Agricultural vehicle tire featuring an improved tread

Abstract

The present invention relates to a tire for agricultural vehicles, and in particular its tread, and aims to increase its traction capacity in the field on soft ground. According to the invention, the tire having a nominal section width L, a central portion of tread (211), centered on an equatorial plane (E) of the tire and having an axial width L1 of at least 0.15*L and at most 0.35*L, comprises tread elements (221) distributed circumferentially, two by two separated by transverse grooves (231) forming with the circumferential direction (XX') an angle of at least 30°, and the central portion of tread (211) has a local volumetric notch ratio TEVL1, defined as the ratio between the volume VC1 of the transverse grooves (231) and the total volume V1 of said central portion of tread (21), between the bearing surface (24) and the tread surface (25), of at most 15%.Figure for the abridged version: Fig.6.

Description

Title of the invention: Agricultural vehicle tire comprising an improved tread

[0001] The present invention relates to a tire for an agricultural vehicle, such as an agricultural tractor or an agro-industrial vehicle, and more particularly relates to its tread.

[0002] The dimensional specifications (section width, overall diameter, diameter and width of the mounting rim) and the conditions of use (load, speed, pressure) of a tire for an agricultural vehicle are defined in standards, such as, for example, the “ETRTO” or “European Tyre and Rim Technical Organization” standard in its “Standards Manual-2018”, in the section devoted to “Agricultural equipment tires”. For example, a radial tire for the drive wheel of an agricultural tractor is intended to be mounted on a rim whose diameter is generally between 16 inches and 46 inches, or even 54 inches. It is intended to run on an agricultural tractor whose power is between 50 HP and more than 250 HP (up to 550 HP) and which can travel up to 65 km / h.For this type of tire, the minimum recommended inflation pressure corresponding to the indicated load capacity is most often at most 400 kPa, but can go down to 240 kPa, for an “IF” or “Improved Flexion” tire, or even 160 kPa, for a “VF” or “Very High Flexion” tire.

[0003] Like any tire, a tire for an agricultural vehicle comprises a tread, intended to come into contact with the ground via a rolling surface - contact surface on rigid ground - and the two axial ends of which are connected via two sidewalls with two beads ensuring the mechanical connection between the tire and the rim on which it is intended to be mounted.

[0004] In the following, the circumferential (or longitudinal), axial (or transverse) and radial directions respectively designate a direction tangent to the rolling surface and oriented in the direction of rotation of the tire, a direction parallel to the axis of rotation of the tire and a direction perpendicular to the axis of rotation of the tire. A radial (or meridian) plane is defined by a radial direction and the axial direction, and contains the axis of rotation of the tire. A circumferential plane is defined by a radial direction and a circumferential direction, and is therefore perpendicular to the axis of rotation of the tire. The circumferential plane passing through the The middle of the tread is called the equatorial plane.

[0005] The tread of a tire for an agricultural vehicle generally comprises a plurality of raised elements, called sculpture elements, extending radially outward from a bearing surface to the rolling surface, and separated from each other by hollows.

[0006] The proportion of hollows is usually quantified by an overall volumetric notch rate TEV, defined as the ratio between the volume VC of hollows and the total volume V of the tread assumed to be without hollows corresponding to the geometric volume delimited by the bearing surface and the rolling surface. The rolling surface varying with the wear of the tread, the overall volumetric notch rate TEV is generally, but not necessarily, variable with the level of wear. Thus, the overall volumetric notch rate TEV can be defined for a new condition or for a given state of wear. For example, a tire for the drive wheel of an agricultural tractor in new condition has an overall volumetric notch rate TEV generally at least equal to 50% and often at least equal to 60%. In the following, the expression "overall volumetric notch rate TEV" implicitly means "overall volumetric notch rate TEV in new condition".

[0007] It is also possible to define a local volumetric notch rate TEVL for any portion of tread, extending circumferentially over the entire circumference of the tire and extending axially from a first circumferential plane to a second circumferential plane, the distance between these two circumferential planes representing the axial width, more simply called width, of the portion of tread. The local volumetric notch rate TEVL is defined as the ratio between the volume of hollows VCL and the total volume VL of the portion of tread assumed to be without hollows, corresponding to the geometric volume delimited by the bearing surface, the rolling surface and the two circumferential planes. Like the overall volumetric notch rate TEV, the local volumetric notch rate TEVL can be defined for a new condition or for a given state of wear.In the following, the expression "local volumetric notch rate TEVL" implicitly means "local volumetric notch rate TEVL in new condition".

