Tire for a heavy construction vehicle with improved grip

Abstract

The present invention relates to a tire (1) for a heavy construction vehicle, and aims to improve the performance compromise between wear life, resistance to aggressions and the grip of its tread (2).According to the invention, the arrangement of the cutouts (3) evolves during tire wear, such that, for a maximum cutout depth (D) of at least 70% and at most 90% of the initial thickness (D0), the central portion (21) of the tread (2) comprises cutouts (3) of which none are effective, and every lateral portion (22, 23) of the tread (2) comprises at least one effective cutout (3), and such that, for a maximum cutout depth (D) of at least 20% and at most 40% of the initial thickness (D0), the central portion (21) of the tread (2) comprises exclusively transverse effective cutouts (32), and every lateral portion (22, 23) of the tread (2) comprises at least one effective cutout (3). Figure for the abstract: Fig. 1.

Description

Title of the invention: Tire for a heavy construction vehicle with improved grip

[0001] The present invention relates to a tire for a heavy construction vehicle, designed to carry heavy loads and to travel on uneven and stony ground such as that found in mines. This invention relates in particular to the tread of such a tire, the grip of which is satisfactory at all levels of tire wear.

[0002] The invention relates more particularly to a tire intended for use on heavy construction equipment, such as a dumper truck for transporting materials extracted from quarries or surface mines. A dumper truck is subjected to particularly harsh driving conditions: heavy loads, sustained speeds, inclines and curves, and uneven and stony ground. For example, at material extraction sites, such as ores or coal mines, the use of a dumper truck consists, in simplified terms, of alternating loaded outbound and empty return trips. During a loaded outbound trip, the loaded vehicle transports the extracted materials, mainly uphill, from loading areas at the bottom of the mine, or pit, to unloading areas: this requires good traction from the tires.During an empty return cycle, the empty vehicle returns, primarily downhill, to the loading areas at the bottom of the mine: this requires good tire braking grip. The tracks, which are often sloping, also frequently include curves, which necessitates good lateral tire grip. Furthermore, the tracks on which the vehicles travel are made of materials generally sourced from the mine, for example, crushed and compacted rock, to ensure the track's wear layer remains intact during vehicle traffic, and are regularly watered, resulting in them often being covered in mud and water.Therefore, it is necessary to allow, on the one hand, efficient evacuation of this mixture of mud and water through the tread, to guarantee satisfactory grip on this muddy ground, and, on the other hand, good resistance to wear and damage from the stones present on the ground.

[0003] The specific use of a dumper, as previously described, entails a particular management of the tires equipping it.

[0004] When new, a tire is usually mounted on the front axle, or steering axle, of the vehicle. At this front position, the load applied to the tire is generally estimated to be between 60% and 100% of its nominal load capacity. Depending on whether the vehicle is running empty or loaded, this nominal load capacity is defined by, for example, ISO 4250 and the Tire and Rim Association (TRA) standard. Within this load range, the contact between the tire and the ground is made across the entire width of the tire tread, and the tire is subjected to limited or even low longitudinal stress, but to high lateral stress due to tire slippage.

[0005] When the tire reaches approximately one-third of its wear, that is, when the thickness of its tread is reduced by one-third compared to its initial thickness when new, the tire is removed from the front axle and mounted on a rear axle, or drive axle, of the vehicle, to wear the remaining two-thirds of the tread. At this rear position, the load applied to the tire is generally estimated to be between 30% and 100% of its nominal load capacity, depending on whether the vehicle is traveling empty or loaded. In the lower part of this load range, corresponding to traveling empty, the contact between the tire and the ground is made over only a portion of the tread width.At this rear position, the tire is subjected to a significant longitudinal force (engine and brake), even when unloaded when only a central or median portion of the tread surface is in contact with the ground, and a low transverse force.

[0006] Finally, the tire is permanently removed from the drive axle when its tread reaches a residual thickness corresponding to a totally worn state in accordance with current practices.

[0007] A tire tread, intended to form the peripheral part of the tire, usually comprises at least one rubber-based material and is intended to be worn when it comes into contact with a ground via a tread surface.

[0008] Typically, the following is referred to as: - Radial direction: a direction perpendicular to the axis of rotation of the tire, - Axial or transverse direction: a direction parallel to the axis of rotation of the tire. -circumferential or longitudinal direction: a direction tangent to the periphery of the tire and perpendicular to the radial and axial directions respectively, -medial or equatorial circumferential plane: a plane containing the radial direction and the circumferential direction, perpendicular to the axis of rotation of the tire and dividing the tire into two equal portions.

