Bead for a tire for a heavy civil-engineering vehicle

Abstract

The invention relates to improving the endurance of a bead of a radial tire for a heavy vehicle of construction plant type by reducing the compression to which the turn-up is subjected when the tire is driven on. According to the invention, for a tire for a heavy vehicle of construction plant type comprising two beads intended to come into contact with a rim having two rim flanges, a carcass reinforcement comprising at least one carcass reinforcement layer having a main part wrapped, within each bead, from the inside towards the outside of the tire, around a bead wire of substantially circular meridian section, to form a turn-up, a filling element extending the bead wire radially towards the outside and axially separating the main part and the turn-up, the distance (d) between a first segment of turn-up and the main part decreasing continuously, radially towards the outside, from the bead wire as far as a minimum distance (d.sub.1), the distance (d.sub.2) between a second segment of turn-up, extending the first segment of turn-up radially towards the outside, and the main part is substantially constant and equal to the minimum distance (d.sub.1) between the first segment of turn-up and the main part.

Claims

1. A wheel assembly for a heavy vehicle of construction plant type, comprising: at least two rims with a respective rim flange; a tire comprising: two beads intended to come into contact with the two rim flanges, a carcass reinforcement comprising at least one carcass reinforcement layer having a main part wrapped, within each bead, from the inside towards the outside of the tire, around a bead wire of substantially circular meridian section, to form a turn-up, the bead wire being made of a circumferential reinforcing element surrounded by a polymer coating element, a filling element extending the bead wire radially towards the outside and axially separating the main part and the turn-up, the distance (d) between a first segment of the turn-up and the main part decreasing continuously, radially towards the outside, from the bead wire as far as a minimum distance (d.sub.1), wherein the distance (d.sub.2) between a second segment of the turn-up, extending the first segment of the turn-up radially towards the outside, and the main part is substantially constant and equal to the minimum distance (d.sub.1) between the first segment of the tum-up and the main part, wherein a minimum thickness (e) of the polymer coating element of the bead wire is at least equal to 0.04 times the diameter (L.sub.2) of a meridian section of the circumferential reinforcing element of the bead wire, and the second segment is defined where the first segment tapers to a minimal distance from the main part, and ends where the tum up begins to taper out, and where the first segment tapers to the minimal distance and where the second segment's distance from the main part varies at most 10% from where the first segment tapers to a minimal distance from the main part to where the tum up begins to taper out, wherein the distance (d) between a third segment of the tum-up extending the second segment of the tum-up radially outwards, and the main part reaches a maximum distance (d.sub.3) at a point C on the third segment of the tum-up, wherein a point C of the third segment of the tum-up at which the maximum distance (d.sub.3) between the third segment of the tum-up and the main part is reached is a radially outermost point E of the tum-up, wherein the turn-up extends a radial distance HE that is so dimensioned to be at least equal to 0.80 times a radial distance HF corresponding to an axially outermost point F of the carcass reinforcement layer defining the main part.

2. The wheel assembly for a heavy vehicle of construction plant type according to claim 1, wherein the substantially constant distance (d.sub.2) between the second segment of the tum-up and the main part is at most equal to the diameter (L.sub.1) of the substantially circular meridian section of the bead wire divided by 4.

3. The wheel assembly for a heavy vehicle of construction plant type according to claim 2, wherein (d.sub.2) is at most equal to (L.sub.1) divided by 6.

4. The wheel assembly for a heavy vehicle of construction plant type according to claim 1, wherein a radial distance (H.sub.A) between a radially innermost point A of the second segment of the tum-up and an axial straight line (S) positioned radially at a nominal diameter (D) of a rim is at least equal to a radial height (H) of a rim flange.

5. The wheel assembly for a heavy vehicle of construction plant type according to claim 1, wherein a radial distance (H.sub.A) between a radially innermost point A of the second segment of the tum-up and an axial straight line (S) positioned radially at a nominal diameter (D) of a rim is at most equal to 2 times, the radial height (H) of a rim flange.

6. The wheel assembly for a heavy vehicle of construction plant type according to claim 5, wherein (H.sub.A) is at most equal to 1.2 times (H).

7. The wheel assembly for a heavy vehicle of construction plant type according to claim 1, wherein a difference between a radial distance (H.sub.B) between a radially outermost point B of the second segment of the tum-up and an axial straight line (S) positioned radially at a nominal diameter (D) of a rim, and a radial distance (H.sub.A) between a radially innermost point A of the second segment of the tum-up and an axial straight line (S) positioned radially at the nominal diameter (D) of the rim is at most equal to a radial height (H) of a rim flange.

8. The wheel assembly for a heavy vehicle of construction plant type according to claim 1, wherein the maximum distance (d.sub.3) between the third segment of the turn-up and the main part is at least equal to 1.2 times, the distance (d.sub.2) between the second segment of the turn-up and the main part.

