Pneumatic tire for a heavy civil engineering vehicle with improved wear and endurance performance

Abstract

The present invention relates to a tire (1) for a heavy civil engineering vehicle making it possible to improve the performance compromise between its wear life and its thermal endurance, in the case of a tread with an evolving sculpture. According to the invention, the lateral tread portion (21) comprising an alternation of at least one first transverse cutout (321) and at least one second transverse cutout (322), both evolving during wear, the outer groove (321E) of any first transverse cutout (321) is extended radially inward by an inner cavity (321I) having an emerging surface whose closed contour has a largest dimension (W1I) at least equal to 10% of the width (L21) of the lateral portion (21) and extending radially inward up to at most the maximum cutout depth (D0). Figure for abstract: Fig. 1

Description

Title of the invention: Pneumatic tire for a heavy civil engineering vehicle with improved wear and endurance performance

[0001] The present invention relates to a tire for a heavy civil engineering vehicle, intended to carry heavy loads and to roll on uneven and stony ground such as that of mines. This invention relates more particularly to the tread of such a tire for which the compromise between wear and endurance performance, at the edges of the tread, is improved.

[0002] The invention relates more particularly to a tire intended to equip a heavy civil engineering vehicle, such as a dumper intended for the transport of materials extracted from quarries or surface mines. A dumper is subject to particularly severe driving conditions: high loads, sustained speeds, sloping and curved travel, uneven and stony ground. For example, on sites where materials, such as ores or coal, are extracted, the use of a dumper-type vehicle consists, in a simplified manner, of alternating loaded outward cycles and empty return cycles. During a loaded outward cycle, the loaded vehicle transports, mainly uphill, the extracted materials from loading areas at the bottom of the mine, or bottom of the "pit", to unloading areas: this requires good traction grip of the tires.During an empty return cycle, the empty vehicle returns, mainly downhill, to the loading areas at the bottom of the mine: this requires good braking grip from the tires. The tracks, which are usually on a slope, also often include bends, which requires good transverse grip from the tires. In addition, the tracks on which the vehicles travel are made of materials generally from the mine, for example, crushed and compacted rock, to ensure the wear layer of the track holds when the vehicles pass, and are regularly watered, which means that they are often covered with mud and water.Therefore it is necessary to allow, on the one hand, an effective evacuation of this mixture of mud and water by the tread, to guarantee satisfactory grip on this muddy ground, and, on the other hand, good resistance to wear and to attacks by stones present on the ground.

[0003] The specific use of a dumper, as previously described, requires special management of the tires fitted to it.

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

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

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

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

[0008] Usually, we designate by: - radial direction: a direction perpendicular to the axis of rotation of the tire, - axial or transverse direction: a direction parallel to the axis of rotation of the tire, - circumferential or longitudinal direction: a direction tangent to the periphery of the tire and perpendicular to the radial and axial directions respectively, - median or equatorial circumferential plane: a plane containing the radial direction and the circumferential direction, perpendicular to the axis of rotation of the tire and dividing the tire into two equal portions.

[0009] The tread, for any state of wear of the tire, is geometrically characterized by an axial width, measured in the axial direction and called plus simply width, and a radial thickness, measured in a radial direction and more simply called thickness. The width is defined, by convention, as the width of the portion of the rolling surface, in contact with a smooth ground, the tire being mounted on a recommended rim and subjected to nominal pressure and load conditions recommended by the usual standards. The thickness is defined, by convention, as the maximum depth measured in the cutouts, also called maximum cutout depth. In other words, the thickness of the tread corresponds to the material thickness of the raised element delimited by the deepest cutout and is equal to the maximum cutout depth.In the case of a tyre for a civil engineering vehicle, in new condition, i.e. before running, and by way of example, the width in new condition, or initial width LO, is at least equal to 600 mm and the thickness in new condition, or initial thickness DO, defined as the maximum initial cutting depth, is at least equal to 60 mm, or even 70 mm. But the characteristics of width and maximum cutting depth vary according to the state of wear of the tyre. In particular, the maximum cutting depth varies between a maximum initial cutting depth DO, in the new condition of the tyre, and a maximum residual cutting depth DR, in the worn condition of the tyre, value at which the tyre is removed from the vehicle in accordance with current practices.

