WO2015197295A1

WO2015197295A1 - Tyre comprising a layer of circumferential reinforcement elements

Info

Publication number: WO2015197295A1
Application number: PCT/EP2015/061718
Authority: WO
Inventors: Hichem Rehab; Nathalie Salgues; Jacques Besson
Original assignee: Compagnie Generale Des Etablissements Michelin; Michelin Recherche Et Technique S.A.
Priority date: 2014-06-26
Filing date: 2015-05-27
Publication date: 2015-12-30
Also published as: FR3022847B1; FR3022847A1

Abstract

Tyre comprising a crown framework formed from at least two working layers each formed of reinforcement elements inserted between two calendering layers of rubber mixture, a first layer S of polymer mixture being in contact with at least one working layer and the carcass framework, and the crown framework comprising at least one layer of circumferential reinforcement elements. The modulus of elasticity under tension at 10% elongation of layer C is greater than 9 MPa, the maximum value of tan(5), denoted tan(5) max, of said layer C is less than 0.100, said first layer S consists of a filled elastomer mixture having a macro dispersion score Z greater than or equal to 65 and a maximum value of tan(5), denoted tan(5)max, less than 0.100 and the complex dynamic shear modulus G* thereof, measured at 10% and 60°C on the return cycle, is greater than 1.35 MPa.

Description

PNEUMATIC COMPRISING A LAYER OF ELEMENTS OF

CIRCUMFERENTIAL REINFORCEMENT

The present invention relates to a tire, radial carcass reinforcement and more particularly to a tire intended to equip vehicles carrying heavy loads and rolling at a high speed, such as, for example, trucks, tractors, trailers or road buses.

[0002] In general, in heavy-vehicle tires, the carcass reinforcement is anchored on both sides in the bead zone and is radially surmounted by a crown reinforcement consisting of at least two layers, superimposed and formed of son or parallel cables in each layer and crossed from one layer to the next in making with the circumferential direction angles between 10 ° and 45 °. Said working layers, forming the working armature, can still be covered with at least one so-called protective layer and formed of advantageously metallic and extensible reinforcing elements, called elastic elements. It may also comprise a layer of low extensibility wires or metal cables forming with the circumferential direction an angle of between 45 ° and 90 °, said triangulation ply being radially located between the carcass reinforcement and the first ply of plywood. so-called working top, formed of parallel wires or cables having angles at most equal to 45 ° in absolute value. The triangulation ply forms with at least said working ply a triangulated reinforcement, which presents, under the different stresses it undergoes, few deformations, the triangulation ply having the essential role of taking up the transverse compression forces of which the object all the reinforcing elements in the area of the crown of the tire. Cables are said to be inextensible when said cables have under a tensile force equal to 10% of the breaking force a relative elongation at most equal to 0.2%.

Cables are said elastic when said cables have under tensile force equal to the breaking load a relative elongation of at least 3% with a maximum tangent modulus of less than 150 GPa. [0005] Circumferential reinforcing elements are reinforcing elements which make angles with the circumferential direction in the range + 2.5 °, -2.5 ° around 0 °.

The circumferential direction of the tire, or longitudinal direction, is the direction corresponding to the periphery of the tire and defined by the rolling direction of the tire.

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

The radial direction is a direction intersecting the axis of rotation of the tire and perpendicular thereto.

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

A radial or meridian plane is a plane which contains the axis of rotation of the tire. The circumferential mid-plane, or equatorial plane, is a plane perpendicular to the axis of rotation of the tire and which divides the tire into two halves.

The term "modulus of elasticity" of a rubber mix, a secant modulus of extension at 10% deformation and at room temperature.

As regards the rubber compositions, the modulus measurements are made in tension according to the AFNOR-NFT-46002 standard of September 1988: the secant modulus is measured in second elongation (ie, after an accommodation cycle). nominal (or apparent stress, in MPa) at 10% elongation (normal conditions of temperature and hygrometry according to AFNOR-NFT-40101 of December 1979).

