阅读说明：本技术 具有包括优化结构的工作层和胎面设计的轮胎 (Tire with working layer and tread design comprising optimized structure ) 是由 V·图尔纳 D·法宾 P·弗雷斯 M·阿尔布伊 F·尚布里亚 于 2020-03-19 设计创作，主要内容包括：本发明涉及一种轮胎,所述轮胎在其胎冠的中央部分包括径向最外胎冠层的具有径向幅度A的至少一个波状部(51)、周向沟槽(24)和连接凹槽(25),这些凹槽中的一些在径向上位于波状部(51)的外侧。这些凹槽(25)中的至少50％是被称为适应于波状部的凹槽。在波状部的径向外侧适应于波状部的连接凹槽使得凹槽的底部曲线Cf和沟槽(24)的交点Ps与底部曲线Cf的径向最外点Pext分隔开的径向距离d2至少等于波状部(51)的径向幅度的三分之一(A/3),并且使得曲线Cf从交点Ps朝向点Pext沿径向增加。(The invention relates to a tyre comprising, in a central portion of its crown, at least one undulation (51) of radially outermost crown layer having a radial amplitude A, a circumferential groove (24) and connecting grooves (25), some of these grooves being radially on the outside of the undulation (51). At least 50% of these grooves (25) are what are called undulation-adapted grooves. The connecting groove adapted to the wave portion radially outside the wave portion is such that a radial distance d2 separating an intersection point Ps of a bottom curve Cf of the groove and the groove (24) from a radially outermost point Pext of the bottom curve Cf is at least equal to one third (A/3) of a radial extent of the wave portion (51) and such that the curve Cf increases radially from the intersection point Ps towards the point Pext.)

1. A tyre (1) comprising:

-a tread (2), said tread (2) being intended to be in contact with the ground through a tread surface (21), having an axial width L and comprising a central portion (22) of tread having a width equal to 0.8 x L, the central portion (22) of tread (2) comprising at least two circumferential grooves (24),

-a circumferential groove (24) forming a space open to the tread surface (21) around the entire circumference of the tyre and delimited by two main lateral faces (241, 242) connected by a bottom face (243), said circumferential groove (24) having an average width Ws at least equal to 6mm and a depth D at least equal to 4mm,

-the central portion (22) of the tread comprises a groove forming a space open to the tread surface (21), forming an angle at least equal to 15 ° with the circumferential axis and delimited by two main lateral faces (251, 252) connected via a bottom face (253); the groove (25) has a width Wr defined by the average distance between the two sides (251, 252) and has a width Wr at least equal to 0.5 mm; at least fifty percent of these grooves are open grooves, i.e. grooves leading to one or two circumferential grooves,

-each open groove (25) comprises a bottom curve Cf formed by all the radially innermost points of the bottom surface of the groove, each bottom curve comprising at least one and at most two points Ps common to the groove or to both grooves to which the groove opens, and a radially outermost point Pext,

-a carcass layer (9) and a crown reinforcement (3), the crown reinforcement (3) being radially internal to the tread (2) and comprising at least one crown layer (5, 41, 42) being a layer of reinforcing elements,

-the crown reinforcement comprises a working reinforcement (4), the working reinforcement (4) comprising at least one working layer (41, 42),

-each working layer (41, 42) comprises reinforcing elements (411) at least partially made of metal coated with elastomeric material, said reinforcing elements (411) being parallel to each other and forming an orientation angle with the circumferential direction (XX') of the tyre at least equal to 15 ° and at most equal to 50 ° in absolute value,

-each crown layer (5, 41, 42) extending radially from a radially inner Surface (SRI) to a radially outer Surface (SRE),

-the radially outermost crown layer (5) located vertically below the central portion (22) of the tread (2) comprises at least one wave, called central wave (51), having a radial amplitude A,

-the portion of the radially external Surface (SRE) of the crown layer (5) of the central undulations (51) is radially outside the point of the radially outermost crown layer (5) vertically below the bottom face (243) of the circumferential groove (24) closest to the undulations (51),

-the radial distance (do) between the radially outer Surface (SRE) of the radially outermost crown layer (5) and the tread surface (21) at said undulations (51) is at least 1mm smaller over at least 10% of the radially outer Surface (SRE) of said crown layer (5) located vertically below the central portion of the tread than the radial distance (dc) between the radially outer Surface (SRE) of the radially outermost crown layer (5) and the tread surface (21) at a position vertically below the floor (243) of the circumferential groove (24), wherein said circumferential groove (24) is the one closest to the point considered on said surface,

-the radial distance (d1) between the radially outer Surface (SRE) of the radially outermost crown layer (5) and the floor (243) of the circumferential groove (24) is at most equal to 4mm,

characterized in that at least 50% of the open grooves (25) situated radially outside the central wavy portion (51) of the radially outermost layer of the reinforcing element (5) are referred to as adaptation-to-central wavy portion, the adaptation-to-wavy-portion open grooves being situated radially outside the wavy portion such that the radial distance (d2) of the intersection point Ps of a bottom curve Cf of the open grooves adapted to wavy portions (25) with a circumferential groove (24) to which the open grooves adapted to wavy portions (25) lead, from the radially outermost point Pext of the bottom curve Cf, is at least equal to one third (a/3) of the radial amplitude of the central wavy portion (51) situated vertically below the open groove adapted to wavy portions (25), and the curve Cf increases radially from the intersection point Ps to the point Pext.

2. A tyre according to the preceding claim, wherein the open grooves (25) of the central undulations (51) are adapted radially outside the central undulations (51) of the radially outermost crown layer (5) such that the radial distance (d2) between the intersection point Ps of the bottom curve Cf of the groove with the circumferential groove (24) to which the groove (25) opens and the radially outermost point Pext of the bottom curve Cf is at least equal to half (0.5 a) and at most equal to 1.5 times (1.5 a) the radial amplitude of the central undulations (51) located vertically below the groove (25).

3. A tyre according to any one of the preceding claims, wherein all the crown layers (41, 42, 5) have undulations and their undulations (51) are substantially identical in terms of position and radial amplitude a in a portion vertically below the central portion of the tread.

