Tyre having optimized rolling resistance and roadholding

Abstract

The present invention relates to a tyre (1) for a motor vehicle comprising, in a meridian plane: two beads (50) intended to be mounted on a rim, two sidewall layers (30) connected to the beads (50), a crown (20) comprising a tread (10), the crown (20) having a first side connected to the radially outer end of one of the two sidewall layers (30) and having a second side connected to the radially outer end of the other of the two sidewall layers (30); at least one carcass reinforcement (90) extending from the two beads (50) to the crown (20), the carcass reinforcement (90) being anchored in the two beads (50) to a bead core (53); the tyre (1) comprises a stitched composite material consisting of an elastomer compound and comprising threads stitched into the elastomer compound such that reinforcements oriented in stitching directions are formed.

Description

Tire optimized for rolling resistance and road handling Field of invention [OOOlJThe present invention relates to a tire whose bead is optimized to achieve an advantageous performance compromise in rolling resistance and road behavior compared to conventional designs. Although not limited to this type of application, the invention is more particularly described with reference to a radial tire intended to be mounted on a passenger vehicle or van. Definitions

[0002] By convention, we consider a reference (O, OX, OY, OZ), whose center O coincides with the geometric center of the tire, the circumferential OX, axial OY, and radial OZ directions respectively designate a direction tangent to the rolling surface of the tire according to the direction of rotation, a direction parallel to the axis of rotation of the tire, and a direction orthogonal to the axis of rotation of the tire.

[0003] By radially inner, respectively radially outer, we mean closer, respectively further from the axis of rotation of the tire.

[0004] Axially inner, respectively axially outer, means closer, respectively further from the equatorial plane of the tire, the equatorial plane of the tire being the plane passing through the middle of the tire tread and perpendicular to the axis of rotation of the tire.

[0005] The tire's construction is usually described by a representation of its constituents in a meridian plane, i.e. a plane containing the tire's axis of rotation. Such a choice is motivated by, as a first approximation, the axisymmetry of the tire's geometry around its axis of rotation.

[0006] A tire comprises a crown, intended to come into contact with the ground via a tread, the two axial ends of which are connected via two sidewalls with two beads ensuring the mechanical connection between the tire and the rim on which it is intended to be mounted.

[0007] A radial tire further comprises a reinforcing reinforcement, consisting of a crown reinforcement, radially inside the tread, and a carcass reinforcement, radially inside the crown reinforcement.

[0008] The crown reinforcement of a radial tire comprises a superposition of crown layers extending circumferentially, radially outside the carcass reinforcement. Each crown layer is made up of reinforcements parallel to each other and coated with a polymeric material of the elastomer type or elastomeric mixture. The assembly consisting of the crown reinforcement and the tread is called the crown. [0009JThe carcass reinforcement of a radial tire concerned by the invention usually comprises at least one carcass layer consisting of metallic or textile reinforcing elements each coated in an elastomeric coating mixture. Said at least one carcass layer comprises a main part, connecting the two beads together and is wound, in each bead, around an annular reinforcing structure, which is most often a bead wire. Generally, each bead comprises a filler layer positioned axially external to the bead wire and axially internal to a sidewall. [OOlOJBy elastomeric mixture is meant an elastomeric material obtained by mixing its various constituents. An elastomeric mixture conventionally comprises an elastomeric matrix with at least one diene elastomer of natural or synthetic rubber type, at least one reinforcing filler of carbon black type and / or silica type, a crosslinking system most often based on sulfur, and protective agents. [OOllJBy the expression "based on" composition, we mean a composition comprising the mixture and / or the reaction product of the different constituents used, some of these basic constituents being capable of, or intended to, react with each other, at least in part, during the different phases of manufacture of the composition, in particular during its crosslinking or vulcanization.

[0012] By the expression "part by weight per hundred parts by weight of elastomer" (or pce), it is meant, within the meaning of the present invention, the part, by mass per hundred parts of elastomer present in the rubber composition considered.