Some current tires, called "road", are intended to run at high speed and on longer and longer journeys, due to the improvement of the road network and the growth of the motorway network in the world. The set of conditions, under which such a tire is called to roll, undoubtedly makes it possible to increase the number of kilometers traveled, with less tire wear; against the endurance of the latter and in particular of the crown reinforcement is penalized.

There are indeed constraints at the crown reinforcement and more particularly shear stresses between the crown layers, allied to a significant increase in the operating temperature at the ends of the crown layer. axially the shortest, which result in the appearance and propagation of cracks of the rubber at said ends.

In order to improve the endurance of the crown reinforcement of the tire type 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 tire. plies and more particularly the ends of the axially shortest ply have already been made.

It is in particular known to introduce a layer of rubber mixture between the ends of the working layers to create a decoupling between said ends to limit the shear stresses. However, such decoupling layers must have a very good cohesion. Such layers of rubber compounds are described, for example, in the patent application WO 2004/076204.

Patent FR 1 389 428, to improve the resistance to degradation of rubber compounds located in the vicinity of the crown reinforcement edges, recommends the use, in combination with a low hysteresis tread, of a rubber profile covering at least the sides and the marginal edges of the crown reinforcement and consisting of a rubber mixture with low hysteresis.

FR 2 222 232, to avoid separations between crown reinforcement plies, teaches to coat the ends of the frame in a rubber mat, whose Shore A hardness is different from that of the strip. rolling overlying said armature, and greater than the Shore A hardness of the rubber mix profile disposed between the edges of crown reinforcement plies and carcass reinforcement.

The tires thus produced can actually improve performance especially in terms of endurance. Furthermore, it is known to make tires with a very wide tread or to give tires of a given size larger load capacities to introduce a layer of circumferential reinforcing elements. The patent application WO 99/24269 describes for example the presence of such a layer of circumferential reinforcing elements.

The layer of circumferential reinforcing elements is usually constituted by at least one wire rope wound to form a turn whose laying angle relative to the circumferential direction is less than 2.5 °.

During tests, the inventors have shown that during solicitations of certain designs of this type of tire, having a layer of circumferential reinforcing elements, drift severe and frequent such that we can find them. when driving on winding roads, said tires could exhibit properties in terms of drift rigidity such that a cleavage appears at the level of the rubber compounds constituting the crown reinforcement that is found between the working layers. Such cleavage is of course penalizing in terms of endurance properties of the tire. Such cleavages are further accentuated during overload and high speed runs, always on winding roads.

An object of the invention is to provide tires whose endurance properties are retained regardless of the use and whose performance in terms of rolling resistance are improved to contribute to a lower fuel consumption by the vehicles equipped with such tires. The invention aims in particular at improving the dynamic properties of the tires, and in particular the rigidity of drift so that the endurance properties are retained whatever the use and in particular under conditions of overloading and at high speeds [ This object is achieved according to the invention by a radial carcass reinforcement tire comprising a crown reinforcement formed of at least two working crown layers of reinforcing elements, crossed from one layer to the other in accordance with the invention. forming with the circumferential direction angles of between 10 ° and 45 °, a layer C of rubber mixture being disposed between at least the ends of said at least two working crown layers, a first layer S of polymeric mixture being in contact with at least one working crown layer and in contact with the carcass reinforcement, said first polymeric mixture layer extending axially to at least the axial end of the tread, said tread capping the reinforcement top, said tread being joined to two beads through two sidewalls, the crown reinforcement having at least one layer of circumferential reinforcing elements, the tensile modulus of elasticity at 10% elongation of layer C being greater than 9 MPa and the maximum value of tan (δ), denoted tan (δ) _max , of layer C being less than 0.100, said first layer S of polymeric mixture consisting of a charged elastomer mixture having a macro dispersion score Z greater than or equal to 65 and a maximum value of tan (δ), denoted tan (δ) max, less than 0.100 and the complex dynamic shear modulus G *, measured at 10% and 60 ° C on the return cycle of said first polymeric mixture layer S being greater than 1.35 MPa.