[0009] The tread, for any state of tire wear, is geometrically characterized by an axial width, measured along the axial direction and called The width is defined simply as the width, and the radial thickness as the thickness, measured radially and also simply called the tread depth. The width is conventionally defined as the width of the portion of the tread surface in contact with a smooth surface, with the tire mounted on a recommended rim and subjected to the nominal pressure and load conditions recommended by standard specifications. The thickness is conventionally defined as the maximum depth measured in the grooves, also called the maximum groove depth. In other words, the tread depth corresponds to the thickness of the material of the raised element delimited by the deepest groove and is equal to the maximum groove depth.In the case of a tire for a construction vehicle, when new (i.e., before being driven on), and as an example, the new width (or initial width LO) is at least 600 mm and the new tread depth (or initial tread depth DO), defined as the maximum initial cut depth, is at least 60 mm, or even 70 mm. However, the maximum width and maximum cut depth characteristics vary depending on the tire's wear. In particular, the maximum cut depth varies between a maximum initial cut depth DO, when the tire is new, and a maximum residual cut depth DR, when the tire is worn, which is the value at which the tire is removed from the vehicle in accordance with current practices.

[0010] To ensure satisfactory performance in longitudinal grip, under engine torque and under braking torque, as well as in transverse grip, it is necessary to form, in the tread, a sculpture which is a system of cutouts separating raised elements.

[0011] A cutout is a space delimited by facing walls of material and spaced apart by a distance defining the width of the cut, and extending from the tread surface in a radial direction to a given depth. Depending on its width, measured perpendicular to its center line between the walls of the raised features it separates at the tread surface, a cut is either a notch or a groove. In the case of a notch, this width is suitable to allow at least partial contact between the opposing walls delimiting said notch, at least when the tread is in contact with the ground, when the tire is subjected to the recommended nominal load and pressure conditions, for example, those defined by the TRA standard. In the case of a groove, the walls of this groove generally do not come into contact with each other under these recommended nominal driving conditions.

[0012] The cutouts delineate raised elements of the block or rib type. A block comprises a contact face, contained within the tread surface, and at least three, and most often four, lateral faces cutting into the tread surface. A rib comprises a contact face and two lateral faces extending, in the circumferential direction, along the entire length of the tread. A rib is thus delimited, in the axial direction, by one or two longitudinal cutouts.

[0013] The proportion of cuts contained in the tread or in a portion of the tread can be defined, for any state of wear, by a volumetric notch ratio TEV or by a surface notch ratio TES.

[0014] By definition, the volumetric notch ratio (TEV) of the tread, for a given wear state, is equal to the ratio between the total volume (VD) of the cuts, measured on the tire when unmounted and uninflated, and the sum of the total volume (VD) of the cuts and the total volume (VR) of the raised features delimited by these cuts. The sum (VD + VR) corresponds to the volume radially between the tread surface, at the given wear level, and a base surface, translated radially inward from the tread surface by a radial distance equal to the maximum cut depth. This volumetric notch ratio (TEV), expressed as a percentage, determines wear performance, through the volume of material available for wear, and longitudinal and transverse grip performance, through the presence of transverse and longitudinal edges, respectively, and cuts capable of storing or evacuating water and / or mud.

[0015] By definition, the tread area cut ratio TES, for a given wear condition, is defined in the contact area of ​​the tire with a rigid surface, when the tire, mounted on its nominal rim, is inflated to its nominal pressure and compressed under its nominal load, these nominal characteristics being recommended, for example, by the TRA standard. This tread area cut ratio TES is equal to the ratio between the total area SD of the cuts and the sum of the total area SD of the cuts and the total area SR of the raised features delimited by these cuts, the areas SD and SR being determined in the contact area. The sum SD+SR corresponds to the contact area.This surface notch ratio (TES), expressed as a percentage, determines wear performance, through the surface area of ​​material in contact with the ground impacting the distribution of pressures exerted by the ground on the rolling surface, and longitudinal and transverse grip performance, through the length of the respective transverse and longitudinal edges determining the effectiveness of the tread pattern indentation.

[0016] These volumetric TEV and surface TES notch ratios can be determined either in the new condition of the tread, before use of the tire in motion, or for a given state of tread wear, characterized by a maximum remaining cutting depth.

