Tire tread for heavy civil engineering vehicles with improved compromise between strength / thermal wear

Abstract

This invention relates to a tire tread 1 for heavy-duty civil engineering vehicles, and aims to provide a compromise between resistance to mechanical impact and thermal ventilation in stony soils. The tread has a central portion 11 comprising at least one longitudinal row of block portions 3, each block portion 3 being defined laterally by two longitudinal grooves 41 and longitudinally by two inter-block cutouts 42, the longitudinal grooves 41 having a radially outer portion 411 and a radially inner portion 412, and the inter-block cutouts 42 having a radially outer portion 421 and a radially inner portion 422. According to the invention, the maximum thickness (E11max, E21max) of each radially outer portion (411, 421) is at most equal to 20% of the depth (P1, P2) of the cut (41, 42) and strictly less than the maximum thickness (E12max, E22max) of the radially inner portion (412, 422), and the minimum thickness (E11min, E21min) of each radially outer portion (411, 421) is at least equal to 5% of the depth (P1, P2) of the cut (41, 42).

Description

Technical Field

[0001] The present invention relates to a tire tread for heavy vehicles (e.g., civil engineering vehicles of the dump truck type used in mines or quarries) designed to carry heavy loads and travel on irregular, stony and / or muddy surfaces. Background Technology

[0002] The tread contains at least one rubber-based material and is designed to form the outer periphery of the tire and wear when its driving surface comes into contact with the ground.

[0003] The tread is geometrically defined by three dimensions: the minimum dimension (or thickness) perpendicular to the running surface, the intermediate dimension (or width) in the lateral direction, and the maximum dimension (or length) in the longitudinal direction. When the tread is integrated into the tire, the direction perpendicular to the running surface is also called the radial direction because it is defined along the tire's radius; the lateral direction is also called the axial direction because it is parallel to the tire's axis of rotation; and the longitudinal direction is also called the circumferential direction because it is tangent to the tire's circumference in the tire's direction of travel. In the following text, "radial" means "perpendicular to the running surface" or "radial direction".

[0004] To ensure satisfactory performance in terms of longitudinal and lateral grip under engine and braking torque, a combination of cuts must be formed in the tread to separate raised elements (called engravings).

[0005] The geometry of the cut lies in its thickness (the distance between the material walls defining the cut) and its depth (the distance between the driving surface and the bottom of the cut (i.e., its radially innermost point)). The thickness can vary depending on the radial position of the measurement point between the driving surface and the bottom of the cut.

[0006] Cuts can be of two types: grooves and sipes. Grooves are wide cuts primarily used to store and remove water or mud present on the ground. A cut is called a wide cut when the thickness of the cut is such that the opposing walls of the material defining the cut do not come into contact with each other as the tread moves across the contact patch, provided the tire meets recommended inflation and load conditions (e.g., particularly those specified in ISO 4250 and the Tire & Rim Association (TRA) standards). Sipes are narrow cuts whose intersection (or edge) with the driving surface contributes to grip on wet surfaces because the edge effect in contact with the ground can disrupt the water film present on the ground. A cut is called a narrow cut if, under the load and pressure conditions specified in the aforementioned TRA standards, the cut width is such that the opposing walls of the material defining the cut at least partially come into contact with each other as the tread moves across the contact patch.

[0007] A slit is typically characterized by a central surface equidistant from the wall that defines the slit and cuts through the driving surface. The intersection of this central surface and the driving surface is called the centerline of the slit. The centerline of the slit is not necessarily a straight line, but can be, for example, wavy or zig-shaped. When the centerline of the slit has a longitudinal average direction (i.e., when its average angle with the longitudinal direction is no greater than 45°), the slit is called longitudinal. Longitudinal slits typically extend around the tire. When the centerline of the slit has a transverse average direction (i.e., when its average angle with the transverse direction is no greater than 45°), the slit is called transverse. Transverse slits connect two longitudinal slits to each other, or connect longitudinal slits to the edge of the tread.

[0008] In the case of tire treads used on heavy-duty civil engineering vehicles, the raised elements are typically block-shaped portions. A block is a volume of material defined by a contact surface, a bottom surface, and sides connecting the contact surface to the bottom surface, all contained within the running surface. These blocks can be arranged in longitudinal rows forming blocks, separated in pairs by longitudinal cuts in the form of grooves or sipes (also called longitudinal channels). Within a single longitudinal row of blocks, the blocks are typically separated in pairs by transverse cuts in the form of grooves or sipes.

[0009] The geometry of the tread incorporated into a tire typically consists of a width L in the lateral direction and a height H in the direction perpendicular to the road surface. Width L is defined as the lateral width of the contact patch of a brand-new tire tread on a flat surface (e.g., paved road) when the tire meets the nominal pressure and load conditions (e.g., the nominal pressure and load conditions recommended by TRA standards). Height H is conventionally defined as the maximum radial depth measured in the cut, corresponding to the maximum radial block height in a brand-new condition. In the case of tires for dump truck-type civil engineering vehicles, as an example, the width L is at least 600 mm, and the height H is at least 60 mm, or possibly 70 mm.

[0010] The tires of civil engineering vehicles operate under particularly harsh conditions. These vehicles are typically designed to travel on rough, rocky trails, requiring tires with excellent impact resistance to ensure a satisfactory service life. Furthermore, the typically high loads on the tires result in considerable heat dissipation (especially in the tire tread), causing temperature rise that can degrade the rubber base material of the tread and lead to premature tire failure. Therefore, impact resistance of the tread and thermal control of the tread are two key requirements for tires mounted on heavy-duty civil engineering vehicles.

