Tires with improved grip for heavy-duty civil engineering vehicles

Abstract

The present invention relates to a tire (1) for heavy-duty civil engineering vehicles, the purpose of which is to improve the performance trade-off between wear service life, impact resistance and grip. The tread (2) has an axial width L0 and includes on each side of the equatorial plane (XZ) at an axial distance LE equal to at least 0.5*L0 / 2 and at least an internal longitudinal cut (42) at an axial distance LI equal to at most 0.4*L0 / 2, the at least one external longitudinal cut (41) including an external radial portion (411) extending to the tread surface (3) and having an average width WE1 equal to at least 0.6 times the height HE1 of the external radial portion (411), and the at least one internal longitudinal cut (42) including an internal radial portion (422) not extending to the tread surface (3) and having an average width WI2 equal to at least 0.6 times the height HI2 of the internal radial portion (422).

Description

Technical Field

[0001] This invention relates to a tire for heavy-duty vehicles used in construction sites, designed to bear heavy loads and travel on uneven, stony surfaces (such as those found in mines). The invention particularly relates to a tire tread whose grip is improved throughout the tire's service life.

[0002] This invention relates more particularly to a tire intended for use on heavy-duty vehicles of the construction site type, such as dump trucks intended for transporting materials extracted from quarries or open-pit mines. Dump trucks endure particularly harsh operating conditions: high loads, sustained speeds, sloping and winding routes, and uneven and stony terrain. For example, in sites where materials such as ore or coal are mined, the use of dump truck-type vehicles typically involves alternating loaded outward cycles and unloaded return cycles. In the loaded outward cycle, the loaded vehicle transports the extracted material primarily upward from the loading area at the bottom of the mine or pit to the unloading area, requiring the tire to have good traction under traction. In the unloaded return cycle, the unloaded vehicle returns primarily downward to the loading area at the bottom of the mine, requiring good tire traction under braking. The sloping paths are often also winding, thus requiring the tire to have good lateral traction. Furthermore, the paths vehicles travel on are typically made of materials sourced from mines (such as crushed and compacted stones) to ensure the integrity of the wear layer as vehicles pass over them. These stones are often wet, meaning they are frequently covered in mud and water. Therefore, on the one hand, the tire tread must be able to effectively remove this mixture of mud and water to ensure satisfactory grip on muddy surfaces; on the other hand, it must also have good resistance to abrasion and impact caused by stones present on the ground. Background Technology

[0003] As mentioned above, the specific use of dump trucks requires special management of the tires mounted on them. In their new condition, tires are typically mounted to the front axle or steering axle of the vehicle. In this front position, the load applied to the tire is typically estimated to be between 80% and 100% of its nominal load capacity, depending on whether the vehicle is operating unloaded or loaded, as defined, for example, by standard ISO 4250 and the Tire & Rim Association or TRA standards. When the tire reaches approximately one-third wear (meaning the tread height has decreased by one-third from its initial new condition), the tire is removed from the front axle and mounted to the rear axle or driven axle of the vehicle. In this rear position, the load applied to the tire is typically estimated to be between 25% and 100% of its nominal load capacity, depending on whether the vehicle is operating unloaded or loaded. Finally, according to current practice, when the tire tread reaches the remaining height corresponding to a fully worn state, the tire is permanently removed from the driven axle.

[0004] The tire tread, which is intended to form the outer periphery of the tire, comprises at least one rubber-based material and is intended to wear down when in contact with the ground via the tread surface.

[0005] The following definitions apply:

[0006] - Radial direction: The direction perpendicular to the tire's axis of rotation.

[0007] - Axial or lateral direction: The direction parallel to the tire's axis of rotation.

[0008] - Circumferential or longitudinal direction: The direction tangent to the outer circumference of the tire and perpendicular to the radial and axial directions, respectively.

[0009] - Equatorial or intermediate circumferential plane: A plane containing both radial and circumferential directions, perpendicular to the tire's axis of rotation and dividing the tire into two equal parts.

[0010] The geometric characteristics of the tread integrated into a tire typically consist of an axial width L along the axial direction and a radial thickness E along the radial direction. The axial width L is defined as the axial width of the portion of the tread surface in contact with the flat ground, where the tire is mounted on a recommended rim and subjected to given pressure and load conditions. The radial thickness E is conventionally defined as the maximum depth Dmax measured in a cut. In the case of tires in a brand-new condition for construction site vehicles, for example, the axial width L is at least equal to 600 mm, and the maximum depth Dmax is at least equal to 60 mm, or even 70 mm. However, these characteristics of the axial width L and the maximum depth Dmax depend on the tire's wear condition. In particular, the maximum depth Dmax varies between the initial depth D0 of the tire in a brand-new condition and the remaining depth DR of the tire in a worn condition (at which, according to current practice, the tire is removed from the vehicle).

[0011] To ensure satisfactory longitudinal grip performance (under engine torque and braking torque) and lateral grip performance, a tread pattern is required, which is a system of cuts forming the tread as separating raised elements.

[0012] A slit is a space defined by material walls that extend radially at a given height from the tread surface, the material walls being opposite each other and spaced apart by a distance that defines the width of the slit. Depending on the value of its width, the slit can be a sipe or a groove. In the case of a sipe, when the tire is under nominal load and pressure conditions recommended by, for example, TRA standards, the width is suitable to allow the opposing walls defining the sipe to at least partially contact each other, at least in the contact patch between the tread and the ground. In the case of a groove, under these recommended nominal driving conditions, the walls of the groove typically do not contact each other.

[0013] The slits define raised elements of the tread block or rib type. A tread block includes a contact surface and at least three (usually four) side surfaces, the contact surface being contained within the tread surface and intersecting it. A rib includes a contact surface and two sidewalls extending circumferentially along the entire length of the tread. Therefore, a rib is defined circumferentially by one or two circumferential slits.

[0014] The proportion of cuts contained in the tread or tread portion can be defined by volumetric porosity (TEV) or surface porosity (TES).

[0015] By definition, the tread volumetric porosity (TEV) is equal to the ratio between the total volume of the slits (VD) and the sum of the total volume of the slits (VD) and the total volume of the raised elements defined by these slits (VR). The total volume of the slits (VD) is measured on an unused tire, i.e., an unmounted and uninflated tire. The sum of VD+VR corresponds to the volume contained radially between the tread surface and the subsurface (which is radially translated inward from the tread surface by a distance equal to the maximum tread depth Dmax). This volumetric porosity (TEV), expressed as a percentage, determines wear performance based on the available abrasion-resistant materials and determines longitudinal and lateral grip performance based on the presence of lateral and longitudinal corners, as well as the presence of slits capable of storing or removing water or mud.

[0016] By definition, when a tire mounted on a nominal rim is inflated to nominal pressure and compressed under nominal load (these nominal characteristics are recommended, for example, by TRA standards), the surface area void ratio (TES) of the tread is defined in the contact surface area between the tire and the rigid ground. This surface area void ratio (TES) is equal to the ratio between the total surface area of ​​the cuts (SD) and the sum of the total surface area of ​​the cuts (SD) and the total surface area of ​​the raised elements defined by these cuts (SR), which are determined in the contact surface area. The sum of SD + SR corresponds to the contact surface area. This surface area void ratio (TES) (expressed as a percentage) influences wear performance based on the surface area of ​​the material in contact with the ground (which affects the distribution of pressure applied by the ground to the tread surface) and influences longitudinal and lateral grip performance based on the respective lengths of the lateral and longitudinal corners (which influence the effectiveness of tread pattern indentation).