A Z macro dispersion note greater than or equal to 65 of a charged elastomeric mixture means that the filler is dispersed in the elastomeric matrix of the composition with a dispersion score Z greater than or equal to 65.

In the present description, the charge dispersion in an elastomer matrix is characterized by the note Z, which is measured, after crosslinking, according to the method described by S. Otto and Al in Kautschuk Gummi Kunststoffe, 58 Jahrgang, NR 7 - 8/2005, in accordance with ISO 11345. [0028] The calculation of the Z score is based on the percentage of area in which the charge is not dispersed ("% undispersed area"), as measured by the device "disperGRADER +" supplied with its operating mode and its operating software "disperDATA" by the company Dynisco according to the equation:

Z = 100 - (% undispersed area) /0.35

The percentage of non-dispersed surface is, meanwhile, measured by a camera observing the surface of the sample under an incident light at 30 °. The bright spots are associated with filler and agglomerates, while the dark spots are associated with the rubber matrix; digital processing transforms the image into a black and white image, and allows the determination of the percentage of undispersed surface, as described by S. Oto in the aforementioned document. The higher the Z score, the better the dispersion of the load in the rubber matrix (a Z score of 100 corresponding to a perfect dispersion and a Z score of 0 to a poor dispersion). It will be considered that a note Z greater than or equal to 65 corresponds to a satisfactory dispersion of the charge in the elastomer matrix. The elastomeric mixtures constituting the layer S are prepared according to known methods.

In order to achieve a macrodispersion Z score greater than or equal to 65, the elastomer mixture constituting the S layer may advantageously be prepared by forming a masterbatch of diene elastomer and reinforcing filler. For the purposes of the invention, the term "master mix" (commonly referred to by its English name "masterbatch"), an elastomer-based composite into which a load has been introduced.

There are different methods for obtaining a masterbatch of diene elastomer and reinforcing filler. In particular, one type of solution consists in improving the dispersion of the filler in the elastomer matrix by mixing the elastomer and the "liquid" phase filler. To do this, an elastomer in the form of latex has been used in the form of elastomer particles dispersed in water, and an aqueous dispersion of the filler, that is to say a dispersed filler. in water, commonly called "slurry". Thus, according to one of the variants of the invention, the masterbatch is obtained by mixing in the liquid phase from a diene elastomer latex comprising natural rubber and an aqueous dispersion of a filler comprising carbon black.

More preferably still, the masterbatch according to the invention is obtained according to the following process steps, making it possible to obtain a very good dispersion of the filler in the elastomer matrix: feeding, with a first continuous stream of a diene elastomer latex, a mixing zone of a coagulation reactor defining an elongate coagulation zone extending between the mixing zone and an outlet,

supplying said mixing zone of the coagulation reactor with a second continuous flow of a fluid comprising a charge under pressure to form a mixture with the elastomer latex by mixing the first fluid and the second fluid in the mixing zone so as to sufficiently energetic to coagulate the elastomer latex with the charge before the exit, said mixture flowing as a continuous flow towards the exit zone and said charge being capable of coagulating the elastomer latex,,

recovering at the outlet of the reactor the coagulum obtained previously in the form of a continuous stream and drying it in order to recover the masterbatch.

Such a process for preparing a masterbatch in the liquid phase is described, for example, in WO 97/36724. Advantageously according to the invention, the elastomer-charge bond of the first layer S of polymeric mixture is characterized by a "bond rubber" rate, measured before crosslinking, greater than 35%.

The so-called "bound rubber" test makes it possible to determine the proportion of elastomer, in a non-vulcanized composition, which is associated with the reinforcing filler so intimately that this proportion of elastomer is insoluble in the usual organic solvents. Knowledge of this insoluble proportion of rubber, fixed by the reinforcing filler during mixing, gives a quantitative indication of the reinforcing activity of the filler in the rubber composition. Such a method has been described, for example, in standard NF-T-45-114 (June 1989) applied to the determination of the level of elastomer bound to carbon black.

