Heavy vehicle tire with specified carcass turn-up, bead protection element, bead filler element, and bead transition element

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 on the axially outer face of the turn-up and spreads through the polymer coating and filler materials. According to the invention, a transition element made of a polymer transition material, is in contact, via its axially inner face, with the polymer coating material of the axially outer face of the turn-up and, via its axially outer face, with the polymer filler 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 polymer coating material and of the polymer filler material.

Claims

1. A tire for a heavy vehicle of construction plant type mounted on a rim comprising two rim flanges which are at least partially circular, the tire comprising: two beads contacting the rim, a carcass reinforcement comprising a carcass reinforcement layer made of metal reinforcing elements coated in a polymer coating material, the carcass reinforcement 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, the distance (a) between the turn-up and the main part decreasing continuously radially towards the outside, from a bead wire as far as a minimum distance (a.sub.1), then increasing continuously as far as a maximum distance (a.sub.2), each bead comprising a protection element extending a sidewall radially towards the inside, and a filler element axially on the inside of the protection element and of the sidewall and axially on the outside of the turn-up, the protection and filler elements being respectively made of at least one polymer protection material and one polymer filler material, the polymer filler material having an elastic modulus at 10% elongation that is lower than the elastic modulus at 10% elongation of the polymer coating material, wherein a transition element, made of a polymer transition material, is in contact, via its axially inner face, with the polymer coating material of the axially outer face of the turn-up via its axially outer face, with the polymer filler material, and wherein the elastic modulus at 10% elongation of the polymer transition material is somewhere between the respective elastic moduli at 10% elongation of the polymer coating material and of the polymer filler material, wherein the radially outer end (E) of the transition element is radially on the outside of the straight line (Dmin) passing through the centre (O) of the circle of the rim flange and making an angle of +70 with respect to the axial direction (YY), and the radially outer end (E) of the transition element is radially on the inside of a point A of the turn-up, the point A being positioned at the minimum distance (a.sub.1) between the turn-up and the main part.

2. The tire for a heavy vehicle of construction plant type according to claim 1, mounted on the rim, wherein a radially inner end (I) of the transition element is radially on the inside of a straight line (dmax) passing through a centre (O) of a circle of the rim flange, and making an angle of +40 with respect to an axial direction (YY).

3. The tire for a heavy vehicle of construction plant type according to claim 1, mounted on the rim, wherein a thickness (e) of the transition element is at least equal to a thickness of the polymer coating material.

4. The tire for a heavy vehicle of construction plant type according to claim 1, mounted on the rim, wherein a thickness (e) of the transition element is at most equal to 5 times a thickness of the polymer coating material.

5. The tire for a heavy vehicle of construction plant type according to claim 1, mounted on the rim, wherein the elastic modulus at 10% elongation of the polymer transition material is at least equal to 0.9 times and at most equal to 1.1 times the arithmetic mean of the respective elastic moduli at 10% elongation of the polymer coating material and of the polymer filler material.

6. The tire for a heavy vehicle of construction plant type according to claim 1, mounted on the rim, wherein the maximum distance (a.sub.2) between the turn-up and the main part is at least equal to 1.1 times the minimum distance (a.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 the rim and comprising a point A of the turn-up, which point is positioned at the minimum distance (a.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, a 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 (a.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, wherein S is the bead base line.

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

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 the 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 the construction plant type of the prior art, comprising:

(6) a carcass reinforcement comprising a single carcass reinforcement layer 1 made of metallic reinforcing elements coated in a polymer coating material with a main part 1a wrapped from the inside towards the outside of the tire, around a bead wire 2 to form a turn-up 1b,

(7) the distance a 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 a.sub.1, then increasing continuously as far as a maximum distance a.sub.2,

(8) a filling element 3 extending the bead wire 2 radially outwards, and made of two polymer filling materials,

(9) a first polymer filling material 3a being radially on the outside of and in contact with the bead wire 2,

(10) a second polymer filling material 3b being radially on the outside of and in contact with the first polymer filling material 3a,

(11) a protection element 4 extending a sidewall 5 radially towards the inside and made of at least one polymer protection material,

(12) a filler element 6 axially on the inside of the protection element 4 and of the sidewall 5 and axially on the outside of the turn-up 1b, and made of a polymer filler material.