[0017] The volumetric void ratio (TEV) and the surface area void ratio (TES) can be determined in the new condition of the tread (before the tire is used for driving) or in a given wear condition of the tread (characterized by the remaining depth of the tread).

[0018] Tires used on construction site vehicles typically have treads that can be longitudinal or lateral. The bisectors of longitudinal grooves form an angle of less than 45° with the longitudinal direction of the tire. The bisectors of lateral grooves form an angle of greater than 45° with the longitudinal direction of the tire. Generally, the width of the grooves gradually decreases from the tread surface to the bottom of the groove due to the inclination of the walls of the raised elements defining the grooves. Therefore, the volumetric porosity decreases as the tire transitions from a new to a worn state. For example, to ensure that the volumetric porosity of a tire at the end of its life (when the tire is fully worn) is approximately 8%, the corresponding volumetric porosity in the new state needs to be at least approximately 22%. However, a high volumetric porosity in the new state has several disadvantages. First, it encourages stones to be trapped and retained in the grooves, which can potentially damage the tire crown through cracks they may cause. Secondly, the high volumetric porosity in a new tire condition means a similarly high surface porosity. Therefore, the contact area between the raised elements and the ground is slightly smaller, resulting in greater pressure on the ground. This enhances tread wear and thus increases tread traction. Finally, the high volumetric porosity in a new tire condition allows the raised elements to undergo lateral deformation known as "barrel-shaped" deformation due to the Poisson effect. This reduces the effective volume of the grooves (characterized by their ability to store and remove water or mud mixtures), causing the tire to lose traction on muddy surfaces. However, as tread wear increases, these Poisson deformations tend to decrease due to the reduced height of the raised elements.

[0019] Therefore, it is difficult to achieve a satisfactory compromise among the following performance aspects: anti-aggression, wear life, and grip on wet or muddy surfaces. For this reason, tire manufacturers have so far chosen to prioritize one or two given performance aspects. For example, grip on wet or muddy surfaces may take precedence over wear life and anti-aggression. According to the first option, the Michelin 24.00R 35XTRA LOAD GRIP product offers an open tread pattern comprising a network of wide longitudinal and lateral grooves in the middle section and two side sections extending from the middle section, which allows mud to be trapped across the entire tread surface and at least partially removed via the lateral grooves leading outwards at the edges of the tread. In another example, wear life and anti-aggression performance aspects may take precedence over grip. According to the second option, the Michelin 24.00R 35X TRALOADGRIP product offers a tread pattern that is more closed in the middle section and more open on the two side sections that extend from the middle section. The more closed tread pattern means that the tread pattern includes narrow longitudinal grooves and lateral grooves (which ensure a certain volume of wear material and prevent damage), while the more open tread pattern means that in each case, the tread pattern includes lateral grooves leading to the edge of the tread for at least partial removal of water or mud mixtures. Summary of the Invention

[0020] The inventors set their own goal as designing a tire tread for heavy-duty vehicles used on construction sites that improves the performance trade-off between wear life, impact resistance and grip when used on paths that may be covered by water and mud, while ensuring durable grip throughout the tire's lifespan.

[0021] According to the present invention, this objective is achieved by a tire for heavy-duty vehicles of the construction site type, the tire comprising a tread in a brand-new state before driving, the tread being designed to contact the ground via its surface:

[0022] -When a tire mounted on a nominal rim is inflated to a nominal pressure Pn and compressed under a nominal load Zn, the tread surface has an axial width L0.

[0023] - The tread includes separating raised elements and cuts with a maximum depth D0.

[0024] - The tread includes at least one outer longitudinal cut and at least one inner longitudinal cut on each side of the equatorial plane, the outer longitudinal cut having bisectors at an axial distance LE of at least 0.5 * L0 / 2 relative to the equatorial plane of the tire, and the inner longitudinal cut having bisectors at an axial distance LI of at most 0.4 * L0 / 2 relative to the equatorial plane of the tire.

[0025] - At least one external longitudinal cut includes an external radial portion extending to the tread surface and having a height HE1 and an average width WE1, the average width WE1 being at least 0.6 times the height HE1.

[0026] - At least one internal longitudinal cut includes an internal radial portion that does not extend toward the tread surface, the internal radial portion extending at least partially radially inside the external radial portion of the external longitudinal cut, and the internal radial portion having a height HI2 and an average width WI2, the average width WI2 being at least 0.6 times the height HI2.

[0027] The principle of this invention is to provide a tire for heavy-duty vehicles of the construction site type, whose grip (especially on wet and / or muddy surfaces) is ensured at any level of tread wear, between a brand-new condition characterized by a maximum depth D0 and a wear condition, for example according to current practice, characterized by a maximum depth DR at least equal to D0 / 10, particularly regardless of the load level applied to the tire (between 25% and 100% of its recommended load Zn). 25% Zn corresponds to the load applied to a tire mounted on the rear axle of an unloaded vehicle, and 100% Zn corresponds to the load applied to a tire mounted on the front or rear axle of a fully loaded vehicle.

[0028] When the vehicle is fully loaded, regardless of whether the tire is located on the front or rear axle, the tire mounted on the nominal rim is inflated to the nominal pressure Pn and compressed under the nominal load Zn, as defined by standards such as ISO 4250 and the Tire & Rim Association or TRA standards. Under these conditions, the tire tread surface contacts a supposedly flat ground surface over a load contact surface area with an axial width L0, measured between the axial ends of the load contact surface area.

[0029] When the vehicle is unloaded and the tires are mounted to the rear axle, the tires mounted on the nominal rim are inflated to the nominal pressure Pn and compressed under a load equal to approximately 0.25*Zn. Under these conditions, the tire tread surface contacts a hypothetically flat ground surface in an unloaded contact surface area with an axial width L1, measured between the axial ends of the unloaded contact surface area. The axial width L1 is less than the axial width L0.

[0030] Between these two extreme loads—loaded on any type of axle and unloaded on the rear axle—there exists an intermediate condition: when a tire is fitted to the front axle with an unloaded tire, the tire mounted on the nominal rim is inflated to a nominal pressure Pn and compressed under a load equal to 0.8*Zn, more typically at least equal to 0.75*Zn and at most equal to 0.85*Zn.

[0031] The tread includes slits that separate the raised elements and have a maximum depth D0. D0 is the maximum depth of the slit in a brand-new state, meaning the maximum distance between the radially inner point of the deepest slit in the brand-new state and the tread surface. D0 allows for the definition of a theoretical bottom surface parallel to the tread surface and the maximum tread thickness expected to wear. D0 is the reference upon which various wear states of the tread are defined, each characterized by a maximum depth Dmax that can be expressed as a percentage of D0.

[0032] More specifically, the tread includes at least one external longitudinal cut and at least one internal longitudinal cut on each side of the equatorial plane, the external longitudinal cut having bisectors at an axial distance LE of at least 0.5 * L0 / 2 relative to the equatorial plane of the tire, and the internal longitudinal cut having bisectors at an axial distance LI of at most 0.4 * L0 / 2 relative to the equatorial plane of the tire.

[0033] A longitudinal cut is understood as a cut where the bisector forms an angle of at most 45° with the circumferential direction of the tire. The bisector forms a zero angle and is strictly longitudinal, or the bisector includes at least one inclined portion forming a non-zero angle, such as when the cut undulates around the circumferential direction.

[0034] An outer longitudinal cut having a bisector located at an axial distance LE of at least 0.5 * L0 / 2 relative to the tire's equatorial plane is a longitudinal cut extending outward from the unloaded contact surface area. In other words, the bisector of the outer longitudinal cut is located axially at a distance LE relative to the tire's equatorial plane, which is greater than the sum of the axial half-width L1 / 2 of the unloaded contact surface area and the average half-thickness WE1 of the outer longitudinal cut. Therefore, when the tire is mounted to a loaded vehicle or on the front axle of an unloaded vehicle, the outer longitudinal cut contacts the ground; however, when the tire is mounted to the rear axle of an unloaded vehicle, the outer longitudinal cut does not contact the ground.

