tire tread for agricultural vehicle

Abstract

A tire (1) for an agricultural vehicle having a tread (2) comprising tread elements (22), including tread blocks separated from each other by grooves (23) and extending radially outwards along faces (24) to a running surface (25) with a tread height (Hs) of at least 35 mm. A stubble barrier (224) whose upper surface has at least two inclined planes (2242, 2243) from each of its lateral faces to a ridge line (2241) connects two tread blocks. The mean angle (Ap) of the normal to these planes with the radial direction is at least 10° and at most 20°. (See diagram: Figure 1)

Description

Title of the invention: Tire tread for agricultural vehicles

[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 to the tread 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] An agricultural vehicle tire is designed to operate on various types of terrain, such as the more or less compacted soil 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 comprising an elastomer, obtained by blending, also called an elastomeric compound or rubber compound.

[0006] 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, for 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, specific tread blocks. specific to agricultural tires called slats.

[0007] 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.

[0008] The leading face of a tread block is, by definition, the face whose radially outer edge, or leading edge, first comes into contact with the ground as the block passes through the contact patch of the tire with the ground during the tire's rotation. The trailing face is, by definition, the face whose radially outer edge, or trailing edge, last comes into contact with the ground as the block passes through the contact patch of the tire with the ground during the tire's rotation. The definitions are identical when the tread blocks considered are slats. Depending on the direction of rotation, the leading face is said to be forward relative to the trailing face. The average distance between the leading face and the trailing face defines the average slat 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.

[0009] 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.

[0010] Regarding field performance, a key concern for tire designers is improving the lug resistance 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, the free end of which 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 contact of the lug leading edges with 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.

[0011] 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.

[0012] Furthermore, to improve the flattening of agricultural tires, it is advantageous to incorporate discontinuities in the tread blocks. With an average transverse thickness, measured between its leading edge and trailing edge, of at least 40 mm, a continuous tread block extending from the center of the tread to one of its axial ends resists crushing and, in particular, axial flattening of the contact patch, which would increase rolling resistance on the road and decrease grip by preventing the axial ends of the tread blocks from gaining contact with soft ground. However, it is important to manage this discontinuity, particularly in terms of circumferential rigidity, to avoid uneven wear between the two parts of a tread block and, more generally, between two tread blocks.If one of the tread blocks is circumferentially much more flexible than a neighboring tread block, under load it will deform much more than its neighbor and therefore wear more when it slides out of the contact patch. One solution to reduce the differences in rigidity between the two tread blocks to avoid uneven wear while maintaining a degree of discontinuity to improve flatness is to connect the two tread blocks with a bridge, namely a tread element whose radially outer face does not lie on the tread surface. Indeed, it is the part closest to the contact patch, and therefore furthest from the tire's crown reinforcement, that most resists flatness.

[0013] The inventors have set themselves the objective of using the geometric shape of the tread pattern, including the tread pattern using optimized bridging and groove geometry to improve resistance to stubble while increasing performance in uneven wear, traction, and traction without degrading rolling resistance.

[0014] This objective has been achieved according to the invention by a tire for an agricultural vehicle, having an axis of rotation, along an axial direction (YY') and a recommended direction of travel, along a circumferential direction (XX') and comprising a tread: -the tread having an axial width L and comprising tread elements, including tread blocks separated from each other by hollows and extending radially outwards from a bearing surface to a running surface, the radial distance from the bearing surface to the running surface, measured at the center of the tread determining the tread height, being at least equal to 35 mm, - every block of sculpture being delimited, radially on the outside, by a contact face, intended to come into contact with the ground, and, circumferentially, by a leading face, whose edge of intersection with the contact face is intended to come into contact with the ground first, and by a trailing face, whose edge of intersection with the contact face is intended to come into contact with the ground last, -the tread comprising two lateral portions, each lateral portion comprising a circumferential distribution of bar-shaped tread blocks, two by two separated by transverse grooves, and forming, with the circumferential direction (XX1) of the tire, an angle of at least 40° and at most 60°, - at least two blocks of sculpture being connected by a bridge delimited by at least two substantially radial lateral faces and one radially external face, connecting the two lateral faces and radially internal to the running surface, - at least one bridging being a thatch bridging having a radially external face comprising at least two inclined sections, extending respectively from each of its lateral faces to a ridge line, - the average angle of the normal to each of the inclined sides with the radial direction (ZZ') being at least equal to 10° and at most equal to 20°.

