TIRES FOR A MIXED-USE AGRICULTURAL VEHICLE

Description

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

[0002] Like any tire, a tire for an agricultural vehicle includes a tread, intended to come into contact with the ground via a rolling surface, 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.

[0003] In the following, and by convention, the circumferential (or longitudinal), axial (or transverse) and radial directions respectively designate a direction tangent to the tread 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 middle of the tread is called the median circumferential plane or equatorial plane.

[0004] The tread of an agricultural vehicle tire generally comprises a sculpture consisting of a plurality of raised elements extending radially outward from a bearing surface to the rolling surface, and separated from each other by hollows.

[0005] In the prior art, a tread for an agricultural vehicle usually comprises tread pattern 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.

[0006] The lugs are distributed circumferentially according to a constant or variable pitch, measured between the respective average lines of two consecutive lugs, 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 chevron pattern) being intended to enter the contact patch 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.

[0007] 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 tarred 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.

[0008] When road use of the agricultural vehicle becomes predominant, with a distance traveled on the road representing, for example, up to 80% of the total distance traveled, on the road and in the field, the road performance of the tire becomes essential. The tire, initially designed for efficiency in the field, must also have high road performance, particularly in terms of energy efficiency and wear life. Energy efficiency means a significant contribution to the vehicle's fuel economy, thanks to limited resistance to forward movement, and in particular limited rolling resistance. Regarding road wear, the tire must allow for high road mileage, thanks to a wear rate that is not too rapid and controlled forms of wear on its tread.

[0009] However, the search for an optimal compromise in road use, between rolling resistance and wear life, must not lead to a deterioration in road braking grip, which must remain at a level compatible with the required safety requirements, while ensuring the shortest possible braking distance. Indeed, it is known that the simultaneous improvement of rolling resistance, wear life and grip is complex. Thus, to reduce rolling resistance, reducing the hysteresis of the rubber materials constituting the tread, i.e. reducing their capacity to dissipate heat, is effective, but, in return, it reduces braking grip. Similarly, increasing the volume of rubber material to be used in the tread makes it possible to increase wear life, but at the risk of increasing rolling resistance.

[0010] Furthermore, the search for the compromise in road performance described above must not lead to a degradation of field performance, such as traction capacity and flotation, i.e. the ability to not sink deeply into the ground.

[0011] Documents WO 00 / 13923 A1 and WO 2020 / 201028 A1 disclose prior art agricultural vehicle tires.

[0012] Therefore, the inventors set themselves the objective of proposing an optimal compromise between rolling resistance and wear life of a tire for agricultural vehicles, in road use, without degrading either the grip when braking on the road, or the essential performances in the field such as traction capacity and flotation.

[0013] This aim has been achieved according to the invention by a tire for an agricultural vehicle comprising a tread having an axial width and consisting of blocks, two by two separated by hollows and arranged, in the width of the tread, in a middle row, two intermediate rows and two lateral rows, the hollows being either transverse hollows, forming, with a circumferential direction of the tire, an angle at least equal to 60°, or circumferential hollows, forming, with the circumferential direction, an angle at most equal to 30°, the middle row being centered on a median circumferential plane of the tire, the two intermediate rows being axially positioned on either side of the middle row and separated from it by circumferential hollows, and the two lateral rows being respectively axially positioned outside an intermediate row and separated from it by a circumferential hollow, each row respectively middle, intermediate and lateral being constituted by a circumferential distribution of blocks two by two separated by transverse hollows and each having an average radial height,an average circumferential length and an average circumferential slenderness defined as the ratio between the average radial height and the average circumferential length of the block, the blocks of the same lateral row extending axially outwards in the extension of the blocks of the adjacent intermediate row, such that any set of two blocks respectively of lateral row and intermediate row, in the extension of one another, forms a bar, two consecutive blocks of the middle row being separated by a transverse hollow having a width at most equal to 2.5 mm, the average circumferential slenderness of any block of the middle row being at least equal to 0.95 and at most equal to 1.15, any block of each intermediate row comprising a leading face, in the circumferential direction of rolling of the tire, forming, with a radial direction of the tire, an average angle at least equal to 30°,and the average circumferential slenderness of any block in each side row is at most 0.9. ,

[0014] The tread of a tire according to the invention comprises sculpture elements which are not traditional bars, extending axially from a median zone of the tread to its axial ends or shoulders, but blocks distributed across the width of the tread.

