Heavy vehicle tire bead

Abstract

Heavy vehicle tire with two beads (2) contacting rim (3) an outer face (21), radial carcass reinforcement (4) having carcass layer (41) wound within each bead (2) around bead wire (5) having center (O) to form turnup (411), additional circumferential reinforcement (6), in each bead (2), having additional layer (61, 62), additional reinforcement (6) extending radially from radially inner end (E.sub.1) to radially outer end (E.sub.2) and axially on outerside of axially outermost turnup (411). The orthogonal projection (P.sub.1) of radially inner end (E.sub.1) of additional circumferential reinforcement (6) onto axially outer face (21) of bead (2) is radially on outside of center (O) of bead wire (5), the orthogonal projection (P.sub.2) of radially outer end (E.sub.2) of additional circumferential reinforcement (6) onto axially outer face (21) of the bead (2) contacting point (P.sub.2) of rim (3) that is axially on inside of point (C) of last contact of rim (3) when tire (1) is mounted and inflated, and radial distance (d) between end (E.sub.1) and end (E.sub.2) of additional circumferential reinforcement (6) is at most 20 mm.

Claims

1. A heavy vehicle tire to be mounted on a rim, the tire comprising: two beads configured to come into contact with the rim via at least one respective axially outer face; a radial carcass reinforcement comprising at least one carcass layer wound within each bead around a bead wire having a center to form a turnup; an additional circumferential reinforcement, in each bead, comprising at least two additional layers, the additional circumferential reinforcement extending radially from a radially inner end to a radially outer end and axially on the outerside of the axially outermost turnup; wherein two of the at least two additional layers of the additional circumferential reinforcement are adjacent along a single edge of each of the two additional layers, wherein an orthogonal projection of the radially inner end of the additional circumferential reinforcement onto an axially outer face of the bead is radially on the outside of the center of the bead wire, and wherein an orthogonal projection of the radially outer end of the additional circumferential reinforcement onto the axially outer face of the bead is positioned to come into contact with a point of the rim that is axially on the inside of a point of last contact of the rim when the tire is mounted on the rim and inflated to a recommended pressure.

2. The heavy vehicle tire according to claim 1, wherein the sum of the widths of the at least two additional layers of the additional circumferential reinforcement is at least equal to 20 mm.

3. The heavy vehicle tire according to claim 1, wherein the circumferential tensile tangent stiffness of the at least two additional layers of the additional circumferential reinforcement is at least equal to 250 daN/mm.

4. The heavy vehicle tire according to claim 1, wherein the at least two additional layers of the additional circumferential reinforcement comprises metal reinforcers.

5. The heavy vehicle tire according to claim 1, wherein the at least two additional layers of the additional circumferential reinforcement comprises reinforcers made of aromatic polyamide.

6. The heavy vehicle tire according to claim 1, wherein the at least two additional layers of the additional circumferential reinforcement comprises reinforcers made of aromatic polyamide and of aliphatic polyamide.

7. The heavy vehicle tire according to claim 1, wherein the two additional layers of the additional circumferential reinforcement are partially superposed.

8. The heavy vehicle tire according to claim 1, wherein the radial distance between the radially inner end and the radially outer end of the at least two additional layers of additional circumferential reinforcement is at most equal to 20 mm.

Description

BRIEF DESCRIPTION OF THE SINGLE DRAWING

(1) The features of the invention will be better understood with the aid of the description of FIG. 1 which is a view in cross section on a meridian plane of a bead of a tire for a heavy goods vehicle according to a preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE SINGLE DRAWING

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

(3) FIG. 1 depicts a bead 2 of a tire 1 for a heavy vehicle according to the invention. The bead 2 is intended to come into contact with a rim 3 via at least one axially outer face 21.

(4) The radial carcass reinforcement 4 is made up of a carcass layer 41 wound within the bead 2 around a bead wire 5 having a centre O to form a turnup 411.

