Tire tread comprising cutouts of different depths

Abstract

Tread (1) of a tire for an off-road vehicle, with total width (W) and total thickness of wearable material at least equal to 60 mm. The tread is delimited axially by shoulder regions (5) provided with grooves (7). This tread (1) comprises, in central region (6), narrow groove (61) and, between each shoulder region (5) and the central region (6), an intermediate region (4) in which there are formed a plurality of oblique or transverse narrow grooves (411, 412). Narrow groove (61) of the central part is made up of first narrow-groove parts (611) of depth (P1) and of second narrow-groove parts (612) of depth (P2). Depth (P1) is greater than depth (P2). Narrow grooves (411, 412) of one same intermediate region comprise, in the circumferential direction, an alternation of narrow grooves (411) of first depth (P11) and of narrow grooves (412) of second depth (P22).

Claims

1. A tread of a tire adapted to be fitted to an off-road vehicle, this tread having; a tread surface which is adapted to come into contact with the ground when the tire is running, a total width and a total thickness of wearable material at least equal to 60 mm, this tread being delimited axially by shoulder regions, each shoulder region having a width comprised between 15% and 35% of the total width of the tread and comprising a plurality of transverse or oblique grooves of depth (P), said shoulder-region grooves being arranged in the circumferential direction with a mean spacing, the tread further comprising a central region centered on the equatorial mid-plane and having a narrow groove that occupies the entire width of said central region, said narrow groove comprising an alternation of first narrow-groove parts and of second narrow-groove parts, said first and second narrow-groove parts being connected to each other by joining regions, a circumferential distance between two circumferentially adjacent joining regions within which a said first narrow groove part and a said second narrow groove part are received is equal to the mean spacing of the shoulder-region grooves, said tread comprising, between each said shoulder region and the central region, an intermediate region in which there are formed a plurality of oblique or transverse narrow grooves the mean orientation of which makes an angle at most equal to 60 degrees with the axial direction, each of said narrow grooves beginning in a joining region of the narrow groove of the central part and connecting into a transverse or oblique groove formed in one of the shoulders, wherein the narrow groove of the central part is comprised of first narrow-groove parts of depth (P1) and of second narrow-groove parts of depth (P2), the depth (P1) being greater than the depth (P2), said depths (P1, P2) being less than the depth (P) of the grooves in the shoulder regions, and wherein the narrow grooves of one same intermediate region comprise, in the circumferential direction, an alternation of said narrow grooves of a first depth (P11) and of narrow grooves of a second depth (P22), said depths (P11, P22) being less than the depth P of the grooves in the shoulder regions.

2. The tread according to claim 1, wherein the narrow groove of the central part comprises said first narrow groove parts of a first length and of depth (P1) and said second narrow groove parts of a second length and of depth (P2) less than the depth (P1), said second length being greater than the first length.

3. The tread according to claim 1, wherein each said shoulder region is separated from the intermediate region directly contiguous with it by a narrow groove of circumferential overall orientation.

4. The tread according to claim 1, wherein a narrow groove of circumferential overall orientation is formed between each said intermediate region and the central region.

5. The tread according to claim 1, wherein, in each intermediate region, the narrow grooves make a mean angle at most equal to 45 degrees with the axial direction.

6. The tread according to claim 1, wherein the difference between the as-new depths of the narrow grooves is at least equal to 15% and at most equal to 70% of the maximum depth of the grooves formed on the shoulder regions of the tread.

7. The tread according to claim 1, comprising a first material and a second material configured so that initially the first material is in contact with the ground and subsequently, after wear of the first material, the second material comes into contact with the ground.

8. The tread according to claim 7, wherein the first material comprises a first number of edge corners formed by the grooves configured for grip performance and thermal ventilation of the tread, and wherein the second material comprises a second number of edge corners formed by the grooves, wherein the second number of edge corners is less than the first number of edge corners.

9. The tread according to claim 7, wherein the second material is resistant to attack from objects present on the ground.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 depicts a partial view of the surface of a tread according to a first alternative form of the invention;

(2) FIG. 2 depicts a view in section on a plane perpendicular to the plane of FIG. 1, and the line of which is indicated by the line II-II;

(3) FIG. 3 shows a partial view of the surface of a tread according to the first alternative form of the invention, after partial wear;

(4) FIG. 4 shows a view of a second alternative form of embodiment of a tread according to the invention.

DETAILED DESCRIPTION OF THE FIGURES

(5) 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.

(6) FIG. 1 depicts a partial view of the tread surface 10 of a tread 1 when new according to a first alternative form of the invention. When new, this tread, which is intended to equip a tire with a diameter of 57 inches, has a wearable thickness of material equal to 100 mm and a total width W equal to 982 mm.

(7) According to this alternative form of a tread of a tire intended, initially, to be fitted to the front axle of a vehicle for off-road use, shoulder regions 5 can be discerned, these axially delimiting the tread, each shoulder region 5 having a width 220 mm being bordered by a narrow circumferential groove 2. In these shoulder regions 5 are formed a plurality of wide grooves 7 of width 50 mm and of depth P equal to 100 mm. These wide grooves 7 in the shoulder regions 5 are oriented transversely and arranged in the circumferential direction with a mean spacing D equal to 255 mm. These wide grooves 7, arranged with the same mean spacing on each shoulder 5, are circumferentially offset from one shoulder with respect to the other.

(8) A central region 6 is defined, this being centred on the equatorial mid-plane and delimited in the present alternative form of embodiment by narrow circumferential grooves 3 and 3′. This central region 6 has a width equal to the amplitude of the zigzag of a narrow groove 61 occupying the entire width of this central region. In the example described, this amplitude is equal to 96 mm. The narrow grooves have a width suited to allowing their opposing walls to come into contact with one another when in the contact patch.