[0035] The internal longitudinal cut, having a bisector located at an axial distance LI of at most 0.4*L0 / 2 relative to the tire's equatorial plane, is a longitudinal cut extending inside the unloaded contact surface area. In other words, the bisector of the internal longitudinal cut is located axially at a distance LI relative to the tire's equatorial plane, which is smaller than the axial half-width L1 / 2 of the unloaded contact surface area minus the average half-thickness WI1 of the internal longitudinal cut. Therefore, the internal longitudinal cut is in contact with the ground when the tire is mounted to a loaded vehicle and when the tire is mounted to the rear axle of an unloaded vehicle.

[0036] According to a first essential feature of the invention, at least one external longitudinal cut includes an external radial portion extending to the tread surface and having a height HE1 and an average width WE1, the average width WE1 being at least 0.6 times the height HE1.

[0037] Height HE1 is measured between the outermost radial point of the outer radial portion (which, in a brand-new condition, is located on the tread surface) and the innermost radial point of the outer radial portion. Average width WE1 is the average width of the outer radial portion over the entire height HE1, measured between the facing material walls (which define the outer radial portion of the cut) at a given horizontal height. An average width WE1 at least 0.6 times the height HE1 means that the outer radial portion is considered an effective groove. A groove is a cut that is wide enough that its walls generally do not contact each other under recommended nominal driving conditions. Furthermore, it is considered effective because its cross-section does not decrease significantly due to deformation of adjacent raised elements caused by the Poisson effect.

[0038] Therefore, the cross-section of the open outer radial portion remains sufficiently open to allow for the storage and removal of water or mud present on the ground, thereby ensuring the required grip. Thus, the presence of an outer longitudinal cutout in the outer radial portion ensures the removal of water and mud from tires in a pristine (i.e., unworn) condition and mounted to the front axle of a fully loaded vehicle; the outer radial portion is an open and effective groove type.

[0039] According to a second essential feature of the invention, at least one internal longitudinal cut includes an internal radial portion that does not extend toward the tread surface, the internal radial portion extending at least partially radially inside the external radial portion of the external longitudinal cut, and the internal radial portion having a height HI2 and an average width WI2, the average width WI2 being at least 0.6 times the height HI2.

[0040] Height HI2 is measured between the outermost radial point of the inner radial portion (located radially inside the tread surface) and the innermost radial point of the inner radial portion. Average width WI1 is the average width of the outer radial portion over the entire height HI2. An average width WI2 at least 0.6 times the height HI2 means that the inner radial portion is considered an effective groove, as described above. Unlike the outer longitudinal cut, the inner longitudinal cut includes an inner radial portion that does not extend to the tire tread surface in the new condition, meaning it only extends to the tread surface from the intermediate wear state. In other words, this inner radial portion is hidden in the new condition and extends down to the intermediate wear state. This intermediate wear state typically corresponds to the wear level at which a tire initially fitted to the front axle is transferred to the rear axle. Furthermore, this inner radial portion extends at least partially radially inside the outer radial portion of the outer longitudinal cut. In other words, the innermost radial point of the inner radial portion of the inner longitudinal cut is radially inside the innermost radial point of the outer radial portion of the outer longitudinal cut. Therefore, there is a partial overlap between the inner radial portion of the inner longitudinal cut and the outer radial portion of the outer longitudinal cut, but not a complete overlap, or even no overlap at all.

[0041] Therefore, the effectiveness of internal longitudinal cuts in removing water or mud only becomes apparent from the point where the tire reaches a certain level of partial wear, and in appropriate cases, until the tire is completely worn. Thus, the presence of internal longitudinal cuts with internal radial portions ensures the removal of water and mud from tires in an intermediate wear state (which can extend down to complete wear) fitted to the rear axle of an unloaded vehicle, wherein the internal radial portions are effective groove types that open from a certain wear level.

[0042] Advantageously, the average width WE1 of the outer radial portion of at least one outer longitudinal cut is at most twice the height HE1, preferably at most equal to the height HE1. If the average width WE1 increases to more than twice the height HE1, the load contact surface area decreases, thus increasing the contact pressure and leading to increased wear.

[0043] Preferably, the outer radial portion of at least one outer longitudinal cut extends radially inward to a radial depth DE1 at least equal to D0 / 4, preferably at least equal to D0 / 3. The radial depth DE1 corresponds to the radial distance between the tread surface in the new condition and the innermost radial point of the outer radial portion. Therefore, in the new condition, since the outer radial portion is open, the radial depth DE1 is equal to the height HE1. Thus, the outer radial portion is an effective groove extending at least downward to one-quarter of the tread thickness (corresponding to a remaining maximum cut depth equal to 3*D0 / 4), preferably at least one-third of the tread thickness (corresponding to a remaining maximum cut depth equal to 2*D0 / 3).

[0044] Also preferably, the outer radial portion of at least one outer longitudinal cut extends radially inward to a radial depth DE1 of at most 2*D0 / 3, preferably at most D0 / 2. Thus, the outer radial portion is an effective groove that extends at most down to two-thirds of the wear portion (corresponding to the remaining maximum cut depth equal to D0 / 3), preferably down to half the wear portion of the tread thickness (corresponding to the remaining maximum cut depth equal to D0 / 2).

[0045] Preferably, the meridional section of the outer radial portion of at least one outer longitudinal cut is constant along the circumferential direction, thereby ensuring that the removal rate of water or mud mixture is constant around the entire circumference of the tire.

[0046] Preferably, the outer radial portion of at least one outer longitudinal cut has a circular circumferential bisector centered on the tire's axis of rotation. Therefore, the outer radial portion does not fluctuate circumferentially in terms of tread thickness.

[0047] Preferably, at least one external longitudinal slit includes an internal radial portion leading to its external radial portion, the internal radial portion having a height HE2 and an average width WE2, the average width WE2 being at most 0.2 times the height HE2. The average width WE2 being at most 0.2 times the height HE2 means that the internal radial portion is a sipe, meaning a slit narrow enough to allow its walls to contact each other under recommended nominal driving conditions. This sipe is not open in a new condition. When the wear level causes the sipe to open (meaning beyond the radial depth DE1), this prevents the removal of water or mud, but under lateral loads, the concave effect of the open corners of its walls contributes to grip. Furthermore, the open sipe allows for a localized increase in the flexibility of the tread on its axially outer side, thereby promoting tire flattening. Additionally, the sipe allows for the limitation of slip deformation due to the independence of the protruding elements defining it. Effective flattening and limitation of slip deformation result in reduced wear. Finally, the sipes allow heat to be removed, thereby reducing the temperature of the tire crown, which is beneficial to the durability of the crown.

[0048] Advantageously, the average width WI2 of the inner radial portion of at least one inner longitudinal cut is at most twice the height HI2, preferably at most equal to the height HI2. When the inner radial portion is open, if the average width WI2 increases to more than twice the height HI2, the unloaded contact surface area decreases, thus increasing the contact pressure and leading to increased wear.

