Heavy-duty vehicle tire with an improved wear tread

Abstract

The present invention aims to improve the resistance to irregular wear of a tire tread for a heavy vehicle, comprising at least three complex cutouts (31, 32, 33). According to the invention, they are arranged relative to each other, along a first direction (D1), such that the midpoint (I) of any external cavity (41) of a first cutout (31), interposed between a second and a third cutout (32, 33), is aligned, along a second direction (D2) with the respective midpoints (J, K) of the incisions (42) of the second and third cutouts (32, 33), and such that the midpoint (L) of any incision (42) of the first cutout (31) is aligned, along the second direction (D2), with the respective midpoints (M, N) of the external cavities (43) of the second and third cutouts (32, 33).Furthermore, the incisions (52) separating two consecutive blocks (51) are parallel to each other and distributed, along the first direction (D1), according to a constant average pitch (Pi). Abbreviated figure: Fig.1.

Description

Title of the invention: Heavy-duty vehicle tire with an improved wear tread

[0001] The present invention relates to a tire for heavy goods vehicles, intended for driving on tarmac roads, and more particularly to its tread.

[0002] A tread, located at the periphery of the tire and intended to wear down upon contact with the ground via a tread surface, is made of at least one rubber-based material. It generally includes a tread pattern that is a combination of cutouts, or grooves, and raised elements, designed in particular to ensure satisfactory grip performance, especially on wet pavement.

[0003] As is known, the driving conditions of a vehicle in wet weather, and more particularly those of a heavy goods vehicle, require rapid evacuation of water present in the contact area between the tire tread and the road surface. This evacuation ensures direct contact of the tread material with the road surface via the tread. Water that is not pushed forward or to the sides of the tire flows off or is partially captured in the grooves formed in the tread.

[0004] Water drainage is ensured by the cutouts that form a fluid drainage network which should preferably be permanent, that is to say, effective throughout the entire service life of the tire between its new condition and its maximum wear. The maximum wear, as defined by current regulations, is the condition at which the tire must be removed from the vehicle for safety reasons.

[0005] Heavy-duty vehicle tires generally have a relatively large available cavity volume in the contact area when new. Available cavity volume refers to the volume of cavities that can be filled by water present on the road surface. The cavity volume opening onto the tread surface is evaluated when the tire is subjected to recommended inflation and load conditions as defined, in particular, by the European standards of the European Tyre and Rim Technical Organization (ETRTO) in its "Standards Manual 2022 - Commercial Vehicle Tyres".

[0006] Among the cutouts, a distinction is made between incisions and grooves. Incisions are wide enough that the opposing material walls delimiting them come into at least partial contact with each other when the tread passes over the contact patch, under the tire load and pressure conditions specified by the ETRTO: this limits the deformation of the opposing material portions and therefore wear. In contrast, grooves, which are wider than incisions, delimit portions of material that can deform without coming into contact with each other when the tread passes over the contact patch. These deformations of the material portions, under compression and shear, contribute to increased tread wear.Furthermore, in the case of grooves, an increase in deformations generates an increase in hysteretic losses of the tread, therefore of rolling resistance and, consequently, higher fuel consumption.

[0007] To limit the reduction in the volume of material of the tread resulting from the presence of grooves, it has been proposed to use so-called complex cutouts which, compared to conventional 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 hollows for water storage beyond a determined threshold, regardless of the level of wear of the tire.

[0008] Treads comprising such complex cutouts have been described in particular in documents WO 2011039194 A1, WO 2011101495 A1, WO 2012130735 A1, WO 2020030667 A1 and WO 2020058622 A1. A complex cutout opens discontinuously, at regular or irregular intervals, onto the new running surface. Each complex cutout has external cavities, open onto the running surface and separated from each other in the principal direction of the complex cutout. The principal direction of the complex cutout corresponds to the direction of water flow in said cutout when rolling on a water-covered surface. This complex cutout comprises, in addition to the external cavities, internal cavities formed within the tread and generally connected to the running surface by incisions.These internal cavities are positioned radially and entirely within the new tread surface, and are sandwiched between the external cavities. The internal cavities can be positioned at various depths within the tread thickness. Furthermore, the continuity of water flow, or more generally fluid flow, in the new condition, within each complex cutout is ensured by the connection between the external and internal cavities. The connections between the internal and external cavities thus form a continuous groove, regardless of the local orientation of the internal or external cavities. In contrast, the juxtaposition of unconnected internal and external cavities... They, and therefore not allowing fluid to flow from one to the other over the entire circumference of the tire, do not constitute a continuous groove.