[0015] These blocks are arranged in five circumferential rows: a middle row, two intermediate rows, axially positioned on either side of the middle row, and two lateral rows, respectively axially positioned outside an intermediate row. However, the arrangement of the respective blocks of a lateral row and the neighboring intermediate row constitutes a system of partial bars.

[0016] Any block comprises a contact face, positioned in the rolling surface and intended to come into full contact with the ground, a leading face, intersecting the rolling surface and whose intersection edge with it is intended to come into contact first with the ground, a trailing face, intersecting the rolling surface and whose intersection edge with it is intended to come into contact last with the ground, and two lateral faces. The leading and trailing faces respectively, not necessarily contained in a plane, are generally characterized by the average angle that it forms with a radial direction of the tire.

[0017] Any block 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 ​​measured on the block. Generally, the axial width and the circumferential length vary over the height of the tread element: they can, for example, decrease from the bearing surface at the bottom of the groove to the rolling surface, due to the inclination of the faces of the block. In the case of a radial tire for the drive wheel of an agricultural tractor, the radial height H is generally at least equal to 50 mm and most often 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 determining the rigidities of the tread element can be defined for a given block.

[0018] The circumferential rows of blocks are separated in pairs by circumferential hollows. A circumferential hollow, in a broad sense, forms, with the circumferential direction, an angle at most equal to 30°. In other words, its mean line forms an average angle, with respect to the circumferential direction of the tire, which is not zero, but included in the range of values ​​[0°; 30°]. Its mean line forms a smaller inclination with respect to the circumferential direction than with respect to the axial direction. The hollow is therefore not strictly circumferential, but globally circumferential.

[0019] The blocks of the same circumferential row are separated in pairs by transverse hollows. A transverse hollow, in a broad sense, forms, with the circumferential direction, an angle at least equal to 60°. In other words, its mean line forms an average angle, with respect to the circumferential direction of the tire, which is not zero, but included in the range of values ​​[60°; 90°]. Its mean line forms a greater inclination with respect to the circumferential direction than with respect to the axial direction. The hollow is therefore not strictly transverse, but globally transverse.

[0020] A hollow is delimited by the two walls of the blocks it separates. When the blocks deform as they pass through the contact area of ​​the tire with the ground while rolling, these walls tend to move closer together and the hollow they delimit to close. These deformations depend on the mechanical stresses applied to the tire while rolling, these being themselves functions of the conditions of use of the tire. The conditions of use (load, speed, pressure) of a tire for agricultural vehicles are defined in standards, such as, for example, the "ETRTO" standard or "European Tire and Rim Technical Organization" in its "Standards Manual-2019" (Standards Manual 2019), in the section dedicated to "Agricultural equipment tires".When a tire is used under these conditions of use recommended by the standards, the block walls delimiting a hollow may or may not come into contact with each other at least in part, that is to say that the hollow may or may not close. When there is no contact between the walls, the hollow is called a groove. When there is at least partial contact between the walls, the hollow is called an incision.

[0021] A hollow is generally characterized geometrically by a width and a depth. The width of a hollow is measured perpendicular to the average surface of the hollow, positioned equidistant from the walls delimiting the hollow, and at the level of the rolling surface, or possibly in the vicinity of it in the case of the presence of chamfers on the blocks opposite. The depth of the hollow is measured perpendicular to the rolling surface, between the emerging surface and the bottom of the hollow.

[0022] According to a first essential characteristic of the invention, two consecutive blocks of the middle row are separated by a transverse hollow having a width at most equal to 2.5 mm.

[0023] In other words, a middle row transverse hollow is an incision, likely to close at least partially as it passes through the contact patch.