[0049] Preferably, the inner radial portion of at least one internal longitudinal cut extends radially inward to a radial depth DI2 at least equal to D0 / 2, preferably at least equal to 2*D0 / 3. The radial depth DI2 corresponds to the radial distance between the tread surface in the new condition and the innermost radial point of the inner radial portion. In the new condition, since the inner radial portion is not open, the radial depth DI2 is not equal to the height HI2. Therefore, the inner radial portion is an effective groove that extends at least downward to half the wear portion of the tread thickness (corresponding to the remaining maximum cut depth equal to D0 / 2), preferably at least downward to two-thirds of the wear portion (corresponding to the remaining maximum cut depth equal to D0 / 3).

[0050] Also preferably, the inner radial portion of at least one inner longitudinal cut extends radially inward to a radial depth DI2 at most equal to D0. Thus, the inner radial portion is an effective groove that extends at most downward to the fully worn portion of the tread thickness (corresponding to the maximum cut depth equal to D0). Preferably, the inner longitudinal cut, or the inner radial portion of each inner longitudinal cut, extends radially inward to a radial depth DI2 at most equal to 9*D0 / 10, or even more preferably at most equal to 3*D0 / 4.

[0051] Preferably, the meridional section of the inner radial portion of at least one inner longitudinal cut is constant along the circumferential direction, thereby ensuring that the removal rate of water or mud mixture is constant around the entire circumference of the tire.

[0052] Preferably, the inner radial portion of at least one inner longitudinal cut has a circular circumferential bisector centered on the tire's axis of rotation. Therefore, the inner radial portion does not fluctuate circumferentially in terms of tread thickness.

[0053] Preferably, at least one internal longitudinal cut includes an external radial portion leading to the tread surface and its internal radial portion, the external radial portion having a height HI1 and an average width WI1, the average width WI1 being at most 0.2 times the height HI1. As shown above, in the case of an external longitudinal cut, this external radial portion is an open sipe that has a favorable effect on grip, wear, and the thermal durability of the tread. Furthermore, it offers technical advantages in tread pattern production, allowing for molding and demolding of the internal radial portion, which is of a non-open groove type, to which it is connected.

[0054] According to a particular embodiment, the inner radial portion of at least one inner longitudinal cut is continued radially inward by a supplementary inner radial portion having a height HI3 and an average width WI3 (which is at most equal to 0.2 times the height HI3). When the radial depth DI2 of the inner radial portion of the inner longitudinal cut is significantly less than D0, preferably less than 9*D0 / 10, the inner radial portion of the effective groove type itself can be continued radially inward by a supplementary inner radial portion of the groove type, down to a depth at most equal to D0, preferably at most equal to 9*D01 / 10.

[0055] According to another specific embodiment, the tread includes two internal longitudinal grooves, each of which has an internal radial portion that is radially offset relative to each other in terms of tread thickness. Thus, the effective radial portions of the external and internal longitudinal grooves form a stepped arrangement of three effective radial portions that at least partially overlap radially in pairs.

[0056] When a tire mounted on a nominal rim is inflated to a nominal pressure Pn and compressed under a nominal load Zn, the tire has an outer diameter D measured in the equatorial plane and a load-contact surface area of ​​circumferential length C0. At least one external longitudinal cut is preferably connected to at least NE external lateral cuts, which open outwards at the axial ends of the tread, NE being at least equal to Π*D / C0, such that the load-contact surface area includes at least one external lateral cut. A lateral cut is understood as a cut where the bisector forms an angle of at least 45° with the circumferential direction of the tire. The bisector forms an angle of 90° and is strictly lateral, or the bisector includes at least one inclined portion forming an angle strictly less than 90°.

[0057] As described above, when a tire is fitted to the front axle of a vehicle, whether in a brand-new condition or at the onset of wear, each external longitudinal slit allows for the removal of water and dirt that may be present on the ground in the circumferential direction through its external radial portion. In addition to this longitudinal removal, each external longitudinal slit connects to a set of lateral slits called external transverse slits, which ensure lateral removal of water and dirt at the side edges of the tread (often referred to as the tire shoulder). However, this lateral removal requires the presence of at least one such external transverse slit leading to the load-bearing contact surface area. This minimum requirement is ensured by a regular circumferential distribution of NE external transverse slits (but not necessarily at a constant spacing), where NE is at least equal to Π*D / C0, where D is the outer diameter of the tire and C0 is the circumferential length of the load-bearing contact surface area.

[0058] Advantageously, the outer radial portion of at least one outer longitudinal cut extends radially inward to a radial depth DE1, and the outer radial portion of each outer transverse cut has a height HTE1 at least equal to HE1, an average width WTE1 at least equal to 0.6*HTE1 (preferably at least equal to WE1), and a depth DTE1 at least equal to DE1. Therefore, the outer radial portion of the outer transverse cut is an effective groove whose height and depth are at least equal to the height and depth of the outer radial portion of the outer longitudinal cut, but with at least equal widths, to ensure that the transverse removal rate is at least equal to the longitudinal removal rate.

[0059] Advantageously, each outer transverse cut has an inner radial portion leading to its outer radial portion, the inner radial portion having a height HTE2 and an average width WTE2, the average width WTE2 being at most equal to 0.2 times the height HTE2. Therefore, each outer transverse cut has a groove-type inner radial portion connected to the groove-type inner radial portion of the outer longitudinal cut.

[0060] When a tire mounted on a nominal rim is inflated to a nominal pressure Pn and compressed under a load equal to about 0.25*Zn, the tire has an outer diameter D measured in the equatorial plane and a circumferential length C1 of unloaded contact surface area, with at least one internal longitudinal cut advantageously connected to at least NI internal transverse cuts that open to the outside at the axial ends of the tread, NI being at least equal to Π*D / C1, such that the unloaded contact surface area includes at least one internal transverse cut.

[0061] When a tire is fitted to the rear axle of an unloaded vehicle, for wear conditions at least at the bottom of the outer radial portion of the outer longitudinal cut, each inner longitudinal cut allows for the removal of water and dirt that may be present on the ground in the circumferential direction through its inner radial portion. In addition to this longitudinal removal, each inner longitudinal cut is connected to a set of lateral cuts called inner lateral cuts, which ensure lateral removal of water and dirt at the side edges of the tread (commonly referred to as the tire shoulder). However, this lateral removal requires the presence of at least one such inner lateral cut leading to the unloaded contact surface area. This minimum requirement is ensured by a regular circumferential distribution of NI inner lateral cuts (but not necessarily at a constant spacing), where NI is at least equal to Π*D / C1, where D is the outer diameter of the tire and C1 is the circumferential length of the unloaded contact surface area.

[0062] Advantageously, the inner radial portion of at least one inner longitudinal cut extends radially inward to a radial depth DI2, and the inner radial portion of each inner transverse cut has a height HTI2 at least equal to HI2, an average width WTI2 at least equal to 0.6*HTI2 (preferably at least equal to WI2), and a depth DTI2 at least equal to DI2. Therefore, the inner radial portion of the inner transverse cut is an effective groove whose height and depth are at least equal to the height and depth of the inner radial portion of the inner longitudinal cut, but with at least equal widths, to ensure that the transverse removal rate is at least equal to the longitudinal removal rate.

[0063] Advantageously, each internal transverse cut has an external radial portion leading to the tread surface and to its internal radial portion, the external radial portion having a height HTI1 and an average width WTI1, the average width WTI1 being at most 0.2 times the height HTI1. Therefore, each internal transverse cut has a groove-type external radial portion connected to the groove-type external radial portion of the external longitudinal cut.

[0064] The external longitudinal cuts, or each external longitudinal cut, have bisectors located at an axial distance LE of at most 0.8 * L0 / 2 relative to the tire's equatorial plane. This upper limit ensures that each tread sidewall end has sufficient width relative to tread edge wear.

