agricultural vehicle tire tread

Abstract

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

Description

Title of the invention: Tire tread 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 more particularly relates to the tread of such a tire.

[0002] Like any tire, a tire for an agricultural vehicle comprises 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, 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 an agricultural vehicle comprises a reinforcing reinforcement, 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 the following, 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] A tire for an agricultural vehicle is intended to run on various types of soil such as more or less compacted earth in fields, unpaved access roads to fields and paved road surfaces. Given the diversity of use, in the field and on the road, a tire for an agricultural vehicle, and in particular its tread, must offer a compromise of performance between, but not limited to, traction in the field, resistance to tearing, resistance to wear on the road, resistance to forward movement, and vibration comfort on the road. The tread is essentially composed of a polymeric material comprising an elastomer, obtained by mixing, also called an elastomeric mixture or rubber mixture.

[0006] To satisfy this set of performances, the tread of a tire for an agricultural vehicle generally comprises a plurality of raised elements, called sculpture elements, extending radially from a bottom surface and for the sculpture blocks to the rolling surface. The subject of the invention is an agricultural tire offering optimal traction in the field and therefore comprising at least on the lateral portions of its tread, special sculpture blocks specific to agricultural tires called bars.

[0007] A bar generally has a generally elongated parallelepiped shape, consisting of at least one rectilinear or curvilinear portion, and is separated from the adjacent bars by grooves. A bar may consist of a succession of rectilinear portions, as described in documents US3603370, US4383567, EP795427 or have a curvilinear shape, as presented 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 distribution of lugs, two by two separated by transverse hollows forming, with a circumferential direction (XX1) of the tire, an average angle at least equal to 40° and at most equal to 60°, the axially innermost part of each lug coming into contact with the ground before its axially outer part when the tire rolls on ground in the recommended direction of rotation. For complex lug geometries, the average profile of the lug will be drawn, which is the line of the contact surface passing through the middle of the lug, of which a linear interpolation will be made 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 point 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, when the block passes through the contact surface of the tire with the ground, during the rotation of the tire. The trailing face is, by definition, the face whose radially outer edge or trailing edge last comes into contact with the ground, when the block passes through the contact surface of the tire with the ground, during the rotation of the tire. The definitions are identical when the tread blocks considered are lugs. Depending on the direction of rotation, the leading face is said to be in front of the trailing face. The average distance between the leading face and the trailing face defines the average lug thickness.For a tread element whose radially outermost face is not included in the rolling surface, the leading and trailing faces are determined by projecting that regular wear of the tire has caused the rolling surface to descend to the radially outer surface of the tread element considered.

[0009] The two rows of bars have a symmetry with respect to the equatorial plane of the tire, with most often a circumferential offset between the two rows of bars, resulting from a rotation around the axis of the tire of one half of the tread with respect to the other half of the tread. In addition, the bars can be continuous or discontinuous, and distributed circumferentially with a constant or variable pitch.

[0010] Regarding field operation, an important concern of the tire designer is improving the resistance of the bars to attacks, and more particularly to attacks by residual stubble or stubbles in fields after harvesting, particularly corn or cotton. A stubble is a portion of plant stem whose free end is generally sharp. The sharp free end of a stubble, which comes into contact with the leading face of a bar, is likely to perforate it locally and superficially, which results in local tearing of the elastomeric material constituting the bar. Repeated attacks on the leading faces of the bars by stubble can cause significant deterioration in the appearance of the bars, or even tearing, particularly in the vicinity of the axially inner ends of the bars.These degradations are a potential reason for complaints from users, which may require the tire to be replaced.

[0011] Documents EP 2714431 BI and FR3068648 describe the tread of a tire for an agricultural vehicle with a reduced risk of attack on the leading faces of the axially outer ends of the bars by residual stubble after harvesting ("stubble") and therefore of tearing.