[0017] A tire tread for construction equipment typically includes cuts that may be longitudinal or transverse. A longitudinal cut has a centerline forming an angle of less than 45° with the longitudinal or circumferential direction of the tire and is characterized by extending around the entire circumference of the tire. The centerline may form a zero angle and be strictly longitudinal, or it may include at least one oblique portion forming a non-zero angle, for example, in the case of a cut that oscillates around the circumferential direction. A transverse cut has a centerline forming an angle greater than 45° with the longitudinal or circumferential direction of the tire and is characterized by crossing at least part of the tread.Generally, the width of a groove decreases progressively from the tread surface to the bottom of the groove, due to the inclination of the walls of the tread elements that define these grooves. However, a high volumetric groove ratio when new presents several disadvantages. First, it promotes the trapping and retention of stones in the grooves, which can damage the top of the tire through the cracks they potentially cause. Second, a high volumetric groove ratio when new implies a similarly high surface groove ratio, resulting in a relatively small contact area between the tread elements and the ground, and consequently, high ground pressures that exacerbate tread abrasion and therefore wear.Finally, a high volumetric notch ratio when new allows for lateral deformation, known as "barreling," of the raised elements due to the Poisson effect. This reduces the effective volume of the cutouts, which characterizes their capacity to store and evacuate water or mud, resulting in a loss of tire grip on muddy surfaces. However, these Poisson-effect deformations tend to decrease as tread wear increases, due to the reduction in the height of the raised elements.

[0018] In document WO 2022064134 A1, for a 24.00R35 tire intended for use on a construction vehicle, a system of grooves with widths that vary according to the tread wear level was proposed. The principle of this invention is to provide a tire for a heavy construction vehicle whose grip, particularly on wet and / or muddy ground, is guaranteed at any wear level. During the first third of wear, the tire is mounted on the front of the vehicle and is subjected to a load of at least 60%, for an empty vehicle, and at most 100%, for a fully loaded vehicle, of the recommended load Zn. During the last two-thirds of wear The remaining tires are mounted on the rear of the vehicle and are subjected to a load of at least 30%, for an unladen vehicle, and at most 100%, for a fully loaded vehicle, of the recommended load Zn. This invention aims more specifically to improve the performance compromise between wear life, resistance to damage, and tire grip. According to the invention, the tread has an axial width LO and comprises, on each side of an equatorial plane, at least one outer longitudinal groove at an axial distance LE of at least 0.5*L0 / 2, and at least one inner longitudinal groove at an axial distance LI of at most 0.4*L0 / 2. The at least one outer longitudinal groove comprises an outer radial portion opening onto the tread surface and having an average width of at least 0.6 times its height, and at least one internal longitudinal cutout includes an internal radial portion not opening onto the running surface and having an average width at least equal to 0.6 times its height.

[0019] The inventors have set themselves the objective of designing a tread for a tire for heavy construction vehicle, making it possible to further improve, compared to the aforementioned prior art, the performance compromise between wear life, resistance to aggressions and grip, when used on tracks that may be covered with water and mud, while guaranteeing the durability of grip throughout the life of the tire.

[0020] This objective is achieved, according to the invention, by a tire for a heavy construction vehicle comprising a tread comprising an arrangement of cutouts separating raised elements, -the tread having, in the new condition of the tire, an initial width, measured along an axial direction parallel to the axis of rotation of the tire and between two edges of the tread, and having an initial thickness, measured along a radial direction perpendicular to a tread surface and defined as the maximum initial cut depth, -the tread comprising a central portion extending symmetrically on either side of a median plane of the tire and having an initial median width equal to 50% of the initial width, and two lateral portions each extending from the central portion to a tread edge, -the cutouts being either longitudinal cutouts having a mean line forming, with a circumferential direction, an angle of less than 45°, or transverse cutouts having a mean line forming, with the circumferential direction, an angle greater than 45°, -a cut is said to be effective, at a given level of wear, when its width, measured perpendicular to its average line, at the level of wear considered, between the walls of the raised elements that it separates, at the level of the running surface, is at least equal to 25% of the initial thickness, -the arrangement of the cuts being evolving during the wear of the tire, such that, for a maximum cut depth of at least 70% and at most 90% of the initial thickness, the middle portion of the tread includes cuts among which none are effective, and every lateral portion of the tread includes at least one effective cut, and such that, for a maximum cut depth of at least 20% and at most 40% of the initial thickness, the middle portion of the tread includes exclusively transverse effective cuts, and every lateral portion of the tread includes at least one effective cut.

[0021] The principle of the invention is to have a tread that, at all levels of wear, maintains good performance in terms of wear resistance, resistance to damage, and grip; that is to say, to guarantee the continuity of these three essential performance characteristics throughout the tire's life, thanks to a tread pattern that evolves during wear. Thus, the contributions of the central and lateral portions of the tread to grip performance will vary according to the degree of tire wear.

[0022] According to a first essential feature of the invention, for a maximum cut depth of at least 70% and at most 90% of the initial thickness, the central portion of the tread comprises cuts, none of which are effective, and each lateral portion of the tread comprises at least one effective cut. In other words, at the beginning of wear, the central portion of the tread consists only of cuts that are considered ineffective from the point of view of grip, with a width, at the considered wear level, of less than 25% of the initial thickness: the central portion of the tread is not effective in terms of grip. Conversely, each lateral portion of the tread contributes to grip thanks to the presence of at least one effective cut.

