A tire is composed of reinforced tread elements wrapped transversely with reinforcing metal parts.

Abstract

Invention details;

Description

PNEUMATIC INCLUDING A CUT-IN TOP REINFORCEMENT WITH METALLY REINFORCED TOP

[0001] The present invention relates to a tire with a radial carcass reinforcement and more particularly to a tire intended to equip vehicles carrying heavy loads, such as, for example, trucks, tractors, trailers, road buses or civil engineering equipment.

[0002] In general, in heavy-duty tires, the carcass reinforcement is anchored on both sides in the bead area and is radially surmounted by a crown reinforcement consisting of at least two superimposed layers formed of parallel wires or cables in each layer and crossed from one layer to the next at angles between 10° and 45° with the circumferential direction. These working layers, forming the working reinforcement, may be further covered by at least one protective layer formed of advantageously metallic and extensible reinforcing elements, known as elastic elements.It may also include a layer of wires or cables forming an angle of between 45° and 90° with the circumferential direction. This layer, called the triangulation layer, is radially positioned between the carcass reinforcement and the first crown layer, known as the working layer, which is formed of parallel wires or cables having angles of no more than 45° in absolute value. The triangulation layer, together with at least the aforementioned working layer, forms a triangulated reinforcement, which exhibits minimal deformation under the various stresses it is subjected to. The essential role of the triangulation layer is to resist the transverse compression forces exerted on all the reinforcing elements in the crown area of ​​the tire.

[0003] Cables are said to be inextensible when, under a tensile force equal to 10% of the breaking force, said cables exhibit a relative elongation of no more than 0.2%.

[0004] Cables are said to be elastic when, under a tensile force equal to the breaking load, said cables exhibit a relative elongation of at least 3% with a maximum tangent modulus less than 150 GPa.

[0005] Circumferential reinforcement elements are reinforcement elements that make angles with the circumferential direction within the range of +2.5°, -2.5° around 0°.

[0006] The circumferential direction of the tire, or longitudinal direction, is the direction tangent to the periphery of the tire and defined by the direction of rolling of the tire.

[0007] The transverse or axial direction of the tire is parallel to the axis of rotation of the tire.

[0008] Radial direction is a direction that intersects the axis of rotation of the tire and is perpendicular to it.

[0009] The axis of rotation of the tire is the axis around which it rotates in normal use.

[0010] A radial or meridian plane is a plane that contains the axis of rotation of the tire.

[0011] The circumferential median plane, or equatorial plane, is a plane perpendicular to the axis of rotation of the tire and which divides the tire into two halves.

[0012] Some modern tires, known as "road" tires, are designed for high speeds and increasingly long journeys, due to improvements in road networks and the growth of highways worldwide. The overall conditions under which such a tire is expected to operate undoubtedly allow for an increase in mileage, as tire wear is reduced; however, the tire's durability, and particularly that of the tread, is compromised.

[0013] There are indeed constraints at the level of the top reinforcement and more particularly shear stresses between the working top layers, combined with a significant rise in operating temperature at the ends of the axially shortest working top layer, which result in the appearance and propagation of cracks in the rubber at said ends.

[0014] In order to improve the endurance of the crown reinforcement of the type of tire studied, solutions relating to the structure and quality of the layers and / or profiles of rubber compounds which are arranged between and / or around the ends of the plies and more particularly the ends of the axially shortest working plies have already been provided.

[0015] It is known to introduce a layer of rubbery compound between the ends of the working layers to create decoupling between said ends and limit shear stresses. Such decoupling layers must, however, exhibit very good cohesion. Such layers of rubbery compounds are described, for example, in patent application WO 2004 / 076204.

[0016] French patent FR 1 389 428, to improve the resistance to degradation of rubber compounds located in the vicinity of the edges of the top reinforcement, recommends the use, in combination with a low hysteresis tread, of a rubber profile covering at least the sides and marginal edges of the top reinforcement and made of a low hysteresis rubber compound.

[0017] French patent FR 2 222 232, to avoid separations between layers of top reinforcement, teaches to encase the ends of the reinforcement in a rubber mat, the Shore A hardness of which is different from that of the tread surmounting said reinforcement, and greater than the Shore A hardness of the rubbery mixture profile disposed between the edges of the layers of top reinforcement and carcass reinforcement.

[0018] Furthermore, it is known for producing tires with very wide treads or for increasing the load-bearing capacity of tires of a given size by incorporating a layer of circumferential reinforcing elements. Patent application WO 99 / 24269, for example, describes the presence of such a layer of circumferential reinforcing elements.

