Agricultural vehicle tire top

Abstract

A tire (1) for an agricultural vehicle having a tread (2) radially internal to a crown reinforcement (3) comprising crown layers (31, 32, 33, 34) including textile reinforcing elements. The tread (2) comprises a central portion and two lateral portions. The volumetric notch ratio of the central portion (Pc) is between 35 and 45%, and the volumetric notch ratios of the lateral portions (Pl) are between 50 and 65%. The crown reinforcement (3) comprises at most 5 crown layers, and the reinforcing elements of the crown layers (31, 32, 33, 34) have a tensile breaking strength of at least 32 daN. (See abstract figure: Figure 3)

Description

Title of the invention: Tire crown for agricultural vehicle

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

[0002] Like any tire, an agricultural vehicle tire includes a tread, intended to come into contact with the ground via a tread surface, the two axial ends of which are connected, via two sidewalls, to two beads ensuring the mechanical connection between the tire and the rim on which it is intended to be mounted.

[0003] A radial tire for agricultural vehicles includes a reinforcing structure, consisting of a crown reinforcement, radially inside the tread, and a carcass reinforcement, radially inside the crown reinforcement and connecting two beads intended to be in contact with a rim through two sidewalls.

[0004] In what follows, the circumferential, axial 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.

[0005] The dimensional specifications and conditions of use (load, speed, pressure) of a tire for an agricultural vehicle, or agricultural tire, are defined by its intended use. Tires range from medium to large in size depending on the type of crop. The diameter of the mounting rims for agricultural tires is at least 16 inches and at most 46 inches. For agricultural tires, the minimum recommended inflation pressure corresponding to the indicated load capacity is most often no more than 300 kPa, but can be as low as 240 kPa for an IF (Improved Flexion) tire, or even 160 kPa for a VF (Very Improved Flexion) tire.IF tires differ from standard tires known as NF ("Normal Flexion"), which do not fall under the IF or VF classification according to the ETRTO 2020 standard, by having a load capacity that is 20% higher at constant pressure or 20% lower at the same load, and 40% lower with VF ("Very Improved Flexion") tires. The maximum speed of these tires is 65 km / h, corresponding to speed rating D. The load index of these tires is at least equal to 107 (975 kg) and at most equal to 189 (10300 kg).

[0006] An agricultural vehicle tire is designed to operate on various types of soil, such as the more or less compacted earth of fields, unpaved access roads to fields, and paved road surfaces. Given the diversity of its use, both in the field and on the road, an agricultural vehicle tire, and in particular its tread, must offer a performance compromise between, but not limited to, field traction, tear resistance, road wear resistance, rolling resistance, and vibration comfort on the road. The tread is essentially composed of a polymeric material, or elastomeric compound, or rubber compound, comprising an elastomer, obtained by blending.

[0007] To meet this set of performance requirements, the tread of an agricultural vehicle tire generally comprises a plurality of raised elements, known as tread blocks, extending radially from a base surface and, in the case of the tread blocks, to the tread surface. The invention relates to an agricultural tire offering optimal field traction and therefore comprising, at least on the lateral portions of its tread, tread blocks specific to agricultural tires called lugs.

[0008] A bar generally has an overall elongated parallelepiped shape, consisting of at least one straight or curved portion, and is separated from adjacent bars by grooves. A bar may consist of a succession of straight portions, as described in documents US3603370, US4383567, EP795427, or have a curved shape, as shown in documents US4446902, EP903249, EP1831034. The bars are such that the tire has a recommended direction of rotation.Furthermore, each lateral portion comprises a circumferential arrangement of lugs, two by two separated by transverse grooves, forming, with a circumferential direction (XX1) of the tire, an average angle of at least 40° and at most 60°. The innermost axial part of each lug makes contact with the ground before its outermost axial part when the tire rolls on a surface in the recommended direction of rotation. For complex lug geometries, the average lug profile is drawn, which is the line of the contact surface passing through the middle of the lug. A linear interpolation is then performed to measure the average angle. A tread therefore comprises two rows of lugs in a V or chevron pattern, the tire having a preferred direction of rotation according to the tips of the chevrons.