[0011] Regarding the thermal control of the tire tread, it is known that the tire tread temperature decreases with increasing tread ventilation, in other words, it decreases with increasing volume of slits providing ventilation. However, the current trend is to develop treads with longer lifespans, thus having increased volume of wearable material, i.e., reduced slit volume. Therefore, document WO2017162953A1 proposes a so-called sipe tread; however, the sipes may be sensitive to attack and are not sufficiently effective in terms of thermal ventilation. Document WO 2020229176A1 proposes a sipe tread in which the sipes have enhanced attack resistance by improving their geometry, but without any improvement in the effectiveness of ventilation provided by the sipes. Summary of the Invention

[0012] The inventors set a goal for themselves to improve the trade-off between the mechanical impact resistance and thermal ventilation of tire treads for heavy civil engineering vehicles on rocky surfaces, said tire treads comprising at least in part blocks separated from each other by sipes.

[0013] This objective has been achieved through tire treads used in heavy-duty civil engineering vehicles, which are designed to contact the ground via a running surface, comprising blocky portions defined by cuts, and having a width and a thickness defined as the maximum cut depth.

[0014] - The tread has a central portion that is symmetrical with respect to a central longitudinal plane and has a width not exceeding 60% of the tread width.

[0015] - The middle portion includes at least one longitudinal row of block-shaped portions, wherein each block-shaped portion is defined laterally by two longitudinal channels and longitudinally by a transverse cut between two block-shaped portions.

[0016] - Each longitudinal channel and each lateral cut between block sections has a depth of at least 50% of the tread thickness and is a staged cut, the staged cut including a radially outer portion leading to the driving surface and a radially inner portion extending from the radially outer portion to the radially inner ends (4121, 4221).

[0017] - The thickness of each radially outer portion, measured between the material walls defining the radially outer portion, is within the range of minimum to maximum thickness.

[0018] - The thickness of each radial inner portion, measured between the material walls defining the radial inner portion, is within the range of minimum to maximum thickness.

[0019] - The maximum thickness of each radially outer portion shall not exceed 20% of the depth of the corresponding cut, and shall be strictly less than the maximum thickness of the corresponding radially inner portion.

[0020] - The minimum thickness of each radially outer portion shall be at least 5% of the depth of the corresponding cut.

[0021] This invention is essentially based on optimizing the respective thicknesses of the radially outer and radially inner portions of each longitudinal or transverse cut in each block portion that defines a longitudinal row of blocks belonging to a specific block portion. The longitudinal row of said specific block portions is located in the middle portion of the tread. This invention aims to provide a trade-off between crack resistance and thermal ventilation of said cuts.

[0022] In the context of this invention, the central portion of the tread is a tread portion that is symmetrical with respect to a central longitudinal plane passing through the center of the tread and perpendicular to the driving surface, and has a width not exceeding 60% of the tread width, which is measured in the lateral direction between the two side edges of the driving surface. The central portion includes one or more longitudinal rows of blocky portions according to the invention, but may also include other sculpted elements. In other words, the central portion does not necessarily consist only of longitudinal rows of blocky portions according to the invention.

[0023] By definition, the longitudinal cuts that define the blocky portions in the middle part of the tread are called longitudinal grooves, and the transverse cuts that define the blocky portions in the middle part of the tread are called inter-block transverse cuts.

[0024] Each longitudinal channel and each lateral cut between block sections are staged cuts, each staged cut including a radially outer portion leading to the driving surface and a radially inner portion extending from the radially outer portion to the bottom of the cut. The thickness of each radially outer portion, measured between the material walls defining the radially outer portion, can vary between the driving surface (i.e., the radially outermost point of the portion) and the radially innermost point of the portion in a direction perpendicular to the driving surface; therefore, the thickness of the radially outer portion is in the range of minimum to maximum thickness. Similarly, the thickness of each radially inner portion, measured between the material walls defining the radially inner portion, can vary between the radially outermost point of the portion and the bottom of the cut (i.e., the radially innermost point of the portion) in a direction perpendicular to the driving surface; therefore, the thickness of the radially inner portion is in the range of minimum to maximum thickness. These thicknesses are typically measured in a tread cross-section defined by two lateral planes perpendicular to the driving surface.

[0025] Each longitudinal channel and each lateral cut between blocks has a measured depth in a direction perpendicular to the driving surface, between the bottom of the driving surface and the bottom of the longitudinal channel or the bottom of the lateral cut between the blocks. In the context of this invention, this depth is at least 50% of the maximum cut depth, conventionally referred to as the tread height, which corresponds to the maximum thickness of the material to be worn before all engravings on the driving surface disappear.

[0026] According to a first fundamental feature of the invention, the maximum thickness of each radially outer portion is no greater than 20% of the depth of the corresponding cut, and is strictly less than the maximum thickness of the corresponding radially inner portion.

[0027] Setting the maximum thickness of the radially outer portion of the cut to 20% of the cut depth limits the volume of the cut and thus its impact on the reduction of the volume of the wearable material, thereby improving its wear life. Furthermore, it strengthens the blocky portion defined by the cut by making the wall defining the radially outer portion contact the cut, thus limiting deformation at the bottom of the cut and limiting the risk of cracking at the bottom of the cut. The radially outer portion with this limited thickness is called a groove.