[0013] The dynamic shear modulus G* is a dynamic property well known to those skilled in the art and is measured on a Metravib VA4000 or DMA+450 type viscoanalyzer using specimens comprising a cured composition extracted from the tire. The response of the specimen subjected to a sinusoidal alternating simple shear stress is recorded at a frequency of 10 Hz under determined temperature conditions (here 23°C) according to the ASTM D1349-99 standard. An amplitude sweep is carried out. of strain from 0.1% cc to 100% cc (forward cycle), then from 100% cc to 0.1% cc (return cycle), cc meaning peak-peak. The specimen is of cylindrical section as described in ASTM D 5992 - 96 (version reapproved in 2011, originally approved in 1996) in Figure X2.1 (circular embodiment) and has a diameter of 10 mm [0 to + 0.04 mm] and a thickness of 2 mm [1.83-2.33], The dynamic shear modulus G* is defined as the square root of the sum of the square of G' and the square of G” in which G' represents the elastic modulus and G” represents the viscous modulus. The dynamic shear modulus G* is measured at 10% cc of strain on the return cycle. Prior art

[0014] The skilled person, a tire designer, knows that the expected functions of a tire are at least three in number. Firstly, it is a question of carrying the load, resulting from the mass of the vehicle and all the overloads linked to the dynamic movements of the vehicle as well as any aerodynamic overloads at high speed. Secondly, it is necessary to be able to guide the vehicle on the trajectories decided by the driver, and finally, it is necessary to transmit to the ground the acceleration or braking forces decided by the driver.

[0015] The crown reinforcement is an essential element that contributes decisively to the three functions of carrying, guiding, and transmitting. In conventional design, the crown reinforcement with at least two crossed metal layers surrounds the carcass reinforcement to provide the tire with the necessary strength to fulfill its carrying function.

[0016] The Steering function is also known as "road handling." It refers to the responses of a vehicle / tire assembly to multiple driver inputs (steering, acceleration, braking, etc.). Handling is essential both in terms of safety for the vehicle's stability and for driving pleasure.

[0017] The tire plays a key role in road behavior because it ensures, at the end of the chain, the transmission of forces between the vehicle and the ground in order to maintain the trajectory defined by the driver.

[0018] When cornering, to keep the vehicle on a trajectory, it is necessary to generate a force equivalent to (but in the opposite direction) the centrifugal force that tends to eject the vehicle from the trajectory. This lateral force must be generated by the vehicle's 4 tires to overcome the centrifugal force.

[0019] The deformation of the rubber blocks in contact with the ground generates a lateral force. The mechanism that allows the tire to deform the rubber blocks when cornering is called drift. Drift is the angle between the direction of the wheel and the trajectory followed by the vehicle. When cornering, this angle is not zero in order to allow the tire to deform the rubber blocks of the tread and thus generate the necessary lateral forces.

[0020] Transverse drift stiffness is the variation of transverse forces generated in the contact patch of the moving tire crushed by the load carried, as a function of the drift angle applied to the tire. Transverse drift stiffness is expressed in Newton per degree (N / °).

[0021] For small drift angles, i.e. angles less than 4°, the transverse force, in a direction parallel to the tire's axis of rotation, is proportional to the drift angle. The transverse drift stiffness is equal to this coefficient of proportionality.

[0022] Transverse drift stiffness is an essential mechanical quantity which connects the tire to the vehicle and which determines the quality of the vehicle's behavior on the road.

[0023] Rolling resistance is another performance addressed in the invention. Rolling resistance is one of the forces that oppose the vehicle's forward movement. The rolling resistance coefficient of a tire (RRC) is the rolling resistance force related to the load carried by the tire. The coefficient is expressed in kg / t.

[0024] Rolling resistance is primarily related to tire deformation. For example, the beads associated with the sidewalls represent 20% to 30% of the tire's rolling resistance, while the tread contributes 60% to 80%.

[0025] Reducing greenhouse gas emissions from transport is one of the major challenges facing vehicle manufacturers today. Tires represent an important source of progress, through a reduction in rolling resistance, as this has a direct impact on the vehicle's fuel consumption. For example, a 20% reduction in the rolling resistance of a passenger car tire saves approximately 3% of fuel per 100 km in a combined cycle.

[0026] The choice of bead architecture plays a key role in establishing a compromise between road handling and rolling resistance. Among the tire design parameters, the skilled person knows the impact of the filler layers on the desired performance compromise. In each bead, the filler layer is chosen so that its dynamic shear modulus in the transverse direction (tire axis, OY direction) is greater than 10 MPa. In this way, the filler layers contribute to the drift stiffness of the tire. But in general, this high level of dynamic shear modulus of a filler layer is also accompanied by a high level of its hysteresis, and therefore degrades the rolling resistance of the tire. It is known that for a passenger car tire, the filler layer intervenes at a height of approximately 10% of the rolling resistance of the tire.