[0015] The bearing surface is a theoretical surface constituted by the torus obtained by rotating around the tire's axis of rotation YY' of all the most radially inner points of the tread grooves on all the meridian planes. The maximum tread depth is the maximum distance between the bearing surface, which includes the most radially inner points of the grooves, and the running surface. The distance between the most radially inner point of the grooves and the The tread area gives an idea of ​​the tread depth of an agricultural tire. It is at least 35 mm to ensure good grip in the fields.

[0016] The invention therefore consists of using the geometry of the radially outer face of a bridging structure to orient the stubble that comes into contact with it at an angle almost parallel to the supporting surface. The radially outer face of the bridging structure is thus divided into two inclined sections, thereby reducing the probability that a misoriented stubble will bear against a surface at a constant angle and tear away part of the bridging structure. The angle of the sections of the radially outer surface of the bridging structure is significant but remains small, between 10 and 20°, in order to allow the stubble to slide on the surface and also to orient it at an angle that minimizes the possibility of damage to the supporting surface and the radially inner reinforcement at the top. With a smaller angle, the device is less effective at allowing the stubble to slide, and the sections would be more damaged.With a steeper angle, the device tends to orient the stubble in a direction less favorable to preserving the bearing surface. These stubble barriers, whose radially superior face is two-sided, are so named to distinguish them from other possible barriers, but this does not limit their technical effect to this single function. Depending on their position, these barriers, as mentioned previously, facilitate flattening for better traction and rolling resistance, and help regulate uneven wear. "Stubble barrier" is an adjective combining the suffix "pare," meaning protecting, and the noun "chaume," which refers to the stubble left after grain harvest, a layer of cotton with sufficient rigidity to damage agricultural tires that might drive over it.This adjective allows us to differentiate 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 were created for this function; this does not imply that they eliminate all thatch or that they cannot be improved.

[0017] For effective control of uneven wear and to avoid creating wedges in which a stubble end could become stuck, increasing the risk of damage to the carving, any stubble bridge has an average transverse thickness, measured between its leading and trailing lateral faces respectively, at least equal to 60% of the average transverse thickness of the carving blocks it connects, preferably at least equal to 80%, and preferably equal to 100%. The thicker the bridge, the greater its rigidity, the more it homogenizes the rigidities of the carving blocks it connects, and the greater its influence on uneven wear. The average transverse thickness is measured at mid-height of the carving, in the middle of the sculpture element in question, perpendicular to the attack face of the sculpture element.

[0018] Similarly, to better manage uneven wear and also to maximize the effectiveness of the thatch-proofing effect of the bridging, it is advantageous for the radially superior face of the two-sided bridging to be sufficiently far from the hollows of the carving. With a bridging that is too low in height, its influence on the rigidity of the carving blocks thus connected would be weak, and it would only deflect the thatch from the bottom of the hollows too late. Thus, it is advantageous for the outermost radial point of the ridge line of a thatch-proof bridging to be at a radial distance from the bearing surface of between 70% and 85% of the carving height, and for the outermost radial points of the lateral faces of the bridging to be at a radial distance from the bearing surface of between 55% and 70% of the carving height.In the event of a rounding over a total ATR between the leading and trailing faces and the radially superior face, the outermost radial points of the lateral faces will be considered as the mean angular points (ATR / 2) of the rounding.