[0065] The internal longitudinal slits, or each internal longitudinal slit, also advantageously have bisectors located at an axial distance LI of at least 0.15 * L0 / 2 relative to the tire's equatorial plane. This lower limit ensures that the central portion of the tread has sufficient width relative to its impact resistance.

[0066] The difference between the axial distance LE and the axial distance LI is also advantageously at least equal to 0.2*L0 / 2, preferably at least equal to 0.3*L0 / 2. This feature ensures a balanced distribution of the outer longitudinal cut and the inner longitudinal cut across the tread width, thereby ensuring a balanced distribution of pressure in the contact surface area and thus ensuring more uniform wear across the tread width.

[0067] The tread volumetric porosity (TEV) is equal to the ratio between the total volume of the cuts (VD, measured on an unused tire, i.e., an unmounted and uninflated tire) and the sum of the total volume of the cuts (VD) and the total volume of the raised elements defined by these cuts (VR). At any wear level between a brand-new condition corresponding to the maximum cut depth D0 and a wear condition corresponding to the maximum cut depth DR (which is at least equal to D0 / 10 and at most equal to D0 / 3, preferably at most equal to D0 / 4), the TEV must be at least 12%, preferably at least 14%. A minimum TEV of 12% (preferably 14%) is necessary at any wear level within the desired range for storing and removing water or mud mixtures that may be present on the driving surface.

[0068] The tread volumetric void fraction (TEV) is equal to the ratio between the total volume of the cuts (VD, measured on an unused tire, i.e., an unmounted and uninflated tire) and the sum of the total volume of the cuts (VD) and the total volume of the raised elements defined by these cuts (VR). At any wear level between a brand-new state corresponding to the maximum cut depth D0 and a wear state corresponding to the maximum cut depth DR (which is at least equal to D0 / 10 and at most equal to D0 / 3, preferably at most equal to D0 / 4), the TEV volumetric void fraction is preferably at most 20%, more preferably at most 18%. To ensure sufficient rubber compound volume associated with tread wear, a maximum TEV of 20% (preferably 18%) is necessary at any wear level within the desired range.

[0069] The surface area porosity (TES) of the tread is equal to the ratio between the total surface area of ​​the cuts (SD) and the sum of the total surface area of ​​the cuts (SD) and the total surface area of ​​the raised elements defined by these cuts (SR), where the surface areas (SD) and (SR) are determined in the contact surface area. At any wear level between a brand-new state corresponding to the maximum cut depth (D0) and a wear state corresponding to the maximum cut depth (DR), which is at least equal to D0 / 10 and at most equal to D0 / 3, preferably at most equal to D0 / 4), the surface area porosity (TES) is preferably at least 10%, preferably at least 13%. At any wear level within the desired range, a minimum surface area porosity (TES) of 10% (preferably 3%) ensures the number of slits leading to the tread surface associated with effective denting and grip on the ground.

[0070] The surface area porosity (TES) of the tread is equal to the ratio between the total surface area of ​​the cuts (SD) and the sum of the total surface area of ​​the cuts (SD) and the total surface area of ​​the raised elements defined by these cuts (SR), where the surface areas (SD) and (SR) are determined in the contact surface area. At any wear level between a virgin state corresponding to the maximum cut depth (D0) and a wear state corresponding to the maximum cut depth (DR), which is at least equal to D0 / 10 and at most equal to D0 / 3, preferably at most equal to D0 / 4), the surface area porosity (TES) is preferably at most 24%, more preferably at most 20%. At any wear level within the desired range, a maximum surface area porosity (TES) of 24% (preferably 20%) ensures sufficient loaded and unloaded contact surface areas, thereby limiting contact pressure and thus limiting wear.

[0071] At any wear level, the tread has a volumetric porosity TEV equal to the ratio between the total volume of the cuts (VD, which is measured on an unused tire, i.e., on a tire that is not mounted and not inflated) and the sum of the total volume of the cuts and the total volume of the protrusions defined by these cuts (VR), and a surface area porosity TES equal to the ratio between the total surface area of ​​the cuts (SD) and the sum of the total surface area of ​​the cuts and the total surface area of ​​the protrusions defined by these cuts (SR). The surface areas (SD and SR) are determined in the contact surface region. Between a brand-new state corresponding to the maximum cut depth D0 and a wear state corresponding to the maximum cut depth DR (which is at least equal to D0 / 10 and at most equal to D0 / 3, preferably at most equal to D0 / 4), the TEV / TES ratio is preferably at least equal to 0.8 on average. The inventors have devised a method to achieve the highest possible TEV / TES ratio by maximizing the volumetric porosity (TEV) related to grip on wet or muddy surfaces, with the goal of effectively storing and removing water or mud mixtures, and minimizing the abrasion-related surface porosity (TES) by seeking to achieve the largest possible contact surface area. Attached Figure Description

[0072] schematic drawing not to scale Figures 1 to 12 Description of the features of the present invention:

[0073] - Figure 1 A top view of the tread portion of the tire according to the invention in a brand-new condition (maximum cut depth D0).

[0074] - Figure 2 A top view of the tread portion of the tire according to the present invention in a wear condition of 2 / 3 wear (maximum cut depth D0 / 3).

[0075] - Figure 3A perspective view of the tread portion of a tire according to the present invention in a brand-new state.

[0076] - Figure 4 The meridional section of the tire tread in a brand-new state according to the present invention.

[0077] - Figure 5 A perspective view of the tread portion of a tire according to the present invention in a brand-new state.

[0078] - Figure 6 A side view of the tread portion of a tire according to the invention in a brand-new condition.

[0079] - Figure 7 The volumetric porosity (TEV) of tire I according to the present invention and two prior art reference tires R1 and R2 varies with the maximum cut depth Dmax (in percentage of the maximum cut depth D0 in the brand new state).

[0080] - Figure 8 The variation of surface area porosity TES (in percentage) with volume porosity TEV (in percentage) of tire I according to the present invention and two prior art reference tires R1 and R2,

[0081] - Figure 9 The change of the ratio of volumetric porosity to surface porosity (TEV / TES) of tire I according to the present invention and two prior art reference tires R1 and R2 as a function of maximum cut depth Dmax (in percentage of maximum cut depth D0 in brand new condition).

[0082] - Figure 10 The variation of the total effective groove volume (VCE) (which leads to the tread under a given wear condition) of tire I according to the present invention and two prior art reference tires R1 and R2 as a function of the maximum cut depth Dmax (in percentage of the maximum cut depth D0 in a brand-new condition).

[0083] - Figure 11 Top view of the tread section of the reference tire R1 in brand new condition (Michelin 24.00R 35XTRALOAD PROTECT product).

[0084] - Figure 12 Top view of the tread portion of the reference tire R2 in brand new condition (Michelin 24.00R 35XTRALOAD GRIP product). Detailed Implementation

[0085] Figure 1This is a top view of the tread portion 2 of the tire 1 according to the invention in a brand-new state, having a maximum cut depth D0 (not shown). The tire 1, intended for heavy-duty vehicles of the construction site type, includes a tread 2 in its brand-new state before driving, designed to contact the ground via the tread surface 3. When the tire is inflated to a nominal pressure Pn and compressed under a nominal load Zn while mounted on a nominal rim, the tread surface 3 has an axial width L0. When the tire is inflated to a nominal pressure Pn and compressed under a load equal to approximately 0.25*Zn, the tread surface 3 has an axial width L1 (not shown). The tread 2 includes a cut 4 with a maximum depth D0 (not shown) separating the raised elements 6. The tread 2 includes an outer longitudinal cut 41 and an inner longitudinal cut 42 on each side of the equatorial plane XZ. The outer longitudinal cut 41 has a bisector ME located at an axial distance LE of at least 0.5 * L0 / 2 relative to the equatorial plane XZ of the tire, and the inner longitudinal cut 42 has a bisector MI located at an axial distance LI of at most 0.4 * L0 / 2 relative to the equatorial plane XZ of the tire. The cuts are described in a novel manner below. The outer longitudinal cut 41 includes an outer radial portion 411 of the groove type with an average width WE1. Furthermore, the outer longitudinal cut 41 is connected to an outer lateral cut 51, each of which includes an outer radial portion 511 of the groove type with an average width WTE1. The inner longitudinal cut 42 includes an outer radial portion 421 of the sipe type with an average width WI1. Furthermore, the inner longitudinal cut 42 is connected to an inner lateral cut 52, each of which includes an outer radial portion 521 of the sipe type with an average width WTI1.