(5) The additional circumferential reinforcement 6 comprises two additional layers (61, 62). The additional circumferential reinforcement 6 extends radially from a radially inner end E.sub.1 to a radially outer end E.sub.2 and axially on the outside of the turnup 411. In the case of FIG. 1, the two additional layers (61, 62) of the additional circumferential reinforcement 6 are partially superposed: they are said to scaled. The radially inner end E.sub.1 of the additional circumferential reinforcement 6 is the radially inner end of the radially innermost additional layer 61 whereas the radially outer end E.sub.2 of the additional circumferential reinforcement 6 is the radially outer end of the radially outermost additional layer 62. The respective radially inner end E.sub.1 and radially outer end E.sub.2 of the additional circumferential reinforcement 6 are positioned relative to one another at a radial distance d. The additional layers (l1, l2) have respective widths l.sub.1 and l.sub.2 which are curved widths measured along the profile of the layers in a meridian plane.

(6) According to the invention, the orthogonal projection P.sub.1 of the radially inner end E.sub.1 of the additional circumferential reinforcement 6 onto the axially outer face 21 of the bead 2 is radially on the outside of the centre O of the bead wire 5. In other words, the orthogonal projection P.sub.1 onto the axially outer face 21 of the bead 2 of the radially inner end E.sub.1 of the additional circumferential reinforcement 6 is positioned radially on the outside of the straight line OH passing through the centre O of the bead wire 5 and perpendicular at the point H to the axially outer face 21 of the bead 2.

(7) The orthogonal projection P.sub.2 of the radially outer end E.sub.2 of the additional circumferential reinforcement 6 onto the axially outer face 21 of the bead 2 is intended to come into contact with a point P.sub.2 of the rim 3 axially on the inside of the point C of last contact of the rim 3 when the tire 1 is mounted on its rim 3 and inflated to a recommended pressure. The profile of the bead of the mounted and inflated tire is depicted in dotted line in FIG. 1.

(8) The invention has been studied in more particular depth in the case of a tire of size 305/75R20 intended to be fitted to a metro train.

(9) At this size, the additional circumferential reinforcement is made up of two partially superposed or scaled additional layers. The additional circumferential reinforcement is made by helically winding two turns of a strip. The strip is made up of aramid reinforcers of 167/2 construction, namely made up of two 167 tex strands twisted together, these reinforcers being distributed at a density of 98 threads/dm.

(10) Numerical simulations have been performed on three tires comprising three different bead configurations in order to evaluate the respective impacts they have on load-bearing wear: a first tire comprising beads with no additional reinforcement, a second tire referred to as conventional comprising beads with an additional reinforcement comprising metal reinforcers making an angle of 22 with the circumferential direction, the additional reinforcement being characterized by a circumferential tensile tangent stiffness equal to 250 daN/mm and by a radial distance between the radially inner end and the radially outer end of the additional circumferential reinforcement equal to 20 mm, a third tire according to the invention comprising beads with an additional circumferential reinforcement made up of two additional layers of aramid reinforcers, the additional reinforcement being characterized by a circumferential tensile tangent stiffness equal to 1200 daN/mm and by a radial distance between the radially inner end and the radially outer end of the additional circumferential reinforcement equal to 10 mm.

(11) The parameter adopted for estimating the intensity of load-bearing wear that the additional reinforcement is supposed to combat is the maximum amplitude of cyclic circumferential movement (expressed in mm) of the points of the bead in contact with the rim in a contact that is assumed to be a perfect sliding contact. The lower the maximum amplitude of cyclic circumferential movement, the more limited the load-bearing wear will be.

(12) For the first tire comprising beads with no additional reinforcement, the calculated maximum amplitude of cyclic circumferential movement is equal to 4.7 mm. For the second tire comprising beads with an additional reinforcement comprising metal reinforcers making an angle of 22 with the circumferential direction, the calculated maximum amplitude of cyclic circumferential movement is equal to 3.2 mm. Finally, for the third tire according to the invention comprising beads with an additional circumferential reinforcement made up of two additional layers of aramid reinforcers, the calculated maximum amplitude of cyclic circumferential movement is equal to 3.8 mm. The calculated maximum amplitude of cyclic circumferential movement for the third tire according to the invention is therefore somewhere between the amplitudes calculated respectively for the first and second tires: this value is considered to be good enough to obtain satisfactorily limited load-bearing wear.

(13) The invention must not be interpreted as being restricted to the foregoing but may be extended to other embodiments such as, for example and nonlimitingly, additional reinforcements comprising additional layers the reinforcers of which are spaced by a constant or variable spacing, are broken up or are wavy.