MXPA00006854A - Tyre bead with reinforcing circumferential elements - Google Patents

Abstract

The invention concerns a tyre comprising at least a radial body ply (2) anchored in each tyre bead (B) to at least one bead wire (1) to form a ply turn-up (20), characterised in that, viewed in meridian cross-section, the body ply (2) has a meridian profile whereof the outline, between point A of the largest axial width and point T tangent with the circumscribed circle at the casing layer (10) of the anchoring bead wire (1), is convex over its whole length, and such that the thickness e of the tyre bead (B), measured in a plane perpendicular to said meridian profile at a point C of height hc, ranging between 30 and 40 mm and measured relative to the base YY'ranges between 2.5 and 3.0 times the thickness e of the sidewall measured on the straight line D"of the largest axial width, said body ply (2) being reinforced in its non upturned part, with a supplementary reinforcing ply (6) formed by at least one ply (61) of circumferential reinforcing elements axially arranged inside said non-upturned part.

Description

PNEUMATIC HEEL WITH CIRCUMFERENTIAL REINFORCEMENT ELEMENTS DESCRIPTION OF THE INVENTION The present invention relates to a radial carcass reinforcement tire intended to carry heavy loads and, more particularly, to a tire for heavy goods vehicles, intended to equip vehicles such as, for example, trucks, road tractors, buses, trailers and others and, more particularly, to the new reinforcement structure of the heels of said tire. A tire of the type considered comprises, in general, a carcass reinforcement formed by at least one wire rope fabric, anchored in each bead, at least to a rod, forming a fold. The carcass reinforcement has radially superimposed a crown reinforcement, composed of at least two metallic wire fabrics, crossed from one fabric to the next, forming with the circumferential direction angles comprised between 10 ° and 45 °. The folds of the carcass reinforcement are generally reinforced by at least one bead reinforcement fabric formed REF.121724 by metal cables oriented at a small angle, with respect to the circumferential direction, generally comprised between 10 ° and 30 °. In the case of the presence of a single heel reinforcement fabric, the latter is generally located axially to the outside, along the fold of the carcass reinforcement, with a radially superior end located above or below. of the radially superior end of the fold of the carcass reinforcement. As regards the radially inferior end of such a reinforcing fabric, it is generally located in a line parallel to the axis of rotation and passing approximately through the center of gravity of the meridian section of the anchor rod the carcass armor. The object of the known solution is to avoid the deradialization of the cables of the bending of the carcass reinforcement, as well as to minimize the radial and circumferential deformations suffered by the end of said bending, and by the outer rubber layer that covers the bead and which ensures the union with the rim. The useful life of the tires for large-tonnage vehicles, due to the progress made, due to the fact that certain taxiings become less penalizing in terms of wear of the tread, has become such that it is still necessary improve the resistance of the heels. The aforementioned improvement should fall on the degradation of the rubber layers at the level of the fold ends of the carcass reinforcement and the radially outer ends of the heel reinforcement fabrics. More particularly, in the case of tires subjected to prolonged rolling, which often induce a high temperature in the beads, due to the temperatures reached by the mounting rims, the rubber mixtures in contact with the rim are subjected, then, to a decrease of its rigidity, as well as to a more or less slow oxidation, which gives rise to a very marked tendency of the carcass reinforcement to unwind around the rod under the effect of the internal inflation pressure , despite the presence of one or more reinforcing fabrics of the heels. There are then movements of the rod, and shear deformations at all ends of the fabrics, which lead to the destruction of the heel. The mentioned improvement must refer, also, and mainly, to this second possibility of degradation.