[0086] Figure 2 This is a top view of the tread portion 2 of the tire 1 according to the invention in a wear state of 2 / 3 wear, wherein the maximum cut depth Dmax is equal to D0 / 3 (not shown). Figure 1 Some markers in Figure 2 The text repeats itself. In the following description, the cuts are described in terms of wear state (typically 2 / 3 wear). The outer longitudinal cut 41 includes an inner radial portion 412 of the groove type with an average width WE2. Furthermore, the outer longitudinal cut 41 is connected to an outer transverse cut 51, each of which includes an inner radial portion 512 of the groove type with an average width WTE2. The inner longitudinal cut 42 includes an inner radial portion 422 of the groove type with an average width WI2. Furthermore, the inner longitudinal cut 42 is connected to an inner transverse cut 52, each of which includes an inner radial portion 522 of the groove type with an average width WTI2.

[0087] Figure 3The image shows a perspective view of the tread portion 2 of the tire according to the invention in a brand-new state, wherein the system of longitudinal cuts (41, 42) is shown more specifically from a perspective angle.

[0088] Figure 4 To and Figure 3 The relevant meridional sections depict the system of longitudinal cuts (41, 42). According to the invention, the outer longitudinal cut 41 includes an outer radial portion 411 extending toward the tread surface 3, the outer radial portion 411 having a height HE1 and an average width WE1 at least 0.6 times the height HE1, i.e., it is an effective groove; the inner longitudinal cut 42 includes an inner radial portion 422 not extending toward the tread surface 3, the inner radial portion 422 extending at least partially radially inside the outer radial portion 411 of the outer longitudinal cut 41 and having a height HI2 and an average width WI2 at least 0.6 times the height HI2, i.e., it is also an effective groove. Therefore, there is typically (but not necessarily) radial overlap between the bottom of the effective groove type outer radial portion 411 of the outer longitudinal cut 41 and the top of the equally effective groove type inner radial portion 422 of the inner longitudinal cut 42. Advantageously, the average width WE1 of the outer radial portion 411 of the outer longitudinal cut 41 is at most twice its height HE1, preferably at most equal to its height HE1. Furthermore, the outer radial portion 411 of the outer longitudinal cut 41 extends radially inward to a radial depth DE1, which is advantageously at least equal to D0 / 4, preferably at least equal to D0 / 3, and also advantageously at most 2*D0 / 3, preferably at most equal to D0 / 2. Finally, the outer longitudinal cut 41 preferably includes an inner radial portion 412 leading to its outer radial portion 411, the inner radial portion 412 having a height HE2 and an average width WE2 at most 0.2 times the height HE2, i.e., it is a sipe that does not extend to the tread surface in a brand-new state. Advantageously, the average width WI2 of the inner radial portion 422 of the inner longitudinal cut 42 is at most twice its height HI2, preferably at most equal to its height HI2. Furthermore, the inner radial portion 422 of the inner longitudinal cut 42 extends radially inward to a radial depth DI2, which is advantageously at least equal to D0 / 2, preferably at least equal to 2*D0 / 3, and also advantageously at most equal to D0, preferably at most equal to 9*D0 / 10, and even more preferably at most equal to 3*D0 / 4. Preferably, the inner longitudinal cut 42 includes an outer radial portion 421 leading to the tread surface 3 and to its inner radial portion 422, the outer radial portion 421 having a height HI1 and an average width WI1 at most 0.2 times the height HI1, i.e., it is a sipe leading to the tread surface in a brand-new state.

[0089] Figure 5The image shows a perspective view of the tread portion 2 of the tire according to the invention in a brand-new state, wherein the system of lateral cuts (51, 52) is shown more specifically from a perspective angle.

[0090] Figure 6 To and Figure 5The relevant side view depicts the system of lateral cuts (51, 52). Advantageously, when the tire mounted on the nominal rim is inflated to the nominal pressure Pn and compressed under the nominal load Zn, the tire has an outer diameter D (not shown) measured in the equatorial plane YZ and a load contact surface area (not shown) with a circumferential length C0. An outer longitudinal cut 41 is connected to at least NE outer lateral cuts 51, which open outward at the axial end of the tread 2, NE being at least equal to Π*D / C0, such that the load contact surface area includes at least one outer lateral cut. Advantageously, when a tire mounted on a nominal rim is inflated to a nominal pressure Pn and compressed under a load equal to approximately 0.25*Zn, the tire has an unloaded contact surface area (not shown) with a circumferential length C1, an internal longitudinal cutout 42 connecting to at least NI internal lateral cutouts 52, the internal lateral cutouts 52 opening to the outside at the axial end 21 of the tread 2, NI being at least equal to Π*D / C1, such that the unloaded contact surface area in contact with the ground includes at least one internal lateral cutout. Each external lateral cutout 51 preferably includes an external radial portion 511 having a height HTE1 equal to HE1, an average width WTE1 at least equal to 0.6*HTE1 (preferably at least equal to WE1), and a depth DTE1 equal to DE1. Therefore, the outer radial portion 511 is an effective groove having the same height and depth as the outer radial portion 411 of the outer longitudinal cut 41 to which it is connected, and having at least equal average width, to ensure that the removal rate of the water or mud mixture is at least as high as that of the outer longitudinal cut 41. Advantageously, each outer transverse cut 51 has an inner radial portion 512 leading to its outer radial portion 511, the inner radial portion 512 having a height HTE2 and an average width WTE2 equal to at most 0.2 times the height HTE2, i.e., it is a non-open cutter groove connected to the inner radial portion 412 of the outer longitudinal cut 41 in a brand-new state. Similarly, each inner transverse cut 52 preferably includes an inner radial portion 522 having a height HTI2 equal to HI2, an average width WTI2 at least equal to 0.6 * HTI2 (preferably at least equal to WI2), and a depth DTI2 equal to DI2. Therefore, the inner radial portion 522 has the same height and depth as the inner radial portion 422 of the inner longitudinal cut 42 to which it is connected, and has at least equal average width, to ensure that the removal rate of water or mud mixture is at least as high as that of the inner longitudinal cut 42.Advantageously, each internal transverse cut 52 has an external radial portion 521 leading to the tread surface and to its internal radial portion 522, the external radial portion 521 having a height HTI1 and an average width WTI1 equal to at most 0.2 times the height HTI1, i.e., it is a non-open sipe connected to the external radial portion 421 of the internal longitudinal cut 42 in a brand-new state.