[0028] The strict limitation of the maximum thickness of the outer radial portion of the cut to the maximum thickness of the corresponding inner radial portion ensures sufficient excess thickness in the inner radial portion, thus limiting stress at the bottom of the cut and helping to minimize the risk of cracking at the bottom. Furthermore, this excess thickness in the inner radial portion also creates an air circulation channel at the bottom of the engraved part (where heat removal is most difficult), facilitating ventilation of the cut and thus limiting the tread temperature level. According to a specific embodiment of the inner radial portion, its thickness increases from a minimum at the interface with the outer radial portion to a maximum near the bottom of the cut. In this case, the shape of this inner radial portion is referred to as a teardrop shape.

[0029] According to a second fundamental feature of the invention, the minimum thickness of each radially outward portion is at least equal to 5% of the depth of the corresponding cut.

[0030] Setting the minimum thickness of each radially outer portion to 5% of the depth of the corresponding cut ensures air circulation in the radially outer portion, which helps with ventilation of the cut and thus limits the temperature level of the tread.

[0031] Preferably, the minimum thickness of each radially outer portion is at least equal to 10% of the depth of the corresponding cut. Setting the minimum thickness of each radially outer portion to 10% of the depth of the corresponding cut also improves air circulation in the radially outer portions, facilitates better ventilation of the cut, and thus provides further and even more effective limitation on the temperature level of the tread, while still maintaining sufficient locking force in the contact patch.

[0032] Furthermore, preferably, the minimum and maximum thicknesses of each radially outer portion are equal to each other, such that the thickness is constant at every point of the radially outer portion. In this case, the thickness of the radially outer portion is constant over its entire height, enabling the provision of an air circulation channel with a constant cross-section, thereby ensuring uniform and effective ventilation over the entire height of the radially outer portion.

[0033] Advantageously, the maximum thickness of each radially inner portion is at least 15% of the depth of the corresponding cut. Setting the lower limit of the maximum thickness of each radially inner portion to 15% of the depth of the corresponding cut prevents cracking at the bottom of the cut within the time it takes for the wear level of the tread to reach the bottom of the cut. In other words, this lower limit ensures that the wear level reaches the depth of the cut without cracking.

[0034] Furthermore, the height of each radially inner portion is at least 1.5 times the maximum thickness of the corresponding radially inner portion. If the radially inner portion has a teardrop shape and its thickness varies from the minimum thickness at the transition level of the radially outer portion to the maximum thickness at the bottom of the cut, then the angle of each wall of the radially inner portion relative to the radial direction (commonly referred to as the gap angle) can, on the one hand, limit the demolding force on the strip used for molding the cut, and on the other hand, limit the deterioration caused by tearing of the transition area between the radially outer and radially inner portions.

[0035] Advantageously, each radially inner portion has a circular radially inner end, the diameter of which is equal to the corresponding maximum thickness of the radially inner portion. The arc at the radially inner end of the radially inner portion (i.e., at the bottom of the cut) is a shape that provides the maximum constant radius of curvature, so that for a given volume of radially inner portion, the reduction of stress concentration can be optimized, thereby reducing the risk of cracking.

[0036] Advantageously, each block has a longitudinal length, and the depth of the transverse cut between each block is equal to or less than the longitudinal length of the block, or preferably equal to or less than 0.8 times the longitudinal length of the block. The ratio between the depth of the transverse cut between each block and the longitudinal length of the block is commonly referred to as the longitudinal protrusion of the block and is characterized in geometric terms as its longitudinal stiffness. Limiting the longitudinal protrusion to 1, preferably 0.8, is particularly effective in limiting the bending of the block under torque, and thus limiting irregular wear known as serrated wear. Despite the risk of temperature rise, a longitudinal protrusion of up to 0.8 or even 1 can be achieved due to the good ventilation of the cuts defining the block.

[0037] According to a first particular embodiment, the tread includes outer lateral cuts leading to longitudinal channels defining the block portions. Each outer lateral cut has a depth at least equal to 50% of the tread height and includes radially outer and radially inner portions. The thickness of each radially outer portion is in the range of a minimum to a maximum thickness, and the thickness of each radially inner portion is also in the range of a minimum to a maximum thickness. In this particular embodiment, the maximum thickness of each radially outer portion is equal to or less than 20% of the depth of the corresponding cut, and strictly less than the maximum thickness of the corresponding radially inner portion. Furthermore, the minimum thickness of each radially outer portion is at least equal to 5% of the depth of the corresponding cut. In other words, these outer lateral cuts have the same characteristics as the lateral cuts between the longitudinal channels and the block portions, and therefore possess the same technical advantages in crack resistance and thermal ventilation.

[0038] Preferably, the minimum thickness of the radially outer portion of each outer lateral cut is at least equal to 10% of the depth of the corresponding cut. Setting the minimum thickness of each radially outer portion to 10% of the depth of the corresponding cut also improves air circulation in the radially outer portion, facilitates better ventilation of the cut, and thus provides further and even more effective limitation on the temperature level of the tread, while still maintaining sufficient locking force in the contact patch.

[0039] Furthermore, preferably, the minimum and maximum thicknesses of the radially outer portions of each outer transverse cut are equal to each other. In this case, the thickness of the radially outer portion is constant over its entire height, enabling the provision of an air circulation channel with a constant cross-section, thereby ensuring uniform and effective ventilation over the entire height of the radially outer portion.

