Bead of a tire for a heavy vehicle of construction plant type

Abstract

The invention relates to improving the endurance of the beads of a radial tire for a heavy vehicle of construction plant type, by reducing the cracking that starts at the surface of contact between a first polymer filling material that is radially furthest towards the inside and in contact with the bead wire and a second polymer filling material that is radially on the outside of the first polymer filling material. According to the invention, a transition element, made of a polymer transition material, is in contact, via its radially inner face, with the first polymer filling material and is in contact, via its radially outer face, with the second polymer filling material, and the elastic modulus at 10% elongation of the polymer transition material is somewhere between the respective elastic moduluses at 10% elongation of the first and second polymer filling materials.

Claims

1. A tire for a heavy vehicle of construction plant type comprising: two beads adapted to come into contact with a rim, a carcass reinforcement comprising: at least one carcass reinforcement layer made of a metal reinforcing elements, the carcass reinforcing layer comprising: a main part wrapped, within each bead, from the inside towards the outside of the tire around a bead wire to form a turn-up, wherein the distance (d) between the turn-up and the main part decreases continuously, radially towards the outside, from the bead wire, as far as a minimum distance (d.sub.1), then increases continuously as far as a maximum distance (d.sub.2), wherein each bead comprises: a filling element extending the bead wire radially towards the outside, wherein the filling element is formed of at least two polymer filling materials, wherein a first polymer filling material is radially furthest towards the inside and in contact with the bead wire, and wherein a second polymer filling material is radially on the outside of the first polymer filling material, and having an elastic modulus at 10% elongation that is lower than the elastic modulus at 10% elongation of the first polymer filling material, wherein a transition element, made of a polymer transition material, is in contact, via its radially inner face, with the first polymer filling material and in contact, via its radially outer face, with the second polymer filling material, and wherein the elastic modulus at 10% elongation of the polymer transition material is between the respective elastic moduli at 10% elongation of the first and second polymer filling materials; wherein the radially inner face of the transition element is in continuous contact with the main part between a first point of contact and a last point of contact which is a radially outermost point of the transition element.

2. The tire for a heavy vehicle of construction plant type according to claim 1, wherein a thickness (e) of the transition element is at least equal to 0.1 times a distance (d.sub.3) between an end of the turn-up and the main part.

3. The tire for a heavy vehicle of construction plant type according to claim 1, wherein a thickness (e) of the transition element is at most equal to 0.5 times a distance (d.sub.3) between the end of the turn-up and the main part.

4. The tire for a heavy vehicle of construction plant type according to claim 1, wherein the elastic modulus at 10% elongation of the polymer transition material is at least equal to 0.9 times, and at most equal 1.1 times, the arithmetic mean of the respective elastic moduli at 10% elongation of the first and second polymer filling materials.

5. The tire for a heavy vehicle of construction plant type according to claim 1, wherein the radially inner face of the transition element is in continuous contact with the main part between a first point of contact and a last point of contact which is a radially outermost point of the transition element.

6. The tire for a heavy vehicle of construction plant type according to claim 1, wherein the maximum distance (d2) between the turn-up and the main part is at least equal to 1.1 times the minimum distance (d.sub.1) between the turn-up and the main part.

7. The tire for a heavy vehicle of construction plant type according to claim 1, mounted on a rim, and comprising a point A on the turn-up, which point is positioned at the minimum distance (d.sub.1), axially on the outside of the main part, and at a distance (H.sub.A), radially on the outside of a reference line (S) of the rim, the radially outermost point F of the rim being positioned at a distance (H.sub.F), radially on the outside of a reference line (S) of the rim, wherein the distance (H.sub.A) from the point A of the turn-up, positioned at the minimum distance (d.sub.1) axially on the outside of the main part, to the reference line (S) of the rim is at least equal to 1.25 times and at most equal to 2.5 times the distance (H.sub.F) from the radially outermost point F of the rim to the reference line (S) of the rim.