[0027] Various techniques are known to those skilled in the art, sometimes based on the geometry of the filler layer, sometimes on its mechanical properties to achieve a relevant choice with regard to the compromise between rolling resistance and road behavior. In documents FR2983123, FR2971733, FR2970902, FR2968601, a compromise is sought by reducing the dynamic shear modulus of the filler layer while increasing its volume to compensate for the lack of rigidity. This results in a significant increase in the mass of the tire and therefore its cost price, which makes this type of approach prohibitive. [0028JD' other approaches have been initiated by increasing the rigidity of the stuffing layer by adding synthetic or organic fibers, as taught in documents EP3057810, or JP2013079050, but again without achieving conclusive results.

[0029] Finally, in documents EP2655098 and EP185871, a layer of composite material was introduced into the bead. This layer includes metal or fabric reinforcements coated with an elastomeric mixture and positioned in the bead. But this intrusive approach to bead manufacturing degrades the industrial cost of the tire too much.

[0030] The inventors set themselves the goal of establishing an advantageous compromise of rolling resistance and road handling performance that solves the difficulties listed above. Statement of the invention

[0031] This aim has been achieved by a tire for a motor vehicle comprising in a meridian plane: two beads intended to be mounted on a rim, two layers of sidewalls connected to the beads, a crown comprising a tread, said crown having a first side connected to the radially outer end of one of the two layers of sidewalls and having a second side connected to the radially outer end of the other of the two layers of sidewalls; at least one carcass reinforcement extending from the two beads to the crown, the carcass reinforcement comprising a plurality of carcass reinforcement elements and being anchored in the two beads to a bead wire, said tire comprises at least one stitched composite material consisting of an elastomeric mixture comprising threads stitched into said elastomeric mixture to form reinforcements oriented in stitching directions.

[0032] The principle of the invention is to replace initial elastomeric mixture profiles obtained after an extrusion phase, with composite materials resulting from the sewing of textile threads in said elastomeric mixture profiles. In this way, part of the mixture volumes of the initial profiles are replaced by sewing threads which are less hysteretic. In addition, the composite material profiles are more rigid than the initial mixture profiles, that is to say their dynamic shear moduli are significantly higher. It follows that a tire of the invention comprising such composite profiles deforms less than a tire of the state of the art and therefore the rolling resistance of said tire of the invention is lower.

[0033] In particular, composite material profiles can be used in the beads, providing the expected level of transverse shear stiffness (OY axis direction of the tire) to improve the transverse drift stiffness and therefore the vehicle's road behavior. Furthermore, with lower deformations, rolling resistance decreases. [0034JI1 There are two main methods for obtaining composite fabrics used in tire design. There are fabrics resulting from the direct calendering of a network of parallel and equidistant reinforcements which consists of applying a layer of elastomeric mixture on either side of the network of parallel reinforcements to obtain a composite layer. This is the so-called "straight grain" method. [0035JI1 There is another approach which consists of connecting the reinforcements by a weft thread often orthogonal to the direction of said reinforcements so that the parallel reinforcements and the weft threads form a woven fabric. A calendering step is then carried out on either side of the woven fabric to result in a composite layer. [0036JThe use of woven fabrics in the design of passenger car, aircraft and agricultural tires is known per se. Weft yarns were initially introduced to improve the productivity of fabric manufacturing compared to straight-thread processes. [0037JThe invention proposes a new approach where the reinforcements are sewn directly into the elastomeric mixture, thus avoiding the calendering step, but introduces a sewing step downstream of the extrusion phase.

[0038] According to the invention, each reinforcement of the stitched composite material, allowing reinforcement, has a sewing direction which follows a sewing line. Each reinforcement comprises at least one thread extending along the sewing line. Thus the stitched composite material comprises a plurality of reinforcements, each extending in a sewing direction. The direction of each reinforcement may, in a non-limiting manner, follow one or more trajectories such as rectilinear, curved, sinusoidal, notched trajectories or a combination thereof. A sewing line is a succession of stitches in a given direction, the stitches being connected to each other continuously by the thread. [0039JThe sewing step has a limited impact on the process, thus avoiding excessive deterioration in the cost price of the tire.

[0040] The main characteristic of the invention leads to the tire of the invention characterized in that it achieves a compromise of performance in road behavior and rolling resistance thanks to the use of composite profiles providing additional transverse shear rigidity. [0041JD' other characteristics linked to different embodiments of the invention, contribute to further improving the compromise of performances of the tire. Most often, these characteristics concern properties of the seam such as the direction, the density of the sewing thread.