[0019] Preferably, the length of a thatch bridge, defined as the distance separating the sculpture blocks connected by said bridge, is at least equal to 25 mm, a length which allows the thatches to pass between the sculpture blocks, above the radially superior face of the bridge.

[0020] 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.

[0021] Advantageously, the lateral portions are axially external to a central portion comprising a circumferential arrangement of tread blocks, two by two separated by transverse grooves, in which 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. The regular distribution of bridges between a central portion and lateral portions promotes a circumferentially regular flattening of the tire during rolling, prevents the generation of flat spots, a form of irregular wear, in areas that would lack bridges, and protects the area in the central portion in contact with the lateral portions from stubble damage.

[0022] Preferably, to better resist stubble, the tread blocks are more massive than the bars. On the lateral parts, the angle formed by the bars, combined with the possible escape of stubble towards the axial outside of the tire, makes the bars less susceptible to damage. This is one way of reflecting the advantage that the blocks To ensure the central section of the tread is more substantial, consider the volumetric notch ratios of the axial and central parts 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 free of grooves), measured between the bearing surface and the tread surface, of the central portion is preferably between 35% and 50%, and / or the volumetric notch ratio of the lateral portions is preferably between 50% and 65%. The groove volume and total volume will be evaluated for each of the central and lateral zones respectively, and then the ratio will be calculated for each zone.

[0023] 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 center of the tread. 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.

[0024] It is advantageous to facilitate the sliding of the stubble, which would come 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, thus avoiding a discontinuity between the lateral faces of the blocks in the central section, the stubble barriers, and the lateral faces of the slats. Since 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°.

[0025] A preferred solution is for the space radially above the stubble decking framed by the lateral faces of the bars to be rather open on the leading face side to capture a maximum of stubble and / or rather closed to direct it onto the most resistant part of the carving, namely the central portion. This effect can be achieved by orienting the faces of the bar connected to the flats of the radially upper face of the stubble decking. Thus, a preferred solution is for the inclined flat connected to the leading face of the stubble decking to be connected to the carving block of the lateral portion by a lateral face making an angle of between 30° and 40° with the circumferential direction (XX') and / or for the inclined flat connected to the trailing face of the stubble decking to be connected to the carving block of the lateral portion by a lateral face making, with the circumferential direction (XX'), an angle between 0° and 20°.

[0026] To optimize the rigidity of the sculpture blocks of the central part, it is advantageous that the inclined faces of the leading edge of the thatch decking be connected to the sculpture block of the central portion by lateral faces having draft angles between 30° and 40°.

[0027] To increase the tire's resistance in the central portion of the tread compared to the lateral portions, and to achieve a good balance between the tire's mass and its grip, it is advantageous for the top layers of the tire to be protected by an extra layer of elastomeric compound in the central portion of the tread. This extra thickness is measured from the outermost radially outermost top layer to the innermost radially innermost points of the tread grooves, i.e., the bearing surface. These measurements are easily taken by a person skilled in the art from a cross-section of the tire. An extra thickness of 4 mm provides optimal resistance to damage from stubble relative to the added mass of elastomeric compound.It is also possible, given the geometric shape of the top layers between the central portion of the tread and the centers of the side sections, to measure the radii of their respective centers and verify that, at the central portion, the bearing surface is radially outside by at least 4 mm relative to the points of the bearing surface at the centers of the side sections. Thus, it is advantageous for the central portion of the bearing surface to be radially outside the bearing surface of the side sections by a radial distance of at least 4 mm, measured between the bearing surface at the center of the central portion and each of the centers of the side sections.

[0028] It can be advantageous, particularly in cases where there is an excess thickness of elastomeric compound, but not only there, for each recess in each lateral portion to include 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 also allows the stubble in this area to be oriented towards the axial exterior of the tire. In order to avoid creating a portion of this face more prone to tearing, it is advantageous for the angle of the normal to the so-called stubble guard face of the lateral portion with the circumferential direction to vary continuously from the leading edge to the trailing edge. Similarly, in order for this orientation to be compatible with the orientation of the lugs, the angle of the normal to the so-called stubble guard face advantageously forms an angle between 40 and 60° with the circumferential direction (XX') at its axial end.