4. Tyre according to any one of the preceding claims, wherein at least 90% of the open grooves (25), preferably all of the open grooves (25), radially outside the central undulations (51) of the radially outermost crown layer (5), are respectively adapted to said central undulations (51) radially outside the central undulations (51) of the radially outermost crown layer (5).

5. Tyre according to any one of the preceding claims, wherein, for the portion of the crown reinforcement (3) vertically below the central portion of the tread, the radial distance (do) between the radially outer Surface (SRE) of the radially outermost crown layer (5) and the tread surface (21) is at least 1.5mm, preferably 2mm, less than the radial distance (dc) between the radially outer Surface (SRE) of the radially outermost crown layer (5) and the tread surface (21) measured vertically below the radially innermost point of the bottom face (243) of the circumferential groove (24) which is the closest circumferential groove to said central undulations (51) at the point considered, over at least 20%, preferably at least 30% and at most 85% of the radially outer Surface (SRE) of the radially outermost crown layer (5).

6. Tyre according to any one of the preceding claims, wherein the radial distance (d1) between the radially outer Surface (SRE) of the radially outermost crown layer (5) and the floor (243) of the circumferential groove (24) is at least equal to 0.5mm and at most equal to 3mm, preferably at least equal to 0.7mm and at most equal to 2 mm.

7. Tyre according to any one of the preceding claims, comprising at least one wear indicator (11), wherein the minimum radial distance (d0) between the radially outer Surface (SRE) of the radially outermost crown layer (5) of the crown reinforcement (3) and the tread surface (21) is at least equal to the radial distance (df) between the tread surface (21) and the radially outermost point of the wear indicator (11).

8. Tyre according to any one of the preceding claims, wherein the minimum radial distance (do) between the radially outer Surface (SRE) of the radially outermost crown layer (5) of the crown reinforcement (3) and the tread surface (21) is at most equal to the depth D of the closest circumferential groove (24) plus 2mm and at least equal to the depth D of the closest circumferential groove (24) minus 2mm, preferably substantially equal to the depth D of the closest circumferential groove (24).

9. Tyre according to any one of the preceding claims, wherein at least one filling material (6) having a radial thickness at least equal to 0.3mm is provided vertically below each central undulation (51) of the radially outermost crown layer (5), and preferably radially on the outside of the carcass layer (9), preferably radially on the inside of the radially innermost working layer (42).

10. Tyre according to the preceding claim, the tread (2) being made of at least one rubber compound, wherein the filling rubber (6) is a rubber compound having a dynamic loss tan δ 1 measured at a temperature of 10 ℃, a stress of 0.7MPa and 10Hz, said dynamic loss tan δ 1 being at most equal to the dynamic loss tan δ 2 of the rubber material from which the tread (2) is made and preferably 30% less than said dynamic loss tan δ 2, said dynamic loss tan δ 2 being measured at a temperature of 10 ℃, a stress of 0.7MPa and 10 Hz.

Technical Field

The present invention relates to a tyre intended to be mounted on a vehicle, and more particularly to the crown of such a tyre.

Background

Since the geometry of the tire exhibits rotational symmetry about the axis of rotation, the geometry of the tire is generally described in a meridian plane including the axis of rotation of the tire. For a given meridian plane, the radial direction, the axial direction and the circumferential direction respectively denote a direction perpendicular to the rotation axis of the tyre, a direction parallel to the rotation axis of the tyre and a direction perpendicular to the meridian plane. The intermediate circumferential plane, known as the equatorial plane, divides the tyre into two substantially symmetrical semi-toroidal shapes, it being possible for the tyre to present tread or structural asymmetries related to manufacturing precision or dimensions.

In the following, the expressions "radially on the inside" and "radially on the outside" mean "closer to the axis of rotation of the tyre in the radial direction" and "further away from the axis of rotation of the tyre in the radial direction", respectively. The expressions "axially on the inside" and "axially on the outside" mean "closer to the equatorial plane in the axial direction" and "further from the equatorial plane in the axial direction", respectively. "radial distance" is the distance relative to the axis of rotation of the tire and "axial distance" is the distance relative to the equatorial plane of the tire. The "radial thickness" is measured in the radial direction and the "axial width" is measured in the axial direction.

In the following, the expression "vertically below" means "radially inside, for each meridian, within the boundaries of the axial coordinate defined by. Thus, "a point of the working layer located vertically below the groove" means, for each meridian, a set of points of the working layer located radially inside the groove within the boundary of the axial coordinate defined by the groove.

The tire comprises a crown comprising a tread intended to be in contact with the ground through a tread surface, two beads intended to be in contact with a rim, and two sidewalls connecting the crown and the beads. Furthermore, the tire comprises a carcass reinforcement comprising at least one carcass layer radially inside the crown and connecting the two beads.

The crown comprises at least one crown reinforcement located radially inside the tread. The crown reinforcement comprises at least one working reinforcement comprising at least one working layer consisting of mutually parallel reinforcing elements forming an angle of between 15 ° and 50 ° with the circumferential direction. The crown reinforcement may also comprise a hooping reinforcement comprising at least one hooping layer made up of reinforcing elements forming an angle of between 0 ° and 10 ° with the circumferential direction, the hooping reinforcement being generally (but not necessarily) radially on the outside of the working layer.

For any layer of reinforcing elements of the crown reinforcement, working reinforcement or other reinforcement, a continuous surface of said layer, called the radially outer Surface (SRE), passes through the radially outermost point of each reinforcing element of each meridian. For any layer of reinforcing elements of the crown reinforcement, working reinforcement or other reinforcement, a continuous surface of said layer, called the radially inner Surface (SRI), passes through the radially innermost point of each reinforcing element of each meridian. The radial distance between the layer of reinforcing elements and any other point is measured from one or other of these surfaces in a manner that does not include the radial thickness of the layer. The radial distance is measured from the radially outer surface SRE to another measuring point if this other measuring point is located radially outside the layer of reinforcing elements, or from the radially inner surface SRI to another measuring point if this other measuring point is located radially inside the layer of reinforcing elements. This makes it possible to take into account consecutive radial distances from one meridian to the other, without having to take into account possible local variations related to the cross-sectional shape of the reinforcing elements of the layer.

