Abstract
A tire for an agricultural vehicle, and in particular its tread, which aims to increase its traction capability in the field on loose ground. The tire having a nominal section width L, a central tread portion (211), centred on an equatorial plane (E) of the tire and having an axial width L1 at least equal to 0.15*L and at most equal to 0.35*L, has circumferentially distributed tread pattern elements (221), which are separated in pairs by transverse voids (231) forming an angle at least equal to 30° with the circumferential direction (XX′), and the central tread portion (211) has a local volumetric void ratio TEVL1, defined as being the ratio between the volume VC1 of the transverse voids (231) and the total volume V1 of the central tread portion (21), between the bearing surface (24) and the tread surface (25), is at most equal to 15%.
Claims
1. A tire for an agricultural vehicle, having a nominal section width L and comprising, radially from the outside to the inside, a tread and a crown reinforcement; the tread comprising tread pattern elements, which are separated from one another by voids and extend radially outwards from a bearing surface to a tread surface, the tread having an overall volumetric void ratio TEV, defined as being the ratio between the volume VC of voids and the total volume V of the tread assumed to be free of voids, comprised between the bearing surface and the tread surface, each tread pattern element having a circumferential slenderness H/B at most equal to 1.5, H being a mean radial height between the bearing surface and the tread surface at least equal to 20 mm, and B being a mean circumferential length, the tread comprising a central portion, centred on an equatorial plane (E) of the tire and having an axial width L1 at least equal to 0.15*L and at most equal to 0.35*L, and two intermediate portions, each of which continues the central portion axially outwards to an axial distance D2 equal to 0.3*L, measured from the equatorial plane (E), the central portion and each intermediate portion respectively being made up of a circumferential distribution of tread pattern elements, which are separated in pairs by transverse voids forming an angle at least equal to 30° with a circumferential direction (XX′) of the tire, the crown reinforcement comprising at least two crown layers, each of which comprises mutually parallel reinforcers that are coated with an elastomeric material, are crossed from one layer to the next, and form an angle at least equal to 10° with the circumferential direction (XX′), wherein the central portion has a local volumetric void ratio TEVL1, defined as being the ratio between the volume VC1 of the transverse voids and the total volume V1 of said central portion, comprised between the bearing surface and the tread surface, at most equal to 15%.
2. The tire according to claim 1, wherein the transverse voids of the central portion form an angle at least equal to 60° with the circumferential direction (XX′).
3. The tire according to claim 1, wherein the transverse voids of the central portion are transverse sipes that are able to close when they enter the contact patch in which contact is made with the ground when the tire is running.
4. The tire according to claim 1, wherein the transverse voids of each intermediate portion form an angle at least equal to 60° with the circumferential direction (XX′).
5. The tire according to claim 1, wherein each tread pattern element of the central portion has a mean radial height H1, a mean circumferential length B1, and a circumferential slenderness H1/B1, and each tread pattern element of each intermediate portion has a mean radial height H2, a mean circumferential length B2, and a circumferential slenderness H2/B2, and wherein the circumferential slenderness H1/B1 is strictly greater than the circumferential slenderness H2/B2.
6. The tire according to claim 5, wherein the circumferential slenderness H2/B2 of each tread pattern element of each intermediate portion is at most equal to 0.6.
7. The tire according to claim 1, wherein a median portion that is centred on the equatorial plane (E) of the tire and has an axial width L2 equal to 2*D2=0.60*L has a local volumetric void ratio TEVL2, defined as being the ratio between the volume VC2 of the voids and the total volume V2 of said median portion, comprised between the bearing surface and the tread surface, at most equal to 45%.
8. The tire according to claim 1, wherein the tread comprises exclusively transverse voids.
9. The tire according to claim 1, wherein the central portion is axially delimited on either side by circumferential voids.
10. The tire according to claim 1, wherein each tread pattern element has a mean radial height H at most equal to 55 mm.
11. The tire according to claim 1, wherein the tread has an overall volumetric void ratio TEV at most equal to 56%.
12. The tire according to claim 1, wherein at least some of the tread pattern elements comprise at least one chamfer which opens out on the tread surface with the formation of an angle D at least equal to 30° and at most equal to 70° with a radial direction (ZZ′) and has a radial height C at least equal to 3 mm and at most equal to 10 mm.
