Anchoring of the carcass of a tyre

The present invention relates to tires. More particularly, it relates to the arrangement of the reinforcing wires in the sidewalls and in the beads; it also relates to the anchoring of the carcass wires in the bead.

The carcass reinforcement of tires is currently constituted by one or more plies, most often radial, turned around around one or more bead wires arranged in the beads. The beads constitute the means for fixing the tire on the rim. The rigidity of the bead thus formed is very great.

It is desirable to ensure a progressive evolution of the rigidity of the bead when one moves radially upwards in the direction of the sidewall. In the current technique, it is quite difficult to ensure such a progressive change in rigidity between the sidewall and the bead. The sidewall must have significant flexibility, and the bead must on the contrary have significant rigidity. In fact, the reinforcements that are available in this part of the tire always inevitably have a discontinuity: at the radially upper end of the carcass reversal, one passes without transition into an area devoid of this carcass reversal, an area which is therefore inevitably less rigid. As a reminder, "radially upwards", or "radially higher" means towards the largest radii.

In the case of radial carcasses, the state of the art already knows other design principles which make it possible to avoid reversals around a rod. By way of example, mention may be made of US Pat. No. 3,072,171, in which it was proposed to suppress the inversion of the carcass plies, and to have wires oriented circumferentially next to the carcass wires oriented radially. In the known structure, it is however difficult to ensure sufficiently strong anchoring of the carcass wires to the circumferentially oriented wires, which means that this proposal has never known any real application.

The object of the invention is to propose a new way of arranging the carcass reinforcement wire in order to be able to ensure as progressive a change as possible in the bending stiffness of the sidewall of the tire when one approaches the bead, while allowing the anchoring of a very large number of carcass wires.

Another object pursued by the invention is to propose a reinforcement structure for a tire which easily lends itself to mechanized manufacturing.

The tire according to the invention, comprising at least one carcass anchored on each side of the tire downwards in a bead the base of which is intended to be mounted on a rim seat, each bead extending upwards by a sidewall, the sides joining up a tread, the carcass comprising carcass yarn portions disposed adjacent to one another and forming in the upper part of the sidewall a single circumferential alignment of yarn portions going from top to bottom in the sidewall, said carcass being anchored in said bead by means of at least one stack of circumferentially oriented wires, is characterized in that, by moving radially from the top of the sidewall towards the bottom of the bead, said alignment is divided into at least two axially spaced circumferential alignments, separated by a filling material devoid of circumferentially oriented wires, and in that at least one of said bead alignments is bordered laterally, axially on the side opposite to said material filling, at least with said stack of circumferentially oriented threads, and in that the carcass is made from a continuous carcass thread, all said portions of wire of each of the alignments of the bead being connected two by two by a loop located at the radial level closest to the base of the bead.

In the present specification, the term “thread” generally designates both monofilaments and multifilaments, or assemblies such as cables, twists or else any equivalent type of assembly, and this, whatever the material and the treatment of these threads, for example surface treatment or coating or pre-sizing to promote adhesion to the rubber. A carcass will be said to be radial when its wires are arranged at 90 °, but also, according to the terminology in use, at an angle close to 90 °.

In the bead produced in accordance with the present invention, passing from the sidewall to the bead, the carcass wires are distributed on either side of a filling material. Preferably, so that each of the carcass wire portions contributes in a substantially identical manner to the resumption of the forces due to inflation, each of said alignments of the bead is bordered laterally by at least one stack of circumferentially oriented wires, disposed axially on the side opposite to said filling material.

Preferably, the circumferentially oriented wires are not in direct contact with the radially oriented wires. For tires subjected to significant stresses, in order to ensure good transmission of forces between the portions of carcass wire and the circumferentially oriented wires, a rubber with high elasticity is interposed, ie a mixture of rubber having a Shore A hardness greater than 70, between the circumferentially oriented wires and the alignment of adjacent carcass wires.

It is known that in the current technique, the carcass ply (s) are turned around around a rod. The rod then fulfills a carcass anchoring function, that is to say takes up the tension developing in the carcass wires under the effect of the inflation pressure. The arrangement claimed here ensures the anchoring function of the carcass.