In order to obtain good grip on wet ground, incisions are made in the tread. The incisions represent wells, or grooves, or sipes, or circumferential grooves, and form spaces open to the tread surface.

The groove has two characteristic main dimensions on the tread surface: width W and length Lo, length Lo being at least equal to twice width W. The groove is thus delimited by at least two main sides determining its length Lo and connected via a bottom surface, the distance between the two main sides (called the width W of the groove (sometimes called sipe)) being different from zero. A sipe is a specific groove whose width W is small enough to make its side surfaces contact when the sipe is in contact with the ground.

An open groove is a groove that leads to a groove that may be a circumferential groove. The circumferential groove is a groove having a large width Ws at least equal to 6mm, locally forming an angle at most equal to 45 ° with the circumferential direction and forming a space open to the entire circumference of the tire. In many tire variants, the angle formed by the circumferential groove with the circumferential direction is constant and zero around the entire circumference. In other variants, some grooves are a continuous series of grooves around the entire circumference, forming different angles and the continuity thereof forming a space open to the entire circumference of the tyre.

The depth of the cut is the maximum radial distance between the tread surface and the bottom of the cut. The maximum value of the depth of the cut is called the tread depth D.

The grooves and circumferential grooves define blocks or ribs of rubber material in the tread, according to their circumferential or transverse arrangement. The ribs may comprise grooves. In a complex tread, a rib in a completely new state may become a series of blocks after wear. The sides of the groove and circumferential groove are also referred to as the "cliff" of the block or rib they define.

The bottom surface is constituted by a point connecting the side surfaces of the groove, said side surfaces forming an angle of between 0 and 70 ° with the radial direction. The side surface may comprise discontinuous projections, wherein the local angle is not within this range. However, despite these discontinuities, one skilled in the art would know how to determine the side and bottom surfaces.

The bottom surface of the opening has a bottom curve. The most clearly determined point of the bottom curve is the common point Ps between the bottom surface of the groove and the side or bottom surface of the circumferential groove to which the groove under consideration opens. The bottom curve corresponds mathematically to the body line of the bottom surface, i.e. to the radially innermost point of the bottom surface from two points PS if the groove leads to two circumferential grooves, or from a single point PS to the other axial end point of the groove in the case of a blind blade groove terminated by a third side surface, said end point Pe being determined as the radially innermost point of the joining curve between the bottom surface of the groove under consideration and said third side surface.

For a groove forming an average angle with the circumferential axis at least equal to 15 °, the bottom curve is determined by all the points of the radially innermost point of the curve produced by the intersection between the bottom surface of the groove and the circumferential plane passing between the two points of junction PS of the bottom surface of the groove and the circumferential groove or between the two end points PS and Pe of the groove. If there are multiple points of intersection between one of the planes and the bottom curve, the point considered to be part of the curve will be the point most equidistant from the radially innermost point of intersection between the two sides and the circumferential plane under consideration.

Tires need to meet numerous performance criteria related to phenomena such as wear, grip on various types of ground, rolling resistance, dynamics and noise. These performance criteria sometimes result in solutions that degrade other criteria. Thus, documents FR3057810 and FR3057811 disclose tires having a crown layer with undulations. These undulations make it possible to increase the transverse stiffness of the joint between the crown reinforcement and the tread. Depending on the material chosen for the tread, the generation of undulations in the crown layer makes it possible to improve the performance of the tire in terms of running properties by improving the grip (more particularly wet grip) and to improve the rolling resistance performance without modifying the wear and crown endurance properties of the tire.

However, this technique has an effect on the manner in which the tread wears. The undulations discussed in the cited documents and in the present invention satisfy: the point of the undulation is radially outside the point of the undulated crown layer below the groove, which is the groove closest to the point in question. The objective is to reduce the thickness of the tread radially outward of the undulations to reduce the shear of the tread rubber composition, thereby improving the stiffness of the tire crown and thus improving the runnability and rolling resistance properties. Depending on the type of rubber composition in the tread and its properties in terms of hysteresis at 0 ° and 60 ° which determine its wet grip and rolling resistance properties, the grip and/or rolling resistance may be improved.

In this configuration, the undulations of the radially outermost crown layer or layers (the distance between these layers being substantially constant over the surface of the central portion of the crown) cause a particular circumferential wear pattern that is more pronounced at the axial edges of the ribs or blocks radially outside the undulations (i.e. close to the cliff of said ribs or blocks).

Specifically, under the internal pressure of the pneumatic tire, the carcass layer and the crown layer are subjected to axial and circumferential tensions, so that the radial amplitude of the beads tends to decrease. This movement of the crown layer also causes the rubber compound located radially outside the undulations to move radially. In areas where the undulations are minimal or absent, particularly vertically below the circumferential groove, motion is minimal. Therefore, with the blocks or the rib located radially outside the wavy portion, the movement of the cliff of the rib is smaller than the movement at the center of the block or rib. As a result, the contact pressure is increased in the contact region close to the cliff of the substantially longitudinal rib, resulting in more wear. This wear is particularly pronounced for the flanks of the circumferential groove. This wear can be counteracted by using an at least axially arched profile of the blocks and ribs. When the tire is sized appropriately, the camber of the blocks and ribs may be maintained throughout the life of the tire.

Since the undulations of the crown layer are present throughout the life of the tire, this overpressure at the cliff of the blocks or ribs is sustained throughout the life of the tire. According to the prior art, the grooves present in the tread (whether open or not) have a bottom surface, the radially innermost point or bottom curve of which is not adapted to the undulations of the crown layer and is therefore substantially the same radial distance from the axis of rotation of the tire. The wear of the tire caused by the corrosion of the rubber composition constituting the tread causes the tread pattern height to gradually decrease.

This wear occurs in an arcuate lateral wear profile because the cliff of a rib or block wears faster than its center. Therefore, in the case where the bottom curves are located at the same radius, the portion of the open groove that is close to the cliff of the rib or block where it is located corrodes faster and disappears before the portion of the groove that is located at the center of the groove or block.