[0029] 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 bridge, - [Fig.3]: Diagram of a meridional half-section of the tire according to the invention.

[0030] 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 an 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 parts 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 sculpture blocks 221, 222 extend radially outwards from a bearing surface 233 to a rolling 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 the rotation around the axis YY' of rotation of the tire of all the most radially interior points of the hollows 23 of the sculpture on all the meridian planes.Each tread block 221, 222 is delimited radially on the outside by a contact face 251, intended to come into contact with the ground, and circumferentially by a leading face, whose edge of intersection with the contact face is intended to come into contact with the ground first, and by a trailing face, whose edge of intersection with the contact face is intended to come into contact with the ground last, respectively 2211 and 2212 for the block 221 of the central portion. The bars 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 bars of the two lateral parts. Each barrette 221 is connected to a sculpture block 222 of the central part by a bridge 224 whose average transverse thickness is equal to the average thickness emt of the barrette, equal to 44.5 mm.The length Ipc of a stubble barrier bridge, defined as the distance separating the sculpted blocks connected by said bridge 224, is 27.5 mm. The volumetric notching ratio, defined as the ratio between the volume VC of the hollows 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 43.2%, and the volumetric notching ratio of the lateral portions PI is 57%. The leading faces of the blocks 222 of the central portion Pc, the bridges 224, and the bars are continuous. The figure also represents a thatch guard face 234, whose trailing edge 2342 is axially external to its leading edge 2341, continuous and whose normal makes an angle of 43° with the circumferential direction (XX') at its axial end. The angle Apa is equal to 35° and the angle Apf is equal to 0°.

[0031] Fig. 2 represents the cross-section of the thatch decking along line AA mentioned in [Fig. 1]. The bridge 224 is connected to a block 222 of the central portion, the radially outer surface of which forms part of the running surface 25. The bridge 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. The face 2244 is the leading face of the bridge and the 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.

[0032] 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 crest line of which 2241 is shown.The tread has an axial half-width L / 2 and comprises a central portion of an axial half-width Lc / 2 and two axially external 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, being at least equal to 35 mm. A face 234 with a radial height of at least 3 mm, called the thatch guard, whose trailing edge 2342 is axially external to its leading edge 2341, is present in the groove 23. This face 234 creates an excess of rubber compound in the central portion and a radial offset between the central portion of the tread on the bearing surface 233 and the center of the lateral portion PI on the bearing surface 233. The [Fig.[3] also shows the radial distance hc from the bearing surface 233 to the outermost radially outer top layer 31 at the center of the tread and 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. .

[0033] 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 © with a tread width of 327 mm. Its tread pattern consists of continuous lugs with a radial height of 33 mm at the center of the tread and making an angle of 47° with the circumferential direction, of an average transverse thickness emt of 46 mm and of an axial width representing 56% of the total width of the tread without having any bridging of extra thickness in the central portion of the tread between the outermost radially outer top layer and the bearing surface compared to the lateral portions.

[0034] The tread depth 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 groove-free, between the bearing surface 233 and the tread surface 25, of the central portion Pc, is equal to 46.2%, and the volumetric tread depth 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.

[0035] 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 being arranged at a pitch of 1.27 mm.

[0036] 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 forming an angle of 47.3° with the circumferential direction, with an average transverse thickness emt equal to 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 = 5 mm).This increased thickness results in the presence of a face with a radial height of at least 5 mm, called the stubble guard, whose trailing edge 2342 is axially external to its leading edge. This face is continuous and its trailing edge is tangent to the bar. The volumetric notching ratio of the central portion Pc is equal to 43.2% and the volumetric notching ratio of the lateral portions PI is equal to 57%.