The carcass reinforcement of a radial tire, mounted on its service rim, and inflated to the recommended pressure, has, on one side, a regularly convex meridian profile between, approximately, the splice areas with the meridian profile of the tire reinforcement. crown and with the heel. In particular, from the radius where the carcass reinforcement "is influenced by the fabric or the reinforcement fabrics of the heels, said armature has a substantially rectilinear meridian profile, or even curved in the opposite direction to the curvature at the sides, that is to say, substantially parallel to the curvature of the rim flanges from a radially located turning point, approximately , at the level of the radially superior end of the heel reinforcement fabric, placed along the fold of the carcass reinforcement. An architecture of this type leads to relatively thick tire beads. The resistance problems mentioned above, which are influenced by the operating temperature of the beads, have been resolved, in a very small part, by a very reinforced bead structure. The French patent no. 2 654 988 describes a tire, particularly adapted for heavy vehicles, with a radial carcass reinforcement formed by inextensible reinforcement elements and anchored in each bead. Said heel is reinforced by two steel cable fabrics, a first fabric bent around the rod to form two branches, and a second fabric axially disposed inside the main part of the carcass reinforcement. Said problems can also be solved by a thinned bead structure, obtained, for example, by the means described in French patent no. 2 451 016 which, for this purpose, teaches to confer to the outer wall of the tire, comprised between the point at which said wall leaves contact with the rim and the point at which said wall reaches its maximum distance with respect to the plane Equatorial, a relatively large concavity, when the tire is mounted on your service tire and inflated to the recommended pressure. Such an arrangement becomes insufficient, in particular when the relation between the height H of the tire mounted on its rim and the maximum width S of the tire decreases, and must be improved when the loads supported become higher, or the inflation pressures lower , at the recommended loads and pressures.

The investigations carried out by the applicant have led to the conclusion that the thinning of the heels should be done, not by the outside of the tire, but by the interior, and that this should be done in combination with precise characteristics of reinforcement of the heels mentioned. . In order to improve the resistance of the heels of a tire, for a vehicle intended to carry heavy loads, said pneumatic tire, according to the invention, comprises, at least, a radial carcass reinforcement, formed by at least one fabric. of inextensible reinforcing elements and anchored in each bead B, at least, to a rod to form a bend, each bead B being reinforced by an additional reinforcement reinforcement formed by metallic elements. This is characterized in that, seen in meridian section, the carcass reinforcement has a meridian profile, the tracing of which, comprising the point A of greatest axial width and the first tangency point T with the almost circular coating layer of the rod of anchoring, is convex along its entire length, and such that the thickness e of the heel B, measured in a perpendicular to said meridian profile at a point C of height hc, comprised between 30 and 40 mm and measured with respect to the base of the heel YY ', is comprised between 2.5 and 3.0 times the thickness e of the side measured on line D ", line of greatest axial width, said reinforcement being reinforced, in its non-bent part, by the additional reinforcement reinforcement, formed, at least, by a web of circumferential reinforcing elements axially disposed within said unfolded part.The point A of greatest axial width is, by definition, the point of the meridian profile of the corresponding carcass reinforcement. to the point of greatest axial width of the carcass reinforcement when the tire is mounted on its service rim and inflated to the recommended pressure and not loaded, and the line D "of greatest axial width, is the line parallel to the axis of rotation and passing through A. The elements of the additional reinforcement reinforcement are called circumferential, if the angle they form with the circumferential direction is between + 5 ° and -5 °. The convex outline of the meridian profile of the carcass reinforcement is generally formed by several adjacent circular arcs, whose radii of curvature are increasing from the point A of greatest axial width to the point of tangency T with the coating layer, almost circular, of the anchor rod, but the path between point A and point T can be convex and circular with a center of curvature located on the line of greatest axial width. The fabric or fabrics of the additional reinforcement reinforcement, axially inside the unfolded part of the carcass reinforcement, will advantageously have their radially lower ends radially below the line D ', parallel to the axis of rotation and passing by the point of the coating layer of the anchor rod radially farthest from the axis of rotation, but above the line D, parallel to the axis of rotation and passing through the point of the coating layer of the anchor rod radially closer to the axis of rotation, and the radially upper ends located at a radial distance from line D, comprised between an amount equal to the radial half-distance between lines D and D "increased by the radial half-distance between lines D and D ', and an amount equal to the radial half-distance between lines D and D "decreased in the radial half-distance between lines D and D'. This structure thus allows a partial absorption of the meridian tension stresses suffered by the carcass reinforcement, and thus minimizes the radial deformations at the ends of the bending of the carcass reinforcement, irrespective of the taxi conditions. The absorption of the forces will be greater the more numerous the reinforcing elements of the additional reinforcement are; these will be, preferably, metallic, steel, parallel to each other in the additional fabric and will be together over the entire width of the reinforcement reinforcement. It is said that the reinforcing elements are together, if, in the direction perpendicular to said elements, the distance separating two adjacent elements is reduced to the maximum. The absorption of the stresses of the meridian tension of a carcass reinforcement is known per se from numerous documents. The French patent no. 750 726 of the applicant teaches the gluing of carcass reinforcement fabrics to auxiliary reinforcements, each formed by spirally wound yarn and which, consequently, exhibits remarkable flexibility in the transverse direction. Said gluing is carried out in such a way that two fabrics of the carcass reinforcement enclose an auxiliary reinforcement, said enclosure being made in the absence of a rod and a bending of the carcass reinforcement.