In travel, in the contact surface, the cliff closes the groove on the side where the groove is open in the new state due to overpressure. This closure of the grooves generates sound waves that increase the noise level of the running tire in the same manner as non-open sipes.

Disclosure of Invention

It is therefore a main object of the present invention to improve the noise and wet grip performance of a tire whose crown layer comprises undulations radially inside the central portion of the tread and comprises open grooves radially outside the undulations, this improvement being observable when said grooves are still visible but have a shallow depth due to their wear.

This object is achieved by a tyre comprising:

-a tread intended to be in contact with the ground through a tread surface, having an axial width L and comprising a tread central portion having a width equal to 0.8 x L, this central portion of the tread comprising at least two circumferential grooves,

a circumferential groove forming a space open to the tread surface around the entire circumference of the tyre and delimited by two main sides connected by a bottom face, said circumferential groove having an average width Ws at least equal to 6mm and a depth D at least equal to 4mm,

the central portion of the tread comprises a groove forming a space open to the tread surface, forming an angle at least equal to 15 ° with the circumferential axis and delimited by two main lateral faces connected via a bottom face; the groove has a width Wr defined by the average distance between the two sides and has a width Wr at least equal to 0.5 mm; at least 50% of these grooves are open grooves, i.e. grooves leading to one or two circumferential grooves,

each open groove comprises a bottom curve Cf formed by all radially innermost points of the bottom surface of the groove, each bottom curve comprising at least one and at most two points Ps common to the groove or to both grooves to which the groove opens, and a radially outermost point Pext,

-a carcass layer and a crown reinforcement radially on the inside of the tread and comprising at least one crown layer, the crown layer being a layer of reinforcing elements,

the crown reinforcement comprising a working reinforcement comprising at least one working layer,

-each working layer comprises reinforcing elements at least partially made of metal coated with elastomeric material, parallel to each other and forming, with the circumferential direction (XX') of the tyre, an orientation angle at least equal to 15 ° and at most equal to 50 ° in absolute value,

-each crown layer extending radially from a radially inner Surface (SRI) to a radially outer Surface (SRE),

the radially outermost crown layer located vertically below the central portion of the tread comprises at least one wave called central wave and having a radial amplitude a,

-the portion of the radially outer Surface (SRE) of the crown layer of the central wave is radially outside the point of the radially outermost crown layer which is vertically below the floor of the circumferential groove closest to the wave,

-the radial distance (do) between the radially outer Surface (SRE) of the radially outermost crown layer and the tread surface at said undulations is at least 1mm less, over at least 10% of the radially outer Surface (SRE) of said crown layer located vertically below the central portion of the tread, than the radial distance (dc) between the radially outer Surface (SRE) of the radially outermost crown layer and the tread surface (this being the distance vertically below the bottom face of the circumferential groove closest to the point considered on said surface),

-the radial distance (d1) between the radially outer Surface (SRE) of the radially outermost crown layer and the bottom face of the circumferential groove is at most equal to 4mm,

at least 50% of the open recesses situated radially outside the central undulations of the radially outermost layer of the reinforcing element are said to be adapted to the central undulations, the open recesses adapted to the undulations radially outside the undulations being such that the radial distance (d2) of the intersection point Ps of the bottom curve Cf of the open recesses adapted to the undulations with the circumferential groove to which they lead from the radially outermost point Pext of the bottom curve Cf is at least equal to one third (a/3) of the radial amplitude of the central undulations situated vertically below the open recesses adapted to the undulations, and the curve Cf increases radially from the intersection point Ps to the point Pext.

The grooves discussed in this disclosure may have a constant or non-constant width. The present invention also uses grooves with variable widths, for example, with greater widths at the bottom surface, to create more clearance in the ground plane at wear levels that expose these increased widths, thereby improving grip. For the invention to work, it is sufficient that the bottom curve is adapted to the undulations. In this way, the bottom curve ensures that the groove is open, regardless of wear, eliminating the following risks: edge ridge loss can thus reduce grip and create non-open or blind grooves and thus impair noise performance compared to a new tire.

Depending on the depth of the grooves radially outside the undulations of the radially outermost layer of the crown reinforcement or layer, the effect of the invention can be observed throughout the service life of the tire. If the groove has a shallow depth, the effect of the invention is observed at the onset of tire wear. The effect of the invention is observed at the wear limit of the tire if the bottom profile of the groove is close to the radially outermost point of the wear indicator. This effect can be perceived during the entire service life of the tyre if the grooves considered have different depths.

The radially outermost crown layer needs to have at least one corrugation. The radial amplitude of these undulations is at least equal to 1mm, preferably at least equal to 1.5mm, and preferably at least equal to 2 mm. The greater the radial amplitude of the undulations, the greater the effect on the stiffness of the tire, and the better the performance in terms of rolling resistance, runnability and grip associated with such a structure. The greater the radial amplitude of these undulations, the greater the overpressure of the tread surface at the cliff of the ribs or blocks of the tread, the greater the degree to which the ribs or blocks located radially outside the undulations need to be arched and the greater the degree to which the bottom profile of the groove needs to be curved in order to maintain these improvements throughout the service life of the tire.

It is necessary that the radial distance (d2) of the intersection point Ps of the bottom curve Cf of the groove with the groove to which the groove leads, from the radially outermost point Pext of the bottom curve Cf, is at least equal to one third (a/3) of the radial amplitude of the undulations located vertically below the groove, and that the curve increases radially from the intersection point Ps to the point Pext.

The expression "radially increasing" is understood to mean that the derivative of the radial distance of a point of the bottom curve from the axis of rotation of the tyre as a function of the horizontal axis of the curve of points, starting from the starting point Ps and ending at the point Pext, is at least equal to 0, the presence, at 90% of the points of the bottom curve, of local irregularities having a smaller radial amplitude than 20% of the radial amplitude of the bottom curve having no adverse effect on the invention. If the groove leads to two circumferential grooves and thus has two points Ps, it is necessary to verify this property starting from the second point Ps.

