Heavy-duty tire tread for heavy vehicles with improved robustness

Abstract

The present invention relates to a tire tread for heavy vehicles and aims to improve the pull-out resistance of oblique cuts opening into its external cavities. The tread (1) comprises at least one substantially longitudinal cut (3) including at least one external cavity (6) open onto the tread surface (2) with a through-section (7) having a closed contour (8). Each external cavity (6) is connected to two substantially longitudinal cuts (91) and to at least one oblique cut (92) having a mean trace (M2) intersecting the contour (8) at a connection point (I).According to the invention, the average trace (M2) of each oblique incision (92) forms an angle (A1, A2) strictly greater than 90° with at least two lines (T1, T2), tangent to the contour (8) respectively at two points (I1, I2) of the contour (8) positioned on either side of the average trace (M2) and at a curvilinear distance (d1, d2) from the point of connection (I) of at most 2 mm. Figure for the abstract: Fig.2.

Description

Title of the invention: Improved robustness tire tread for heavy-duty vehicles

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

[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 further comprises a tread pattern, which is a combination of cutouts, or grooves, and raised elements, designed to ensure satisfactory grip performance, particularly on wet pavement.

[0003] A tread can be geometrically defined by three dimensions: a smaller dimension along a radial direction, or thickness; an intermediate dimension along a transverse direction, or width; and a larger dimension along a longitudinal direction, or length. By convention, the thickness is the distance, measured along a radial direction, between the tread surface and a base surface, defined as a surface parallel to the tread surface and tangent to the deepest groove. The width is the distance between the transverse ends of the tread surface. The length is equal to the outer circumference of the tire.

[0004] A tread is often characterized by a volumetric notch ratio, defined as the ratio between the groove volume and the total tread volume, this total volume being measured between the tread surface and the base surface without taking the grooves into account. For prior art tires for heavy-duty vehicles, the volumetric notch ratio is generally between 10% and 25% for a tire in its new condition, before driving.

[0005] 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 the 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.

[0006] Water drainage is ensured by the cutouts which form a fluid flow network that should preferably be permanent, i.e., efficient throughout the tire's lifespan, from its new condition to its maximum wear level. The maximum wear level, as defined by current regulations, is the point at which the tire must be removed from the vehicle for safety reasons.

[0007] 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 2020 - Commercial Vehicle Tyres".

[0008] 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.

[0009] To limit the reduction in the volume of material of the tread resulting from the presence of grooves, it has been proposed to propose so-called complex cutouts which allow, compared to usual grooves, which are fully open on the tread surface, to increase the volume of material of the tread while respecting the volume of hollows for water storage beyond a determined threshold, regardless of the level of wear of the tire.

[0010] Treads comprising such complex cutouts have been described in particular in documents WO 2011039194, WO 2011101495 and WO 2012130735. A complex cutout opens discontinuously, at regular or irregular intervals, onto the new tread surface. Each complex cutout has external cavities, open onto the tread surface and separated from one another. of the others in the principal direction of the complex cut. The principal direction of the complex cut corresponds to the direction of water flow within said cut when driving on a water-covered surface. This complex cut includes, in addition to the external cavities, internal cavities formed within the tread and generally connected to the running surface by grooves. These internal cavities are positioned radially and entirely within the running surface when new, and are interspersed between the external cavities. The internal cavities can be positioned at different depths within the tread thickness. Furthermore, the continuity of water flow, or more generally fluid flow, when new, within each complex cut is ensured by the connection between the external and internal cavities, respectively.The connections between the internal and external cavities thus form a continuous groove, regardless of the local orientation of the internal or external cavities. Conversely, the juxtaposition of internal and external cavities not connected to each other, and therefore not allowing fluid flow from one to the other over the entire circumference of the tire, does not constitute a continuous groove.

[0011] 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.

[0012] 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.

[0013] 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-duty 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.

[0014] Oblique incisions opening into the external cavities of complex cutouts are, however, often susceptible to tearing. For example, such tearing can occur on the treads of tires fitted to truck axles frequently subjected to lateral slippage stresses.

[0015] The inventors also set themselves the objective of improving the resistance to tearing of oblique incisions opening into external cavities of tire treads for heavy goods vehicles, in particular in those of complex cutouts.