The French patent no. 1 169 474 teaches, also, to suppress the rod usually used, by small fabrics of wires or metal cables, inclined with respect to the anchoring parallel, being able to descend the angle of inclination up to 5 °, being bent, or not, the fabric or the fabrics of the carcass reinforcement. The French patent no. 1 234 995 provides for the replacement of the reinforcing elements, usually oblique, of the fabric or the heel reinforcement fabrics, intended to reduce the movements of the anchor against the rim flange, by circumferential elements, the reinforcement being able to be arranged reinforcement between the main part of the carcass reinforcement and the bending of said reinforcement, or axially to the exterior of said carcass reinforcement bending. In the French patent no. 1 256 432, there are the same heel reinforcement structures, of circumferential elements, said elements being intended for the total absorption of the stresses of the carcass reinforcement, and in the case of tires for passenger vehicles , in the absence of anchor rods or any other reinforcing fabric.

FR 2 055 988 describes a certain number of possible applications of a reinforcement reinforcement, of circumferential elements, in particular, the use of such reinforcement instead of the usual reinforcement of oblique elements disposed axially to the outside of the bend of the reinforcement. the carcass armor. The combination of the meridian profile according to the invention, in the presence of a heel reinforcement reinforcement, of circumferential elements, and in which at least one fabric is disposed inside the unfolded or main part of the reinforcement of housing, allows not only the improvement of the resistance of the heels,. but, moreover, when combining the presence of a reinforcement heel reinforcement, described above, with the replacement of the rod of rectangular wires used, generally, in the type of tire considered, by a more economical rod of braided type , that is, formed by a helical braid of several metallic threads, or by a package-type rod of polygonal section, that is to say, a rod obtained by winding on a shape of a metallic thread, which leads to several layers of different widths, it allows to obtain a very clear reduction of the weight of a tire, without altering, on the other hand, its properties. The above types of rods allow a smaller volume due to the shape of their cross section, but also, because the absorption of the stresses by the additional reinforcement, allows a sensible decrease of said sections. Whatever the type of rod, braid or package, the cross section can be reduced by 30 to 50%, which leads, with respect to the application of the invention to the case of a more bulky rectangular rod, to have a thinner heel thickness, or a constant bead thickness, but with a meridian profile called more tense, in the sense that its convexity is less pronounced. The bead reinforcement reinforcement, thus described, can be made separately, by spirally winding it on a horizontal support in an appropriate manner and then transferring it to the unvulcanized tire blank. However, the manufacture of such a tire will be facilitated, advantageously, by the use, as reinforcement elements, of sections, or of groups or groups of sections, of cables of circumferential length comprised between 0.2 and 0.4 times the average circumferential length of the reinforcement reinforcement, which allows, without major difficulties, the placement of the bead reinforcement reinforcement on the construction drum of the crude blank of the carcass reinforcement and the toric conformation of the said reinforcement. blank, and the aforementioned average length being measured during the positioning on said manufacturing drum. Interstices or circumferential cuts between cut elements will be, preferably, displaced from each other. In order to impart an increased transverse stiffness to the bead of the tire, while at the same time allowing an increased improvement of the heel strength, it may also be advantageous that at least one formed fabric be present in the additional reinforcement reinforcement. by circumferential metal elements and axially disposed to the outside of the unfolded part of the carcass reinforcement. Said additional fabric, axially to the outside, will have its radially upper end located radially in the same manner as the cloth or the fabrics axially to the interior, while the radially inferior end of this second fabric will be located, ventily, between the straight D and a line parallel to D 'radially to the outside and radially distant from D' an amount equal to the radial distance separating D 'from D. The reinforcing elements of said second fabric will preferably be sections or a set of sections of metallic steel cables, of circumferential length equal, at most, to 0.4 times the average circumferential length of the reinforcement reinforcement thus formed. The features of the invention will be better understood with the help of the description that follows and which refers to the drawings, which illustrate, but are not limited to, exemplary embodiments, and in which: Figure 1 schematically represents a tire structure FIG. 2 shows schematically and in enlarged view a first variant of the bead according to the invention, in its more simplified version, FIG. 3 schematically represents a second variant of the invention. heel according to the invention, the rod being a braided rod, and with a reinforcement reinforcement of two-heel heel. The tire P shown in FIG. 1 is a tire measuring 315/80 R 22.5 intended to be mounted on a rim comprising rim seats inclined 15 °. Said tire comprises a tread band (4) joined to two heels B by means of two sides (5). Each bead B is reinforced by a rod (1) formed by the winding on an appropriate form of a wire of quadrilateral section until obtaining several rows of radially juxtaposed threads. Around said rod (1) is anchored a carcass reinforcement (2), composed of a single wire rope. The anchoring is made by a fold (20) around the layer (10) of rubber mixture, which covers the rod (1), the radial distance h being that separates the radially superior end of said fold (20), with respect to the line YY ', parallel to the axis of rotation and defining the nominal diameter of the bead (which, in the case described, is the same as the diameter of the service rim), equal to 37 mm, in the studied example of the tire of measurements 315/80 R 22.5. Between the carcass reinforcement (2) and its fold (20), a rod filling (71) of rubber mixture of generally high Shore hardness is disposed radially above the rod (1).