[0091] Figure 7 The diagram shows the variation of the volumetric void fraction (TEV) as a percentage of the maximum cut depth Dmax (in the form of a percentage of the maximum cut depth D0 in the new condition) for tire I according to the invention and two prior art reference tires R1 and R2. The maximum cut depth D0 in the new condition is the base of the horizontal axis in the figure, 100. The Dmax / D0 ratio defines a given tread wear state. For tire I according to the invention, the volumetric void fraction TEV decreases slightly on average from 17.5% in the new condition (where Dmax equals D0) to 14% in the fully worn condition (where Dmax equals D0 / 10). For the prior art reference tire R1 (corresponding to the Michelin 24.00R 35XTRALOAD PROTECT product, which aims to provide attack protection through a more closed tread in the middle section in the new condition), the volumetric void fraction TEV decreases from 12.5% ​​in the new condition (where Dmax equals D0) to 5% in the fully worn condition (where Dmax equals D0 / 10). Finally, for the prior art reference tire R2 (corresponding to the Michelin 24.00R 35XTRA LOAD GRIP product, which aims to achieve grip through a more open tread across the entire axial width), the volumetric void fraction TEV is reduced from 22% in the new condition (where Dmax equals D0) to 5% in the fully worn condition (where Dmax equals D0 / 10). Therefore, the tire according to the invention has the advantage of having a substantially constant volumetric void fraction TEV, thus enabling substantially constant removal of water or mud mixtures throughout the tire's lifespan under all wear conditions.

[0092] Figure 8The diagram shows the variation of surface area porosity (TES) as a function of volumetric porosity (TEV) (in%) with respect to tire I according to the invention and two prior art reference tires R1 and R2. For tire I according to the invention, the volumetric porosity TEV varies between 14% and 17.5%, as shown above, and the surface area porosity TES varies between 12% and 24%. For the prior art reference tire R1 (corresponding to Michelin 24.00R 35XTRALOAD PROTECT), the volumetric porosity TEV varies between 5% and 12.5%, as shown above, and the surface area porosity TES varies between 6% and 18%. For the prior art reference tire R2 (corresponding to Michelin 24.00R 35XTRALOAD GRIP), the volumetric porosity TEV varies between 5% and 22%, as shown above, and the surface area porosity TES varies between 7% and 42%. Therefore, the tire I according to the invention has a much narrower range of variation in volumetric porosity (TEV) and surface porosity (TES), thereby making the tire durable in terms of grip and wear performance throughout its entire lifespan.

[0093] Figure 9 The diagram shows the variation of the volumetric porosity to surface porosity ratio (TEV / TES) as a function of the maximum cut depth Dmax (as a percentage of the maximum cut depth D0 in a brand-new condition) for tire I according to the invention and two prior art reference tires R1 and R2. For tire I according to the invention, the TEV / TES ratio varies between 0.75 and 1.3. For prior art reference tire R1 (corresponding to Michelin 24.00R 35XTRALOAD PROTECT), the TEV / TES ratio varies between 0.6 and 0.75. For prior art reference tire R2 (corresponding to Michelin 24.00R 35XTRALOAD GRIP), the TEV / TES ratio varies between 0.5 and 0.8. Therefore, tire I according to the invention has a TEV / TES ratio that is always greater than that of tires R1 and R2. This slightly higher TEV / TES ratio is achieved by maximizing the volumetric porosity (TEV) related to grip on wet or muddy surfaces, with the goal of effectively storing and removing water or mud mixtures, and by minimizing the abrasion-related surface porosity (TES) by seeking to achieve the largest possible contact surface area.

[0094] Figure 10The figure shows the variation of the total effective groove volume (VCE) of tire I according to the invention and two prior art reference tires R1 and R2 as a function of the maximum cut depth Dmax (in percentage of the maximum cut depth D0 in a brand-new state). It is clear from the figure that in the portion exceeding half-wear, i.e., for a Dmax / D0 ratio of less than 50%, the total effective groove volume VCE of the tread of tire I according to the invention is greater than the total effective groove volume VCE of the corresponding treads of the two reference tires R1 and R2, thus providing a larger volume for storing water or mud present on the ground. However, it should be noted that for a Dmax / D0 ratio greater than 50%, the total effective groove volume VCE of tires I and R1 is very similar, meaning that the treads of both tires ensure equivalent storage volume before the tire is half-worn, and therefore have equivalent grip performance.

[0095] Figure 11 This image shows a top view of the tread portion of the reference tire R1 in a brand-new condition (Michelin 24.00R35XTRA LOAD PROTECT). The tread pattern is more closed in the middle section and more open on the two side sections that extend from the middle. The more closed tread pattern includes narrow longitudinal and lateral grooves (which ensure a certain volume of wear material is contained and protected against impact), while the more open tread pattern includes lateral grooves leading to the tread edges in each case to at least partially remove water or mud mixtures. In this design, wear life and impact resistance take precedence over grip. More specifically, only the lateral grooves leading to the tread edges, with a width of 45 mm and a height of 74 mm, are effective. The other grooves in the middle section have a width of 7 mm and a maximum height of 60 mm, meaning that these other grooves are closed in the contact surface area regardless of whether the vehicle is unloaded or loaded.

[0096] Figure 12The image shows a top view of the tread portion of the reference tire R2 in a brand-new condition (Michelin 24.00R35XTRA LOAD GRIP product). The open tread pattern comprises a network of wide longitudinal and lateral grooves in the center section and two side sections extending from the center section. These longitudinal and lateral grooves allow for the trapping of mud across the entire tread surface and at least partial removal of mud via lateral grooves extending outwards at the edges of the tread. More specifically, the longitudinal grooves substantially do not meet the groove effectiveness criteria (W > 0.6 * H). Specifically, the longitudinal grooves in the center section have a width of 21 mm and a height of 44 mm, and the longitudinal grooves in each side section have a width of 37 mm and a height of 70 mm. Only the lateral grooves meet the groove effectiveness criteria, with a width of 44 mm and a height of 74 mm in each side section, and a width of 48 mm and a height of 67 mm in the center section.

[0097] The present invention has been studied more specifically in the case of tires for construction site vehicles of the dump truck type with a size of 24.00R35, but it is also applicable to sizes such as 18.00R33 and 59 / 80R63.

[0098] Table 1 below shows the features of the embodiments studied by the inventors:

[0099] [Table 1]

[0100]

[0101]

[0102]

[0103] As shown above, in Figure 10 In the description of the figures, particularly when the tire is worn beyond 50%, the tire I according to the invention is more effective in terms of grip on wet or muddy surfaces because the effective clearance volume VCE is greater than that of the reference tires R1 and R2. However, below 50% wear, the tire I according to the invention and the reference tire R1 have substantially equivalent grip performance.

[0104] Furthermore, the inventors discovered that, compared to a reference tire R1, the tire I according to the invention exhibits a reduced pressure difference between the central portion and each side portion, the pressure being measured in the contact surface area in contact with the ground. This pressure difference in the reference tire R1 is equal to 1.75 bar, while in the tire I according to the invention it is equal to 1 bar. In other words, the tire I according to the invention provides a more uniform pressure distribution in the contact surface area, thereby ensuring more uniform wear across the axial width of the tread.

Claims

1. A tire (1) for heavy-duty vehicles used in construction site types, which, in a brand-new condition before driving, includes a tread (2) designed to contact the ground via a tread surface (3): - When a tire mounted on a nominal rim is inflated to a nominal pressure Pn and compressed under a nominal load Zn, the tread surface (3) has an axial width L0. - The tread (2) includes a separating raised element (6) and a cut (4) with a maximum depth D0. - The tread (2) includes at least one external longitudinal cut (41) and at least one internal longitudinal cut (42) on each side of the equatorial plane (XZ), the external longitudinal cut (41) having a bisector (ME) at an axial distance LE of at least 0.5*L0 / 2 relative to the equatorial plane (XZ) of the tire, and the internal longitudinal cut (42) having a bisector (MI) at an axial distance LI of at most 0.4*L0 / 2 relative to the equatorial plane (XZ) of the tire. Its features are, At least one external longitudinal cut (41) includes an external radial portion leading to the tread surface (3) and having a height HE1 and an average width WE1, the average width WE1 being at least 0.6 times the height HE1; at least one internal longitudinal cut (42) includes an internal radial portion not leading to the tread surface (3), the internal radial portion extending at least partially radially inside the external radial portion of the external longitudinal cut (41) and having a height HI2 and an average width WI2, the average width WI2 being at least 0.6 times the height HI2.