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

[0011] A cutout is a space delimited by walls of material facing each other and spaced from each other by a distance defining the width of the cutout, and extending from the rolling surface, in the radial direction, over a given depth. Depending on the value of its width, measured perpendicular to its mean line, between the walls of the raised elements that it separates, at the level of the rolling surface, a cutout is either an incision or a groove. In the case of an incision, this width is appropriate to allow at least partial contact of the opposite walls delimiting said incision, at least during the passage of the tread in contact with the ground, when the tire is subjected to nominal load and pressure conditions recommended, for example, by the TRA standard.In the case of a groove, the walls of this groove do not generally come into contact with each other under these recommended nominal rolling conditions.

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

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

[0014] By definition, the volumetric notch rate TEV of the tread, for a given state of wear, is equal to the ratio between the total volume VD of the cutouts, measured on the free tire, i.e. unmounted and uninflated, and the sum of the total volume VD of the cutouts and the total volume VR of the raised elements delimited by these cutouts. The sum VD+VR corresponds to the volume comprised radially between the rolling surface, at the given level of wear, and a bottom surface, translated from the rolling surface radially inwards by a radial distance equal to the maximum depth of cutout. This volumetric notch rate TEV, expressed in %, conditions the wear performance, by the volume of material to be worn available, and the longitudinal and transverse adhesion performance, by the presence of respectively transverse and longitudinal edges and cutouts having the capacity to store or evacuate water and / or mud.

[0015] By definition, the surface notch rate TES of the tread, for a given state of wear, is defined in the contact surface of the tire with a rigid ground, when the tire, mounted on its nominal rim, is inflated to its nominal pressure and crushed under its nominal load, these nominal characteristics being recommended, for example, by the TRA standard. This surface notch rate TES is equal to the ratio between the total surface SD of the cutouts, and the sum of the total surface SD of the cutouts and the total surface SR of the raised elements delimited by these cutouts, the surfaces SD and SR being determined in the contact surface. The sum SD+SR corresponds to the contact surface.This surface notch rate TES, expressed in %, conditions the wear performance, by the surface of material in contact with the ground impacting the distribution of pressures exerted by the ground on the rolling surface, and the performance in longitudinal and transverse grip, by the length of the transverse and longitudinal edges respectively conditioning the effectiveness of the indentation of the sculpture.

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

[0017] A tire tread for a civil engineering vehicle usually comprises cutouts that may be longitudinal or transverse. A longitudinal cutout has a mean line forming, with the longitudinal or circumferential direction of the tire, an angle of less than 45°, and has the particularity of extending over the entire circumference of the tire. Either the mean line forms a zero angle and is strictly longitudinal, or it comprises at least one oblique portion forming a non-zero angle, for example, in the case of a cutout oscillating around the circumferential direction. A transverse cutout has a mean line forming, with the longitudinal or circumferential direction of the tire, an angle of greater than 45°, and has the particularity of crossing at least part of the tread.Generally, the width of a cutout decreases progressively from the rolling surface to the bottom of the groove, due to the inclination of the walls of the raised elements delimiting said cutouts. However, a high volumetric notch rate in the new condition has a certain number of disadvantages. First of all, it promotes the capture and retention of stones in the cutouts, these being likely to damage the crown of the tire by the cracks that they potentially induce. Then, a high volumetric notch rate in the new condition implies an equally high surface notch rate, therefore a rather reduced contact surface with the ground of the raised elements, and, consequently, high pressures on the ground which accentuate the phenomenon of abrasion of the tread and therefore its wear.Finally, a high volumetric notch rate in new condition allows lateral deformations, called "barrel", of the raised elements, by Poisson effect: which reduces the effective volume of the cutouts, characterizing their capacity for storing and evacuating water or muddy mixture, hence a loss of grip of the tire on muddy ground. However, these deformations by Poisson effect tend to decrease when the wear of the tread increases, due to the reduction in the height of the raised elements.

