Tire tread for heavy vehicle with improved resistance to attacks

Abstract

The present invention relates to a tire tread (1) for heavy vehicles and intended to improve its resistance to stone attacks. The tread (1) in a brand new state comprises at least one complex incision (5) comprising, along a bisector (Lm), an alternating arrangement of external cavities (6) opening onto the tread surface (2) and internal cavities (7) not opening onto the tread surface (2), two successive cavities respectively of external cavities (6) and of internal cavities (7) being connected to each other by a connecting channel (8) of non-zero length, the height (H11) of each external cavity (6) being at least equal to half the height (H) of the complex incision (5), the height (H3) of each connecting channel (8) being at most equal to one third of the height (H) of the complex incision (5).

Description

Technical Field

[0001] This invention relates to a tire tread for heavy-duty vehicles, and more specifically, to a tire tread for heavy-duty vehicles used for mixed purposes, which can travel on highways and asphalt roads as well as off-road on stony surfaces. Background Technology

[0002] The tread, made of at least one rubber-based material, is the wear portion of a tire, located on the outer periphery of the tire and worn down as it comes into contact with the ground. The tread typically includes a tread pattern, which is a combination of cuts (or gaps) and blocky (or rib-like) raised elements, primarily designed to ensure satisfactory grip performance, especially on wet surfaces.

[0003] As is well known, wet driving conditions for vehicles (especially heavy vehicles) require the rapid expulsion of water present in the contact patches between the tire tread and the road surface. This expulsion ensures that the materials that make up the tire tread are in direct contact with the road surface through the tread surface. Water that is not pushed to the front or side of the tire flows through or partially accumulates in the slits formed in the tread.

[0004] Water is drained through slits that form a fluid flow network that needs to be effective throughout the tire's lifespan, from brand new to maximum wear. Current regulations define maximum wear as the condition beyond which a tire must be removed from the vehicle for safety reasons.

[0005] More specifically, the cuts that allow water to drain are essentially wide cuts called grooves. When a tire is subjected to the recommended inflation and load conditions defined specifically by the European Standards Manual 2020 – Commercial Vehicle Tires, of the European Standards Organization (ETRTO), the width of the grooves ensures that the opposing walls of the material defining the grooves do not come into contact with each other when the tread enters the contact patch. The deformation of the raised elements defining the grooves under compression and shear determines the pressure in the contact patch in contact with the ground, and thus determines wear. Furthermore, these deformations affect rolling resistance due to hysteresis losses in the tread material, and therefore affect the vehicle's fuel consumption.

[0006] The tread may also include narrow slits or grooves. Under the tire load and pressure conditions specified by ETRTO (as described above), the width of the grooves is such that when the tread enters a contact patch, the opposing walls of the material defining the grooves are at least partially in contact with each other. The grooves do not expel water, but relative to grip, they have an edge corner effect in contact patches in contact with the ground, thus being particularly effective at disrupting water films present on the ground.

[0007] To limit the reduction in the volume of tread material to be worn due to the presence of grooves and sipes, so-called complex cuts have been proposed. Compared with normal cuts that open completely to the tread surface, complex cuts can increase the tread material volume while meeting a void volume for water storage above a given threshold, regardless of the tire's wear level.

[0008] Treads incorporating such complex cuts have been specifically described in documents WO 2011039194, WO 2011101495, WO2012130735, WO 2016188956, WO 2019008276, and WO 2019122677. When brand new, the complex cuts extend to the tread surface in a discontinuous manner at regular or irregular intervals. Each complex cut has an outer cavity that extends to the tread surface and is separated from each other in the main direction of the complex cut. The main direction of the complex cut generally corresponds to the direction in which water flows through the cut when driving on a water-covered surface. In addition to the outer cavities, the complex cut also includes inner cavities formed inside the tread and typically connected to the tread surface via sipes. These inner cavities are radially located entirely inside the tread surface in the brand-new condition and are situated between the outer cavities. The inner cavities can be located at different depth levels of the tread thickness. Furthermore, the continuity of water flow in each complex cut in a brand-new state is ensured by a connecting portion (typically a connecting channel) between two continuous cavities (an outer cavity and an inner cavity, respectively). Thus, the assembly consisting of the outer cavity, the inner cavity, and the connecting channel forms a continuous groove. In contrast, the juxtaposition of an inner cavity and an outer cavity that are not connected to each other and therefore do not allow fluid to flow from one cavity to another around the entire circumference of the tire does not constitute a continuous groove.

