CIVIL ENGINEERING VEHICLE TIRE WITH IMPROVED ENDURANCE

Abstract

The tire has a crown part with sidewalls that end in beads. The crown part has a tread and a crown reinforcement. The crown reinforcement has protective, working and additional reinforcements. The protective reinforcement has a protective layer with elastic metal reinforcers which form an angle at least equal to 10. The working reinforcement has working layers with crossed metal reinforcers and forming, with the circumferential direction, an angle at most equal to 60. The additional reinforcement has a layer with an axial width at most equal to 0.9 times the shortest of the axial widths of the working layers and comprising metal reinforcers which form an angle at most equal to 25. A tread pattern design of the tread has circumferentially oriented grooves. The mean axial distance between the two grooves closest to the equatorial midplane is greater than the maximum axial width of the additional reinforcement.

Claims

1. A tire for a heavy vehicle of civil engineering type, comprising: a crown part extended on each side by sidewalls, the sidewalls ending in beads, a carcass reinforcement extending into the crown part, the sidewalls and the beads, the crown part comprising a tread having a wearing thickness and a crown reinforcement, the crown reinforcement being situated radially between the tread and the carcass reinforcement, the crown reinforcement comprising a protective reinforcement, a working reinforcement and an additional reinforcement, the protective reinforcement comprising at least one protective layer comprising elastic metal reinforcers which form, with the circumferential direction, an angle at least equal to 10, the working reinforcement comprising at least two working layers having a respective axial width and comprising inelastic metal reinforcers crossed from one working layer to the next and forming, with the circumferential direction, an angle at most equal to 60, the additional reinforcement, centered axially on the equatorial midplane of the tire, comprising at least one layer having an axial width at most equal to 0.9 times the shortest of the axial widths of the at least two working layers and comprising metal reinforcers which form, with the circumferential direction, an angle at most equal to 25, the tread being provided with a tread pattern design comprising at least one circumferentially oriented groove on each side of the equatorial midplane, the two circumferential grooves closest to the equatorial midplane delimiting a central region having a width equal to the mean distance between the said circumferential grooves, the central region being provided with a plurality of grooves of oblique or transverse orientation so as to form a plurality of blocks, wherein the number of blocks in the central region over the entire periphery is at least equal to 42, and wherein the mean axial distance between the two circumferential grooves closest to the equatorial midplane is greater than the maximum axial width of the additional reinforcement, the maximum axial width being measured between the ends of the layers of this additional reinforcement that are axially furthest from the equatorial midplane, the axial ends of this additional reinforcement being offset axially towards the inside with respect to the said two circumferential grooves.

2. The tire for a heavy vehicle of civil engineering type as set forth in claim 1, wherein the mean depth of the circumferential grooves is comprised between 65% and 80% of the wearing thickness of material.

3. The tire for a heavy vehicle of civil engineering tire as set forth in claim 1, wherein the mean axial distance between the two grooves closest to the equatorial midplane is at least equal to 1.1 times the axial width of the additional reinforcement.

4. The tire for a heavy vehicle of civil engineering tire as set forth in claim 3, wherein the mean axial distance between the two grooves closest to the equatorial midplane is at least 1.5 times the axial width of the additional reinforcement and at most 2.1 times.

5. The tire for a heavy vehicle of civil engineering type as set forth in claim 1, wherein a circumferential groove is also positioned on the midplane in order to split the central region into two halves.

6. The tire for a heavy vehicle of civil engineering type as set forth in claim 1, wherein the additional reinforcement comprises at least two layers.

7. The tire for a heavy vehicle of civil engineering type as set forth in claim 6, wherein the metal reinforcers of at least one layer of the additional reinforcement are inelastic.

8. The tire for a heavy vehicle of civil engineering type as set forth in claim 7, wherein the metal reinforcers of at least one layer of the additional reinforcement are elastic.

9. The tire for a heavy vehicle of civil engineering type as set forth in claim 1, wherein the elastic metal reinforcers of each protective layer preferably form, with the circumferential direction, an angle at least equal to 15 and at most equal to 40.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0060] FIG. 1 shows a surface view of one alternative form of tire according to the disclosure;

[0061] FIG. 2 shows a cross section through the tire depicted in FIG. 1.

[0062] This tire 1 is of size 50/80 R 57. It comprises a crown part comprising radially on the outside a tread 2 a surface of which constitutes a tread surface 20 intended to come into contact with the ground during running. This crown part is extended on each side by sidewalls 3, these sidewalls each ending in a bead (not depicted here) intended to come into contact with a mounting rim.