[0019] The layer of circumferential reinforcing elements is usually made up of at least one wire rope wound to form a spiral whose angle of laying with respect to the circumferential direction is less than 2.5°.

[0020] Document WO 05 / 113258 further proposes a radially working top layer closest to the frame reinforcement, the ends of which are folded to to cover the edges of another layer of the top reinforcement. Such a design also eliminates at least some of the layer ends that can be the source of the crack initiations described earlier.

[0021] In another area of ​​tire manufacturing, namely aircraft tires, which are also designed to carry heavy loads but operate at high pressure and much higher speeds on non-aggressive surfaces, it is known to use a so-called sliced ​​crown reinforcement, and more specifically, a sliced ​​working reinforcement. Documents WO 2015059172, WO 2015063131, WO 2015071152, WO 2015124758, and WO 2015150133 describe such a crown reinforcement, comprising at least one crown bilayer formed by a circumferential zigzag winding of a strip, along a circumferential direction of the tire. Such a crown reinforcement has the advantage of limiting the number of individual crown layers and eliminating the free ends of these layers.

[0022] However, this stepped crown reinforcement, for an aircraft tire, is made up of crown layers incorporating textile reinforcements. In the field of heavy-duty tires, given the particularly harsh operating conditions, the use of textile reinforcements is hardly feasible, and the use of metal reinforcements is generally accepted as a preferable solution.

[0023] Furthermore, the use of tires on heavy goods vehicles can lead to impacts on the tires when driving on stony surfaces. These impacts are obviously detrimental to performance in terms of durability.

[0024] It is still known to those skilled in the art to increase the number of plies constituting the crown reinforcement to improve the tire's endurance against such shocks.

[0025] Such solutions lead to a greater mass of the tire and higher tire manufacturing costs.

[0026] The inventors have thus set themselves the mission of providing tires for "Heavy Goods Vehicles", whose endurance performance, particularly with regard to the stresses generated at the ends of the plies, is improved while maintaining endurance performance in relation to the shocks sustained on the tread regardless of driving conditions.

[0027] This objective is achieved according to the invention by a tire comprising a radial carcass reinforcement, said tire comprising a crown reinforcement, comprising at least a first crown bilayer consisting of a circumferential zigzag winding of at least one strip of at least one metallic reinforcing element embedded in an elastomeric compound, the crown reinforcement being radially capped by a tread, said tread being joined to two beads by means of two sidewalls, in which: - said at least one strip has a width of 1b, - the trajectory of the circumferential zigzag winding is a periodic curve, whose origin is fixed in the equatorial plane, having a period T and an amplitude 1s, - said periodic curve forming, with the circumferential direction, an angle α measured at the points of the curve positioned in the equatorial plane greater than 15°, - said periodic curve extending over a number N of periods T distributed over a number P of tire rotations, - the apparent average density of metallic reinforcing elements of said at least one strip in the equatorial plane is greater than 0.6, - the number of metallic reinforcing elements of said at least one radially overlapped strip is less than or equal to 5, - the minimum radius of curvature R m in metallic reinforcing elements satisfies the relationship 14 * R 2 / ls < R m in < 3 / 2*R 2 / ls, with R: the radius of curvature in the equatorial plane of the strip's application surface, measured on a meridional section of the tire, - the amplitude 1s of said periodic curve varies within a range between 70% and 100% of the maximum value of the amplitude Ismax, and - the amplitude 1s of at least one period T is less than 95% of the amplitude Ismax.

[0028] Preferably according to the invention, when the strip is made up of at least two reinforcing elements, said at least two reinforcing elements are arranged parallel and advantageously inserted between two calendered layers of elastomeric mixture.

[0029] In the context of the invention, when a strip is made up of at least two reinforcing elements, said reinforcing elements are separated from each other by a pitch measured along the direction normal to the principal mean direction of the reinforcing elements at the level of the equatorial plane.

[0030] In the context of the invention, in the case of a strip made up of a single reinforcing element, the width 1b of said strip is the circumscribed diameter of said reinforcing element.

[0031] According to the invention, in the case of a strip made up of at least two reinforcing elements, the width 1b of said strip is the distance measured at the equatorial plane, along the direction normal to the principal mean direction of the reinforcing elements, between the outermost points of the two outermost reinforcing elements of the strip. The outermost points and the outermost reinforcing elements are those furthest from the center of the strip along the direction normal to the principal mean direction of the reinforcing elements.

