0066] In embodiments that enable achieving the performance aspects of a tire called a radial tire as defined by ETRTO, the carcass reinforcement includes at least one carcass layer, and the above or each carcass layer has carcass filamentary reinforcement elements, and each carcass filamentary reinforcement element extends in a main direction forming an angle ranging from 80° to 90° in absolute value with the circumferential direction of the tire.

[0067] Advantageously, the tire comprises a crown reinforcement arranged radially inside the tread, and in the axial center portion of the tread, the average distance between the layer comprising the radially outermost reinforcing element of the crown reinforcement and the radially innermost point of said or each deepest cut is less than or equal to 2.50 mm, preferably less than or equal to 2.25 mm. As described above, when the tire is mold-formed, an outward axial flow of the elastomeric tread material and the elastomeric backing material positioned radially below the cut and an outward radial flow of the elastomeric tread material and the elastomeric backing material positioned in a location radially close to the resulting cut are seen. These flows are even more significant when the thickness of the elastomeric material positioned radially outside the crown reinforcement and radially inside each cut, more preferably inside the deepest cut, is small. The present invention allows local exposure of the backing layer through the tread layer, so that the thickness of the elastomeric material positioned radially outside the crown reinforcement and radially inside each cut, more preferably inside the deepest cut, can be reduced. This reduction makes it possible not only to reduce the mass of the tire but also its rolling resistance.

[0068] When a plurality of cuts having the same depth are the deepest ones, the above-mentioned features are verified for each deepest cut. Preferably, since the deepest cuts are circumferential grooves, in the axial center portion of the tread, the average distance between the layer comprising the radially outermost reinforcing element of the crown reinforcement and the radially innermost point of each circumferential groove is less than or equal to 2.50 mm, preferably less than or equal to 2.25 mm.

[0069] Notwithstanding the above, in order to protect the crown reinforcement from external corrosion, the tire comprises a crown comprising a crown reinforcement arranged radially inside the tread, and in the axial center portion of the tread, the average distance between the layer comprising the radially outermost reinforcing element of the crown reinforcement and the radially innermost point of said or each deepest cut is greater than or equal to 1.0 mm.

[0070] When a plurality of cuts having the same depth are the deepest ones, the above-mentioned features are verified for each deepest cut. Preferably, since the deepest cuts are circumferential grooves, within the axial center portion of the tread, the average distance between the layer comprising the radially outermost reinforcing element of the crown reinforcement and the radially innermost point of each circumferential groove is greater than or equal to 1.0 mm.

[0071] In order to determine the average straight-line distance between the layer comprising the radially outermost reinforcing element of the crown reinforcement and the above-mentioned or each deepest cut or the radially innermost point of each circumferential groove, the average of the straight-line distances between the layer comprising the radially outermost reinforcing element of the crown reinforcement and the above-mentioned or each deepest cut or the radially innermost point of each circumferential groove will be taken, for example, in millimeters.

[0072] The straight-line distance between the layer comprising the radially outermost reinforcing element of the crown reinforcement and the above-mentioned or each deepest cut or the radially innermost point of each circumferential groove is measured in the meridian plane between the above-mentioned or each deepest cut or the radially innermost point and the projection point of this radially innermost point onto a locus passing through the radially outermost point of the reinforcing element of the radially outermost crown layer.

[0073] For example, in an embodiment that is easily industrially implemented using extrusion means, the axial portion of the tread positioned radially below the above-mentioned or each deepest cut comprises a tread layer with a non-zero radial thickness and a backing layer with a non-zero radial thickness. Preferably, in order to reduce the problem of non-uniform flow of the elastomer material under the cuts during the extrusion process, the ratio of the radial thickness of the tread layer to the radial thickness of the backing layer ranges from 0.40 to 0.60.

[0074] In embodiments where the backing layer is arranged only in places that improve the grip performance on a wet ground and thus make it possible to minimize the amount of elastomeric backing material used, the axial portion of the tread positioned radially below the above or each deepest cut is constituted by the tread layer. Preferably, the axial portion of the tread positioned radially below each circumferential groove is constituted by the tread layer. In other words, there is no elastomeric backing material positioned radially below the above or each deepest cut or radially below each circumferential groove within the tread.

[0075] In the above-described embodiments, the axial portion of the tread positioned radially below the above or each deepest cut or each circumferential groove is axially bounded by two straight lines perpendicular to the tread surface that, when the tire is new, delimit the cuts or each groove and pass through each axial end of the tread pattern block that is part of the tread surface.