[0012] Furthermore, to improve the flattening of agricultural tires, it is advantageous to provide discontinuities in the lugs. With an average transverse thickness, measured between its leading face and its trailing face, at least equal to 40 mm, a continuous lug from the center of the tread to one of its axial ends, opposes crushing and in particular the axial flattening of the contact area with an increase in rolling resistance on the road and a reduction in grip by preventing the axial ends of the lugs from bearing in soft ground. Nevertheless, it is important to be able to manage this discontinuity, in particular in terms of circumferential rigidity in order not to generate irregular wear between the two parts of a lug and more generally of two blocks of sculpture element.If one of the tread blocks is circumferentially much more flexible than a neighboring tread block, under the passage of force, it will deform much more than its neighbor and therefore wear more when it slides out of the contact area. A solution to reduce the differences in rigidity between the two tread blocks to avoid problems of irregular wear while maintaining a form of discontinuity in order to improve flattening is to connect the two tread blocks by a bridge, namely a tread element but whose radially outer face does not belong to the rolling surface. It is in fact the part closest to the contact surface and therefore the furthest from the crown reinforcement of the tire which most opposes flattening.

[0013] The inventors set themselves the objective of using the geometric shape of the tread, including the sculpture using optimized bridges and the geometry of the hollows to improve resistance to stubble while increasing performance in irregular wear, traction, and driveability 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, in an axial direction (YY') and a recommended rolling direction, in 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 rolling surface, the radial distance from the bearing surface to the rolling surface, measured at the centre of the tread determining the tread height, being at least 35 mm, - any block of sculpture being delimited, radially on the outside, by a contact face, intended to come into contact with a ground, and, circumferentially, by a leading face, the edge of which intersects with the contact face and is intended to come into contact with the ground first, and by a trailing face, the edge of which intersects with the contact face and is intended to come into contact with the ground last, -the tread comprising two lateral portions, each lateral portion comprising a circumferential distribution of sculpture blocks in the form of bars, two by two separated by transverse hollows, and forming, with the circumferential direction (XX1) of the tire, an angle at least equal to 40° and at most equal to 60°, - at least two sculpture blocks being connected by a bridge delimited at least by two substantially radial lateral faces and one radially outer face, connecting the two lateral and radially inner faces to the rolling surface, - at least one bridge being a thatch protection bridge having a radially outer face comprising at least two inclined sides, 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 the rotation around the YY' axis of rotation of the tire of all the radially innermost points of the tread grooves on all the meridian planes. The maximum tread height 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 The tread surface gives an idea of ​​the tread height of an agricultural tire. It is at least 35 mm in order to have good grip in the fields.

[0016] The invention therefore consists in using the geometry of the radially outer face of a bridge to orient the culms which would come into contact with it at an angle almost parallel to the bearing surface. The radially outer face of the bridge is therefore divided into two inclined sides, thus making it possible to reduce the probability that a poorly oriented culm will bear on a surface at a constant angle and tear off part of the bridge. The angle of the sides of the radially outer surface of the bridge is significant but remains small, between 10 and 20° in order to allow the culm to slide on the surface but also to orient it at an angle minimizing the possibility of attacking the bearing surface and the crown reinforcement which is radially internal to it. With a smaller angle, the device lacks effectiveness in making the culms slide. The sides would be more damaged.With a higher angle, the device tends to orient the stubble in a direction less favorable to the preservation of the bearing surface. These so-called stubble-guard bridges, whose radially upper face is double-sided, are so named to distinguish them from other possible bridges, this does not reduce their technical effect to this sole function. These bridges, depending on their position, allow, as mentioned previously, to facilitate flattening for better grip, rolling resistance, and allow irregular wear to be adjusted. "Stubble guard" is an adjective combining the suffix "pare" meaning protecting and the noun "stubble" which are the remains of cereal mowing, cotton having sufficient rigidity to damage agricultural tires which would roll over them.This adjective makes it possible to differentiate the bridges or other sculptural elements according to the invention and other possible bridges or respectively other sculptural elements which could be present in the sculpture but would not have the same geometric characteristics. These bridges were created for this function, this does not presage the fact that they remove all the stubble nor that they cannot be improved.

[0017] For effective adjustment of irregular wear but also to avoid generating corners in which a culm end could get stuck, increasing the risk of damage to the sculpture, any culm bridging has an average transverse thickness measured between its lateral faces respectively of attack and of trailing edge, at least equal to 60% of the average transverse thickness of the sculpture blocks that it connects, preferably at least equal to 80%, preferably equal to 100%. The thicker the bridging, the greater its rigidity, the more it homogenizes the rigidities of the sculpture blocks that it connects, the greater its influence on irregular wear. The average transverse thickness is measured at mid-height of the sculpture, in the middle of the sculpture element considered, perpendicular to the leading face of the sculpture element.