(9) This narrow zigzag groove 61 is made up of an alternation of first narrow-groove parts 611 and second narrow-groove parts 612, these first and second narrow-groove parts being connected to one another by joining regions indicated by the letters A, B (the connecting regions A all being on the one same side of the equatorial mid-plane embodied by the line XX′ in FIG. 1, the joining regions B all being on the other side of the said plane).

(10) The circumferential distance L between two joining regions on the one same side of the equatorial mid-plane within which a first groove part 611 and a second groove part 612 can be found is equal to the mean spacing D of the transverse grooves 7 of the shoulder regions 5.

(11) An intermediate region 4 of a width substantially equal to the width of the shoulder parts 5 is formed between each shoulder region 5 and the central region 6. These intermediate parts comprise a plurality of oblique narrow grooves 41, which means to say grooves the mean orientation of which makes an angle here equal to 30 degrees with the axial direction YY′, each of these narrow grooves beginning in a joining region A or B of the narrow groove of the central part and connecting into a transverse or oblique groove formed on one of the shoulders.

(12) Furthermore, the narrow groove 61 of the central part is made up of first narrow-groove parts 611 having a depth P1 equal to 80 mm and of second narrow-groove parts 612 having a depth P2 equal to 60 mm. In this example, the first and second narrow-groove parts have the one same length.

(13) In this example, an alternation of narrow grooves 411 of a first depth P11 equal to the depth P1 of the first narrow-groove parts 611 of the central part and of narrow grooves 412 of a second depth P22 equal to the depth P2 of the second parts 612 of the groove 61 of the central part 6 is formed in each intermediate part 4.

(14) FIG. 2 shows a cross section in a plane of which the line is indicated in FIG. 1 by the line II-II.

(15) In this alternative form of embodiment, the presence of narrow grooves of different depths is combined with the presence of two materials M1, M2 superposed within the thickness of the tread. A first material M1, chosen because it has good wearing performance, is positioned radially on the outside so that it comes into contact with the ground when the tread is new; this first material extends into a depth equal to the depth P2 of the second narrow-groove parts 612 of the central part. Radially on the inside of this first material M1 is placed a second material M2 which is chosen for its good resistance to attack.

(16) In this preferred alternative form, the narrow groove parts of least depth P2, P22 disappear when the first material is fully worn away.

(17) As can be seen from FIG. 3 which shows the same tread after it has become partially worn and corresponding to the disappearance of the groove parts of least depth P2, the surface void ratio is reduced in comparison with the same ratio when new. In this configuration, in which only the narrow grooves 611, 411 that were initially the deepest remain, the tire can be fitted to a rear axle of a vehicle as the reduction in the number of narrow grooves in the central part and in the intermediate parts desensitizes the tread with respect to attack under engine torque, which attack is caused by foreign bodies present on the ground and over which the tire runs. Furthermore, the reduction in the volume of tread material appreciably reduces the level of heat during operation.

(18) In an alternative form of embodiment not illustrated here, the narrow circumferential grooves 2, 3 delimiting the intermediate parts and the central part may be omitted right from new or alternatively may have depths smaller than the depth of the grooves in the shoulder regions so that they disappear after a predetermined amount of partial wear.

(19) In another alternative form of embodiment of the invention, as shown in FIG. 4, the target is for the corner angles of the elements of material delimited by the narrow grooves to be at least equal to 90°, if not as close as possible to 90, so as to avoid weak spots when new.

(20) FIG. 4 shows a partial view of the tread surface 10 of a tread 1 when new according to a second alternative form of the invention.

(21) According to this alternative form of a tread of a tire intended, initially, to be fitted to the front axle of a vehicle for off-road use, shoulder regions 5 can be discerned, these axially delimiting the tread, each shoulder region 5 being bordered by a narrow circumferential groove 21 starting in wide cutouts 22 which themselves open onto oblique grooves 7. The oblique grooves 7 are circumferentially offset from one shoulder with respect to the other.

(22) A central region 6 centred on the equatorial mid-plane comprises a narrow groove 61 comprising two parts: a first part 611 of depth P1 and a second part 612 of depth P2, these parts being connected to one another by joining regions A and B. The depth P1 is greater than the depth P2.

(23) Furthermore, the length S1 of the groove part 611 is shorter than the length S2 of the groove part 612, while maintaining between two connecting regions AA or BB a length equal to the mean spacing of the transverse shoulder grooves. By virtue of that, it is possible to have corner angles alpha (α) and beta (β) which are close to or greater than 90° for the tips of the elements of material delimited by the narrow grooves 411, 412, 611, 612. The angle alpha (α) corresponds to the angle between a first groove part 611 of the central region 6 and a groove 411 or 412 of an intermediate region 4. The angle beta (β) corresponds to the angle between a first groove part 611 of the central region 6 and a second part 612 of the same central region 6.

(24) Thanks to this arrangement in the central part, the effect in the first phase of tread wear can also be accentuated while at the same time limiting the lengths of narrow grooves after partial wear.

(25) Furthermore, in this alternative form of embodiment, it is found that the volume void ratios of the shoulder regions and of the intermediate regions and central region differ greatly. In the shoulder regions, there is a volume void ratio when new of 20%, whereas across the rest of the tread (intermediate and central regions) the volume void ratio is equal to 6%.

(26) The invention described here is not intended to be limited to these two examples, and various modifications can be made thereto without departing from the scope as defined by the claims. In particular, the blocks may be bounded by narrow grooves that have curved geometries.