[0023] At the beginning of a tire's life, and therefore at the beginning of tread wear, the tire is generally mounted on the vehicle's front axle. When the vehicle is loaded, which corresponds to a load applied to the tire substantially equal to the nominal load Zn, as defined by standards, the tread makes contact with the ground over its entire initial width. When the vehicle is unloaded, which corresponds to a load applied to the tire approximately equal to 60% of the nominal load Zn, the tread makes contact with the ground substantially over its entire initial width. Therefore, whether fully loaded or unloaded, the The central and lateral portions of the tread, respectively, come into contact with the ground during rolling. Under these conditions, the central portion of the tread, lacking effective grooves and therefore only slightly grooved, provides good resistance to wear in this high-pressure zone and ensures a high volume of rubber material, which is beneficial for wear life. Grip is then primarily ensured by the lateral portions of the tread, which have effective grooves of sufficient depth at the beginning of their service life to evacuate the necessary volume of water and mud.

[0024] According to a second essential feature of the invention, for a maximum groove depth of at least 20% and at most 40% of the initial thickness, the central portion of the tread comprises exclusively transverse effective grooves, and each lateral portion of the tread comprises at least one effective groove. In other words, at the end of wear, the central portion of the tread comprises grooves that are effective, from the point of view of grip, and are oriented exclusively transversely, thus capable of evacuating water and mud towards the lateral portions of the tread: the central portion therefore contributes to grip. Simultaneously, each lateral portion of the tread also contributes to grip thanks to the presence of at least one effective groove.The contribution of the middle portion compensates for the decrease in the contribution of the lateral portions, due to the reduction in the depth of the cuts at the end of wear, which allows for the evacuation of a volume of water and mud roughly identical to that evacuated at the beginning of wear.

[0025] At the end of its service life, i.e., at the end of its tread wear, the tire is generally mounted on a rear axle of the vehicle. When the vehicle is loaded, which corresponds to a load applied to the tire substantially equal to the nominal load Zn, as defined by standards, the contact of the tread with the ground is made across its entire width. Conversely, when the vehicle is unloaded, which corresponds to a load applied to the tire approximately equal to 30% of the nominal load Zn, the contact of the tread with the ground is limited substantially to the central portion of the tread. Whether the vehicle is loaded or unloaded, sufficient traction is therefore ensured by the presence of effective transverse grooves in the central portion of the tread.

[0026] In a first preferred embodiment, for a maximum cut depth of at least 70% and at most 90% of the initial thickness, every lateral portion of the tread comprises at least one effective transverse cut. The presence of effective transverse cuts on the portions Lateral treads, at the beginning of wear, when the tire is mounted on the steering axle, contribute to the transmission of braking forces.

[0027] In a second preferred embodiment, for a maximum cut depth of at least 70% and at most 90% of the initial thickness, every lateral portion of the tread includes at least one effective longitudinal cut. In the specific case where the only effective cuts present on the lateral portions of the tread, at the beginning of wear, when the tire is mounted on the steering axle, are longitudinal, the shoulder ribs, delimited axially on the inside by an effective longitudinal cut, are continuous, since they are not cut with effective transverse cuts. However, a continuous edge rib is rigid and therefore less susceptible to the appearance of wear patterns, the risk of which is high for a tire mounted on a steering axle and therefore not subjected to torque forces.

[0028] According to an advantageous embodiment, the median tread portion having a median surface notch ratio TESm equal to the ratio between the total area SDm of its cutouts and the sum of the total area SDm of its cutouts and the total area SRm of the raised elements delimited by these cutouts, and any lateral tread portion having a lateral surface notch ratio TES1 equal to the ratio between the total area SD1 of its cutouts and the sum of the total area SD1 of its cutouts and the total area SRI of the raised elements delimited by these cutouts, for a maximum cutout depth of at least 70% and at most 90% of the initial thickness, the median surface notch ratio TESm is at most equal to the lateral surface notch ratio TES1, preferably at most equal to 70% of the lateral surface notch ratio. TES1.In other words, at the beginning of wear, the central portion of the tread is less open than the lateral portions of the tread. This implies that the central portion of the tread primarily contributes to wear resistance and lifespan, while the lateral portions of the tread ensure grip.

[0029] According to an advantageous variant of the preceding embodiment, the median surface notch ratio TESm is at most equal to 12%. At the beginning of wear, this upper limit of the median surface notch ratio TESm limits the risk of damage in the middle part of the tread, an area of ​​high pressure in contact with the ground, and therefore the most exposed to damage.