8. The tire for a heavy vehicle of construction plant type according to claim 1, mounted on a rim, and comprising a point B of the turn-up, which point is positioned at the maximum distance (d.sub.2), axially on the outside of the main part, and at a distance (H.sub.B), radially on the outside of a reference line (S) of the rim, the radially outermost point (F) of the rim being positioned at a distance (H.sub.F), radially on the outside of a reference line (S) of the rim, wherein the distance (H.sub.B) from the point B of the turn-up, positioned at the minimum distance (d.sub.2) axially on the outside of the main part, to the reference line (S) of the rim is at least equal to 2 times and at most equal to 4 times the distance (H.sub.F) from the radially outermost point F of the rim to the reference line (S) of the rim.

9. A tire for a heavy vehicle of construction plant type comprising: two beads adapted to come into contact with a rim, a carcass reinforcement comprising: at least one carcass reinforcement layer made of a metal reinforcing elements, the carcass reinforcing layer comprising: a main part wrapped, within each bead, from the inside towards the outside of the tire around a bead wire to form a turn-up, wherein the distance (d) between the turn-up and the main part decreases continuously, radially towards the outside, from the bead wire, as far as a minimum distance (d.sub.1), then increases continuously as far as a maximum distance (d.sub.2), wherein each bead comprises: a filling element extending the bead wire radially towards the outside, wherein the filling element is formed of at least two polymer filling materials, wherein a first polymer filling material is radially furthest towards the inside and in contact with the bead wire, and wherein a second polymer filling material is radially on the outside of the first polymer filling material, and having an elastic modulus at 10% elongation that is lower than the elastic modulus at 10% elongation of the first polymer filling material, wherein a transition element, made of a polymer transition material, is in contact, via its radially inner face, with the first polymer filling material and in contact, via its radially outer face, with the second polymer filling material, and wherein a distance (a) between a first point of contact and a last point of contact of the radially inner face of the transition element with the main part is at least equal to the distance (d.sub.3) between an end of the turn-up and the main part.

10. A tire for a heavy vehicle of construction plant type comprising: two beads adapted to come into contact with a rim, a carcass reinforcement comprising: at least one carcass reinforcement layer made of a metal reinforcing elements, the carcass reinforcing layer comprising: a main part wrapped, within each bead, from the inside towards the outside of the tire around a bead wire to form a turn-up, wherein the distance (d) between the turn-up and the main part decreases continuously, radially towards the outside, from the bead wire, as far as a minimum distance (d.sub.1), then increases continuously as far as a maximum distance (d.sub.2), wherein each bead comprises: a filling element extending the bead wire radially towards the outside, wherein the filling element is formed of at least two polymer filling materials, wherein a first polymer filling material is radially furthest towards the inside and in contact with the bead wire, and wherein a second polymer filling material is radially on the outside of the first polymer filling material, and having an elastic modulus at 10% elongation that is lower than the elastic modulus at 10% elongation of the first polymer filling material, wherein a transition element, made of a polymer transition material, is in contact, via its radially inner face, with the first polymer filling material and in contact, via its radially outer face, with the second polymer filling material, wherein a distance (a) between a first point of contact and a last point of contact of the radially inner face of the transition element with the main part is at most equal to 3 times the distance (d.sub.3) between an end of the turn-up and the main part.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The features of the invention will be better understood from the description of the attached FIGS. 1 and 2:

(2) FIG. 1 is a view in section on a meridian plane of the bead of a tire for a heavy vehicle of construction plant type, of the prior art.

(3) FIG. 2 is a view in 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

(4) In order to make them easier to understand, FIGS. 1 and 2 are not drawn to scale.

(5) FIG. 1 depicts a bead of a tire for a heavy vehicle of construction plant type according to the prior art, comprising: a carcass reinforcement comprising at least one carcass reinforcement layer 1 made of metal reinforcing elements, the carcass reinforcement layer comprising a main part 1a wrapped, within each bead, from the inside towards the outside of the tire, around a bead wire 2, to form a turn-up 1b, the distance d between the turn-up 1b and the main part 1a decreasing continuously, radially towards the outside, from the bead wire 2, as far as a minimum distance d.sub.1, then increasing continuously as far as a maximum distance d.sub.2, each bead comprising a filling element 3 extending the bead wire 2 radially outwards, the filling element being made of two polymer filling materials (3a, 3b), a first polymer filling material 3a being radially innermost and in contact with the bead wire core 2, a second polymer filling material 3b being radially on the outside of the first polymer filling materials 3a and having an elastic modulus at 10% elongation that is lower than the elastic modulus at 10% elongation of the first polymer filling material 3a.