[0037] The bridging between the bars has a width equal to that 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 related to the leading face 2244 with the radial direction (ZZ') is equal to 13°, and the mean angle Ap of the normal to the plane inclined 2243 linked to the trailing face 2245 with the radial direction (ZZ') at most equal to 14°. The face connecting the radially superior surface of the central portion block to the bridging makes a mean angle of 43° and the face connecting the radially superior surface of the bar to the bridging has two facets, one facet on the side of the leading edge of the bart with an angle Apa of 35° with the circumferential direction and another facet on the side of the trailing edge of the bart having an angle Apf of 0° with the circumferential direction.

[0038] 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 in the working layers at a pitch of 0.86 mm. The reinforcement elements have a breaking strength of 37 daN.

[0039] 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.

[0040] 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 traveled in a plowed field with an average slope of 11%. The measurement was taken uphill. The bridging increased the ground contact area and improved traction performance by 30% by reducing the slippage rate from 50% to 35%.

[0041] The tire was also tested for traction, that is, its ability to pull a tool. The tires are inflated to the pressure and load of the vehicle in the field for cyclic use well known to users, identical to the previous test. The vehicle equipped with the tested tires pulls a wheeled mass in 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.

[0042] Since resistance performance to stubble attack is difficult to measure outside of a full-scale test over extended use, an initial estimate is based on the expert knowledge of technical advisors to users. Experts predict an improvement in resistance to stubble damage due to the sculpting's ability to evacuate or deflect it, on the order of 20 to 30%. This performance is assessed by the presence and number of visible stubble impacts after rolling in a field following mowing.

[0043] Rolling resistance with identical materials is estimated by finite element analysis as equivalent to that of the control tire. Thus, despite an increase in tread depth, improved resistance to residual stubble due to the increased percentage of rubber compound in the central portion in terms of notch ratio and thickness between the bearing surface and the outermost radially facing top layer, and the greater flexibility of the tread pattern during flattening thanks to the bridging, allows for maintaining good rolling resistance.

[0044] Thus the invention improves resistance to stubble while increasing performance in irregular wear, traction, and traction without degrading rolling resistance.

Claims

Demands

1. Tire (1) for an agricultural vehicle, having an axis of rotation, along an axial direction (YY') and a recommended direction of travel (12), along a circumferential direction (XX') and comprising a tread (2): - the tread (2) having an axial width L and comprising tread elements (22), including tread blocks (221, 222) separated from each other by recesses (23) and extending radially outwards from a bearing surface (233) to a running surface (25), the radial distance from the bearing surface (233) to the running surface (25), measured at the center of the tread determining the tread height (Hs), being at least 35 mm, - each tread block (221, 222) being delimited radially outwards by a contact face (251), intended to come into contact with a ground, and circumferentially by a leading face (241), whose edge of intersection with the contact face is intended to come into contact with the ground first, and by a trailing face (242), whose edge The intersection with the contact face is intended to be the last point to come into contact with the ground. -the tread (2) comprising two lateral portions (PI), each lateral portion comprising a circumferential distribution of tread blocks (221) in the form of bars, two by two separated by transverse grooves (231), and forming, with the circumferential direction (XX1) of the tire, an angle (Al) of at least 40° and at most 60°, - at least two sculpture blocks (221, 222) being connected by a bridge (224) delimited at least by two substantially radial lateral faces (2244, 2245) and one radially external face, connecting the two lateral faces (2244, 2245) and radially internal to the rolling surface, characterized in that at least one bridging (224) is a thatch bridging having a radially external face comprising at least two inclined sections (2242, 2243), extending respectively from each of its lateral faces (2244, 2245) to a ridge line (2241), and in that the mean angle (Ap) of the normal to each of the inclined sections (2242, 2243) with the radial direction (ZZ') is at least equal to 10° and at most equal to 20°.