[0076] To achieve a tire with the lowest possible rolling resistance, the elastomeric tread material exhibits a dynamic loss tanDMAX23_1 ranging from 0.13 to 0.70, preferably from 0.13 to 0.47, when measured according to standard ASTM D - 5992 - 96 at a temperature of 23 °C and a frequency of 10 Hz. The reason is that the dynamic loss tanDMAX23 measured at a temperature of 23 °C and a frequency of 10 Hz characterizes the hysteresis of the elastomeric material and thus its rolling resistance.

[0077] Similarly, to minimize the influence of the backing layer on the rolling resistance of the tire, the elastomeric backing material exhibits a dynamic loss tanDMAX23_2 ranging from 0.13 to 0.53, preferably from 0.13 to 0.46, when measured according to standard ASTM D - 5992 - 96 at a temperature of 23 °C and a frequency of 10 Hz.

[0078] As described above, the legal wear indicator is very preferably arranged at the bottom of the deepest cut. The wear indicator is very preferably arranged at the bottom of the circumferential groove.

[0079] In an embodiment that is particularly easy to implement, the wear indicator is formed by a protrusion that extends radially outward from the bottom of the cut over a radial height ranging from 1.45 mm to 1.75 mm and preferably substantially equal to 1.6 mm.

[0080] Advantageously, the tread pattern height of the tire when new ranges from 5.0 mm to 9.0 mm, preferably from 6.0 mm to 7.5 mm, in order to give the tire a relatively large wear potential and thus a long service life. The maximum value of the cut depth is the tread pattern height.

[0081] In order to enable water to be substantially discharged when driving on a wet ground, the surface area porosity ratio of the tire showing a tread pattern height equal to 2.0 mm after wear ranges from 20% to 35%, preferably from 22% to 30%. The use of the backing layer according to the present invention is more advantageous in the case of a tire showing such a surface area porosity ratio after wear, since it is possible to compensate for a more severe decrease in the drainage function that occurs with wear and when the surface area porosity ratio is small.

[0082] The surface area porosity ratio of the tire is the ratio between the difference between the total area AT of the contact surface of the tread of the tire inflated to the nominal pressure and under the nominal load and in contact with a smooth ground, for example a glass plate, and the area AC of the elements of the tread in contact with the ground on which the tire is running, and the total area AT of the contact surface of the tread of the tire inflated to the nominal pressure and under the nominal load and in contact with a smooth ground.

[0083] To determine the surface area porosity ratio, the nominal load is equal to 80% of the rated load indicated by the 2019 standard of the European Tyre and Rim Technical Organisation or "ETRTO", and the nominal pressure is 2.5 bar.

[0084] To minimize the amount of the elastomeric backing material used, the volume of the elastomeric tread material within the axial central portion of the tread is greater than or equal to 60% of the volume of the axial central portion of the tread, preferably greater than or equal to 65%, and the volume of the elastomeric backing material within the axial central portion of the tread is less than or equal to 40% of the volume of the axial central portion of the tread, preferably less than or equal to 35%.

[0085] In an embodiment that is particularly advantageous from the perspective of industrial complexity and the process for manufacturing the tread, at least 90% of the volume of the axial central portion of the tread is manufactured from the tread material and the backing material. In the case of the axial central portion of the tread, which can extend up to a maximum of 10% of the volume of the axial central portion of the tread, the remaining volume, the tread can comprise a thin axial thickness layer having an axial thickness of less than 0.4 mm for providing a connection between these two layers disposed between the radially outermost layer of the crown reinforcement and the backing layer. Further, to enable the tire to satisfy the conductivity standard, the tread can also comprise a strip having a small axial width and manufactured from a conductive material for forming a conductive path between the ground on which the tire is running and the crown reinforcement.

[0086] In an embodiment where the backing layer axially protrudes into the axial transverse portion disposed axially outside the axial central portion of the tread and has an effect on the above-mentioned press-fitting and blistering mechanisms outside the axial central portion, the axial width of the backing layer is greater than or equal to 90% of the axial width of the tread surface, preferably, the axial width of the backing layer is greater than or equal to 100% of the axial width of the tread surface.

[0087] In another embodiment where the backing layer is axially limited to the central portion in order to minimize the amount of the elastomeric backing material, the axial width of the backing layer is less than or equal to 90% of the width of the tread.

[0088] The present invention and its advantages will be readily understood with reference to FIGS. 1 through 8 related to these examples in light of the following detailed description and non-limiting exemplary embodiments.

Brief Description of the Drawings

[0089]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Modes for Carrying Out the Invention

[0090] In the figures related to the tire, reference coordinate systems X, Y, Z corresponding to the normal axial direction (Y), radial direction (Z), and circumferential direction (X) of the tire are illustrated respectively.