[0009] For a tread with complex cutouts, the volume of all the cavities, internal and external, is reduced compared to that of grooves that are fully open on the new tread surface and have a depth corresponding to the maximum depth of the internal or external cavities. The presence of complex cutouts thus limits the reduction in tread stiffness when new due to the presence of the grooves.

[0010] A tread pattern may include both complex cutouts, opening onto the tread surface intermittently, and conventional grooves, opening onto the tread surface along their entire length.

[0011] However, it has been observed that the mere presence of complex cutouts is insufficient to achieve the required level of traction and braking grip on certain heavy goods vehicles, and that it is advisable to combine these complex cutouts with oblique incisions, i.e., incisions inclined relative to the main direction of the grooves, opening onto the tread surface when new. These oblique incisions generate additional edge length in the tread surface, enabling a good level of traction and satisfactory grip in so-called "slippery" conditions, particularly on wet surfaces.

[0012] It has also been observed that irregular wear patterns appear on tire treads for heavy vehicles, which include complex cutouts. These irregular wear patterns generate vibrations while the vehicle is in motion, which can degrade comfort, particularly for tires mounted on the front axle. This degradation of ride comfort can lead to premature tire removal before complete wear. Furthermore, the presence of irregular wear patterns can result in complete wear of some parts of the tread, while other parts 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.

[0013] The causes of uneven wear are often linked to geometric singularities in the tread pattern that induce pressure differentials in the contact area of ​​the tire with the ground. These geometric singularities are inherent in the design choices of recent tread patterns, generally comprising a network of complex, substantially circumferential cuts and substantially transverse incisions generating heterogeneous tread blocks of different shapes and sizes.

[0014] Therefore, the inventors set themselves the objective of improving resistance to the uneven wear of a tire tread for a heavy vehicle, including complex circumferential cuts, consisting of an alternation of external and internal cavities, and transverse incisions, i.e. to delay as much as possible the appearance of forms of irregular wear on said tread.

[0015] This objective has been achieved by a tire for a heavy goods vehicle comprising a tread, intended to come into contact with a ground via a tread surface, comprising, along a first direction tangent to the tread surface, at least three exclusively complex cutouts, -each complex cut being constituted, at least in the new state of the tire, by an alternation of external cavities, open on the tread surface, and incisions, extended radially towards the inside of the tread by internal cavities, two consecutive external and internal cavities respectively being connected to each other, -two consecutive complex cuts being separated by a row of blocks placed two by two adjacent and separated by an incision opening at each of its two ends into external cavities of the two consecutive complex circumferential cuts, -the at least three complex cuts being two by two equidistant and arranged relative to each other, along the first direction, -such that the midpoint of the largest dimension of any external cavity of a first complex cut, interposed between a second and a third complex cut adjacent to said first complex cut, is aligned, along a second direction, with the respective midpoints of the incisions of the second and third complex cuts, closest to said external cavity of the first complex cut, -and in such a way that the midpoint of any incision in the first complex cut is aligned, along the second direction, with the respective midpoints of the largest respective dimensions of the external cavities of the second and third complex cuts, closest to said incision in the first complex cut, -and the incisions separating two consecutive blocks of the same row of blocks being parallel to each other, and distributed, along the first direction, according to a constant average pitch.

[0016] The invention is essentially characterized, on the one hand, by the alignment, along a second direction, of the respective media of the external cavities and the incisions of three consecutive complex cuts parallel to each other and oriented along a given first direction, and, on the other hand, by a circumferential distribution, according A constant pitch, with blocks in rows separating two consecutive complex cuts. This design allows for a homogeneous distribution of the blocks separating the complex cuts in both the first and second directions, ensuring a balanced distribution of ground contact pressures, which is favorable to the later appearance of irregular wear patterns.

[0017] Advantageously, the first direction along which any complex cut extends forms an angle of at most 70° with a circumferential direction. This condition therefore excludes complex cuts forming an angle of less than 30° with respect to the axial direction, that is to say, substantially transverse cuts.