13. The tire according to claim 1, wherein the crown reinforcement comprises crown layers comprising metal reinforcers, preferably at most two crown layers comprising metal reinforcers.
14. The tire according to claim 1, wherein the tire for an agricultural vehicle is an “IF”, or “Improved Flexion”, tire within the meaning of the standard of the “ETRTO”, or “European Tire and Rim Technical Organisation”, in its “Standards Manual-2018”, in the section devoted to “Agricultural equipment tires”.
15. The tire according to claim 1, wherein the tire for an agricultural vehicle is a “VF”, or “Very high Flexion”, tire within the meaning of the standard of the “ETRTO”, or “European Tire and Rim Technical Organisation”, in its “Standards Manual-2018”, in the section devoted to “Agricultural equipment tires”.
Description
[0048] The features of the invention are illustrated by the schematic FIGS. 1 to 12, which are not drawn to scale:
[0049] FIG. 1: Perspective overview of a tire for an agricultural vehicle according to a first embodiment variant of the invention.
[0050] FIG. 2: Detailed perspective view of the tread of a tire for an agricultural vehicle according to the first embodiment variant of the invention (detail C1 from FIG. 1).
[0051] FIG. 3: Face-on overview of a tire for an agricultural vehicle according to the first embodiment variant of the invention.
[0052] FIG. 4: Detailed face-on view of the tread of a tire for an agricultural vehicle according to the first embodiment variant of the invention (detail D1 in FIG. 3).
[0053] FIG. 5: Circumferential section of the tread of a tire for an agricultural vehicle according to the first embodiment variant of the invention (section A-A from FIG. 3).
[0054] FIG. 6: Meridian half-section of a tire for an agricultural vehicle according to the invention (section B-B from FIG. 3).
[0055] FIG. 7: Perspective overview of a tire for an agricultural vehicle according to a second embodiment variant of the invention.
[0056] FIG. 8: Detailed perspective view of the tread of a tire for an agricultural vehicle according to the second embodiment variant of the invention (detail C2 from FIG. 7).
[0057] FIG. 9: Face-on overview of a tire for an agricultural vehicle according to a third embodiment variant of the invention.
[0058] FIG. 10: Detailed perspective view of the tread of a tire for an agricultural vehicle according to the third embodiment variant of the invention (detail D3 from FIG. 9).
[0059] FIG. 11: View in section of a transverse void comprising a single chamfer.
[0060] FIG. 12: View in section of a transverse void comprising two facing chamfers.
[0061] FIGS. 1 to 5 illustrate a tire 1 for an agricultural vehicle according to a first embodiment variant of the invention. The tread 2 comprises tread pattern elements 22 that are separated from one another by voids 23 and extend radially outwards from a bearing surface 24 to a tread surface 25 (the bearing surface and the tread surface are shown in FIG. 6). In this first embodiment variant, the tread 2 comprises exclusively transverse voids 231 (FIGS. 2, 4 and 5). In the central tread portion 211, the transverse voids 231 are transverse sipes, of width I, that are able to close when they enter the contact patch in which contact is made with the ground when the tire is running (FIGS. 4 and 5), when the tire is subjected to pressure and load conditions as defined by the ETRTO standard. The tread pattern elements 221 of the central portion 211 of the tread, which are separated by said transverse sipes, have a mean radial height H and a mean circumferential length B (FIG. 5), and consequently a circumferential slenderness H/B.