We also know that, still in the state of the art, the same rod also provides a function of tightening the bead on its rim. The arrangement claimed here is also capable of ensuring sufficient tightening.

It goes without saying that the invention can be used by adding on one side and / or the other of the claimed structure other elements also forming part of the carcass or of its anchoring, as certain variants will illustrate. . Similarly, the invention can be used by multiplying carcasses of the same kind, or even by adding another type of carcass to a carcass according to the invention. All the details of construction are given in the description which follows, to be consulted with the following figures:<ul id="ul0001" list-style="none"><li>FIG. 1 is a radial section essentially showing a sidewall and a bead of a tire according to the invention;</li><li>Figure 2 is a perspective view, schematically showing the arrangement of the reinforcing wires and certain layers of rubber;</li><li>Figure 3 is a radial section showing a second alternative embodiment of the invention;</li></ul>

Figures 1 and 2 illustrate the simplest variant. We can see the various well known parts of a tire, more particularly concerned with the present invention, namely the sidewall 1 and the bead 2. The carcass reinforcement consists of portions of carcass wire, here oriented radially in the flanks 1. It should be understood that the carcass wire may not be oriented radially, in particular where it is bordered axially by circumferentially oriented wires. The reinforcement is of the mono-carcass type. In other words, in the sidewall, the carcass wire is arranged in a single layer and is therefore arranged in a single alignment 3.

At the base of the bead, the carcass wire forms juxtaposed and adjacent loops. By placing the wire in loops, we avoid all cut edges, which are as many discontinuities. Indeed, the reinforcing wire is generally a cable; the cable ends have, at the point of cutting, openings in which all the monofilaments deviate from each other. This constitutes incipient fractures inside the tire. When the threads are made of textile material, they are glued to ensure very good adhesion to the rubber. Unfortunately, there is no pre-gluing on each end of the cable after it has been cut, which again means that the rubber does not adhere to the place of the cut, hence the risk of priming. of rupture inside the bead. With the arrangement described here, this kind of drawback is not to be feared.

By the presence of loops between back and forth, we see that the carcass is of the "single wire" type, that is to say that the carcass is manufactured from a single wire, and not from as many sections (individualized by a cut) that there are radial arches in the carcass, all calendered beforehand to form a ply. Of course, the carcass might not be made in its entirety from a single wire. It is advisable however to use only a small number of threads and to arrange the ends and the beginnings of thread rather under the tread than in the beads.

In FIGS. 1 to 3, it can be seen that the carcass wire, which forms in each flank a single circumferential alignment 3 back and forth forming juxtaposed portions of wire, is arranged so that, starting from a flank to reach the base of a bead 2, the carcass is divided into two circumferential alignments of radial wires 31, 32 deviating axially progressively from one another.

Preferably, the carcass wire portions are arranged so that, in the flanks, two adjacent carcass wire portions come from different alignments of the bead 2. In other words, in the flank, there is alternation of wires from each of the alignments 31 and 32 of the bead 2.

These implementations of the invention are very particularly advantageous because, at the sidewall 1 of the tire, there is a single circumferential alignment of portions of cords (that is to say a single layer of cords). This is such as to allow very great flexibility of the sidewalls: the bending stiffness of the sidewall when crushing a tire provided with such a reinforcement structure remains low, much lower than when there are two plies of carcass as in architectures commonly used when the number of carcass cords is multiplied, for highly stressed tires, or when less resistant cords are used.

This results in a staggered arrangement which appears very well from the perspective of FIG. 2. The two alignments are separated by a layer of rubber 8 called filling, which allows the wires to be well impregnated and to ensure the perfect cohesion of the bead. , while maintaining the alignments 31 and 32 separated axially from each other. This distribution of the wires promotes perfect positioning of the wire portions, and also of their loops, with good impregnation by the rubber. You can adjust the height at which this separation is organized in several alignments, by interposing rubber in layer 8 over a selected height, and if necessary in progressively variable axial thickness. In this way, the flexural rigidity is very gradually raised.