[0040] Advantageously, the maximum thickness of the radially inner portion of each outer lateral cut is at least 15% of the depth of the corresponding cut. Setting the lower limit of the maximum thickness of each radially inner portion to 15% of the depth of the corresponding cut prevents cracking at the bottom of the cut within the time it takes for the wear level of the tread to reach the bottom of the cut. In other words, this lower limit ensures that the wear level reaches the depth of the cut without cracking.

[0041] Furthermore, the height of the radially inner portion of each outer transverse cut is at least 1.5 times the maximum thickness of the corresponding radially inner portion. If the radially inner portion has a teardrop shape and its thickness varies from the minimum thickness at the transition level of the radially outer portion to the maximum thickness at the bottom of the cut, then the angle of each wall of the radially inner portion relative to the radial direction (commonly referred to as the gap angle) can, on the one hand, limit the release force on the strip used to mold the cut, and on the other hand, limit the deterioration caused by tearing of the transition area between the radially outer and radially inner portions.

[0042] Advantageously, the radially inner portion of each outer transverse cut has a circular radially inner end, the diameter of which is equal to the maximum thickness of the corresponding radially inner portion. The arc at the radially inner end of the radially inner portion (i.e., at the bottom of the cut) is a shape that provides the maximum constant radius of curvature, so that for a given volume of radially inner portion, the reduction of stress concentration can be optimized, thereby reducing the risk of cracking.

[0043] According to a second particular embodiment, each block portion includes at least one internal slit, the depth of which is no greater than the minimum depth of each longitudinal channel defining the block portion and the respective depth of the transverse slits between each block portion. The presence of at least one slit within the block portion provides supplemental cooling of the tread, which allows for the use of a more hysteretic tread rubber composition—in other words, a tread rubber composition that generates more heat but has better impact resistance. Preferably, but not necessarily, the internal slit opens to the surface of the block portion. If it does not open to the surface of the block portion, it is referred to as a “blind” slit.

[0044] Advantageously, each inner cut includes a radially outer portion with a thickness ranging from a minimum to a maximum thickness. The maximum thickness of the radially outer portion of the inner cut is equal to or less than the minimum maximum thickness of the radially outer portion of the transverse cut defining each longitudinal channel and each block portion. Inner cuts with a depth and maximum thickness less than the longitudinal channel and the transverse cut between the block portions have the same ventilation capacity as the transverse cut between the longitudinal channel and the block portions. This limited inner cut volume avoids excessive reduction in the volume of abrasive material and thus avoids excessive reduction in wear life.

[0045] Furthermore, advantageously, the maximum thickness of the radially outer portion of the inner notch is at least 5% and at most 20% of the depth of the corresponding inner notch. This range of maximum thickness provides a satisfactory trade-off between the ventilation capacity of the inner notch and its effect on the reduction of the volume of abrasive material.

[0046] Advantageously, the minimum thickness of the radially outer portion of the inner incision is at least 5% of the depth of the corresponding inner incision, and preferably at least 10% of the depth of the corresponding inner incision. This upper limit of the minimum thickness contributes to optimal ventilation of the inner incision.

[0047] Preferably, the minimum and maximum thicknesses of the radially outer portions of each inner cut are equal to each other, such that the thickness is constant at every point in the radially outer portions. In this case, the thickness of the radially outer portions is constant over the entire height of the radially outer portions, enabling the provision of an air circulation channel with a constant cross-section, thereby ensuring uniform and effective ventilation over the entire height of the radially outer portions.

[0048] Furthermore, preferably, each inner slit includes a radially inner portion with a thickness ranging from a minimum to a maximum thickness, and the maximum thickness of the radially outer portion of the inner slit is strictly less than the maximum thickness of the corresponding radially inner portion. If the tread rubber composition has a low wear rate, the time required for wear to reach the bottom of the inner slit and cause cracking to begin at the bottom of the slit may be long enough. In this case, it is helpful for the slit to have a thickened radially inner portion, shaped like a teardrop, thereby reducing the risk of cracking.

[0049] Advantageously, the maximum thickness of the radially inner portion of the inner cut is at least 15% of the depth of the corresponding inner cut. Setting the lower limit of the maximum thickness of each radially inner portion to 15% of the depth of the corresponding inner cut prevents cracking at the bottom of the inner cut within the time it takes for the wear level of the tread to reach the bottom of the inner cut. In other words, this lower limit ensures that the wear level reaches the depth of the cut without cracking.

[0050] Furthermore, the height of the radially inner portion of each inner cut is at least 1.5 times the maximum thickness of the corresponding radially inner portion. If the radially inner portion has a teardrop shape and its thickness varies from the minimum thickness at the transition level of the radially outer portion to the maximum thickness at the bottom of the cut, then the angle of each wall of the radially inner portion relative to the radial direction (commonly referred to as the gap angle) can, on the one hand, limit the release force on the strip used to mold the cut, and on the other hand, limit the deterioration caused by tearing of the transition area between the radially outer and radially inner portions.

[0051] Advantageously, the radially inner portion of each inner cut has a circular radially inner end, the diameter of which is equal to the maximum thickness of the corresponding radially inner portion of the inner cut. The arc at the radially inner end of the radially inner portion (i.e., at the bottom of the cut) is a shape that provides the maximum constant radius of curvature, so that for a given volume of the radially inner portion, the reduction of stress concentration can be optimized, thereby reducing the risk of cracking.