[0091] FIG. 1 illustrates a tire according to the present invention, indicated by the overall reference numeral 10. The tire 10 has a substantially annular shape around a turning axis that is substantially parallel to the axial direction Y. The tire 10 has a size of 225 / 45R17 with respect to a passenger car. In the various figures, the tire 10 is depicted as new, i.e., when it has not yet been driven.

[0092] The tire 10 includes a crown 12 provided with a tread 14 intended to be in contact with the ground when in use, and a crown reinforcement 16 extending in the circumferential direction X within the crown 12. Further, the tire 10 includes an airtight layer 18 for an inflation gas intended to define the boundary of a closed internal cavity together with its mounting support, for example, when mounted on a rim.

[0093] The crown reinforcement 16 includes an actuating reinforcement 20 and a hoop reinforcement 22. The actuating reinforcement 16 includes at least one actuating layer, in this case two actuating layers 24, 26. In this particular case, the actuating reinforcement 16 is composed of two actuating layers 24, 26. The radially inner actuating layer 24 is arranged radially inside the radially outer actuating layer 26.

[0094] The hoop reinforcement 22 includes at least one hooping layer, in this case one hooping layer 28. The hoop reinforcement 22 is, in this case, composed of the hooping layer 28.

[0095] The tread 14 is radially covered over the crown reinforcement 16. In this case, the hoop reinforcement 22, in this case the hooping layer 28, is arranged radially outside the actuating reinforcement 20 and is thus sandwiched radially between the actuating reinforcement 20 and the tread 14. Preferably, the hoop reinforcement 22 has an axial width that is at least as large as the axial width of the actuating reinforcement 20, and in this particular case in the embodiment illustrated in FIG. 1, it is conceptually possible for the hoop reinforcement 22 to have an axial width that is larger than the axial width of the actuating reinforcement 20.

[0096] The tire 10 includes two sidewalls 30 extending radially inward from the crown 12. Further, the tire 10 has two beads 32 radially inside the sidewalls 30. Each sidewall 30 connects each bead 32 to the crown 12.

[0097] The tire 10 includes a carcass reinforcement 34 fixed within each bead 32 and wound around a bead wire 33 in this particular case. The carcass reinforcement 34 extends radially inside the crown 12 within each sidewall 30. The crown reinforcement 16 is disposed radially between the tread 14 and the carcass reinforcement 34. The carcass reinforcement 34 includes at least one carcass layer, and in this case, includes a single carcass layer 36. In this particular case, the carcass reinforcement 34 is composed of a single carcass layer 36.

[0098] Each of the working layers 24, 26, the hooping layer 28, and the carcass layer 36 includes an elastomeric matrix in which one or more filamentous reinforcing elements of the corresponding layer are embedded. These layers will then be described below with reference to FIG. 2.

[0099] The hoop reinforcement 22, in this case the hooping layer 28, is axially bounded by two axial edges 28A, 28B of the hoop reinforcement 22. The hoop reinforcement 22 includes one or more hooping filamentous reinforcing elements 280, and the hooping filamentous reinforcing elements 280 are wound helically circumferentially so as to extend in the main direction D0 of each hooping filamentous reinforcing element 280 from the axial edge 28A of the hooping layer 28 to the other axial edge 28B in the axial direction. The main direction D0 forms an angle AF with the circumferential direction X of the tire 10 that is less than or equal to 10° in absolute value, preferably less than or equal to 7°, more preferably less than or equal to 5°. In this case, AF = -5°. The hooping layer 28 has a density of 98 filamentous reinforcing elements per decimeter of the hooping layer, and this density is measured perpendicular to the direction D0.

[0100] The radially inner working layer 24 is axially bounded by two axial edges 28A, 28B. The radially inner working layer 24 comprises working filamentary reinforcing elements 240 extending in a substantially parallel manner to each other along the main direction D1 from one axial edge 24A to the other axial edge 24B axially. Similarly, the radially outer working layer 26 is axially bounded by two axial edges 26A, 26B. The radially outer working layer 26 comprises working filamentary reinforcing elements 260 extending in a substantially parallel manner to each other along the main direction D2 from one axial edge 26A to the other axial edge 26B axially. The main direction D1 in which each working filamentary reinforcing element 240 of the radially inner working layer 24 extends, and the main direction D2 in which each working filamentary reinforcing element 260 of the other radially outer working layer 26 extends, form angles AT1 and AT2 respectively in directions opposite to the circumferential direction X of the tire 10. Each main direction D1, D2 forms angles AT1, AT2 respectively that are strictly greater in absolute value than 10° with respect to the circumferential direction X of the tire 10, preferably ranging from 15° to 50°, and more preferably ranging from 15° to 30°. In this case, AT1 = -26° and AT2 = +26°.

