Tread for the tire of a farm tractor

Abstract

A tread and tire for a multipurpose agricultural machine, that improves field traction while ensuring a satisfactory compromise with wear under engine torque and vibratory comfort on the road having a tread having a plurality of lugs distributed in a first row extending axially from a first axial end of the tread and in a second row extending axially from a second axial end of the tread, the second row differing from the first row by a symmetry relative to the equatorial plane of the tire followed by a rotation about the rotation axis of the tire, each row having an alternation of long lugs and of short lugs. The axially inner end face of a first long lug of a row of lugs is separated from the trailing lateral face of the second long lug of the symmetrical row of lugs, closest to the axially inner end face of the first long lug, by an end groove with a width at least equal to 10% and at most equal to 100% of the lug height.

Claims

1. A tire for a multipurpose agricultural machine, comprising: a tread designed to come into contact with the ground via a tread surface having two axial ends, the axial distance between the axial ends being the width of the tread (L), the tread comprising a plurality of lugs extending radially between an inner surface of revolution about the rotation axis of the tire and the tread surface, the radial distance between the said surfaces being the lug height (H), each lug comprising a leading lateral face, a trailing lateral face, an axially outer end face, an axially inner end face and a contact face, the plurality of lugs being distributed in a first row of lugs extending axially from a first axial end of the tread and a second row of lugs extending axially from a second axial end of the tread, the second row of lugs being identical to the first row of lugs and placed as a mirror image of the first row of lugs that is offset in the circumferential direction of the tire, each row of lugs consisting of an alternation of long lugs, of which an axial distance (L.sub.1) between the respectively axially outer and inner end faces is at least equal to half the width of the tread (L), and of short lugs, of which an axial distance (L.sub.2) between the respectively axially outer and inner end faces is at most equal to half the width of the tread (L), wherein the axially inner end faces of a plurality of first long lugs of the first row of lugs are separated from the trailing lateral faces of a plurality of second long lugs of the second row of lugs, closest to the axially inner end faces of the plurality of first long lugs, by an end groove with a width (e) at least equal to 10% and at most equal to 100% of the lug height (H), and wherein the end groove between the axially inner end face of at least one first long lug of the plurality of first long lugs and the trailing lateral face of at least one second long lug of the plurality of second long lugs, closest to the axially inner end face of the at least one first long lug, includes an elastomeric linking element extending radially outwards from the inner surface of the tread between the axially inner end face of the at least one first long lug and the trailing lateral face of the at least one second long lug having a radial height (h), wherein the entire elastomeric linking element is spaced from the equatorial plane, wherein each of the first and second long lugs connecting to an elastomeric linking element comprises at least one inner groove between its respectively axially outer end face and inner end face.

2. The tire according to claim 1, wherein the end groove between the axially inner end face of at least one first long lug and the trailing lateral face of at least one second long lug, closest to the axially inner end face of the at least one first long lug, extends radially between the inner surface of revolution about the rotation axis of the tire and the tread surface of the tread.

3. The tire according to claim 1, wherein the radial height (h) of the elastomeric linking element is at most equal to 75% of the lug height (H).

4. The tire according to claim 1, wherein the axial distance (L.sub.1) between the respectively axially outer end face and inner end face of each long lug is at most equal to 70% of the tread width (L).

5. The tire according to claim 1, wherein the axial distance (L.sub.2) between the respectively axially outer end face and inner end face of each short lug is at least equal to 20% of the tread width (L).

6. The tire according to claim 1, wherein the axial distance (L.sub.2) between the respectively axially outer end face and inner end face of each short lug is at most equal to 40% of the tread width (L).

7. The tire according to claim 1, wherein an angle of inclination (a) of a tangent (t.sub.e) to a centre line (m) of the contact face of each lug at an axially outer end point (E) of the said centre line, relative to the circumferential direction (X), is at least equal to 45 and at most equal to 90.