[0052] According to a preferred variant of the second specific embodiment, each inner cut is a lateral inner cut. The lateral direction of the inner cuts is beneficial to the tire's grip during braking, and thus to safety. On the other hand, the presence of longitudinal inner cuts near the central longitudinal plane of the tread weakens the tread subjected to high ground contact pressure in that area.

[0053] According to a preferred embodiment, the central portion of the tread includes longitudinal rows of blocky sections centered on a central longitudinal plane. For tires mounted on heavy-duty civil engineering vehicles and operating under normal load and pressure conditions, ground contact pressure is greatest at the center of the tread defined by the central longitudinal plane. The presence of blocky sections, rather than longitudinal channels, in this area makes the tread more robust.

[0054] To prevent being attacked by stones, it may be advantageous to have extra thickness at the bottom of the cut (especially at the intersection of the various cuts mentioned above, i.e., longitudinal channels, transverse cuts between blocky parts, and outer transverse cuts).

[0055] The presence of ribbed stone blocks protecting the protrusions can be advantageous, especially in longitudinal channels.

[0056] The present invention also relates to a tire mounted on a heavy civil engineering vehicle, the tire comprising the tread described in any of the above embodiments. Attached Figure Description

[0057] Indicative and not proportional to the following Figures 1 to 8 The characteristics of the present invention are described in the following:

[0058] - Figure 1 Top view of the tire tread according to the present invention

[0059] - Figure 2A Top view of the middle portion of the tread according to the present invention.

[0060] - Figure 2B Cross-sectional view of the longitudinal channel in the middle portion of the tread according to the present invention.

[0061] - Figure 2C Cross-sectional view of the transverse cut between the block-shaped portions of the tread according to the present invention.

[0062] - Figure 2D Cross-sectional view of the outer transverse cut of the middle portion of the tread according to the present invention.

[0063] - Figure 3A A top view of the middle portion of the tread according to a particular embodiment of the present invention, which includes an inner transverse cut.

[0064] - Figure 3B A cross-sectional view of the middle portion of the tread according to a particular embodiment of the present invention, which includes an inner transverse cut.

[0065] - Figure 3C : Cross-sectional view including the inner transverse cut of a single part

[0066] - Figure 3D : Cross-sectional view including the radially outer portion and the radially inner portion with an inner transverse cut.

[0067] - Figure 4 The first range of variation of the thickness of the radially outer portion of the longitudinal channel, the transverse incision between the blocky parts, and the outer transverse incision with respect to the incision depth.

[0068] - Figure 5The first range of variation of the thickness of the radially outer portion of the longitudinal channel, the transverse incision between the blocky parts, and the outer transverse incision with respect to the incision depth.

[0069] - Figure 6 The first range of variation in the thickness of the radially outer portion of the internal incision with the depth of the internal incision.

[0070] - Figure 7 The second range of variation in the thickness of the radially outer portion of the internal incision with the depth of the internal incision.

[0071] - Figure 8 The third range of variation in the thickness of the radially outer portion of the internal incision as the depth of the internal incision changes. Detailed Implementation

[0072] Figure 1 This is a top view of the tire tread 1 according to the present invention. The tire tread 1 for heavy-duty civil engineering vehicles is designed to contact the ground via a running surface 2. The tire tread 1 includes block-shaped portions 3 defined by cutouts (41, 42), and has a width L in the lateral direction YY' and a height H in the direction perpendicular to the running surface 2 ZZ'. Figure 1 (Not shown in the diagram), the height H is defined as the maximum cut depth. The tread has a central portion 11, which is symmetrical with respect to the central longitudinal plane XZ and has a width L1, which is not greater than L1max = 60% of the tread width L. Figure 1 In the illustrated embodiment, the intermediate portion 11 is formed by a single longitudinal row of block-shaped portions 3, each block-shaped portion 3 being laterally defined in the transverse direction YY' by two longitudinal channels 41 and longitudinally defined in the longitudinal direction XX' by a transverse cut 42 between the two block-shaped portions. This single longitudinal row of block-shaped portions 3, having a width L1, is centered on the intermediate longitudinal plane XZ. More generally, the intermediate portion 11 may comprise a plurality of longitudinal rows of block-shaped portions according to the invention, or a combination of at least one longitudinal row of block-shaped portions according to the invention in the transverse direction with other engraved elements. Figure 1 In the embodiment shown, the tread 1 further includes an outer transverse cut 43, which leads to a longitudinal channel 41 defining the block portion 3.

[0073] Figure 2A This is a top view of the middle portion of the tread according to the present invention. Figure 1 It can be seen that the middle portion of the tread has a width L1, which is no greater than 60% of the tread width L. Each block 3 in the middle portion has a longitudinal length B, which can vary from one block to another. The cross-sectional plane AA defines the cross-section passing through the longitudinal channel 41, as shown... Figure 2BAs shown. The cross-sectional plane CC defines the cross-section passing through the transverse cut 42 between the blocky parts, as... Figure 2C As shown. The cross-sectional plane DD defines the cross-section passing through the outer transverse cut 43, as follows. Figure 2D Limited by.