(6) FIG. 2 shows a bead of a tire for a heavy vehicle of construction plant type, according to the invention, comprising: a carcass reinforcement comprising a carcass reinforcement layer 21 made up of metal reinforcing elements, the carcass reinforcement layer comprising a main part 21a wrapped, in each bead, from the inside towards the outside of the tire, around a bead wire 22, to form a turn-up 21b, the distance d between the turn-up 21b and the main part 21a decreasing continuously, radially towards the outside, from the bead wire 22, as far as a minimum d.sub.1, then increasing continuously as far as a maximum distance d.sub.2, the bead comprising a filling element 23 extending the bead wire 22 radially outwards, the filling element being formed of two polymer filling materials (23a, 23b), a first polymer filling material 23a being radially furthest towards the inside and in contact with the bead wire 22, a second polymer filling material 23b being radially on the outside of the first polymer filling material 23a and having an elastic modulus at 10% elongation that is lower than the elastic modulus at 10% elongation of the first polymer filling material 23a, a transition element 24, made of a polymer transition material, of thickness e, being in contact, via its radially inner face 24a, with the first polymer filling material 23a and in contact, via its radially outer face 24b, with the second polymer filling material 23b, and the elastic modulus at 10% elongation of the polymer transition material 24 being somewhere between the respective elastic moduluses at 10% elongation of the first and second polymer filling materials.

(7) The geometry of the turn-up 21b is characterized by the point A of the turn-up 21b, which point is positioned at the minimum distance d.sub.1, axially on the outside of the main part 21a, and at a distance H.sub.A, radially on the outside of a reference line S of the rim 25, and by the point B of the turn-up 21b, which point is positioned at the maximum distance d.sub.2, axially on the outside of the main part 21a, and at a distance H.sub.B, radially on the outside of a reference line S of the rim 25. The respective positions of the points A and B are defined with respect to the radially outermost point F of the rim 25 which point is positioned at a distance H.sub.F, radially on the outside of a reference line S of the rim 25.

(8) The transition element 24 has a thickness e that is generally constant, but does not have to be so, away from the zones of contact with, respectively, the main part and the turn-up, in which zones the transition element tapers as far as the radially outer E.sub.24 and radially inner I.sub.24 ends of the transition element respectively, where the radially inner 24a and radially outer 24b faces of the transition element 24 meet.

(9) The radially inner face 24a of the transition element 24 is delimited respectively by its radially innermost point I.sub.24 in contact with the turn-up 23b and by its radially outermost point E.sub.24 in contact with the main part 21a.

(10) The radially outer face 24b of the transition element 24 is delimited respectively by its radially innermost point I.sub.24 in contact with the turn-up 23b and by its radially outermost point E.sub.24 in contact with the main part 21a.

(11) The zone of continuous contact between the transition element 24 and the main part 21a is created along the radially inner face 24a of the transition element 24 and is delimited radially by the radially innermost first point of contact E.sub.24 and the radially outermost last point of contact E.sub.24, which is also the radially outer end of the transition element.

(12) The zone of continuous contact between the transition element 24 and the turn-up 21a is created along the radially outer face 24b of the transition element 24 and is delimited radially by the radially outermost first point of contact I.sub.24 and the radially innermost last point of contact I.sub.24, which is also the radially inner end of the transition element 24.

(13) The distance d.sub.3 between the end E.sub.21 of the turn-up 21b and the main part 21a is the distance measured, along the straight line D passing through the end E.sub.21 of the turn-up and perpendicular to the main part, between the axially inner generatrix of the reinforcing elements of the turn-up and the axially outer generatrix of the reinforcing elements of the main part.