[0008] Each sculpture element can be geometrically characterized by a radial height H in a radial direction, an axial width A in an axial direction and a circumferential length B in a circumferential direction. These three dimensions H, A and B are average values, knowing that they can vary according to the measurement points selected on the sculpture element. Concerning the axial width A and the circumferential length B, they can increase from the rolling surface to the bearing surface, at the bottom of the hollow, due to the presence of reliefs. Concerning the radial height H, for a radial tire for the drive wheel of an agricultural tractor, the radial height H of a tread element is generally at least equal to 50 mm and most generally at least equal to 60 mm. From these three dimensions H, A and B, a circumferential slenderness H / B, an axial slenderness H / A and a surface aspect ratio B / A can be defined for a given tread element.

[0009] A tread for an agricultural vehicle usually comprises tread elements in the form of bars. A bar generally has an elongated, generally parallelepipedal shape, continuous or discontinuous, and consisting of at least one rectilinear or curvilinear portion. A bar is separated from adjacent bars by hollows or grooves. A bar extends axially from a median zone of the tread to its axial ends or shoulders. A bar comprises a contact face, positioned in the tread surface and intended to come into full contact with the ground, a leading face, intersecting the tread surface and the intersection edge of which with the latter is intended to come into contact with the ground first, a trailing face, intersecting the tread surface and the intersection edge of which with the latter is intended to come into contact with the ground last, and two lateral faces.

[0010] The lugs are distributed circumferentially with a constant or variable pitch and are generally arranged on either side of the equatorial plane of the tire, so as to form a V-shaped pattern, the tip of the V-shaped pattern (or even chevron pattern) being intended to enter the contact area with the ground first. The lugs generally have symmetry with respect to the equatorial plane of the tire, with most often a circumferential offset between the two rows of lugs, obtained by a rotation around the axis of the tire of one half of the tread relative to the other half of the tread.

[0011] A radial tire for an agricultural vehicle further comprises a reinforcing reinforcement, consisting of a crown reinforcement, radially inside the tread, and a carcass reinforcement, radially inside the crown reinforcement.

[0012] The carcass reinforcement of a radial tire for an agricultural vehicle comprises at least one carcass layer connecting the two beads together. The reinforcements of a carcass layer are substantially parallel to each other and form, with the circumferential direction, an angle of between 75° and 105°, preferably between 85° and 95°. A carcass layer comprises reinforcements, most often textile, coated with a polymeric material of the elastomer or elastomeric type called a coating mixture.

[0013] The crown reinforcement of a radial tire for an agricultural vehicle comprises a superposition of crown layers extending circumferentially, radially outside the carcass reinforcement. Each crown layer is made up of reinforcements coated with an elastomeric mixture and parallel to each other. When the crown layer reinforcements form, with the circumferential direction, an angle of less than 10°, they are called circumferential, or substantially circumferential, and provide a hooping function limiting the radial deformations of the tire. When the crown layer reinforcements form, with the circumferential direction, an angle at least equal to 10° and most often at most equal to 30°, they are called angle reinforcements and have a function of absorbing the transverse forces, parallel to the axial direction, applied to the tire.The top layer reinforcements may be made of textile-type polymeric materials, such as a polyester, for example polyethylene terephthalate (PET), an aliphatic polyamide, for example nylon, an aromatic polyamide, for example aramid, or rayon, or of metallic materials, such as steel.

[0014] A tire for an agricultural vehicle is intended to run on various types of soil such as more or less compacted earth in fields, unpaved access roads to fields and paved road surfaces. Given the diversity of use, in fields and on roads, a tire for an agricultural vehicle must offer a compromise of performance between, but not limited to, traction in the field on soft ground, resistance to tearing, resistance to wear on the road, resistance to forward movement and vibration comfort on the road.

[0015] A key problem when using a tire in a field is to limit as much as possible the compaction of the soil by the tire, which could harm crops.

[0016] This is why, in the agricultural sector, low-pressure tires, therefore with high flexion, have been developed. The ETRTO standard thus distinguishes between IF (Improved Flexion) tires, with a minimum recommended inflation pressure generally equal to 240 kPa, and VF (Very high Flexion) tires, with a minimum recommended inflation pressure generally equal to 160 kPa. According to the standard, compared to a standard tire, an IF tire has a load capacity increased by 20%, and a VF tire has a load capacity increased by 40%, for an inflation pressure equal to 160 kPa.

[0017] However, the use of low-pressure tires has a negative impact on field behavior. Thus, the reduction in inflation pressure has led to a reduction in the transverse and drift rigidities of the tire, resulting in a reduction in the transverse thrust of the tire, and, consequently, a deterioration in its behavior under transverse stresses.