[0074] Figure 2B This is a cross-sectional view of the longitudinal channel 41 in the middle portion of the tread according to the present invention. Figure 2B A cross-section AA passing through the entire longitudinal channel 41 is shown on one side, and a detailed view A1 of the radially inner portion 412 of the longitudinal channel 41 is shown on the other side. The longitudinal channel 41 has a depth P1 and includes a radially outer portion 411 and a radially inner portion 412, the depth P1 being at least 50% of the tread height H. In general, the thickness of the radially outer portion 411, measured between the material walls defining it, ranges from a minimum thickness E11min to a maximum thickness E11max. In the case shown herein, the minimum thickness E11min and the maximum thickness E11max of the radially outer portion 411 are equal to each other, such that the thickness is constant at every point in the radially outer portion 411. The thickness of the radially inner portion 412, measured between the material walls defining it, ranges from a minimum thickness E12min to a maximum thickness E12max, which are generally not equal. According to the invention, the maximum thickness E11max of the radially outer portion 411 is not greater than 20% of the corresponding depth P1 of the cut 41, and is strictly less than the corresponding maximum thickness E12max of the radially inner portion 412, and the minimum thickness E11min of each radially outer portion 411 is not greater than 5% of the corresponding depth P1 of the cut 41. In detail drawing A1, according to a particular embodiment, the radially inner portion 412 has a height H12 and a circular radially inner end portion 4121, the height H12 being at least equal to 1.5 times the maximum thickness E12max, and the diameter D1 of the circular radially inner end portion 4121 being equal to the maximum thickness E12max.

[0075] Figure 2C This is a cross-sectional view of the transverse block-shaped cut 42 in the middle portion of the tread according to the present invention. Figure 2COne view shows a cross-section CC passing through the entire inter-block transverse cut 42, and another view shows a detailed view C1 of the radially inner portion 422 of the inter-block transverse cut 42. The inter-block transverse cut 42 has a depth P2 and includes a radially outer portion 421 and a radially inner portion 422, the depth P2 being at least 50% of the tread height H. In general, the thickness of the radially outer portion 421 ranges from a minimum thickness E21min to a maximum thickness E21max. In the case shown herein, the minimum thickness E21min and the maximum thickness E21max of the radially outer portion 421 are equal to each other, such that the thickness is constant at every point of the radially outer portion 421. The thickness of the radially inner portion 422 ranges from a minimum thickness E22min to a maximum thickness E22max, which are generally not equal. According to the invention, the maximum thickness E21max of the radially outer portion 421 is not greater than 20% of the corresponding depth P2 of the cut 42, and is strictly less than the maximum thickness E22max of the corresponding radially inner portion 422, and the minimum thickness E21min of each radially outer portion 421 is at least equal to 5% of the depth P2 of the corresponding cut 42. In detail drawing C1, according to a particular embodiment, the radially inner portion 422 has a height H22 and a circular radially inner end portion 4221, the height H22 being at least equal to 1.5 times the maximum thickness E22max, and the diameter D2 of the circular radially inner end portion 4221 being equal to the maximum thickness E22max.

[0076] Figure 2D This is a cross-sectional view of the outer transverse cut 43 in the middle portion of the tread according to a particular embodiment of the present invention. Figure 2DOne view shows a cross-section DD passing through the entire outer transverse cut 43, and another view shows a detailed view D1 of the radially inner portion 432 of the outer transverse cut 43. The outer transverse cut 43 has a depth P3 and includes a radially outer portion 431 and a radially inner portion 432, the depth P3 being at least 50% of the tread height H. In general, the thickness of the radially outer portion 431 ranges from a minimum thickness E31min to a maximum thickness E31max. In the case shown herein, the minimum thickness E31min and the maximum thickness E31max of the radially outer portion 431 are equal to each other, such that the thickness is constant at every point of the radially outer portion 431. The thickness of the radially inner portion 432 ranges from a minimum thickness E32min to a maximum thickness E32max, which are generally not equal. According to a particular embodiment of the invention, the maximum thickness E31max of the radially outer portion 431 is not greater than 20% of the depth P3 of the corresponding cut 43, and is strictly less than the maximum thickness E32max of the corresponding radially inner portion 432, and the minimum thickness E31min of each radially outer portion 431 is at least equal to 5% of the depth P3 of the corresponding cut 43. In detail drawing D1, according to a particular embodiment, the radially inner portion 432 has a height H32 and a circular radially inner end portion 4321, the height H32 being at least equal to 1.5 times the maximum thickness E32max, and the diameter D3 of the circular radially inner end portion 4321 being equal to the maximum thickness E32max.

[0077] Figure 3A This is a top view of the middle portion of the tread according to a particular embodiment of the invention, which includes an inner lateral cut 44. In this particular embodiment, each block portion 3 includes an inner lateral cut 44, which is substantially parallel to the inter-block lateral cut 42 defining the block portion 3 and leads to two longitudinal channels 41 defining the block portion 3. According to the intermediate longitudinal plane XZ, the cross-sectional plane EE defines a cross section passing through the alternating inner lateral cuts 44 and the inter-block lateral cuts 42, as shown... Figure 2B As shown. Furthermore, Figure 3C and Figure 3D The two types of internal cuts 44 are shown in detail diagram E1.

[0078] Figure 3B This is a cross-sectional view of the middle portion of the tread according to a particular embodiment of the present invention, which includes an inner transverse cut 44. Along the longitudinal direction X, the inner transverse cut 44 having a depth P4 alternates with a block-shaped inter-transverse cut 42 having a depth P2.