[0024] As a result, the middle row, consisting of blocks separated by incisions, constitutes a quasi-continuous rib incised periodically, which is favorable with regard to wear and rolling resistance performance in road use. Due to the small thickness of the median transverse hollows, the volume of rubber material of the middle part, intended to be worn by abrasion, is high, which is favorable to the service life with regard to wear. In addition, the surface area of ​​rubber material of the middle part, intended to come into contact with the ground, is also high, which reduces the contact pressures with the ground, and therefore abrasion, and consequently wear.The presence of incisions facilitates the flattening of the middle row of blocks in the circumferential direction, which, on the one hand, limits the sliding of the blocks on the ground, and consequently the wear, and on the other hand limits the deformation of the rubber material and therefore their energy dissipation, which reduces the rolling resistance. In addition, the closure of the median transverse hollows in the contact area leads to a compactness of the middle row of blocks, that is to say, the blocks come into contact with each other, which allows a reduction in the deformations of the middle blocks by Poisson effect and in shear. This results in less energy dissipation of the rubber material in the blocks of the middle row, which reduces the rolling resistance.

[0025] Furthermore, in the case of field use, the limitation of contact pressures, maximum at the center of the tread, avoids significant compaction of the soil, which helps to preserve it.

[0026] According to a second essential characteristic of the invention, the average circumferential slenderness of any block of the middle row is at least equal to 0.95 and at most equal to 1.15.

[0027] A circumferential slenderness of a middle row block close to 1 is considered optimal with respect to the compromise, for the middle row, between its circumferential flattening, for wear and rolling resistance, and the level of slip obtained in the contact patch, for braking on a wet road.

[0028] According to a third essential characteristic of the invention, each block of each intermediate row comprises a leading face, in the circumferential rolling direction of the tire, forming, with a radial direction of the tire, an average angle at least equal to 30°.

[0029] An average intermediate row block leading face angle of at least 30° allows for an intermediate block with a high material volume and high circumferential stiffness. A high material volume ensures satisfactory wear life. High circumferential stiffness limits sliding of the intermediate row block in the contact patch, and therefore abrasion, and consequently wear. In addition, circumferential deformations of the intermediate row block, due to Poisson and shear effects, are also limited. This results in less energy dissipation of the rubber material in the intermediate row blocks, which reduces rolling resistance.

[0030] In field use, an average angle of attack face of intermediate row block, at least equal to 30°, therefore high, makes it possible to increase the cohesion of the soil in front of and under the block, which makes it possible to develop a greater traction force.

[0031] According to a fourth essential characteristic of the invention, the average circumferential slenderness of any block of each lateral row is at most equal to 0.9.

[0032] Compared to a circumferential slenderness close to 1 for a state-of-the-art lug tire, the reduction in the average circumferential slenderness of any block in each lateral row is achieved by increasing the circumferential length of the block, which allows for a large volume of material to be worn, favorable to wear, and high circumferential rigidity. A high volume of material ensures a satisfactory wear life. High circumferential rigidity limits sliding of the intermediate row block in the contact patch, and therefore abrasion, and consequently wear. In addition, circumferential deformations of the intermediate row block, by Poisson effects and in shear, are also limited. This results in less energy dissipation of the rubber material in the intermediate row blocks, which reduces rolling resistance.

[0033] Preferably, the middle row has an axial width at least equal to 15% and at most equal to 25% of the axial width of the tread.

[0034] The axial width of the middle row must be sufficient so that the desired technical advantages in terms of wear and rolling resistance in road use are significant, but not too high so that the traction function in the field can be properly ensured.

[0035] Advantageously, the middle row has a local volume hollow rate of at most 20%.

[0036] The proportion of cavities in a tread is usually quantified by an overall volumetric cavity ratio, defined as the ratio between the cavity volume and the total volume of the tread assumed to be void-free, corresponding to the geometric volume delimited by the bearing surface and the rolling surface. The overall volumetric cavity ratio is also called the overall volumetric gouging ratio. Since the tread surface varies with tread wear, the overall volumetric cavity ratio generally, but not necessarily, varies with the level of wear. Thus, the overall volumetric cavity ratio 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 cavity ratio generally at least equal to 50% and often at least equal to 60%.In the following, the expression "overall volumetric hollow rate" implicitly means "overall volumetric hollow rate in new condition".