[0018] One solution to restore correct transverse thrust was to stiffen trans versally the crown reinforcement of the tire, by replacing the textile-reinforced crown layers with metal-reinforced crown layers. Thus, for example, a crown reinforcement comprising 6 rayon textile-reinforced crown layers has been replaced by a crown reinforcement comprising 2 steel-reinforced crown layers. Document EP 2934917 thus describes an IF tire comprising a crown reinforcement comprising at least two metal-reinforced crown layers, combined with a carcass reinforcement comprising at least two textile-reinforced carcass layers.

[0019] The inventors then set themselves the objective of increasing the field traction capacity on soft ground of a tire for an agricultural vehicle in general, and, in particular, that of a tire for an agricultural vehicle, comprising a crown reinforcement with metal reinforcements and / or operating at low pressure such as an IF (Improved Flexion) tire or a VF (Very High Flexion) tire.

[0020] This objective is achieved, according to the invention, by a tire for an agricultural vehicle having a nominal section width L and comprising, radially from the outside to the inside, a tread and a crown reinforcement: -the tread comprising tread elements, separated from each other by hollows and extending radially outwards from a bearing surface to a rolling surface, - the tread having an overall volumetric notch rate TEV, defined as the ratio between the volume VC of hollow and the total volume V of the tread assumed to be without hollow, between the bearing surface and the rolling surface, -each tread element having a circumferential slenderness H / B at most equal to 1.5, H being an average radial height between the bearing surface and the rolling surface at least equal to 20 mm, and B being an average circumferential length, -the tread comprising a central portion, centered on an equatorial plane of the tire and having an axial width L1 at least equal to 0.15*L and at most equal to 0.35*L, and two intermediate portions, each extending axially outwards the central portion up to an axial distance D2 equal to 0.3*L, measured from the equatorial plane, - the central portion and each intermediate portion comprising tread elements distributed circumferentially, two by two separated by transverse hollows forming, with a circumferential direction of the tire, an angle at least equal to 30°, - the crown reinforcement comprising at least two crown layers, each comprising reinforcements coated in an elastomeric material, parallel to each other, crossed from one layer to the next, and forming, with the circumferential direction, an angle at least equal to 10°, -the central portion having a local volumetric notch rate TEVL1, defined as the ratio between the volume VC1 of the transverse hollows and the total volume VI of said central portion, between the bearing surface and the rolling surface, at most equal to 15%.

[0021] The tread, according to a first characteristic of the invention, comprises tread elements having a circumferential slenderness H / B at most equal to 1.5, H being an average radial height between the bearing surface and the rolling surface at least equal to 20 mm, and B being an average circumferential length. For a given tread element, the radial height between the bearing surface and the rolling surface is substantially constant, therefore the average radial height H is equal to this substantially constant radial height. On the other hand, the circumferential length of a tread element can vary substantially depending on the depth at which it is measured, due to the inclination of the front (or leading) and rear (or trailing) faces of the tread element, depending on the rolling direction: hence the need to define an average circumferential length B.The circumferential slenderness H / B, which geometrically characterizes the circumferential rigidity of the sculpture element, is not necessarily constant and can vary between two sculpture elements.

[0022] The tread further comprises, according to a second characteristic of the invention, a central portion, centered on an equatorial plane of the tire and having an axial width L1 at least equal to 0.15*L and at most equal to 0.35*L, and two intermediate portions, each extending axially outwardly the central portion up to an axial distance D2 equal to 0.3*L, measured from the equatorial plane. The nominal tire section L is the “design section width” defined in the ETRTO standard.

[0023] Furthermore, according to a third characteristic of the invention, the central portion and each intermediate portion comprise tread pattern elements distributed circumferentially, two by two separated by transverse hollows forming, with a circumferential direction of the tire, an angle at least equal to 30°. These hollows are described as transverse, insofar as their direction forms a sufficiently large angle with the circumferential direction, and cannot therefore be described as circumferential or longitudinal. In other words, their direction varies between an oblique position and a transverse position, parallel to the axis of rotation of the tire. By definition, the angle formed by the hollows is the angle formed by their average surface, generally constituted by a plane perpendicular to the rolling surface. In the case where this average surface is constituted by a succession of planes, each of these planes forms an angle at least equal to 30°.

[0024] According to a fourth characteristic of the invention, the crown reinforcement comprises at least two crown layers, each comprising reinforcements coated in an elastomeric material, parallel to each other, crossed from one layer to the next, and forming, with the circumferential direction, an angle at least equal to 10°.

[0025] According to a fifth and final characteristic of the invention, the central portion has a local volumetric notch rate TEVL1 at most equal to 15%, that is to say a low volumetric notch rate reflecting the presence of a small hollow volume.