[0018] Advantageously, the second direction forms an angle of at least 45° with the first direction. This angle defines the positioning of the mean line of the incision separating two blocks, relative to the edge of the external cavity, and consequently defines the angular sector of the portion of material delimited by the incision and the edge of the external cavity. Thus, the larger this angle, the less sharp the angular sector of the portion of material forms, which reduces the risk of local detachment at the edge of the external cavity, near its intersection with the incision.

[0019] Advantageously, the tread having an axial width, measured along an axial direction, between a first and a second edge of the tread, and each external cavity of a complex cutout having a smaller dimension called its width, measured on the tread surface between two walls of said external cavity, the width of any external cavity is at least equal to 2% and at most equal to 7% of the axial width of the tread. Within this range of values, the external cavity allows, on a wet surface, the evacuation of the quantity of water necessary for good grip. Moreover, the width of this cavity is small enough to provide a compact and rigid tread, whose low deformations limit energy dissipation and, consequently, rolling resistance.

[0020] Also advantageously, since each incision in a complex cutout has a smaller dimension called the width, measured on the bearing surface between two walls of said incision, the width of any incision is at most 2 mm. Below 2 mm, the walls of the incision no longer necessarily come into contact and no longer perform their function of locking and stiffening between the rows of blocks.

[0021] Advantageously, each incision separating two adjacent blocks in the same row of blocks has a smaller dimension called the width, measured on the bearing surface between two walls of said incision. The width of any incision is at most 2 mm. As seen previously, below 2 mm, the walls of the incision no longer necessarily come into contact and no longer perform their function of blocking and stiffening between the blocks of the same row.

[0022] According to a preferred embodiment of the invention, the first direction according which extends any complex cutout is circumferential. This is the optimal embodiment for using a tire according to the invention on the steering axle of a heavy goods vehicle.

[0023] According to a first advantageous embodiment of the preferred design with a first circumferential direction, the tread having an axial width, measured along an axial direction, between a first and a second edge of the tread, the at least three complex circumferential cutouts are distributed, along the axial direction, with a constant average axial pitch of at least 10% and at most 25% of the axial width of the tread. This range of axial pitch values ​​between two complex circumferential cutouts makes it possible to obtain a satisfactory compromise between the tread's durability and grip performance. Below 10%, the number of complex cutouts becomes too high, which limits the tread's durability, as it is then heavily cut and therefore more fragile.Beyond 25%, the number of complex cuts is insufficient for wet surface adhesion, as the water evacuation potential is limited, and insufficient for transverse adhesion on dry surface, as the edge effect of complex circumferential cuts is then limited.

[0024] According to a second advantageous embodiment of the preferred design with a first circumferential direction, the tread having a circumferential length, measured along the circumferential direction at the center of the tread surface, the constant average circumferential pitch between two consecutive cuts is at least 0.5% and at most 2% of the tread's circumferential length. The technical effect described with respect to the axial pitch of complex circumferential cuts is applicable to that of the circumferential pitch of transverse cuts between blocks. Thus, this range of circumferential pitch values ​​between two cuts makes it possible to obtain a compromise between the tread's durability and grip performance. Below 10%, the number of cuts becomes too high, which limits the tread's durability, as it is then heavily cut and therefore more fragile.Beyond 25%, the number of incisions is insufficient with regard to longitudinal adhesion, because the effect of the incision edges is then limited.

[0025] According to a preferred embodiment with a first circumferential direction, the tread comprises at least four, preferably five, complex circumferential cutouts. This configuration ensures a satisfactory compromise between grip and tread durability, particularly in terms of block tear-out resistance.

[0026] The features of the invention are illustrated by schematic figures 1 and 2, which are not drawn to scale: -[Fig.1]: Partial front view of a tire tread according to a preferred embodiment of the invention, -[Fig.2]: Circumferential cross-sectional view of a complex circumferential cut of a tread according to the preferred embodiment of the invention of [Fig.1].