[0009] For treads with complex cuts, the volumes of all internal cavities, external cavities, and connecting channels are reduced compared to the volume of a groove that fully extends to the tread surface in the new condition and whose depth corresponds to the maximum depth of the internal or external cavities. Therefore, the presence of complex cuts can limit the reduction in tread stiffness in the new condition associated with the presence of grooves.

[0010] Tread patterns can simultaneously have complex cuts that intermittently extend to the tread surface and regular grooves that extend to the tread surface along their entire length.

[0011] When a tire is driven on a rocky surface, stones are likely to remain in the tread, especially in the grooves. These stones left in the grooves can cause perforations in the tread, which can damage the tire's crown reinforcement located radially inside the tread, and ultimately, the breakage of the crown reinforcement renders the tire unusable.

[0012] This stone trapping phenomenon is particularly noticeable in complex cuts. Specifically, complex cuts can trap stones in their external cavities, and more specifically, these stones may become trapped in the connecting channels between the external and internal cavities, thus damaging the tire tread. Summary of the Invention

[0013] Therefore, the inventors set their own goal as improving the stone-resistant properties of tire treads for heavy vehicles, which include complex cuts consisting of alternating outer cavities, inner cavities, and connecting channels between the outer and inner cavities.

[0014] This objective has been achieved through tire treads for heavy-duty vehicles, which are designed to contact the ground through their tread surfaces and include cutouts defining raised elements.

[0015] - The tread of a brand-new tire includes at least one complex cut, which includes alternating outer and inner cavities along a bisecting line. The outer cavity opens to the tread surface, while the inner cavity does not. Two consecutive cavities, the outer and inner cavities respectively, are connected to each other by a connecting channel.

[0016] Each external cavity has a height and a length on a bisecting plane that includes a bisector and a radial direction perpendicular to the tread surface. The height is measured radially between the tread surface and the bottom of the external cavity, and the length is measured along the bisector at the tread surface.

[0017] - Each internal cavity has a height and a length on the bisecting plane, the height being the height measured radially between the top of the internal cavity and the bottom of the internal cavity located radially inside the bottom of the external cavity, and the length being the length measured along the bisecting line at the bottom of the internal cavity.

[0018] Each connecting channel has a height and a length on the bisecting surface, the height being the height measured radially between the circumferential junction of the outer cavity and the connecting channel, and between the top and bottom of the connecting channel; the length being a non-zero length measured along the bisecting line between the outer cavity and the inner cavity.

[0019] - Each complex cut has a height on the bisecting surface, the height being the radial height measured between the tread surface and the bottom of the internal cavity.

[0020] - The height of each external cavity is at least half the height of the complex incision.

[0021] - The height of each connecting channel is at most one-third the height of the complex cut.

[0022] Therefore, the present invention relates to a tread comprising at least one complex cut, the at least one complex cut being formed along a bisecting line by alternating outer cavities and inner cavities, the outer cavities opening to the tread surface and the inner cavities not opening to the tread surface, two consecutive cavities, the outer cavity and the inner cavity respectively, being connected to each other by a connecting channel, the connecting channel ensuring a gradual transition between the cavities (the outer cavity and the inner cavity respectively).

[0023] The bisectors of a complex tread pattern are not necessarily straight lines and can, for example, have a wavy or zigzag shape. Furthermore, the bisectors can extend in any direction: longitudinal, lateral, or diagonal. Conventionally, the longitudinal direction is the direction of the maximum dimension or length of the tread, the lateral direction is the direction of the intermediate dimension or width of the tread, and the radial direction is the direction of the minimum dimension or thickness of the tread. The diagonal direction has an intermediate overall orientation between the longitudinal and lateral directions. When the diagonal direction forms an angle of at most 45° with the longitudinal direction, it is called substantially longitudinal, and when the diagonal direction forms an angle of at most 45° with the lateral direction, it is called substantially lateral.

[0024] The complex cut creates continuous wavy grooves in a cross-section on a bisecting plane defined by its bisectors and a radial direction perpendicular to the tread surface. These grooves include alternating outer cavities, inner cavities, and connecting channels between two consecutive outer and inner cavities, respectively. In other words, two consecutive outer cavities are separated along the bisectors by a single inner cavity, and vice versa. Due to the circumferential undulation of the complex cut across the tread thickness, the bottom of any inner cavity is radially located inside the bottom of the adjacent outer cavity.