[0062] FIG. 6 is a meridian half-section of a tire for an agricultural vehicle according to the invention. This radial section is made along the plane B-B of FIG. 3. This figure shows a tire 1 for an agricultural vehicle, having a nominal section half-width L/2 and comprising, radially from the outside to the inside, a tread 2 and a crown reinforcement 3. The tread 2 comprises tread pattern elements 22 that are separated from one another by voids 23 and extend radially outwards from a bearing surface 24 to a tread surface 25. The tread 2 has an overall volumetric void ratio TEV, defined as being the ratio between the volume VC of voids 23 and the total volume V of the tread 2 assumed to be free of voids, comprised between the bearing surface 24 and the tread surface 25, at least equal to 35%. Each tread pattern element 22 has a circumferential slenderness H/B at most equal to 0.8, H being the mean radial height between the bearing surface 24 and the tread surface 25 at least equal to 20 mm, and B being the mean circumferential length of the tread pattern element 22 (not shown). The crown reinforcement 3 comprises two crown layers 31, 32, each of which comprises mutually parallel, preferably metal, reinforcers that are coated with an elastomeric material, are crossed from one layer to the next, and form an angle at least equal to 10° with the circumferential direction XX′ of the tire. A carcass reinforcement 4 is positioned radially on the inside of the crown reinforcement 3. According to the invention, a central tread portion 211, centred on an equatorial plane E of the tire and having an axial width L1 at least equal to 0.15*L and at most equal to 0.35*L, comprises circumferentially distributed tread pattern elements 221 (identified by the generic reference 22 of the tread pattern elements, in FIG. 6), which are separated in pairs by transverse voids 231 (not shown in FIG. 6) forming an angle at least equal to 30° with the circumferential direction XX′, and the central tread portion 211 has a local volumetric void ratio TEVL1, defined as being the ratio between the volume VC1 of the transverse voids 231 and the total volume V1 of said central tread portion 211, comprised between the bearing surface 24 and the tread surface 25, at most equal to 15%. FIG. 6 shows a central tread half-portion of width L1/2. The tread 2 moreover comprises two intermediate portions 212, each axially continuing the central portion 211 outwards to an axial distance D2 equal to 0.3*L, measured from the equatorial plane E. FIG. 6 shows a single intermediate tread portion 212 of width D2-L1/2. With preference, a median tread portion 20 that is centred on the equatorial plane of the tire and has an axial width L2 equal to 2*D2=0.60*L, made up of the entirety of the central portion 211 and the two intermediate portions 212, has a local volumetric void ratio TEVL2, defined as being the ratio between the volume VC2 of the voids and the total volume V2 of said median tread portion 20, comprised between the bearing surface 24 and the tread surface 25, at most equal to 45%. FIG. 6 shows a median tread half-portion of width D2=L2/2.
[0063] FIGS. 7 and 8 illustrate a tire 1 for an agricultural vehicle according to a second embodiment variant of the invention as overall figure and figure of a detail C2, respectively. The tread 2 comprises tread pattern elements 22 that are separated from one another by voids 23. In this second embodiment variant, the tread 2 comprises a central portion 211, comprising circumferentially distributed tread pattern elements 221, which are separated from one another by voids 231 of transverse sipe type that are able to close when they enter the contact patch in which contact is made with the ground when the tire is running. Moreover, the central tread portion 211 is axially delimited on either side by circumferential voids 233.
[0064] FIGS. 9 and 10 illustrate a tire for an agricultural vehicle according to a third embodiment variant of the invention as overall figure and figure of a detail D3, respectively. In this third embodiment variant, the tread 2 of the tire of nominal section width L comprises a central portion 211 which is centred on an equatorial plane E of the tire and has an axial width L1 at least equal to 0.15*L and at most equal to 0.35*L, and two intermediate portions 212, each axially continuing the central portion 211 outwards to an axial distance D2 equal to 0.3*L, measured from the equatorial plane E. The assembly made up of the central portion 211 and the two intermediate portions 212 constitutes a median portion 20 which is centred on the equatorial plane E of the tire and has an axial width L2 equal to 2*D2=0.60*L. The central portion 211 comprises circumferentially distributed tread pattern elements 221, which are separated in pairs by transverse voids 231 forming an angle at least equal to 30° and, in the present case, at least equal to 60° with the circumferential direction XX′ of the tire. The transverse voids 231 of the central portion 211 are transverse sipes that are able to close when they enter the contact patch in