[0018] In document WO 2022064134 A1, for a tire of size 24.00R35 intended to equip a civil engineering vehicle, a system of cutouts with widths that evolve according to the level of wear of the tread has been proposed. The principle of this invention is to propose a tire for a heavy civil engineering vehicle whose grip, more particularly on wet and / or muddy ground, is guaranteed at any level of wear. During the first third of wear, the tire is mounted at the front of the vehicle and is subjected to a load at least equal to 60%, for a vehicle traveling unladen, and at most equal to 100%, for a vehicle traveling fully loaded, of the recommended load Zn. During the remaining two-thirds of wear, the tire is mounted at the rear of the vehicle and is subjected to a load at least equal to 30%, for a vehicle running empty, and at most equal to 100%, for a vehicle running fully loaded, of the recommended load Zn. This invention aims more specifically to improve the performance compromise between wear life, resistance to aggression and grip of the tire. According to the invention, the tread having an axial width LO and comprising, on each side of an equatorial plane, at least one external longitudinal cutout at an axial distance LE at least equal to 0.5*L0 / 2, and at least one internal longitudinal cutout at an axial distance LI at most equal to 0.4*L0 / 2, the at least one external longitudinal cutout comprises an external radial portion opening onto the rolling surface and having an average width at least equal to 0.6 times its height, and the at least one inner longitudinal cutout comprises an inner radial portion not opening onto the tread surface and having an average width at least equal to 0.6 times its height. According to a particular embodiment, as shown in Figures 5 and 6 of document WO 2022064134 A1, the tread portion axially outside the outer longitudinal cutout comprises an alternation of first and second transverse cutouts. Any first transverse cutout preferably comprises an outer radial portion opening onto the tread surface, having an average width at least equal to 0.6 times its height and extended radially inwards by an inner radial portion having an average width at most equal to 0.2 times its height.Any second transverse cutout preferably comprises an outer radial portion opening onto the tread surface, having an average width at most equal to 0.2 times its height and extended radially inwards by an inner radial portion having an average width at least equal to 0.6 times its height. The tire having an outer diameter D, measured in the equatorial plane, and a contact surface under load having a circumferential length C0, when the tire mounted on a nominal rim is inflated to a nominal pressure Pn and crushed under a nominal load Zn, the tread comprises at least NE first transverse cutouts opening at an axial end of the tread, NE being at least equal to n*D / C0, such that the contact surface under load comprises at least one first transverse cutout.

[0019] Any portion of material delimited respectively by a first and a second transverse cutout, having a substantially equal depth, constitutes a relatively flexible block of rubber whose radially outer face, intended to come into contact with the ground, will be subject to significant sliding, in particular when the tire is subjected to engine or braking torque, which is detrimental in terms of wear.

[0020] Furthermore, any first transverse cut is not very effective in terms of thermal, because its inner radial portion having an average width at most equal to 0.2 times its height is not very effective in evacuating the calories generated during rolling, in the portion of the crown of the tire radially inside the tread, which can lead to thermal degradation of the crown of the tire and therefore to a reduction in the endurance of the tire, and premature withdrawal of the latter.

[0021] The inventors set themselves the objective of designing a tire for a heavy civil engineering vehicle with a tread comprising an arrangement of cutouts, in particular transverse cutouts, which evolves during wear of the tire, making it possible to improve the performance compromise between the wear life and the thermal endurance of the tire, more particularly at the edges of the tread.

[0022] This objective is achieved, according to the invention, by a tire for a heavy civil engineering vehicle comprising a tread comprising an arrangement of cutouts separating raised elements, - the cutouts being either longitudinal cutouts having a mean line forming, with a circumferential direction, an angle at most equal to 45°, or transverse cutouts having a mean line forming, with the circumferential direction, an angle greater than 45°, - the tread having, when the tire is new, a width, measured in an axial direction parallel to the axis of rotation of the tire, and having a maximum cutting depth, measured in a radial direction perpendicular to a rolling surface, -the tread comprising, on each side of an equatorial plane, an external longitudinal cutout, having a mean line, positioned, relative to the equatorial plane, at an axial distance at least equal to 25% of the width and delimiting axially towards the outside a lateral portion of the tread, -the lateral portion of the tread comprising an alternation of at least one first transverse cutout and at least one second transverse cutout, - any first transverse cutout comprising an external groove opening onto the rolling surface and having a width at least equal to 30% of its height, - any second transverse cutout comprising an external incision opening onto the rolling surface, having a width at most equal to 20% of its height and extended radially inwards by an internal groove having a width at least equal to 30% of its height, - the outer groove of any first transverse cutout being extended radially inwards by an inner cavity having an emerging surface whose closed contour has a largest dimension at least equal to 10% of the width of the lateral portion and extending radially inward to at most the maximum cutting depth.