[0027] Figure 1 is a partial front view of a tread 2 of a tire 1 according to a preferred embodiment of the invention. The tread 2, intended to come into contact with a ground via a tread surface 20, comprises, along a first circumferential direction DI tangent to the tread surface 20, three central complex circumferential cutouts (31, 32, 33), and two edge complex circumferential cutouts (not referenced in Figure 1). Each complex circumferential cutout (31, 32, 33) is formed, in the new state of the tire, by an alternation of external cavities 41, open onto the tread surface 20, and incisions 42, extended radially towards the interior of the tread 2 by internal cavities 43 (see Figure 2).Two consecutive external cavities 41 and internal 43 are connected. The width Wcc of any external cavity 41 is equal to 5% of the axial width W of the tread 2 for central complex circumferential cutouts, and to 2.5% of said axial width W for edge complex circumferential cutouts, therefore, in both cases, at least equal to 2% and at most equal to 7% of said axial width W. The width Wic of any incision 42 is equal to 0.6 mm, therefore at most equal to 2 mm. Two consecutive complex circumferential cutouts (31, 32, 33) are separated by a row of adjacent blocks 51, separated by an incision 52 opening at each of its two ends into external cavities 41 of the two consecutive complex circumferential cutouts. The width Wi of any incision 52 is equal to 0.4 mm, therefore at most equal to 2 mm. According to the invention, the three complex circumferential cuts (31, 32,33) are in pairs equidistant and arranged with respect to each other, along the first circumferential direction D1, such that the midpoint I of the largest dimension of any external cavity 41 of a first complex circumferential cut 31, interposed between a second and a third complex circumferential cut (32, 33) adjacent to said first complex circumferential cut 31, is aligned, along a second direction D2 with the respective midpoints (J, K) of the incisions 42 of the second and third complex circumferential cuts (32, 33), closest to said external cavity 41 of the first complex circumferential cut 31, and such that the midpoint L of any incision 42 of the first complex circumferential cut 31 is aligned, along the second direction D2, with the respective midpoints (M,N) of the largest respective dimensions of the external cavities 43 of the second and third complex circumferential cutouts (32, 33), the largest, close to said incision 42 of the first complex circumferential cut 31. According to the invention, the incisions 52 separating two consecutive blocks 51 of the same row of blocks are parallel to each other and distributed, along the first circumferential direction D1, at a constant average pitch Pi (see [Fig. 2]) equal to 0.9% of the circumferential length of the tread (not shown), therefore at least equal to 0.5% and at most equal to 2% of said circumferential length. The second direction D2 forms, with the first circumferential direction D1, an angle B equal to 80°, therefore at least equal to 45°. The three complex circumferential cutouts (31, 32, 33) are distributed, along the axial direction YY', according to a constant average axial pitch Pd equal to 16% of the axial width W of the tread 2, therefore at least equal to 10% and at most equal to 25% of said axial width W.

[0028] Figure 2 is a circumferential cross-sectional view of a complex circumferential cut in a tread 2 according to the preferred embodiment of the invention of Figure 1. The complex circumferential cut 31, adjacent to the complex circumferential cut 32, is formed, in the new state of the tire, by an alternation of external cavities 41, open onto the tread surface 20, and incisions 42, extended radially towards the interior of the tread 2 by internal cavities 43, two consecutive external cavities 41 and internal 43 being connected to each other. Figure 2 also shows, in circumferential cross-section, a row of blocks 51, two by two adjacent and separated by an incision 52 opening at each of its two ends into external cavities 41 of the two consecutive complex circumferential cuts.The incisions 52 separating two consecutive blocks 51 have a width Wi and are distributed, along the first circumferential direction Dl, according to a constant average pitch Pi. .

[0029] The inventors have more particularly studied this invention for a tire for heavy goods vehicles in the size 315 / 70 R 22.5.

[0030] Table 1 below presents the characteristics of the tread of the tire according to the invention shown in Figures 1 and 2 described above. [Tables 1] Characteristics I Comments Axial tread width W 269 mm Circumferential tread length 3187 mm Angle A of the first direction DI of a complex cut relative to the circumferential direction XX' 0° Less than 70° Mean pitch Pd between two consecutive complex circumferential cuts 43 mm 16% of W Axial width Wcc of an external cavity 41 of a complex circumferential cut 14 mm (center cut) and 7.2 mm (edge ​​cut) 5% of W and 2.5% of W Axial width Wic of a cut 42 of a complex circumferential cut 0.6 mm Less than 2 mm Mean pitch Pi between two cuts 52 separating two adjacent blocks 51 29.5 mm 0.9% of the circumferential tread length Angle B of a cut 52 separating two adjacent blocks 51 with respect to the circumferential direction XX' 80° Greater than 45° Axial width Wi of an incision 52 separating two adjacent blocks 51 XX' 0.4 mm Less than 2 mm

[0031] The rolling tests, carried out on the embodiment described above, showed a significant improvement in the robustness of the tread with respect to wear patterns, i.e. a later appearance of irregular wear patterns.