Preferably, the radial distance (d2) of the intersection point Ps of the bottom curve Cf of the groove with the groove to which the groove leads, from the radially outermost point Pext of the bottom curve Cf, is at least equal to half (a/2) of the radial amplitude of the central undulation located vertically below the groove, and preferably at most equal to 1.5 times (1.5 a) the radial amplitude of the central undulation located vertically below the groove. For a distance d2 at least equal to A/2, the risk of the pattern of wear of the ribs or blocks not providing the desired effect is reduced and the reliability of the invention is increased. For distances d2 greater than 1.5A, the cliff of the ribbing is less stiff than its center, increasing local wear, which should be avoided.

For the invention to work well, the radially outermost crown layer needs to have undulations. The other crown layers preferably have undulations having substantially the same radial amplitude and the same position as the radially outermost crown layer, in order to keep the stacking thickness of the undulated layers constant over the maximum surface area of these crown layers. This makes it possible to obtain maximum effectiveness from the undulations.

Preferably, all the crown layers have undulations, and their undulations are substantially identical in position and radial amplitude in the portion located vertically below the central portion of the tread, allowing for manufacturing differences.

Preferably, at least 90% of the open recesses, preferably all of the open recesses, which are located radially outside the central undulations of the radially outermost crown layer, are each adapted to said central undulations (51) radially outside the central undulations (51) of the radially outermost crown layer.

In a conventional structure comprising a hoop layer (preferably a fabric) and two working layers (comprising metal reinforcing elements), the hoop layer is located radially outermost of the crown layer, which is required to be corrugated. The performance in terms of rolling resistance, grip or runnability is better if the working layer adjacent to the hoop layer is corrugated, wherein the corrugations have the same radial amplitude and the same position over at least part of the surface of the hoop layer and better over the whole surface of the hoop layer. These same performance aspects are even better if both working layers and hoop layers are corrugated with corrugations having the same radial amplitude and the same location. The invention works even if the portions of the working layer adjacent to the hoop layer are corrugated and coupled to the hoop layer over these corrugations while another portion is not.

One necessary condition for the invention to function is that the crown layer is at a limited distance from the tread surface, in particular at the radially outermost point of the undulations. The thickness of the rubber compound between the radially outermost crown layer and the bottom of the groove is at least equal to 0.5mm and at most equal to 4mm, depending on the degree of protection required for the radially outermost crown layer. This is not a problem of increasing the thickness of the rubber compound, but rather of reducing the distance between the tread surface and the radially outermost point of the undulations in the completely new state. In fact, a sufficient condition is that the radial distance (do) between the radially outer Surface (SRE) of the radially outermost crown layer and the tread surface at the undulations is at least 1mm less than the radial distance (dc) between the radially outer Surface (SRE) of the radially outermost crown layer and the tread surface, which is the distance (dc) at a point vertically below the centre of the base of the circumferential groove closest to the point considered on said surface. This condition ensures that the minimum radial amplitude of the undulations is 1mm, and that the undulations vertically below the ribs or blocks are indeed intended to reduce the distance between the radially outermost layer and the tread surface compared to a tire without undulations.

The radial amplitude of each wave in a crown layer is measured as the radial distance between the radially outermost point P1 of the radially outer Surface (SRE) of the crown layer, which radially outermost point P1 is located vertically below the block or rib in question, and the radially innermost point of the radially outer Surface (SRE) of the crown layer, which radially innermost point is located vertically below the circumferential groove closest to point P1. If there are two circumferential grooves equidistant from the radially outermost point P1 of the wave under consideration, the point under consideration for calculating the radial amplitude will be the point that produces the highest radial amplitude value. The radial amplitude is measured in a meridian section which includes the rotation axis of the tyre and is perpendicular to the circumferential direction of the tyre. If the radial amplitude varies in the circumferential direction, the value reserved for the radial amplitude is the highest one.

The waves considered are waves called central waves; they are located in the central portion of the tread, centered on the equatorial plane and having a width of 0.8L, L being the width of the tread surface of the tire in the new state. The width L is measured on a tire mounted on a nominal rim and inflated to a nominal pressure. The non-coupling areas between the crown layers in the axially outermost part of the tire outside the central part or in the shoulder area (the purpose of said areas being only to decouple the crown layers at their ends to avoid compound cracking in this area) are not considered to be undulations.

Motorcycle tires are typically not arranged with a substantially constant radius. However, for these tires, the layers of material in the crown are arranged in a continuous convex curve. The invention can also be applied to these tires, the undulations creating areas of greater concavity and convexity everywhere in the continuous curve of a motorcycle tire according to the prior art.

It appears that 10% of the radially outer surface of the radially outermost crown layer, vertically below the tread center portion, is wavy enough to show an improvement in the dynamic performance under transverse loads. The radial amplitude of such undulations needs to be at least equal to 1mm in order to have a significant effect on the dimensions of the tyre. Thus, in the present invention, the difference between the radial distance (do) between the radially outer Surface (SRE) of the radially outermost working layer and the tread surface is at least 1mm less, in particular on at least 10% of the surface of said layer, than the radial distance (dc) between the radially outer Surface (SRE) of the radially outermost working layer and the tread surface, which is the distance vertically below the centre of the bottom face of the circumferential groove closest to said undulations.

The optimal solution takes into account the tire characteristics and possibly the vehicle characteristics. Optimization can be achieved based on the directional characteristics of the tire, the asymmetry of the tire, and the camber angle of the mounted assembly relative to the vehicle.

Preferably, for the portion of the crown reinforcement vertically below the central portion of the tread, the radial distance (do) between the radially outer Surface (SRE) of the radially outermost crown layer and the tread surface is less than the radial distance (dc) between the radially outer Surface (SRE) of the radially outermost crown layer and the tread surface (this being the distance measured vertically below the radially innermost point of the bottom face (243) of the circumferential groove closest to said central wave at the point considered) by at least 1.5mm, preferably 2mm, over at least 20%, preferably at least 30% and at most 85% of the radially outer Surface (SRE) of the radially outermost crown layer. Design parameters that enable the dynamic response to be adjusted at large lateral loads (i.e., loads that account for at least about 50% of the nominal tire load) are:

the size of the undulations of the radially outermost working layer (tensdie), it being understood that a porosity of the tread pattern of almost no less than 15% limits this size to at most 85% (85% ═ 100% -15%). The larger the undulations, the stiffer the tire under lateral load, which is the primary role of the undulations.