This test, well known to those skilled in the art to characterize the quality of reinforcement provided by the reinforcing filler, has for example been described in the following documents: Plastics, Rubber and Composites Processing and Applications, Vol. 25, No 7, p. 327 (1996); Rubber Chemistry and Technology, Vol. 69, p. 325 (1996). In the present case, the level of non-extractable elastomer with toluene is measured after swelling for 15 days of a sample of rubber composition (typically 300-350 mg) in this solvent (for example in 80- 100 cm3 of toluene), followed by a drying step of 24 hours at 100 ° C, under vacuum, before weighing the sample of rubber composition thus treated. Preferably, the above swelling step is conducted at room temperature (about 20 ° C) and away from light, and the solvent (toluene) is changed once, for example after the first five days swelling. The "bound rubber" content (% by weight) is calculated in a known manner by difference between the initial weight and the final weight of the rubber composition sample, after taking into account and eliminating, in the calculation, the fraction intrinsically insoluble components, other than elastomer, initially present in the rubber composition.

The loss factor tan (δ) is a dynamic property of the layer of rubber mix. It is measured on a viscoanalyzer (Metravib VA4000), according to ASTM D 5992-96. The response of a sample of vulcanized composition (cylindrical specimen 4 mm in thickness and 400 mm ² in section), subjected to sinusoidal stress in alternating simple shear, at the frequency of 10 Hz, at a temperature of 60 is recorded. ° C. A strain amplitude sweep of 0.1 to 50% (forward cycle) and then 50% to 1% (return cycle) are performed. The results exploited are the complex dynamic shear modulus (G ^* ) and the loss factor tan (δ). For the return cycle, the maximum value of tan (O) observed, denoted tan (O) _max.

The rolling resistance is the resistance that appears when the tire rolls. It is represented by the hysteretic losses related to the deformation of the tire during a revolution. The frequency values related to the revolution of the tire correspond to values of tan (δ) measured between 30 and 100 ° C. The value of tan (δ) at 100 ° C thus corresponds to an indicator of the rolling resistance of the rolling tire.

It is still possible to estimate the rolling resistance by measuring energy losses by rebound energy samples imposed at temperatures of 60 ° C and expressed as a percentage. Advantageously according to the invention, the loss at 60 ° C, denoted P60, of the layer of rubber mix C is less than 20%.

The layer C rubbery mixture provides a decoupling of said working crown layers to distribute the shear stresses on a greater thickness.

Within the meaning of the invention, the coupled layers are layers whose respective reinforcing elements are radially separated by at most 1.5 mm, said rubber thickness being measured radially between the respectively upper and lower generatrices of said elements of enhancement. The use of such mixtures whose elastic modulus are greater than or equal to 9 MPa and whose tan (δ) _max is less than 0.100 will improve the properties of the tire in terms of rolling resistance. retaining satisfactory endurance properties.

According to a preferred embodiment of the invention, the layer C of rubber mixture is an elastomeric mixture based on natural rubber or synthetic polyisoprene predominantly with cis-1,4 linkages and optionally at least one another diene elastomer, the natural rubber or the synthetic polyisoprene in the case of cutting being present at a majority rate with respect to the rate of the other diene elastomer or diene elastomers used and a reinforcing filler consisting of: BET surface area carbon of less than 60 m ² / g, regardless of its structural index, employed at a level of between 40 and 100 phr, and preferably between 60 and 90 phr, or with a white charge of the same type silica and / or alumina having SiOH and / or AlOH surface functions selected from the group consisting of precipitated or pyrogenic silicas, aluminas or alumino silicates or else blacks of modified carbon in process or after BET specific surface area synthesis between 30 and 260 m ² / g employed at a rate of between 40 and 100 phr, and preferably between 60 and 90 phr, c) either by a carbon black cutting described in (a) and a white filler described in (b), in which the overall filler content is between 40 and 100 phr, and preferably between 60 and 90 phr; .

The measurement of BET specific surface area is carried out according to the method of BRUNAUER, EMMET and TELLER described in "The Journal of the American Chemical Society", vol. 60, page 309, February 1938, corresponding to standard NFT 45007 of November 1987.