[0030] Advantageously, for a maximum cut depth of at least 20% and at most 40% of the initial thickness, every lateral portion of the tread comprises at least one effective transverse cut. The presence of effective transverse cuts, at the end of wear, on the lateral portions of The tread of a tire mounted on a drive axle of a vehicle, particularly when loaded, contributes to grip and the transmission of longitudinal forces under engine or braking torque.

[0031] According to an advantageous embodiment, the median portion of the tread having a median surface notch ratio TESm equal to the ratio between the total area SDm of its cutouts and the sum of the total area SDm of its cutouts and the total area SRm of the raised elements delimited by these cutouts, and any lateral portion of the tread having a lateral surface notch ratio TES1 equal to the ratio between the total area SD1 of its cutouts and the sum of the total area SD1 of its cutouts and the total area SRI of the raised elements delimited by these cutouts, for a maximum cutout depth of at least 20% and at most 40% of the initial thickness, the median surface notch ratio TESm is at least 70% and at most 130% of the lateral surface notch ratio TES1.At the end of its wear, for a tire mounted on a vehicle's drive axle, the respective median and lateral surface groove ratios remain sufficiently close to guarantee an equivalent level of traction between an unladen vehicle and a laden vehicle. Thus, both the median and lateral portions of the tread contribute to grip.

[0032] According to an advantageous variant of the preceding embodiment, the median surface notch ratio TESm is at least equal to 10%. At the end of wear, this lower bound of the median surface notch ratio TESm guarantees traction capacity by the central part of the tread, in particular when the vehicle is traveling unladen.

[0033] Advantageously, the median surface notch ratio TESm, for a maximum notch depth of at least 70% and at most 90% of the initial thickness, is at most equal to the median surface notch ratio TESm, for a maximum notch depth of at least 20% and at most 40% of the initial thickness. This condition aims to maximize, at the beginning of wear, the volume of rubber material in the central part of the tread, the area most subjected to wear.

[0034] The features of the invention are illustrated by schematic figures 1 to 8, which are not drawn to scale: -[Fig.1]: Partial front view of a tire tread according to a first embodiment of the invention, at the beginning of wear, -[Fig.2]: Circumferential cross-sectional view of a tire tread according to the first embodiment of the invention, at the beginning of wear, -[Fig.3]: Partial front view of a tire tread according to the first embodiment of the invention, at the end of wear, -[Fig.4]: Partial front view of a tire tread according to a second embodiment of the invention, at the beginning of wear, -[Fig.5]: Partial front view of a tire tread according to a preferred variant of the first embodiment of the invention, at the beginning of wear, -[Fig.6]: Partial front view of a tire tread according to the preferred variant of the first embodiment of the invention, at the end of wear, -[Fig.7]: Partial front view of a tire tread according to a preferred variant of the second embodiment of the invention, at the beginning of wear, -[Fig.8]: Partial front view of a tire tread according to the preferred variant of the second embodiment of the invention, at the end of wear.

[0035] Figure 1 is a partial front view of a tread 2 of a tire 1, for a heavy construction vehicle, according to a first embodiment of the invention, at the beginning of wear. The tread 2 comprises an arrangement of cutouts 3 separating raised elements 4. The tread 2 has, in the new condition of the tire, an initial width LO, measured along an axial direction YY' parallel to the axis of rotation of the tire and between two tread edges (24, 25), and having an initial thickness DO (not shown in Figure 1), measured along a radial direction ZZ' perpendicular to a tread surface 20 and defined as the maximum initial cutout depth.The tread 2 comprises a central portion 21 extending symmetrically on either side of a median plane XZ of the tire and having an initial median width LCO equal to 50% of the initial width LO, and two lateral portions (22, 23) each extending from the central portion 21 to a tread edge (24, 25). The cutouts are either longitudinal cutouts 31 having a mean line forming, with a circumferential direction XX', an angle of less than 45°, or transverse cutouts 32 having a mean line forming, with the circumferential direction XX', an angle of more than 45°. A cut 3 is said to be effective, at a given level of wear, when its width W, measured, perpendicular to its average line, between the walls of the raised elements 4 that it separates, at the level of the rolling surface 20, is at least equal to 25% of the initial thickness D0 (not shown on [Fig.1]), at the level of wear considered.According to the invention, the arrangement of the cutouts 3 is evolving during tire wear. According to a first feature of the invention, as shown in [Fig. 1], for a maximum cutout depth D of at least 70% and at most 90% of the initial thickness D0, the medial portion 21 of the tread 2 comprises cutouts 3, none of which are effective, and any lateral portion. (22, 23) of the tread 2 includes at least one effective groove 3. A maximum groove depth D of at least 70% and at most 90% of the initial thickness DO corresponds to a state at the beginning of wear. A central portion 21 of the tread 2 comprising grooves 3, none of which are effective, is a closed portion that contributes primarily to resistance to damage and wear life, but not to grip on wet or muddy surfaces. Conversely, lateral portions (22, 23) of the tread 2 comprising effective grooves 3, transverse in this case, contribute to grip on wet or muddy surfaces.