[0016] This objective was achieved by a tire tread for heavy goods vehicles, intended to come into contact with a ground via a tread surface, comprising cutouts delimiting raised elements, and having a thickness, in a radial direction, between the tread surface and a base surface, -the tread comprising at least one substantially longitudinal cut, having, on the tread surface, an average trace whose tangent at every point forms an angle of no more than 45° with a longitudinal direction of the tread, -at least one substantially longitudinal cut comprising at least one external cavity open to the rolling surface along a through section having a closed contour, -each external cavity being connected by two substantially longitudinal incisions, extending along the average trace of the substantially longitudinal cut and intersecting the contour at two points of connection, -the opening section of each external cavity having a length, measured along a first straight line passing through the two connection points, and a width at most equal to the length and measured along a second straight line perpendicular to the first line, -at least one oblique incision opening into each external cavity and having, on the rolling surface, a mean trace not parallel to the first straight line and cutting the contour at a point of connection, -the average trace of each oblique incision forming an angle strictly greater than 90°, with at least two tangent lines to the contour respectively at two points of the contour, positioned on either side of the average trace of the oblique incision and at a curvilinear distance from the point of connection of at most 2 mm.

[0017] The tread for a heavy-duty vehicle, intended to come into contact with the ground via a tread surface, comprises cutouts delimiting raised elements and extends between the tread surface and a base surface. In the context of the invention, the tread surface is considered to be in the new condition of the tire before any use in driving. The base surface is a surface parallel to the tread surface and tangent to the bottom of the deepest cutout. The distance between the tread surface and the base surface defines the tread thickness in the new condition of the tire, i.e. the thickness of material to be worn.

[0018] The tread comprises at least one substantially longitudinal cut, having an average trace whose tangent at every point forms an angle of at most 45° with a longitudinal direction of the tread. The average trace of a cut is defined as the intersection between an average surface of the cut perpendicular to the tread and the tread. A substantially longitudinal direction forms an angle between 0° and 45°. A zero angle defines a strictly longitudinal direction. Beyond 45°, the direction is said to be substantially transverse. By way of example, a substantially longitudinal cut may have a straight, zigzag, or wavy average trace.

[0019] At least one substantially longitudinal cut comprises at least one external cavity open to the tread surface with a through-section having a closed contour. By external cavity is meant all or part of a cut, open to the tread surface of the tire with a through-section in the new condition of the tire. The through-section has a closed contour, possibly with at least one local discontinuity corresponding to the connection with a cut.

[0020] Each external cavity is connected by two substantially longitudinal incisions, extending along the average trace of the substantially longitudinal cut and intersecting the contour at two points of connection. In other words, a substantially longitudinal incision has an average trace coinciding with that of the substantially longitudinal cut. Most often, a substantially longitudinal incision connects two consecutive external cavities of the same substantially longitudinal cut. A point of connection is a point at which the substantially longitudinal incision opens into the external cavity.

[0021] The opening section of each external cavity has a length, measured along a first straight line passing through the two connection points, and a width at most equal to the length and measured along a second straight line perpendicular to the first. This length and width are measured on the tread surface of the tire when new. In other words, an opening section of an external cavity generally fits within a rectangular envelope having a longer side defining the length and a shorter side defining the width. However, in a particular embodiment, the length and width may be equal, which implies that the rectangular envelope of the opening section is then a square.

[0022] At least one oblique incision opens into each external cavity and has, on the rolling surface, a mean trace not parallel to the first straight line and intersecting the contour at a point of connection. By definition, an oblique incision is not parallel to a substantially longitudinal incision.

[0023] The essential characteristic of the invention is that the average trace of each oblique incision forms an angle strictly greater than 90°, with at least two tangent lines to the contour respectively at two points of the contour, positioned on either side of the average trace of the oblique incision and at a curvilinear distance from the point of connection not more than 2 mm.