[0009] The leading face of a sculpture block is, by definition, the face whose radially external edge or leading edge first comes into contact with the ground, when The tread block's passage through the tire's contact patch with the ground during tire rotation is defined as the surface whose radially outer edge, or trailing edge, is the last to make contact with the ground as the block passes through the tire's contact patch during rotation. The definitions are identical when the tread blocks are lugs. Depending on the direction of rotation, the leading edge is said to be forward relative to the trailing edge. The average distance between the leading edge and the trailing edge defines the average lug thickness.For a tread element whose outermost radial face is not included in the tread surface, the leading and trailing faces are determined by projecting that regular tire wear has brought the tread surface down to the outermost radial surface of the tread element in question.

[0010] The two rows of lugs exhibit symmetry with respect to the equatorial plane of the tire, most often with a circumferential offset between the two rows of lugs, resulting from a rotation around the tire axis of one half of the tread relative to the other half of the tread. Furthermore, the lugs may be continuous or discontinuous, and circumferentially distributed with a constant or variable pitch.

[0011] The carcass reinforcement of a radial tire for agricultural vehicles comprises at least one carcass layer connecting the two beads. A carcass layer includes reinforcements, or reinforcing elements, coated with a polymeric material comprising an elastomer, obtained by blending, or an elastomeric blend. The carcass layer reinforcements are most often made of textile polymeric materials, such as polyester. The reinforcements of a carcass layer are substantially parallel to each other and form an angle of between 85° and 95° with the circumferential direction.

[0012] The crown reinforcement of a radial tire for agricultural vehicles comprises a superposition of crown layers extending circumferentially and radially outside the carcass reinforcement. Each crown layer consists of reinforcements coated with an elastomeric compound and parallel to each other. When the reinforcements of a crown layer form an angle of 10° or less with the circumferential direction, they are called circumferential, or substantially circumferential, and provide a constraint function limiting radial deformation of the tire. When the reinforcements of a crown layer form an angle of at least 10° with the circumferential direction, and most often less than 40° but up to 50°, they are called angled reinforcements and have a function of resisting circumferential and transverse forces, parallel to the axial direction, applied to the tire. The crown layers are then called working layers. The reinforcements of the top layers can be made of textile polymer materials, such as polyester, for example, or of metallic materials, such as steel.

[0013] Regarding field performance, a key concern for tire designers is improving the resistance of the lugs and the top surface to wear and tear, particularly from residual stubble in fields after harvest, especially of corn or cotton. Stubble is a portion of a plant stem whose free end is generally sharp. The sharp free end of stubble, when it comes into contact with the leading edge of a lug, can puncture it locally and superficially, resulting in local tearing of the elastomeric material constituting the lug. Repeated wear on the leading edges of the lugs by stubble can cause significant degradation of the lugs' appearance, or even tearing, particularly near the inner axial ends of the lugs.These damages are a potential reason for complaints from users, which may necessitate tire replacement.

[0014] Moreover, these residual stubble and more particularly for cotton stubble can pierce the top and cause a loss of pressure.

[0015] Documents EP 2714431 BI and FR3068648 describe the tread of a tire for agricultural vehicles with a reduced risk of attack on the attack faces of the axially external ends of the bars by residual stubble after harvest ("stubble") and therefore of tearing.

[0016] Thus it is important to increase resistance to residual stubble but in a context of limited energy, this increase in resistance must not be accompanied by a deterioration of the energy efficiency index, namely rolling resistance and traction.

[0017] The inventors have set themselves the objective of improving resistance to damage from stubble, using a coupled optimization of the tread and the top reinforcement while improving rolling resistance and traction.