[0079] Figure 3C This is a cross-sectional view of the inner transverse cut 44, which includes a single section, and corresponds to... Figure 3BDetails E1. In this particular case, the individual radially inner portions and radially outer portions are combined into a single portion 441. Furthermore, in the embodiment shown herein, the minimum thickness E41min and the maximum thickness E41max of portion 441 are equal to each other, such that the thickness is constant at every point of said portion 441.

[0080] Figure 3D This is a cross-sectional view of the inner transverse cut 44, including the radially outer portion 441 and the radially inner portion 442, which corresponds to... Figure 3B Detail E1. In general, the thickness of the radially outer portion 441 ranges from a minimum thickness E41min to a maximum thickness E41max. In the case shown herein, the minimum thickness E41min and the maximum thickness E41max of the radially outer portion 441 are equal to each other, such that the thickness is constant at every point of the radially outer portion 441. The thickness of the radially inner portion 442 ranges from a minimum thickness E42min to a maximum thickness E42max, which are generally not equal. In detail figure E1, according to a particular embodiment, the radially inner portion 432 has a height H42 and a circular radially inner end portion 4421, the height H42 being at least 1.5 times the maximum thickness E42max, and the diameter D4 of the circular radially inner end portion 4421 being equal to the maximum thickness E42max.

[0081] Figure 4 The thickness Ei1 of the radially outer portion 4i1 of the cut 4i varies with the depth Pi of the cut 4i, where the exponent i can take values ​​of 1, 2, or 3. An exponent i equal to 1 represents the longitudinal channel 41, an exponent i equal to 2 represents the transverse cut 42 between the blocky parts, and an exponent i equal to 3 represents the outer transverse cut 43. The thickness Ei1 is the thickness measured at any point of the radially outer portion 4i1. For a depth Pi between 50% and H, at any point of the cut 4i, the thickness Ei1 of the radially outer portion is between 5% and 20% of Pi.

[0082] Figure 5 The second range is defined as the variation of the thickness Ei1 of the radially outer portion 4i1 of the cut 4i with the depth Pi of the cut 4i, where the exponent i can take values ​​of 1, 2, or 3. Thickness Ei1 is the thickness measured at any point on the radially outer portion 4i1. For a depth Pi between 50% and H, at any point on the cut 4i, the thickness Ei1 of the radially outer portion is between 10% and 20% of Pi; therefore, it is a more restricted range than the first range.

[0083] Figure 6The thickness E41 of the radially outer portion 441 of the inner cut 44 varies with its depth P4 within a first range. The thickness E41 is the thickness measured at any point in the radially outer portion 441. Within this first range, the inner cut 44 formed in the block portion 3 has a depth P4 that is not greater than the smaller of the depths (P1, P2) of each longitudinal channel 41 and the transverse cut 42 between each block portion 3, and a thickness E41 measured at any point in the radially outer portion 441. Therefore, the maximum thickness E41max is not greater than the smaller of the maximum thicknesses (E11max, E21max) of the radially outer portions (411, 421) of each longitudinal channel 41 and the transverse cut 42 between each block portion 3.

[0084] Figure 7 The second variation range is defined as the thickness E41 of the radially outer portion 441 of the inner cut 44 varying with its depth P4. Thickness E41 is the thickness measured at any point on the radially outer portion 441. Within this second variation range, the inner cut 44 formed in the block portion 3 has a depth P4 not greater than min(P1, P2) (i.e., the smaller of the depths (P1, P2) of each longitudinal channel 41 and the transverse cut 42 between each block portion 3) and a thickness E41 measured at any point on the radially outer portion 441 between 5% and 20% of P4. This variation range is more restrictive than the first range described above.

[0085] Figure 8 This is a third variation range for the thickness E41 of the radially outer portion 441 of the inner cut 44, which varies with its depth P4. Thickness E41 is the thickness measured at any point on the radially outer portion 441. Within this third variation range, the inner cut 44 formed in the block portion 3 has a depth P4 not greater than the smaller of min(P1, P2) (i.e., the smaller values ​​of the depths (P1, P2) of each longitudinal channel 41 and the transverse cut 42 between each block portion 3) and a thickness E41 measured at any point on the radially outer portion 441 between 10% and 20% of P4. This variation range is more restrictive than the second range described above.

[0086] The inventors tested the tread according to the invention, as shown in the foregoing figures, of a tire with a size of 53 / 80R 63 for mounting on heavy-duty civil engineering vehicles (more particularly rigid dump truck types). This tire is designed to withstand a load of 82,500 kg at an inflation pressure of 6 bar.

[0087] Table 1 below shows the characteristics of the tested tread:

[0088] Table 1

[0089]

[0090]

[0091] Driving tests were conducted on tires according to the invention in a mine, and compared with control tires whose treads included a single slit (particularly a lateral slit) but did not have a radially inner portion, the tires according to the invention exhibited significantly improved resistance to mechanical impact. Particularly noteworthy is the absence of cracks at the bottom of the radially inner portion of the slit, and the absence of tearing in the tread blocks. In other words, the tread according to the invention reached full wear without cracking, while the control tread cracked and / or tore in blocks during wear.

[0092] Regarding the improvement in thermal ventilation capacity of staged incisions, numerical simulations have demonstrated that when these incisions specifically include internal transverse incisions, the internal temperature of the block portion is reduced by 8°C.