[0032] In the context of the invention, the amplitude 1s of said periodic curve is the axial distance measured between the two outermost axially positioned points of a reinforcing element over the same period. These two outermost axially positioned points of a reinforcing element over the same period correspond to the two points for which the radius of curvature of the reinforcing element is the smallest. The largest amplitude 1s of the periodic curve according to the invention corresponds to the axial width of the working layers formed by the strip.

[0033] In the context of the invention, the apparent average density of metallic reinforcing elements of said at least one strip in the equatorial plane is given by the ratio of the length of metal in the equatorial plane, measured along the circumferential direction over one wheel revolution, to the circumference in the equatorial plane corresponding to 2TTR.

[0034] These different measurements are carried out on a stripped tire, that is to say, one whose tread has been at least partially removed to reveal at least one strip.

[0035] According to the invention, the number of radially overlapping metallic reinforcing elements of said at least one strip is determined on a meridional cross-section of the tire. The maximum number of radially overlapping metallic reinforcing elements is determined by observation on four meridional cross-sections made at 90° intervals around the tire's circumference. Each cross-section has a circumferential length of 5 centimeters, and the observation is made on each face of each cross-section.

[0036] The results obtained with tires conforming to the invention have indeed demonstrated that performance in terms of endurance can be improved. These results confirm, in particular, that the absence of free ends in the tread layers improves endurance performance during tire rolling, regardless of driving conditions.

[0037] The crown bilayer, consisting of a circumferential zigzag winding of at least one strip of metallic reinforcing elements inserted between two calendered layers of elastomeric mixture, constituting at least part of the crown reinforcement of the tire, replaces the usual working layers of more common tires as described previously.

[0038] Applying these layers by laying a zigzag strip effectively eliminates free ends due to the strip being turned over at the point where it forms the edge of the top reinforcement.

[0039] This bilayer, forming at least part of the top reinforcement, has the particularity of being obtained by the trancaning of a strip including metallic reinforcements, whereas the trancaning process is usually used for textile reinforcements, which are much simpler to trancanize due to their greater deformability.

[0040] The inventors have further demonstrated that the combination of an apparent average density of metallic reinforcing elements in said strip in the equatorial plane greater than 0.6, a number of radially superimposed metallic reinforcing elements less than or equal to 5, and a minimum radius of curvature of the metallic reinforcing elements satisfying the relation 14 * R 2 / ls < R m in < 3 / 2*R 2 / ls, with an amplitude of 1s of said periodic curve varying in a range between 70% and 100% of the maximum value of the 1s amplitude, the 1s amplitude of at least one period T being less than 95% of the Ismax amplitude, makes it possible not to disrupt unacceptably the other performance of the tire and in particular the performance in terms of endurance in connection with the use of a strip made up of metallic reinforcement elements laid in a zigzag pattern.

[0041] Indeed, the apparent average density of metallic reinforcing elements of said at least one strip in the equatorial plane will translate, for a fixed density of reinforcing elements in the strip and the width of the strip, into an overlap rate r in the equatorial plane during the manufacture of the tire on a mounting surface of radius R, in the equatorial plane, on which the zigzag strip is wound.

[0042] The overlap ratio r can be expressed as: N*(lb / sina) / 2TTR. The expression N*(lb / sina) represents the circumferential length developed by the strip, where 1b / sina is the width of the strip projected onto the circumferential direction, and N is the number of periods T forming the bilayer. An apparent average density of metallic reinforcing elements in at least one strip in the equatorial plane greater than 0.6 will be obtained for an overlap ratio r such that 0.6 <T<1. Cette plage de recouvrement traduit le fait que la longueur circonférentielle développée d’une couche de sommet est inférieure ou égale à la circonférence 2KR de la surface de pose de rayon R, dans le plan équatorial, c’est-à-dire que la juxtaposition de portions de bandelette n’est pas réalisée, sauf pour T = 1.The chosen range, which is directly related to the apparent average density of metallic reinforcing elements of said at least one strip in the equatorial plane, reflects the near absence of gaps between adjacent strip portions.

[0043] The inventors have demonstrated that this apparent average density of metallic reinforcing elements in at least one strip in the equatorial plane contributes to achieving highly satisfactory endurance performance, particularly with regard to impacts sustained at the tread level. The inventors believe they interpret these results as resulting from a satisfactory overlap, similar to the two layers of cross-laminated reinforcing elements found in more conventional tire designs.

[0044] To obtain these recovery rate values ​​r during tire manufacturing, the inventors were able to translate the previous relationship as follows to use the manufacturing parameters: angle a is defined according to the manufacturing parameters as follows: atan meaning: arctangent.

