Anchoring of a tyre carcass

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 stiffness 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 evolution of rigidity between the sidewall and the bead. The flank must have significant flexibility, and the bead must on the contrary have significant rigidity. Indeed, the reinforcements that are available in this part of the tire always inevitably have a discontinuity: at the radially upper end of the carcass upturn, one passes without transition into an area devoid of this carcass upturn, which area 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, corresponding to the preamble of claim 1, in which it was proposed to suppress the inversion of the carcass plies, and to have wires oriented circumferentially next to the carcass wires radially oriented. 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 gradual 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 object of the invention is achieved by means of the combination of the features of independent claim 1.

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. The term "section" means that it is not a single-wire carcass, manufactured from a single continuous wire arranged along an adequate path. A section is a piece of wire identified by a cut. A section has two cut edges, at least one of which is in the present invention disposed in a bead, at a location close to its base. 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 cords are distributed on either side of a filling element, which may include cords oriented circumferentially. Preferably, so that each of the sections of carcass wire contributes in a substantially identical manner to the recovery of the forces due to inflation, each of said alignments of the bead is bordered laterally by at least one stack of wires oriented circumferentially.

For tires subjected to significant stresses, in order to ensure good transmission of forces between the sections 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 each alignment of carcass wires. Thus, the circumferentially oriented wires are not in direct contact with the radially oriented wires.

We know 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 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;</li><li>Figure 3 is a radial section showing a second alternative embodiment of the invention;</li></ul> Figures 1 and 2 illustrate a first alternative embodiment. We can see the different 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 sections of wire 3, here oriented radially in the sidewalls 1.

In FIGS. 1 to 3, it can be seen that, in each flank 1, the carcass wire 3 forms a single circumferential alignment 30 of sections of wire, and that, starting from a flank to join the base of a bead 2, the carcass is divided into two circumferential alignments of wires 31, 32 progressively deviating axially from one another.

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

This results in a staggered arrangement which appears very well from the perspective of FIG. 2. The two alignments 31 and 32 are separated by a filling element, which makes it possible to very gradually increase the bending stiffness. In addition, the number of threads is halved in an alignment inside the bead, relative to the number of threads present in the alignment of the sidewall. This arrangement is very interesting because the radius being smaller at the height of the bead, there is less room to accommodate the aligned wires than in the sidewall. The invention makes it possible to use a greater 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.

The invention also makes it possible to well impregnate the threads with rubber and to ensure perfect cohesion of the bead, because this distribution of the threads favors the perfect positioning of all the sections of carcass thread.

There could of course be, in the bead, more than two circumferential alignments of wires diverging axially progressively from one another, all resulting from an alignment of the sidewall. In this case, the number of threads in each alignment of the bead is divided by more than two relative to the number of threads in the alignment of the flank from which they come.

This variant, like that illustrated in FIG. 3, is very particularly interesting because, at the sidewall 1 of the tire, there is a single circumferential alignment of sections of wires (ie a single layer of wires) . This is likely 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.

In order to ensure perfect anchoring of a carcass, a laminated composite bead is produced. Inside the bead 2, axially on either side of each alignment 31, 32 of the bead, is arranged at least one stack of circumferentially oriented wires 61, 62 and 62, 63, with the interposition of a layer 5 of rubber compound having a Shore A hardness greater than 70.

The layers 5 can be obtained in the vulcanized tire because, at the time of 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, 63, and / or possibly to form the carcass, of the 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, 63, 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 wires of the batteries 61, 62 and on the textile wires 3 of the carcass, and to guarantee good endurance of this bonding at high temperature, said layer 5 of rubber has a high sulfur content and adhesion promoting additives 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 solely to ensure the impregnation of the carcass wire 3, or of the wire windings forming the batteries 61 or 62. The same type of mixture as that formulated for the layers 5 provides the calendering and bonding functions between the wire sections of the same stack, and between the different wire stacks, by impregnation during molding.

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 the radially lowest end of the carcass wires is arranged radially at a level below the lowest part of the adjacent circumferential wire pile (s).

Preferably, the carcass wire 3 is continuous from one bead to the other and passes under the tread. 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, and / or it is used as a filling element.

In Figure 3, we see another alternative embodiment of the invention. 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 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 64 and 65 and also, if necessary, the batteries 61, 62 and 63.

If necessary, the stacks of windings of adjacent circumferential wires are multiplied to reinforce the beads. The grouping of several adjacent piles like 61, 64 or 63, 65, 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 66 circumferentially oriented rising radially upwards in the part of the flank 1 situated under the equator. This makes it possible to give different looks to 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 wires 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 sidewall pneumatic. Similarly, each of the stacks of circumferentially wound wire, for example the stacks 61, 62, 63, may terminate radially upward in an area of ​​lower density.

In order to ensure as smooth a transition as possible between the contact area with the rim and the equator, above the contact area with the rim and below the equator, the rubber components located on both sides other of the carcass respect the following relation:<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="EP0664231B1_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 rubber component "i" or "j" 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 modulus 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 development by very simply varying the density of the circumferentially oriented cords, and possibly the number of circumferential alignments of carcass cords 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.