[0018] This objective has been achieved according to the invention by Pneumatic for an agricultural vehicle, comprising, radially from the outside in, a tread and a crown reinforcement comprising crown layers comprising textile reinforcement elements: -the tread having an axial width L and comprising tread blocks separated from each other by recesses and extending radially outwards from a bearing surface to a running surface, the radial distance measured at the center of the tread from the bearing surface to the tread surface determining the tread height being at least equal to 35 mm, - the tread comprising two lateral portions whose axial width is between 30 and 40% of the axial width L of the tread, axially external to a central portion, each lateral portion comprising a circumferential distribution of tread blocks in the form of bars, two by two separated by transverse grooves forming, with a circumferential direction (XX1) of the tire, an angle of at least equal to 40° and at most equal to 60°, - the central portion comprising a circumferential arrangement of sculpted blocks, two by two separated by transverse hollows, - the central and lateral portions having volumetric notch ratios, defined as the ratio between the volume VC of the grooves and the total volume V of the tread assumed to be without grooves, between the bearing surface and the tread surface, - the volumetric notching ratio of the central portion being strictly lower than the volumetric notching ratios of the lateral portions, - the top reinforcement comprises at most 5 top layers and the top layer reinforcement elements having a tensile breaking strength of at least 32 daN.

[0019] The solution is more advantageous for a VF tire (“very improved flexion”).

[0020] The bearing surface is a theoretical surface formed by the torus obtained by rotating the tire's axis of rotation YY', encompassing all the radially innermost points of the tread grooves along all the meridian planes. The maximum tread depth is the maximum distance between the bearing surface, which includes the radially innermost points of the grooves, and the rolling surface. The distance between the radially innermost point of the grooves and the rolling surface provides an indication of the tread depth of an agricultural tire. It is at least 35 mm to ensure good grip in the field.

[0021] The invention is based on the observation that stubble resistance problems are linked to the strength of the center of the tread pattern. It therefore consists, first and foremost, of having tread blocks that are more massive than the lugs. On the lateral portions, the angle formed by the lugs, combined with the possibility of stubble escaping towards the axial outside of the tire, makes them less susceptible to damage. Regarding the central portion of the tread, it is advantageous to increase the rigidity of the tread pattern in order to limit the impact of stubble damage. For the same contact material, one way to express the benefit of having the tread blocks of the central portion be The most important factor is to consider the volumetric notch ratios of the central and axial portions of the tire. Thus, the volumetric notch ratio, defined as the ratio between the groove volume (VC) and the total tread volume (V) of the tread (assumed to be without grooves), measured between the bearing surface and the tread surface, of the central portion must be strictly lower than the volumetric notch ratios of the lateral portions. More specifically, the volumetric notch ratio of the central portion is between 35% and 45%, and the volumetric notch ratios of the lateral portions are between 50% and 65%. The groove volume and the total volume will be evaluated for each of the central and lateral zones respectively, and then the ratio will be calculated for each zone. However, by increasing the volume of rubber compound in the center of the tire, the total rubber compound volume, and therefore the rolling resistance, is also increased.A surprising compromise solution is to reduce the number of crown layers to five, whereas commercially available tires typically have six. This is achieved by maintaining the puncture resistance of the crown layers using crown reinforcement elements with a tensile strength of at least 32 daN, measured according to standard D885 / D885M-10A (2014). This design effectively reduces the flattening force by decreasing the thickness of the crown reinforcement beam, while simultaneously compensating for the reduced resistance to stubble penetration by increasing the tensile strength of the crown reinforcement elements.

[0022] Advantageously, the top layers comprise reinforcing elements including an aramid strand and a strand of a PET or nylon textile fiber, the aramid strand having a tensile breaking strength of at least 30 daN. This type of hybrid reinforcement is particularly suitable for reducing the number of top layers. Preferably, the top layers comprise reinforcing elements including an aramid strand and a strand of a PET textile fiber.

[0023] An advantageous solution in terms of endurance and mass is that the reinforcing elements of the working layers are hybrid cables made up of an aramid strand with a linear mass between 160 and 180 g per km and a PET strand with a linear mass between 140 and 160 g per km, the reinforcing elements of the working layers being arranged in the working layers at a pitch between 0.8 mm and 1 mm.

[0024] In order to lighten the tire as much as possible to conserve material and reduce the crown thickness for a good balance of durability and rolling resistance, the crown reinforcement comprises at most 4 crown layers of a linear breaking strength at least equal to 30 daN / mm, preferably at least equal to 40 daN / mm.

[0025] Preferably, any bar-shaped tread block of the lateral portions of the tread has an average transverse thickness, measured between its leading and trailing faces, of at least 40 mm and at most 60 mm. These thicknesses have proven effective in agricultural treads in terms of robustness and rigidity for minimizing wear and transmitting torque.