[0036] Figure 2 is a circumferential cross-sectional view of a tread 2 of A tire according to the first embodiment of the invention, at the beginning of its wear. The circumferential cross-sectional view is taken along the cutting plane AA shown in [Fig. 1]. [Fig. 2] more particularly shows the effective transverse cuts 32, separating raised elements 4, present in a lateral portion 23 and extending radially inwards from the tread surface 20. Such a cut 32 is defined by its width W, measured at the tread surface 20 between the walls of the two raised elements 4 that it delimits, and by its depth D, measured along the radial direction ZZ' between the tread surface 20 and the bottom of the cut. The initial thickness D0, defined in the new condition of the tire before rolling as the initial maximum cut depth, measured over all the cuts in the tread, effective or not, is represented by a dashed line.At the beginning of wear, by convention, the maximum cutting depth D is at least equal to 70% and at most equal to 90% of the initial thickness D0.

[0037] Figure 3 is a partial front view of a tread 2 of a tire 1, for a heavy construction vehicle, according to the first embodiment of the invention, at the end of its wear. The elements of Figure 3 are referenced identically to those of Figure 1. Figure 3 illustrates the second essential feature of the invention: for a maximum cut depth D of at least 20% and at most 40% of the initial thickness D0, the central portion 21 of the tread 2 comprises exclusively transverse effective cuts 32, and any lateral portion (22, 23) of the tread 2 comprises at least one effective cut (3). A maximum cut depth D of at least 20% and at most 40% of the initial thickness D0 corresponds to a state at the end of its wear. Figure 33] shows, in particular, the presence of effective transverse grooves 32, present both in each lateral portion (22, 23) and in the median portion 21. In the case represented, the effective transverse cuts 32 of the lateral portions (22, 23) extend into the median portion 21. This. This allows for the formation of continuous channels that evacuate water and mud transversely, from the central portion 21 to each lateral portion (22, 23). Thus, the central portion 21 and the lateral portions (22, 23) work together to ensure traction on wet or muddy ground.

[0038] Figure 4 is a partial front view of a tread 2 of a tire 1 according to a second embodiment of the invention, at the beginning of wear. This second embodiment of the invention, shown in Figure 4, differs from the first embodiment of the invention, shown in Figure 1, by the presence, in the lateral portions (22, 23), of a network of interconnected longitudinal 31 and transverse 32 effective grooves. This two-dimensional network of effective grooves, at the edge of the tread, is particularly efficient with respect to grip on wet or muddy surfaces, thanks to a high groove ratio. The central portion of this second embodiment of the invention remains identical to that of Figure 1.

[0039] Figure 5 is a partial front view of a tread 2 of a tire 1 according to a preferred embodiment of the first of the invention, at the beginning of wear. In this preferred embodiment, the raised elements of the lateral portions of the tread include cavities or wells extending radially inwards from the tread surface. These wells, in particular, limit the temperature rise in the lateral portions of the top of the tire, and thus contribute to increasing the tire's thermal endurance. The raised elements of the central portion further include incisions that contribute to longitudinal grip under braking or engine torque.

[0040] Figure 6 is a partial front view of a tire tread 2 according to the preferred embodiment of the first incarnation of the invention, shown in Figure 5, at the end of its wear. At the end of its wear, the lateral portions of the tread consist exclusively of effective transverse grooves, which extend into the central portion of the tread. This central portion comprises a circumferential distribution of adjacent raised elements. It should be noted that the grooves and incisions mentioned in the description of Figure 5 have partially disappeared during the wear of the tire.

[0041] Figure 7 is a partial front view of a tread 2 of a tire 1 according to a preferred embodiment of the second embodiment of the invention, at the beginning of wear. In this preferred embodiment, the raised elements of the lateral and central portions of the tread include incisions that contribute to longitudinal grip under braking or engine torque.

[0042] Figure 8 is a partial front view of a tire tread 2 according to the preferred embodiment of the second incarnation of the invention, at the end of its wear. At the end of its wear, the lateral portions of the tread include exclusively effective transverse cutouts, which extend into the central portion of the tread, which includes in its central part a circumferential distribution of adjacent raised elements. It should be noted that the incisions mentioned in the description of [Fig. 7] have completely disappeared during tire wear.