[0037] A local volumetric void ratio can also be defined 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 void ratio is defined as the ratio between the void volume and the total volume of the portion of tread assumed to be void-free, corresponding to the geometric volume delimited by the bearing surface, the rolling surface and the two circumferential planes. The local volumetric void ratio is also called the local volumetric notch ratio. Like the overall volumetric void ratio, the local volumetric void ratio can be defined for a new condition or for a given state of wear.In the following, the expression "local volumetric hollow rate" implicitly means "local volumetric hollow rate in the new state".

[0038] A local volumetric hollow rate of at most 20%, for the middle row, guarantees a significant favorable impact on wear and rolling resistance performance, in road use.

[0039] Advantageously, any transverse hollow separating two consecutive blocks of the middle row forms, with the circumferential direction, an angle at least equal to 70°.

[0040] The circumferential flattening of the middle row is facilitated by a transverse hollow angle as close as possible to the axial direction, i.e. as close as possible to 90°. The inventors found that an angle value of 70° was a minimum value for the effectiveness of this flattening.

[0041] Advantageously, any transverse hollow separating two consecutive blocks of the middle row has a depth at least equal to 50%, preferably at least equal to 70%, of the average radial height of the block.

[0042] Below 50% of the mean radial block height, the middle row transverse hollow depth is insufficient to ensure a hinge effect allowing circumferential flattening of the middle row with a significant impact on rolling resistance.

[0043] According to a particular advantageous embodiment, any transverse hollow separating two consecutive blocks of the middle row is extended radially inwards by a cavity.

[0044] The presence of a cavity, most often spherical, at the bottom of the transverse hollow, reduces the risk of crack initiation from the bottom of the hollow, by avoiding a concentration of stresses. In addition, when the wear level reaches the bottom of the hollow, at the end of its life, the cavity then forms two edges, which helps to maintain minimum grip on wet roads.

[0045] Advantageously, each intermediate row has an axial width at least equal to 15% and at most equal to 25% of the axial width of the tread.

[0046] This range of axial width values ​​for each intermediate row guarantees effective field traction over a significant portion of the tread.

[0047] Advantageously, each intermediate row has a local volumetric hollow rate at least equal to 40%, preferably at least equal to 55%.

[0048] A minimum value of 40% for the local intermediate row volumetric hollow rate is required for effective field traction.

[0049] Advantageously, the average circumferential slenderness of any block respectively of each intermediate row is at least equal to 0.5 and at most equal to 1.

[0050] An average circumferential slenderness of any intermediate row block in the range of values ​​[0.5; 1], combined with an average leading face angle of said block at least equal to 30°, makes it possible to obtain an optimal circumferential rigidity of the block with respect to the compromise between road performance of wear and rolling resistance and field traction.

[0051] Preferably, any block of an intermediate row comprises a leading face forming, with a radial direction of the tire, an average angle at least equal to 35°.

[0052] The higher the average angle of attack face of an intermediate row block, the more the cohesion of the soil, in use in the field, is reinforced in front of and under the block: this makes it possible to develop an even greater traction force in the field.

[0053] Advantageously, each lateral row has an axial width at least equal to 15% and at most equal to 25% of the axial width of the tread.

[0054] Advantageously, each lateral row has a local volumetric hollow rate at least equal to 40%, preferably at least equal to 55%.

[0055] The combination of a side row having an axial width and a local volumetric hollow rate in the previously defined ranges, and an intermediate row as previously described, constitutes a partial bar system effective with respect to field traction.

[0056] Advantageously, the average circumferential slenderness of any block respectively of each lateral row is at most equal to 0.8.

[0057] Advantageously, the average circumferential slenderness of any block respectively of each lateral row is at least equal to 0.6.

[0058] An average circumferential slenderness of any side row block in the range of values ​​[0.6; 0.8] allows to obtain an optimal circumferential stiffness of the block with respect to the compromise between road performance of wear and rolling resistance and performance in traction field and earth evacuation.