[0026] The combination of these characteristics guarantees in particular, for the central portion of the tread, a high circumferential rigidity, due to its low volumetric notch rate and a limited circumferential slenderness for the tread elements, as well as an easier circumferential flattening, when passing through the contact area, due to the presence of transverse hollows which act as hinges: hence an increase in the traction capacity. Indeed, a cut central portion, consisting of blocks separated by transverse hollows, has a better circumferential flattening than a continuous central portion, consisting of at least one continuous rib without transverse hollows.

[0027] Advantageously, the transverse hollows of the central portion of the tread form with the circumferential direction of the tire an angle at least equal to 60°. An angle at least equal to 60° is characteristic of a substantially transverse hollow, which plays the role of a substantially transverse hinge further facilitating the circumferential flattening of the tread, at the level of its central portion.

[0028] Preferably, the transverse hollows of the central portion of the tread are transverse incisions, capable of closing when they pass through the contact area with a ground during rolling of the tire. The transverse incisions are transverse hollows having a very small width, since they are capable of closing when they pass through the contact area. More precisely, at the entrance and exit of the contact area, these incisions are open and facilitate the circumferential flattening of the tread in these zones. In the contact area, these incisions close and create a continuous rib having a greater circumferential rigidity than that obtained with transverse hollows which remain open. The ability of the transverse incisions to close when they pass through the contact area is defined on a tire subjected to pressure and load conditions as defined by the ETRTO standard.

[0029] Advantageously, the transverse hollows of each intermediate portion form, with the circumferential direction, an angle at least equal to 60°. An angle at least equal to 60° is characteristic of a substantially transverse hollow, which plays a role of substantially transverse hinge further facilitating the circumferential flattening of the tread, at the level of its intermediate portions.

[0030] According to a preferred embodiment, each tread pattern element of the central portion having an average radial height H1, an average circumferential length B1, and a circumferential slenderness H1 / B1, and each tread pattern element of each intermediate portion having an average radial height H2, an average circumferential length B2, and a circumferential slenderness H2 / B2, the circumferential slenderness H1 / B1 is strictly greater than the circumferential slenderness H2 / B2. In this embodiment, there is therefore a circumferential slenderness differential between the tread pattern elements of the central portion and those of each intermediate portion.A circumferential slenderness Hl / Bl of a tread element in the central portion, strictly greater than the circumferential slenderness H2 / B2 of a tread element, implies that the circumferential rigidity of a tread element in the central portion is lower than that of a tread element in the intermediate portions. A relatively high circumferential rigidity of the tread elements in the intermediate portion advantageously guarantees a traction capacity of the tire when rolling in a field on relatively cohesive soil, for example dry wheat stubble.It should be noted that the circumferential slenderness conditioning this circumferential rigidity results from a compromise between the field traction capacity on dry ground, the field traction capacity on waterlogged ground obtained by an adapted volumetric notch rate of each intermediate portion, and the life of the tread obtained by a sufficient average radial height H2 of the intermediate portion tread element.

[0031] According to a preferred variant of the preferred embodiment previously described, the circumferential slenderness H2 / B2 of each tread pattern element (222) of each intermediate portion (212) is at most equal to 0.6. This condition means that the circumferential rigidity of a tread pattern element of an intermediate portion necessary for sufficient traction capacity of the tire when rolling in the field on relatively cohesive ground is obtained for a tread pattern element that is rather elongated in the circumferential direction, with an average radial height H2 at most equal to 60% of the average circumferential length B2.

[0032] Still preferably, a median portion of the tread, centered on the equatorial plane of the tire and having an axial width L2 equal to 2*D2=0.40*L, has a local volumetric notch rate TEVL2, defined as the ratio between the volume VC2 of the hollows and the total volume V2 of said median portion of the tread, between the bearing surface and the rolling surface, at most equal to 45%. In other words, the volumetric notch rate TEVL2, determined on a median portion having a width L2 equal to 40% of the nominal section width L of the tire, and consisting of the central portion and the two intermediate portions previously described, is greater than the volumetric notch rate TEVL1 of the central portion, without however exceeding 45%. Consequently, the hollow volume increases as one moves away from the equatorial plane of the tire, which in particular makes it possible to guarantee satisfactory traction on wet soils with low cohesion.

[0033] According to a first embodiment, the tread comprises exclusively transverse hollows. Consequently, the tread does not comprise any circumferential hollows.

[0034] According to a second embodiment, the central portion of the tread is axially delimited, on either side, by circumferential hollows. By circumferential hollow, we mean a hollow that is either strictly circumferential or oblique with an angle of inclination relative to the circumferential direction of at most 45°.