[0042] Advantageously, the stitched composite material is stitched with a seam such that the distance between two consecutive stitches is between 1 mm and 50 mm.

[0043] The distance between two stitching points is illustrated in Figures 3-A and 3-C. These are textile threads that provide rigidity to the composite profile. Thus, the composite profile is all the more rigid as the distance between two stitching points is small. According to the inventors, when the distance is less than or equal to 1 mm, the difficulty of obtaining a quality composite profile leads to many rejections. When the distance is greater than 50 mm, the gain in rigidity can be affected downwards.

[0044] According to a first preferred embodiment, the sewn composite material is sewn according to a seam such that the distance between two consecutive stitches is constant, alternatively according to a second embodiment, the sewn composite material is sewn according to a seam such that the distance between two consecutive stitches is variable. This latter alternative is encountered when producing composite profiles with complex geometry.

[0045] Advantageously, the stitched composite material is stitched according to a seam such that the distance between two consecutive stitching lines is variable, a stitching line being a succession of stitching points in a given direction. As seen in the previous case, this embodiment is particularly suitable for profiles that have a complex geometry. Alternatively, another choice is possible: the stitched composite material is stitched according to a seam such that the distance between two consecutive stitching lines is constant, a stitching line being a succession of stitching points in a given direction.

[0046] Advantageously, the thread density of a stitched composite material being the number of stitching lines per decimeter, measured in the direction orthogonal to said stitching threads, the stitched composite material has a thread density of between 15 threads per decimeter and 150 threads per decimeter.

[0047] Thread density is another parameter that controls the stiffness level of the stitched composite material. The higher the thread density, the stiffer the stitched composite material. [0048JD' other characteristics of the invention linked to the nature and assembly of the sewing thread contribute to further improving the desired performance compromise.

[0049] Advantageously, the sewing threads are textile cables, each cable being obtained by twisting a twist T2 of N strands of a textile material in a given direction DI (respectively direction S or Z), with N>1, each strand resulting from overtwisting a twist T1 of a yarn of said textile material, in an opposite direction D2 (respectively Z or S).

[0050] The raw material used in the manufacture of a textile cable is the yarn stored by winding on reels of 4 to 12 kg. It is a flat roving composed of continuous elementary filaments, identical in both appearance and mechanical properties, said roving comes directly from the spinning installations. A yarn is generally defined by the nature of the material which constitutes the filaments (polyethylene terephthalate, aliphatic polyamide (Nylon), Rayon, aromatic polyamide (Aramid)); its linear mass which is expressed in tex and which represents the mass in grams of 1000 meters of yarn; the number of elementary filaments constituting the yarn (200 to 1500), and the degree of intermingling of the elementary filaments.

[0051] From the yarns, double-twisted textile cables (Tl, T2) are produced, which are prepared by a process called twisting in which: - during a first stage, the overtwisting, each yarn or multifilament fiber (in English "yarn") constituting the final cable is first of all individually twisted on itself (according to an initial twist Tl) in a given direction DI (respectively direction S or Z), to form a strand (in English "strand") in which the elementary filaments are subjected to a helical deformation around the fiber axis (or axis of the strand); - then, during a second stage, twisting, several strands, generally two, three or four in number, of identical or different natures in the case of so-called hybrid or composite cables, are then twisted together according to a final twist T2 (which may be equal to or different from Tl) in the opposite direction D2 (respectively direction Z or S, according to a recognized nomenclature designating the orientation of the turns according to the crossbar of an S or a Z), to obtain the cable (in English "cord") or final assembly with several strands.

[0052] The role of twisting is to adapt the material properties in order to create transverse cohesion of the cable, improve endurance to compressive stresses and distribute the stresses over all the filaments. This step of the twisting process is accompanied by a decrease in breaking force and longitudinal modulus and an increase in fatigue endurance with increasing twist. Ultimately, the process is parameterized to achieve a compromise between fatigue resistance and breaking force.

[0053] The cable production process continues with a gluing phase to ensure the bond between the cable and the surrounding elastomeric mixture. The quality of the textile / mixture interface influences the fatigue performance of the glued cable.