[0026] Advantageously, directly above the central portion, the radial distance from the bearing surface to the outermost radially facing top layer is at least equal to the distance from the bearing surface to the outermost radially facing top layer measured at the center of each lateral portion plus 4 mm. Indeed, it is advantageous not only to reduce the notch depth at the center but also to increase the thickness of the rubber compound between the outermost radially facing top layer and the bearing surface in the central portion of the tread compared to the same thickness in the lateral portions, in order to better protect the grooves from this type of wear in the area most subjected to it.

[0027] The expression "above" means "for each meridian, radially inside substantially within the limit of the axial coordinates delimited by". Thus, "the points of a working layer above a sculpture block" designate, for each meridian, the set of points of the working layer radially inside the sculpture block within the limit of the axial coordinates delimited by said block.

[0028] Advantageously, each tread block of the central portion is connected to at least one tread block of a lateral portion in the form of bars by a stubble bridge whose radially outer face comprises two oblique sections designed to deflect the stubble during rolling. The regular distribution of bridges between the central portion and the lateral portions promotes a circumferentially even flattening of the tire during rolling, significantly reduces the differences in rigidity between the more massive blocks of the central portion and the bars of the lateral portions, and the generation of flat spots, a form of irregular wear. The presence of bridges protects the axially inner part of the lateral portions in contact with the central portion from stubble damage."Pare-chaume" is an adjective combining the suffix "pare," meaning protecting, and the noun "chaume," which refers to the stubble left after grain harvesting, a layer of cotton with sufficient rigidity to damage agricultural tires that might drive over it. This adjective allows for differentiation between the bridging or other sculptural elements according to the invention and other possible bridging or sculptural elements that might be present in the sculpture but do not have the same geometric characteristics. These bridging elements have been created. For this function, this does not imply that they remove all the stubble or that they cannot be improved.

[0029] Advantageously, the bridging between the sculpted blocks of the central portion is thatch-resistant bridging having a radially external face comprising at least two inclined sections, extending respectively from each of its lateral faces to a ridge line, and the average angle of the normal to each of the inclined sections with the radial direction is at least 10° and at most 20°. These angles are optimum for managing the compromise between the homogenization of the stiffness of the sculpted elements and the effectiveness of the bridging in separating the thatches. For these same reasons, the most radially external point of the ridge line of a thatch-resistant bridging is at a radial distance from the bearing surface of between 70 and 80% of the sculpted height.

[0030] To protect the most sensitive part of the tire, the axial width of the central portion is advantageously between 20% and 25% of the axial width L of the tread for optimal protection of the tread center. It represents the axial width of the tread blocks of the central portion. Similarly, the axial width of each lateral portion is advantageously between 30% and 40% of the axial width L of the tread.

[0031] It is advantageous to facilitate the sliding of stubble that comes to rest on the lateral faces of a tread block in the central section towards the lateral face of the stubble barrier to which it is connected, and then along the face of the slat continuously towards the axial outside of the tire. It is therefore advantageous to avoid a discontinuity between the lateral faces of the tread blocks in the central section, the slats, and the lateral faces of the slats, which could impede the sliding of the stubble. Given that the faces of the slats have an angle optimized for traction in the field, to promote this continuity and this technical effect, one leading face of each tread block in the central section is advantageously substantially continuous with the leading face of a stubble barrier, and forms an angle with the circumferential direction (XX') of at least 40° and at most 60°, preferably between 45° and 50°.Advantageously, the leading face of the thatch bridging is substantially continuous with the leading face of the bar to which it is connected, and makes an angle with the circumferential direction (XX') of at least 40° and at most 60°, preferably between 45 and 50°.

[0032] To enable this solution to operate as efficiently as possible in endurance conditions, particularly in thermal conditions despite the increased volume of rubber compound in the central portion, it is advantageous for the tread to include a so-called contact material intended to come into contact with the ground, of which the dynamic loss tanô, measured according to the same ASTM D 5992 - 96 standard, at a temperature of 60°C and under a strain of 50% at 10 Hz, i.e. less than 0.3.

