Tire Tread for a Heavy Construction-Plant Vehicle

Abstract

A Tire tread with blocks for a heavy construction-plant vehicle, to improve the compromise between traction on muddy ground and lifetime in terms of wear on rough ground. A tread (1) has blocks (4), which are separated by cuts (3) and raised with respect to a bottom surface (5). Any block (4) have a contact face (41) having a polygonal shape of surface area SC, which is contained in a tread surface (2), lateral faces (42), and a base section (43) , which has a polygonal shape of surface area SB. The contact face (41) of any block (4) has a polygonal shape that is at least partially concave, wat least two consecutive sides (411, 412) that form between them an interior angle A1 of the polygonal shape that is greater than 180° and the surface area SC of the contact face (41) is at most equal to 0.9 times the surface area SB of the base section (43).

Claims

1. A tire tread for a heavy construction-plant vehicle, which tread is intended to come into contact with the ground via a tread surface and comprises cuts delimiting blocks that are raised with respect to a bottom surface, in a radial direction (ZZ′), any block being made up of at least one rubber-based material and having a radial height H, which is measured between a contact face, contained in the tread surface, and the bottom surface, any block comprising lateral faces which connect the contact face to the bottom surface, and a base section, which is parallel to the bottom surface radially towards the outside at a radial distance H′ equal to 0.25*H, the contact face having a polygonal shape of surface area SC and perimeter PC, and the base section having a polygonal shape of surface area SB and perimeter PB, wherein the contact face of any block has a polygonal shape that is at least partially concave, comprising at least two consecutive sides that form between them an interior angle A1 of the polygonal shape that is greater than 180° and in that the surface area SC of the contact face is at most equal to 0.9 times the surface area SB of the base section.

2. The tread according to claim 1, wherein the contact face of any block has a polygonal shape that is at least partially concave, comprising at least three pairs of two consecutive sides that form between them an interior angle (A1, A2, A3) of the polygonal shape that is greater than 180°.

3. The tread according to claim 1, wherein the surface area SC of the contact face is at least equal to 0.6 times the surface area SB of the base section.

4. The tread according to claim 1, wherein the base section of any block has a convex polygonal shape.

5. The tread according to claim 1, wherein the base section of any block has a convex polygonal shape comprising at least six sides.

6. The tread according to claim 1, wherein the perimeter PC of the contact face is at least equal to the perimeter PB of the base section.

7. The tread according to claim 1, wherein any block comprises a succession of radial portions (4A, 4B) extending, in the radial direction (ZZ′), between the contact face and the bottom surface.

8. The tread according to claim 1, wherein any block comprises a first radial portion extending, in the radial direction (ZZ′), between the contact face and an intermediate section and a second radial portion (4B) extending, in the radial direction (ZZ′), between the intermediate section and the bottom surface.

9. The tread according to claim 7, wherein the first radial portion (4A) of the block extends, in the radial direction (ZZ′), over a radial height H1 at least equal to 0.1 times and at most equal to 0.6 times the radial height H of the block, and the second radial portion (4B) of the block extends, in the radial direction (ZZ′), over a radial height H2=H-H1.

10. The tread according to claim 1, the tread having a width W.sub.T and any block being inscribed in a cylindrical surface, which has a radial axis of revolution (Z1) and a circular section of diameter D in any plane perpendicular to the radial axis of revolution (Z1), wherein the circular section of the cylindrical surface in which the block is inscribed has a diameter D at least equal to 0.2 times and at most equal to 0.5 times the width W.sub.T of the tread.

11. The tread according to claim 1, the tread having a middle part (11) having a width W1 at least equal to 0.2 times and at most equal to 0.7 times the width W.sub.T of the tread, wherein a middle part of the tread comprises, in the transverse direction (XX′), at least one and at most four longitudinal rows of blocks.

12. The tread according to claim 11, a middle part of the tread having a surface void ratio TES, defined as the ratio between the voids surface area and the total surface area of said middle part, wherein the surface void ratio TES of the middle part of the tread is at least equal to 30% and at most equal to 50%.

13. The tread according to claim 11, the middle part of the tread having a volumetric void ratio TEV, defined as the ratio between the voids volume and the total volume of said middle part, wherein the volumetric void ratio TEV of the middle part of the tread is at least equal to 10% and at most equal to 30%.

14. A tire for a heavy construction-plant vehicle, which tire comprises a tread according to claim 1.

Description

[0036] The features of the invention are illustrated by the schematic FIGS. 1 to 4, which are not drawn to scale:

[0037] FIG. 1: Perspective view of a portion of a tread according to the invention,

[0038] FIG. 2: View from above of a portion of a tread according to the invention,

[0039] FIG. 3: Sectional view of a portion of a tread according to the invention, at the level of the base sections of the blocks,

[0040] FIG. 4: Perspective view of a block of a tread according to the invention.

[0041] FIG. 1 is a perspective view of a portion of a tread according to the invention. The tire tread 1 for a heavy construction-plant vehicle, which tread is intended to come into contact with the ground via a tread surface 2, comprises cuts 3 delimiting blocks 4 that are raised with respect to a bottom surface 5. Any block 4 comprises lateral faces 42, which connect the contact face 41 to the bottom surface 5, and a base section 43, which is parallel to the bottom surface 5.

[0042] FIG. 2 is a view from above of a portion of a tread according to the invention. As seen above, the tread 1, which tread is intended to come into contact with the ground via a tread surface 2, comprises cuts 3 delimiting blocks 4 that are raised with respect to a bottom surface 5, and any block 4 comprises lateral faces 42, which connect the contact face 41 to the bottom surface 5, and a base section 43, which is parallel to the bottom surface 5. The contact face 41 and the base section 43 respectively have a polygonal shape. In the embodiment shown, the contact face 41 of any block 4 has a polygonal shape that is at least partially concave, comprising three pairs of two consecutive sides ((411, 412); (421, 422); (431, 432)) that form between them an interior angle (A1, A2, A3) of the polygonal shape that is greater than 180°. In addition, the base section 43 of any block 4 has a convex polygonal shape comprising six sides. The tread thus shown has a tread pattern with what are known as tripod blocks.