[0043] The invention has been studied more particularly for a tire for a dumper-type civil engineering vehicle in the dimension 53 / 80R63, according to two variants A and B, variant A corresponding to figures 5 and 6 and variant B to figures 7 and 8, the tire dimension taken as a reference being a 24.00R35.

[0044] Table 1 below presents the characteristics of the reference dimension, as well as those of variants A and B of the invention: [Tables 1] Features 24.00R35 (Reference) 53 / 80R63 (Variant A) 53 / 80R63 (Variant B) Initial tread width LO 600mm 1188mm 1188mm Initial tread thickness DO in new condition, before driving 74mm 121mm 121mm Transverse cut width W in each lateral portion (at 20% wear) Effective 22 mm (30%D0) Effective 60 mm (50%D0) Effective 42 mm (35%D0) Longitudinal cut width W in each lateral portion (at 20% wear) Effective 21 mm (28%D0) Not effective 12 mm (10%D0) Effective 36 mm (30%D0) Cut width W transverse in the median portion (at 20% wear) Not effective 2 mm (3%D0) Not effective 12 mm (10%D0) Not effective 12 mm (10%D0) Longitudinal cut width W in the median portion (at 20% wear) Not effective 6 mm (8%D0) Not effective 12 mm (10%D0) Not effective 12 mm (10%D0) Transverse cut width W in each lateral portion (at 70% wear) Effective 21 mm (28%D0) Effective 42 mm (35%D0) Effective 36 mm (30%D0).Longitudinal cut width W in each lateral portion (at 70% wear) Ineffective 2 mm (3% D0) Ineffective 12 mm (10% D0) Ineffective 0 mm (0% D0) Transverse cut width W in the median portion (at 70% wear) Effective 21 mm (28% D0) Effective 36 mm (30% D0) Effective 36 mm (30% D0) Longitudinal cut width W in the median portion (at 70% wear) Effective 21 mm (28% D0) Ineffective 24 mm (20% D0) Ineffective 24 mm (20% D0) Overall volumetric notch rate TEV at new 16.4% 16.1% 16% Overall surface notch rate TES at 20% wear 14.6% 18.2% 17.8% Lateral surface notch rate TES1 at 20% wear 23.2% 28.1% 27.3% Median surface notch rate TESm at 20% wear 5.8% 8.3% 8.3% Overall surface notch rate TES at 70% wear 16.9% 15.9% 15.6% Lateral surface notch rate TES1 at 70% wear 13.9% 17.3% 16.6% Median surface notch rate TESm at 70% wear 20% 14.5% 14.5% Effective notch of lateral portion at 20% wear Longitudinal and transverse Transverse Longitudinal and transverse Effective notch of median portion at 20% wear None None None Effective notch of lateral portion at 70% wear Transverse Transverse Transverse Effective notch of median portion at 70% wear Longitudinal and transverse Transverse Transverse. Note: (1) A percentage of wear quantifies a loss of material height (raised elements), therefore a reduction in initial thickness DO (2) 20% wear is a state of wear at the beginning of life (or beginning of wear) (3) 70% wear is a state of wear at the end of life (or end of wear)

[0045] Table 2 below shows the estimated braking and wear performance for the reference size, as well as for variants A and B of the invention: [Tables 2] Specifications 24.00R35 (Reference) 53 / 80R63 (Variant A) 53 / 80R63 (Variant B) Braking performance, at 20% wear, unloaded or loaded 100% 103% 102% Braking performance, at 70% wear, unloaded 106% 96% 96% Braking performance, at 70% wear, loaded 101% 99% 98% Wear performance at 20% wear, unloaded and loaded 100% 98% 99% Wear performance, at 70% wear, unloaded 96% 103% 103% Wear performance, at 70% wear, loaded 100% 101% 101%

[0046] Regarding braking performance, the reference value, with a base of 100, is the reference size at 20% wear, for a loaded vehicle. The braking performance indicator is defined as follows: Braking performance at x% wear, for the size considered = braking distance at 20% wear, for the reference size / braking distance at x% wear, for the size considered. A braking performance indicator greater than 100% indicates a reduction in the braking distance of the size considered compared to the reference size at 20% wear. Table 1 shows that variants A and B according to the invention, at 20% wear, offer better braking performance than the reference size, but this trend reverses at 70% wear.

[0047] Regarding wear performance, the reference value, based on 100, is the reference dimension at 20% wear, for a loaded vehicle. The wear performance indicator is defined as follows: Wear performance at x% wear, for the dimension concerned = (1 - TES at x% wear of the dimension concerned) / (1 - TES (at 20% wear of the reference dimension). Under these conditions, a wear performance indicator greater than 100% indicates a gain in the material in contact with the ground for the dimension in question compared to the reference dimension at 20% wear. Table 2 shows that variants A and B according to the invention, at 70% wear, perform better in terms of wear than the reference dimension, but this trend reverses at 20% wear.