8. The tire according to claim 7, wherein the angle of inclination (a) is at least equal to 50 and at most equal to 75.

9. The tire according to claim 1, wherein an angle of inclination (b) of a tangent (t.sub.1) to a centre line (m) of the contact face of each long lug at an axially inner end point (I) of the said centre line, relative to the circumferential direction (X), is at least equal to 15 and at most equal to 45.

10. The tire according to claim 9, wherein the angle of inclination (b) is at least equal to 25 and at most equal to 35.

11. The tire according to claim 1, wherein an average angle of inclination (c) of a straight line (D) passing through the respectively axially outer end point (E) and inner end point (I) of a centre line (m) of the contact face of each long lug, relative to the circumferential direction (X), is at least equal to 40 and at most equal to 60.

12. The tire according to claim 1, wherein the at least one inner groove has a width (e.sub.1) at most equal to 100% of the lug height (H).

13. The tire according to claim 1, wherein a radial depth (p) of the at least one inner groove is at least equal to 25% of the lug height (H).

14. The tire according to claim 1, wherein each long lug comprises only one inner groove between its respectively axially outer end face and inner end face.

15. The tire according to claim 14, wherein the inner groove of each long lug is disposed at an equal axial distance to the equatorial plane as the axially inner end face of a short lug of the same row of lugs.

16. The tire according to claim 1, wherein a distance in the contact face of each lug measured between the leading lateral face and the trailing lateral face is constant along the entire length of each respective lug.

17. The tire according to claim 16, wherein each elastomeric linking element extends at a distance from the leading lateral face to the trailing lateral face of the at least one first long lug in the plurality of first long lugs that remains constant along the entire width (e) of each respective end groove.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

(2) FIG. 1 shows a view in perspective of a tire according to the invention,

(3) FIGS. 2 and 3 show the tread surface of a tire according to the invention opened out in a plane,

(4) FIG. 4 shows a section of an end groove of a long lug,

(5) FIG. 5 shows a section of an inner groove of a long lug.

(6) FIG. 1 shows a view in perspective of a tire 1 according to the invention, comprising a tread 2 designed to come into contact with the ground via a tread surface 3. The tread 2 comprises a plurality of lugs (15, 16, 25, 26) extending radially between an inner surface 4 of revolution about the rotation axis of the tire and the tread surface 3. Each lug (15, 16) comprises a leading lateral face (151, 161), a trailing lateral face (152, 162), an axially outer end face (153, 163), an axially inner end face (154, 164), and a contact face (155, 165). The plurality of lugs is distributed in a first row of lugs (15, 16) and a second row of lugs (25, 26) extending axially respectively from a first axial end and from a second axial end of the tread. Each row of lugs consists of an alternation of long lugs (15, 25) and short lugs (16, 26). According to the invention, the axially inner end face (154) of a first long lug (15) of a row of lugs is separated from the trailing lateral face (252) of the second long lug (25) of the symmetrical row of lugs, closest to the axially inner end face of the first long lug, by an end groove (156).

(7) FIG. 2 shows the tread surface of a tire 1 according to the invention, opened out in a plane (X, Y), that is to say the contact faces of the long lugs (15, 25) and of the short lugs (16, 26). FIG. 2 repeats the elements of FIG. 1, with two additional elements: the elastomeric linking element 157 extending radially in the end groove 156, and an inner groove 158 positioned in the long lug 15, between its respectively axially outer end face 153 and inner end face 154.

(8) FIG. 3 shows the geometric parameters of the tread surface, according to the invention. The tread surface comprises two axial ends, the axial distance between the axial ends being the tread width L. The tread 2 comprises a plurality of lugs distributed in a first row of lugs (15, 16) extending axially from a first axial end of the tread and a second row of lugs (25, 26) extending axially from a second axial end of the tread, the second row of lugs (25, 26) differing from the first row of lugs (15, 16) by a symmetry relative to the equatorial plane (P) of the tire followed by a rotation about the rotation axis (Y) of the tire. Each row of lugs consists of an alternation of long lugs 15, of which the axial distance L.sub.1 between the respectively axially outer and inner end faces (153, 154) is at least equal to half the tread width L, and of short lugs 16, of which the axial distance L.sub.2 between the respectively axially outer and inner end faces (163, 164) is at most equal to half the tread width L.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

(9) According to the invention, the axially inner end face 154 of a first long lug 15 of a row of lugs is separated from the trailing lateral face 252 of the second long lug 25 of the symmetrical row of lugs, closest to the axially inner end face of the first long lug, by an end groove 156 with a width e at least equal to 10% and at most equal to 100% of the lug height.