The radial amplitude of the undulations is at least equal to 1mm, but limited to 5mm, due to the radius of curvature that must be imparted to the crown layer.

Thus, a preferred solution is that the radial distance (do) between the radially outer Surface (SRE) of the radially outermost working layer and the tread surface is at least 20%, preferably at least 30% and at most 85%, smaller than the radial distance (dc) between the radially outer Surface (SRE) of the radially outermost working layer and the tread surface, which is the distance vertically below the centre of the bottom face of the circumferential groove closest to the undulations, by at most 5mm, preferably at most 3mm, over at least 20%, preferably at least 30% and at most 85% of the radially outer Surface (SRE) of the radially outermost working layer.

In order to obtain optimum performance in terms of penetration and attack on the crown without compromising rolling resistance, the radial distance (d1) between the radially external Surface (SRE) of the radially outermost working layer and the bottom face of the circumferential groove is at least equal to 0.5mm and at most equal to 4mm, preferably at least equal to 0.7mm and at most equal to 2 mm. Below the lower limit, the tire proves to be too sensitive to attack. Beyond the upper limit, the rolling resistance of the tire will suffer.

Advantageously, the tread (for example the circumferential groove of the tread) comprises at least one wear indicator, and the minimum radial distance (do) between the radially outer Surface (SRE) of the radially outermost layer of the crown reinforcement and the tread surface is at least equal to the radial distance (df) between the tread surface and the radially outermost point of the wear indicator. In particular, it is important that the user is able to see that the tyre has worn using the wear indicator and to do so before the reinforcing elements of the radially outermost layer of the crown reinforcement start to appear on the tread surface.

Advantageously, the minimum radial distance (do) between the radially outer Surface (SRE) of the radially outermost layer of the crown reinforcement and the tread surface is at most equal to the depth D of the closest circumferential groove plus 2mm and at least equal to the depth D of the closest circumferential groove minus 2mm, preferably substantially equal to the depth D of the closest circumferential groove. This solution makes it desirable to arrange the radially outermost layer of reinforcing elements of the crown reinforcement and the tread surface. The minimum radial distance (do) between the radially outer Surface (SRE) of the radially outermost layer of the crown reinforcement and the tread surface needs to be measured on the radially outer portion of the crown reinforcement, and therefore at the undulations.

Preferably, the depth D of the circumferential groove is at least equal to 5mm and at most equal to 20 mm. In many passenger vehicle tires, a tread depth of between 6mm and 10mm allows a good compromise to be achieved in terms of wear and rolling resistance performance. For the same compromise in tires for heavy load-bearing vehicles, tread depths between 10mm and 20mm are considerable. The present invention is not limited to tires for particular uses.

In the case where the radially outermost layer of reinforcing elements is a hoop layer, it is advantageous for the radially outermost layer of reinforcing elements in the crown reinforcement to comprise reinforcing elements made of a fabric, preferably of the aliphatic polyamide, aromatic polyamide type, type comprising a combination of aliphatic polyamide and aromatic polyamide, polyethylene terephthalate or rayon type, said reinforcing elements being parallel to each other and forming an angle B with the circumferential direction (XX') of the tire, the absolute value of which is at most equal to 10 °.

A preferred solution is to arrange at least one filling rubber having a radial thickness at least equal to 0.3mm vertically below each central undulation of the radially outermost crown layer, and preferably radially outside the carcass ply, preferably radially inside the radially innermost working ply. The purpose of this is to make the plies wavy during the shaping and curing process. These filler rubbers may be present around the entire circumference of the tire or arranged in certain portions of the tire, as desired. Depending on the tire specification, multiple types of filler rubber having different properties may be laid at different radius values vertically below one or more beads. If only one filling rubber is laid, its maximum thickness is approximately equal to the radial amplitude of the wave for a given wave.

The invention is not particularly suitable for tyres configured to be used in inflated mode, i.e. at tyre internal pressures lower than 1 bar. This is because such tires are provided with variable thickness innerliners that are high at the sidewalls and axially outermost points of the tire. This additional thickness makes the sidewalls stiffer in the radial direction, but at the expense of rolling resistance, which is not an object of the present invention. The tyre according to the invention preferably has an inner liner having a thickness at most equal to 1.5 mm. Another characteristic of the tyres according to the invention is that their thickness varies by at most 30% from one bead to the other.

The tire in which the portion of the carcass layer vertically below the central portion of the crown is located radially inside these points of the carcass layer which are located vertically below the ends of the radially innermost crown layer is less compatible with the present invention. Such a crown has undulations in all the crown and carcass layers, but with a radial amplitude greater than that of the present invention, and is used for the phenomena of drift or for some other purpose. This type of construction does not satisfy the geometric definition of the present invention or solve the same technical problem.

In the case where the tread is made of a rubber compound, it is advantageous that the filling rubber laid vertically below the undulations is a rubber compound whose dynamic loss tan δ 1, measured at a temperature of 10 ℃, a stress of 0.7MPa and 10Hz, is at most equal to the dynamic loss tan δ 2 of the rubber material from which the tread is made and preferably 30% less than said dynamic loss tan δ 2, said dynamic loss tan δ 2 being measured at a temperature of 10 ℃, a stress of 0.7MPa and 10 Hz. For filler materials with the same hysteresis, the improvement in rolling resistance is achieved only by reducing the shear stress load to which the material is subjected. Since the filler material does not bear the same stress as the rubber material of which the tread is made, its characteristics can be changed to improve the rolling resistance even further. The 30% reduction in hysteresis makes the improvement of the present invention significantly greater.

The crown reinforcement preferably consists of two working plies with opposite angles and of a hooping ply, as in the numerous crown structures of today.