[0059] Advantageously, any block of a lateral row comprises a leading face forming, with a radial direction of the tire, an average angle at least equal to 10° and at most equal to 30°.

[0060] Beyond a value of 30° for the average angle of attack face, the widths of transverse hollows separating two consecutive blocks of side row become too small to guarantee sufficient traction capacity and earth evacuation (or clearing) capacity. To compensate for a risk of loss of traction in the field, a reduction in the width of the transverse hollows can be at least partly compensated by an increase in the depth of the transverse hollows.

[0061] According to a particular embodiment, each block of a lateral row comprises a leading face and a trailing face forming, with a radial direction of the tire, respective average angles equal in absolute value. This configuration therefore implies a symmetry of the inclinations of the leading and trailing faces of a lateral row block.

[0062] Preferably each intermediate and lateral row comprises at least 26 blocks.

[0063] Preferably, each intermediate and lateral row comprises at most 32 blocks.

[0064] The choice of the number of blocks distributed circumferentially, for any lateral or intermediate row, results from a compromise between wear on the road, depending on the volume of material to be worn and the surface area of ​​material in contact with the ground, and noise and vibration comfort on the road, depending in particular on the pitch separating two consecutive blocks in the same row.

[0065] The present invention will be better understood with the aid of the figures 1 to 6 described below: Figure 1 : Perspective view of a tire according to the invention, Figure 2 : Front view of a tire according to the invention, Figure 3 : Meridian sectional view of a tread of a tire according to the invention, Figure 4: Circumferential sectional view of a portion of the middle row of a tread of a tire according to the invention, Figure 5 : Circumferential sectional view of a portion of an intermediate row of a tread of a tire according to the invention, Figure 6 : Circumferential sectional view of a portion of a lateral row of a tread of a tire according to the invention.

[0066] There Figure 1 is a perspective view of a tire according to the invention. The tire 1 for an agricultural vehicle comprises a tread 2 consisting of blocks (31, 32, 33), two by two separated by hollows (41, 42, 43, 51, 52) and arranged, across the width of the tread 2, in a middle row 21, two intermediate rows 22 and two lateral rows 23. The hollows (41, 42, 43, 51, 52) are either transverse hollows (41, 42, 43) or circumferential hollows (51, 52).

[0067] There Figure 2is a front view of a tire according to the invention. The tire 1 for an agricultural vehicle, having an outside diameter D in a state not mounted on a rim and not inflated, comprises a tread 2 having an axial width L, in an axial direction YY', and consisting of blocks (31, 32, 33), two by two separated by hollows (41, 42, 43, 51, 52) and arranged, in the width of the tread 2, in a middle row 21, two intermediate rows 22 and two lateral rows 23. The hollows (41, 42, 43, 51, 52) are either transverse hollows (41, 42, 43), forming, with a circumferential direction XX' of the tire 1, an angle at least equal to 60°, or circumferential hollows (51, 52), forming, with the circumferential direction XX', an angle at most equal to 30°. The middle row 21, having an axial width L1, is centered on a median circumferential plane E of the tire.The two intermediate rows 22, each having an axial width L2, are axially positioned on either side of the middle row 21 and separated from the latter by circumferential hollows 51, each having a width E2. The two lateral rows 23, each having an axial width L3, are respectively axially positioned outside an intermediate row 22 and separated from the latter by a circumferential hollow 52, ​​having a width E3. Each row respectively middle 21, intermediate 22 and lateral 23 is constituted by a circumferential distribution of blocks (31, 32, 33) two by two separated by transverse hollows (41, 42, 43) and each having an average circumferential length (B1, B2, B3). The circumferential length B1 of a block 31 of middle row 21 is the circumferential distance measured between the two transverse hollows 41, of incision type, delimiting it.The circumferential length B2 of a block 32 of intermediate row 22 is the average circumferential distance measured between a leading face 321 and a trailing face 322 of said block 32. The circumferential length B3 of a block 33 of lateral row 23 is the average circumferential distance measured between a leading face 331 and a trailing face 332 of said block 33. The blocks 33 of the same lateral row 23 extend axially outwards in the extension of the blocks 32 of the adjacent intermediate row 22, such that any set of two blocks (33, 32) respectively of lateral row 23 and intermediate row 22, in the extension of one another, forms a bar.