[0023] The principle of the invention is to produce cavities, or wells, at the bottom of the outer grooves of the first transverse cutouts, present in the lateral portions of the tread, to evacuate the heat dissipated at the edge of the tread, when the tire is rolling, while minimizing the impact of these cavities on wear at the edge of the tread.

[0024] The essential characteristic of the invention is therefore to have transverse external grooves, opening onto the rolling surface, extended radially inwards by an internal cavity having an opening surface whose closed contour has a largest dimension at least equal to 10% of the width of the lateral portion and extending radially inwards up to at most the maximum cutting depth.

[0025] An internal cavity according to the invention has a sufficient size to allow effective evacuation of the heat generated in the thickness of the crown, thanks to an appropriate heat exchange surface between the tread and the outside air, but a size that is not too large so as not to excessively reduce the rigidity of the lateral portion of the tread, and consequently not to excessively negatively impact the wear life under torque.

[0026] Advantageously, the closed contour of the emerging surface of the inner cavity extending the outer groove of any first transverse cutout has a larger dimension at most equal to 30% of the width of the lateral portion. This upper limit makes it possible to limit the reduction in rigidity of the lateral portion of the tread, and therefore the impact on the wear life under torque.

[0027] Also advantageously, the inner cavity extending the outer groove of any first transverse cutout extends radially inwards up to at least 60% of the maximum cutout depth, preferably up to at least 70% of the maximum cutout depth. Effective evacuation of the heat generated during rolling by the crown of the tire requires having a heat exchange surface that is as large as possible and as close as possible to the heat sources, therefore as deep as possible. A recommended minimum depth guarantees thermal efficiency of the inner cavity.

[0028] Advantageously, the outer groove of any first transverse cutout has a width at least equal to 40% of its height, preferably at least equal to 50% of its height. The higher the width to height ratio of the outer groove, the lower the deformation of the walls of the outer groove, due to the Poisson effect. This guarantees conservation of the volume of the outer groove, when rolling, during its passage in contact with the ground, and therefore the maintenance of its capacity to evacuate water or mud, that is to say, maintaining its effectiveness with regard to grip.

[0029] Also advantageously, the outer groove of the very first transverse cut extends radially inwards up to at most 50% of the maximum cut depth. A limited depth of the outer groove makes it possible to maintain rigidity of the lateral portion of the tread, making it possible not to significantly degrade the wear life.

[0030] Advantageously, the outer incision of any second transverse cutout has a width at most equal to 10% of its height. When rolling, as it passes through contact with the ground, the walls of the outer incision come into contact with each other, which contributes to stiffening the lateral portion of the tread. The smaller the width of the incision, the easier the contact between the walls, and the greater the stiffening of the lateral portion of the tread.

[0031] Also advantageously, the outer incision of any second transverse cutout extends radially inward up to at most 50% of the maximum cutout depth. The less deep the outer incision, the more quickly the inner groove extending it radially inward appears during wear, which makes it possible to compensate for the reduction in the water or mud evacuation capacity, due to the progressive disappearance of the outer grooves of the first transverse cutouts. In other words, from a certain level of wear, the second transverse cutouts take over from the first transverse cutouts with regard to grip on wet or muddy ground.

[0032] Advantageously, the inner groove of any second transverse cutout has a width at least equal to 40% of its height, preferably at least equal to 50% of its height. As seen previously, the higher the width to height ratio of the inner groove, the lower the deformation of the walls of the inner groove, due to the Poisson effect. This guarantees conservation of the volume of the inner groove, when rolling, during its passage in contact with the ground, and therefore the maintenance of its capacity to evacuate water or mud, that is to say the maintenance of its effectiveness with regard to grip.