2. The tire (1) according to claim 1, wherein, The average width WE1 of the outer radial portion of at least one outer longitudinal cut (41) is at most twice the height HE1.

3. The tire (1) according to any one of claims 1 and 2, wherein, The outer radial portion of at least one external longitudinal cut (41) extends radially inward to a radial depth DE1 equal to at least D0 / 4.

4. The tire (1) according to claim 1, wherein, The outer radial portion of at least one external longitudinal cut (41) extends radially inward to a radial depth DE1 of at most 2*D0 / 3.

5. The tire (1) according to claim 1, wherein, At least one external longitudinal cut (41) includes an internal radial portion leading to its external radial portion, the internal radial portion having a height HE2 and an average width WE2, the average width WE2 being at most equal to 0.2 times the height HE2.

6. The tire (1) according to claim 1, wherein, The average width WI2 of the inner radial portion of at least one inner longitudinal cut (42) is at most twice the height HI2.

7. The tire (1) according to claim 1, wherein, The inner radial portion of at least one internal longitudinal cut (42) extends radially inward to a radial depth DI2 equal to at least D0 / 2.

8. The tire (1) according to claim 1, wherein, The inner radial portion of at least one internal longitudinal cut (42) extends radially inward to a radial depth DI2 equal to at most D0.

9. The tire (1) according to claim 1, wherein, At least one internal longitudinal cut (42) includes an external radial portion leading to the tread surface (3) and to its internal radial portion, the external radial portion having a height HI1 and an average width WI1, the average width WI1 being at most equal to 0.2 times the height HI1.

10. The tire (1) according to claim 1, wherein when the tire mounted on a nominal rim is inflated to a nominal pressure Pn and compressed under a nominal load Zn, the tire has an outer diameter D measured in the equatorial plane (YZ) and a load contact surface area with a circumferential length C0, wherein, At least one external longitudinal cut (41) is connected to at least NE external transverse cuts (51), the external transverse cuts (51) opening to the outside at the axial end (21) of the tread (2), NE being at least equal to Π*D / C0, such that the load contact surface area includes at least one external transverse cut (51).

11. The tire (1) according to claim 10, wherein the outer radial portion of at least one outer longitudinal cut (41) extends radially inward to a radial depth DE1, wherein, Each external transverse cut (51) includes an external radial portion having a height HTE1 at least equal to HE1, an average width WTE1 at least equal to 0.6*HTE1, and a depth DTE1 at least equal to DE1.

12. The tire (1) according to claim 1, wherein when the tire mounted on a nominal rim is inflated to a nominal pressure Pn and compressed under a load of approximately 0.25*Zn, the tire has an outer diameter D measured in the equatorial plane (YZ) and an unloaded contact surface area with a circumferential length C1, wherein, At least one internal longitudinal cut (42) is connected to at least NI internal transverse cuts (52), the internal transverse cuts (52) opening to the outside at the axial end (21) of the tread (2), NI being at least equal to Π*D / C1, such that the unloaded contact surface area includes at least one internal transverse cut (52).

13. The tire (1) according to claim 12, wherein the inner radial portion of at least one inner longitudinal cut (42) extends radially inward to a radial depth DI2, wherein, Each internal transverse cut (52) includes an internal radial portion having a height HTI2 at least equal to HI2, an average width WTI2 at least equal to 0.6*HTI2, and a depth DTI2 at least equal to DI2.

14. The tire (1) according to claim 1, wherein, At least one external longitudinal cut (41) has a bisector (ME) located at an axial distance LE of at most 0.8 * L0 / 2 relative to the equatorial plane (XZ) of the tire.

15. The tire (1) according to claim 1, wherein, At least one internal longitudinal cut (42) has a bisector (MI) located at an axial distance LI of at least 0.15*L0 / 2 relative to the equatorial plane (XZ) of the tire.

16. The tire (1) according to claim 15, wherein, The difference between the axial distance LE and the axial distance LI is at least equal to 0.2*L0 / 2.

17. The tire (1) according to claim 1, wherein the volumetric porosity TEV of the tread (2) is equal to the ratio between the total volume VD of the cuts and the sum of the total volume VD of the cuts and the total volume VR of the protruding elements defined by these cuts, said total volume VD being measured on an unused tire, i.e., on a tire that is not installed and is not inflated, wherein, At any wear level between the brand-new state corresponding to the maximum cut depth D0 and the wear state corresponding to the maximum cut depth DR, the volumetric porosity TEV is at least equal to 12%, wherein the maximum cut depth DR is at least equal to D0 / 10 and at most equal to D0 / 3.

18. The tire (1) according to claim 1, wherein the volumetric porosity TEV of the tread (2) is equal to the ratio between the total volume VD of the cuts and the sum of the total volume VD of the cuts and the total volume VR of the protruding elements defined by these cuts, said total volume VD being measured on an unused tire, i.e., on a tire that is not installed and is not inflated, wherein, At any wear level between the brand-new state corresponding to the maximum cut depth D0 and the wear state corresponding to the maximum cut depth DR, the volumetric porosity TEV is at most 20%, wherein the maximum cut depth DR is at least equal to D0 / 10 and at most equal to D0 / 3.

19. The tire (1) according to claim 1, wherein the surface area porosity TES of the tread (2) is equal to the ratio between the total surface area SD of the cuts and the sum of the total surface area SD of the cuts and the total surface area SR of the protruding elements defined by these cuts, wherein the surface areas SD and SR are determined in the contact surface region, wherein, At any wear level between the brand-new state corresponding to the maximum cut depth D0 and the wear state corresponding to the maximum cut depth DR, the surface area porosity TES is at least equal to 10%, wherein the maximum cut depth DR is at least equal to D0 / 10 and at most equal to D0 / 3.

20. The tire (1) according to claim 1, wherein the surface area porosity TES of the tread (2) is equal to the ratio between the total surface area SD of the cuts and the sum of the total surface area SD of the cuts and the total surface area SR of the protruding elements defined by these cuts, wherein the surface areas SD and SR are determined in the contact surface region, wherein, Between the brand-new state corresponding to the maximum cut depth D0 and the wear state corresponding to the maximum cut depth DR, the surface area porosity TES is at most 24%, wherein the maximum cut depth DR is at least equal to D0 / 10 and at most equal to D0 / 3.

21. The tire (1) according to claim 1, wherein the tread (2) has a volumetric porosity TEV and a surface porosity TES, the volumetric porosity TEV being equal to the ratio between the total volume VD of the cuts and the sum of the total volume VD of the cuts and the total volume VR of the protrusions defined by these cuts, the total volume VD being measured on an unused tire, i.e., on a tire that is not installed and is not inflated, and the surface porosity TES being equal to the ratio between the total surface area SD of the cuts and the sum of the total surface area SD of the cuts and the total surface area SR of the protrusions defined by these cuts, the surface areas SD and SR being determined in the contact surface region, wherein, Between the brand-new condition corresponding to the maximum cut depth D0 and the tire wear condition corresponding to the maximum cut depth DR, the TEV / TES ratio is at least equal to 0.8 on average, and the maximum cut depth DR is at least equal to D0 / 10 and at most equal to D0 / 3.

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