[0068] There Figure 3is a meridian sectional view of a tread of a tire according to the invention. The tread has an axial width L and is divided into a middle row 21 having an axial width L1, two intermediate rows 22 each having an axial width L2 and two lateral rows 23 each having an axial width L3. Each intermediate row 22 is respectively separated from the middle row 21 by a circumferential hollow 51 having a width E2 and a depth P2, and from the nearest lateral row 23 by a circumferential hollow 52 having a width E3 and a depth P3.

[0069] There Figure 4is a circumferential sectional view, along a plane XZ, of a portion of the middle row 21 of a tread of a tire according to the invention. The middle row 21 is constituted by a circumferential distribution of blocks 31, each having a circumferential length B1 and a height H1. The blocks 31 are separated in pairs by transverse hollows 41, of the incision type, having a width E1. According to the invention, two consecutive blocks 31 of the middle row 21 are separated by a transverse hollow 41 having a width E1 at most equal to 2.5 mm. In the embodiment shown, there is an alternation of transverse incisions 41 having respectively a depth H1 and a lower depth H1. This choice makes it possible to facilitate the manufacture of the tire, by reducing the effort required to demold the tire after curing thanks to a lesser depth of a portion of the transverse incisions.

[0070] There Figure 5is a circumferential sectional view, along a plane XZ, of a portion of an intermediate row 22 of a tread of a tire according to the invention. The intermediate row 22 is constituted by a circumferential distribution of blocks 32, each having a circumferential length B2, average distance measured between a leading face 321 and a trailing face 322, and a height H2. The blocks 32 are separated in pairs by transverse hollows 42, of the groove type. According to the invention, each block 32 of each intermediate row 22 comprises a leading face 321, along the circumferential rolling direction of the tire, forming, with a radial direction ZZ' of the tire, an average angle D2 at least equal to 30°, and a trailing face 322 forming, with the radial direction ZZ' of the tire, an average angle D'2.

[0071] There Figure 6is a circumferential sectional view, along a plane XZ, of a portion of a lateral row 23 of a tread of a tire according to the invention. The lateral row 23 is constituted by a circumferential distribution of blocks 33, each having a circumferential length B3, average distance measured between a leading face 331 and a trailing face 332, and a height H3. The blocks 33 are separated in pairs by transverse hollows 43, of the groove type. According to the invention, the average circumferential slenderness of any block 33 of each lateral row 23 is at most equal to 0.9. Furthermore, each block 33 of each lateral row 23 comprises a leading face 331, in the circumferential rolling direction of the tire, forming, with a radial direction ZZ' of the tire, an average angle D3 at least equal to 10° and at most equal to 30°, and a trailing face 332 forming, with the radial direction ZZ' of the tire, an average angle D'3.

[0072] The invention has been more particularly studied for an agricultural tire of dimension 600 / 70 R 30.