[0035] Advantageously, each tread element has an average radial height H at most equal to 55 mm. Beyond this value, the circumferential slenderness H / B of a tread element risks being greater than 0.8. Consequently, the bending and shear rigidities, in the circumferential direction, of each tread element become too low to guarantee, in particular in the central portion of the tread, an overall circumferential rigidity sufficient for the desired level of traction. Furthermore, a radial height that is too high penalizes the thermal level of the crown of the tire, and therefore its endurance.

[0036] Advantageously, the tread has an overall volumetric notch rate TEV of at most 56%. Beyond this overall volumetric notch rate value TEV, the hollow volume becomes too high. Correlatively, the volume of material becomes too low to guarantee a sufficient service life with respect to wear.

[0037] In a particular embodiment of the transverse hollows, at least a portion of the transverse hollows comprises at least one chamfer opening onto the tread surface, forming, with a radial direction, an angle D at least equal to 30° and at most equal to 70° and having a radial height C at least equal to 3 mm and at most equal to 10 mm. Most often, all the transverse hollows comprise at least one chamfer. According to a first variant, all the transverse hollows comprise a single chamfer. According to a second variant, all the transverse hollows comprise two facing chamfers. The presence of chamfers contributes to a significant improvement in the traction of the tread.

[0038] According to a preferred embodiment of the crown reinforcement of the tire, the crown reinforcement comprises crown layers comprising metal reinforcements, preferably at most two crown layers comprising metal reinforcements. The presence of metal reinforcements makes it possible to obtain the desired crown rigidity, with a limited number of crown layers, implying a limited crown thickness. This results in a lower crown bending rigidity than for a usual crown of the state of the art, which facilitates the flattening of the tire. Thus the contact surface with the ground is increased, which, on the one hand, reduces ground pressures, and therefore soil compaction, and, on the other hand, increases the traction capacity.

[0039] In a first preferred field of tire, the tire for agricultural vehicle is an “IF” or “Improved Flexion” tire within the meaning of the “ETRTO” or “European Tire and Rim Technical Organization” standard, in its “Standards Manual-2018”, in the section devoted to “Agricultural equipment tires”, having a load capacity 20% higher than that of a standard tire at iso-pressure.

[0040] In a second preferred field of tire, the tire for agricultural vehicles is a “VF” or “Very High Flexion” tire within the meaning of the “ETRTO” or “European Tire and Rim Technical Organization” standard, in its “Standards Manual-2018”, in the section devoted to “Agricultural equipment tires”, having a load capacity 40% higher than that of a standard tire at iso-pressure.

[0041] The characteristics of the invention are illustrated by schematic figures 1 to 12, not shown to scale: -Figure 1: Overall perspective view of a tire for an agricultural vehicle according to a first variant embodiment of the invention. -Figure 2: Detailed perspective view of the tread of a tire for an agricultural vehicle according to the first variant embodiment of the invention (detail Cl of figure 1). -Figure 3: Overall front view of a tire for an agricultural vehicle according to the first embodiment of the invention. -Figure 4: Detailed front view of the tread of a tire for an agricultural vehicle according to the first variant embodiment of the invention (detail DI of figure 3). -Figure 5: Circumferential section of the tread of a tire for an agricultural vehicle according to the first variant embodiment of the invention (section AA of figure 3). -Figure 6: Half meridian section of a tire for an agricultural vehicle according to the invention (section BB of figure 3). -Figure 7: Overall perspective view of a tire for an agricultural vehicle according to a second variant embodiment of the invention. -Figure 8: Detailed perspective view of the tread of a tire for an agricultural vehicle according to the second variant embodiment of the invention (detail C2 of figure 7). -Figure 9: Overall front view of a tire for an agricultural vehicle according to a third variant embodiment of the invention. -Figure 10: Detailed perspective view of the tread of a tire for an agricultural vehicle according to the third variant embodiment of the invention (detail D3 of figure 9). -Figure 11: Sectional view of a transverse hollow comprising a single chamfer. -Figure 12: Sectional view of a transverse hollow comprising two facing chamfers.

[0042] Figures 1 to 5 illustrate a tire 1 for an agricultural vehicle according to a first alternative embodiment of the invention. The tread 2 comprises sculpture elements 22, separated from each other by hollows 23 and extending radially outwards from a bearing surface 24 to a rolling surface 25 (the bearing surface and the rolling surface are shown in Figure 6). In this first alternative embodiment, the tread 2 comprises exclusively transverse hollows 231 (Figures 2, 4 and 5). In the central portion 211 of the tread, the transverse hollows 231 are transverse incisions, of width I, capable of closing when they pass through the area of ​​contact with a ground during the rolling of the tire (figures 4 and 5), when the tire is subjected to pressure and load conditions as defined by the ETRTO standard.The sculpture elements 221 of the central portion 211 of the tread, separated by said transverse incisions, have an average radial height H and an average circumferential length B (figure 5), consequently a circumferential slenderness H / B.