Claims

Claims

1. A tire (1) for a heavy goods vehicle comprising a tread (2), intended to come into contact with a ground via a rolling surface (20), comprising, in a first direction (Dl) tangent to the rolling surface (20), at least three exclusively complex cutouts (31, 32, 33), -each complex cutout (31, 32, 33) being constituted, at least in the new state of the tire, by an alternation of external cavities (41), open on the rolling surface (20), and incisions (42), extended radially towards the inside of the tread (2) by internal cavities (43), two consecutive external (41) and internal (43) cavities respectively being connected to each other, -two complex cutouts (31, 32,33) consecutive being separated by a row of blocks (51) two by two adjacent and separated by an incision (52) opening at each of its two ends into external cavities (41) of the two consecutive complex circumferential cutouts, characterized in that the at least three complex cutouts (31, 32, 33) are two by two equidistant and arranged relative to each other, in the first direction (D1), in such a way that the middle (I) of the largest dimension of any external cavity (41) of a first complex cutout (31), interposed between a second and a third complex cutout (32, 33) adjacent to said first complex cutout (31), is aligned, in a second direction (D2) with the respective middles (J, K) of the incisions (42) of the second and third complex cutouts (32, 33), closest to said external cavity (41) of the first complex cutout (31),and such that the middle (L) of any incision (42) of the first complex cutout (31) is aligned, along the second direction (D2), with the respective middles (M, N) of the respective largest dimensions of the external cavities (43) of the second and third complex cutouts (32, 33), closest to said incision (42) of the first complex cutout (31), and in that the incisions (52) separating two consecutive blocks (51) of the same row of blocks are parallel to each other, and distributed, along the first direction (D1), according to a constant average pitch (Pi).,

2. A tire according to claim 1 wherein the first direction (Dl) along which any complex cut (31, 32, 33) extends, forming, with a circumferential direction (XX'), an angle at most equal to 70°.

3. Tire according to one of claims 1 or 2 in which the second direction (D2) forms, with the first direction (D1), an angle (B) at least equal to 45°.

4. A tire according to any one of claims 1 to 3, the tread (2) having an axial width (W), measured in an axial direction (YY'), between a first and a second edge of the tread (21, 22), and each external cavity (41) of a complex cutout (31, 32, 33) having a smaller dimension called width (Wcc), measured on the tread surface (20) between two walls of said external cavity (41), wherein the width (Wcc) of any external cavity (41) is at least equal to 2% and at most equal to 7% of the axial width (W) of the tread (2).

5. A tire according to any one of claims 1 to 4, each incision (42) of a complex cutout (31, 32, 33) having a smallest dimension called width (Wic), measured on the rolling surface (20) between two walls of said incision (42), wherein the width (Wic) of any incision (42) is at most equal to 2 mm.

6. A tire according to any one of claims 1 to 5, each incision (52) separating two adjacent blocks (51) of the same row of blocks having a smaller dimension called width (Wi), measured on the rolling surface (20) between two walls of said incision (52), in which the width (Wi) of any incision (52) is at most equal to 2 mm

7. 111111. A tire according to any one of claims 1 to 6 wherein the first direction (Dl) along which any complex cutout (31, 32, 33) extends is circumferential.

8. A tire according to claim 7, the tread (2) having an axial width (W), measured in an axial direction (YY'), between a first and a second edge of the tread (21, 22), in which the at least three circumferential complex cutouts (31, 32, 33) are distributed, in the axial direction (YY'), according to a constant average axial pitch (Pd) at least equal to 10% and at most equal to 25% of the axial width (W) of the tread (2).

9. A tire according to one of claims 7 or 8, the tread (2) having a circumferential length, measured in the circumferential direction, (XX'), at the center of the tread surface (20), in which the constant average circumferential pitch (Pi) between two consecutive incisions (52) is at least equal to 0.5% and at most equal to 2% of the circumferential length of the tread (2).

10. A tire according to any one of claims 7 to 9 wherein the tread (2) comprises at least four, preferably five, complex circumferential cutouts (31, 32, 33).

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