[0045] The inventors further demonstrated that the number of radially overlapped metallic reinforcement elements in said strip, at least one strip, of less than or equal to 5, contributes in particular to achieving satisfactory endurance performance, especially from a thermal perspective at the top reinforcement. The inventors also demonstrated that laying a strip in a zigzag pattern leads to overlapping strip thicknesses, with the greatest number occurring at the axial ends of the top reinforcement, i.e., in the strip's fold zones. An excessive number of overlaps results in localized thicknesses that generate temperature rises, impacting endurance performance. The combination of a minimum radius of curvature for the metallic reinforcement elements, satisfying the relationship 14 * R, is also relevant. 2 / ls < R m in < 3 / 2*R 2 / ls, and with an amplitude of 1s of said periodic curve varying within a range between 70% and 100% of the maximum amplitude Ismax, the amplitude 1s of at least one period T being less than 95% of the amplitude Ismax, makes it possible to reduce the number of overlaps of the tread in the outermost axial zone. Conversely, the design according to the invention, compared to an unselected design with a constant amplitude, leads to outermost axial zones with larger axial widths and radial overlaps of tread passes close to the defined maximum overlap value. Surprisingly, this finding does not lead to any negative effect on the expected performance of the tire.

[0046] To obtain this minimum radius of curvature of the metallic reinforcement elements R mIn this case, the inventors define it based on manufacturing characteristics according to the following relationship:

[0047] Regarding the variation of the amplitude 1s of the period T, the inventors propose, during the tire manufacturing simulation, to initiate production with a maximum amplitude Ismax corresponding to the desired crown reinforcement width. This desired crown reinforcement width is defined by the tire designer according to standard practices to achieve the desired tire performance, particularly in terms of drift stiffness. The periods T are wound on the mounting surface of radius R in the equatorial plane as long as the number of radially overlapped metallic reinforcement elements of said strip remains less than or equal to 5. As soon as this value is exceeded, the amplitude 1s is decreased.

[0048] The inventors propose, for example, that when the simulation of a zigzag winding results in a radial overlap of six or more metal reinforcement elements, the last period T is discarded and modified by reducing the amplitude 1s. If the new simulation of this modified period T satisfies the condition of a radial overlap of five or fewer metal reinforcement elements, the following period T is simulated again with a maximum amplitude Ismax. Otherwise, if the new simulation of this modified period T fails to satisfy the condition of a radial overlap of five or fewer metal reinforcement elements, a new simulation of the period T is performed with a greater reduction in amplitude.This operation is repeated until a radial superposition of a number of metallic reinforcement elements of said strip less than or equal to 5 is obtained, and finally returns to the next period again simulated with a maximum amplitude Ismax.

[0049] According to a preferred embodiment of the invention, the periodic curve is a sinusoid.

[0050] Preferably, the maximum amplitude Ismax of the periodic curve is greater than 60% and even more preferably less than 90% of the tread width. Such a design allows for the formation of a crown reinforcement similar to conventional designs where the crown reinforcement consists of several working layers.

[0051] Preferably according to the invention, the angle a is less than 45°. During the variations of the amplitude 1s, the inventors choose to maintain the angle in a range between 15° and 45° to lead to the desired properties of the tire, in particular in terms of drift rigidity.

[0052] According to an advantageous embodiment of the invention, the difference in amplitude ls between two periods T of different amplitudes is greater than 100% of the width 1b of the strip. The inventors have demonstrated that below this value, achieving a reduction in the number of radial overlaps of the metallic reinforcement elements is much more uncertain. This choice of reducing the amplitude ls allows the reduction in the number of radial overlaps of the metallic reinforcement elements to be achieved in a single iteration in most cases.

[0053] Advantageously, according to the invention, the difference in angle α between two periods T of different amplitudes is less than 8°. According to the inventors, installation under these conditions ensures that the desired performance of the tire is maintained without undesirable effects appearing during driving under specific stress conditions.

[0054] According to a preferred embodiment of the invention, the metallic reinforcement elements are cables.

[0055] According to this preferred embodiment of the invention, the diameter of the cables is less than 1.60 mm and preferably less than 1.00 mm.

[0056] Preferably according to the invention, the cables are made of wires with diameters less than 0.30 mm and preferably with diameters less than 0.20 mm.

[0057] These dimensional choices of the cables and wires constituting them are particularly favorable for facilitating the turning of the strip during zigzag installation.

[0058] An advantageous variant of the invention provides that the strip has a breaking strength per unit width greater than 2*Pg*R, with R: the radius of curvature in the equatorial plane of the strip's application surface, measured on a meridional section of the tire, Pg: the nominal inflation pressure of the tire according to the ETRTO standard.