[0024] According to the invention, the orientation of any oblique incision opening into an external cavity, and therefore of its average trace in the tread surface, is optimized to minimize the risk of this oblique incision being torn away during tire rolling. This optimization consists of having an angle greater than 90° between the average trace of the oblique incision and at least two tangents to the contour at two points on the contour, positioned on either side of the average trace of the incision and located near the point where the incision opens onto the contour. These points of tangency are positioned on either side of the point where the incision opens, within a curvilinear distance range of no more than 2 mm, these curvilinear distances being measured on the contour from the point where the incision opens.Such an obtuse angle implies that the portions of material between the oblique incision and the external cavity are relatively massive, and therefore less deformable, which reduces the risk of crack initiation at the oblique incision. However, there may be at least one point on the contour where the tangent to the contour forms an angle of less than 90° with the average trace of the oblique incision, i.e., an acute angle, which could potentially lead to localized tread detachment. Such highly localized and, a priori, small-scale detachment remains permissible within the scope of the invention.

[0025] Preferably, the average trace of each oblique incision forms an angle strictly greater than 90° with any line tangent to the contour at any point on the contour positioned at a curvilinear distance from the connection point of no more than 2 mm. In this preferred embodiment, no tangent to the contour at any point near the connection point can form an acute angle, which implies that the inventors aim, in this embodiment, for a total absence of tread detachment, even if very localized and of small dimensions.

[0026] Advantageously, the width of the opening section of each external cavity is at least 4 mm. Consequently, the length of the opening section of each external cavity is also at least 4 mm. Below 4 mm, the water storage capacity of the external cavity, when driving on a wet surface, is insufficient to guarantee adequate tire grip.

[0027] Advantageously, the width of the opening section of each external cavity is at most 17 mm. Above 17 mm, the probability of irregular wear patterns appearing on the contour of the external cavity becomes high.

[0028] Advantageously, the length of the opening section of each external cavity is at most equal to 10 times the width of said through section. Above this value, the through section, whose surface area becomes large, contributes to a significant decrease in the rigidity of the tread which can negatively impact wear and rolling resistance.

[0029] Advantageously, each external cavity has a depth, measured between the tread surface and a cavity bottom, at least equal to 0.25 times the tread thickness. The depth of the external cavity is the distance measured between the opening section and the bottom of the external cavity, more precisely between the deepest point of the external cavity and its orthogonal projection onto the tread surface. The tread thickness is the distance measured between the tread surface and the bottom surface, parallel to the tread surface and tangent to the bottom of the deepest cutout, more precisely between the point of tangency of the bottom surface with the bottom of the deepest cutout and its projection onto the tread surface. Below 0.At 25 times the tread thickness, the depth of the external cavity is insufficient to guarantee adequate water storage capacity for the external cavity when driving on wet surfaces, ensuring proper tire grip.

[0030] Advantageously, each external cavity has a depth, measured between the tread surface and a cavity bottom, that is at most equal to the tread thickness. Above this value, the depth of the external cavity results in a reduction in the thickness of the rubber-based layer, interposed between the tread surface and the crown reinforcement of the tire, and increases the risk of mechanical damage to the crown reinforcement by external objects.

[0031] Advantageously, each oblique incision has a thickness, measured between the two walls that delimit it, of at least 0.2 mm. This minimum value corresponds to a technological minimum related to the manufacturing technology of the incision by molding using a mold slat, generally metallic.

[0032] Advantageously, each oblique incision has a thickness, measured between the two walls that delimit it, of at most 1.2 mm. Above this value, the contact of the portions of material on either side of the incision is no longer guaranteed, hence local deformations on either side of the incision leading to an increase in the wear rate of the tread.

[0033] Advantageously, each oblique incision has a depth, measured between the rolling surface and a bottom of the incision, of at least 2 mm. Below 2 mm, the edge effect provided by the incision is insufficient to guarantee good adhesion, an edge being the intersection of a wall delimiting the incision with the rolling surface.

[0034] Advantageously, each oblique incision has a depth, measured between the bearing surface and the bottom of the incision, at most equal to the depth of the external cavity. Above this value, the portions of material delimited by the incision become too soft, which can increase the risk of local detachments.

[0035] According to a preferred orientation, the first line, along which the length of the opening section of each external cavity is measured, is parallel to a longitudinal direction of the tread, and the second line, along which the width of the opening section of each external cavity is measured, is parallel to a transverse direction of the tread. The longitudinal direction is the preferred direction for aligning the external cavities, along their longest dimension, because it corresponds to the direction of rolling and therefore the preferred direction of water flow.