In order to measure various geometric dimensions, including the radial amplitude of the undulations and the size of the undulations, the person skilled in the art generally makes measurements on a section of the tyre taken in a meridian plane or on a meridian section. To obtain greater accuracy, these measurements may be the average of 4 measurements taken on 4 sub-noon planes 90 ° apart, the tire section being buffed to reveal the interfaces between the various compounds constituting the tire. Since the tire is in the shape of a toroidal body, measurement of the size of the surface of the bead is equivalent to measurement of the length in a meridian section. For example, an inspection is carried out on a meridian section to ensure that, for 10% of the length of the radially outermost crown layer at the tread central portion, the radial distance between the radially outer surface of the radially outermost crown layer and the tread surface at the undulations is at least 1mm less than the radial distance between the radially outer Surface (SRE) of the radially outermost crown layer and the tread (this is the distance vertically below the bottom face of the circumferential groove closest to the point considered on said surface).

Drawings

The features and other advantages of the invention will be better understood with the aid of fig. 1 to 7, which are not drawn to scale but in a simplified manner in order to make the invention easier to understand:

figure 1 shows the crown portion of the tire, the crown layer and its tread.

Figure 2 shows a meridian half section through the crown of a tyre according to the invention, provided with open grooves (25), said open grooves (25) being radially outside the undulations and having a bottom profile Cf adapted to the undulations. It shows the radial amplitude a of the undulations (51) of the radially outermost crown layer 5, the various radial distances do, dl, D, df, dc, and the filling material (6) suitable for creating the undulations, in particular of the radially outermost crown layer.

Fig. 3 shows the open recess 25, its bottom surface and the bottom curve or body line Cf, as well as the intersection Ps with the circumferential groove (24) and the radially outermost point Pext of the bottom curve Cf.

Figures 4, 5 and 6 show a portion of a meridional section through the central portion 22 of the tread and the portion of the crown vertically below it. These figures show a variant of the position of the filling material (6) in the crown layers (41, 42, 5) and a variant of the open grooves (25) (radially on the outside of the undulations (51)) adapted to the undulations (51).

Figure 7 shows a part of a meridional section through the central portion 22 of the tread and the portion of the crown vertically below it, with the beads a1 and B1 in the brand new state and a2 and B2 in the worn state, provided according to the invention and according to the prior art, respectively, illustrating the effect of wear on both variants.

Detailed Description

A meridian section through the tyre is obtained by cutting the tyre in two meridian planes. The cross-sections are used to define various radial distances, the center of the groove floor and the center of the groove floor.

Fig. 1 shows a portion of the crown of a tire. It shows a carcass layer 9, said carcass layer 9 being radially inside a crown layer 3, said crown layer 3 comprising a working reinforcement 4 and a hoop layer 5, said working reinforcement 4 comprising in this case two working layers 41 and 42 constituted by reinforcing elements 411, said reinforcing elements 411 being made at least partially of metal coated with elastomeric material, parallel to each other and forming, with the circumferential direction (XX') of the tyre, an orientation angle at least equal to 15 ° in absolute value and at most equal to 50 °. The tyre further comprises a tread 2, said tread 2 being delimited by the tread surface 21 and the outer lateral surface 26 and comprising incisions, in this case two circumferential grooves 24 of width Ws at least equal to 5mm and grooves 25 of width Wr at least equal to 0.5 mm. The circumferential groove 24 includes two side surfaces 241 and 242 and a bottom surface 243. Fig. 1 also shows a groove 25 leading to two circumferential grooves 24 and surrounded by two blind grooves 25 leading to one groove. The recess includes side surfaces 251 and 252 and a bottom surface 253 not shown in fig. 1. The portion of the circumferential groove shown in fig. 1 forms in this case an angle of zero with the direction XX'; the circumferential grooves may consist of a series of incisions which are at a non-zero angle to the direction XX' and which are mutually connected so as to form a continuous incision over the entire circumference of the tyre.

In fig. 2, 4, 5, 6 and 7, the grooves are shown as belonging to meridional planes for ease of depiction, but the grooves may have any form known in the art, including in terms of angles and shapes: simple, wavy, complex, with or without variations in thickness.

Figure 2 schematically shows a meridian half-section through the crown of a tyre according to the invention. It shows in particular the undulations of all the layers (3) of the crown reinforcement, including the working layers (41, 42) and the radially outermost crown layer (5), by means of a filler material (6) arranged between the carcass layer (9) and the radially innermost working layer (42). This filler material undulates all the crown layers 41, 42, 5 and thus creates undulations 51 in the radially outermost hoop layer 5 of the crown layers.

Fig. 2 shows how the width L of the tread is determined. The width L of the tread is determined on a tire mounted on a nominal rim and inflated to a nominal pressure. The width of the tread is determined in a simple manner by the person skilled in the art if there is a distinct boundary between the tread surface and the rest of the tire. If the tread surface 21 is continuous with the outer lateral surface 26 of the tire, the axial borderline of the tread passes through the point where the angle between the tangent of the tread surface 21 and the axial direction YY' is equal to 30 °. When the angle of a plurality of points in the meridian plane is equal to 30 °, the radially outermost point is used. The width of the tread is equal to the axial distance between two axial borderlines of the tread surface on either side of the equatorial plane.

Fig. 2 also shows the following radial distances:

-D: the depth of the circumferential groove (24), which is the maximum radial distance between the tread surface (21) and the bottom surface (243) of the groove (excluding the retread well),

-dc: the radial distance between the radially outer Surface (SRE) of the radially outermost crown layer (5) and the tread surface (21), which is the distance vertically below the radially innermost point of the floor (243) of the circumferential groove (24),

-do: the radial distance between the radially outer Surface (SRE) of the radially outermost crown layer (5) and the tread surface (21) at the undulations (51),

-d 1: a minimum radial distance (d1) between a radially outer Surface (SRE) of a radially outermost crown layer (5) of the crown reinforcement (3) and a floor (243) of the circumferential groove (24),

-df: a radial distance between the tread surface (21) and a radially outermost point of the wear indicator (11),

-A: the radial amplitude of the undulations, for a given undulation, is measured between the radially outermost point of the undulation and the radially innermost point of the point located vertically below the nearest circumferential groove 24.