[0033] Also advantageously, the inner groove of any second transverse cut extends radially inward up to at least 70% of the maximum cut depth, and preferably up to 100% of the maximum cut depth. At the end of wear, the transverse notching of each lateral portion of the tread is essentially ensured by the inner grooves of the second transverse cuts. Consequently, it is important to maintain this transverse notching for as long as possible to guarantee the durability of grip on wet or muddy ground. It is therefore advantageous to have an inner groove of the second transverse cut as deepest possible.

[0034] The characteristics of the invention are illustrated by schematic figures 1 to 11, not shown to scale: -[Fig.l]: Partial front view of a tire tread according to the invention, in new condition, -[Fig.2]: Partial front view of a tire tread according to the invention, at the end of wear, -[Fig.3]: Detailed front view of a lateral portion of a tire tread according to the invention, in new condition, -[Fig.4]: Detailed view, in longitudinal section, of a lateral portion of tire tread according to the invention, in new condition, -[Fig.5]: Detailed view, in cross section, of a lateral portion of tire tread according to the invention, in new condition, -[Fig.6]: Graph representing the rigidity of a lateral portion of tread as a function of the maximum internal temperature radially inside said lateral portion, according to different transverse notch configurations, -[Fig.7]: First configuration of transverse notch V0 of a lateral portion of tread, taken as reference, -[Fig.8]: Second transverse notch configuration VI of a lateral portion of tread, in accordance with the invention, -[Fig.9]: Third configuration of transverse notching V2 of a lateral portion of tread, -[Fig.10]: Fourth configuration of transverse notching V3 of a lateral portion of tread -[Fig.l 1]: Fifth configuration of transverse notching V4 of a lateral portion of tread.

[0035] [Fig. 1] is a partial front view of a tread 2 of a tire 1 according to the invention, in the new condition. The tire 1 for a heavy civil engineering vehicle comprises a tread 2 comprising an arrangement of cutouts 3 separating raised elements 4. The cutouts 3 are either longitudinal cutouts 31 having a mean line forming, with a circumferential direction XX', an angle at most equal to 45°, or transverse cutouts 32 having a mean line forming, with the circumferential direction XX', an angle greater than 45°. The tread 2 has, in the new condition of the tire, a width L0, measured in an axial direction YY' parallel to the axis of rotation of the tire, and having a maximum cutout depth D0 (see Figures 4 and 5), measured in a radial direction ZZ' perpendicular to a tread surface 20.The tread 2 comprises, on each side of an equatorial plane XZ, a longitudinal cutout. outer tudinal 311, having a mean line, positioned, relative to the equatorial plane XZ, at an axial distance LE at least equal to 25% of the width LO and delimiting axially towards the outside a lateral portion of tread 21, having a lateral width L21. The lateral portions of tread 21 are separated from each other by a median portion 22 having a median width equal to L0-2*L21. The lateral portion of tread 21 comprises an alternation of first transverse cutouts 321 and second transverse cutouts 322. Any first transverse cutout 321 comprises an outer groove 321E opening onto the tread surface 20 and having a width W1E at least equal to 30% of its height H1E. The width W1E is measured, perpendicular to the mean line of the outer groove 321E, between the walls of the raised elements 4 which it separates, at the level of the rolling surface 20.The height H1E (see figures 4 and 5) is measured radially between the radially innermost and outermost points respectively of the outer groove 321E. Any second transverse cutout 322 comprises an outer incision 322E opening onto the rolling surface, having a width W2E at most equal to 20% of its height H2E (see figures 4 and 5) and extended radially inwards by an inner groove 3221 having a width W2I at least equal to 30% of its height H2I (see figures 4 and 5). According to the invention, the outer groove 321E of the very first transverse cutout 321 is extended radially inwards by an inner cavity 3211 having an emerging surface whose closed contour has a largest dimension W1I at least equal to 10% of the width L21 of the lateral portion 21 and extending radially inwards up to at most the maximum depth of cutout D0.The largest dimension is generally measured along the major axis of the outer groove 321E.