Axially to the outside of the fold (20), there is a reinforcing fabric (6) formed by inextensible metallic cables, weakly oriented with respect to the circumferential direction and whose radially upper end is farther from the axis of rotation than the upper end of the fold (20) of the carcass reinforcement (2). Said fabric (6) is separated from the rod filling (71) by a second blocking filler (72), and from the protective rubber mixture (8), which surrounds the heel B, by a rubber mixing profile (73). The bead B of the tire, of the same dimension, according to the invention and shown in figure 2, is reinforced, in an identical manner, by a rod (1) of rectangular threads and surrounded by a layer (10) of rubber mixture of high elongation module, around which the carcass reinforcement is anchored (2) to form a fold (20). Said heel B has, in combination, the following two essential characteristics: the carcass reinforcement (2), seen in meridian section, has a meridian profile, between the point A of greatest axial width and the first tangency point T of the aforementioned profile with the coating layer (10), almost circular, of the rod (1), which is, in a continuous manner, convex, and the reinforcing reinforcement of the bead (6), composed, in the example described, by a single fabric (6) of circumferential elements, is placed axially inside the unfolded part of the carcass reinforcement (2) and not axially outside the fold (20) of the carcass reinforcement (2). The convexity of the meridian profile, continuous from point A to point T, allows, with respect to the prior art tire, with a profile tracing that passes from convex to concave, a not insignificant thinning of heel B. If the thickness is considered e of the bead, such as the distance, measured in a perpendicular to the meridian profile of the carcass reinforcement drawn from the point C of said meridian profile of height hc, comprised between 30 and 40 mm and measured with respect to the line YY ', the The bead, according to the invention, has a thickness equal to 2.9 times the thickness e of the side, measured on line D "parallel to the axis of rotation and of greatest axial width, while the bead B of the tire of figure 1 has a thickness, measured under the same conditions, equal to 3.4 times the thickness e.The aforementioned thinning, visualized in figure 2 by the difference of the tracings of the inner walls, respectively, of a prior art tire and of a Pneumatic according to the invention, can only give satisfactory results, if the heel B is reinforced by at least one additional reinforcing fabric (61) of elements of high modulus of elasticity and arranged circumferentially, said fabric being located (61). ) axially inside the carcass reinforcement (2) whose meridian profile is convex. The reinforcing elements of the fabric (61) are sections of metallic cables of 27 x 23, the length of said elements or sections of cables being equal to a quarter of the length circumferentially of said fabric (61) measured during its positioning on the building drum of the blank of the carcass reinforcement. The spaces between ends of elements are of small amplitude: 3 mm (measured, also, during placement) and are circumferentially displaced between them. The radially lower end of the fabric (61) is arranged substantially in a line parallel to the axis of rotation and passing through the point of the rod (1) closest to the axis of rotation, which is located at a distance from the "axis of rotation of 290 mm, comprised between the distance of 280 mm that separates from the axis of rotation the line D passing through the point of the covering layer (10) of the anchor rod (1) closest to the axis of rotation and the distance of 305 mm separating the straight line D 'from the axis of rotation passing through the point of the covering layer (10) farthest from said axis of rotation., this is located radially, in the described case, at a distance re from the axis of rotation equal to 335 mm, which is comprised between a measurement of 357.5 mm, equal to the semisum of 345 mm of the respective distances to the axis of rotation of the straight lines D and D ", (410 + 280) / 2, being the straight line D" of greater axial width that passes through the point A to 410 mm of the axis of rotation, increased in the radial half-distance of 12.5 mm between the straight lines D and D ', (305 - 280) / 2, and a measurement of 332.5 mm, equal to the semisum 345 mm of the respective distances to the axis of rotation of the straight lines D and D "decreased in the radial half-distance of 12.5 mm between the straights D and D 'The heel B is completed by a filler (71), uniquely and radially above the rod (1), and by a protective layer (8) The heel B, shown