[0025] The outer cavity, inner cavity, and connecting channel are characterized by their respective geometric dimensions defined on the bisecting plane of the complex cut, namely, a height measured radially in the tread thickness and a length measured along the bisecting line of the complex cut between two references depending on the portion of the complex cut under consideration. Each height can be defined relative to the height of the complex cut, which is the height measured between the tread surface in its new condition (to which the outer cavity leads) and the bottom surface passing through the bottom of the inner cavity (i.e., the radially innermost point of the complex cut). Within the scope of this invention, the height of each outer cavity is at least half the height of the complex cut, ensuring sufficient outer cavity volume necessary for water storage on wet surfaces when the tread is in its new condition. Furthermore, the length of any connecting channel is non-zero, ensuring a gradual transition between the cavities connected by the connecting channel (the outer cavity and the inner cavity, respectively).

[0026] The key feature of this invention is limiting the height of the connecting channel, which is measured at the junction of the channel and the external cavity (in other words, at its cross-section leading to the external cavity). According to the invention, this height is optimized to prevent excessively large stones (i.e., stones that could cause significant damage to the tire crown) from passing through. The inventors have estimated a critical stone size characterized by a diameter greater than one-third of the height of the complex cut; therefore, the height of the connecting channel at its junction with the external cavity is at most equal to one-third of the height of the complex cut.

[0027] Preferably, the height of each connecting channel is at least one-tenth the height of the complex cut. Below this value, due to excessive contraction of the complex cut at the connecting channel, the water flow rate in the complex cut becomes insufficient to ensure adequate tread grip on wet surfaces.

[0028] Advantageously, the height of each outer cavity is at most three-quarters the height of the complex cut. This maximum outer cavity height ensures a sufficient thickness of rubber-based material radially inside the outer cavity to protect the crown reinforcement located radially inside the tread and vertically aligned with the outer cavity.

[0029] Advantageously, the length of each connecting channel is at least equal to the height of the connecting channel. If the connecting channel is long enough (i.e., if the connecting channel provides contraction over a sufficient distance), the connecting channel can effectively block stones captured by the external cavity to which it is connected.

[0030] Advantageously, the height of each internal cavity is at least one-third the height of the complex cut. This minimum internal cavity height ensures sufficient external cavity volume for water storage on wet surfaces when the tread reaches the wear level corresponding to the top of the internal cavity—in other words, when the internal cavity is worn and then opens to the tread surface.

[0031] Advantageously, the height of each internal cavity is at most three-quarters the height of the complex cut. This maximum internal cavity height ensures a certain thickness of rubber-based material radially outside the internal cavity, sufficient, in a brand-new condition, to protect the crown reinforcement located radially inside the tread and vertically aligned with the internal cavity.

[0032] The ratio between the length of the internal cavity and the length of the external cavity is advantageously at least 0.8. Below this value, the length of the external cavity becomes excessive and negatively impacts the volume of material to be worn.

[0033] The ratio between the length of the internal cavity and the length of the external cavity is also advantageously at most 1.5, preferably at most 1.2. Beyond this value, the length of the external cavity becomes insufficient to ensure adequate collection of water present on the ground.

[0034] According to a preferred embodiment of the internal cavity variant, due to technical limitations in manufacturing the external cavity by forming it from the outside of the tread, the top of the internal cavity of each internal cavity extends radially outward through a sipe to the tread surface.

[0035] According to a variant of the outer cavity implementation, the bottom of each outer cavity extends radially inward through at least one sipe to the bottom surface of the inner cavity. At least one sipe appears when the tread wears down to the bottom of the outer cavity; this sipe enhances grip by creating an edge corner effect that disrupts the water film present on the ground, particularly on wet surfaces.

[0036] According to a preferred embodiment of the tread, at least one bisector of the complex cut is substantially longitudinal, and the bisector forms an angle of at most 45°, preferably at most 20°, relative to the longitudinal direction of the tread at any point. In other words, the bisector is preferably oriented in the longitudinal direction, which is the direction of the tire's forward travel and the main flow direction of water discharged from the contact patch in contact with the ground.

[0037] According to a variant of a preferred embodiment of the tread, at least one complex cutout having substantially longitudinal bisectors is located axially in the central portion of the tread, the axial width of which is at most two-thirds of the axial width of the tread, the central portion being centered on a central plane that passes through the middle of the tread surface and is perpendicular to the tread surface. When the tire is inflated and compressed under the pressure and load conditions recommended by ETRTO standards, the axial width of the tread is the axial distance between the axial ends of the tread surface. The advantage of having a complex cutout in the central portion of the tread compared to conventional grooves is that it reduces the surface area of ​​the cutout leading to the tread surface, and thus reduces the risk of stone trapping, as this central portion, characterized by a high contact pressure distribution, is known to have a strong ability to trap stones. Specifically, this central portion is characterized by a larger radial radius, so the relatively flat outer profile does not allow for hinge effects (hinge effects that can release stones trapped on the road surface). Additionally, this central portion corresponds to the high-stiffness portion of the tire crown.

