Tire for a heavy vehicle

Abstract

A tire for a heavy vehicle with a radial carcass reinforcement anchored in two beads by wrapping around bead wires. In a radial plane, radially on the inside of the radially innermost point of the at least one layer of carcass reinforcement and axially on the outside of the geometric center of the bead wire, the radius of curvature at a point on the exterior surface of the bead is greater than the radius of curvature at the point of orthogonal projection of the point of the exterior surface of the bead onto the at least one layer of carcass reinforcement.

Claims

1. A tire for a heavy vehicle with a radial carcass reinforcement comprising at least one layer of reinforcing elements, the tire comprising: a crown reinforcement radially capped by a tread, said tread being connected to two beads by two sidewalls, each of said two beads comprising a bead wire for anchoring said carcass reinforcement into said two beads by wrapping said at least one layer of reinforcing elements around said bead wires, wherein, in a radial plane, in a first region of the exterior surface of each of said two beads, with said first region being the entire area of the exterior surface of each of said two beads that is radially on the inside of the radially innermost point of said at least one layer of carcass reinforcement and axially on the outside of the geometric center of said bead wire, the radius of curvature at each point on said first region of the exterior surface is greater than the radius of curvature at the point of orthogonal projection of said each point onto said at least one layer of carcass reinforcement, wherein the first region and the area of the orthogonal projection are both arcuate, wherein said bead wires have a ratio of axial width to radial height that is greater than 1.5, and wherein over at least 30 mm of the base of each of said two beads, an angle formed by the base with a direction parallel to the direction of the axis of rotation of the tire is between 6 and 7.5°.

2. The tire according to claim 1, wherein, in a radial plane, in a second region of said at least one layer of carcass reinforcement, which second region is radially on the inside of the radially innermost point of said bead wire and axially on the outside of the geometric center of said bead wire, the radius of curvature at a point on said second region of said at least one layer of carcass reinforcement is smaller than the radius of curvature at the point of orthogonal projection of said point on said second region onto the exterior surface of said bead.

3. The tire according to claim 1, wherein said bead wire is a bead bundle formed of a plurality of cords stacked on top of one another.

4. The tire according to claim 1, wherein a radial thickness of rubber mass measured between said bead wire and the exterior surface of each of said two beads is greater than 10 mm.

5. The tire according to claim 1, wherein the tire has a width greater than or equal to 25 inches.

6. The tire according to claim 1, wherein a radial thickness of rubber mass measured between the inside of the radially innermost point of said bead wire and the exterior surface of each of said two beads is greater than 10 mm.

7. The tire according to claim 1, wherein said bead wires are of bead bundle type having a hexagonal shape.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1, a schematic depiction of a tire according to an embodiment of the invention,

(2) FIG. 2, a schematic depiction of a bead of the tire of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

(3) To make them easier to understand, the figures have not been drawn to scale. FIG. 1 depicts just half a tire which continues symmetrically with respect to the axis X-X′ which represents the circumferential median plane of the said tire.

(4) FIG. 1 is a diagram viewed in radial section of a tire 1 produced according to the invention. The tire 1, of size 26.5R25, has a carcass reinforcement layer 2, made up of a ply of inextensible steel metallic cords, anchored in each bead 3 to a bead wire 4 to form a turned-back portion 5. The carcass reinforcement layer 2 is radially surmounted by a crown reinforcement 6. The said crown reinforcement 6 usually consists, on the one hand, of two plies known as working plies and, on the other hand, of two protective plies. The collection of these plies that constitute the crown reinforcement is not depicted in detail in the figures. The working plies are themselves made up of inextensible steel cords parallel to one another within each ply and crossed from one ply to the next, making angles that may be comprised between 15° and 40° with the circumferential direction. The protective plies are generally made up of elastic steel metallic cords, parallel to one another within each ply and crossed with one another from one ply to the next making angles that may be comprised between 15 and 45°. The cords in the radially outer working ply usually are crossed with the cords of the radially inner protective ply. The crown reinforcement is finally surmounted by a tread 7 which is connected to the beads 3 by the sidewalls 8.

(5) The bead wire 4 is of the bead bundle type of hexagonal shape; in accordance with the invention it has a ratio of axial width L (equal to 47 mm) to radial height H (equal to 15 mm) of 3.1, which is therefore higher than 1.5.

(6) FIG. 2 illustrates a schematic depiction, in radial section, of one bead 3 of the tire of FIG. 1.

(7) According to the invention, in the region of the exterior surface 9 of the bead 3 which surface is delimited by the points O and P, that is to say in a region of the exterior surface 9 of the bead 3 that is radially on the inside of the radially innermost point E of the layer of carcass reinforcement 2 and axially on the outside of the geometric center C of the bead wire 4, the radius of curvature at the point R of the exterior surface 9 of the bead 3 is greater than the radius of curvature at the point S of orthogonal projection of the said point R onto the carcass reinforcement layer 2.

(8) At the point R, the radius of curvature of the exterior surface 9 of the bead 3 is equal to 40 mm.

(9) At the point S, the radius of curvature of the layer of carcass reinforcement 2 is equal to 35 mm.

(10) Likewise, in that region of the layer of carcass reinforcement 2 that is delimited by the points E and M, that is to say in a region of the layer of carcass reinforcement 2 that is radially on the inside of the radially innermost point G of the bead wire and axially on the outside of the geometric center C of the bead wire, the radius of curvature at the point U of the layer of carcass reinforcement 2 is less than the radius of curvature at the point V of orthogonal projection of the said point U onto the exterior surface 9 of the bead 3.

(11) At the point U, the radius of curvature of the layer of carcass reinforcement 2 is equal to 20 mm.

(12) At the point V, the radius of curvature of the exterior surface 9 of the bead 3 is equal to 40 mm.

(13) The tire illustrated in the figures was mounted on a rim of the 25 inches size and inflated to a pressure of 5.5 bar. Compared to the mounting of a conventional tire, that is to say one comprising a bead wire in which the ratio of width to height is substantially equal to 1, the tire appeared to be easier to mount. Likewise, after running on a vehicle simulating use in an underground mine in terms of the loads transported and the torques transmitted, the tire according to the invention appeared to be easier to remove.

(14) Further, the airtightness notably afforded by contact between the rim and the bead region was satisfactory and completely comparable with that of a conventional tire.

(15) Comparative tests were run using a tire according to the one depicted in the figures. The comparison was made using an identical reference tire comprising a bead of the bead bundle type in which the ratio of width to height was substantially equal to one and the width of the base of the bead of which was of course smaller.

(16) The width of the base of the bead of the tire according to the invention was equal to 93 mm and that of the reference tire was equal to 62 mm. The angle α formed by the taper of the base of the bead with a direction parallel to the axis of rotation was equal to 7°, over a length of the said base of the order of 35 mm. The tests notably demonstrated that such a taper made the tire easier to mount on a rim and that, as stated previously, no slippage on the rim during driving was observed.

(17) The tires were tested on one and the same vehicle, this vehicle travelling along the same path simulating a journey that was highly penalizing to tires and driven by the same driver. The journey, which reproduced use of a vehicle driven around in underground mines, notably comprised phases over short distances running in forward gear and in reverse gear, pulling away in forward and reverse gear requiring significant torque to be transmitted starting from a zero speed, and phases of driving over longer distances including cornering.

(18) The tests confirmed, after running for 200 hours, that the tires according to the invention showed no degradation in the bead regions whereas the reference tires were exhibiting damage in the said bead regions that could require the tire to be replaced.