Tread for a tire of a heavy civil engineering vehicle

Abstract

Tire (1) for a heavy-duty vehicle of civil engineering type, and more particularly to the tread (2) thereof, and seeks to improve the grip thereof, while at the same time ensuring a satisfactory compromise with wearing and thermal endurance. The tread (2) comprises cuts (3, 4, 5) distributed, in a circumferential direction (XX′) of the tire, among circumferential grooves (3) and, in an axial direction (YY′) of the tire, transverse sipes (4) and transverse grooves (5), the cuts (3, 4, 5) delimiting elements in relief (6), each cut (3, 4, 5) being delimited by two faces facing one another and each face intersecting the tread surface (21) along an edge corner (311, 321; 411, 421; 511, 521). The tread (2) having a longitudinal edge corners ratio TA.sub.X equal to the ratio L.sub.X/S between the sum L.sub.X of the projections, on to the circumferential direction (XX′), of the effective edge corner lengths, contained in an elementary tread surface portion of surface area S, and the surface area S, and a transverse edge corners ratio TA.sub.Y equal to the ratio L.sub.Y/S between the sum L.sub.Y of the projections, onto the axial direction (YY′), of the effective edge corner lengths, contained in an elementary tread surface portion of surface area S, and the surface area S, the longitudinal edge corners ratio TA.sub.X is at least equal to 4 m.sup.−1 and the transverse edge corners ratio TA.sub.Y is at least equal to 6 m.sup.−1.

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 cuts distributed, in a circumferential direction of the tire, among circumferential grooves and, in an axial direction of the tire, transverse sipes and transverse grooves, wherein the transverse grooves have a constant circumferential width across their axial length, wherein the entire axial length of each transverse groove having the constant circumferential width is defined between a respective circumferential groove and an axial end of the axial width W.sub.T, the cuts delimiting elements in relief, each cut being delimited by two faces facing one another and each said face the tread surface along an edge corner, wherein the two faces forming each respective transverse groove are planar, the tread having a longitudinal edge corners ratio TA.sub.X and a transverse edge corners ratio TA.sub.Y, the longitudinal edge corners ratio TA.sub.X being equal to the ratio L.sub.X/S between the sum L.sub.X of the projections, onto the circumferential direction, of the effective edge corner lengths, contained in an elementary tread surface portion of surface area S, and the surface area S, the transverse edge corners ratio TA.sub.Y being equal to the ratio L.sub.Y/S between the sum L.sub.Y of the projections, onto the axial direction, of the effective edge corner lengths, contained in an elementary tread surface portion of surface area S, and the surface area S, wherein the longitudinal edge corners ratio TA.sub.X is at least equal to 4 m.sup.−1 and in that the transverse edge corners ratio TA.sub.Y is at least equal to 8 m.sup.−1.

2. The tire for a heavy-duty vehicle of civil engineering type according to claim 1, wherein the sum of the longitudinal edge corners ratio TA.sub.X and of the transverse edge corners ratio TA.sub.Y is at least equal to 12 m.sup.−1.

3. The tire for a heavy-duty vehicle of civil engineering type according to claim 1: the tread having an overall volume voids ratio TE.sub.G equal to the ratio between the total volume V.sub.D of the cuts and the sum of the total volume V.sub.D of the cuts and of the total volume V.sub.R of the elements in relief which are delimited by these cuts, the overall volume voids ratio TE.sub.G being equal to the sum of a longitudinal volume voids ratio TE.sub.X and of a transverse volume voids ratio TE.sub.Y, the longitudinal volume voids ratio TE.sub.X being equal to the ratio between the total volume V.sub.DX of the longitudinal cuts, of circumferential groove type, and the sum of the total volume V.sub.D of the cuts and of the total volume V.sub.R of the elements in relief delimited by these cuts, the transverse volume voids ratio TE.sub.Y being equal to the ratio between the total volume V.sub.DY of the transverse cuts, of sipe and groove type, and the sum of the total volume V.sub.D of the cuts and of the total volume V.sub.R of the elements in relief delimited by these cuts, wherein the overall volume voids ratio TE.sub.G is at least equal to 8% and at most equal to 17%, wherein the longitudinal volume voids ratio TE.sub.X is at least equal to 0.25 times and at most equal to 0.50 times the overall volume voids ratio TE.sub.G and wherein the transverse volume voids ratio TE.sub.Y is at least equal to 0.50 times and at most equal to 0.75 times the overall volume voids ratio TE.sub.G.