[0073] Table 1 below shows the technical characteristics of an example of a preferred embodiment of the invention, as shown in the figures 1 to 6 : Table 1 Geometric characteristics Values Comments Axial width L of the tread 2 606 mm Outer diameter D of the tire 1609 mm Measured on the tire not mounted on the rim and not inflated Axial width L1 of the middle row 21 124 mm 124 / 606=20% of L => Between 15% and 25% of L Axial width L2 of each intermediate row 22 115 mm 115 / 606=19% of L => Between 15% and 25% of L Axial width L3 of each lateral row 23 104 mm 115 / 606=19% of L => Between 15% and 25% of L Overall tread volumetric hollow rate 2 53% Local volumetric dip rate of middle row 21 11% Less than 20% Local volumetric hollow rate of each intermediate row 22 64% Greater than 55% Local volumetric hollow rate of each side row 23 63% Greater than 55% Average radial height H1 of a block 31 of middle row 21 48 mm Average circumferential length B1 of a block 31 of middle row 21 43 mm Circumferential slenderness H1 / B1 of a block 31 of middle row 21 1.12 Between 0.95 and 1.15 Width E1 of transverse hollow 41 between two consecutive blocks 31 of middle row 21 1.6 mm Less than 2.5 mm => Incision Depth of transverse hollow 41 between two consecutive blocks 31 of middle row 21 48 mm Equal to the height H1 of the block Secondary transverse incision depth 411 in a block 31 of middle row 21 31 Equal to 70% of the height H1 of the block Average transverse hollow angle 41 between two consecutive blocks 31 of middle row, relative to the circumferential direction XX4 75° Greater than 60° Average radial height H2 of a block 32 of intermediate row 22 46 mm Average circumferential length B2 of a block 32 of intermediate row 22 71 mm Circumferential slenderness H2 / B2 of a block 32 of intermediate row 22 0.65 Between 0.5 and 1 Average angle D2 of attack face 321 of block 32 of intermediate row 22 Between 34° and 45° Greater than 30° Average transverse hollow angle 42 between two consecutive blocks 32 of intermediate row 22, relative to the circumferential direction 67° Greater than 60° Average radial height H3 of a block 33 of side row 23 46 mm Average circumferential length B3 of a block 33 of side row 23 64 mm Circumferential slenderness H3 / B3 of a block 33 of lateral row 23 0.72 Less than 0.9, and even between 0.6 and 0.8 Average angle D3 of attack face 331 of a block 33 of side row 23 Between 20° and 28° Greater than 10° and less than 30° Average transverse hollow angle 43 between two consecutive blocks 33 of lateral row 23 75° Greater than 60° Number of blocks N in an intermediate row 22 or lateral row 23 (along the entire circumference of the tire) 28 Between 26 and 32 Width E2 of intermediate circumferential hollow 51 131 mm At the level of the running surface in new condition Depth P2 of intermediate circumferential hollow 51 46 mm Width E3 of lateral circumferential hollow 52 121.5 mm At the level of the running surface in new condition P3 depth of lateral circumferential hollow 52 46 mm

[0074] The inventors compared, on digital simulations and / or internal tests, the performances of the invention and those of a reference tire 600 / 70 R 30 Michelin MACHXBIB. The rolling resistance, in road use, for a tire subjected to a load Z = 3801 kg, inflated to a pressure P = 1.8 bar and traveling at a speed V = 15 km / h, went from 14.8 kg / t, for the reference tire, to 11.6 kg / t for the tire according to the invention, a reduction of 21%. The wear life, defined as the mileage traveled on the road before removal of the tire at complete wear, for the tire according to the invention, is 20% greater than that of the reference tire.

Claims

1. A tyre (1) for an agricultural vehicle, comprising a tread (2) with an axial width (L) and consisting of pairs of blocks (31, 32, 33) separated by voids (41, 42, 43, 51, 52) and arranged, over the width of the tread (2), in a median row (21), two intermediate rows (22) and two lateral rows (23), - the voids (41, 42, 43, 51, 52) being either transverse voids (41, 42, 43) which form an angle at least equal to 60° with a circumferential direction (XX') of the tyre (1), or circumferential voids (51, 52) which form an angle at most equal to 30° with the circumferential direction (XX'), - the median row (21) being centred on a median circumferential plane (E) of the tyre, the two intermediate rows (22) being positioned axially on either side of the median row (21) and separated therefrom by circumferential voids (51), and the two lateral rows (23) being positioned respectively axially outside an intermediate row (22) and separated therefrom by a circumferential void (52), - each median row (21), intermediate row (22) and lateral row (23) comprising a circumferential distribution of pairs of blocks (31, 32, 33) separated by transverse voids (41, 42, 43) and each having a mean radial height (H1, H2, H3), a mean circumferential length (B1, B2, B3) and a mean circumferential slenderness ratio defined as the ratio between the mean radial height and the mean circumferential length of the block, - the blocks (33) of a same lateral row (23) extending axially towards the outside in the extension of the blocks (32) of the adjacent intermediate row (22), such that any set of two blocks (33, 32) of the lateral row (23) and intermediate row (22) respectively, in the extension of one another, forms a lug, - the mean circumferential slenderness of any block (33) in each lateral row (23) being at most equal to 0.9, characterized in that two consecutive blocks (31) in the median row (21) are separated by a transverse void (41) with a width (E1) equal at most to 2.5 mm, in that the mean circumferential slenderness of any block (31) in the median row (21) is at least equal to 0.95 and at most equal to 1.15, and in that every block (32) of each intermediate row (22) comprises a leading face (321) in the circumferential rolling direction of the tyre which forms a mean angle (D2) equal at least to 30° with a radial direction (ZZ') of the tyre.