[0101] The carcass layer 36 is axially bounded by two axial edges 36A, 36B. The carcass layer 36 comprises carcass filamentary reinforcing elements 360 extending in a main direction D3 that forms an angle AC, in this case AC = +90°, that is greater than or equal to 60° in absolute value with respect to the circumferential direction X of the tire 10, preferably ranging from 80° to 90°.

[0102] Conventionally, each hoop filamentary reinforcing element 280 comprises two multifilament plies each composed of spun yarns of aliphatic polyamide, in this case nylon monofilaments having a yarn count equal to 140 tex, the two multifilament plies being individually helically twisted 250 times per meter in one direction and helically twisted 250 times per meter in the opposite direction to each other. The two multifilament plies are helically wound around each other. As a variant, it is considered possible to use a hoop filamentary reinforcing element 280 comprising one multifilament ply composed of spun yarns of aliphatic polyamide, in this case nylon monofilaments having a yarn count equal to 140 tex, and one multifilament ply composed of spun yarns of aromatic polyamide, in this case aramid monofilaments having a yarn count equal to 167 tex, the two multifilament plies being individually helically twisted 290 times per meter in one direction and helically twisted 290 times per meter in the opposite direction to each other. The two multifilament plies are helically wound around each other.

[0103] Each actuating filamentary reinforcing element 180 is an assembly of two steel monofilaments each having a diameter equal to 0.30 mm and helically wound with a pitch of 1.2 mm or 1.05 mm. In another embodiment, each actuating filamentary reinforcing element 180 is composed of a steel monofilament having a diameter equal to 0.30 mm. More generally, the steel monofilaments have diameters ranging from 0.25 mm to 0.32 mm.

[0104] Conventionally, each carcass filament-like reinforcing element 340 comprises two multifilament plies each composed of a spun yarn of polyester, in this case a monofilament of PET, and these two multifilament plies are individually twisted 240 times per meter in a helical manner in one direction and 240 times per meter in a helical manner in the opposite direction to each other. Each of these multifilament plies has a yarn count equal to 220 tex. In other variations, it is considered possible to use a yarn count equal to 144 tex or 334 tex.

[0105] Referring to FIG. 1, the tread 14 comprises a tread surface 38 that places it in contact with the ground. Further, the tread 14 comprises cuts 40 and tread pattern blocks 42, and the cuts 40 separate the tread pattern blocks 42 from each other. In the meridian cross-sectional plane shown in FIG. 1, the cuts 40 comprise a plurality of circumferential grooves 44, at least one of which forms the deepest cut of the tire 10. The depth of this deepest cut 44, when the tire is new, defines the tread pattern height HS of the tire as shown in FIG. 6, and this height HS ranges from 5.0 mm to 9.0 mm, preferably from 6.0 mm to 7.5 mm, and in this case HS = 7.0 mm.

[0106] The tread surface 38 is intended to be in contact with the ground when the tire 10 is traveling along the ground, passes through each point N disposed on each side of the meridian plane M, and is axially bounded by axial limits 39 where the angle between the tangent T to the tread surface 38 and the line R passing through the point parallel to the axial direction Y is equal to 30°.

[0107] In this case, the tread 14 comprises the meridian plane of the tire 10 and, in this case, an axially central portion P1 centered axially on the meridian plane M of the tire 10. The axially central portion P1 has an axial width L1 equal to at least 70% of the axial width of the tread surface 38, and in this case L1 = L.

[0108] The tread 14 further comprises a plurality of legal wear indicators 46 that define a legal wear threshold below which the tire does not comply with the regulations regarding wear. The wear indicators 46 shown in FIGS. 1 and 3 to 6 are disposed at the bottom 48 of the deepest cut, in this case the bottom 48 of one of the circumferential grooves 44. In this particular case, the legal wear indicator 46 extends radially outward from the bottom 48 of the circumferential groove 44 over a radial height HT that ranges from 1.45 mm to 1.75 mm and is substantially equal to 1.6 mm in this case. The legal wear indicator 46 has a radially outermost point formed by the radially outer surface 51 of the legal wear indicator 46 in this case.

[0109] After wear has occurred up to a tread pattern height equal to 2.0 mm, the surface area porosity ratio of the tire ranges from 20% to 35%, preferably from 22% to 30%, and is equal to 25% in this case.

[0110] Referring to FIGS. 1 and 3, the tread 14 comprises a tread layer 52 that carries the tread surface 38 and a backing layer 54 disposed radially inside the tread layer 52 against the tread layer 52. Such a backing layer 54 is generally referred to as a base layer. The axial width J of the backing layer 54 is greater than or equal to 90% of the axial width L of the tread surface 38, and in this case the axial width J of the backing layer 54 is greater than or equal to 100% of the axial width L of the tread surface 38, and in this case is equal to 105% of the axial width L of the tread surface 38.