4. 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 We 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 middle portion and each lateral portion having a middle volume voids ratio TE.sub.C and a lateral volume voids ratio TE.sub.S, respectively, the middle volume voids ratio TE.sub.C being equal to the ratio between the total volume V.sub.DC of the cuts in the middle portion and the sum of the total volume V.sub.DC of the cuts in the middle portion and of the total volume V.sub.RC of the elements in relief of the middle portion which are delimited by these cuts, the lateral volume voids ratio TE.sub.S being equal to the ratio between the total volume V.sub.DS of the cuts in the lateral portion and the sum of the total volume V.sub.DS of the cuts in the lateral portion and of the total volume V.sub.RS of the elements in relief of the lateral portion which are delimited by these cuts, wherein the middle volume voids ratio TE.sub.C is at least equal to 8% and at most equal to 13% and wherein the lateral volume voids ratio TE.sub.S is at least equal to 19% and at most equal to 25%.

5. The tire for a heavy-duty vehicle of civil engineering type according to claim 1: 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 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 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 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 25% of the axial width W.sub.T of the tread.

6. The tire for a heavy-duty vehicle of civil engineering type according to claim 5, wherein the ratio W/H is at most equal to 0.15.

7. The tire for a heavy-duty vehicle of civil engineering type according to claim 5, wherein the axial distance L.sub.E is at least equal to 30%, of the axial width W.sub.T of the tread.

8. The tire for a heavy-duty vehicle of civil engineering type according to claim 5, wherein the axial distance L.sub.E is at most equal to 40% of the axial width W.sub.T of the tread.

9. The tire for a heavy-duty vehicle of civil engineering type according to claim 5, 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.

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

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

12. 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 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 the said transverse sipes and of circumferential length B1 equal to the mean distance between two consecutive transverse sipes, wherein for all the elements in relief delimited by two consecutive transverse sipes of the middle portion, the ratio H1/B1 is at least equal to 0.5 and at most equal to 2.5.

13. 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 at least a lateral portion comprises transverse cuts, of transverse sipe or transverse groove type, opening on one side into a circumferential groove and on the other side into an axial end of the tread, these 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 transverse cuts, wherein, for all the elements in relief delimited by two consecutive transverse cuts of at least one lateral portion, the ratio H2/B2 is at least equal to 0.5 and at most equal to 2.5.

14. The tire for a heavy-duty vehicle of civil engineering type according to claim 13, wherein at least one lateral portion comprises an alternation of said transverse sipes and of said transverse grooves such that any element in relief is delimited by a transverse sipe and a transverse groove which are consecutive.

15. The tire for a heavy-duty vehicle of civil engineering type according to claim 1, wherein facing walls of the transverse sipes extend radially in a non-linear manner.

16. The tire for a heavy-duty vehicle of civil engineering type according to claim 15, wherein the facing walls of the transverse sipes extend radially in a zig-zag pattern.

17. The tire for a heavy-duty vehicle of civil engineering type according to claim 1, wherein each transverse groove forms an angle of at least equal to 45° with the circumferential direction.

18. The tire for a heavy-duty vehicle of civil engineering type according to claim 1, wherein the transverse sipes have a constant circumferential width across their axial length, and wherein the axial length of each transverse sipe is measured between two respective circumferential grooves.

19. 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 cuts distributed, in a circumferential direction of the tire, among circumferential grooves and, in an axial direction of the tire, transverse sipes and transverse grooves, wherein the transverse grooves have a constant circumferential width across their axial length, the cuts delimiting elements in relief, each cut being delimited by two faces facing one another and each said face the tread surface along an edge corner, wherein the two faces forming each respective transverse groove are planar, the tread having a longitudinal edge corners ratio TA.sub.X and a transverse edge corners ratio TA.sub.Y, the longitudinal edge corners ratio TA.sub.X being equal to the ratio L.sub.X/S between the sum L.sub.X of the projections, onto the circumferential direction, of the effective edge corner lengths, contained in an elementary tread surface portion of surface area S, and the surface area S, the transverse edge corners ratio TA.sub.Y being equal to the ratio L.sub.Y/S between the sum L.sub.Y of the projections, onto the axial direction, of the effective edge corner lengths, contained in an elementary tread surface portion of surface area S, and the surface area S, wherein at least one of: the longitudinal edge corners ratio TA.sub.X is at least equal to 8 m.sup.−1 and the sum of the longitudinal edge corners ratio TA.sub.X and of the transverse edge corners ratio TA.sub.Y is at least equal to 12 m.sup.−1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The features of the invention are illustrated by the schematic drawings which are not drawn to scale.