[0018] Similarly, still to better regulate irregular wear, but also to maximize the effectiveness of the thatch-proof effect of the bridges, it is advantageous for the radially upper two-sided face of the bridge to be sufficiently far from the hollows of the sculpture. With a bridge of too low a height, its influence on the rigidity of the sculpture blocks thus connected would be weak and it would only deflect the thatch from the bottom of the hollow too late. Thus, it is advantageous for the most radially outer point of the ridge line of a thatch-proof bridge to be at a radial distance from the bearing surface of between 70 and 85% of the sculpture height and the most radially outer points of the lateral faces of the bridge to be at a radial distance from the bearing surface of between 55% and 70% of the sculpture height.In case of the presence of a rounding on a total ATR between the leading and trailing faces and the radially upper face, the most radially outer points of the lateral faces will be considered as the average angular points (ATR / 2) of the rounding.

[0019] Preferably, the length of a thatch-guard 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 upper face of the bridge.

[0020] Preferably, any bar-shaped sculpture block of the lateral portions of the tread has an average transverse thickness, measured between its leading face and its trailing face, at least equal to 40 mm and at most equal to 60 mm. These thicknesses have demonstrated their effectiveness in agricultural sculptures in terms of robustness, rigidity to minimize wear and transmit torque.

[0021] Advantageously, the lateral portions are axially external to a central portion comprising a circumferential distribution of sculpture blocks, two by two separated by transverse hollows, in which each sculpture block of the central portion is connected to at least one sculpture block of a lateral portion in the form of bars by a stubble protection bridge. The regular distribution of bridges between a central portion and lateral portions promotes circumferentially regular flattening of the tire during rolling, avoids the generation of flat spots, a form of irregular wear, in areas which would be devoid of bridges and protects the area in the central portion in contact with the lateral portions between the lateral portions from the aggression of the stubble.

[0022] Preferably to better resist stubble, the sculpture blocks are more massive than the bars. On the lateral parts, the angle made by the bars plus the possible escape of the stubble towards the axial exterior of the tire, makes the bars less sensitive to aggression. A way of expressing the interest that the blocks of the sculpture of the central part are more massive is to consider the volumetric notch rates of the axial and central parts of the tire. Thus the volumetric notch rate, defined as the ratio between the volume VC of hollow and the total volume V of the tread assumed without hollow, included between the bearing surface and the rolling surface, of the central portion, is preferably between 35% and 50% or / and the volumetric notch rate of the lateral portions is preferably between 50 and 65%. The volume of hollow and the total volume will be evaluated respectively for each of the central and lateral zones then the ratio will be calculated for each of the zones.

[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 sculpture 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 promote the sliding of the stubble which would come to bear on the lateral faces of a sculpture block of the central part towards the lateral face of the stubble bridge to which it is connected then along the face of the bar continuously towards the axial exterior of the tire and therefore to avoid a discontinuity between the lateral faces of the blocks of the central portion, of the bridges and of the lateral faces of the bars. Given that the faces of the bars have an angle optimized for traction in the fields, to promote this continuity and this technical effect, a leading face of each sculpture block of the central portion is advantageously substantially continuous with the leading face of a stubble bridge, and makes an angle with the circumferential direction (XX') at least equal to 40° and at most equal to 60°, preferably between 45 and 50°.Advantageously, the leading face of the thatch guard bridges is substantially continuous with the leading face of the bar to which it is connected, and makes an angle with the circumferential direction (XX') at least equal to 40° and at most equal to 60°, preferably between 45 and 50°.

[0025] A preferred solution is that the space radially superior to the thatch-proof bridging framed by the lateral faces of the bars is rather open on the leading face side to capture a maximum of thatches and / or rather closed to direct them onto the most resistant part of the sculpture, namely the central portion. It is possible to obtain this effect by orienting the faces of the bar connected to the sides of the radially upper face of the thatch-proof bridging. Thus a preferred solution is that the inclined side connected to the leading face of the thatch-proof bridging is connected to the sculpture block of the lateral portion by a lateral face making, with the circumferential direction (XX'), an angle of between 30° and 40° and / or the inclined side connected to the trailing face of the thatch-proof bridging is connected to the sculpture 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 tread blocks of the central portion, it is advantageous for the inclined sides of the leading edge of the thatch guard to be connected to the tread block of the central portion by lateral faces having clearance angles of between 30° and 40°.