[0063] As may be seen in FIG. 2, this tire structure is reinforced, working from the crown part towards each bead, by a carcass reinforcement 4 formed in this instance of a reinforcing layer made up of a plurality of metal cords anchored at their ends to circumferential reinforcements arranged in each bead.

[0064] The crown part of this tire comprises a reinforcing structure comprising a working reinforcement 5 surmounted by a protective reinforcement 6 and by an additional reinforcement 7 between the working reinforcement 5 and the carcass reinforcement 4.

[0065] The working reinforcement 5 is formed of two working layers:

[0066] a first working layer 51 of width equal to 802 mm, this first working layer being made up of cords consisting of the assembly of 77 threads each 0.35 mm in diameter, each cord having a tensile breaking strength equal to 1900 daN; the cords of this layer make an angle close to 33 degrees with the circumferential direction;

[0067] a second working layer 52 formed with the same cords as the first working layer, these cords being laid at a mean angle equal to 19 degrees, these cords crossing the cords of the first working layer; the axial width of this layer is equal to 711 mm;

[0068] The working reinforcement 5 is surmounted radially on the outside by a protective reinforcement 6 made up of two layers referred to as protective layers, each protective layer being made up of a plurality of elastic cords formed, in the case of the layer 61 radially in contact with the second working layer 52, by the assembly of 24 threads measuring 0.26 mm in diameter and, in the case of the second protective layer 62, of cords referred to as elastic cords formed by the assembly of 52 threads measuring 0.26 mm in diameter; the cords of each protective layer are laid to make a mean angle equal to 24 degrees. The innermost protective layer 61 has a width equal to 939 mm whereas the outermost protective layer 62 has a width equal to 666 mm.

[0069] Finally, the working reinforcement 5 radially surmounts a limiting block 7 forming an additional reinforcement and consisting of a stack in the radial direction of two additional layers the metal reinforcers of which are not very extensible, namely are inelastic, and form, with the circumferential direction (perpendicular to the plane of the figure) angles that are opposite from one layer to the other and at most equal to half the smallest angle of the working layers and, in this instance, equal to 8 degrees. This limiting block 7 comprises a first layer 71 of axial width equal to 451 mm and radially on the outside of this first layer a second layer 72 of axial width equal to 380 mm. The cords that make up these layers 71, 72 are identical to those of the working layers 51, 52. This limiting block 7 is centered on the equatorial midplane (line XX in the plane of the figure) of the tire as are the other working and protective layers.

[0070] The tread of this tire has a width W and is provided with a tread pattern design as can be seen in FIG. 1 which shows a view of the tread surface of this tread. The tread pattern comprises three main grooves 8, 9, 10 of circumferential overall orientation making a complete circuit of the tire. The main groove 9 in the equatorial midplane XX has a width on the tread surface when new equal to 10 mm and a mean depth equal to 89 mm. The other two main grooves 8 and 10 on each side of the equatorial midplane have mean widths equal to 12 mm and mean depths equal to 70 mm.

[0071] Each main groove 8, 10 closest to the equatorial midplane XX is situated at a distance equal to 275 mm away from this equatorial midplane (this distance being measured between the midplane and a plane that divides each main groove into two equal parts). The two grooves 8 and 10 closest to the equatorial midplane delimit a central region in which there are formed several cuts oriented obliquely with respect to the transverse direction, these obliquely oriented grooves delimiting with the circumferential grooves a plurality of blocks of material in this central region. Over the entirety of the periphery of the tire the number of these blocks is, in this instance, equal to 42 (there are therefore two rows of 42 blocks because of the presence of a circumferential groove in the equatorial midplane). Another advantageous value for the number of blocks is 49 or even more.

[0072] The mean axial distance between the two axially outermost grooves is in this instance equal to 550 mm (this distance is measured between planes dividing each groove into two equal halves).

[0073] Thanks to this arrangement that combines both a high number of oblique grooves in the central region and the position of the ends of the layers of the limiting block 7 with respect to the circumferential main grooves, it is possible to improve the impact resistance and resistance to repeated bending of the crown part when running over ground covered with aggressive bodies, without thereby losing efficiency.

[0074] In the case of a very wide tread (which means to say one with a tread value greater than 900 mm, for example equal to at least 1040 mm), it is judicious to plan for the presence of four main grooves of circumferential overall orientation, two main grooves being located one on each side of the equatorial midplane. In this case, the position of the ends of the layers forming the limiting block is then determined so that these ends are situated between the main grooves closest to the equatorial midplane and on each side of this plane.

[0075] The disclosure described in connection with an example must not be restricted to this example alone and various modifications may be made thereto without departing from the scope as defined by the claims.