[0036] In a preferred embodiment of the tread, the tread comprises at least two substantially longitudinal cutouts, at least one of which is a complex cutout comprising alternating external cavities, open to the tread surface, and internal cavities, concealed within the tread thickness in its new state and connected to the tread surface by a substantially longitudinal incision, said external and internal cavities respectively being connected to each other so as to form a continuous channel. As previously seen, the complex cutouts offer a number of technical advantages as described, for example, in documents WO 2011039194, WO 2011101495 and WO 2012130735.

[0037] The invention also relates to a tire for heavy goods vehicles comprising a tread according to any one of the embodiments described above.

[0038] The features of the invention are illustrated by schematic figures 1 to 8, which are not shown to scale: -[Fig.1]: Top view of a tread according to a first embodiment of the invention, -[Fig.2]: Top view of an external tread cavity according to a first embodiment of the invention, -[Fig.3]: Partial cross-sectional view of an external tread cavity according to a first embodiment of the invention, -[Fig.4]: Top view of a tread according to a second embodiment of the invention, -[Fig.5]: Top view of an external tread cavity according to a second embodiment of the invention, -[Fig.6]: Top view of a tread according to a third method of Implementation of the invention, comprising a complex longitudinal cut, -[Fig.7]: Cross-sectional view, at the level of an internal cavity, of a tread according to a third embodiment of the invention, comprising a complex longitudinal cut. -[Fig.8]: Cross-sectional view, at the level of an external cavity, of a tread according to a third embodiment of the invention, comprising a complex longitudinal cut.

[0039] Figure 1 is a top view of a tread according to a first embodiment of the invention. The tread 1, intended to come into contact with a ground via a running surface 2, comprises cutouts 3 and raised elements 4. Among the cutouts 3, five longitudinal cutouts, extending along a longitudinal direction XX', and cutouts oblique to the longitudinal direction XX' are distinguished. Among the longitudinal cutouts, the following are distinguished: -in two lateral parts of the tread 1, two longitudinal grooves fully open on the tread surface 2, -in two intermediate parts of the tread 1, two complex longitudinal cutouts, each consisting of external cavities 6 of hexagonal shape, connected to each other in pairs by longitudinal incisions 91, -in the central part of the tread 1, a longitudinal incision. In each external cavity 6 of a complex longitudinal cut open oblique incisions 92. Every external cavity 6 is open on the rolling surface 2 according to an opening section 7 having a closed contour 8.

[0040] Figure 2 is a top view of an external tread cavity according to the The first embodiment of the invention is shown in [Fig. 1]. The external cavity 6 is connected by two longitudinal incisions 91, extending along the average trace M1 of the longitudinal cut 3 and intersecting the contour 8 at two connection points J1 and J2. The average trace M1 of a longitudinal incision 91 is the line of intersection of its average surface, which is flat in the case shown, with the rolling surface 2. The opening section 7 of the external cavity 6 has a length B, measured along a first line DI passing through the two connection points J1 and J2, and a width A at most equal to the length B and measured along a second line D2 perpendicular to the first line DI. Two oblique incisions 92 open into the external cavity 6, each having, on the rolling surface 2, an average trace M2 not parallel to the first line DI and intersecting the contour 8 at a connection point I.The average trace M2 of an oblique incision 92 is the line of intersection of its average plane with the rolling surface 2. According to the invention, the average trace M2 of each oblique incision 92 forms an angle (Al, A2) strictly greater than 90°, with . at least two lines (Tl, T2) tangent to contour 8 respectively at two points (II, 12) of contour 8, positioned on either side of the average trace M2 of the oblique incision 92 and at a curvilinear distance (dl, d2) from the connection point I of at most 2 mm.

[0041] Figure 3 is a partial cross-sectional view of a tread according to the first embodiment of the invention, shown in Figure 1. The partial cross-section CC is made along the mean plane of the oblique incision 92 as shown in Figure 2. The distance between the tread surface 2 and the base surface 5 defines the thickness E of the tread. By convention, the base surface 5 is a surface parallel to the tread surface 2 and tangent to the bottom of the deepest cut (not shown). The base surface delimits the maximum thickness of wear material. The external cavity 6, open onto the tread surface 2 along the through section 7, has a depth P. The oblique incision 92 has a depth PI that is less than the depth P of the external cavity, which is itself less than the thickness E of the tread.