[0027] To increase the resistance of the tire in the central portion of the tread compared to the lateral portions, for a good balance between the mass of the tire and its grip, it is advantageous for the crown layers of the tire to be protected by an excess thickness of elastomeric compound in the central portion of the tread. This excess thickness is measured from the radially outermost crown layer and the radially innermost points of the tread hollows, namely the bearing surface. These measurements are easily made by a person skilled in the art from a meridian section of the tire. An excess thickness of 4 mm gives optimal resistance to damage by stubble relative to the mass of elastomeric compound added.It is also possible, taking into account the geometric shape of the crown layers between the central portion of the tread and the center of the lateral portions, to measure the radii of their respective centers and to 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 lateral portions. Thus, it is advantageous for the central portion of the bearing surface to be radially outside the bearing surface of the lateral portions by a radial distance of at least 4 mm measured between the bearing surface at the center of the central portion and at each of the centers of the lateral portions.

[0028] It may be advantageous in particular in the case where there is an excess thickness of elastomeric mixture, but not only, for any hollow of each lateral portion to comprise a face with a radial height at least equal to 3 mm, called the stubble guard, the trailing edge of which is axially outside its leading edge, this face also making it possible to orient the stubble in this zone towards the axial outside of the tire. In order not to create a part 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 evolve 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 makes at its axial end with the circumferential direction (XX') an angle of between 40 and 60°.

[0029] The characteristics of the invention are illustrated by schematic figures 1 to 3, not shown to scale: - [Fig.l]: portion of the sculpture of the tire according to the invention, - [Fig.2]: detail of the thatch protection bridge, - [Fig.3]: diagram of a half-meridian section of the tire according to the invention.

[0030] [Fig.l][Fig.l] represents a portion of the tread 2 of a tire for an agricultural vehicle having a recommended rolling direction 12. The tread 2, of an axial width L, comprises tread elements 22 including tread blocks 221, 222 separated from each other by hollows (23), in this case bars 221 of the lateral parts PI of axial width Lp separated by hollows 231 and blocks 222 of the central portion Pc of an axial width Le separated by hollows (232). The tread blocks 221, 222 extend radially outwards from a bearing surface 233 to a rolling surface 25, the bearing surface 233 of which only one 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 inner points of the hollows 23 of the tread on all the meridian planes.Each tread block 221, 222 being delimited, radially on the outside, by a contact face 251, intended to come into contact with a ground, and, circumferentially, by a leading face, the edge of intersection of which with the contact face is intended to come into contact with the ground first, and by a trailing face, the edge of intersection of which 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 at least equal to 40° and at most equal to 60° and are arranged in a chevron pattern with a circumferential offset between the bars of the two lateral parts. Each bar 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 bar, equal to 44.5 mm.The length Ipc of a thatch guard bridge, defined as the distance separating the tread blocks connected by said bridge 224, is equal to 27.5 mm. The volumetric notch rate, defined as the ratio between the volume VC of hollows 23 and the total volume V of the tread 2 assumed to be without hollows, between the bearing surface 233 and the rolling surface 25, of the central portion Pc, is equal to 43.2% and the volumetric notch rate of the lateral portions PI is equal to 57%. The leading faces of the blocks 222 of the central portion Pc, of the bridges 224 and of the bars are continuous. The figure also represents a thatch guard face 234, the trailing edge 2342 of which is axially external to its leading edge 2341, continuous and the normal of which makes with the circumferential direction (XX'), at its axial end, an included angle of 43°. The angle Apa is equal to 35° and the angle Apf is equal to 0°.

[0031] [Fig.2] [Fig.2] represents the section of the thatch protection bridge along the line AA mentioned in [Fig.l]. The bridging 224 is connected to a block 222 of the central portion whose radially outer surface is part of the rolling surface 25. The bridging 224 has two substantially radial lateral faces 2244, 2245 and a radially outer face, connecting the two lateral faces 2244, 2245 and radially inner to the rolling surface 25. The radially outer face comprising at least two inclined faces 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 bridging 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 plane is respectively equal to 13° for the inclined plane 2242 and equal to 14° for the inclined plane 2243.