[0033] To resist well the penetration of stubble and wear, it is preferred that the so-called contact material have an elastic shear modulus G' at 50% of peak strain, measured according to ASTM D 5992 - 96, greater than 1.50 MPa.

[0034] Rolling resistance performance can be improved if the tread comprises a so-called underlayer material, radially internal to the so-called contact material, whose dynamic loss tanô, measured according to the same ASTM D 5992-96 standard, at a temperature of 60°C and under a 50% strain at 10 Hz, is at most 0.15. Similarly, it is advantageous for the so-called underlayer material to have an elastic shear modulus G' at 50% peak strain, measured according to ASTM D 5992-96, of at least 1.0 MPa. The underlayer material is preferably radially internal to the bearing surface.

[0035] The terms elastic modulus and viscous modulus refer to well-known dynamic properties for someone in the elastomers trade. The phase angle θ between the force and the displacement, expressed as a dynamic loss tanθ, is equal to the ratio of the viscous and elastic moduli G" / G'.

[0036] These properties can be measured on bonded test specimens extracted from a tire tread. Specimens such as those described in ASTM D 5992-96 (September 2006 edition) can be used. The specimen used is cylindrical with a diameter of 10 mm and a height of 2 mm.

[0037] The specimen is subjected to sinusoidal alternating simple shear loading at a frequency of 10 Hz with imposed stress, symmetrically around its equilibrium position. The specimen is accommodated prior to the temperature sweep measurement. For this purpose, the specimen is subjected to sinusoidal shear loading at 10 Hz, at 100% peak-to-peak strain at a temperature of 60°C.

[0038] The temperature sweep measurement is performed during a temperature ramp increasing by 1.5°C per minute, starting from a minimum temperature below the glass transition temperature Tg of the material up to a maximum temperature. Before taking the measurements, the specimen is stabilized at the minimum temperature for at least 20 minutes. The glass transition temperature Tg is the temperature at which the dynamic heat loss tanô reaches a maximum during the temperature sweep.

[0039] It can be advantageous, particularly in the case where there is an excess thickness of elastomeric compound, but not only, that every hollow in each lateral portion includes a face with a radial height of at least 3 mm, called a stubble guard, whose trailing edge is axially external to its leading edge, this face allowing the stubble to be oriented towards the axial outside of the tire in this area. To avoid creating a section of this face more prone to tearing, it is advantageous for the angle between the normal to the stubble-guarding face of the lateral portion (PI) and the circumferential direction to vary continuously from the leading edge to the trailing edge. Similarly, to ensure this orientation is compatible with the orientation of the tread blocks, the angle between the normal to the stubble-guarding face and the circumferential direction (XX') at its axial end should be between 40 and 60°.

[0040] The features of the invention are illustrated by schematic figures 1 to 3, which are not drawn to scale: - [Fig. 1]: portion of the tire tread pattern according to the invention, - [Fig.2]: Detail of the thatch barrier - [Fig.3]: Diagram of a meridional half-section of the tire according to the invention.

[0041] Fig. 1 represents a portion of the tread 2 of an agricultural vehicle tire having a recommended direction of travel 12. The tread 2, of axial width L, comprises tread elements 22, including tread blocks 221, 222 separated from each other by grooves 23, in this case bars 221 of the lateral portions PI of axial width Lp separated by grooves 231 and blocks 222 of the central portion Pc of axial width Le separated by grooves 232. The tread blocks 221, 222 extend radially outwards from a bearing surface 233 to a tread surface 25, the bearing surface 233 of which only a line is visible, being in fact a theoretical surface constituted by the torus obtained by rotation around the axis YY' of rotation of the tire of the set of the most radially inner points of the hollows 23 of the sculpture on the set of meridian planes.The slats 221 of the lateral portions form, with the circumferential direction (XX1) of the tire, an angle Al of at least 40° and at most 60° and are arranged in a chevron pattern with a circumferential offset between the slats of the two lateral portions. Each slat 221 is connected to a tread block 222 of the central portion by a bridge 224 whose average transverse thickness is equal to the average transverse thickness emt of the slat, which is 44.5 mm. The length Ipc of a stubble bridge, defined as the distance separating the tread blocks connected by said bridge 224, is equal to 27.5 mm. The volumetric notch ratio, defined as the ratio between the volume VC of the hollow 23 and the total volume V of the tread 2 assumed to be without hollows, between the bearing surface 233 and the tread surface 25, of the central portion Pc, is less than the volumetric notch ratio of the lateral portions PI.The attack faces of blocks 222 of the central portion Pc, of the bridgings 224 and of the . The bars are continuous. The figure also represents a stubble guard face 234, whose trailing edge is axially external to its leading edge, and continuous.