There could of course be, in the bead, more than two circumferential alignments of wires diverging axially progressively from one another, all coming from the same alignment of the sidewall.

In all cases, we divide by two or by more than two the number of threads in each alignment of the bead relative to the number of threads in the alignment of the flank from which they come, which is very interesting because the radius being more small at the bead, there is less room to accommodate the aligned wires than in the side.

The invention makes it possible to use a higher density of wires. In other words, thanks to the invention, the number of carcass yarns is increased from which a separate additional carcass will have to be used, due to the lack of space in the bead to accommodate all of the yarns.

In all the variants described, the tire comprises a laminated composite structure formed by the following adjacent layers: a stack of circumferentially oriented wires 61, a layer 5 of a rubber mixture having a Shore A hardness greater than 70, a circumferential alignment 31 of carcass wires, a layer 8 of a filling rubber mixture, a circumferential alignment 32 of carcass wires, a layer 5 of a rubber mixture having a Shore A hardness greater than 70, and a stack of wires 62 oriented circumferentially. This makes it possible to balance the recovery of the tension appearing in the carcass wires under the effect of the inflation pressure.

The layers 5 can be obtained in the vulcanized tire because, during the assembly of the tire, rubber has been deposited for the sole purpose of producing said layers, or else because it has been used, to obtain the windings 61, 62, and / or possibly to form the carcass, wire sufficiently coated with rubber so that, after molding, the layers 5 that have just been described appear.

The wire used for the circumferentially oriented wire stacks is preferably brass plated wire. In each stack 61, 62, the wires are substantially concentric and superimposed. As for the manner of obtaining said stacks of wire, one can superimpose rings of progressively increasing diameter, or else one can for example wind several turns of wire.

The experiments revealed very interesting results in endurance using, for the rubber layers 5, a mixture containing a synthetic elastomer SBR used alone, or in blending with polybutadiene, said SBR having a glass transition temperature (Tg) between -70 ° C and -30 ° C and said polybutadiene having a Tg of between -40 ° C and -10 ° C, said synthetic elastomer (s) being used in a totalized proportion of at least 40% of the total weight of elastomer, the balance being constituted by natural rubber. The Tg considered are measured by differential thermal analysis.

Preferably, an SBR solution is used. For example, using a mixture containing 50% of SBR solution having a Tg of -48 ° C, containing 50% of NR, with the addition of reinforcing fillers and resin to obtain the desired Shore A hardness.

To obtain a good bonding of a layer 5 of rubber both on the brass-plated metallic threads of the batteries 61, 62 and on the textile threads of the carcass, and to guarantee good endurance of this bonding at high temperature, said layer 5 rubber has a high sulfur content and adhesion promoters are used (for example metal salts of cobalt or nickel) in well-adjusted proportions. For example, a sulfur content of between 5 and 8% of the total weight of elastomer and cobalt in an amount of 0.2% of the total weight of elastomer is used.

It is not necessary to add a rubber mixture formulated specifically and only to ensure the impregnation of the carcass wire, or wire windings forming the piles 61 or 62. The same type of mixture as that formulated for the layers 5 provides the calendering and connection functions between the wire portions of the same stack, and between the different wire stacks, by impregnation during molding. For convenience, the rubber mixture of layer 8 can be the same as that of layers 5.

In order to ensure an excellent recovery of the tension appearing in the carcass wires under the effect of the inflation pressure, it is desirable that said loops are arranged radially at a level below the lowest part of the stacks of adjacent wires. , oriented circumferentially.

Preferably, the carcass wire forms back and forth from a bead 2 to the other of the tire passing under the tread; the thread is therefore continuous from one bead to another. The various means of reinforcing the structure of the tire under the tread are not part of the present invention. It suffices to point out that they can be formed by all the appropriate reinforcement methods, such as for example wires arranged so as to ensure a triangulated belt. In addition, in the bead, one can of course have a very stiff rubber mixture, of the kind used for bead stuffing in conventional tires. This stuffing rubber is provided on one side and / or the other of the carcass reinforcement.