Fig. 2 shows two undulations 51 of the radially outermost crown layer in the central portion 22 of the tyre, said central portion 22 being centred on the equatorial plane and having a width equal to 0.8 × L. Each of these undulations is located radially inside the open recess 25, the bottom curve Cf of the bottom surface 253 of said open recess 25 being adapted to the undulation. The bottom curve Cf is adapted in that the intersection point Ps of the bottom curve with the side walls 241, 242 of the circumferential groove 24 to which the groove 25 opens is radially inside a point Pext (the radially outermost point of the bottom curve Cf) such that the radial distance d2 between Pext and the two points Ps is at least equal to one third of the radial amplitude of the wave in question, which can vary from one rib to the other. Further, the bottom curve increases radially from point Ps to point Pext.

Fig. 3 shows two grooves leading to two trenches 24. In the prominently located first trench, only side 241 is depicted. In a' of the figure, the bottom surface 253 has a single bottom curve or body line, and it can be easily determined. The intersection curve of the side surface 241 of the circumferential groove and the bottom surface 253 of the groove is determined, and the radially innermost point Ps (the starting point of the bottom curve) thereof is determined. Similarly, the other end point of the bottom curve Cf is determined by following the same procedure with another trench or by finding the intersection curve between the bottom surface 253 and the surface of the closed groove in the case of a blind groove. Next, a set of points forming the bottom curve Cf is determined by the intersection of the circumferential plane contained between the endpoints of the curve Cf and the bottom surface 253. In B' of fig. 3, there is not only one curve Cf, but in this case an average curve Cf is considered, which consists of the points of possible intersection with the circumferential groove PS that are most equidistant from the flanks 251, 252 of the groove 25 under consideration. Next, the same procedure is performed on the curve resulting from the intersection of the circumferential plane with the bottom surface 253 to determine the remainder of Cf. The person skilled in the art knows how to determine the bottom curve of the groove without difficulty.

Fig. 4, 5 and 6 show variants of possible positions of the filling material 6 in the crown 3:

between the carcass layer 9 and the radially innermost working layer, as shown in figure 6,

between the working layers 41 and 42, as shown in figure 4,

between the radially outermost working layer 41 and the radially outermost crown layer 5, as shown in figure 5.

It is conceivable to provide a plurality of filling materials at the different positions shown here, which have a suitable thickness to obtain undulations with the desired radial amplitude.

Fig. 4 shows a blind groove 25, which thus leads to a single circumferential groove (24).

Fig. 5 shows that the groove 25 may have a shallow depth of less than 2 mm.

Fig. 6 shows a bottom curve with multiple curve levels. It may have a straight bottom curve or a bottom curve that is straight in a stepwise manner.

Fig. 7 shows the rib of the tread radially outside the undulations 6, which comprises a groove 25 leading to two circumferential grooves 24 on either side of the rib and the bottom curve Cf of said groove. For a1 of the figure, Cf is adapted to the undulations according to the invention. For B1 of the figure, Cf does not adapt according to the prior art to the undulations of the radially outermost crown layer vertically below the ribs. A2 and B2 of the figure show ribs a1 and B1, respectively, after wear. Due to the undulations, the ribs will exhibit more pronounced wear at the cliff of the circumferential groove. Under pressure, the working layer becomes taut, the undulations lose radial amplitude a, and the center of the rib is depressed relative to the cliff of the groove, creating a more prominent wear pattern at this location. For a bottom curve Cf that is not compliant, the groove will disappear at the cliff of the rib, as shown at B2. Such grooves, which are not provided over the entire width of the ribs, will trap air in the ground plane, generating noise when leaving the ground plane. In the case of the adapted bottom curve, the groove remains open, so that the noise level does not deteriorate.

The invention was implemented on a tire a of size 295/35ZR20 intended to equip a passenger vehicle. For a width Ws varying around 4mm, the depth D of the circumferential groove in the tread pattern is equal to 7.5 mm. The crown reinforcement is made up of two working layers, the reinforcing elements of which form an angle of +38 or-38 with the circumferential direction, and of a hoop layer, the reinforcing elements of which form an angle of +3 or-3 with the circumferential direction. The reinforcing elements of the working layer are continuous metal cords. The radially outermost crown layer is contoured such that 50% of its radially outer Surface (SRE) is radially distant by at least 1mm compared to the same surface vertically below the closest circumferential groove. The radial amplitude of the undulations is 2 mm. The radial distance (d1) between the radially outer Surface (SRE) of the radially outermost working layer (41) and the bottom face (243) of the circumferential groove (24) is equal to 1.6 mm. The tread pattern has 4 circumferential grooves and 4 ribs in the central portion 22 of the tread. Each rib of the central portion 22 is located radially outside the undulations of the crown layers 41, 42, 5. The ribs comprise grooves 25 and are spaced apart from one another at an average pitch equal to 30mm, said grooves 25 opening into the circumferential groove 24 at a depth of 3 mm. The bottom curves of the grooves are each adapted to the undulations of the crown layers 5, 41, 42. The distance d2 between the intersection point Ps of the bottom curve and the circumferential groove and the radially outermost point Pext of the groove bottom curve is at least equal to 0.7 mm. The bottom curve increases radially from point Ps to Pext.

Comparing tire a with tire B of the same size, tire B has the same characteristics, except that the bottom curve of the groove in the central rib does not adapt to the undulations of the crown layer, from one groove to the other, the bottom curve of the groove being on the same radius.

The tires were tested under new conditions for noise according to the current european standard. There was no difference in the measured properties. The tires were then worn at the same speed on an open road using the same type of vehicle under the same driving conditions. Most of the grooves of the tire a according to the invention and the tire B according to the prior art exhibited greater wear at the cliff of the rib than at their center after 1.7mm of wear. In the tire a according to the invention, the majority of the grooves remain open, since the bottom curve Cf is adapted to the presence of undulations of the crown layer. For tire B, the groove is worn at the cliff so that the end of the groove is at the top of the rib under the wear pattern. The sliding noise tests carried out on these two tires show that the performance of tire a is about 0.7dB better than that of tire B under the test protocol according to the current european directive 2001_43_ CE.