HEAVY DUTY VEHICLE TIRE WITH COMPLEX TRAFFIC TRAFFIC

Description

[0001] The present invention relates to a tire for a heavy goods vehicle and concerns its tread, comprising more particularly complex and evolving cutouts opening discontinuously, at regular or irregular intervals, onto the tread surface in the new state of the tire.

[0002] A tread, made of at least one rubber-based material, is the peripheral part of a tire, designed to wear down upon contact with the ground via a tread surface and to grip the ground. It generally includes a tread pattern, consisting of grooves separating raised elements.

[0003] By definition, the circumferential or longitudinal direction is the direction of rotation of the tire, the axial or transverse direction is the direction parallel to the axis of rotation of the tire, and the radial direction is a direction perpendicular to the axis of rotation of the tire.

[0004] Any tread cut with a center line that is not necessarily straight—that is, it can be wavy or zigzag—is circumferential, transverse, or oblique. By convention, a cut is said to be circumferential when its center line has a roughly circumferential average direction, meaning it forms an average angle of less than 30° with the circumferential direction. A cut is said to be transverse when its center line has a roughly transverse average direction, meaning it forms an average angle of at least 60° with the circumferential direction. A cut is said to be oblique when its center line has a roughly oblique average direction, meaning it forms an average angle of between 30° and 60° with the circumferential direction.

[0005] As is well known, driving conditions in wet weather for a vehicle, and particularly for a heavy goods vehicle, require rapid evacuation of water from the contact patch between the tread and the road surface. This evacuation ensures direct contact between the tread material and the road surface. Water that is not deflected forward or to the sides of the tire flows away or is partially captured in the grooves formed in the tread. Water evacuation is ensured by these grooves, which form a fluid drainage network that must be effective throughout the tire's service life, from when it is new until it reaches its maximum wear. The maximum wear level, defined by current regulations, is the point at which the tire must be removed from the vehicle for safety reasons.

[0006] Generally, the cutouts that allow water evacuation are essentially wide cutouts called grooves. A groove is wide enough that the opposing material walls defining it do not come into contact with each other when the tread passes over the contact patch, under recommended inflation and load conditions as defined, in particular, by the European Tyre and Rim Technical Organization (ETRTO) standards in its "Standards Manual 2020 - Commercial Vehicle Tyres." The compression and shear deformations of the raised elements defining the groove determine the pressures in contact with the ground and therefore the wear.Moreover, these deformations, by generating hysteretic losses in the tread material, impact rolling resistance, and therefore the vehicle's fuel consumption.

[0007] A tread pattern may also include narrow cuts or incisions. An incision has a width such that the opposing material walls delimiting it come into at least partial contact with each other as the tread passes over the contact patch, under the tire load and pressure conditions specified by the ETRTO and described previously. An incision does not allow water to be evacuated, but, with regard to grip, it has an edge effect in the contact patch, which in particular helps to break up any film of water that may be present on the ground.

[0008] To limit the reduction in the volume of material to be worn from the tread resulting from the presence of grooves and incisions, so-called complex cuts have been proposed which, compared to usual grooves, which are fully open on the tread surface, allow the volume of material of the tread to be increased while respecting the volume of cuts for water storage beyond a determined threshold, regardless of the level of wear of the tire.

[0009] Tread patterns incorporating such complex cutouts have been described in particular in documents WO2011039194, WO2011101495, WO2012130735, WO2016188956, WO2017174925, WO2019008276, and WO2019122677. A complex cutout opens discontinuously, at regular or irregular intervals, onto the new running surface. Each complex cutout has external cavities, open to the running surface and separated from each other in the principal direction of the complex cutout. The principal direction of the complex cutout often, but not necessarily, corresponds to the direction of water flow within the cutout when driving over a water-covered surface. This complex cutout includes, in addition to external cavities, internal cavities formed inside the tread, not directly open to the tread surface and generally connected to the tread surface by incisions.These internal cavities are positioned radially and entirely within the tread surface when new, and are sandwiched between the external cavities. The internal cavities can be positioned at varying depths within the tread thickness. Furthermore, the external and internal cavities of a single complex cut are interconnected in such a way that continuous water flow within each complex cut is ensured at all tread wear levels, as with a conventional continuous groove. Conversely, the juxtaposition of unconnected internal and external cavities, which therefore do not allow fluid flow from one to the other, does not constitute a continuous groove and is thus not considered a complex cut.