which contact is made with the ground when the tire is running Each tread pattern element 221 has a circumferential slenderness H1/B1 at most equal to 1.5, H1 being a mean radial height between the bearing surface and the tread surface at least equal to 20 mm (not shown in FIGS. 8 and 9), and B1 being a mean circumferential length. B1 is measured at the tread surface, since the leading and trailing faces of the tread pattern elements 221 are substantially radial. According to the invention, the central portion 211 has a local volumetric void ratio TEVL1, defined as being the ratio between the volume VC1 of transverse voids 231 and the total volume V1 of said central portion 211, comprised between the bearing surface and the tread surface, at least equal to 15%. Each central portion 212 comprises circumferentially distributed tread pattern elements 222, which are separated in pairs by transverse voids 232 forming an angle at least equal to 30° and, in the present case, at least equal to 60° with the circumferential direction XX′ of the tire. Each tread pattern element 222 has a circumferential slenderness H2/B2 at most equal to 1.5, H2 being a mean radial height between the bearing surface and the tread surface at least equal to 20 mm (not shown in FIGS. 8 and 9), and B2 being a mean circumferential length. B2 is measured between two points situated substantially in the middle of the leading face and in the middle of the trailing face, respectively, in the knowledge that they exhibit an inclination referred to as taper with respect to a radial plane YZ. In the embodiment shown in FIGS. 9 and 10, the circumferential slenderness H1/B1 is strictly greater than the circumferential slenderness H2/B2, which itself is strictly less than 0.6. Lastly, the median portion 20 that is centred on the equatorial plane E of the tire and has an axial width L2 equal to 2*D2=0.60*L has a local volumetric void ratio TEVL2, defined as being the ratio between the volume VC2 of the voids and the total volume V2 of said median portion 20, comprised between the bearing surface and the tread surface, at most equal to 45%.
[0065] FIGS. 11 and 12 show a view in section of a transverse void comprising a single chamfer and a view in section of a transverse void comprising two facing chamfers, respectively. Each chamfer 26 opens out on the tread surface 25 with the formation of an angle D at least equal to 30° and at most equal to 70° with a radial direction and has a radial height C at least equal to 3 mm and at most equal to 10 mm.
[0066] The invention has been studied more particularly for a tire for an agricultural vehicle of size VF 600/70R30 165D, corresponding to an embodiment of the invention as shown in FIGS. 9 and 10 with circumferential elements of tread pattern elements that are different between the central portion and the intermediate portions.
[0067] Table 1 below shows the characteristics of the example studied by the inventors:
TABLE-US-00001 TABLE 1 Characteristic Characteristics values Comments Nominal section width L 600 mm Overall volumetric void ratio 48% At most equal to TEV 56% Width L1 of central tread 160 mm 27% of L, thus portion comprised between 15% and 35% of L Local volumetric void ratio 8% Less than 15% TEVL1 of central portion Width L2 of median tread 360 mm Equal to 60% of L portion Local volumetric void ratio 35% Less than 45% TEVL2 of median portion Mean radial height H1 of a tread 42 mm Comprised between pattern element of the central 20 mm and 55 mm portion Mean circumferential length B1 41 mm of a tread pattern element of the central portion Circumferential slenderness 1.02 Less than 1.5 H1/B1 of a tread pattern element of the central portion Mean radial height H2 of a tread 37 mm Comprised between pattern element of the 20 mm and 55 mm intermediate portion Mean circumferential length B2 110 mm of a tread pattern element of the intermediate portion Circumferential slenderness 0.34 Less than 0.6 H2/B2 of a tread pattern element of the intermediate portion Width I of a sipe of the central 2.7 mm Width making it portion possible for the sipe to close in the contact patch in the recommended running conditions. Angle of a sipe of the central 85° Greater than 60° portion with respect to the and thus greater circumferential direction than 30° Angle D of a chamfer of a sipe 45° Comprised between of the central portion with 30° and 70° respect to a radial direction Radial height C of a chamfer of 5 mm Comprised between a sipe of the central portion 3 mm and 10 mm Mean width of a transverse sipe 140 mm (outside of the central portion) Mean angle of a transverse void 80° Greater than 30° (outside of the central portion) with respect to the circumferential direction
[0068] The inventors have found that a tire according to the invention having the characteristics described in Table 1 confers a gain in traction of about 27% over a reference tire of the prior art for a low degree of slip on the ground of between 4% and 10%, that is to say is able to develop a traction force approximately 27% greater than that developed by a tire of the prior art.