[0043] Figure 6 is a half-meridian section of a tire for an agricultural vehicle according to the invention. This radial section is made along the plane BB of Figure 3. This figure shows a tire 1 for an agricultural vehicle having a half-width of nominal section L / 2, and comprising, radially from the outside towards the inside, a tread 2 and a crown reinforcement 3. The tread 2 comprises sculpture elements 22, separated from each other by hollows 23 and extending radially towards the outside from a bearing surface 24 to a rolling surface 25. The tread 2 has an overall volumetric notch ratio TEV, defined as the ratio between the volume VC of hollows 23 and the total volume V of the tread 2 assumed to be without hollows, between the bearing surface 24 and the rolling surface 25, at least equal to 35%. Each tread element 22 has a circumferential slenderness H / B at most equal to 0.8, H being the average radial height between the bearing surface 24 and the rolling surface 25 at least equal to 20 mm and B being the average circumferential length of the tread element 22 (not shown). The crown reinforcement 3 comprises two crown layers (31, 32), each comprising preferably metallic reinforcements coated in an elastomeric material, parallel to each other, crossed from one layer to the next, and forming, with a circumferential direction XX' of the tire, an angle at least equal to 10°. Radially inside the crown reinforcement 3, a carcass reinforcement 4 is positioned. According to the invention, a central portion of tread 211, centered on an equatorial plane E of the tire and having an axial width L1 at least equal to 0.15*L and at most equal to 0.35*L, comprises tread pattern elements 221 (identified under the generic reference 22 of the tread pattern elements, in FIG. 6) distributed circumferentially, two by two separated by transverse hollows 231 (not shown in FIG. 6) forming with the circumferential direction XX' an angle at least equal to 30°, and the central tread portion 211 has a local volumetric notch rate TEVL1, defined as the ratio between the volume VC1 of the transverse hollows 231 and the total volume VI of said central tread portion 211, between the bearing surface 24 and the rolling surface 25, at most equal to 15%. In FIG. 6 is shown a central half-portion of tread of width Ll / 2. The tread 2 further comprises two intermediate portions 212, each extending axially outwards the central portion 211 up to an axial distance D2 equal to 0.3*L, measured from the equatorial plane E.In Figure 6 is shown a single intermediate portion 212 of tread of width D2-L1 / 2. Preferably a middle portion of tread 20, centered on the equatorial plane of the tire and having an axial width L2 equal to 2*D2=0.60*L, consisting of the whole of the central portion 211 and the two intermediate portions 212, has a local volumetric notch rate TEVL2, defined as the ratio between the volume VC2 of the hollows and the total volume V2 of said middle portion of tread 20, between the bearing surface 24 and the rolling surface 25, at most equal to 45%. In Figure 6 is shown a half-middle portion of tread of width D2=L2 / 2.

[0044] Figures 7 and 8 illustrate a tire 1 for an agricultural vehicle according to a second alternative embodiment of the invention, respectively as an overall figure and a detail figure C2. The tread 2 comprises sculpture elements 22 separated from each other by hollows 23. In this second alternative embodiment, the tread 2 comprises a central portion 211, comprising circumferentially distributed sculpture elements 221, separated from each other by transverse incision-type hollows 231, capable of closing when they pass through the area of ​​contact with a ground during the rolling of the tire. In addition, the central portion 211 of the tread is axially delimited, on either side, by circumferential hollows 233.