(14) The distance a between the respective first and last points of contact of the radially inner face 24a of the transition element 24 with the main part 21a is the distance measured between the straight lines D and D which are perpendicular to the main part 21a at E.sub.24 and E.sub.24.

(15) The invention has been studied more particularly in the case of a tire for a heavy vehicle of the dumper type of size 59/80R63. According to the ETRTO standard, the nominal service conditions for such a tire are an inflation pressure of 6 bars, a static load of 99 tones, and covering a distance of between 16 and 32 km each hour.

(16) The 59/80R63 tire was designed according to the invention, as depicted in FIG. 2.

(17) As far as the geometry of the turn-up 21b is concerned, the point A of the turn-up 21b is positioned at the minimum distance d.sub.1 equal to 18 mm, axially on the outside of the main part 21a, and at a distance H.sub.A equal to 200 mm, radially on the outside of a reference line S of the rim 25. The point B of the turn-up 21b is positioned at the maximum distance d.sub.2 equal to 27 mm, axially on the outside of the main part 21a, and at a distance H.sub.B equal to 390 mm, radially on the outside of a reference line S of the rim 25. The respective positions of the points A and B are defined with respect to the radially outermost point F of the rim 25, which point is positioned at a distance H.sub.F equal to 127 mm radially on the outside of a reference line S of the rim 25.

(18) The thickness e of the transition element 24 is constant and equal to 4.5 mm, namely 0.3 times the distance d.sub.3 between the end E.sub.21 of the turn-up and the main part 21a which is equal to 15 mm.

(19) The elastic moduluses at 10% elongation of the first polymer filling material, the polymer transition material and the second polymer filling material are respectively equal to 10 MPa, 6.5 MPa and 3.5 MPa. As a result, the elastic modulus at 10% elongation of the polymer transition material is somewhere between the respective elastic moduluses at 10% elongation of the first and second polymer filling materials and is equal to 0.96 times the arithmetic mean of the respective elastic moduluses at 10% elongation of the first and second polymer filling materials.

(20) The distance a between the first point of contact E.sub.24 and the last point of contact E.sub.24 of the radially inner face 24a of the transition element 24, with the main part 21a, is equal to 22.5 mm, namely 1.5 times the distance d.sub.3 between the end E.sub.21 of the turn-up 21b and the main part 21a.

(21) Simulations of finite-element calculations were carried out respectively on a reference tire, as depicted in FIG. 1, and on a tire according to the invention, as depicted in FIG. 2. For the reference tire, the elongation of the second polymer filling material 3b, in the region of the radially inner face thereof, is equal to 2.5 times the elongation of the first polymer filling material 3a, in the region of the radially outer face thereof. For the tire according to the invention, the elongation of the polymer transition material 24, in the region of the radially inner face 24a thereof, is equal to 1.5 times the elongation of the first polymer filling material 23a in the region of the radially outer face thereof. Likewise, for the tire according to the invention, the elongation of the second polymer filling material 23b, in the region of the radially inner face 24a thereof, is equal to 1.5 times the elongation of the polymer transition material 24, in the region of the radially outer face thereof.

(22) As a result, the rate at which a crack spreads from the first polymer filling material 23a to the polymer transition material 24, then from the polymer transition material 24 to the second polymer filling material 23b, in the case of the invention, is slower than the rate at which a crack spreads from the first polymer filling material 3a to the second polymer filling material 3b in the case of the reference tire, because the ratio of the elongation of the polymer transition material 24 with respect to the elongation of the first polymer filling material 23a, and the ratio of the elongation of the second polymer filling material 23b with respect to the elongation of the polymer transition material 24, are lower than the ratio of the elongation of the second polymer filling material 3b with respect to the elongation of the first polymer filling material 3a.

(23) The invention should not be interpreted as being restricted to the example illustrated in FIG. 2, but may be extended to other alternative forms of embodiment, for example and nonlimitingly, relating to the number of polymer transition materials forming a stack in the radial direction between the first and second polymer filling materials, or to the number of filling materials, greater than 2, forming the filling element.