[0036] [Fig.2] is a partial front view of a tire tread according to the invention, at the end of wear. In the lateral portions of tread 21 having a lateral width L21, the inner cavities 3211 of the first transverse cutouts 321 and the inner grooves 3221 of the second transverse cutouts 322 appear. On the other hand, the outer longitudinal cutouts 311, located at the distance LE from the median plane XZ, and shown in [Fig.l], have disappeared, at the end of wear. The middle portion, having a width L0-2*L21, comprises transverse grooves extending the inner grooves of the second transverse cutouts and a circumferential juxtaposition of hexagonal relief elements 4.

[0037] [Fig. 3] is a detailed front view of a lateral portion of a tire tread according to the invention, in new condition. This lateral portion of the tread is delimited inwardly by an external longitudinal cutout 311. As described previously, the lateral portion of the tread 21 comprises an alternation of first transverse cutouts 321 and second cutouts transverse 322. Any first transverse cutout 321 comprises an outer groove 321E, opening onto the rolling surface and having a width W1E, and extended radially inwards by an inner cavity 3211 having an opening surface whose closed contour has a larger dimension W1I. Any second transverse cutout 322 comprises an outer incision 322E opening onto the rolling surface, having a width W2E, and extended radially inwards by an inner groove 3221 having a width W2I. In [Fig.3] are shown a longitudinal section plane AA and a transverse section plane BB.

[0038] [Fig.4] is a detail view, in longitudinal section AA, of a lateral portion of tire tread according to the invention, in new condition, as shown in [Fig. 3]. [Fig. 4] shows, in longitudinal section, the alternation of first transverse cutouts 321 and second transverse cutouts 322. As described previously, any first transverse cutout 321 comprises an outer groove 321E, opening onto the tread surface 20 and having a width W1E at least equal to 30% of its height H1E, and extended radially inwards by an inner cavity 3211 having an opening surface whose closed contour has a larger dimension W1I (see [Fig. 5]) and having a height H1I. Any second transverse cutout 322 comprises an external incision 322E opening onto the rolling surface, having a width W2E at most equal to 20% of its height H2E, and extended radially inwards by an internal groove 3221 having a width W2I at least equal to 30% of its height H2I.

[0039] [Fig. 5] is a detail view, in cross-section BB, of a lateral portion of tread 21 of a tire according to the invention, in new condition, as shown in [Fig. 3]. This cross-section is made along the main axis of the outer groove 321E, of height H1E, of a first transverse cutout 321. The outer groove 321E opens into the outer longitudinal cutout 311. According to the invention, the outer groove 321E of the first transverse cutout 321 is extended radially inwards by an inner cavity 3211 having an emerging surface whose closed contour has a largest dimension WII, measured along the main axis of the outer groove 321E, at least equal to 10% of the width L21 (see [Fig.l]) of the lateral portion 21 and extending radially inwards up to at most the maximum depth of cutout D0.

[0040] [Fig. 6] is a graph representing the rigidity of a lateral portion of tread as a function of the maximum internal temperature, measured at the edge of the tire crown radially inside said lateral portion, according to different transverse notch configurations. On the abscissa are represented the internal temperatures Ti, defined by deviation from a reference internal temperature T0 corresponding to the maximum temperature at the edge of the crown of the tire, directly above a reference lateral portion of the tread whose transverse notch configuration VO is shown in [Fig.7]. The ordinates represent the stiffnesses R of the lateral portion of the tread, defined on a base of 100 relative to the stiffness of the first transverse notch configuration VO taken as a reference and shown in [Fig.7]. More precisely, the stiffnesses represented R are the shear stiffnesses of the raised elements of the lateral portion of the tread. A simulation of compression and then shearing of a tread element allows, by dividing the tangential force by the imposed displacement, to measure the shear stiffness of this tread element. It is known to those skilled in the art that increasing the shear stiffness makes it possible to improve wear performance when the tire is subjected to a torque.