(13) FIG. 2 shows a bead of a tire for a heavy vehicle of construction plant type, according to the invention, comprising:

(14) a carcass reinforcement comprising a single carcass reinforcement layer 21 made of metallic reinforcing elements coated with a polymer coating material, with a main part 21a wrapped, from the inside towards the outside of the tire, around a bead wire 22 to form a turn-up 21b,

(15) the distance a 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 distance a.sub.1 then increasing continuously as far as a maximum distance a.sub.2,

(16) a filling element 23 extending the bead wire 22 radially outwards and formed of two polymer filling materials,

(17) a first polymer filling material 23a being radially on the outside of and in contact with the bead wire 22,

(18) a second polymer filling material 23b being radially on the outside of and in contact with the first polymer filling material 23a,

(19) at protection element 24 extending a sidewall 25 radially towards the inside and consisting of at least one polymer protection material,

(20) a filler element 26 axially on the inside of the protection element 24 and of the sidewall 25 and axially on the outside of the turn-up 21b and made of a polymer filler material.

(21) a transition element 28 in contact, via its axially inner face, with the polymer coating material of the axially outer face of the turn-up and, via its axially outer face, with the polymer filler material.

(22) 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 a.sub.1, axially on the outside of the main part 21a and a distance H.sub.A, radially on the outside of a reference line S of the rim 27, and by the point B of the turn-up 21b, which point is positioned at the maximum distance a.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 27. The respective positions of the points A and B are defined with respect to the radially outermost point F of the rim 27 which point is positioned at a distance H.sub.F, radially on the outside of a reference line S of the rim 27.

(23) The transition element 28 has a thickness e schematically depicted as being constant but which in actual fact is usually tapered at the respectively radially outer E and radially inner I ends thereof.

(24) Respective geometric positions of the radially outer E and radially inner I ends of the transition element 28 are defined with respect to the local frame of reference the origin of which is the centre O of the circle of the rim flange 27 and the axes YY and ZZ of which are two straight lines passing through the centre O of the circle of the rim flange and orientated respectively axially towards the inside of the tire and radially towards the outside of the tire. The angle of a straight line passing through the centre O of the circle of the rim flange is then positive if measured in the counterclockwise direction from the axis YY to the straight line.

(25) The radially outer E and radially inner I ends of the transition element 28 are situated respectively on the straight line D and d, making the angles A and a with the axis YY.

(26) The radially outer E and radially inner I ends of the transition element 28 are respectively radially on the outside of the straight line D.sub.min, making an angle with respect to the axis YY of +70, and radially inside of the straight line d.sub.max, making an angle with respect to the axis YY of +40. As shown in FIG. 2, the radially outer end E is also radially inside of the point A of the turn-up 21b.

(27) 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 bar, a static load of 99 tonnes and covering a distance of between 16 km and 32 km each hour.

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

(29) 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 a.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 27. The point B of the turn-up 21b is positioned at the maximum distance a.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 27. The respective positions of the points A and B are defined with respect to the radially outermost point F of the rim 27, 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 27.

(30) The angle A of the straight line D passing through the radially outer end E of the transition element 28 is equal to +80, and is therefore greater than +70.

(31) The angle a of the straight line d passing through the radially inner end I of the transition element 28 is equal to +35, and is therefore less than +40.

(32) The thickness e of the transition element 28 is equal to 1.5 mm, and is therefore somewhere between the thickness of the polymer coating material equal to 1 mm and 5 times the thickness of the polymer coating material.

(33) The elastic moduluses at 10% elongation of the polymer coating, transition and filler materials are respectively equal to 6 MPa, 4.8 MPa and 3.5 MPa. As a result, the elastic modulus at 10% elongation of the polymer transition material is equal to the arithmetic mean of the respective elastic moduluses at 10% elongation of the polymer coating and filler materials.

(34) 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 polymer filler material 6, in the region sensitive to cracking on the axially outer face of the turn-up 1b, is equal to 1.3 times the elongation of the polymer coating material in contact with it, these elongations being parallel to the turn-up. For the tire according to the invention, the elongation of the polymer transition material 28, in the region sensitive to cracking on the axially outer face of the turn-up 21b, is equal to 1.1 times the elongation of the polymer coating material. As a result, the rate at which a crack in the polymer coating material spreads to the polymer transition material 28, in the case of the invention, is lower than the rate at which a crack in the polymer coating material spreads to the polymer filler material 6 in the case of the reference tire, because the ratio of the elongation of the polymer transition material 28 with respect to the elongation of the polymer coating material, equal to 1.1, is lower than the ratio of the elongation of the polymer filler material 6 with respect to the elongation of the polymer coating material, equal to 1.3.

(35) 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 comprised between the polymer coating material and the polymer filler material.