In FIG. 3, it can be seen that, inside the bead 2, the circumferential windings of wire 63 and 64 have been added. There remains between the wires only thin layers of rubber, that is to say layers no thicker than the diameter of the wires of the windings or alignments. These thin layers can be obtained after molding because, during the assembly of the tire, rubber-coated wire was wound to obtain the batteries 63 and 64 and also, if necessary, the batteries 61 and 62.

If necessary, multiply the stacks of windings of adjacent circumferential wires to reinforce the beads. The grouping of several adjacent piles like 61, 63 or 62, 64, plus other possible piles creates a kind of bundles of wires. It is obvious that another solution could consist in placing all of these wires in a manner other than in stacks oriented substantially radially, as soon as all of the wires occupy an approximately equivalent radial section.

In the same figure, it can be seen that there are windings of wire 65 which are circumferentially oriented and rise radially upwards in the part of the sidewall 1 situated under the equator. This makes it possible to give different gaits from the forms of natural balance of an inflated radial carcass. It is thus possible to perfectly control the shape and the rigidities of the tire when it is inflated on the wheel. It is of course possible to use threads of a different nature in the sides and in the bead, or inside these. Of course, this arrangement can be used with any of the variants described.

Preferably, the density of the circumferentially oriented threads is lower in the sidewall 1 than in the beads 2. It is desirable that the density variation be gradual, so as to ensure as smooth a transition as possible between the bead and the side of the pneumatic. Similarly, each of the stacks of circumferentially wound wire, for example the stacks 61, 62, can terminate radially upward in an area of ​​lower density.

To ensure as smooth a transition as possible between the rim contact area and the equator, above the rim contact area and below the equator, the rubber components located on both sides of the other carcass respect the following relationship:<maths id="math0001" num=""><math display="block"><mrow><mfrac><mrow><apply><sum /><lowlimit><mtext>i</mtext></lowlimit><uplimit /><mrow><msub><mrow><mtext> E</mtext></mrow><mrow><mtext>i</mtext></mrow></msub><msub><mrow><mtext>e</mtext></mrow><mrow><mtext>i</mtext></mrow></msub><mtext>(Ext)</mtext></mrow></apply></mrow><mrow><apply><sum /><lowlimit><mtext>j</mtext></lowlimit><uplimit /><mrow><msub><mrow><mtext> E</mtext></mrow><mrow><mtext>j</mtext></mrow></msub><msub><mrow><mtext>e</mtext></mrow><mrow><mtext>j</mtext></mrow></msub><mtext>(Int)</mtext></mrow></apply></mrow></mfrac><mtext> ≥ 3</mtext></mrow></math><img file="EP0664233B1_D0001.tif" /></maths> where E_i or E_j is the module in the radial direction, e_i or e_j the thickness of each constituent "i" or "j" of rubber respectively outside 70 and inside 71 of the set of carcass wire alignments. When there are several carcass alignments in this part of the tire, for the application of this formula, only the constituents outside the outermost wire and respectively inside the innermost wire are considered.

When the module of all the constituents used is comparable, this means that the carcass should be passed as far as possible from the inner side of the sidewall. You can also use softer erasers (ie with a lower modulus) on the inner side of the sidewall. This ensures a good compromise between the endurance of the tire and the comfort it provides.

We see that the proposed reinforcement structure allows a progressive evolution of the rigidities between the sidewall and the bead. This structure offers the tire designer very large latitudes for adjusting this rigidity and its evolution by very simply varying the density of the circumferentially oriented wires, and possibly the number of circumferential alignments of carcass wires in the beads, and on the nature of the threads.

This composite structure makes it possible to obtain a good seat for the bead on its rim, while being compact and making the best use of the materials used.

The proposed structure has no reinforcement discontinuity, which is very favorable to the endurance of the tire, and which also unexpectedly leads to better comfort of the tire.

In order to position the reinforcement cords as precisely as possible, it is very advantageous to make the tire on a rigid support, for example a rigid core imposing the shape of its internal cavity. All the constituents of the tire are applied to this core, in the order required by the final architecture, which are arranged directly in their final place, without undergoing any shaping at any time during manufacture. In this case, the tire can be molded and vulcanized as described in US Pat. No. 4,895,692.