Claims

1. A tire tread (1) for heavy-duty civil engineering vehicles, said tire tread (1) being designed to contact the ground via a running surface (2), comprising a block-shaped portion (3) defined by cutouts (41, 42), and having a width L and a height H defined as the maximum cutout depth, - The tread has a central portion (11), which is symmetrical with respect to the central longitudinal plane (XZ) and has a width L1 that is no greater than 60% of the width L of the tread. - The middle portion (11) includes a longitudinal arrangement of at least one block portion (3), wherein each block portion (3) is defined laterally by two longitudinal channels (41) and longitudinally by a transverse cut (42) between the two block portions. - Each longitudinal channel (41) and each inter-block transverse cut (42) has a depth (P1, P2) of at least 50% of the tread height H, and are staged cuts, each staged cut including a radially outer portion (411, 421) leading to the driving surface (2) and a radially inner portion (412, 422) extending from the radially outer portion (411, 421) to the radially inner end portion (4121, 4221). - The thickness of each radially outer portion (411, 421) measured between the material walls defining the radially outer portion (411, 421) is within the range of minimum thickness (E11min, E21min) to maximum thickness (E11max, E21max). - The thickness of each radial inner portion (412, 422) measured between the material walls defining the radial inner portion (412, 422) is within the range of minimum thickness (E12min, E22min) to maximum thickness (E12max, E22max). Its features are, The maximum thickness (E11max, E21max) of each radially outer portion (411, 421) is no greater than 20% of the depth (P1, P2) of the corresponding cut (41, 42), and is strictly less than the maximum thickness (E12max, E22max) of the corresponding radially inner portion (412, 422), and the minimum thickness (E11min, E21min) of each radially outer portion (411, 421) is at least equal to 5% of the depth (P1, P2) of the corresponding cut (41, 42). Each block portion (3) includes at least one internal incision (44) having a depth P4, the depth P4 being no greater than the minimum depth (P1, P2) of each longitudinal channel (41) defining the block portion (3) and the transverse incision (42) between each block portion.

2. The tread (1) according to claim 1, wherein, The minimum thickness (E11min, E21min) of each radially outer portion (411, 421) is at least equal to 10% of the depth (P1, P2) of the corresponding cut (41, 42).

3. The tread (1) according to any one of claims 1 and 2, wherein, The minimum thickness (E11min, E21min) and maximum thickness (E11max, E21max) of each radially outer portion (411, 421) are equal to each other, such that the thickness is constant at all points of the radially outer portion (411, 421).

4. The tread (1) according to any one of claims 1 to 3, wherein, The maximum thickness (E12max, E22max) of each radial inner portion (412, 422) is at least 15% of the depth (P1, P2) of the corresponding cut (41, 42).

5. The tread (1) according to any one of claims 1 to 4, wherein, The height (H12, H22) of each radial inner portion (412, 422) is at least 1.5 times the maximum thickness (E12max, E22max) of the corresponding radial inner portion (412, 422).

6. The tread (1) according to any one of claims 1 to 5, wherein, Each radial inner portion (412, 422) has a circular radial inner end (4121, 4221) with a diameter (D1, D2) equal to the maximum thickness (E12max, E22max) of the corresponding radial inner portion (412, 422).

7. The tread (1) according to any one of claims 1 to 6, wherein each block (3) has a longitudinal length B, wherein, The depth P2 of the transverse cut (42) between each block is not greater than the longitudinal length B of the block (3), preferably not greater than 0.8 times the longitudinal length B of the block (3).

8. The tread (1) according to any one of claims 1 to 7, said tread (1) comprising an outer transverse cut (43) leading to a longitudinal channel (41) defining a block portion (3), each outer transverse cut (43) having a depth P3 at least equal to 50% of the tread height H and comprising a radially outer portion (431) and a radially inner portion (432), the thickness of each radially inner portion (431) being in the range of a minimum thickness E31min to a maximum thickness E31max, and the thickness of each radially inner portion (432) being in the range of a minimum thickness E32min to a maximum thickness E32max, wherein, The maximum thickness E31max of each radially outer portion (431) is no greater than 20% of the depth P3 of the corresponding cut (43) and is strictly less than the maximum thickness E32max of the corresponding radially inner portion (412, 422, 432), and the minimum thickness E31min of each radially outer portion (431) is at least equal to 5% of the depth P3 of the corresponding cut (43).

9. The tread (1) according to claim 1, each inner cut (44) includes a radially outer portion (441), the thickness of said radially outer portion (441) being in the range of a minimum thickness E41min to a maximum thickness E41max, wherein, The maximum thickness E41max of the radially outer portion (441) of the inner incision (44) is not greater than the minimum of the maximum thickness (E11max, E21max) of the radially outer portion (411, 421) of each longitudinal channel (41) defining the block portion (3) and the transverse incision (42) between each block portion.

10. The tread (1) according to claim 9, each inner cut (44) comprising a radially inner portion (442) having a thickness ranging from a minimum thickness E42min to a maximum thickness E42max, wherein, The maximum thickness E41max of the radially outer portion (441) of the inner cut (44) is strictly less than the maximum thickness E42max of the radially inner portion (442) of the corresponding inner cut (44).

11. The tread (1) according to any one of claims 9 to 10, wherein, Each internal incision (44) is transverse.

12. The tread (1) according to any one of claims 1 to 11, wherein, The middle part of the tread (1) includes longitudinal rows of blocky parts (3) centered on the central longitudinal plane (XZ).

13. A tire mounted on a heavy civil engineering vehicle, said tire comprising the tread according to any one of claims 1 to 12.

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