[0041] [Fig. 7] represents a first transverse notch configuration VO of a lateral portion of tread, taken as a reference for the comparison of the rigidities of the lateral portions of tread and the maximum internal temperatures, at the edge of the crown, relative to the transverse notch configurations VI, V2, V3 and V4 described below. The first transverse notch configuration VO comprises an alternation of first transverse cutouts 321, comprising an outer groove 321E extended radially inwards by an inner incision 3211, and second transverse cutouts 322, comprising an outer incision 322E extended radially inwards by an inner groove 3221.

[0042] [Fig. 8] represents a second transverse notch configuration VI of a lateral portion of tread, in accordance with the invention. The second transverse notch configuration VI comprises an alternation of first transverse cutouts 321, comprising an outer groove 321E extended radially inwards by an inner cavity 3211, and second transverse cutouts 322, comprising an outer incision 322E extended radially inwards by an inner groove 3221. As shown in [Fig. 6], configuration V1 is the most efficient in terms of the stiffness / maximum internal temperature compromise with, compared to the reference, +13% in stiffness and +0.5°C in maximum internal temperature, which demonstrates the technical advantage of the invention.

[0043] [Fig. 9] represents a third transverse notch configuration V2 of a lateral portion of the tread. The third transverse notch configuration V2 comprises only first transverse cutouts 321, constituted by a deep groove. As shown in [Fig. 6], this configuration V2 is the most rigid (+20% compared to the reference), but also the least efficient in thermal terms (+6.5°C compared to the reference). The configuration V2 is not satisfactory at the thermal level.

[0044] [Fig. 10] represents a fourth transverse notch configuration V3 of a lateral portion of the tread. The fourth transverse notch configuration V3 comprises an alternation of first transverse cutouts 321, constituted by a deep groove, and second transverse cutouts 322, comprising an external incision 322E extended radially inwards by an internal groove 3221. As shown in [Fig. 6], configuration V3 is the most efficient in terms of thermal performance (-5.5°C compared to the reference), but also the least efficient in terms of rigidity (-25% compared to the reference). Configuration V3 is not satisfactory in terms of rigidity.

[0045] [Fig. 11] represents a fifth transverse notch configuration V4 of a lateral portion of tread. The fifth transverse notch configuration V4 comprises an alternation of first transverse cutouts 321, constituted by a shallow groove, and second transverse cutouts 322, comprising an outer incision 322E extended radially inwards by an inner groove 3221. As shown in [Fig. 6], configuration V4 has an acceptable maximum internal stiffness / temperature compromise with, compared to the reference, +17% in stiffness and +1.5°C in maximum internal temperature. However, this compromise is less satisfactory than for configuration VI, in accordance with the invention.

[0046] The invention has been more particularly studied for a tire for a civil engineering vehicle of the dumper type in the dimension 53 / 80 R 63.

[0047] Table 1 below presents the characteristics of the example studied by the inventors: [Tables 1] Characteristics Characteristic values ​​Comments LO tread width 1188 mm Maximum depth of cut DO, new 121 mm Axial distance LE of the outer longitudinal cut 311 from the equatorial plane XZ 340 mm = 28.6% LO Width L21 of the lateral portion 21 265mm Width W1E of outer groove 321E of a first transverse cut 321 45 mm = 100% H1E Height H1E of outer groove 321E of a first transverse cut 321 45 mm = 37% DO Largest dimension WI1 of the inner cavity 3211 of a first transverse cut 321 42 mm = 15.8% L21 Height H11 of inner cavity 3211 of a first transverse cut 321 36 mm (up to 321E) 83 mm (up to the running surface) = 69% DO Width W2E of external incision 322E of a second transverse cut 322 3 mm = 8% H2E Height H2E of external incision 322E of a second cut 39 mm = 32% DO transverse 322 Width W2I of inner groove 3221 of a second transverse cut 322 37 mm = 45% H2I Height H2I of inner groove 3221 of a second transverse cut 322 82 mm (up to 322E) 121 mm (up to the running surface) = 100% D0

[0048] A simulation of compression and then shearing of a tread element allows, by dividing the tangential force by the imposed displacement, to measure the shear rigidity of this tread element. It is known to those skilled in the art that increasing the rigidity makes it possible to improve the wear performance when the tire is subjected to a torque. In the example described in Table 1, and as shown in [Fig. 6], it can be seen that the proposed invention, corresponding to configuration VI, increases the shear rigidity of the lateral portion of the tread by 13%, for a quasi-stable thermal level. Thus, a thermomechanical simulation by finite elements, which makes it possible to calculate the thermal level in the structure of the tire for rolling under nominal usage conditions, shows an increase in the temperature of the hottest zone of the structure of less than 1°C.