[0010] Attention is drawn to the disclosure of US document D 769 796 S which shows a tread comprising a complex circumferential groove having a substantially flat wall.

[0011] The combined volume of all internal and external cavities in a tread with complex cutouts is generally less than that of all the grooves in a conventional tread, which are fully open across the new tread surface and have a depth equal to the maximum depth of the internal or external cavities. Such a tread with complex cutouts is therefore more rigid than an equivalent tread with conventional open grooves.

[0012] A tread pattern can include both complex cutouts, opening intermittently onto the tread surface, and conventional grooves, opening onto the tread surface along their entire length. Such a tread pattern is shown, for example, in document FR 3 099 414 A1.

[0013] On heavy-duty vehicle tire treads with complex circumferential grooves positioned axially near the tread edges, irregular, wavy wear patterns have been observed, extending across the width and thickness of the tread. These irregular wear patterns generate vibrations during vehicle operation, which can degrade comfort, particularly for tires mounted on the front axle. This reduced ride comfort can lead to premature tire removal before complete wear. Furthermore, the presence of irregular wear patterns can result in some parts of the tread being completely worn while others are only partially worn, leading to tire removal with a significant amount of remaining material.Premature tire removal results in an economic loss for the user.

[0014] Therefore, the inventors set themselves the objective of improving the resistance to irregular wear of a tire tread for a heavy vehicle, comprising complex circumferential cutouts made up of an alternation of external and internal cavities, that is to say, to delay as much as possible the appearance of irregular wear patterns on said tread, in particular on the edge ribs, each delimited by a complex circumferential cutout at the outermost axial level and a tread edge.

[0015] This objective was achieved by a tire for a heavy goods vehicle comprising a tread, intended to come into contact with a ground via a tread surface, having an axial width, measured along an axial direction of the tire between a first and a second tread edge, said tread comprising at least one complex circumferential cut, delimited by raised elements, extending in a circumferential direction of the tire, and constituted, in the new condition of the tire, by an alternation of external cavities, open to the tread surface, and internal cavities, hidden inside the tread, two consecutive external and internal cavities respectively being connected to each other, the at least one complex circumferential cut having an axial width, measured on the tread surface between two walls of said complex circumferential cut and variable according to the circumferential direction, the at least one complex circumferential cut having only one of its two walls substantially flat,such that the intersection of said wall with the tread surface forms a trace whose axial variation amplitude is at most equal to 2% of the axial width of the tread.

[0016] A complex circumferential tread cut, as defined in the prior art, consists, in the new state of the tire, of alternating external cavities, open to the tread surface, and internal cavities, concealed within the tread, with two consecutive external and internal cavities connected. Consequently, this complex circumferential cut has an axial width, measured across the tread surface between its two walls, that varies according to the circumferential direction of the tire. This axial width is greatest at the external cavities open to the tread surface and greatest at the incisions that typically connect the internal cavities, located within the tread, to the tread surface.This variable axial width means that the walls of the circumferential cut intersect the tread surface along a non-straight path, meaning it can vary between two extreme positions axially separated by an axial distance corresponding to the amplitude of axial variation of said path. This non-straight path generates variations in contact pressure at the edge of the rib delimited by said wall, along the circumferential direction of the tire, during tire rotation, particularly in relation to Poisson effects at the rib edge. These pressure variations promote the initiation of irregular wear patterns on the edge of the rib in question.The invention, by proposing to limit the amplitude of axial variation of the trace, typically to 2% of the width of my tread, so as to obtain a substantially flat wall, that is to say very close to the same circumferential plane over the entire circumference of the tire, makes it possible to significantly reduce pressure variations at the edge of the rib, and therefore the risk of initiation of irregular wear patterns.

[0017] Preferably, the substantially flat wall of at least one complex circumferential cut is strictly flat, such that the intersection of said wall with the running surface forms a trace whose axial variation is zero. In other words, the trace of the wall is perfectly straight and the wall lies within a circumferential plane. This configuration minimizes contact pressure variations along the circumferential direction at the edge of the rib defined by said wall.

[0018] According to a preferred embodiment, at least one complex circumferential cut having only one of its two substantially flat walls is a complex circumferential edge cut, axially furthest from the tread, that is, furthest from a median circumferential plane perpendicular to the tire's axis of rotation and passing through the middle of the tread. The presence of a substantially flat wall on a complex circumferential edge cut, axially delimiting an intermediate rib inwards and an edge rib outwards, is particularly advantageous in this area of ​​the tread, which is especially susceptible to irregular wear patterns.