[0059] According to a first embodiment of the invention, the top reinforcement comprises at least one layer of circumferential reinforcing elements.

[0060] According to this variant of the invention, said at least one layer of circumferential reinforcing elements is advantageously radially external to said at least one first top bilayer.

[0061] Said at least one layer of circumferential reinforcing elements is thus radially separated from the carcass reinforcement by said at least one first top bilayer so as to limit the stresses on said circumferential reinforcing elements and not to fatigue them too much.

[0062] Advantageously according to the invention, the layer of circumferential reinforcing elements has an axial width greater than 0.5xS.

[0063] S is the maximum axial width of the tire, when it is mounted on its service rim and inflated to its recommended pressure.

[0064] The axial widths of the layers of reinforcing elements are measured on a cross-section of a tire, the tire therefore being in an uninflated state.

[0065] According to an advantageous embodiment of the invention, the reinforcing elements of at least one layer of circumferential reinforcing elements are metallic reinforcing elements having a secant modulus at 0.7% elongation between 10 and 120 GPa and a maximum tangent modulus less than 150 GPa.

[0066] According to a preferred embodiment, the secant modulus of the 0.7% elongation reinforcement elements is less than 100 GPa and greater than 20 GPa, preferably between 30 and 90 GPa and preferably still less than 80 GPa.

[0067] Preferably also, the maximum tangent modulus of the reinforcing elements is less than 130 GPa and preferably even less than 120 GPa.

[0068] The moduli expressed above are measured on a tensile stress-elongation curve determined with a preload of 20 MPa. The tensile stress corresponds to a measured tension referred to the metal cross-section of the reinforcing element. The measurements are taken on cables extracted from the tire along a portion of the layer of circumferential reinforcing elements extending from one axial end of said layer over an axial width of 50 mm towards the interior of said layer.

[0069] The moduli of the same reinforcement elements can be measured on a tensile stress-elongation curve determined with a preload of 10 MPa. The tensile stress corresponds to a measured tension referred to the overall cross-section of the reinforcement element. The overall cross-section of the reinforcement element is the cross-section of a composite element made of metal and rubber, the latter having penetrated the reinforcement element during the tire curing process.

[0070] According to this formulation relating to the overall section of the reinforcement element, the reinforcement elements of the axially external parts and of the central part of at least one layer of circumferential reinforcement elements are metallic reinforcement elements having a secant modulus at 0.7% elongation between 5 and 60 GPa and a maximum tangent modulus less than 75 GPa.

[0071] According to a preferred embodiment, the secant modulus of the 0.7% elongation reinforcement elements is less than 50 GPa and greater than 10 GPa, preferably between 15 and 45 GPa and preferably still less than 40 GPa.

[0072] Preferably also, the maximum tangent modulus of the reinforcing elements is less than 65 GPa and preferably even less than 60 GPa.

[0073] According to a preferred embodiment, the reinforcing elements of at least one layer of circumferential reinforcing elements are metallic reinforcing elements having a tensile stress-as-relative-elongation curve with low slopes for low elongations and a substantially constant and steep slope for higher elongations.

[0074] The different characteristics of the reinforcement elements stated above are measured on reinforcement elements taken from tires.

[0075] Reinforcing elements particularly suited to creating at least one layer of circumferential reinforcement elements according to the invention are, for example, assemblies of formula 21.23, whose construction is 3x(0.26+6x0.23) 4.8 / 7.5 SS; this stranded cable consists of 21 elementary wires of formula 3 x (1+6), with 3 strands twisted together, each consisting of 7 wires, one wire forming a central core with a diameter of 0.26 mm, and 6 wound wires with a diameter of 0.23 mm. Such a cable exhibits a secant modulus at 0.7% of 45 GPa and a maximum tangent modulus of 98 GPa, measured on a tensile stress-elongation curve determined with a prestress of 20 MPa, the tensile stress corresponding to a measured tension referred to the metal cross-section of the reinforcing element.On a tensile stress versus elongation curve determined with a prestress of 10 MPa, the tensile stress corresponding to a measured tension referred to the overall section of the reinforcing element, this cable of formula 21.23 has a secant modulus at 0.7% equal to 23 GPa and a maximum tangent modulus equal to 49 GPa.