[0049] The invention thus makes it possible, while having a controlled thermal level, to significantly improve the rigidity of the lateral portion and therefore its wear performance.

Claims

Claims

1. A tire (1) for a heavy civil engineering vehicle, comprising a tread (2) comprising an arrangement of cutouts (3) separating raised elements (4), -the cutouts (3) being either longitudinal cutouts (31) having a mean line forming, with a circumferential direction (XX'), an angle at most equal to 45°, or transverse cutouts (32) having a mean line forming, with the circumferential direction (XX'), an angle greater than 45°, -the tread (2) having, in the new condition of the tire, a width (LO), measured in an axial direction (YY') parallel to the axis of rotation of the tire, and having a maximum cutout depth (DO), measured in a radial direction (ZZ') perpendicular to a tread surface (20), -the tread (2) comprising, on each side of an equatorial plane (XZ), an external longitudinal cutout (311), having a mean line, positioned,relative to the equatorial plane (XZ), at an axial distance (LE) at least equal to 25% of the width (LO) and delimiting axially towards the outside a lateral portion of tread (21), -the lateral portion of tread (21) comprising an alternation of at least one first transverse cutout (321) and at least one second transverse cutout (322), -any first transverse cutout (321) comprising an external groove (321E) opening onto the tread surface (20) and having a width (W1E) at least equal to 30% of its height (H1E), -any second transverse cutout (322) comprising an external incision (322E) opening onto the tread surface, having a width (W2E) at most equal to 20% of its height (H2E) and extended radially towards the inside by an internal groove (3221) having a width (W2I) at least equal to 30% of its height (H2I),characterized in that the outer groove (321E) of any first transverse cutout (321) is extended radially inwards by an inner cavity (3211) having an emerging surface whose closed contour has a largest dimension (W1I) at least equal to 10% of the width (LL) of the lateral portion (21) and extending radially inwards up to at most the maximum depth of cutout, (DO).

2. Tire (1) according to claim 1 wherein the closed contour of the emerging surface of the inner cavity (3211) extending the outer groove (321E) of any first transverse cutout (321) has a largest dimension (W11) at most equal to 30% of the width (L21) of the lateral portion (21).

3. A tire (1) according to one of claims 1 or 2 wherein the inner cavity (3211) extending the outer groove (321E) of any first transverse cutout (321) extends radially inward up to at least 60% of the maximum cutout depth (DO), preferably up to at least 70% of the maximum cutout depth (DO).

4. Tire (1) according to any one of claims 1 to 3 wherein the outer groove (321E) of any first transverse cutout (321) has a width (W1E) at least equal to 40% of its height (H1E), preferably at least equal to 50% of its height (H1E).

5. A tire (1) according to any one of claims 1 to 4 wherein the outer groove (321E) of any first transverse cutout (321) extends radially inward to at most 50% of the maximum cutout depth (D0).

6. A tire (1) according to any one of claims 1 to 5 wherein the outer incision (322E) of any second transverse cutout (322) has a width (W2E) at most equal to 10% of its height (H2E).

7. A tire (1) according to any one of claims 1 to 6 wherein the outer incision (322E) of any second transverse cutout (322) extends radially inward to at most 50% of the maximum cutout depth (D0).

8. Tire (1) according to any one of claims 1 to 7 wherein the inner groove (3221) of any second transverse cutout (322) has a width (W2I) at least equal to 40% of its height (H2I), preferably at least equal to 50% of its height (H2I).

9. A tire (1) according to any one of claims 1 to 8 wherein the inner groove (3221) of any second transverse cutout (322) extends radially inward up to at least 70% of the maximum cutout depth (D0), and preferably up to 100% of the maximum cutout depth (D0).

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