in figure 3 , differs from that shown in Figure 2, on the one hand, by the fact that the anchor rod (1) of the carcass reinforcement (2) is a rod of t ipo "braided" (could be of the "package" type), which allows a smaller weight gain and volume, while retaining an effective cross section of substantially constant rod and a decrease in the cost price of the tire, and, on the other hand, by the fact that the additional reinforcement reinforcement (6) of the heel comprises two fabrics (61) and (62) of cut reinforcement elements. If the heel of FIG. 3 is compared with that of FIG. 2 and, in particular, the respective meridian profiles of the carcass reinforcement, it is clearly visible that it is heel thickness e, distance always measured perpendicular to the meridian profile of the heel. the carcass reinforcement drawn from the same point C of the citad meridian profile, is smaller and, in this example, equal to 2.5 times the thickness e of the side, of 8.9 mm, measured on line D "parallel to the axis of rotation and greater axial width The first additional reinforcing fabric (61) is, as above, axially to the interior of the convex profile of the unfolded part of the carcass reinforcement (2), while the second fabric (62) is axially to the outside The radial continuity of the stiffness of this part of the tire is ensured by the non-agreement of the respective ends of the two fabrics (61) and (62), the ends of the first fabric (61) remaining within the limits previously defined gone; however, the radially superior end of the second fabric (62) is located radially below the upper end of the first fabric (61), while the radially lower end of the second fabric (62) is very slightly above the straight D '. Pneumatic tires according to the invention and such as those described in the part of the description corresponding to figure 2, have been compared with: - usual tires Pt, that is to say, comprising heels of usual thickness and in which the fabric of Heel reinforcement is a continuous metallic wire fabric oriented at 22 ° with respect to the circumferential direction and axially disposed to the outside of the fold of the carcass reinforcement, as shown in Figure 1 of the drawings, tires PA. comprising heels of normal thickness, but with a heel reinforcement fabric axially positioned within the carcass reinforcement and formed by the same circumferentially oriented lengths of cables, and PB tires comprising heels of thinned thickness with a reinforcing fabric of the bead disposed axially to the outside of the fold of the carcass reinforcement, and formed by continuous metallic cables oriented at an angle of 22 ° with respect to the circumferential direction. The comparison has been made under two criteria of quality, fundamental for the resistance of the heels of tires: the resistance with overload, and the resistance in hot rim. Under the same conditions of taxi for all the tested tires (tested 2 per category), the usual Pr tires make an average of 53,000 km on undercarriage and 5,200 km on hot rim. The PA tires have made, respectively, 101,000 km and 8,100 km, while the PB tires performed 32,000 km and 3,300 km, respectively, and the tires Be according to the invention, 105,000 km and 8,200 km. The above results perfectly highlight the beneficial effect of replacing the reinforcement reinforcement, of angled elements, on the carcass reinforcement bending, by a reinforcing reinforcement, of discontinuous circumferential elements, axially to the interior of the main part of the reinforcement. carcass armor. Moreover, the mentioned results highlight the effect of manifest synergy that exists between the two parameters, the thickness of the heel and the appropriate choice of structures and position of the reinforcement reinforcement of the bead: for example, running on a hot rim, if the reinforcement armor, of discontinuous circumferential cables, placed inside the carcass reinforcement allows a measured gain of 2,900 km in the case of a heel of usual thickness, the same change allows a gain of 4,900 km in the case of a bead slimmed down. The same happens with the results in running with overload: the change of reinforcing armor causes a gain of 48,000 km in the case of a heel of usual thickness, while the same change causes a gain of 73,000 km, that is, almost the double, in the case of a thinned heel. This synergistic effect, unsuspected until then, allows to confer to a tire whose heels have the combination of the described parameters, a resistance clearly much higher than what is known today, while allowing a lightening of the total weight of the tire and a slight decrease in its cost price. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects or products to which it refers.

