Tread for an agricultural vehicle tire

Abstract

Tire (1) for an agricultural vehicle, and more particularly the tread (2) thereof, has improved traction in the field, while reducing the sensitivity of the lugs (3) to attack by stubble. Each lug (3) comprises first lug portion (31), having height H1, and second lug portion (32), having height H2 and having a mean angle of inclination A2 with respect to circumferential direction (XX′) of the tire. The first lug portion (31) is comprised of a radial superposition of N layers C1.sub.i (33), where i varies from 1 to N, each having a height H1.sub.i, each layer C1.sub.i having a mean angle of inclination A1.sub.i strictly less than the mean angle of inclination A2, and, when N is strictly greater than 1, the angle A1.sub.j relative to a layer C1.sub.j, where j varies from 1 to N−1, is strictly less than the angle A1.sub.j+1 relative to the layer C1.sub.j+1.

Claims

1. A fire for an agricultural vehicle, comprising: a tread made up of lugs that are separated from one another by grooves; each said lug extending radially outwards, over a height H, from a bottom surface to a contact face, extending axially inwards from an axially outer end face to an axially inner end face, and extending circumferentially from a trailing face to a leading face; each said lug comprises a first lug portion, extending radially outwards from the bottom surface and having a height H1, and a second lug portion, extending radially outwards from the first lug portion to the contact face, having a height H2 and having a mean angle of inclination A2 with respect to a circumferential direction of the tire, wherein the first lug portion is comprised of a radial superposition of N layers C1.sub.i, where i varies from 1 to N, each having a height H1.sub.i, such that the sum of the heights H1.sub.i is equal to the height H1 of the first lug portion, the layer C1.sub.1 extending radially outwards from the bottom surface and the layer C1.sub.N extending radially outwards to the second lug portion, wherein each said layer C1.sub.i has a mean angle of inclination A1.sub.i, with respect to the circumferential direction of the tire, that is strictly less than the mean angle of inclination A2 of the second lug portion, such that the layer C1.sub.i is positioned in front of the leading face in the vicinity of the axially inner end face, and behind the trailing face in the vicinity of the axially outer end face, and wherein, when N is strictly greater than 1, the angle A1.sub.j relative to a layer C1.sub.j, where j varies from 1 to N−1, is strictly less than the angle A1.sub.j+1 relative to the layer C1.sub.j+1, such that two consecutive layers (C1.sub.j, C1.sub.j+1) are rotationally offset with respect to one another by an angle B1.sub.j=A1.sub.j+1−A1.sub.j.

2. The tire according to claim 1, wherein the height H1 of the first lug portion is strictly less than the height H of the lug.

3. The tire according to claim 1, wherein the height H1 of the first lug portion is at least equal to min (6 mm, 0.25*H).

4. The tire according to claim 1, wherein the height H1.sub.i of each said layer C1.sub.i is at most equal to 0.5 times the height H1 of the first lug portion.

5. The according to claim 1, wherein the height H1.sub.i of each said layer C1.sub.i is at least equal to min (3 mm, 0.1*H1).

6. The tire according to claim 1, wherein the height H1.sub.i of each said layer C1.sub.i, where i varies from 1 to N, is equal to H1/N.

7. The tire according to claim 1, wherein the angle B1.sub.j=A1.sub.j+1−A1.sub.j between two consecutive layers (C1.sub.j, C1.sub.j+1), where j varies from 1 to N−1, is equal to (A1.sub.N−A1.sub.1)/(N−1).

8. The tire according to claim 1, wherein the first lug portion is comprised of a radial superposition of N layers C1.sub.i, where i varies from 1 to N, with N at least equal to 2.

9. The tire according to claim 1, wherein the first lug portion is comprised of a radial superposition of N layers C1.sub.i, where i varies from 1 to N, with N at most equal to 10.

10. The tire according to claim 1, wherein the angle A1.sub.1 relative to the layer C1.sub.1, which is radially innermost, is at least equal to A2−45°.

11. The tire according to claim 1, wherein the angle A1.sub.N relative to the layer C1.sub.N, which is radially outermost, is at most equal to A2−1°.

12. The tire according to claim 1, wherein the angle B2=A2−A1.sub.N is equal to (A1.sub.N−A1.sub.1)/(N−1).

13. The tire according to claim 1, wherein two consecutive layers (C1.sub.j, C1.sub.j+1), where j varies from 1 to N−1, are joined together by fillets.

14. The tire according to claim 1, wherein the tread is comprised of a first and a second row of lugs disposed in chevrons with respect to the equatorial plane (P) of the tire.

15. The tire according to claim 1, wherein the height H1 of the first lug portion is at most equal to 0.5 times the height H of the lug.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will be understood better with the aid of FIGS. 1 to 4 described below, in which:

(2) FIG. 1 shows a perspective view of a tire portion for an agricultural vehicle of the prior art,

(3) FIG. 2 shows a perspective view of a tread portion of a tire for an agricultural vehicle according to a first embodiment of the invention,

(4) FIG. 3 shows a top view of a tread portion of a tire for an agricultural vehicle according to a first embodiment of the invention,

(5) FIG. 4 shows a top view of a tread portion of a tire for an agricultural vehicle according to a second embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(6) FIG. 1 is a perspective view of a portion of a tire 1 for an agricultural vehicle of the prior art. The tread 2 of the tire is made up of lugs 3 that are separated from one another by grooves 4. Each lug 3 extends radially outwards, from a bottom surface 5 to a contact face 6, extends axially inwards from an axially outer end face 7 to an axially inner end face 8, and extends circumferentially from a trailing face 9 to a leading face 10. In the present case, the tread is made up of a first and a second row of lugs 3 disposed in chevrons with respect to the equatorial plane of the tire.

