Tire tread for a heavy civil-engineering vehicle

Abstract

Tread of a tire (1) for a heavy-duty vehicle of civil engineering type. The tread (2), having an axial width W.sub.T and having a radial thickness H.sub.T at least equal to 70 mm, comprises at least two circumferential grooves (3) positioned axially on each side of an equatorial plane (XZ). Each circumferential groove (3) has an axial width W and a radial depth H, such that the ratio W/H is at least equal to 0.06, the axial distance C between two consecutive circumferential grooves (3) is at least equal to 12% and at most equal to 21% of the axial width W.sub.T of the tread and each of the axially outermost circumferential grooves (3) is positioned axially, with respect to the equatorial plane XZ, at an axial distance L.sub.E at least equal to 35% of the axial width W.sub.T of the tread.

Claims

1. A tire for a heavy-duty vehicle of civil engineering type comprising a tread, adapted to come into contact with the ground via a tread surface: the tread having an axial width W.sub.T and a radial thickness H.sub.T at least equal to 70 mm, the tread comprising at least two circumferential grooves, positioned axially one on each side of an equatorial plane passing through the middle of the tread and perpendicular to the axis of rotation of the tire, each said circumferential groove extending axially between two substantially circumferential faces, radially towards the inside from the tread surface as far as a bottom face and circumferentially around the entire circumference of the tire, each said circumferential groove being axially positioned with respect to the equatorial plane at an axial distance L, having an axial width W, measured between the two substantially circumferential faces, and a radial depth H, measured between the tread surface and the bottom face, the radial depth H being at least equal to 70% of the radial thickness H.sub.T and at most equal to the radial thickness H.sub.T, wherein each said circumferential groove has an axial width W and a radial depth H, such that the ratio W/H is at least equal to 0.06, wherein the axial distance C between two consecutive circumferential grooves is at least equal to 12% and at most equal to 21% of the axial width W.sub.T of the tread, and wherein each of the axially outermost circumferential grooves is positioned axially, with respect to the equatorial plane, at an axial distance L.sub.E at least equal to 35% of the axial width W.sub.T of the tread, and wherein the axial distance C between two consecutive circumferential grooves is at least equal to 150% and at most equal to 200% of the radial thickness H.sub.T.

2. The tire for a heavy-duty vehicle of civil engineering type according to claim 1, wherein the ratio W/H is at most equal to 0.15.

3. The tire for a heavy-duty vehicle of civil engineering type according to claim 1, wherein the axial distance L.sub.E is at most equal to 40% of the axial width W.sub.T of the tread.

4. The tire for a heavy-duty vehicle of civil engineering type according to claim 1, wherein at least one said circumferential groove has a rectilinear circumferential mean profile.

5. The tire for a heavy-duty vehicle of civil engineering type according to claim 1, wherein at least one said circumferential groove has a periodic wavy circumferential mean profile.

6. The tire for a heavy-duty vehicle of civil engineering type according to claim 1, wherein each said substantially circumferential face of a circumferential groove forms, with the radial direction, an angle at least equal to 0.5° and at most equal to 5°.

7. The tire for a heavy-duty vehicle of civil engineering type according to claim 1, wherein each said substantially circumferential face of a circumferential groove is connected to the bottom face of the circumferential groove by a circular fillet of fillet radius R at least equal to 0.25 times the axial width W.

8. The tire for a heavy-duty vehicle of civil engineering type according to claim 1, wherein the tread comprises at least four of the circumferential grooves.

9. The tire for a heavy-duty vehicle of civil engineering type according to claim 1, wherein the tread comprises at most eight of the circumferential grooves.

10. The tire for a heavy-duty vehicle of civil engineering type according to claim 1, the tread comprising a middle part having an axial width W.sub.C at least equal to 50% and at most equal to 80% of the axial width W.sub.T, and two lateral portions, respectively positioned axially on either side of the middle part, and each having an axial width W.sub.S at least equal to 10% and at most equal to 25% of the axial width W.sub.T, the tread being such that the middle portion comprises transverse sipes opening into the circumferential grooves, said transverse sipes having a radial depth H1 at least equal to 70% of the radial thickness H.sub.T and delimiting elements in relief of a height equal to the radial depth H1 of said transverse sipes and of circumferential length B1 equal to the mean distance between two consecutive said transverse sipes, wherein, for all the elements in relief delimited by two consecutive said transverse sipes of the middle portion, the ratio H1/B1 is at least equal to 0.5 and at most equal to 2.5.