(2) FIG. 1A: a view from above 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 AA, of a tread of a tire according to an embodiment of the invention.

(4) FIG. 1C: a view in circumferential section, on a circumferential plane BB, of a tread of a tire according to an embodiment of the invention;

(5) FIG. 2A: a plan view of a tread of a tire according to a preferred embodiment of the circumferential grooves;

(6) FIG. 2B: a view in meridian section, on a meridian plane YZ, of a tread of a tire according to one preferred embodiment of the circumferential grooves;

(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 view in circumferential section, on a circumferential plane AA, of a middle part of a tread of a tire according to one preferred embodiment of the transverse cuts;

(9) FIG. 3C: a view in circumferential section, on a circumferential plane BB, of a lateral part of a tread of a tire according to one preferred embodiment of the transverse cuts;

(10) FIG. 4A: the range of the respectively longitudinal TA.sub.X and transverse TA.sub.Y edge corners ratios for a tread according to an embodiment of the invention;

(11) FIG. 4B: the range of the respectively longitudinal TE.sub.X and transverse TE.sub.Y volume voids ratios for a tread according to an embodiment of the invention;

(12) FIG. 4C: the range of the respectively middle TE.sub.C and lateral TE.sub.S volume voids ratios for a tread according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(13) 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 comprises cuts (3, 4, 5) distributed, in a circumferential direction XX′ of the tire, as 5 circumferential grooves 3, in the scenario depicted, and, in an axial direction YY′ of the tire, as transverse sipes 4 and transverse grooves 5. The cuts (3, 4, 5) delimit elements in relief 6. The tread 2 has a longitudinal edge corners ratio TA.sub.X equal to the ratio L.sub.X/S between the sum L.sub.X of the projections, onto the circumferential direction XX′, of the effective edge corner lengths, contained in an elementary tread surface portion of surface area S, and the surface area S, and a transverse edge corners ratio TA.sub.Y equal to the ratio L.sub.Y/S between the sum L.sub.Y of the projections, onto the axial direction YY′, of the effective edge corner lengths, contained in an elementary tread surface portion of surface area S, and the surface area S. It is usually conceded that, for a given cut comprising two edge corners, only one edge corner is effective under the envisaged stress loading. Thus, half the number of edge corners is taken into consideration when determining the sum of the effective edge corner lengths, in projection onto the circumferential direction XX′ or onto the axial direction YY′. According to the invention, the longitudinal edge corners ratio TA.sub.X is at least equal to 4 m.sup.−1 and the transverse edge corners ratio TA.sub.Y is at least equal to 6 m.sup.−1.

(14) FIG. 1B is a view in meridian section, on a meridian plane AA, of a tread 2 of a tire 1 according to the invention, having an axial width W.sub.T and a radial thickness H.sub.T. It depicts in particular the meridian profiles of the cuts of circumferential groove type 3. Each circumferential groove 3 is delimited by two faces (31, 32) facing one another. Each face (31, 32) intersects the tread surface (21) along an edge corner (311, 321).

(15) FIG. 1C is a view in circumferential section, on a circumferential plane BB, of a tread 2 of a tire 1 according to the invention. It depicts in particular, in circumferential section, the circumferential profiles of the transverse cuts of transverse sipe type 4 and transverse groove type 5. Each transverse sipe 4 is delimited by two faces (41, 42) facing one another, each face (41, 42) intersecting the tread surface (21) along an edge corner (411, 421). In the case presented, the transverse sipes 4 have a complex profile of wavy type, in the radial direction ZZ′, which encourages the sipes to close, as the tread enters the contact patch, with a self-locking effect. Each transverse groove 5 is delimited by two faces (51, 52) facing one another, each face (51, 52) intersecting the tread surface (21) along an edge corner (511, 521). In the case presented, the transverse grooves 5 have a rectilinear profile, in the radial direction ZZ′, the width of which ensures that the groove 5 will not close, namely that its faces (511, 521) will not come into contact as the tread enters the contact patch.

(16) FIG. 2A is a plan view of a tread 2 of a tire 1 according to a preferred embodiment of the circumferential grooves. 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 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 this first embodiment of 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 25% of the axial width W.sub.T of the tread.

(17) FIG. 2B is a view in meridian section, in a meridian plane YZ of a tread 2 of a tire 1 according to a preferred embodiment of the circumferential grooves. This FIG. 2B 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 (31, 32), radially toward the inside from the tread surface 21 as far as a bottom face 33 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 (31, 32) and a radial depth H, measured between the tread surface 21 and the bottom face 33. 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 33 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.