9. The wheel assembly for a heavy vehicle of construction plant type according to claim 8, wherein (d.sub.3) is at least equal to 2 times (d.sub.2).

10. The wheel assembly for a heavy vehicle of construction plant type according to claim 1, wherein the carcass reinforcement layer is made up of reinforcing elements coated in a polymer coating material, and wherein the filling element has a filling element segment contained axially between the second segment of the turn-up and the main part, made of a polymer filling material, wherein the polymer filling material of the segment of filling element contained axially between the second segment of the turn-up and the main part is identical to the polymer coating material of the carcass reinforcement layer.

11. The wheel assembly for a heavy vehicle of construction plant type according to claim 1, wherein a radial distance (H.sub.E) between a radially outermost point E of the tum-up, and an axial straight line (S) positioned radially at a nominal diameter (D) of a rim is at least equal to 0.8 times a radial distance (H.sub.F) between an axially outermost point F of the main part and an axial straight line (S) positioned radially at the nominal diameter (D) of the rim.

12. A wheel assembly for a heavy vehicle of construction plant type according to claim 1, wherein a point E is axially the outermost point of the turn-up and spaced axially outwardly from the axially outermost portion of the main part.

13. A method for manufacturing a tire for a heavy vehicle of construction plant type, the tire being placed on at least two rims with a respective rim flange, and tire comprising two beads intended to come into contact with the two nm flanges, comprising: providing a carcass reinforcement for the tire, comprising: at least one carcass reinforcement layer having a main part wrapped, within each bead, from the inside towards the outside of the tire, around a bead wire of substantially circular meridian section, to form a tum-up, the bead wire being made of a circumferential reinforcing element surrounded by a polymer coating element, providing a filling element extending the bead wire radially towards the outside and axially separating the main part and the tum-up; segmenting the tum-up into a first segment, a second segment, and a third segment; sizing with a distance (d) between the first segment of the tum-up and the main part decreasing continuously, radially towards the outside, from the bead wire as far as a minimum distance (d.sub.1), sizing with a distance (d.sub.2) between a second segment of the tum-up, extending the first segment of the tum-up radially towards the outside, and the main part is substantially constant and equal to the minimum distance (d.sub.1) between the first segment of the tum-up and the main part, the second segment further being sized to define where the first segment tapers to a minimal distance from the main part, and ends where the tum up begins to taper out, and where the first segment tapers to the minimal distance and where the second segment's distance from the main part varies at most 10% from where the first segment tapers to a minimal distance from the main part to where the tum up begins to taper out, providing with a minimum thickness (e) of the polymer coating element of the bead wire is at least equal to 0.04 times the diameter (L.sub.2) of a meridian section of the circumferential reinforcing element of the bead wire; positioning the second segment of turn-up on the bead, so that the second segment is configured to wrap around at least one of the rim flanges while the tire is inflated and being driven on; positioning the turn-up such that it extends a radial distance HE that is so dimensioned to be at least equal to 0.80 times a radial distance HF corresponding to an axially outermost point F of the carcass reinforcement layer defining the main part; and sizing the distance (d) between a third segment of the turn-up extending from the second segment of the turn-up radially outwards, and positioning the main part to reach a maximum distance (d.sub.3) at a point C on the third segment of the turn-up, and wherein a point C of the third segment of the turn-up at which the maximum distance (d.sub.3) between third segment of the turn-up and main part is reached is a radially outmost point E of turn-up.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The features of the invention will be better understood with the aid of the description of the attached FIG. 1, which shows a view in cross section, on a meridian plane, of the bead of a tire for a heavy vehicle of construction plant type, according to the invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

(2) In order to make it easier to understand, FIG. 1 has not been drawn to scale.

(3) FIG. 1 depicts a bead 1 of a tire for a heavy vehicle of construction plant type according to the invention, in contact with a rim flange 2, comprising a circular portion around which the bead wraps as it flexes under driving conditions.

(4) The rim flange has a radial height H, measured between the radially outermost point of the circular portion of the rim flange and of the straight line S that passes through the nominal diameter D of the rim, or seat diameter, as defined, for example, by the ETRTO standards.

(5) The bead 1 comprises a carcass reinforcement having a single carcass reinforcement layer 3 made of metal reinforcing elements. The carcass reinforcement layer comprises a main part 31 wrapped, from the inside towards the outside of the tire, around a bead wire 4 to form a turn-up 32. The turn-up 32 and the main part 31 are separated axially by a filling element 5 extending radially on the outside of the bead wire 4. In the configuration shown in FIG. 1, the filling element 5 is made of a radial stack of two polymer filling materials.