2. Pneumatic according to claim 1, wherein each stubble guard bridge (224) has an average transverse thickness measured between its respective leading and trailing lateral faces (2244, 2245), at least equal to 60% of the average transverse thickness (emt) of the tread blocks (223) which it connects, preferably at least equal to 80%, preferably equal to 100%.

3. Pneumatic according to claim 1 or 2, wherein the outermost radial point of the ridge line (2241) of a thatch decking (224) is at a radial distance from the bearing surface (233) between 70 and 85% of the tread height (Hs) and the outermost radial points of the lateral faces (241, 242) of the decking (224) are at a radial distance from the bearing surface (233) between 55% and 70% of the tread height (Hs).

4. Pneumatic according to any one of the preceding claims, wherein the length (Ipc) of a stubble bridge, defined as the distance separating the tread blocks connected by said bridge (224), is at least equal to 25 mm.

5. Tire according to any one of the preceding claims in which each bar-shaped tread block (221) of the lateral portions (PI) of the tread has an average transverse thickness, measured between its leading face (241) and its trailing face (242), of at least 40 mm and at most 60 mm.

6. Pneumatic according to any one of the preceding claims, the lateral portions (PI) being axially external to a central portion (Pc) comprising a circumferential distribution of tread blocks (222), two by two separated by transverse hollows (232), in which each tread block (222) of the central portion (Pc) is connected to at least one tread block (221) of a lateral portion (PI) in the form of bars by a stubble-proof bridge (224).

7. Tire according to claim 6, wherein 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 between 35% and 45% and the volumetric notch ratio of the lateral portions (PI) is between 50 and 65%.

8. Pneumatic according to any one of claims 6 or 7, in in which the axial width (Le) of the central portion (Pc) is between 20% and 25% of the axial width L of the tread (2).

9. Tire according to any one of the preceding claims 6 to 8 wherein the axial width (Lp) of each lateral portion (PI) is between 30 and 40% of the axial width L of the tread.

10. A pneumatic tire according to any one of claims 6 to 9, wherein a leading face (241) of each tread block (222) of the central portion (Pc) is substantially continuous with the leading face (2245) of a stubble bridge (224), and makes an angle with the circumferential direction (XX') of at least 40° and at most 60°, preferably between 45 and 50°.

11. Pneumatic according to any one of claims 6 to 10, wherein the inclined panel (2242) connected to the leading face (2244) of the stubble deflector (224) is connected to the tread block (221) of the lateral portion (PI) by a lateral face (24) making, with the circumferential direction (XX'), an angle (Apa) between 30° and 40° and the inclined panel (2243) connected to the trailing face (2245) of the stubble deflector (224) is connected to the tread block (221) of the lateral portion (PI) by a lateral face making, with the circumferential direction (XX'), an angle (Apf) between 0° and 20°.

12. Pneumatic according to any one of claims 6 to 11, wherein the inclined faces of the leading edge (2242) of the stubble decking (224) are connected to the tread block (222) of the central portion by lateral faces (24) having draft angles between 30° and 40°.

13. Pneumatic according to any one of claims 6 to 12, wherein the bearing surface (233) of the central portion (Pc) is radially outside the bearing surface (233) of the lateral portions (PI) by a radial distance of at least 4 mm measured between the bearing surface (233) at the center of the central portion (Pc) and at each of the centers of the lateral portions (PI).

14. Pneumatic according to claim 13, wherein every hollow (231) of each lateral portion (PI) comprises a face (234) of a radial height of at least 3 mm, called a stubble guard, whose trailing edge (2342) is axially external to its leading edge (2341).

15. Pneumatic according to claim 14, wherein the angle of the normal to the so-called stubble guard face (234) of the lateral portion (PI) with The circumferential direction evolves continuously from the leading edge (2341) to the trailing edge (2342) and makes an angle of between 40 and 60° with the circumferential direction (XX') at its axial end

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