[0042] Figure 4 is a top view of a tread according to a second embodiment of the invention. Figure 4 differs essentially from Figure 1 in the shape of the external cavities 6, which have curvilinear contours 7, and in the distribution of the oblique incisions 92 in the tread 1. In addition, the lateral and medial parts of the tread contain oblique incisions that do not open into the external cavities 6.

[0043] Figure 5 is a top view of an external tread cavity according to the second embodiment of the invention, shown in Figure 4. Figure 5 differs essentially from Figure 2 in the shape of the external cavity 6, which has a curvilinear contour 7.

[0044] Figure 6 is a top view of a tread according to a third embodiment of the invention, comprising a complex longitudinal cut in its central part. The tread 1 comprises three longitudinal cuts 3, including two fully open longitudinal grooves positioned in the lateral parts, and a complex longitudinal cut positioned in the median plane XZ of the tread, dividing the latter into two equal parts. The complex longitudinal cut comprises an alternation of external cavities 61, open onto the tread surface 2, and internal cavities 62, concealed within the tread thickness E in its new state, said external cavities 61 and internal cavities 62 being connected to each other so as to form a continuous channel, shown in dashed lines.Longitudinal incisions 61, along the longitudinal direction XX' of the tread, open into the external cavities 61. Oblique incisions 92, relative to the longitudinal direction XX' of the tread, open into the external cavities 61 in orientations conforming to. the invention.

[0045] Figure 7 is a cross-sectional view, at the level of an internal cavity, of a tread according to the third embodiment of the invention, shown in Figure 6. The cross-section is made along the transverse plane II, perpendicular to the longitudinal direction XX', of Figure 6. This section shows in particular an internal cavity 62, hidden within the thickness E of the tread in its new state and positioned in the median plane of the tread, between the two longitudinal grooves 3 separating the raised elements 4 relative to the base surface 5, and connected to the tread surface 2 by a longitudinal incision 91.

[0046] Figure 8 is a cross-sectional view, at the level of an external cavity, of a tread according to the third embodiment of the invention, shown in Figure 6. The cross-section is made along the transverse plane ILII, perpendicular to the longitudinal direction XX', of Figure 6. This section shows in particular an external cavity 61, open to the tread surface 2 and positioned in the median plane of the tread, between the two longitudinal grooves 3 separating the raised elements 4 relative to the base surface 5.

[0047] The inventors have more particularly studied this invention for a heavy goods vehicle tire in the size 355 / 50 R 22.5, the tread of which includes external hexagonal cavities as shown in Figures 1 and 2.

[0048] Table 1 below presents the characteristics of the tested tread: [Tables 1] Specifications: Tread thickness E 1 14 mm; External cavity width A 6 13.5 mm; External cavity length B 6 23.3 mm; External cavity depth P 6 14 mm; Oblique incision thickness El 92 0.8 mm; Oblique incision depth PI 92 2.5 mm; First angle Al of oblique incision 92 105°; Second angle A2 of oblique incision 92 125°

[0049] The invention has been tested for a tire in the size 355 / 50 R 22.5, intended to carry a load equal to 4000 kg, for an inflation pressure equal to 9 bars, according to the "Standards Manual 2020" of the ETRTO standard.

[0050] During test runs carried out on customer vehicles, the in Researchers observed the pull-out resistance experienced by a tread comprising both a first set of oblique, open-ended cuts, according to the invention, with obtuse angles, and a second set of oblique, open-ended cuts, not according to the invention, with acute angles. They found that crack initiation at the junctions of the oblique cuts with the external cavities primarily affected the second set of oblique, open-ended cuts, not according to the invention, but not the first set of oblique, open-ended cuts, according to the invention. Consequently, they concluded that the pull-out resistance of the oblique cuts opening into external cavities was improved by choosing an optimized orientation for these cuts.

[0051] The tread according to the invention, developed for a conventional tire subjected to inflation pressure, can also be used for a non-pneumatic tire, but also for any non-pneumatic rolling assembly intended to equip a vehicle.