(6) The turn-up 32 is made of three segments of turn-up 321, 322 and 323, extending radially from the last point of contact (not depicted) with the bead wire 4 as far as the end point E of the turn-up 32. The end point E of the turn-up 32 is positioned radially at the radial distance H.sub.E, with respect to the straight line S passing through the nominal diameter D of the rim. The radial distance H.sub.E is preferably at least equal to 0.80 times the radial distance H.sub.F of the axially outermost point F of the carcass reinforcement layer 3 with respect to the straight line S passing through the nominal diameter D of the rim: this is what characterizes a long turn-up 32.

(7) The first segment of turn-up 321 extends from the last point of contact with the bead wire (this point is not depicted) as far as the point A. The distance between the first segment of turn-up 321 and the main part 31 decreases continuously from the width L.sub.1 of the bead wire as far as a distance d.sub.1, which is the minimum distance between the turn-up 32 and the main part 31.

(8) The second segment of turn-up 322 extends the first segment of turn-up 321 radially outwards: it is bounded radially on the inside by the point A and radially on the outside by the point B, these points being respectively positioned radially at the radial distances H.sub.A and H.sub.B with respect to the straight line S that passes through the nominal diameter D of the rim. The distance d.sub.2 between the second segment of turn-up 322 and the main part 31 is substantially constant and equal to the minimum distance d.sub.1 of the first segment of turn-up, to within + or 10%. The filling element 5 has a filling element segment 51, preferably made of a polymer filling material identical to the polymer coating material used on the metal reinforcing elements of the carcass reinforcement layer 3.

(9) Finally, the third segment of turn-up 323 extends the second segment of turn-up 322 radially outwards: it is bounded radially on the inside by the point B and radially on the outside by the point E. The distance d between the third segment of turn-up 323 and the main part 31 has a maximum value d.sub.3 at a point C.

(10) The bead wire 4 is made of a circumferential reinforcing element 41 of which the meridian section, which in the instance depicted is hexagonal, is inscribed inside a circle of diameter L.sub.2, which defines the axial width of the circumferential reinforcing element 41, and of a coating element 42, usually made of a polymer material, the substantially circular meridian section of which has a diameter L.sub.1, which defines the axial width of the bead wire 4, coating element 42 included. The minimum thickness e of the polymer coating element 42 of the bead wire 4 is defined as being half the difference between the axial width L.sub.1 of the bead wire 4 and the axial width L.sub.2 of its circumferential reinforcing element 41. The thickness of the coating element 42 of the bead wire 4 can vary, as FIG. 1 shows and it is the minimum thickness e that governs the torsional stiffness of the bead wire 4. For a given polymer coating material, the greater the minimum thickness e the greater the reduction in torsional stiffness, allowing the bead wire 4 to rotate more and therefore allowing tension to be introduced into the turn-up 32 as the tire is inflated.

(11) The invention has been studied more particularly in the case of a tire for a heavy vehicle of size 40.00R57, mounted on a rim of which the radial height H of the rim flange 2, measured with respect to the straight line S passing through the nominal diameter D of the rim, is equal to 152 mm.

(12) The first segment of turn-up 321 extends from the last point of contact with the bead wire as far as the point A. The distance between the first segment of turn-up 321 and the main part 31 decreases continuously from the width L.sub.1 of the bead wire as far as the distance d.sub.1 equal to 10 mm, which is the minimum distance between the turn-up 32 and the main part 31.

(13) The second segment of turn-up 322 extends the first segment of turn-up 321 radially outwards: it is bounded radially on the inside by the point A and radially on the outside by the point B, which points are respectively positioned radially at the radial distances H.sub.A equal to 211 mm and H.sub.B equal to 311 mm with respect to the straight line S passing through the nominal diameter D of the rim. The radial distance H.sub.A is equal to 1.4 times the radial height H of the rim flange 2, and therefore falls between 1 times and 2 times the radial height H. The difference between the radial distance H.sub.B and the radial distance H.sub.A is equal to 100 mm, and therefore less than the radial height H of the rim flange 2. The distance d.sub.2 between the second segment of turn-up 322 and the main part 31 is substantially constant and equal to the minimum distance d.sub.1, equal to 10 mm, of the first segment of turn-up 321.

(14) The third segment of turn-up 321 extends the second segment of turn-up 322 radially outwards: it is bounded radially on the inside by the point B and radially on the outside by the point E. The distance d between the third segment of turn-up 323 and the main part 31 has a maximum value d.sub.3 at the point C equal to 16 mm. The radial distance H.sub.E of the end point E of the turn-up 32 is equal to 465 mm. The distance between the third segment of turn-up 323 and the main part 31 at the end point E of the turn-up 32 is equal to 14 mm.

(15) Simulations of finite-element calculations, carried out on a tire according to the invention, as depicted in FIG. 1, have shown that the extent to which the turn-up is placed under compression is reduced appreciably when the tire is being driven on.