[0076] Similarly, another example of a reinforcing element is a 21.28 assembly, whose construction is 3x(0.32+6x0.28) 5.6 / 9.3 SS. This cable exhibits a secant modulus at 0.7% of 56 GPa and a maximum tangent modulus of 102 GPa, measured on a tensile stress-strain curve determined with a prestress of 20 MPa, the tensile stress corresponding to a measured tension referred to the metal cross-section of the reinforcing element. On a tensile stress-strain curve determined with a prestress of 10 MPa, the tensile stress corresponding to a measured tension referred to the overall cross-section of the reinforcing element, this 21.28 cable exhibits a secant modulus at 0.7% of 27 GPa and a maximum tangent modulus of 49 GPa.

[0077] The use of such reinforcing elements in at least one layer of circumferential reinforcing elements makes it possible in particular to maintain satisfactory layer stiffness even after the shaping and baking stages in conventional manufacturing processes.

[0078] According to a second embodiment of the invention, the circumferential reinforcing elements can be formed from inextensible metallic elements cut to form sections of length much shorter than the circumference of the shortest layer, but preferably longer than 0.1 times said circumference, the cuts between sections being axially offset from one another. Even more preferably, the tensile modulus of elasticity per unit width of the additional layer is lower than the tensile modulus of elasticity, measured under the same conditions, of the most extensible top working layer.Such an embodiment makes it possible to give, in a simple way, to the layer of circumferential reinforcing elements a modulus that can easily be adjusted (by choosing the intervals between sections of the same row), but, in all cases, lower than the modulus of the layer made up of the same metallic elements but continuous, the modulus of the additional layer being measured on a vulcanized layer of cut elements, taken from the tire.

[0079] According to a third embodiment of the invention, the circumferential reinforcing elements are corrugated metallic elements, the ratio a / X of the wave amplitude to the wavelength being at most equal to 0.09. Preferably, the tensile modulus of elasticity per unit width of the additional layer is less than the tensile modulus of elasticity, measured under the same conditions, of the most extensible working top layer.

[0080] According to a second embodiment of the invention, the inventors propose to substitute for the layer of circumferential reinforcing elements, proposed according to the first embodiment of the invention presented above, a second top bilayer consisting of a circumferential zigzag winding of a strip of metallic reinforcing elements inserted between two calendered layers of elastomeric mixture.

[0081] According to this second embodiment of the invention, the top reinforcement comprises at least a second top bilayer, radially external to said at least a first bilayer, consisting of a circumferential zigzag winding of a strip of metallic reinforcing elements inserted between two calendered layers of elastomeric mixture, in which: - said strip has a width of 1b', - the trajectory of the circumferential zigzag winding is a periodic curve having a period T' and an amplitude 1s', - said periodic curve forming, with the circumferential direction, an angle a' measured at the points of the curve positioned in the equatorial plane greater than 10°, - said periodic curve extending over a number N' of periods T' distributed over a number P' of tire rotations, - the amplitude 1s' being less than the amplitude 1s, - angle a' being less than angle a, of said at least a first vertex bilayer, and less than 20°, - the apparent average density of metallic reinforcing elements of said at least one strip in the equatorial plane is greater than 0.6, - the number of metallic reinforcing elements of said at least one radially overlapped strip is less than or equal to 5, - the minimum radius of curvature Rm in metallic reinforcing elements satisfies the relation % * R 2 / ls' < R min ' < 3 / 2*R 2 / ls', - the amplitude 1s' of said periodic curve varies within a range between 70% and 100% of the maximum value of the amplitude Is'max, and - the amplitude 1s' of at least one period T is less than 95% of the amplitude Is'max,.

[0082] According to this second embodiment of the invention, the inventors propose the realization of a second top bilayer with an amplitude 1s' advantageously less than that of the first top bilayer and thus forming a working reinforcement of narrower axial width, with an angle a' also less than that of the first top bilayer.

[0083] According to this second embodiment of the invention, the angle a' formed by the reinforcing elements of this second bilayer with the circumferential direction in the equatorial plane is less than the angle a formed by the elements of reinforcement of the first crown bi-layer to promote better compression of the tire crown.

[0084] Advantageously, according to this second variant of the invention, the amplitude 1s' is less than 80% of the amplitude 1s.

[0085] Advantageously, according to this second variant of the invention, the maximum value of the amplitude Is'max is between 40% and 80% of the width of the tire tread.

[0086] According to a preferred embodiment of this second variant, the width 1b' of the strip forming the second vertex bilayer is equal to the width 1b of the strip forming the first vertex bilayer.

[0087] The reinforcement elements of this second top layer are preferably cables.

[0088] According to this preferred embodiment of the invention, the diameter of the cables is less than 1.60 mm and preferably less than 1.00 mm.

[0089] Preferably according to the invention, the cables are made of wires with diameters less than 0.30 mm and preferably with diameters less than 0.20 mm.