[0042] Fig. 2 shows the cross-section of the thatch decking along line AA mentioned in Fig. 1. The decking 224 is connected to a block 222 of the central portion, the radially outer surface of which is included in the running surface 25. The decking 224 has two substantially radial lateral faces 2244, 2245 and a radially outer face, connecting the two lateral faces 2244, 2245 and the radially inner face to the running surface 25. The radially outer face comprises at least two inclined planes 2242, 2243 extending respectively from each of its lateral faces 2244, 2245 to a ridge line 2241. Face 2244 is the leading face of the decking and face 2245 its trailing face. The average angle Ap of the normal to the inclined plane considered with the radial direction (ZZ') at each inclined panel is equal to 13° for inclined panel 2242 and equal to 14° for inclined panel 2243.

[0043] Figure 3 represents a portion of the crown of the tire according to the invention in a meridian plane YZ passing through the axis of rotation YY' of the tire. The tire 1 for agricultural vehicles comprises a crown reinforcement 3 radially internal to a tread 2 and radially external to a carcass reinforcement 4. The crown reinforcement 3 comprises four crown layers 31, 32, 33, 34, each comprising textile reinforcement elements embedded in an elastomeric material. The tread 2 comprises grooves 23, bars 221 in the lateral portion of the tread 2, and blocks 222 in the central portion of the tread, the two being connected by a bridge 224. The tread is composed of a contact material 211 and a so-called underlayer material 212.The tread has an axial half-width L / 2 and comprises a central portion of an axial half-width Lc / 2 and two axially outer portions, only one of which is shown, its axial width being equal to Lp. The radial distance from the bearing surface 233 to the tread surface 25, measured at the center of the tread, determines the tread depth Hs, which is at least equal to 35 mm. A face 234 with a radial height of at least 3 mm, called a stubble guard, whose trailing edge 2342 is axially external to its leading edge 2341, is present in the hollow 23. [Fig. 3] also shows the thickness of the rubbery mixture hc equal to the radial distance from the bearing surface 233 to the most radially external top layer 31 and the distance hl from the bearing surface 233 to the most radially external top layer 31 measured at the center of each lateral portion PI.

[0044] The invention has been implemented more particularly for an agricultural tire of size 380 / 90R46. The tire, according to the prior art, is a Michelin "Spraybib®" of this size, whose tread has an axial width equal to 327 mm. Its sculpture is composed of continuous bars of 33 mm radial height at the center of the tread and making an angle of 47° with the circumferential direction, with an average transverse thickness of 46 mm and an axial width representing 56% of the total width of the tread without having any bridging or extra thickness in the central portion of the tread between the outermost radial top layer and the bearing surface compared to the lateral portions.

[0045] The volumetric notch ratio of the tire according to the prior art, defined as the ratio between the volume VC of the groove 23 and the total volume V of the tread 2 assumed to be without grooves, between the bearing surface 233 and the tread surface 25, of the central portion Pc, is equal to 46.2%, and the volumetric notch ratio of the lateral portions PI is equal to 54.3%. As it is not possible to determine a central portion and lateral portions for the control tire, we used for this evaluation an Lc / Lt ratio identical to that of the invention.

[0046] The tire according to the state of the art comprises 6 top layers whose reinforcement elements consist of 3 rayon strands with a linear mass of 240 g per km, the reinforcement elements having a breaking strength of 28 daN and being arranged at a pitch of 1.27 mm, for a breaking strength of the top layer of 22 daN / mm.

[0047] The prior art tire comprises a contact material 211 intended to come into contact with the ground, the dynamic loss tanô of which, measured according to the same ASTM D 5992-96 standard, at a temperature of 60°C and under a 50% strain at 10 Hz, is equal to 0.3 and an elastic shear modulus G' at 50% peak strain, at 1.5 MPa. The prior art tire does not comprise an underlayer material.