[0032] [Fig.3] [Fig.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 an agricultural vehicle comprises a crown reinforcement 3 radially inside a tread 2 and radially outside a carcass reinforcement 4. The crown reinforcement 3 comprises 4 crown layers 31, 32, 33, 34, each comprising textile reinforcement elements coated in an elastomeric material. The tread 2 comprises hollows 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 of which the ridge line 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 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 bearing surface 25, measured at the center of the tread, determines the tread height Hs, being at least equal to 35 mm. A face 234 with a radial height at least equal to 3 mm, called a stubble guard, the trailing edge 2342 of which is axially outer to its leading edge 2341, is present in the hollow 23. This face 234 creates an excess thickness 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. [Fig.3] also shows the radial distance hc from the bearing surface 233 to the radially outermost crown layer 31 at the center of the tread and the distance hl from the bearing surface 233 to the radially outermost crown layer 31 measured at the center of each lateral portion PI.

[0033] The invention has been more particularly implemented for an agricultural tire of dimension 380 / 90R46. The tire according to the state of the art is a Michelin Spraybib © 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 forming an angle of 47° with the circumferential direction, with an average transverse thickness emt of 46 mm and an axial width representing 56% of the total width of the tread without having excess thickness bridging in the central portion of the tread between the most radially outer crown layer and the bearing surface compared to the lateral portions.

[0034] The notch rate of the tire according to the state of the art, defined as the ratio between the volume VC of hollow 23 and the total volume V of the tread 2 assumed to be without hollow, between the bearing surface 233 and the rolling surface 25, of the central portion Pc, is equal to 46.2% and the volume notch rate of the lateral portions PI is equal to 54.3%. As it is not possible to determine the central portion and lateral portions for the control tire, we took for this evaluation a ratio Lc / Lt identical to that of the invention.

[0035] The tire according to the state of the art comprises 6 crown layers whose reinforcing elements are made up of 3 rayon strands with a linear mass of 240 g per km, the reinforcing elements being arranged at a pitch of 1.27 mm.

[0036] The tire according to the invention has a tread with an axial width equal to 327 mm. Its sculpture is composed of central sculpture blocks of 39 mm radial height, with an axial width equal to 22% of the width of the tread, connected by bridges of 27.5 mm length Ipc to continuous bars making 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 width of the tread. The tread has an excess thickness between the most radially outer crown layer 31 and the bearing surface 233 in the central portion of the tread of 5 mm relative to the thickness of the tread at the centers of the lateral portions PI (hc-hl = 5 mm).This excess thickness results in the presence of a face with a radial height of at least 5 mm, called a 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 notch rate of the central portion Pc is equal to 43.2% and the volumetric notch rate of the lateral portions PI is equal to 57%.

[0037] The bridges between the bars have a width equal to that of the bars and their radially outer faces comprise at least two inclined faces 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 bearing surface. The radial heights of the leading and trailing edges of the bearing surface are equal to 26 mm. The average angle Ap of the normal to the inclined face 2242 linked to the leading face 2244 with the radial direction (ZZ') is equal to 13° and the average angle Ap of the normal to the inclined face inclined 2243 linked to the trailing face 2245 with the radial direction (ZZ') at most equal to 14°. The face connecting the radially upper surface of the block of the central portion to the bridging makes an average angle of 43° and the face connecting the radially upper surface of the bar to the bridging has two sides, one side on the side of the leading edge of the bar with an angle Apa of 35° with the circumferential direction and another side on the side of the trailing edge of the bar having an angle Apf of 0° with the circumferential direction.

[0038] The tire according to the invention comprises 4 crown layers whose reinforcing elements are cables made up of an aramid strand having a linear mass equal to 167 g per km and a strand of a PET textile fiber with a linear mass equal to 144 g per km, the reinforcing elements of the working layers being arranged in the working layers at a pitch equal to 0.86 mm. The reinforcing elements have a breaking strength of 37 daN.

[0039] The tire according to the invention was simulated by finite elements for rolling reproducing use measured by position and force sensors on a vehicle in a real work situation and travel from the farm to the fields. The calculations show an improved wear performance of at least 35% for an increase in the height of the sculpture of 16%, 7% of which is due to the performance brought about by the geometry of the sculpture. The bridging allows in particular very good homogenization of the rolling forces and regular wear between the bars and the central blocks.

[0040] The tire was also tested for traction. The tires are mounted on a commercially available sprayer. The tires are inflated to the pressure and load of the vehicle in the field for cyclic use well known to users. The hubs are equipped with force sensors capable of measuring slippage. The sprayer is driven in a plowed field with an average slope of 11%. The measurement is made uphill. The bridging allows for an increase in the footprint and an improvement in "traction" performance of 30% by reducing the slippage rate from 50% to 35%.