[0038] The present invention also relates to a tire for heavy-duty vehicles, the tire comprising the tread described in any of the above embodiments. Attached Figure Description

[0039] Schematic representation drawn out of scale Figure 1 and Figure 2 Description of the features of the present invention:

[0040] - Figure 1A top view of the tread in its brand-new state according to the present invention.

[0041] - Figure 2 A cross-sectional view of a portion of a complex cut on the equally divided plane of the complex cut, the complex cut including an outer cavity, an inner cavity, and connecting channels connecting them. Detailed Implementation

[0042] Figure 1 This is a top view of the tread 1 in its brand-new state according to the invention. The tire tread 1, intended to contact the ground through the tread surface 2, includes cuts 3 defining raised elements 4. In the cuts 3 shown, there are two distinct, substantially longitudinal grooves, each defining a side rib and a central portion 11, the central portion 11 having an axial width Wm in the lateral direction YY' of the tread that is at most two-thirds of the axial width W of the tread. The central portion 11 further includes two substantially longitudinal complex cuts 5, each complex cut 5 separating two longitudinally arranged block-shaped raised elements 4, the raised elements 4 being separated in pairs by sipes. Each complex cut 5 includes alternations of an outer cavity 6 and an inner cavity 7 along the bisector Lm, the outer cavity 6 opening to the tread surface 2, and the inner cavity 7 not opening to the tread surface 2, the two consecutive cavities (outer cavity 6 and inner cavity 7, respectively) connected to each other by a connecting channel 8. The inner cavity 7 and the connecting channel 8, which are not visible when the tread is brand-new, are shown in dashed lines. In the illustrated embodiment, the bisector Lm of each complex cut 5 has a substantially longitudinal zigzag shape, and the tangent of the bisector Lm at any point forms an angle of at most 45° with the longitudinal direction XX' of the tread, preferably at most 20°.

[0043] Figure 2 A cross-sectional view of a portion of a complex cut 5 on the bisecting plane Sm, the complex cut 5 including an outer cavity 6, which is connected to an inner cavity 7 at each end via connecting channels 8. Only half of the inner cavity 7 is shown at each end of the outer cavity 6. The outer cavity 6 has a height H11 and a length L1 on the bisecting plane Sm containing the bisecting line Lm and the radial direction ZZ' (which is perpendicular to the tread surface 2 of the tread 1), the height H11 being the height measured along the radial direction ZZ' between the tread surface 2 and the bottom 62 of the outer cavity, and the length L1 being the length measured along the bisecting line Lm at the tread surface 2. Each internal cavity 7 has a height H22 and a length L2 on the bisecting surface Sm, wherein the height H22 is the height measured in the radial direction ZZ' between the top 71 and the bottom 72 of the internal cavity (which is located radially inside the bottom 62 of the outer cavity), and the length L2 is the length measured along the bisecting line Lm at the bottom 72 of the internal cavity. Figure 2Two half-cavities 7 of length L2 / 2 are shown. Each connecting channel 8 has a height H3 and a length L3 on the bisecting plane Sm, wherein the height H3 is the height measured in the radial direction ZZ' between the circumferential joint between the outer cavity 6 and the connecting channel 8, between the top 81 and the bottom 82 of the connecting channel, and the length L3 is a non-zero length measured along the bisecting line Lm between the outer cavity 6 and the inner cavity 7. Furthermore, each complex cut 5 has a height H on the bisecting plane Sm, wherein the height H is the height measured in the radial direction ZZ' between the tread surface 2 and the bottom 72 of the inner cavity. The height H11 of each outer cavity 6 is at least half the height H of the complex cut 5. According to the invention, the height H3 of each connecting channel 8 is at most one-third the height H of the complex cut 5. In the illustrated embodiment, the outer cavity 6 has an outer cavity bottom 62 that extends radially inward through a groove 63 until it passes through the bottom surface 10 of the inner cavity bottom 72. In addition, each internal cavity 7 has an internal cavity top 71, which extends radially outward through a sipe 73 to the tread surface 2.

[0044] The inventors have studied the invention more specifically for a 13R 22.5 tire, which, according to the ETRTO Standard Manual 2020, is designed to be mounted on the steering axle of a mixed-use heavy vehicle and is designed to carry a load of 4000 kg and an inflation pressure of 8.75 bar.

