Siped tread for off-road tire

Abstract

Tread (10) for a tire of an off-road vehicle. Total width Wt of the tread is greater than 600 mm and has at least three circumferential main grooves (1, 2, 3, 4) at least 60 mm deep that divide the tread into intermediate ribs (51, 52, 53) and edge ribs (8). The edge ribs have a width≤0.25 Wt. At least one of the intermediate ribs (51, 52, 53) has fine grooves (61, 62, 63) of depth H1 delimiting blades of material (71, 72, 73) of mean width B1<2H1. Grooves (61, 62, 63) are oriented in the axial direction of the tire. Each intermediate rib (51, 52, 53) has a mean width≤0.25 Wt and ≥0.75 Ht (thickness of material to be worn away). Grooves, (61, 62, 63) have, over a height H12 at least equal to 65% of H1, a width≤ to the value obtained from 0.04√{square root over (B1.Math.H1)}.

Claims

1. A tread for a tire of an off-road vehicle carrying heavy loads, the tread having a total width Wt greater than 600 mm and a thickness Ht of material to be worn away, the tread having at least three main grooves of circumferential overall orientation and with a depth at least equal to 60 mm, said main grooves dividing the tread into intermediate ribs and edge ribs, the edge ribs axially bounding the tread and having a width at most equal to one quarter of the total width Wt of the tread, at least one of the intermediate ribs having a plurality of fine grooves; each said fine groove opens into a main groove and has a depth H1, said fine grooves, with the main grooves, delimiting blades of material of mean width B1 less than twice the depth H1, said fine grooves being oriented in the transverse direction corresponding to the axial direction of the tire or in an oblique direction, namely with an orientation that makes an angle at most equal to 45 degrees with the transverse or axial direction of the tire, wherein each said intermediate rib has a mean width at most equal to one quarter of the total width Wt of the tread and at least equal to 0.75 times the thickness Ht of material to be worn away, and wherein the fine grooves have, over a height H12 at least equal to 65% of their total depth H1, a width which is at most equal to the value obtained from the following mathematical expression: 0.04√{square root over (B1.Math.H1)} and have, over a height H11 radially outer from the radially outermost portion having the height H12, a wider part, wherein each edge rib comprises alternating wide grooves and fine grooves, each oriented in the transverse direction, and wherein all of the at least one of the intermediate ribs having the plurality of fine grooves has exclusively fine grooves, said fine grooves being rectilinear grooves.

2. The tread according to claim 1, wherein the angle of the fine grooves is at most equal to 20 degrees with respect to the transverse direction.

3. The tread according to claim 1, wherein the intermediate ribs provided with fine grooves are such that a circumferential length B1 between two said fine grooves is at most equal to the depth H1 and at least equal to 0.4 times this same depth H1.

4. The tread according to claim 1, wherein each said circumferential main groove has a width at least equal to 6% of its depth so as to be able to close up when it enters the contact patch in which it is in contact with the ground and generate contact pressures between the opposing walls.

5. The tread according to claim 4, wherein each said circumferential main groove has a width at most equal to 15% of its depth.

6. The tread according to claim 1, wherein the depth H1 of the fine grooves is equal to the depth of the circumferential main grooves.

7. The tread according to claim 1, wherein at least one of said intermediate ribs has no fine groove.

8. The tread according to claim 1, wherein at least one of said intermediate ribs is provided with wide grooves oriented transversely or obliquely.