[0054] Advantageously, the number N of strands of a textile cable is between 1 and 6, and preferably N = 2. An example of such a cable is the A-140 / 2 250 / 300, which means that the cable is composed of the assembly of two aramid strands with a count of 140 tex each. The twist of the yarns during the overtwisting phase is 250 turns per meter, and that of the strands during the twisting phase is 300 turns per meter.

[0055] When N = 1, the cable consists of a single strand.

[0056] When N=2, an industrial direct cabling process allows overtwisting and twisting to be carried out in a single manufacturing step, which results in a significant gain in productivity. On the other hand, when N=3, overtwisting and twisting are done in two separate operations to produce 3-ply constructions.

[0057] Preferably, the filament strands are made up of a homogeneous assembly of filaments of a textile material. Alternatively, it is also possible to have filament strands made up of a hybrid assembly of filaments of textile materials.

[0058] In pneumatic design, the choice of a homogeneous or hybrid assembly depends on the performance compromise sought for the resulting cable, in terms of rigidity, breaking force, endurance, and industrial cost.

[0059] Preferably, the filament strands are chosen from polyester strands, aliphatic polyamide strands, strands comprising aromatic polyamides or aromatic copolyamides and strands comprising mixtures of filaments of these materials, preferably chosen from aliphatic polyamide strands and more preferably made of nylon 6.6.

[0060] Advantageously, the title of the cables in tex is included in the interval [70; 250], more preferably the title of the cables in tex is included in the interval [90; 150]; the title being the linear mass of the cable, that is to say the mass expressed in grams per thousand meters of cable.

[0061] Advantageously, a stitched composite material is stitched with a first thread wound in a bobbin separate from a second thread threaded in a sewing needle so that the stitched composite material has one face with the first thread and a second face with the second thread.

[0062] This embodiment makes it possible to adapt the seam of the sewn composite material according to its environment, and its interaction with other materials of the tire.

[0063] In other embodiments, the sewing thread is comprised of a single monofilament.

[0064] In still other embodiments, the sewing thread comprises several monofilaments assembled in a helix.

[0065] Advantageously, the reinforcements of the sewn composite material comprise a layer of an adhesive composition.

[0066] In variations of the adhesive composition, the adhesive composition is based on an aldehyde / phenol resin based on resorcinol, formaldehyde and an elastomer latex such as as described in WO2013017422. Alternatively, any other adhesive composition described in WO2013017422 may be used.

[0067] Advantageously, each bead comprises a padding layer comprising the stitched composite material.

[0068] Advantageously, the filling layer is axially external to the bead wire and axially internal to the sidewall.

[0069] Advantageously, the dynamic shear modulus G* of the elastomeric mixture of the stitched composite material is between 3 MPa and 55 MPa, G* being measured at 23°C under alternating shear stress at a frequency of 10 Hz and at 10% deformation. Brief description of the drawings

[0070] The present invention will be better understood upon reading the detailed description of embodiments taken as examples, in no way limiting and illustrated by the appended drawings in which: • Figure 1 shows a schematic meridian section of a tire of the invention, with a padding layer 60 representing a stitched composite material. • Figure 2-A shows an enlargement of the bead of the tire of Figure 1, the view Figure 2-B shows the profile 60 which corresponds to the filling layer 60 in the bead. In the extrusion phase, the profile 60 is extruded with a sufficient length, 98, to make one turn of the building drum, as illustrated in Figure 2-C. • Figure 3-A illustrates a seam made in the thickness of the filler layer 60, and in Figure 3-B illustrates a seam made in the circumferential direction. • Figures 4-A, 4-B, 4-C, and 4-D illustrate the sewing of a composite material sewn in four steps. • Figures 5-A and 5-B illustrate the production of the threads used for sewing in the sewn composite material. Figure 5-A shows two strands 300 obtained, one by an S-shaped overtwist, and the other by a Z-shaped overtwist of strands composed of textile filaments. Figure 5-B shows the principle of manufacturing the textile cable, with, for example, the overtwisting of two Z-shaped yarns, which are then twisted in the opposite direction in an S to obtain a cable. Detailed description of the invention [0071JThe invention has been more particularly studied for a passenger car tire of standardized designation, according to the specification standard of the ETRTO (European Technical Organization for Rims and Tires), 245 / 45 RI 8 100W.

[0072] In the various figures, identical or similar elements bear the same references. Given the symmetry of the tread, for the readability of the figures, the elements are referenced only once on one side of a meridian plane.