(18) FIG. 3A depicts a plan view of a tread of a tire according to a preferred embodiment of 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 4 opening into the circumferential grooves 3. As shown in FIG. 3B, in circumferential section CC, these transverse sipes 4 of the middle portion 22 have a radial depth H1 at least equal to 70% of the radial thickness H.sub.T and delimit elements in relief 6 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 4. For all the elements in relief 6 delimited by two consecutive transverse sipes 4 of the middle portion 22, the ratio H1/B1 is at least equal to 0.5 and at most equal to 2.5.

(19) In the embodiment depicted in FIG. 3A, the tread 2 is such that each lateral portion (23, 24) comprises an alternation of transverse sipes 4 and transverse grooves 5 opening on one side into a circumferential groove 3 and on the other side into an axial end of the tread 2. As shown in FIG. 3C, in circumferential section BB, a transverse sipe 4 and a transverse groove 5 which are consecutive both have a radial depth H2 at least equal to 70% of the radial thickness H.sub.T and delimit an element in relief 6 of a height equal to the radial depth H2 of the said transverse sipe and groove (4, 5), and of circumferential length B2 equal to the mean distance between a transverse sipe 4 and a transverse groove 5 which are consecutive. For all the elements in relief 6 delimited by a transverse sipe 4 and a transverse groove 5 which are consecutive in each lateral portion (23, 24) the ratio H2/B2 is at least equal to 0.5 and at most equal to 2.5.

(20) FIG. 4A depicts the range of the longitudinal edge corners ratio TA.sub.X as a function of the transverse edge corners ratio TA.sub.Y for a tread according to the invention, characterized by a longitudinal edge corners ratio TA.sub.X at least equal to 4 m.sup.−1 and a transverse edge corners ratio TA.sub.Y at least equal to 6 m.sup.−1. According to a first preferred embodiment, the transverse edge corners ratio TA.sub.Y is at least equal to 8 m.sup.−1, preferably at least equal to 10 m.sup.−1. According to a second preferred embodiment, the sum of the longitudinal edge corners ratio TA.sub.X and of the transverse edge corners ratio TA.sub.Y is at least equal to 12 m.sup.−1.

(21) FIG. 4B depicts the range of the ratio between the longitudinal voids ratio TE.sub.X and the overall volume voids ratio TE.sub.G as a function of the overall volume voids ratio TE.sub.G, for a tire I according to the invention and for 3 tires R1, R2 and R3 of the prior art taken as reference. A tread according to the invention is characterized by a longitudinal volume voids ratio TE.sub.X is at least equal to 0.25 times and at most equal to 0.50 times the overall volume voids ratio TE.sub.G and an overall volume voids ratio TE.sub.G at least equal to 8% and at most equal to 15%. Remember that the overall volume voids ratio TE.sub.G is the sum of the longitudinal volume voids ratio TE.sub.X for the circumferential direction XX, and of the transverse volume voids ratio TE.sub.Y for the axial direction YY′.

(22) FIG. 4C depicts the range of the middle volume voids ratio TE.sub.C as a function of the lateral volume voids ratio TE.sub.S for a tread according to the invention, characterized by a middle volume voids ratio TE.sub.C at least equal to 8% and at most equal to 13% and a lateral volume voids ratio TE.sub.S at least equal to 19% and at most equal to 25%.

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

(24) The characteristics of the tread for these tires according to the invention and for a tire of the prior art taken as reference, are presented in Table 1 below:

(25) 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.

(26) TABLE-US-00001 TABLE 1 Tire size 40.00R57 XDR2 Michelin 59/ (Reference) 40.00R57 80R63 Axial width W.sub.T (mm) 1000 1000 1200 Radial thickness H.sub.T (mm) 102 108 70 Width of middle zone W.sub.C (mm) 600 725 883 Longitudinal edge corners ratio 3.9 6.6 4.2 TA.sub.X (m.sup.−1) Transverse edge corners ratio 2.9 13.5 8.9 TA.sub.Y (m.sup.−1) Overall volume voids ratio TE.sub.G (%) 19.5 13 14.8 Longitudinal volume voids ratio 2.9 4.2 4.6 TE.sub.X (%) Transverse volume voids ratio 16.6 8.8 10.2 TE.sub.Y (%) Middle volume voids ratio TE.sub.C (%) 15.6 10 11.8 Lateral volume voids ratio TE.sub.S (%) 25.5 21 23.6