11. The tire for a heavy-duty vehicle of civil engineering type according to claim 1, the tread comprising a middle part having an axial width W.sub.C at least equal to 50% and at most equal to 80% of the axial width W.sub.T, and two lateral portions, respectively positioned axially on either side of the middle part, and each having an axial width W.sub.S at least equal to 10% and at most equal to 25% of the total axial W.sub.T, the tread being such that at least a said lateral portion comprises transverse cuts, of transverse sipe or transverse groove type, opening on one side into a said circumferential groove and on the other side into an axial end of the tread, said transverse cuts having a radial depth H2 at least equal to 70% of the radial thickness H.sub.T and delimiting elements in relief of a height equal to the radial depth H2 of said transverse cuts and of circumferential length B2 equal to the mean distance between two consecutive said transverse cuts, wherein, for all the elements in relief delimited by two consecutive said transverse cuts of at least one said lateral portion, the ratio H2/B2 is at least equal to 0.5 and at most equal to 2.5.

12. The tire for a heavy-duty vehicle of civil engineering type according to claim 11, wherein at least one said lateral portion comprises an alternation of said transverse sipes and of said transverse grooves such that any said element in relief is delimited by a said transverse sipe and a said transverse groove which are consecutive.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The features of the invention are illustrated by the schematic FIGS. 1A, 1B, 2A, 2B, 2C and 3A-3C, which are not drawn to scale:

(2) FIG. 1A: a plan view of a tread of a tire according to an embodiment of the invention;

(3) FIG. 1B: a view in meridian section, on a meridian plane YZ, of a tread of a tire according to an embodiment of the invention;

(4) FIG. 2A: a plan view of a circumferential groove of a tread according to a first alternative form of circumferential mean profile;

(5) FIG. 2B: a plan view of a circumferential groove of a tread according to a second alternative form of circumferential mean profile;

(6) FIG. 2C: a view in meridian section of a circumferential groove of a tread;

(7) FIG. 3A: a plan view of a tread of a tire according to a preferred embodiment of the transverse cuts;

(8) FIG. 3B: a sectional view taken along 3B-3B in FIG. 3A; and

(9) FIG. 3C: a sectional view taken along 3C-3C in FIG. 3A.

DETAILED DESCRIPTION OF THE DRAWINGS

(10) FIG. 1A is a plan view of a tread 2 of a tire 1 according to the invention. The tread 2, intended to come into contact with the ground via a tread surface 21, has an axial width W.sub.T and a radial thickness H.sub.T (not depicted) at least equal to 70 mm. The tread 2, in the case depicted, comprises 5 circumferential grooves 3 positioned axially on or on each side of an equatorial plane XZ passing through the middle of the tread and perpendicular to the axis of rotation YY′ of the tire. Each circumferential groove 3 is positioned axially, with respect to the equatorial plane XZ, at an axial distance L, and has an axial width W along the axis YY′, and a radial depth H (not depicted) along the axis ZZ′, the radial depth H being at least equal to 70% of the radial thickness H.sub.T and at most equal to the radial thickness H.sub.T. According to the invention, each circumferential groove 3 has an axial width W and a radial depth H, such that the ratio W/H is at least equal to 0.06, the axial distance C between two consecutive circumferential grooves 3 is at least equal to 12% and at most equal to 21% of the axial width W.sub.T of the tread, and each of the axially outermost circumferential grooves 3 is positioned axially, with respect to the equatorial plane XZ, at an axial distance L.sub.E at least equal to 35% of the axial width W.sub.T of the tread.

(11) FIG. 1B is a view in meridian section, in a meridian plane YZ of a tread 2 of a tire 1 according to the invention. This FIG. 1B in particular depicts the circumferential grooves 3 in meridian section, namely 5 circumferential grooves in the case presented. In general, a circumferential groove 3 extends axially between two substantially circumferential faces (3A, 3B), radially toward the inside from the tread surface 21 as far as a bottom face 3C and circumferentially around the entire circumference of the tire. A circumferential groove 3, positioned axially with respect to the equatorial plane at an axial distance L, has an axial width W, measured between the two substantially circumferential faces (3A, 3B) and a radial depth H, measured between the tread surface 21 and the bottom face 3C. The radial depth H of a circumferential groove 3 is at least equal to 70% and at most equal to 100% of the radial thickness H.sub.T. The radial thickness H.sub.T of the tread 2 is defined as being the maximum radial depth measured in the cuts, namely, in this instance, between the tread surface 21 and the bottom face 3C of the axially outermost circumferential groove 3 which in this instance is the deepest cut. The radial thickness H.sub.T is at least equal to 70 mm.