[0045] Figures 9 and 10 illustrate a tire for an agricultural vehicle according to a third alternative embodiment of the invention, respectively as an overall figure and a detail figure D3. In this third alternative embodiment, the tread 2 of the tire of nominal section width L comprises a central portion 211, centered on an equatorial plane E of the tire and having an axial width L1 at least equal to 0.15*L and at most equal to 0.35*L, and two intermediate portions 212, each extending axially outwardly the central portion 211 up to an axial distance D2 equal to 0.3*L, measured from the equatorial plane E. The assembly constituted by the central portion 211 and the two intermediate portions 212 constitutes a median portion 20, centered on the equatorial plane E of the tire and having an axial width L2 equal to 2*D2=0.60*L.The central portion 211 comprises tread pattern elements 221 distributed circumferentially, two by two separated by transverse hollows 231 forming, with a circumferential direction XX' of the tire, an angle at least equal to 30°, and, in the present case, at least equal to 60°. The transverse hollows 231 of the central portion 211 are transverse incisions, capable of closing when they pass through the area of ​​contact with a ground during the rolling of the tire. Each tread pattern element 221 has a circumferential slenderness H1 / B1 at most equal to 1.5, H1 being an average radial height between the bearing surface and the rolling surface at least equal to 20 mm (not shown in Figures 8 and 9), and B1 being an average circumferential length. B1 is measured at the rolling surface because the leading and trailing faces of the tread elements 221 are substantially radial.According to the invention, the central portion 211 has a local volumetric notch rate TEVL1, defined as the ratio between the volume VC1 of the transverse hollows 231 and the total volume VI of said central portion 211, between the bearing surface and the rolling surface, at most equal to 15%. Each intermediate portion 212 comprises tread pattern elements 222 distributed circumferentially, two by two separated by transverse hollows 232 forming, with the circumferential direction XX' of the tire, an angle at least equal to 30°, and, in the present case, at least equal to 60°. Each sculpture element 222 has a circumferential slenderness H2 / B2 at most equal to 1.5, H2 being an average radial height between the bearing surface and the rolling surface at least equal to 20 mm (not shown in Figures 8 and 9), and B2 being an average circumferential length. B2 is measured between two points respectively. located substantially in the middle of the leading face and in the middle of the trailing face, knowing that these have, with respect to a radial plane YZ, an inclination called clearance. In the embodiment shown in Figures 9 and 10, the circumferential slenderness H1 / B1 is strictly greater than the circumferential slenderness H2 / B2 which itself is strictly less than 0.6. Finally, the median portion 20, centered on the equatorial plane E of the tire and having an axial width L2 equal to 2*D2=0.60*L, has a local volumetric notch rate TEVL2, defined as the ratio between the volume VC2 of the hollows and the total volume V2 of said median portion 20, between the bearing surface and the rolling surface, at most equal to 45%.

[0046] Figures 11 and 12 respectively represent a sectional view of a transverse hollow comprising a single chamfer and a sectional view of a transverse hollow comprising two facing chamfers. Each chamfer 26 opens onto the rolling surface 25, forming, with a radial direction, an angle D at least equal to 30° and at most equal to 70° and having a radial height C at least equal to 3 mm and at most equal to 10 mm.

[0047] The invention has been more particularly studied for a tire for an agricultural vehicle of dimension VF 600 / 70R30 165D, corresponding to an embodiment of the invention as shown in Figures 9 and 10 with circumferential elements of the tread pattern element differentiated between the central portion and the intermediate portions.

[0048] Table 1 below presents the characteristics of the example studied by the inventors: [Tables 1] Characteristics Characteristic values ​​Comments Nominal section width L 600 mm Overall volumetric notch ratio TEV 48% At most equal to 56% Width L1 of central portion of tread 160 mm 27% of L, therefore between 15% and 35% of L Local volumetric notch ratio TEVL1 of central portion 8% Less than 15% Width L2 of median portion of tread 360 mm Equal to 60% of L Local volumetric notch ratio TEVL2 of median portion 35% Less than 45% Average radial height H1 of a central portion tread element 42 mm Between 20 mm and 55 mm Average circumferential length B1 of a central portion tread element 41 mm Circumferential slenderness Hl / Bl of a central portion tread element 1.02 Less than 1.5 Average radial height H2 of an intermediate portion tread element 37 mm Between 20 mm and 55 mm Average circumferential length B2 of an intermediate portion tread element 110 mm Circumferential slenderness H2 / B2 of an intermediate portion tread element 0.34 Less than 0.6 Width I of a central portion incision 2.7 mm Width allowing the incision to close in the contact patch, under the recommended driving conditions. Angle of a central portion incision, relative to the circumferential direction 85° Greater than 60° and therefore greater than 30° Angle D of a chamfer of a central portion incision, relative to a radial direction 45° Between 30° and 70° Radial height C of a chamfer of a central portion incision 5 mm Between 3 mm and 10 mm Average width of a transverse hollow (excluding central portion) 140 mm Average angle of a transverse hollow (excluding central portion), relative to the circumferential direction 80° Greater than 30°

[0049] The inventors have found that a tire according to the invention, having the characteristics described in Table 1, provides, for low ground slip of between 4% and 10%, a gain in traction of the order of 27% compared to a tire of the reference state of the art, that is to say is capable of developing a force traction approximately 27% higher than that developed by a state-of-the-art tire.