2. The tyre (1) as claimed in claim 1, wherein the median row (21) has an axial width (L1) at least equal to 15% and at most equal to 25% of the axial width (L) of the tread (2).

3. The tyre (1) as claimed in claim 1 or 2, wherein the median row (21) has a local volumetric void ratio at most equal to 20%.

4. The tyre (1) as claimed in any of claims 1 to 3, wherein every transverse void (41) separating two consecutive blocks (31) of the median row (21) forms an angle at least equal to 70° with the circumferential direction (XX').

5. The tyre (1) as claimed in any of claims 1 to 4, wherein every transverse void (41) separating two consecutive blocks (31) of the median row (21) has a depth (P1) at least equal to 50%, preferably at least equal to 70%, of the mean radial height (H1) of the block (31).

6. The tyre (1) as claimed in any of claims 1 to 5, wherein every transverse void (41) separating two consecutive blocks (31) of the median row (21) is extended radially inwardly by a cavity (411).

7. The tyre (1) as claimed in any of claims 1 to 6, wherein each intermediate row (22) has an axial width (L2) at least equal to 15% and at most equal to 25% of the axial width (L) of the tread (2).

8. The tyre (1) as claimed in any of claims 1 to 7, wherein each intermediate row (22) has a local volumetric void ratio at least equal to 40%, preferably at least equal to 55%.

9. The tyre (1) as claimed in any of claims 1 to 8, wherein the mean circumferential slenderness ratio of every block (32) of each intermediate row (22) is at least equal to 0.5 and at most equal to 1.0.

10. The tyre (1) as claimed in any of claims 1 to 9, wherein every block (32) of an intermediate row (22) comprises a leading face (321) which forms a mean angle (D2) at least equal to 35° with a radial direction (ZZ') of the tyre.

11. The tyre (1) as claimed in any of claims 1 to 10, wherein each lateral row (23) has an axial width (L3) at least equal to 15% and at most equal to 25% of the axial width (L) of the tread (2).

12. The tyre (1) as claimed in any of claims 1 to 11, wherein each lateral row (23) has a local volumetric void ratio at least equal to 40%, preferably at least equal to 55%.

13. The tyre (1) as claimed in any of claims 1 to 12, wherein the mean circumferential slenderness ratio of every block (33) of each lateral row (23) is at most equal to 0.8.

14. The tyre (1) as claimed in any of claims 1 to 13, wherein the mean circumferential slenderness ratio of every block (33) of each lateral row (23) is at least equal to 0.6.

15. The tyre (1) as claimed in any of claims 1 to 14, wherein every block (33) of a lateral row (23) comprises a leading face (331) which forms a mean angle (D3) at least equal to 10° and at most equal to 30° with a radial direction (ZZ') of the tyre.

16. The tyre (1) as claimed in any of claims 1 to 15, wherein every block (33) of a lateral row (23) comprises a leading face (331) and a trailing face (332) which form, with a radial direction (ZZ') of the tyre, mean angles (D3, D'3) which are equal in absolute values.

17. The tyre (1) as claimed in any of claims 1 to 16, wherein the circumferential distribution of blocks (31, 32, 33) of each intermediate row (22) and lateral row (23) comprises at least 26 blocks.

18. The tyre (1) as claimed in any of claims 1 to 17, wherein the circumferential distribution of blocks (31, 32, 33) of each intermediate row (22) and lateral row (23) comprises at most 32 blocks.