[0041] The tire was also tested in traction, i.e. the ability to pull an implement. 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 tows a mass on wheels in a field. For a slip rate of 15%, the force developed is improved by 15%, again thanks to the improvement in the footprint linked to the invention.

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

[0043] The rolling resistance at iso materials is estimated by finite elements as equivalent to that of the control tire. Thus, despite an increase in the tread height, better resistance to residual stubble due to the increase in the percentage of rubber compound in the central portion in terms of notch rate but also thickness between the bearing surface and the radially outermost crown layer, the greater flexibility of the tread when flattened thanks to the bridging makes it possible to maintain good rolling resistance.

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

Claims

Claims

1. Tire (1) for an agricultural vehicle, having an axis of rotation, in an axial direction (YY') and a recommended rolling direction (12), in 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 hollows (23) and extending radially outwards from a bearing surface (233) to a rolling surface (25), the radial distance from the bearing surface (233) to the rolling surface (25), measured at the centre of the tread determining the tread height (Hs), being at least equal to 35 mm, - each tread block (221, 222) being delimited, radially on the outside, by a contact face (251), intended to come into contact with a ground, and, circumferentially, by a leading face (241), the edge of which intersects with the contact face is intended to come into contact with the ground first, and by a trailing face (242), of which the intersection edge with the contact face is intended to come into contact with the ground last, -the tread (2) comprising two lateral portions (PI), each lateral portion comprising a circumferential distribution of sculpture blocks (221) in the form of bars, two by two separated by transverse hollows (231), and forming, with the circumferential direction (XX1) of the tire, an angle (Al) at least equal to 40° and at most equal to 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 a radially outer face, connecting the two lateral faces (2244, 2245) and radially inner to the rolling surface, characterized in that at least one bridge (224) is a thatch protection bridge having a radially outer face comprising at least two inclined sides (2242, 2243), extending respectively from each of its lateral faces (2244, 2245) to a ridge line (2241), and in that the average angle (Ap) of the normal to each of the inclined sides (2242, 2243) with the radial direction (ZZ') is at least equal to 10° and at most equal to 20°.

2. A tire according to claim 1, wherein any anti-stubble 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. A tire according to claim 1 or 2, wherein the radially outermost point of the ridge line (2241) of a thatch guard bridge (224) is at a radial distance from the bearing surface (233) of between 70 and 85% of the tread height (Hs) and the radially outermost points of the lateral faces (241, 242) of the bridge (224) are at a radial distance from the bearing surface (233) of between 55% and 70% of the tread height (Hs).

4. A tire 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. A tire according to any one of the preceding claims, in which any 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), at least equal to 40 mm and at most equal to 60 mm.

6. A tire 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 protection bridge (224).

7. A tire according to claim 6, wherein the volumetric notch rate, defined as the ratio between the volume VC of hollow (23) and the total volume V of the tread (2) assumed to be without hollow, between the bearing surface (233) and the rolling surface (25), of the central portion (Pc), is between 35% and 45% and the volumetric notch rate of the lateral portions (PI) is between 50 and 65%.

8. A tire 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 in which the axial width (Lp) of each lateral portion (PI) is between 30 and 40% of the axial width L of the tread.

10. A tire according to any one of claims 6 to 9, in which 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 protection bridge (224), and makes an angle with the circumferential direction (XX') at least equal to 40° and at most equal to 60°, preferably between 45 and 50°.

11. A tire according to any one of claims 6 to 10, wherein the inclined face (2242) connected to the leading face (2244) of the stubble bridge (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) of between 30° and 40° and the inclined face (2243) connected to the trailing face (2245) of the stubble bridge (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) of between 0° and 20°.

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

13. A tire according to any one of claims 6 to 12, wherein the bearing surface (233) of the central portion (Pc) is radially external to 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. A tire according to claim 13, in which any hollow (231) of each lateral portion (PI) comprises a face (234) with a radial height at least equal to 3 mm, called a stubble guard, the trailing edge (2342) of which is axially external to its leading edge (2341).

15. A tire 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) towards the trailing edge (2342) and makes at its axial end with the circumferential direction (XX') an angle of between 40 and 60°

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