[0073] In Figure 1, the tire 1 comprises a carcass reinforcement 90 made up of reinforcements coated with rubber composition, and two beads 50 each comprising annular reinforcement structures 51 which hold the tire 1 on the rim 100. The carcass reinforcement 90 is anchored in each of the beads 50. The tire 1 further comprises a crown reinforcement 20 comprising two working layers 21, 22, and a hooping layer 23. Each of the working layers 21 and 22 is reinforced by flaire reinforcement elements which are parallel in each layer and crossed from one layer to the other, making angles of between 10° and 70° with the circumferential direction. The hooping layer 23, arranged radially outside the crown reinforcement 20, this hooping layer 23 being formed of circumferentially oriented and spirally wound reinforcing elements.A tread 10 is laid radially on the hooping layer 23; it is this tread 10 which ensures the contact of the tire 1 with a rolling ground. The tire 1 shown is a “tubeless” tire: it comprises an “inner rubber” 95 made of a rubber composition impermeable to the inflation gas, covering the inner surface of the tire. Each bead 50 comprises a layer of elastomeric mixture 80 positioned radially the innermost and intended to be in contact with the rim 100, a layer of elastomeric filling mixture 70, positioned at least in part between the main part 52 of the carcass reinforcement 90 and the upturn 53. The bead 50 also comprises a lateral filling layer 60 axially outside the upturn 53 and axially inside the sidewall 30. Still in FIG. 1, the reference 49 surrounds the portion of the tire which corresponds to the lower zone 55.

[0074] In Figure 2-A the lower zone 55 of the tire is shown, with a bead 50 which partly comprises a carcass reinforcement 90 which has a main part 52, then wraps around a bead wire 51 to form a turn-up 53. A first layer of filler 70 is positioned between the main part 52 of the carcass reinforcement 90 and its upturn 53. According to the embodiments, the bead 50 may comprise a second lateral reinforcement packing layer 60, positioned axially outside the upturn 53, and axially inside the sidewall layer 30. Axially the innermost of the bead 50, a sealed layer 95 constitutes the inner wall in contact with the internal inflation air.

[0075] Said bead 50 also comprises a protective layer 80 which is in axially external contact with a portion of the rim 100 so as to limit the axial displacement of the bead. Said protective layer 80 also comprises a portion intended to be in contact with the rim at the rim seat 100. A sidewall layer 30 cooperates with the bead 50 and constitutes an external side wall.

[0076] Figure 2-B is an enlargement of the filler layer 60 which shows its profile in a meridian plane, and Figure 2-C shows it at the end of extrusion to then be laid flat on a tire building drum.

[0077] From the extruded profile of Figure 2-C, an additional step is implemented to reinforce the stuffing layer by stitching threads 200 and 210 according to a first embodiment, Figure 3-A, and a second embodiment in Figure 3-B. The two embodiments differ in the orientation of the stitching threads. In these embodiments, the thread 210 wound on the bobbin 260, after stitching, is visible on a first face of the stuffing element and a second thread 200 is visible on another face. The reference 220 of Figure 3-A represents the pitch between two stitching lines, and the element 230 the pitch between two stitching points.

[0078] Figures 4-A, 4-B, 4-C, and 4-D are different stages of a possible sewing phase implemented after the extrusion of a stuffing profile 60 as shown in Figure 2-C. In the first stage (Figure 4-A), the thread 200 threaded into the needle 230 via the opening 240, is drawn through the profile by the needle 230, which forms a loop. Then, Figure 4-B, the hook 250 of the bobbin 220 catches the loop of the thread 200, then the bobbin 220 rotates to pass it around itself, Figure 4-C. The hook 250 releases the thread 200, it therefore makes a loop around the thread of the bobbin 220, it traps it. Finally, the stitch tightens as the needle 230 rises and the claws pull the profile, Figure 4-D, to form a stitch 280.

[0079] The invention is not limited by the sewing principle set out above. Other seams are conceivable.

[0080] Figures 5-A and 5-B illustrate the production of the threads used for sewing in the sewn composite material. Figure 5-A shows two strands 300 obtained, one by an S-shaped overtwist, and the other by a Z-shaped overtwist of strands composed of textile filaments. Figure 5-B shows the principle of manufacturing the textile cable, with, for example, the overtwisting of two Z-shaped yarns, which are then twisted in the opposite direction in an S to obtain a cable. The diameter (|) of the cable is shown.