[0111] The tread layer 52 and the backing layer 54 are adjacent through an interface 56 that shows an interface track 58 in the meridian cross-sectional plane shown in FIG. 3 that includes the legal wear indicator 46.

[0112] Continuing in the meridian cross-sectional plane shown in FIG. 3, a legal wear track 60 is defined that is parallel to the tread surface 38 of the tire 10 and passes through the radially outer surface 51 of the legal wear indicator 46. In FIG. 3, the legal wear track 60 is shown as a dashed line.

[0113] Referring to FIG. 3, within the axial center portion P1 of the tread 14, the interface track 58 has a length l positioned radially below the tread pattern block 42, and the length l is the sum of the lengths l1, l2, l3 positioned radially below the tread pattern block 42. The remainder of the length of the interface track 58 is equal to the sum of the lengths U1 and U2 positioned radially below the cut 40, in this case radially below the circumferential groove 44. In this particular case, within half of the axial center portion P1 of the tread 14, the interface track has a length equal to the sum of the lengths l1, l2, l3, U1, U2 and is 8.13 cm long. In this case, l1 = 2.90 cm, l2 = 2.28 cm, l3 = l2 / 2 = 1.14 cm, U1 = 0.65 cm, and U2 = 1.16 cm.

[0114] Within half of the axial center portion P1 of the tread 14, at least 75%, preferably at least 80%, more preferably 90%, in this case at least 75%, preferably at least 80%, more preferably 90% of the length l of the interface track 58 positioned radially below the tread pattern block 42 is arranged radially inside the legal wear track 60 in the meridian cross-sectional plane shown in FIG. 3. In this particular case, 100% of the length l of the interface track 58 positioned radially below the tread pattern block 42 is arranged radially inside the legal wear track 60 in the meridian cross-sectional plane shown in FIG. 3, such that all of the lengths l1, l2, l3 positioned radially below the tread pattern block 42 are arranged radially inside the legal wear track 60.

[0115] Furthermore, within half of the axial center portion P1 of the tread 14, at least 75%, preferably at least 80%, more preferably 90%, in this case at least 75%, preferably at least 80%, more preferably 90% of the length of the interface track 58 positioned radially below the tread pattern block 42 is less than or equal to 2.0 mm, preferably less than or equal to 1.2 mm, more preferably less than or equal to 1.0 mm from the legal wear track 60 in the meridian cross-sectional plane shown in FIG. 4, and is arranged at an average radial distance d1. In this specific case, the lengths K1 < l1, K2 < l2, K3 < l3 correspond to the length of the interface track 58 positioned at an average radial distance d1 less than or equal to 1.0 mm from the legal wear track 60. In this case, so that 97% of the length l is arranged at an average radial distance d1 less than or equal to 1.0 mm from the legal wear track 60 in the meridian cross-sectional plane shown in FIG. 4, K1 = 2.85 cm, K2 = 2.18 cm, and K3 = 1.09 cm.

[0116] In addition to this, within half of the axial center portion P1 of the tread 14, at least 75%, preferably at least 80%, more preferably 90%, in this case at least 75%, preferably at least 80%, more preferably 90% of the length of the interface track 58 positioned radially below the tread pattern block 42 is greater than or equal to 0.4 mm, preferably greater than or equal to 0.6 mm from the legal wear track 60 in the meridian cross-sectional plane shown in FIG. 4, and is arranged at an average radial distance d1. In this specific case, so that 100% of the length l is arranged at an average radial distance d1 greater than or equal to 0.6 mm from the legal wear track 60 in the meridian cross-sectional plane shown in FIG. 4, all of the lengths l1, l2, l3 positioned radially below the tread pattern block 42 are arranged at an average radial distance d1 greater than or equal to 0.6 mm from the legal wear track 60.

[0117] In this way, the radial distance between the legal wear track 60 and the entire length l of the interface track 58 positioned radially below the tread pattern block 42 varies between 0.8 mm and 2.65 mm. When the lengths K1, K2, and K3 are limited to be positioned radially below the tread pattern block 42, 97% of the length l of the interface track 58 positioned radially below the tread pattern block 42 is arranged at a radial distance between 0.6 mm and 1.0 mm of the legal wear track 60 corresponding to an average radial distance d1 equal to 0.85 mm in the meridian cross-sectional plane shown in FIG. 4.