9. The tread according to claim 1, wherein all of the intermediate ribs are provided with fine grooves.

10. A tread for a tire of an off-road vehicle carrying heavy loads, the tread having a total width Wt greater than 600 mm and a thickness Ht of material to be worn away, the tread having at least three main grooves of circumferential overall orientation and with a depth at least equal to 60 mm, said main grooves dividing the tread into intermediate ribs and edge ribs, the edge ribs axially bounding the tread and having a width at most equal to one quarter of the total width Wt of the tread, at least one of the intermediate ribs having a plurality of fine grooves; each said fine groove opens into a main groove and has a depth H1, said fine grooves, with the main grooves, delimiting blades of material of mean width B1 less than twice the depth H1, said fine grooves being oriented in the transverse direction corresponding to the axial direction of the tire or in an oblique direction, namely with an orientation that makes an angle at most equal to 45 degrees with the transverse or axial direction of the tire, wherein each said intermediate rib has a mean width at most equal to one quarter of the total width Wt of the tread and at least equal to 0.75 times the thickness Ht of material to be worn away, and wherein the fine grooves have, over a height H12 at least equal to 65% of their total depth H1, a width which is at most equal to the value obtained from the following mathematical expression: 0.04√{square root over (B1.Math.H1)} and have, over a height H11 radially outer from the radially outermost portion having the height H12, a wider part, wherein each edge rib comprises alternating wide grooves and fine grooves, each oriented in the transverse direction, wherein all of the at least one of the intermediate ribs having the plurality of fine grooves has exclusively fine grooves, and wherein the alternating wide grooves and narrow fine grooves on the edge ribs each have a mean depth H2, and respectively delimit blocks of mean block width B2, the mean depth H2 being less than 1.2 times the mean block width B2, each said fine groove having a mean width which is less than the value of the expression: 0.04√{square root over (B2.Math.H2)}.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows a partial view of the tread surface of a tread of a tire according to the invention;

(2) FIG. 2 shows a cross section, in a radial plane, of the tread shown in FIG. 1;

(3) FIG. 3 shows a partial view of the tread surface of a tread according to another alternative form of the invention, which has undergone testing;

(4) FIG. 4 shows a view in section on a plane of which the line in FIG. 3 is indicated by the line IV-IV;

(5) FIG. 5 shows a view in section on a plane of which the line in FIG. 3 is indicated by the line V-V.

DETAILED DESCRIPTION OF THE FIGURES

(6) To make the figures easier to understand, identical reference signs have been used in the description of alternative forms of embodiment of the invention where these reference signs refer to elements of the same kind, whether in terms of structure or function.

(7) Of course, the figures serve to support the description without, however, claiming to show the alternative forms of embodiment to any particular scale.

(8) FIG. 1 shows a partial view of a tread 10 of a tire according to the invention intended in a first phase to be fitted to the front axle of an off-road vehicle of the “dumper” type, in order to carry very heavy loads and then in a second phase to be fitted to the rear axle of a similar vehicle. This radial tire of size 40.00 R 57 comprises a tread 10 intended to make the connection between the tire and the ground on which the vehicle is running.

(9) This tread 10 has a total width W greater than 600 mm and has a tread surface 100 intended to come into contact with the ground. This tread has a total thickness Ht of material to be worn away, which is at least equal to 60 mm.

(10) This tread 10 comprises four circumferential main grooves 1, 2, 3, 4 of mean width at least equal to 6 mm on the tread surface of the tire when new and of a depth at most equal to the thickness of material to be worn away.

(11) These circumferential main grooves 1, 2, 3, 4 are arranged symmetrically with respect to the equatorial median plane identified by the line XX′ in FIG. 1.

(12) These four main grooves 1, 2, 3, 4 delimit three intermediate ribs 51, 52, 53 and two edge ribs 8 axially delineating the tread.

(13) The three intermediate ribs have the same width which is less than one quarter of the total width of the tread. Each of these three ribs is provided with a plurality of fine grooves, respectively 61, 62, 63, these fine grooves being oriented in the transverse direction perpendicular to the circumferential direction and therefore parallel to the direction of the axis of rotation of the tire provided with this tread. Each fine transverse groove 61, 62, 63 opens on each side into a circumferential main groove. Furthermore, these transverse fine grooves are offset from one another in the circumferential direction from one row to another.

(14) These fine transverse grooves 61, 62, 63 with the circumferential main grooves delimit, within each circumferential row 51, 52, 53, a plurality of material elements or blades 71, 72, 73 respectively, the mean height of which corresponds to the mean depth H1 of the said fine grooves.

(15) Furthermore, the width of intermediate ribs provided with fine grooves is at least equal to 0.75 times of the thickness of material to be worn away Ht.

(16) The width B1 is defined as being less than the depth H1 of the fine grooves. In this alternative form of embodiment, the widths of the fine grooves have widths at most equal to the value of the mathematical expression: 0.04√{square root over (B1.Math.H1)}.

(17) Axially on the outside the edge ribs are circumferentially continuous and have no grooves.

(18) In FIG. 2, which shows a partial view in cross section on a radial plane, this section being indicated by its line II-II in FIG. 1, the distribution of the fine grooves 63 formed in the circumferential rib 53 can be seen.