[0090] The metallic components are preferably steel cables.

[0091] Other advantageous details and features of the invention will become apparent from the description of the exemplary embodiments of the invention with reference to Figures 1 to 7, which represent: Figure 1, a meridian view of a diagram of a tire according to a first embodiment of the invention; Figure 2, a meridian view of a diagram of a tire according to a second embodiment of the invention; Figure 3, a perspective view of a circumferential zigzag winding of a strip, along a periodic curve, on a mounting surface. Figure 4, a graphic representation in unwinding and flattening of a succession of periods of laying of a strip, Figure 5, a view in projection on a plane of several turns of winding of a strip on a tire with a constant amplitude, Figure 6, a graphic representation in unwinding and flattening of a succession of periods of laying of a strip, Figure 7, a view in projection on a plane of several turns of winding of a strip on a tire with different amplitudes.

[0092] The figures are not drawn to scale for ease of understanding. Figures 1 and 2 represent only a half-view of a tire that extends symmetrically with respect to the XX' axis, which represents the circumferential median plane, or equatorial plane, of a tire.

[0093] In Figure 1, the tire 1 is size 315 / 70 R 22.5. This tire 1 comprises a radial carcass reinforcement 2 anchored in two ribs, not shown in the figure. The carcass reinforcement is formed of a single layer of steel cables. This carcass reinforcement 2 is reinforced by a crown reinforcement 4, formed radially from the inside out: a double layer 41 made by slicing a strip, and a layer of circumferential reinforcing elements 43 formed of 21x23 steel steel cables.

[0094] The top reinforcement is itself capped with a tread 5.

[0095] The strip used to form the bilayer consists of 8 19.18NF cables (1+6+12 0.18 mm wires) with a diameter of 0.9 mm, spaced at 1.23 mm intervals. The strip has a width h of 9.51 mm and a thickness of 1.35 mm.

[0096] The 41 double layer is applied to a mounting surface with a radius R at the equator of 479.2 mm. The axis of the mounting surface corresponds to the axis of rotation of the tire.

[0097] The bilayer 41 is produced using a circumferential zigzag winding of 88 periods T (N=88) over 45 wheel revolutions (P=45). The maximum amplitude Umax is set at 246 mm and the minimum radius R m in at 488.2 mm.

[0098] The chosen reduction of the amplitude 1s is equal to 153% of the width 1b of the strip, i.e. 14.5 mm.

[0099] The applied installation law results in a number of periods per amplitude of 1s according to the distribution in the following table:

[0100] The bilayer was made according to the following sequence: 47 periods of amplitude 246 mm, 4 periods of amplitude 217 mm, 2 periods of 188 mm, 2 periods of 202.5 mm, 2 periods of 246 mm, 4 periods of 202.5 mm, 2 periods of 246 mm, 4 periods of 217 mm, 2 periods of 188 mm, 2 periods of 202.5 mm, 2 periods of 246 mm, 4 periods of 202.5 mm, 2 periods of 246 mm, 4 periods of amplitude 217 mm, 2 periods of 188 mm, 2 periods of 202.5 mm and 1 period of 188 mm.

[0101] The apparent average cable density of the strip measured at the equatorial plane is equal to 0.61.

[0102] In a meridional section of the tire, the maximum number of radially overlapping cords of the band is equal to 5.

[0103] The tire 21 of figure 2 differs from the tire 1 of figure 1 by its apex reinforcement 24 which is formed radially from the inside to the outside: of a first bilayer 241 made by slicing a strip, of a second bilayer 242 made by slicing a strip.

[0104] The innermost radially 241 bilayer is identical to that in Figure 1.

[0105] The 242 double layer is made with the same strip according to a different laying pattern.

[0106] The 242 bilayer is made on a laying surface whose radius R at the equator is equal to 479.7 mm.

[0107] The 242 bilayer is produced using a circumferential zigzag winding of 41 periods T' (N' = 41) over 26 wheel revolutions (P' = 26). The maximum amplitude l s 'max is fixed at 166 mm and the minimum radius R m in' at 1114.9 mm.

[0108] The chosen reduction of the amplitude 1s' is equal to 116% of the width 1b of the strip, i.e. 11 mm.

[0109] The applied installation law leads to a number of periods per amplitude 1s' according to the distribution in the following table:

[0110] The 242 bilayer was produced according to the following sequence: 30 periods of amplitude 166 mm then 11 periods of amplitude 133 mm.

[0111] The apparent average cable density of the strip of the second bilayer 242 measured at the equatorial plane is equal to 0.62.