Claims

Demands

1. Tread (1) of a heavy-duty vehicle tire, intended to come into contact with a ground via a tread surface (2), comprising cutouts (3) delimiting raised elements (4), and having a thickness (E), in a radial direction (ZZ'), between the tread surface (2) and a base surface (5), -the tread (1) comprising at least one substantially longitudinal cut (3), having, on the tread surface (2), an average trace (Ml) whose tangent at every point forms with a longitudinal direction (XX') of the tread (1) an angle of at most equal to 45°, -at least one substantially longitudinal cut (3) comprising at least one external cavity (6) open onto the rolling surface (2) with a through section (7) having a closed contour (8), -each external cavity (6) being connected to two substantially longitudinal incisions (91), extending along the average trace (M1) of the substantially longitudinal cut (3) and cutting the contour (8) at two points of connection (J1, J2), -the open section (7) of each external cavity (6) having a length (B), measured along a first straight line (Dl) passing through the two connection points (Jl, J2), and a width (A) at most equal to the length (B) and measured along a second straight line (D2) perpendicular to the first straight line (Dl), -at least one oblique incision (92) opening into each external cavity (6) and having, on the rolling surface (2), a mean trace (M2) not parallel to the first straight line (Dl) and cutting the contour (8) at a connection point (I), characterized in that the average trace (M2) of each oblique incision (92) forms an angle (Al, A2) strictly greater than 90°, with at least two lines (Tl, T2) tangent to the contour (8) respectively at two points (II, 12) of the contour (8), positioned on either side of the average trace (M2) of the oblique incision (92) and at a curvilinear distance (dl, d2) from the point of connection (I) of at most 2 mm.

2. Tread (1) according to claim 1, wherein the average trace (M2) of each oblique incision (92) forms an angle (A1, A2) strictly greater than 90° with any straight line (T1, T2) tangent to the contour (8) at any point (II, 12) of the contour (8) positioned at a curvilinear distance (dl, d2) from the connection point (I) of at most equal to 2 mm.

3. Tread (1) according to any one of claims 1 or 2, wherein the width (A) of the through section (7) of each external cavity (6) is at least equal to 4 mm.

4. Tread (1) according to any one of claims 1 to 3, wherein the width (A) of the through section (7) of each external cavity (6) is at most equal to 17 mm.

5. Tread (1) according to any one of claims 1 to 4, wherein the length (B) of the through section (7) of each external cavity (6) is at most equal to 10 times the width (A) of said through section (7).

6. Tread (1) according to any one of claims 1 to 5, wherein each external cavity (6) has a depth (P), measured between the tread surface (2) and a cavity bottom (61), at least equal to 0.25 times the thickness (E) of the tread (1).

7. Tread (1) according to any one of claims 1 to 6, wherein each external cavity (6) has a depth (P), measured between the tread surface (2) and a cavity bottom (61), at most equal to the thickness (E) of the tread (1).

8. Tread (1) according to any one of claims 1 to 7, wherein each oblique incision (92) has a thickness (El), measured between the two walls (921) which delimit it, of at least 0.2 mm.

9. Tread (1) according to any one of claims 1 to 8, wherein each oblique incision (92) has a thickness (El), measured between the two walls (921) which delimit it, of at most 1.2 mm.

10. Tread (1) according to any one of claims 1 to 9, wherein each oblique incision (92) has a depth (PI), measured between the tread surface (2) and an incision bottom (922), of at least 2 mm.

11. Tread (1) according to any one of claims 1 to 10, wherein each oblique incision (92) has a depth (PI), measured between the tread surface (2) and an incision bottom (922), at most equal to the depth (P) of the external cavity (6).

12. Tread (1) according to any one of claims 1 to 11, in which the first straight line (D1), along which the length (B) of the through section (7) of each external cavity (6) is measured, is parallel to a longitudinal direction (XX') of the tread (1) and the second straight line (D2), along which the width (A) of the through section (7) of each external cavity (6) is measured, is parallel to a transverse direction (YY') of the tread (1).

13. Tread (1) according to any one of claims 1 to 12, wherein the tread (1) comprises at least two substantially longitudinal cuts (3) of which at least one is a complex cut comprising an alternation of external cavities (61), open on the tread surface (2), and internal cavities (62), hidden in the thickness (E) of the tread in its new state and connected to the tread surface (2) by a substantially longitudinal incision (91), said external (61) and internal (62) cavities respectively being connected to each other so as to form a continuous channel.

14. Heavy vehicle tire comprising a tread (1) according to any one of claims 1 to 13.

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