[0118] In addition to this, within half of the axial center portion P1 of the tread 14, at least 75%, preferably at least 80%, more preferably 90%, in this case at least 75%, preferably at least 80%, more preferably 90% of the length of the interface track 58 positioned radially below the tread pattern block 42 is parallel to the tread surface 38 of the new tire 10, passes through the radially innermost point of the deepest groove in the meridian cross-sectional plane shown in FIG. 5, and in this case is arranged radially outside the track 62 passing through the bottom 48 of each circumferential groove 44. In this particular case, lengths F1, F2, and F3 such that K1 < F1 < l1, K2 < F2 < l2, and K3 < F3 < l3 correspond to the length of the interface track 58 arranged radially outside the track 62. In this case, 97% of the length l of the interface track 58 positioned radially below the tread pattern block 42 is arranged at F1 = 2.86 cm, F2 = 2.20 cm, and F3 = 1.10 cm so as to be arranged within half of the axial center portion P1 of the tread 14 radially outside the track 62 in the meridian cross-sectional plane shown in FIG. 5.

[0119] Referring to FIG. 6, within half of the axial center portion P1 of the tread 14, it is located radially below the deepest cut, and in this case, the axial portion of the tread 14 positioned radially below each circumferential groove 44 has a non-zero radial thickness E1 of the tread layer 52 and a non-zero radial thickness E2 of the backing layer 54. The ratio E1 / E2 varies between 0.40 and 0.60 and is substantially equal to 0.50 in this case.

[0120] Continuing to refer to FIG. 6, within half of the axial center portion P1 of the tread 14, the average distance d2 between the layer comprising the radially outermost reinforcing element of the crown reinforcement 16, in this case the hooping layer 28, and the radially innermost point of the deepest cut, in this instance the bottom 48 of each circumferential groove 44, is less than or equal to 2.50 mm, preferably less than or equal to 2.25 mm and greater than or equal to 1.0 mm. In this particular instance, d2 = 2.10 mm.

[0121] It should be noted that since the tire is symmetric with respect to the meridian plane M, the calculations shown in FIGS. 1, 3 to 6 representing half of the meridian cross-section of the tire 10 and half of the axial center portion P1 are equally valid for the entire meridian cross-section of the tire 10 and the entire axial center portion P1.

[0122] The tread layer 52 comprises an elastomeric tread material M1 and the backing layer 54 comprises an elastomeric backing material M2 different from the elastomeric tread material. In this particular instance, the elastomeric tread material is based on the composition CD1 described in WO2018115722, while the elastomeric backing material is based on the composition CC1 described in WO2018115722. Of course, other compositions can be used by varying the various constituents of the composition in order to achieve properties suitable for a particular use without departing from the scope of the present invention.

[0123] The volume of the elastomer tread material M1 in the central portion P1 is greater than or equal to 60% of the volume of the central portion P1, preferably greater than or equal to 65% of the volume of the central portion P1, and in this case is equal to 70%. The volume of the elastomer backing material M2 in the central portion P1 is less than or equal to 40% of the volume of the central portion P1, preferably less than or equal to 35% of the volume of the central portion P1, and in this case is equal to 30%.

[0124] The elastomer tread material M1 has a complex dynamic shear modulus G ranging from 1.30 MPa to 4.10 MPa, and preferably from 1.30 MPa to 3.00 MPa, when measured at a temperature of 23 °C and a frequency of 10 Hz according to Standard ASTM D - 5992 - 96 at a 10% strain. * _1, and in this case G * _1 = 2.13 MPa is shown.

[0125] The elastomer backing material M2 has a complex dynamic shear modulus G greater than or equal to 2 MPa, preferably from 2.00 MPa to 4.10 MPa and more preferably from 2.15 MPa to 3.50 MPa when measured at a temperature of 23 °C and a frequency of 10 Hz according to Standard ASTM D - 5992 - 96 at a 10% strain. * _2, and in this case G * _2 = 2.14 MPa is shown.

[0126] G * _2 ≧ 0.90 × G * _1, and further G * _2 ≧ 0.92 × G * _1, and further G * _2 ≧ G * _1, and in this case G * _2 > G * _1 must be noted.

[0127] The elastomer tread material M1 exhibits a dynamic loss tanD0_1 ranging from 0.50 to 1.00, and more preferably from 0.50 to 0.85, when measured according to standard ASTM D-5992-96 at a temperature of 0 °C and a frequency of 10 Hz. In this case, tanD0_1 = 0.67.

[0128] The elastomer backing material M2 exhibits a dynamic loss tanD0_2 ranging from 0.60 to 1.10, and more preferably from 0.60 to 1.00, when measured according to standard ASTM D-5992-96 at a temperature of 0 °C and a frequency of 10 Hz. In this case, tanD0_2 = 0.65.