[0081] Tire configurations of the invention were tested to clearly highlight the performance provided by the invention. The results of these tests are compared to those obtained for a control tire. The dimension chosen is the same, namely 245 / 45R18 100W for the control and the tires of the invention. It is a tire designed to carry a load of 800 kilos with an inflation pressure of 290 kPa.

[0082] The T witness is a tire of conventional design not using stitched composite material.

[0083] The first tire PI, in accordance with the invention (figure 3-B) is different from the control T in that it comprises a filling layer sewn with a thread composed of two strands of PET, each with a count of 114 tex. The direction of the stitching is radial.

[0084] The sewing of the stuffing layer results in a sewing thread oriented according to its thickness as shown in Figure 3-B. The pitch between two sewing points is 2 mm, and the density of sewing threads is 50 threads per decimeter.

[0085] The second tire P2 of the invention is identical to PI, except that the direction of the sewing threads is circumferential (figure 3-C).

[0086] Table [1]: [0087JThe abbreviation CRRT is the coefficient of resistance, positioned at a base of 100 for the witness. For the tires Pl, P2, we evaluate the variation in relation to the base of 100 of the witness. We do the same for the transverse drift rigidity.

[0088] It is easily verified that the tires of the invention P1 and P2 are indeed covered by claim 1.

[0089] Rolling resistance and drift stiffness were simulated by the finite element method for tires of the invention and of the state of the art according to the two configurations. The results are shown in Table 1.

[0090] A result above (respectively below) 100% means an improvement (respectively a deterioration) in the performance considered.

[0091] This example confirms that the tires of the invention PI, and P2 with a layer of stuffing sewn with a textile thread in the bead provide an advantageous compromise solution in rolling resistance and drift rigidity and therefore in road behavior.

[0092] The examples presented here are not exhaustive. The invention also works for tires with a non-rolling carcass reinforcement.

Claims

Claims

1. A tire (1) for a motor vehicle comprising in a meridian plane: two beads (50) intended to be mounted on a rim, two layers of sidewalls (30) connected to the beads (50), a crown (20) comprising a tread (10), said crown (20) having a first side connected to the radially outer end of one of the two layers of sidewalls (30) and having a second side connected to the radially outer end of the other of the two layers of sidewalls (30);at least one carcass reinforcement (90) extending from the two beads (50) to the crown (20), the carcass reinforcement (90) comprising a plurality of carcass reinforcement elements and being anchored in the two beads (50) to a bead wire (53), characterized in that said tire (1) comprises at least one stitched composite material consisting of an elastomeric mixture comprising threads stitched into said elastomeric mixture to form reinforcements oriented in stitching directions.;

2. A tire (1) according to the preceding claim, wherein the sewn composite material is sewn in a seam such that the distance between two consecutive stitching points is between 1 mm and 50 mm.

3. A tire (1) according to any one of claims 1 to 2, wherein the stitched composite material is stitched in a seam such that the distance between two consecutive stitching points is constant.

4. A tire (1) according to any one of claims 1 to 2, wherein the stitched composite material is stitched in a seam such that the distance between two consecutive stitching points is variable.

5. A tire (1) according to any one of claims 1 to 4, wherein the sewn composite material is sewn in a seam such that the distance between two consecutive stitching lines is variable, a stitching line being a succession of stitching points in a given direction.

6. A tire (1) according to any one of claims 1 to 4, wherein the sewn composite material is sewn in a seam such that the distance between two consecutive seam lines is constant, a seam line being a succession of stitches in a given direction.

7. A tire (1) according to any preceding claim, wherein the thread density of a stitched composite material being the number of stitching lines per decimeter, measured in the direction orthogonal to said stitching threads of said stitched composite material, the stitched composite material has a thread density of between 15 threads per decimeter and 150 threads per decimeter.

8. A tire (1) according to any one of the preceding claims, wherein the sewing threads are textile cables, each cable being obtained by twisting a twist T2 of N strands of a textile material in a given direction D1, with N>1, each strand resulting from overtwisting a twist T1 of a yarn of said textile material, in an opposite direction D2.

9. A tire (1) according to any preceding claim, wherein each bead (50) comprises a filler layer (60), the filler layer (60) comprises a stitched composite material.

10. Tire (1) according to the preceding claim, in which the dynamic shear modulus G* of the elastomeric mixture of the stitched composite material is between 3 MPa and 55 MPa, G* being measured at 23°C under an alternating shear stress at a frequency of 10 Hz and at 10% deformation.

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