(10) In the embodiment of FIG. 3, the end groove 156 is at least partly filled by an elastomeric linking element 157 extending radially from the inner surface 4 of the tread. Moreover, the long lug 15 comprises a single inner groove 158, with a width e.sub.1 and an axial distance L.sub.1 relative to the equatorial plane P.

(11) The contact face (155, 165) of a lug is moreover defined geometrically by its centre line m limited by the axially outer end point E and the axially inner end point I. The geometric line of the centre line m is characterized by:

(12) the angle of inclination a of the tangent t.sub.e to the centre line m at the axially outer end point E, relative to the circumferential direction X,

(13) the angle of inclination b of the tangent t.sub.i to the centre line m at the axially inner end point I, relative to the circumferential direction X,

(14) the average angle of inclination c of the straight line D passing through the respectively axially outer end point E and inner end point I, relative to the circumferential direction X.

(15) FIG. 4 shows a section of an end groove 156, made along a mid-plane, tangential to the centre line of the contact face 155 at its axially inner end. The end groove 156, with a width e, separates the axially inner end face 154 of the long lug 15 from the trailing lateral face 252 of the long lug 25. The width e of the end groove 156 is defined at the respective contact faces (155, 255) of the long lugs 15 and 25. The end groove 156 extends radially between the inner surface 4 and the contact faces (155, 255) over the lug height H and is at least partly filled by the linking element 157 which extends radially from the inner surface 4 over a radial height h at most equal to 75% of the lug height H.

(16) FIG. 5 shows a section of an inner groove 158, made on a mid-plane, tangential to the centre line of the contact face 155. The inner groove 158, with a width e.sub.1, is positioned in a long lug 15. The width e.sub.1 of the inner groove 158 is defined at the contact face 155 of the long lug 15. The groove 158 extends radially from the contact face 155, over a radial depth p at least equal to 25% of the lug height H, the radial distance between the inner surface 4 and the contact face 155.

(17) The invention has been most particularly studied for an agricultural tire of 600/65 R 38 dimension, in the case of the second embodiment of the invention with an end groove partially filled by an elastomeric linking element, but with no intermediate groove. For this studied dimension, the tread width L is equal to 586 mm, the lug height H is equal to 60 mm, the axial distance L.sub.1 between the respectively axially outer and inner end faces of a long lug is equal to 365.5 mm and the axial distance L.sub.2 between the respectively axially outer and inner end faces of a short lug is equal to 184 mm. The width e of the end groove is equal to 48 mm and the height h of the elastomeric linking element is equal to 5 mm. With respect to the orientation of a long lug, the angles a, b and c are respectively equal to 75, 25 and 49.5.

(18) The inventors have compared the wear performance under torque and in traction, in the field, of the tire being studied, described above, and a benchmark tire. The benchmark tire comprises a tread, comprising two rows of lugs that are identical to one another, that is to say all having the same axial distance between their respectively axially outer and inner end faces, and placed in chevrons, the total volume of lugs being equal to that of the tire being studied. The gain in performance on wear under engine torque of the tire being studied relative to the benchmark tire is estimated at 20%, which produces an additional service life of the tire of 20%, for a total volume of lugs, that is to say a given volume of rubber to be worn. The gain in traction performance, in the field, of the tire being studied relative to the benchmark tire is estimated at 10%, which means an increase in traction capability of 10%, for a given force of slippage of the tire relative to the ground.

(19) The present invention can be extended to other treads, comprising more than two rows of lugs. As an example, the tread may comprise, in addition to the two rows of lugs extending axially respectively from a first axial end and a second axial end of the tread, a row of inner lugs forming a middle portion of the tread and not emerging on an axial end of the tread.