(12) FIG. 2A depicts a plan view of a circumferential groove 3, having an axial width W, measured between the two substantially circumferential faces (3A, 3B), and having a rectilinear circumferential mean profile P.sub.C, according to a first alternative form of circumferential mean profile. FIG. 2B depicts a plan view of a circumferential groove 3, having an axial width W, measured between the two substantially circumferential faces (3A, 3B), and having a periodic wavy circumferential mean profile (P.sub.C) of amplitude A and of period T, according to a second alternative form of circumferential mean profile. FIG. 2C depicts a meridian section, on a plane (often close to a meridian plane) normal to the mean plane of a circumferential groove 3, having an axial width W, measured between the two substantially circumferential faces (3A, 3B), and a radial depth H, measured between the tread surface 21 and the bottom face 3C. Furthermore, each substantially circumferential face (3A, 3B) of the circumferential groove 3 forms, with the radial direction ZZ′, an angle (DA, DB) at least equal to 0.5° and at most equal to 5° and is connected to the bottom face 3C by a circular fillet (3D) of fillet radius R at least equal to 0.25 times the axial width W.

(13) FIGS. 3A-3C depict a preferred embodiment of the invention, with regard to the transverse cuts, in which embodiment the tread 2 comprises a middle portion 22 having an axial width W.sub.C at least equal to 50% and at most equal to 80% of the axial width W.sub.T, delimited axially by the two axially outermost circumferential grooves 3, and two lateral portions (23, 24) axially positioned respectively one on each side of the middle portion 22 and each having an axial width W.sub.S at least equal to 10% and at most equal to 25% of the axial width W.sub.T. The tread 2 is such that the middle portion 22 comprises transverse sipes 42 opening into the circumferential grooves 3. These transverse sipes 42 have a radial depth H1 at least equal to 70% of the radial thickness H.sub.T and delimit elements in relief 62 of a height equal to the radial depth H1 of the said transverse sipes and of circumferential length B1 equal to the mean distance between two consecutive transverse sipes 42. For all the elements in relief 62 delimited by two consecutive transverse sipes 42 of the middle portion 22, the ratio H1/B1 is at least equal to 0.5 and at most equal to 2.5.

(14) In the embodiment depicted in FIGS. 3A-3C, the tread 2 is such that each lateral portion (23, 24) comprises transverse cuts, of transverse sipe (43, 44) and transverse groove (53, 54) type, opening on one side into a circumferential groove (3) and on the other side into an axial end of the tread 2. These transverse cuts (43, 44; 53, 54) have a radial depth H2 at least equal to 70% of the radial thickness H.sub.T and delimit elements in relief (63, 64) of a height equal to the radial depth H2 of the said transverse cuts, and of circumferential length B2 equal to the mean distance between two consecutive transverse cuts (43, 44; 53, 54). For all the elements in relief (63, 64) delimited by two consecutive transverse cuts (43, 44; 53, 54) in each lateral portion (23, 24) the ratio H2/B2 is at least equal to 0.5 and at most equal to 2.5. In the alternative form of embodiment depicted, each lateral portion (23, 24) comprises an alternation of transverse sipes (43, 44) and of transverse grooves (53, 54) such that any element in relief (63, 64) is delimited by a transverse sipe (43, 44) and a transverse groove (53, 54) which are consecutive.

(15) The inventors have studied this invention more particularly in the case of a dumper tire of size 40.00R57 and 59/80R63.

(16) The characteristics of the tread for these tires according to the invention are presented in Table 1 below:

(17) TABLE-US-00001 TABLE 1 Tire size 40.00R57 59/80R63 Axial width W.sub.T (mm) 1000 1200 Radial thickness H.sub.T (mm) 108 70 Axial width W (mm)  8 to 10 10 Radial depth H (mm) 102 to 108 70 Ratio W/H 0.076 to 0.098 0.14 Axial distance C (mm) 173 200 Ratio C/W.sub.T 0.173 0.17 Axial distance L.sub.E (mm) 362 440 Ratio L.sub.E/W.sub.T 0.36 0.37

(18) The improvements made in terms of temperature, in relation to a tire of the prior art of the Michelin XDR2 range, are given in Table 2 below:

(19) TABLE-US-00002 TABLE 2 Tire size 40.00R57 59/80R63 Improvement in terms of temperature at the 20° C. 9° C. centre of the tread (° C.) Improvement in terms of temperature at the  5° C. 4° C. axial ends of the working reinforcement (° C.)

(20) 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.