[0045] Table 1 below shows the characteristics of the tested tread:

[0046] [Table 1]

[0047]

[0048]

Claims

1. A tire tread (1) for heavy vehicles, the tire tread (1) being intended to contact the ground through the tread surface (2) and including a cut (3) defining a raised element (4). - The tread (1) in its brand-new condition includes at least one complex cut (5), which includes alternating outer cavities (6) and inner cavities (7) along a bisecting line (Lm). The outer cavity (6) leads to the tread surface (2), and the inner cavity (7) does not lead to the tread surface (2). The two consecutive cavities, the outer cavity (6) and the inner cavity (7), are connected to each other by a connecting channel (8). - Each external cavity (6) has a height (H11) and a length (L1) on a bisecting plane (Sm) containing a bisecting line (Lm) and a radial direction (ZZ') perpendicular to the tread surface (2), wherein the height (H11) is the height measured in the radial direction (ZZ') between the tread surface (2) and the bottom (62) of the external cavity, and the length (L1) is the length measured along the bisecting line (Lm) at the tread surface (2). - Each internal cavity (7) has a height (H22) and a length (L2) on the bisecting plane (Sm), the height (H22) being the height measured in the radial direction (ZZ') between the top (71) of the internal cavity and the bottom (72) of the internal cavity located radially inside the bottom (62) of the external cavity, and the length (L2) being the length measured along the bisecting line (Lm) at the bottom (72) of the internal cavity. - Each connecting channel (8) has a height (H3) and a length (L3) on the bisecting plane (Sm), the height (H3) being the height measured in the radial direction (ZZ') between the circumferential joint between the outer cavity (6) and the connecting channel (8), and the length (L3) being the non-zero length measured along the bisecting line (Lm) between the outer cavity (6) and the inner cavity (7). - Each complex cut (5) has a height (H) on the bisecting plane (Sm), which is the height measured in the radial direction (ZZ') between the tread surface (2) and the bottom of the internal cavity (72). - The height (H11) of each external cavity (6) is at least half the height (H) of the complex incision (5). Its features are, The height (H3) of each connecting channel (8) is at most one-third of the height (H) of the complex cut (5), the tread (1) having an axial width (W), wherein at least one complex cut (5) having a substantially longitudinal bisector (Lm) is located axially in the middle portion (11) of the tread, the axial width (Wm) of the middle portion (11) being at most two-thirds of the axial width (W) of the tread, the middle portion (11) being centered on a median plane (XZ) that passes through the middle of the tread surface (2) and is perpendicular to the tread surface (2).

2. The tread (1) according to claim 1, wherein, The height (H3) of each connecting channel (8) is at least one-tenth the height (H) of the complex cut (5).

3. The tread (1) according to any one of claims 1 and 2, wherein, The height (H11) of each external cavity (6) is at most three-quarters the height (H) of the complex incision (5).

4. The tread (1) according to any one of claims 1 and 2, wherein, The length (L3) of each connection channel (8) is at least equal to the height (H3) of the connection channel (8).

5. The tread (1) according to any one of claims 1 and 2, wherein, The height (H22) of each internal cavity (7) is at least one-third the height (H) of the complex cut (5).

6. The tread (1) according to any one of claims 1 and 2, wherein, The height (H22) of each internal cavity (7) is at most three-quarters the height (H) of the complex incision (5).

7. The tread (1) according to any one of claims 1 and 2, wherein, The ratio between the length (L2) of the inner cavity (7) and the length (L1) of the outer cavity (6) is at least 0.

8.

8. The tread (1) according to any one of claims 1 and 2, wherein, The ratio between the length (L2) of the inner cavity (7) and the length (L1) of the outer cavity (6) is at most 1.

5.

9. The tread (1) according to any one of claims 1 and 2, wherein, Each internal cavity (7) has an internal cavity top (71) that extends radially outward through a sipe (73) to the tread surface (2).

10. The tread (1) according to any one of claims 1 and 2, wherein, Each outer cavity (6) has an outer cavity bottom (62) that extends radially inward through at least one groove (63) to a bottom surface (10) that passes through the inner cavity bottom (72).

11. The tread (1) according to any one of claims 1 and 2, wherein, At least one of the bisectors (Lm) of the complex cut (5) is substantially longitudinal, and the bisector (Lm) forms an angle of at most 45° relative to the longitudinal direction (XX') of the tread at any point.

12. A tire for heavy vehicles, the tire comprising a tread (1) according to any one of claims 1 to 11.

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