[0019] According to a preferred variant of the previously described preferred embodiment, the substantially flat wall of at least one complex circumferential edge cutout is the outermost axial wall. The outermost axial wall of the complex circumferential edge cutout delimits the edge rib, which is generally particularly susceptible to the development of irregular wear patterns due to its axial positioning at least partially outside the top reinforcement and the generally restraining forces acting on this edge rib.

[0020] Advantageously, the edge rib, delimited by said complex circumferential edge cut and a tread edge, has an axial width not exceeding 25% of the axial width of the tread. Beyond this value, the complex circumferential edge cut, delimiting said edge rib, is no longer an edge cut, due to its small axial distance from the circumferential plane of the tire, not exceeding 30% of the tread width. Consequently, it can no longer provide the expected grip and cooling functions for the top of the tire.

[0021] Advantageously, the edge rib, delimited by the aforementioned complex circumferential edge cutout and a tread edge, has an axial width at least equal to 5% of the axial width of the tread. Below this value, the edge rib, due to its small axial width, is more susceptible to tearing, particularly under the action of transverse forces exerted on the tread.

[0022] In one particular embodiment, the tread comprises at least three, preferably at least five, complex circumferential grooves positioned between the two complex circumferential edge grooves. A sufficiently high number of ribs ensures good lateral grip, due to the presence of a large number of transverse edges, and tread endurance, due to the cooling of the tread by a significant number of grooves.

[0023] The features of the invention are illustrated by the figures 1 to 4 schematic and not drawn to scale: Figure 1 : Top view of a tire tread according to the invention, with circumferential edge cutouts comprising a flat axially external wall, Figure 2 : Top view of a portion of the tread edge of a tire according to the invention, with circumferential edge cutouts comprising a flat axially external wall, Figure 3 : Cross-sectional view B-B', in a meridian plane YZ, of a complex circumferential cutout with an edge comprising a flat axially external wall, at the level of an external cavity, Figure 4 : View in meridian section C-C', in a meridian plane YZ, of a complex circumferential edge cut comprising an axially flat outer wall, at the level of an internal cavity.

[0024] There figure 1is a top view of a tread 2 of a tire 1 according to the invention. The tread 2, intended to come into contact with a ground by means of a tread surface 3, has an axial width L, measured along an axial direction YY' of the tire between a first and a second tread edge 21. Said tread 2 comprises six complex circumferential cutouts (41, 42), each delimited by raised elements (51, 52), extending along a circumferential direction XX' of the tire, and each constituted, in the new state of the tire, by an alternation of external cavities (61, 62), open on the tread surface 3, and internal cavities (71, 72), hidden inside the tread 2, two consecutive external (61, 62) and internal (71, 72) cavities respectively being connected to each other.Of the six complex circumferential cutouts (41, 42), two are edge complex circumferential cutouts 41, axially furthest from the tread 2, i.e., furthest from a median circumferential plane XZ perpendicular to the axis of rotation of the tire and passing through the middle of the tread 2, and four are intermediate complex circumferential cutouts 42. Each complex circumferential cutout (41, 42), whether edge or intermediate, has an axial width Ld, measured on the tread surface 3 between two walls (81, 82) of said complex circumferential cutout (41, 42) and variable along the circumferential direction XX'. In the embodiment shown in the figure. figure 1Each of the two complex circumferential edge cutouts 41 has a strictly planar axially external wall 81, such that the intersection of said wall 81 with the tread surface 3 forms a straight trace 811, i.e., one whose axial variation amplitude A is zero. Furthermore, the edge rib 51, delimited by said complex circumferential edge cutout 41 and a tread edge 21, has an axial width Ln at least equal to 5% and at most equal to 25% of the axial width L of the tread 2.

[0025] There figure 2 is a top view detailing a portion of the tread edge of a tire according to the embodiment of the figure 1 As seen in the description of the figure 1The complex circumferential edge cut 41 has a strictly planar axially external wall 81, with a strictly straight trace 811 on the tread surface 3. Furthermore, the complex circumferential edge cut 41 has a non-substantially planar axially internal wall 81, such that the intersection of said wall 81 with the tread surface 3 forms a wavy trace 811, the axial variation amplitude of which A is strictly greater than 2% of the axial width L of the tread 2. Consequently, the complex circumferential edge cut 41 is asymmetrical with respect to its mean circumferential line Cm.