[0048] The tire according to the invention has a tread with an axial width of 327 mm. Its tread pattern is composed of central tread blocks with a radial height of 39 mm and an axial width equal to 22% of the tread width, connected by 27.5 mm long cross-bridges Ipc to continuous bars making an angle Al of 47.3° with the circumferential direction, with an average transverse thickness emt of 43.8 mm. The axial widths of the lateral portions represent 44% of the total tread width. The tread has an additional thickness between the outermost radially facing top layer 31 and the bearing surface 233 in the central portion of the tread of 5 mm compared to the tread thickness at the centers of the lateral portions PI (hc-hl=5mm). This extra thickness results in the presence of a face with a radial height of 4mm, called a thatch guard.This face is continuous and its trailing edge is tangent to the bar. The volumetric notch ratio of the central portion Pc is . equal to 43.2% and the volumetric notching rate of the lateral portions PI is equal to 57%.

[0049] The bridging between the bars has the width of the bars, and their radially external faces comprise at least two inclined planes 2242, 2243, extending respectively from each of its lateral faces 2244, 2245 to a ridge line 2241 at a radial height of 31 mm from the supporting surface. The radial heights of the leading and trailing edges of the supporting surface are equal to 26 mm. The mean angle Ap of the normal to the inclined plane 2242 with the radial direction (ZZ') is equal to 13°, and the mean angle Ap of the normal to the inclined plane 2243 with the radial direction (ZZ') is equal to 14°.

[0050] The tire according to the invention comprises four top layers, the reinforcement elements of which are cables made of an aramid strand having a linear mass of 167 g / km and a strand of PET textile fiber with a linear mass of 144 g / km, the reinforcement elements of the working layers being arranged within the working layers at a pitch of 0.86 mm. The reinforcement elements have a breaking strength of 37 daN and the top layers a linear breaking strength of 43 daN / mm.

[0051] The tire according to the invention comprises a contact material intended to come into contact with the ground, the dynamic loss tanô of which, measured according to the same standard ASTM D 5992-96, at a temperature of 60°C and under a 50% strain at 10 Hz, is equal to 0.25, and the elastic shear modulus G' at 50% peak strain is equal to 1.55 MPa. The tire according to the invention comprises an underlayer material the dynamic loss tanô of which, measured according to the same standard ASTM D 5992-96, at a temperature of 60°C and under a 50% strain at 10 Hz, is equal to 0.11, and the elastic shear modulus G' at 50% peak strain is equal to 1.19 MPa.

[0052] The tire according to the invention was simulated using finite element analysis for driving conditions reproducing usage measured by position and force sensors on a vehicle in real-world working and field travel situations. The calculations show improved wear performance of at least 35% for a 16% increase in tread depth, of which 7% is due to the performance provided by the tread geometry. The bridging design, in particular, allows for very good homogenization of rolling forces and even wear between the lugs and the central blocks.

[0053] The tire was also tested for traction. The tires were mounted on a commercially available sprayer. The tires were inflated to the pressure and load of the vehicle in the field for cyclic use well known to users. The hubs were equipped with force sensors capable of measuring slippage. The sprayer is traveling in a plowed field with an average slope of 11%. The measurement is taken uphill. The bridging increases the ground contact area and improves traction performance by 30% by reducing slippage from 50% to 35%.

[0054] The tire was also tested for traction, that is, its ability to pull a tool. The pressures and loads are identical to the previous type. The vehicle equipped with the tested tires pulls a wheeled mass across a field. For a slip rate of 15%, the effort developed is improved by 15%, again thanks to the improved contact patch related to the invention.

[0055] Since resistance to stubble damage is difficult to measure outside of a full-scale, long-term use test, an initial estimate is based on the expert knowledge of technical advisors to users. These experts anticipate an improvement in resistance to stubble damage due to the tread pattern's ability to evacuate or deflect it, on the order of 20 to 30%. This performance is assessed by observing the presence and number of visible stubble impacts after rolling in a field following mowing.