Claims

1. Demands Tyre (1) for a heavy construction vehicle, comprising a tread (2) comprising an arrangement of cutouts (3) separating raised elements (4), -the tread (2) having, in the new condition of the tyre, an initial width (LO), measured along an axial direction (YY') parallel to the axis of rotation of the tyre and between two tread edges (24, 25), and having an initial thickness (DO), measured along a radial direction (ZZ') perpendicular to a tread surface (20) and defined as the maximum initial cutout depth, -the tread (2) comprising a median portion (21) extending symmetrically on either side of a median plane (XZ) of the tire and having an initial median width (LCO) equal to 50% of the initial width (LO), and two lateral portions (22, 23) each extending from the median portion (21) to a tread edge (24, 25), -the cutouts being either longitudinal cutouts (31) having a mean line forming, with a circumferential direction (XX'), an angle of less than 45°, or transverse cutouts (32) having a mean line forming, with the circumferential direction (XX'), an angle greater than 45°, -a cut (3) being said to be effective, at a given level of wear, when its width (W), measured perpendicular to its average line, between the walls of the raised elements (4) that it separates, at the level of the tread surface (20), is at least equal to 25% of the maximum tread depth in the new condition (DO), characterized in that the arrangement of the cuts (3) is evolving during the wear of the tire, such that, for a maximum cut depth (D) of at least 70% and at most 90% of the initial thickness (D0), the median portion (21) of the tread (2) includes cuts (3) among which none is effective, and every lateral portion (22, 23) of the tread (2) includes at least one effective cut (3), and such that, for a maximum cut depth (D) of at least 20% and at most equal to 40% of the initial thickness (D0), the median portion (21) of the band bearing (2) includes exclusively transverse effective cutouts (32), and any lateral portion (22, 23) of tread (2) includes at least one effective cutout (3).

2. Tire (1) according to claim 1 wherein, for a maximum cut depth (D) of at least 70% and at most 90% of the initial thickness (DO), any lateral portion (22, 23) of tread (2) includes at least one effective transverse cut (32).

3. Tire (1) according to any one of claims 1 or 2 wherein, for a maximum cut depth (D) of at least 70% and at most 90% of the initial thickness (DO), any lateral portion (22, 23) of tread (2) includes at least one effective longitudinal cut (31).

4. A tire (1) according to any one of claims 1 to 3, the median tread portion (21) having a median surface notch ratio TESm equal to the ratio between the total area SDm of its cutouts and the sum of the total area SDm of its cutouts and the total area SRm of the raised features delimited by these cutouts, and any lateral tread portion (22, 23) having a lateral surface notch ratio TES1 equal to the ratio between the total area SD1 of its cutouts and the sum of the total area SD1 of its cutouts and the total area SRI of the raised features delimited by these cutouts, wherein, for a maximum cut depth (D) of at least 70% and at most 90% of the initial thickness (D0), the median surface notch ratio TESm is at most equal to the ratio TES1 lateral surface notch,preferably at most equal to 70% of the lateral surface notching ratio TES1.

5. Pneumatic (1) according to claim 4 wherein the median surface notch ratio TESm is at most equal to 12%.

6. Tire (1) according to any one of claims 1 to 5 wherein, for a maximum cut depth (D) of at least 20% and at most 40% of the initial thickness (D0), any lateral portion (22, 23) of tread (2) includes at least one effective transverse cut (32).

7. Tire (1) according to any one of claims 1 to 6, the middle portion of the tread (21) having a rate median surface notching TESm equal to the ratio between the total area SDm of its cutouts and the sum of the total area SDm of its cutouts and the total area SRm of the raised elements delimited by these cutouts, and any lateral portion of tread (22, 23) having a lateral surface notching ratio TES1 equal to the ratio between the total area SD1 of its cutouts and the sum of the total area SD1 of its cutouts and the total area SRI of the raised elements delimited by these cutouts, in which, for a maximum cutout depth (D) of at least 20% and at most 40% of the initial thickness (DO), the median surface notching ratio TESm is at least 70% and at most 130% of the lateral surface notching ratio TES1.

8. Pneumatic (1) according to claim 7 wherein the median surface notch ratio TESm is at least equal to 10%.

9. Pneumatic (1) according to any one of claims 1 to 8 wherein the median surface notch ratio TESm, for a maximum cutting depth (D) of at least 70% and at most 90% of the initial thickness (D0), is at most equal to the median surface notch ratio TESm, for a maximum cutting depth (D) of at least 20% and at most 40% of the initial thickness (D0).

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