[0026] There figure 3is a meridional cross-sectional view B-B', in a meridian plane YZ, of a complex circumferential edge cut 41 comprising an axially external planar wall 81, at the level of an external cavity 61, open on the tread surface 3. The wall 81 cuts the tread surface 3 along a trace 811. The complex circumferential edge cut 41 has an axial width Ld and axially delimits inwards an edge rib 51, the latter being axially delimited outwards by a tread edge 21.

[0027] There figure 4 is a meridional cross-sectional view C-C', in a meridian plane YZ, of a complex circumferential cut of edge 41 comprising an axially external flat wall 81, at the level of an internal cavity 71, not directly open on the rolling surface 3 and connected to it by an incision 711.

[0028] The inventors have more specifically studied this invention for a tire of size 315 / 70 R22.5, intended to equip a steering axle for a heavy goods vehicle and having a load capacity of 4000 kg for an inflation pressure of 9 bars.

[0029] Table 1 below presents the comparative characteristics of a tire according to invention I and a reference tire R: [Table 1] Features R I Comments Tread width L 269 ​​mm 269 ​​mm Number of complex circumferential cutouts 0 6 Reference tire R having open circumferential cutouts Type of complex circumferential cutouts having only one of its two walls substantially flat (edge, intermediate) N / A 2 Two complex circumferential cutouts with edge 41 having a flat outermost axial wall 81 Axial variation amplitude A of the substantially flat wall 81 N / A 0 mm Wall 81 is perfectly flat Axial width Ln of the edge rib 51 55 mm 50 mm Ln / L=19%, between 5% and 25%

Claims

1. Tyre (1) for a heavy-duty vehicle comprising a tread (2), intended to come into contact with the ground via a tread surface (3), having an axial width (L), measured in an axial direction (YY') of the tyre between a first and a second tread edge (21), - said tread (2) comprising at least one complex circumferential cut (41, 42), delimited by raised elements (51, 52), extending in a circumferential direction (XX') of the tyre, and consisting, when the tyre is new, of an alternation of external cavities (61, 62), which open onto the tread surface (3), and of internal cavities (71, 72), which are hidden inside the tread (2), two consecutive external cavities (61, 62) and internal cavities (71, 72), respectively, being interconnected, - the at least one complex circumferential cut (41, 42) having an axial width (Ld), measured on the tread surface (3) between two walls (81, 82) of said complex circumferential cut (41, 42) and variable in the circumferential direction (XX'), characterized in that at least one complex circumferential cut (61, 62) has only one of its two walls (81, 82) substantially planar, such that the intersection of said wall (81, 82) with the tread surface (3) forms a line (811, 821) the amplitude of axial variation (A) of which is at most equal to 2% of the axial width (L) of the tread (3).

2. Tyre (1) according to Claim 1, wherein the substantially planar wall (81, 82) of the at least one complex circumferential cut (61, 62) is strictly planar, such that the intersection of said wall (81, 82) with the tread surface (3) forms a line (811, 821) the amplitude of axial variation (A) of which is zero.

3. Tyre (1) according to either of Claims 1 and 2, wherein the at least one complex circumferential cut (61, 62) having only one of its two walls (81, 82) substantially planar is an axially outermost complex circumferential edge cut (61) of the tread (2), that is to say the furthest from a median circumferential plane (XZ) perpendicular to the axis of rotation of the tyre and passing through the middle of the tread (2).

4. Tyre (1) according to Claim 3, wherein the substantially planar wall (81) of the at least one complex circumferential edge cut (61) is the axially outermost wall (81).

5. Tyre (1) according to Claim 4, wherein the edge rib (51), delimited by said complex circumferential edge cut (61) and a tread edge (21), has an axial width (Ln) at most equal to 25% of the axial width (L) of the tread (2).

6. Tyre (1) according to either of Claims 4 and 5, wherein the edge rib (51), delimited by said complex circumferential edge cut (61, 62) and a tread edge (21, 22), has an axial width (Ln) at least equal to 5% of the axial width (L) of the tread (2).

7. Tyre (1) according to any one of Claims 1 to 6, wherein the tread (2) comprises at least three, preferably at least five, complex circumferential cuts (62) positioned between the two complex circumferential edge cuts (61).