[0056] Despite an increase in tread material volume due to a 16% increase in tread depth, thanks to the coupling of the tread and tread materials, the tire according to the invention offers more than 10% better rolling resistance. Furthermore, thanks to the reduced tread height, the total mass of the tire has remained constant, and despite greater stress on each of the tread layers, the maximum tread temperature has been reduced by 20°C during use, resulting in improved durability.

Claims

Demands

1. A tire (1) for an agricultural vehicle, comprising, radially from the outside in, a tread (2) and a crown reinforcement (3) comprising crown layers (31, 32, 33, 34) comprising textile reinforcement elements: - the tread (2) having an axial width L and comprising tread blocks (221, 222) separated from each other by grooves (23) and extending radially outwards from a carrier surface (233) to a running surface (25), the radial distance measured at the center of the tread from the carrier surface to the running surface determining the tread height (Hs) being at least 35 mm, - the tread (2) comprising two lateral portions (PI) having an axial width between 30 and 40% of the axial width L of the tread, axially external to a portion central,each lateral portion comprising a circumferential arrangement of tread blocks (221) in the form of bars, separated in pairs by transverse grooves (231) forming, with a circumferential direction (XX1) of the tire, an angle (Al) of at least 40° and at most 60°, - the central portion (Pc) comprising a circumferential arrangement of tread blocks (222), separated in pairs by transverse grooves (232), - the central and lateral portions having volumetric notch ratios, defined as the ratio between the volume VC of grooves (23) and the total volume V of the tread (2) assumed to be without grooves, between the bearing surface (233) and the tread surface (25), characterized in that the volumetric notch ratio of the central portion (Pc) is between 35 and 45% and the volumetric notch ratios of the lateral portions (P1) are between 50 and 65%,and in that the top reinforcement (3) comprises at most 5 top layers and the reinforcement elements of the top layers (31, 32, 33, 34) have a tensile breaking strength of at least 32 daN.

2. Pneumatic according to claim 1, wherein, perpendicular to the central portion (Pc), the radial distance (hc) of the bearing surface (233) to the outermost radially outer top layer (31) is at least equal to the distance (hl) from the bearing surface (233) to the outermost radially outer top layer (31) measured at the center of each lateral portion (PI) plus 4 mm.

3. Pneumatic according to any one of claims 1 or 2, wherein the top layers (31, 32, 33, 34) comprise reinforcing elements comprising an aramid strand and a strand of a PET or nylon textile fiber, the aramid strand having a tensile breaking strength of at least 30 daN.

4. A tire according to any one of the preceding claims, wherein the top layers (31, 32, 33, 34) comprise reinforcing elements including an aramid strand and a strand of a PET textile fiber

5. Pneumatic according to any one of the preceding claims, wherein the working layer reinforcement elements (31, 32, 33, 34) are hybrid cables made up of an aramid strand with a linear mass between 160 and 180 g per km and a PET strand with a linear mass between 140 and 160 g per km, the working layer reinforcement elements (31, 32, 33, 34) being arranged in the working layers with a pitch between 0.8 mm and 1 mm.

6. Pneumatic according to any one of the preceding claims, wherein the top reinforcement (3) comprises at most 4 top layers of a linear breaking strength of at least 30 daN / mm, preferably at least 40 daN / mm.

7. A tire according to any one of the preceding claims, wherein the tread (2) comprises a contact material (211) intended to come into contact with the ground, the dynamic loss tanô of which, measured according to the same ASTM D 5992-96 standard, at a temperature of 60°C and under a strain of 50% at 10 Hz, is less than 0.30 and the elastic shear modulus G' at 50% of peak strain (5), measured according to ASTM D 5992-96 standard, is greater than 1.50 MPa.

8. A tire according to any one of claims 6 or 7, wherein the tread (2) comprises a material (212) referred to as the underlayer, radially internal to the material (211) referred to as the contact layer, the dynamic loss of which tanô, measured according to the same ASTM standard

9. D 5992 - 96, at a temperature of 60°C and under a deformation of 50% at 10 Hz, is at most equal to 0.

15. Pneumatic according to claim 8, wherein the underlayer material (212) has an elastic shear modulus G' at 50% peak strain (5), measured according to ASTM D 5992-96, of at least 1.0 MPa.