(19) These fine grooves 63 delimit, with the main grooves 3 and 4, a plurality of material elements 73 having a height equal to the depth H1 of the sipes and a circumferential length B1 on the tread surface 100. In the alternative form described, the other fine transverse grooves 61, 62 have the same dimensional characteristics, although of course a person skilled in the art may create variations on these characteristics according to the desired objective.

(20) Under conditions of use it is found that the fine grooves partially close up when they enter the contact patch in which they are in contact with the ground; contact between the facing walls of the fine grooves affects approximately at least 65% of the surface area of the said walls (which means to say that there is contact over at least 65%).

(21) FIG. 3 shows another alternative form of tread according to the invention, which has undergone testing. This tread 10 for a radial tire of size 40.00 R 57 is intended in a first phase to be fitted to the front axle of an off-road vehicle of the “dumper” type, in order to carry very heavy loads and then in a second phase to be fitted to the rear axle of a similar vehicle.

(22) This tread has a total width Wt equal to 999 mm and is intended to come into contact with the ground via a tread surface 100 during running.

(23) This tread 10 comprises five circumferential main grooves 1, 2, 3, 4, 5 of mean width equal to 8 mm with the exception of the groove in the central position, which has a mean width equal to 10 mm when new. These main grooves have a depth equal to 102 mm with the exception of the axially outermost main grooves which have a depth equal to 108 mm. These main grooves have widths suited both to closing up and generating contact pressures between their facing walls when they enter the contact patch, while at the same time allowing sufficient dissipation of heat when not in the contact patch.

(24) These circumferential main grooves 1, 2, 3, 4, 5 generate four intermediate ribs and two edge ribs, these edge ribs axially delineating the tread in the width direction. The edge ribs have a mean width equal to 135 mm whereas the intermediate ribs have a mean width equal to 172 mm in the case of those closest to the edge ribs and 174 mm in the case of the ribs closest to the equatorial median plane, of which the line in the figure is indicated by the line XX′.

(25) Each intermediate rib is provided with a plurality of fine grooves 2.5 mm in width, extending into the thickness of the tread over a height H1. These small-width fine grooves are oriented obliquely, which means to say in a direction that makes an angle of 15 degrees to the axis of rotation of the tire. These fine grooves together with the circumferential main grooves delimit a plurality of blades of material of which the mean width B1 measured in the circumferential direction is equal to the mean height of the blades. This mean height corresponds to the mean depth of said fine grooves.

(26) In this alternative form, all the intermediate ribs are divided up in the same way into material elements the circumferential width B1 of which is equal to 60 mm and the height H1 of which is equal to 101 mm.

(27) As can be seen in FIG. 5 which shows a cross section on a plane the line of which is along the line V-V in FIG. 3, the fine grooves comprise a part of height H12 equal to 71 mm over which their width is 2.5 mm, and to complement that, a wider part of height H11 equal to 30 mm. Over this wider part near the tread surface when new, the width does not satisfy the relationship 0.04√{square root over (B1.Math.H1)}

(28) In the alternative form described, all the material blades of an intermediate rib have the same circumferential length B1 and the same is true of the other intermediate ribs. Of course the invention described here encompasses alternative forms in which the circumferential lengths B1 of the material blades may be different, whether this be on the one same rib or between different ribs, while at the same time satisfying the relationship imposed by the invention, namely that, for each intermediate rib, the width of the fine grooves is less than 0.04√{square root over (B1.Math.H1)}

(29) In this alternative form shown in FIG. 3, each edge rib is provided with a plurality of wide grooves of mean width 45 mm and having the same depth as the circumferential main grooves separating the edges of the intermediate grooves, namely 108 mm. Alternating with these wide grooves there is provision to have narrow grooves of width 2.5 mm. FIG. 4 shows a cross section on a plane of which the line in FIG. 3 is embodied by the line IV-IV.

(30) Thanks to this structure, the tire exhibits a wearing performance that is significantly improved both in a straight line and on cornering, while at the same time maintaining thermal and grip performance equivalent to the control tire, this being regardless of the state of wear of the tread.

(31) The invention which has been described with the aid of these two alternative forms is not intended to be limited to only these examples and various modifications can be made thereto without departing from the scope as defined by the claims.