[0129] It should be noted that tanD0_2 ≧ 0.37 × tanD0_1, further tanD0_2 ≧ 0.5 tanD0_1, and preferably tanD0_2 ≧ 0.75 × tanD0_1. In another highly advantageous embodiment where the elastomer backing material M2 is modified to increase tanD0_2, it can be noted that preferably tanD0_2 ≧ tanD0_1, very advantageously tanD0_2 > tanD0_1, and furthermore tanD0_2 ≧ 1.10 × tanD0_1. As is known to those skilled in the art, it is considered possible to increase the glass transition temperature of the elastomer backing material and / or its silica content in order to increase the value of tanD0_2.

[0130] Among other properties of the elastomer materials M1 and M2, in particular, the elastomer tread material M1 exhibits a dynamic loss tanDMAX23_1 ranging from 0.13 to 0.70, preferably from 0.13 to 0.47, and in this case equal to 0.25, when measured according to the standard ASTM D-5992-96 at a temperature of 23°C and a frequency of 10 Hz. It should be noted that the elastomer backing material M2 exhibits a dynamic loss tanDMAX23_2 ranging from 0.13 to 0.53, preferably from 0.13 to 0.46, and in this case equal to 0.31, when measured according to the standard ASTM D-5992-96 at a temperature of 23°C and a frequency of 10 Hz.

[0131] The tire according to the second embodiment is shown in FIG. 7. Elements similar to those shown in the conventional figures are denoted by the same reference numerals.

[0132] In contrast to the tire according to the first embodiment, the tire according to the second embodiment described in FIG. 7 exemplifies a case of exposure of the backing layer 54 near the circumferential groove 44, i.e., a cut 40 vertically downward of each tread pattern block 42, within the axial center portion P1 of the tread 14. Thus, at least a non-zero length l' of the interface track 58 positioned radially below the tread pattern block 42 within the axial center portion P1 of the tread 14 is arranged radially outside the legal wear track 60 within the meridian cross-sectional plane described in FIG. 7. In this case, l = l1 + l2 + l3 + l4 + l5 + l6 + l7 + l', l = l1' + l2' + l3' + l4', where l1 = 2.44 cm, l2 = 1.64 cm, l3 = l2 / 2 = 0.82 cm, l4 = l5 = l6 = l7 = 0.25 cm, l1 = l2 = l3 = l4 = 0.35 cm. Up to 25% of the total length l of the interface track 58 positioned radially below the tread pattern block 42 is arranged radially outside the legal wear track 60 within the meridian cross-sectional plane described in FIG. 7, and in this case l' / l = 1.40 / 5.9 = 23%.

[0133] The tire according to the third embodiment is shown in FIG. 8. Elements similar to those shown in the conventional figures are denoted by the same reference numerals.

[0134] In contrast to the conventional embodiment, the axial center portion P1 of the tread 14 has an axial length L1 that is strictly smaller than the axial width L of the tread surface 38, such that the tread 14 includes an axial lateral portion P2 disposed axially outside the axial center portion P1. Each axial lateral portion P2 has an axial width L2 that is equal to at most 15% of the axial width L of the tread, and in this case L2 / (L1 + L2)=4%. In the embodiment described in FIG. 8, the tread layer 52 of each axial lateral portion P2 comprises an elastomeric material different from the elastomeric material of the axial center portion P1. For example, as described in WO2014 / 090845, an elastomeric material that exhibits a relatively low rolling resistance, for example, will be selected.

[0135] Comparative test

[0136] In a test regarding grip on a wet ground in a state where the wear potential of the tire exceeded half, the tire 10 according to the first embodiment was compared with a prior art MICHELIN Primacy 4 tire having the same dimensions. For comparison purposes, the elastomeric tread material of the prior art MICHELIN Primacy 4 tire is the same as the elastomeric material M1 of the tire 10 according to the first embodiment. The elastomeric underlay material of the prior art MICHELIN Primacy 4 tire exhibits a complex dynamic shear modulus G * _2T equal to 1.90 MPa when measured at a strain of 10% in accordance with standard ASTM D - 5992 - 96 at a temperature of 23°C, and exhibits a dynamic loss tanD0_2T equal to 0.23 when measured in accordance with standard ASTM D - 5992 - 96 at a temperature of 0°C and a frequency of 10 Hz.

[0137] First, to simulate a usage level greater than half, in this case 93% of the wear potential, each tire was shaved flat until it reached a tread pattern height equal to 2 mm. The tread pattern height is defined as the radial height between the radially innermost point of each deepest groove and the projection point of this groove onto the ground when the tire is in motion. This tread pattern height corresponds to a tread pattern height equal to 1.6 mm and is such that it does not reach the legal wear track representing the progress of tire wear, more than half of the wear potential in this particular case (93% of the wear potential was used). The shaving was carried out using a method known to those skilled in the art by bringing the tire, which was running under driving conditions corresponding to normal driving conditions on a rolling machine equipped with a shaving blade, into contact with this shaving blade.