Claims

Claims

1. A tire (1) for an agricultural vehicle having a nominal section width L and comprising, radially from the outside to the inside, a tread (2) and a crown reinforcement (3): -the tread (2) comprising sculpture elements (22), separated from each other by hollows (23) and extending radially outwards from a bearing surface (24) to a rolling surface (25), -the tread (2) having an overall volumetric notch rate TEV, defined as the ratio between the volume VC of hollow (23) and the total volume V of the tread (2) assumed to be without hollow, between the bearing surface (24) and the rolling surface (25), -each tread element (22) having a circumferential slenderness H / B at most equal to 1.5, H being an average radial height between the bearing surface (24) and the rolling surface (25) at least equal to 20 mm, and B being an average circumferential length, -the tread (2) comprising a central portion (211), centered on an equatorial plane (E) of the tire and having an axial width L1 at least equal to 0.15*L and at most equal to 0.35*L, and two intermediate portions (212), each extending axially outwardly the central portion (211) up to an axial distance D2 equal to 0.3*L, measured from the equatorial plane (E), -the central portion (211) and each intermediate portion (212) being respectively constituted by a circumferential distribution of tread pattern elements (221, 222), two by two separated by transverse hollows (231, 232) forming, with a circumferential direction (XX') of the tire, an angle at least equal to 30°, -the crown reinforcement (3) comprising at least two crown layers (31, 32), each comprising reinforcements coated in an elastomeric material, parallel to each other, crossed from one layer to the next, and forming, with the circumferential direction (XX'), an angle at least equal to 10°, characterized in that the central portion (211) has a local volumetric notch rate TEVL1, defined as the ratio between the volume VC1 of the transverse hollows (231) and the total volume VI of said central portion (211), between the bearing surface (24) and the rolling surface (25), at most equal to 15%.

2. Tire (1) according to claim 1, in which the transverse hollows (231) of the central portion (211) form, with the circumferential direction (XX'), an angle at least equal to 60°.

3. Tire (1) according to one of claims 1 or 2, in which the transverse hollows (231) of the central portion (211) are transverse incisions, capable of closing when they pass through the area of ​​contact with a ground during the rolling of the tire.

4. Tire (1) according to any one of claims 1 to 3, in which the transverse hollows (232) of each intermediate portion (212) form, with the circumferential direction (XX'), an angle at least equal to 60°.

5. A tire (1) according to any one of claims 1 to 4, each tread pattern element (221) of the central portion (211) having an average radial height H1, an average circumferential length B1, and a circumferential slenderness H1 / B1, and each tread pattern element (222) of each intermediate portion (212) having an average radial height H2, an average circumferential length B2, and a circumferential slenderness H2 / B2, in which the circumferential slenderness H1 / B1 is strictly greater than the circumferential slenderness H2 / B2.

6. Tire (1) according to claim 5, in which the circumferential slenderness H2 / B2 of each tread pattern element (222) of each intermediate portion (212) is at most equal to 0.

6.

7. Tire (1) according to any one of claims 1 to 6, in which a median portion (20), centered on the equatorial plane (E) of the tire and having an axial width L2 equal to 2*D2=0.60*L, has a local volumetric notch rate TEVL2, defined as the ratio between the volume VC2 of the hollows (23) and the total volume V2 of said median portion (20), between the bearing surface (24) and the rolling surface (25), at most equal to 45%.

8. A tire (1) according to any one of claims 1 to 7, wherein the tread (2) comprises exclusively transverse hollows (231, 232).

9. A tire (1) according to any one of claims 1 to 7, wherein the central portion (211) is axially delimited, on either side, by circumferential hollows (233).

10. A tire (1) according to any one of claims 1 to 9, wherein each tread pattern element (22) has an average radial height H at most equal to 55 mm.

11. Tire (1) according to any one of claims 1 to 10, in which the tread (2) has an overall volumetric notch rate TEV at most equal to 56%.

12. A tire (1) according to any one of claims 1 to 11, wherein at least a portion of the tread elements (22) comprises at least one chamfer (26) opening onto the rolling surface (25) forming, with a radial direction (ZZ'), an angle D at least equal to 30° and at most equal to 70° and having a radial height C at least equal to 3 mm and at most equal to 10 mm.

13. A tire (1) according to any one of claims 1 to 12, wherein the crown reinforcement (3) comprises crown layers (31, 32) comprising metal reinforcements, preferably at most two crown layers (31, 32) comprising metal reinforcements.

14. A tire (1) according to any one of claims 1 to 13, wherein the agricultural vehicle tire is an “IF” or “Improved Flexion” tire within the meaning of the “ETRTO” or “European Tire and Rim Technical Organization” standard, in its “Standards Manual-2018”, in the section devoted to “Agricultural equipment tires”.

15. A tire (1) according to any one of claims 1 to 13, wherein the agricultural vehicle tire is a “VF” or “Very High Flexion” tire within the meaning of the “ETRTO” or “European Tire and Rim Technical Organization” standard, in its “Standards Manual-2018”, in the section devoted to “Agricultural equipment tires”.

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