[0043] FIG. 3 is a sectional view of a portion of a tread according to the invention, at the level of the base sections of the blocks, in which the middle part of the tread is detailed. The tread 1 has a middle part 11 having a width W1 at least equal to 0.2 times and at most equal to 0.7 times the width W.sub.T of the tread, preferably at least equal to 0.4 times and at most equal to 0.6 times the width W.sub.T of the tread. In the embodiment shown, the middle part 11 of the tread 1 comprises, in the transverse direction XX′, two rows 6 of blocks 4. Any block 4 is inscribed in a cylindrical surface 7, which has a radial axis of revolution Z1 and a circular section of diameter D in any plane perpendicular to the radial axis of revolution Z1. The circular section of the cylindrical surface 7 in which the block 4 is inscribed has a diameter D at least equal to 0.2 times and at most equal to 0.5 times the width W.sub.T of the tread.

[0044] FIG. 4 is a perspective view of a block of a tread according to the invention. The block 4, made up of a rubber-based material, has a radial height H, which is measured between a contact face 41, contained in the tread surface 2, and the bottom surface 5. The block 4 comprises lateral faces 42, which connect the contact face 41 to the bottom surface 5, and a base section 43, which is parallel to the bottom surface 5 radially towards the outside at a radial distance equal to 0.25*H. The base section 43 is connected to the bottom surface 5 by a connecting surface 45 of radius R. The contact face 41 of the block 4 has a polygonal shape that is at least partially concave, comprising three pairs of two consecutive sides ((411, 412); (421, 422); (431, 432)) that form between them an interior angle (A1, A2, A3) of the polygonal shape that is greater than 180°. The base section 43 of the block 4 has a convex polygonal shape comprising at least six sides. The block 4 also comprises a first radial portion 4 A extending, in the radial direction ZZ′, between the contact face 41 and an intermediate section 44, and a second radial portion 4B extending, in the radial direction ZZ′, between the intermediate section 44 and the bottom surface 5. The first radial portion 4A of the block 4 extends, in the radial direction 77′, over a radial height H1 at least equal to 0.1 times and at most equal to 0.6 times the radial height H of the block, and the second radial portion 4B of the block 4 extends, in the radial direction

[0045] ZZ′, over a radial height H2=H-H1.

[0046] The inventors have more particularly studied this invention for a tire of size 35/65 R 33 intended to be mounted on an underground mine dumper. According to the ETRTO standard, such a tire has to be capable of carrying a load equal to 29000 kg, when it is inflated to a pressure equal to 8 bar. The tire according to the invention performs better since it is capable of carrying a load equal to 31500 kg, when it is inflated to a pressure equal to 7 bar.

[0047] The inventors have compared, in the tire size 35/65 R 33, a tread according to the invention I, comprising blocks with a contact face with three concave parts and a hexagonal convex base section, and a reference tread R, comprising blocks with a contact face and a base section that are both convex and hexagonal.

[0048] Table 1 below shows the respective characteristics of the tread according to the invention I and of the reference tread R:

TABLE-US-00001 TABLE 1 Tread according to Reference Characteristics the invention I tread R Tread width W.sub.T 870 mm 870 mm Width of middle portion of tread W1 416 mm 416 mm Ratio W1/W.sub.T 48% 48% Surface void ratio TES of the middle 42.5%   34.5%   portion (new state) Volumetric void ratio TEV of the 20% 19.5%   middle portion (new state) Number of longitudinal rows of 2 2 blocks in the middle portion Radial block height H  67 mm  67 mm Radial height H1 of the first radial  11 mm — block portion Ratio H1/H 15% — Radial height H2 of the second  56 mm — radial block portion Surface area SC of the contact .sup. 326 mm.sup.2 .sup. 371 mm.sup.2 face of a block Perimeter PC of the contact 744 mm 714 mm surface of a block Surface area SB of the base .sup. 425 mm.sup.2 .sup. 425 mm.sup.2 section of a block Perimeter PB of the base .sup. 765 mm.sup.2 .sup. 765 mm.sup.2 section of a block Ratio SC/SB 76% 87% Ratio PC/PB 97% 93% Diameter D of the cylindrical 250 mm 250 mm envelope surface of a block Ratio D/W.sub.T 29% 29% Connecting radius R between the  20 mm  20 mm connecting surface of a block and the bottom surface

[0049] In this example, compared with the reference, the inventors thus reduced the surface area SC of the contact face of each block by 12%, increased the perimeter PC of the contact face of each block by 4%, and increased the surface void ratio TES by 8% for a substantially constant volumetric void ratio TEV (therefore for a constant volume of material), without reducing the surface area of the base section (therefore without reducing the robustness of the anchoring of the blocks). Consequently, the increase in pressure on the ground, due to the reduction in the surface area of the contact face of the block, leads to an improvement in the penetration into the ground, hence better traction on loose ground. The increase in the perimeter PC of the contact face of the block, and therefore in the cumulative length of edges, results in an improvement in grip on smooth ground. Finally, retaining the volume of material ensures that the lifetime in terms of wear and the robustness of the blocks are maintained compared with the reference.

[0050] The tread according to the invention, which was developed for a conventional tire subjected to an inflation pressure, can also be used for a non-pneumatic tire, but also for any non-pneumatic rolling assembly intended to be fitted to an all-terrain vehicle, such as for example a caterpillar track.