[0138] At the end of this shaving step, four shaved MICHELIN Primacy 4 tires and four shaved tires 10 according to the present invention were tested under the same conditions and on one and the same vehicle, thereby determining the average deceleration between 80 km / h and 20 km / h of the vehicle to which these tires were attached. This test was carried out using a method that enables the determination of the braking force coefficient BFCT for the prior art MICHELIN Primacy 4 tire and the braking force coefficient BFCA for the tire 10 according to the present invention, using the recommendations of ISO23671 - 2006 standard. The greater the braking force coefficient, the better the performance of the tested tire. The test results were such that BFCA / BFCT = 106, thereby demonstrating the improved braking performance on wet ground of the tire according to the present invention over the prior art tire.

[0139] The present invention is not limited to the above-described embodiments.

Explanation of Reference Signs

[0140] 10 Tire 12 Crown 14 Tread 40 Groove 54 Lining Layer 56 Interface

Claims

1. A passenger car tire (10) comprising a tread (14) having cuts (40) and tread pattern blocks (42), the cuts (40) separating the tread pattern blocks (42) from each other, the tread (14) being adapted to be in contact with the ground when the tire (10) is running on a tread surface (38), the tread (14) comprising at least one legal wear indicator (46) defining a legal wear threshold, within an axial center portion (P1) of the tread (14) having an axial width (L1) equal to at least 70% of the width (L) of the tread surface (38), the tread (14) being, a tread layer (52) carrying the tread surface (38), an elastomeric tread material exhibiting a complex dynamic shear modulus G * _1, and a dynamic loss tanD0_1 measured according to standard ASTM D - 5992 - 96 at a temperature of 0 °C and a frequency of 10 Hz, said tread layer (52) comprising; a backing layer (54) for the tread layer (52) disposed radially inside the tread layer (52), an elastomeric backing material exhibiting a complex dynamic shear modulus G * _2, and a dynamic loss tanD0_2 measured according to standard ASTM D - 5992 - 96 at a temperature of 0 °C and a frequency of 10 Hz, said backing layer (54) comprising; A passenger car tire (10) comprising, the elastomeric tread material being different from the elastomeric backing material such that the tread layer (52) and the backing layer (54) are adjacent through an interface (56) representing an interface track (58) in a meridian cross - sectional plane comprising the legal wear indicator (46), tanD0_2 ≥ 0.37 × tanD0_1 and G * _2 ≥ 0.90 × G * _1, and within the axial center portion (P1) of the tread (14), in the meridian plane, parallel to the tread surface (38) of the tire (10) when new, and passing through the radially outermost point (51) of the legal wear indicator (46), by defining a legal wear track (60), at least 75% of the length (l) of the interface track (58) positioned radially below the tread pattern block (42) is arranged radially inside the legal wear track (60) in this meridian plane, and within the axial center portion (P1) of the tread (14), at least 75% of the length (l) of the interface track (58) positioned radially below the tread pattern block (42) is arranged at an average radial distance (d1) less than or equal to 2.0 mm from the legal wear track (60) in this meridian plane, A tire (10), characterized in that.

2. The tire (10) according to claim 1, characterized in that tanD0_2 ≥ 0.5 × tanD0_1.

3. The tire (10) according to claim 1, characterized in that tanD0_2 ≥ tanD0_1.

4. G * _2 ≥ G * _1, and the tire (10) according to claim 1 or 2, characterized in that.

5. Within the axial center portion (P1) of the tread (14), at least 75% of the length (l) of the interface track (58) positioned radially below the tread pattern block (42) is arranged radially outside of a track (62) that is parallel to the tread surface (38) of the tire (10) when new and passes through the radially innermost point (48) of the said or each deepest groove (44) within the meridian cross-section plane. Tire (10) according to any one of claims 1 to 4.

6. Within the axial center portion (P1) of the tread (14), at least 75% of the length (l) of the interface track (58) positioned radially below the tread pattern block (42) is arranged at an average radial distance (d1) greater than or equal to 0.4 mm from the legal wear track (60) within the meridian cross-section plane. Tire (10) according to any one of claims 1 to 5.

7. tan D0_1 ranges from 0.50 to 1.

00. Tire (10) according to any one of claims 1 to 6.

8. tan D0_2 ranges from 0.60 to 1.

10. Tire (10) according to any one of claims 1 to 7.

9. G * _1 ranges from 1.30 MPa to 4.10 MPa. Tire (10) according to any one of claims 1 to 8.

10. G * _2 is greater than or equal to 2.00 MPa. Tire (10) according to any one of claims 1 to 9.

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