[0112] In a meridional section of the tire, the maximum number of radially superimposed cords of the second bilayer 242 strip is equal to 4.

[0113] Figures 3 to 7 and the associated descriptions that follow are not made with reference to examples of embodiments of the invention but serve to provide a clarification and a better understanding of the invention by illustrating realizations of bilayers by winding a strip in a zigzag pattern on a laying surface.

[0114] Figure 3 is a perspective view of a circumferential zigzag winding of a strip 6 of width 1b, along a periodic curve 7, on a cylindrical surface of position 8, of revolution around the axis of rotation of the tire and having a radius R. This circumferential zigzag winding of a strip 5 constitutes a top bilayer.

[0115] Figure 4 illustrates a graphical representation, both unrolled and flattened, of a succession of exposure periods for a strip. In this figure, we see a succession of periods T, the amplitude of which is constant (1s), and which will constitute the width of the bilayer formed on the tire.

[0116] Figure 5 shows a projection onto a plane of several turns of a strip wound onto a tire with a constant amplitude. The resulting bilayer on the tire has a width of 1s.

[0117] Figure 6 illustrates a graphical representation, both unrolled and flattened, of a succession of periods T for applying a strip. This figure depicts a succession of periods T whose amplitude 1s alternates between two values, Ismax and Ismin. The amplitude Ismax defines the width of the bilayer formed on the tire.

[0118] Figure 7 shows a projection onto a plane of several turns of a strip wound onto a tire with an amplitude 1s that varies between the two values ​​Ismax and Ismin. The bilayer thus formed on the tire has the width Ismax-

[0119] The tire 21 according to the invention, illustrated in figure 2, is compared to a reference tire H of the same dimension.

[0120] This reference H tire differs from the tires according to the invention by a crown reinforcement formed radially from the inside out: of a first working layer formed of metal cables oriented at an angle of 16°, with respect to the circumferential direction, of a layer of circumferential reinforcing elements formed of steel wire cables 21.23, of a second working layer formed of wire cables oriented at an angle equal to 30° and crossed with the wire cables of the first working layer, the cables of each of the working layers being oriented on either side of the circumferential direction.

[0121] The metal cables of the two working layers are formula 9.35 cables. They are distributed in each of the working layers with a distance between the reinforcing elements, measured along the normal to the direction of the mean line of the cable equal to 2.5 mm.

[0122] The axial width of the first working layer is equal to 246 mm.

[0123] The axial width of the second working layer is equal to 227 mm.

[0124] The axial width of the layer of circumferential reinforcing elements is equal to 200 mm.

[0125] Initial endurance tests, particularly thermally demanding, were carried out on a test machine imposing on each of the tires a straight line run at a speed equal to the maximum speed index prescribed for said tire (speed index) under an initial load of 4000 Kg progressively increased to reduce the duration of the test.

[0126] The tests thus carried out showed that the distance travelled by the tire 21 according to the invention is substantially identical to that travelled by the reference tire H.

[0127] Other endurance tests, particularly demanding mechanically, were carried out on a test machine that cyclically applied a transverse force and a dynamic overload to the tires. The tests were performed on the tire according to the invention under conditions identical to those applied to the reference tires.

[0128] The tests thus carried out showed that the distance traveled by the tire according to the invention is greater than that traveled by the reference tire H by about 45%.

[0129] Tests were also conducted to characterize the breaking strength of a tire crown reinforcement under impact. These tests involved rolling a tire, inflated to a recommended pressure and subjected to a recommended load, over a cylindrical obstacle or indenter with a diameter of 1.5 inches (38.1 mm), a hemispherical head, and a predetermined height, positioned at the center of the tread. The breaking strength is characterized by the critical height of the indenter, that is, the maximum height of the indenter that causes complete rupture of the crown reinforcement, meaning the failure of all crown layers. The results are representative of the energy required to cause rupture of the crown block.

[0130] A third tire F was compared to tire 21 according to the invention and to the reference tire H.

[0131] This tire F is made in a similar way to tire 21 according to the invention but not meeting the criteria of the invention and in particular without varying the amplitude of the winding period of the strips and with an average apparent density of metallic reinforcing elements in the equatorial plane of the first bilayer equal to 0.57 and an average apparent density of metallic reinforcing elements in the equatorial plane of the second bilayer equal to 0.59.

[0132] The tests thus carried out showed that the tire according to the invention leads to values ​​substantially equivalent to those obtained with the reference tire H. These values ​​of the tire according to the invention and of the reference tire H are also on the order of 10% higher than those obtained with the tire F.

Images