Claims (7)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1. Tire, comprising at least one radial carcass reinforcement, formed by at least one fabric of inextensible reinforcement elements and anchored in each bead B to a rod to form a fold, each bead B being reinforced by an additional reinforcement of reinforcement of at least one fabric formed by metallic elements, axially disposed inside the unfolded part of said carcass reinforcement, characterized in that, seen in meridian section, the carcass reinforcement has a meridian profile, whose layout, between the point of tangency A of greatest axial width and the point of tangency T with the almost circular covering layer of the anchor rod, is convex along its entire length, and such that the thickness e of the heel B, measured in a perpendicular to said meridian profile at a point C of height hc, comprised between 30 and 40 mm and measured with respect to the base the heel YY ', is comprised between 2.5 and 3.0 times the thickness e of the measured side in the straight line D "of greater axial width, said casing reinforcement being reinforced in its non-bent part, by the additional reinforcement reinforcement formed by at least one fabric of circumferential reinforcement elements.

2. Tire according to claim 1, characterized in that the fabric or the fabrics of the additional reinforcing reinforcement, axially inside the unfolded part of the carcass reinforcement, advantageously have their radially lower ends radially below the straight line. D ', parallel to the axis of rotation and passing through the point of the cover layer of the anchor rod radially farthest from the axis of rotation, but above the line D, parallel to the axis of rotation and passing through the point of the cover layer of the anchor rod radially closest to the axis of rotation, and whose end or radially upper ends thereof located at a radial distance from the line D, comprised between a quantity equal to the radial half-distance between the lines D and D ", increased at the radial half-distance between lines D and D ', and a magnitude equal to the radial half-distance between lines D and D" decreased in radial distance e Between lines D and D '.

3. A tire according to any of claims 1 or 2, characterized in that the additional reinforcement reinforcement also comprises at least one fabric, formed by circumferential metal elements and axially disposed outside the unfolded part of the carcass reinforcement, said additional fabric having its radially upper end located radially in the same manner as the cloth or fabrics axially inwardly, while its radially lower end is located between the straight D 'and a straight parallel to D' radially to the outside, distant radially of D 'a magnitude equal to the radial distance separating D' from D.

4. Tire according to any of claims 1 to 3, characterized in that the circumferential reinforcement elements of the additional reinforcement are metallic, of steel, and are together over the entire width of said reinforcement.

5. Tire according to any of claims 1 to 4, characterized in that the anchor rod of the carcass reinforcement is a "braided" type rod.

6. Tire according to any of claims 1 to 5, characterized in that the reinforcing elements of the reinforcement reinforcement, are sections, or sets of sections, of cables of circumferential length comprised between 0.2 and 0.4 times the average circumferential length of the reinforcement , measured during the placement on the building drum of the blank of the housing.

7. Tire in accordance with the claim 6, characterized in that the interstices or circumferential cuts between cut sections are displaced with respect to one another.