(7) FIG. 2 is a perspective view of a portion of tread 2 of a tire for an agricultural vehicle according to a first embodiment of the invention, Each lug 3, having a height H, comprises a first, radially inner lug portion 31, extending radially outwards from the bottom surface 5 and having a height H1, and a second lug portion 32, extending radially outwards from the first lug portion 31 to the contact face 6, having a height H2. In this first embodiment, the first lug portion 31 is made up of a single layer C1.sub.1 having a height H1.sub.1 equal to H1. The single layer C1.sub.1 of the first lug portion 31 is positioned in front of the leading face 10, that is to say offset forwards, in the vicinity of the axially inner end face 8, and behind the trailing face 9, that is to say offset towards the rear, in the vicinity of the axially outer end face 7.

(8) FIG. 3 is a top view of a portion of tread 2 of a tire for an agricultural vehicle according to the first embodiment of the invention. Each lug 3 comprises a first lug portion 31, extending radially outwards from the bottom surface 5 and having a height H1, and a second lug portion 32, extending radially outwards from the first lug portion 31 to the contact face 6, having a height H2 and a mean angle of inclination A2 with respect to a circumferential direction XX′ of the tire. In this first embodiment, the first lug portion 31 is made up of a single layer C1.sub.1 having a height H1.sub.1 equal to H1. The single layer C1.sub.1 of the first lug portion 31 has a mean angle of inclination A1.sub.1, with respect to the circumferential direction XX′ of the tire, that is strictly less than the mean angle of inclination A2 of the second lug portion 32, such that the layer C1.sub.1 is positioned in front of the leading face 10, that is to say offset forwards, in the vicinity of the axially inner end face 8, and behind the trailing face 9, that is to say offset towards the rear, in the vicinity of the axially outer end face 7.

(9) FIG. 4 is a top view of a portion of tread 2 of a tire for an agricultural vehicle according to a second embodiment of the invention. Each lug 3 comprises a first lug portion 31, extending radially outwards from the bottom surface 5 and having a height H1, and a second lug portion 32, extending radially outwards from the first lug portion 31 to the contact face 6, having a height H2 and having a mean angle of inclination A2 with respect to a circumferential direction XX′ of the tire. The first lug portion 31 is made up of a radial superposition of 2 layers C1.sub.1 and C1.sub.2 (33, 33), having respective heights H1.sub.1 and H1.sub.2, such that the sum of the heights H1.sub.1 and H1.sub.2 is equal to the height H1 of the first lug portion 31, the layer C1.sub.1 extending radially outwards from the bottom surface 5 and the layer C1.sub.2 extending radially outwards to the second lug portion 32. The layers C1.sub.1 and C1.sub.2 have mean angles of inclination A1.sub.1 and A1.sub.2, respectively, with respect to the circumferential direction XX′ of the tire, that are strictly less than the mean angle of inclination A2 of the second lug portion 32, such that the layers C1.sub.1 and C1.sub.2 are positioned respectively in front of the leading face 10, that is to say offset forwards, in the vicinity of the axially inner end face 8, and behind the trailing face 9, that is to say offset towards the rear, in the vicinity of the axially outer end face 7. Moreover, according to this second embodiment, the angle B1.sub.2=A1.sub.2−A1.sub.1, between the two consecutive layers C1.sub.1 and C1.sub.2 of the first lug portion 31, and the angle B2=A2−A1.sub.2, between the radially outermost layer C1.sub.2 of the first lug portion 31 and the second lug portion 32, are equal to one another.

(10) The invention has been implemented more particularly for an agricultural tire of size 600/70 R30. Table 1 below presents the technical features of an Example 1 of the first embodiment, presented in FIGS. 2 and 3, and those of an Example 2 of the second embodiment, presented in FIG. 4, respectively:

(11) TABLE-US-00001 TABLE 1 Example 1 Example 2 (FIGS. 2 and 3) (FIG. 4) Lug height H 65 mm 65 mm Height of first lug portion 21 mm 42 mm H1 Height of layers H1.sub.i 21 mm for H1.sub.1 21 mm for H1.sub.1 and H1.sub.2 Height of second lug portion 44 mm 23 mm H2 Mean angles of inclination 42° 37°, 42° of layers A1.sub.i Mean angle of inclination of 47° 47° second lug portion A2

(12) The inventors have been able to demonstrate, in internal tests, that the tires of Examples 1 and 2 made it possible to simultaneously improve the traction in the field and reduce the sensitivity of the leading faces of the lugs to attack by residual stubble.

(13) The scope of protection of the invention is not limited to the examples given hereinabove. The invention is embodied in each novel characteristic and each combination of characteristics, which includes every combination of any features which are stated in the claims, even if this feature or combination of features is not explicitly stated in the examples.