In the case of using clear charge or white charge, it is necessary to use a coupling agent and / or covering selected from agents known to those skilled in the art. Examples of preferential coupling agents that may be mentioned are sulphurised alkoxysilanes of the bis (3-trialkoxysilylpropyl) polysulfide type, and of these, in particular, bis (3-triethoxysilylpropyl) tetrasulfide marketed by DEGUSSA under the Si69 denominations for pure liquid product and X50S for solid product (50/50 by weight blend with N330 black). Examples of coating agents that may be mentioned include a fatty alcohol, an alkylalkoxysilane such as hexadecyltrimethoxy or triethoxysilane respectively marketed by DEGUSSA under the names Sil16 and Si166, diphenylguanidine, a polyethylene glycol, a silicone oil which may be modified with OH or alkoxy functions. The covering agent and / or coupling agent is used in a weight ratio relative to the filler> at 1/100 and ≤ at 20/100, and preferably between 2/100 and 15/100 when the clear filler represents the all of the reinforcing filler and between 1/100 and 20/100 when the reinforcing filler is constituted by a carbon black and clear charge cutting.

As other examples of reinforcing fillers having the morphology and SiOH and / or AlOH surface functions of the silica and / or alumina materials previously described and that can be used according to the invention as partial or total replacement thereof , the modified carbon blacks may be mentioned either during the synthesis by addition to the furnace feed oil of a silicon and / or aluminum compound or after the synthesis by adding, to an aqueous suspension of carbon black in a solution of silicate and / or sodium aluminate, an acid so as to at least partially cover the surface of the carbon black of SiOH and / or AlOH functions. As non-limiting examples of this type of carbonaceous feedstock with SiOH and / or AlOH functions at the surface, mention may be made of the CSDP type feeds described in Conference No. 24 of the ACS Meeting, Rubber Division, Anaheim, California, 6-9 May 1997 as well as those of the patent application EP-A-0 799 854. When a clear filler is used as the sole reinforcing filler, the hysteresis and cohesion properties are obtained using a precipitated or fumed silica, or a precipitated alumina or even a BET surface area alumino-silicate of between 30 and 260 m ² / g. As non-limiting examples of this type of filler, mention may be made of the silicas KS404 from Akzo, Ultrasil VN2 or VN3 and BV3370GR from Degussa, Zeopol 8745 from Huber, Zeosil 175MP or Zeosil 1165MP from Rhodia, HI -SIL 2000 of the PPG Company etc.

Among the diene elastomers that can be used in a blend with natural rubber or a synthetic polyisoprene with a majority of cis-1,4 linkages, mention may be made of a polybutadiene (BR), preferably with a majority of cis-1 linkages, 4, a styrene-butadiene copolymer (SBR) solution or emulsion, a butadiene-isoprene copolymer (BIR) or even a styrene-butadiene-isoprene terpolymer (SBIR). These elastomers may be modified elastomers during polymerization or after polymerization by means of branching agents such as divinylbenzene or starch agents such as carbonates, halogenotins, halosilicons or else by means of functionalization leading to a grafting on the chain or at the end of the chain of oxygen functions carbonyl, carboxyl or an amino function such as for example by the action of dimethyl or diethylamino benzophenone. In the case of blends of natural rubber or synthetic polyisoprene with a majority of cis-1,4 linkages with one or more of the diene elastomers mentioned above, the natural rubber or the synthetic polyisoprene is preferably used at a majority rate. and more preferably at a rate greater than 70 phr.

The choice of the reinforcing filler involved in the rubbery mixture constituting the layer C contributes both to obtaining tensile modulus values under tension at 10% elongation and to obtaining the values of tan. (6) _max . However, within the above-mentioned ranges of values for said reinforcing fillers, those skilled in the art will still be able to adapt the quantities of other usual constituents, such as the agents vulcanizing or cobalt derivatives, or adapting the mixing processes to obtain the above modulus of elasticity and tan (δ) _max values.

The most common tire designs provide layers of rubber mixture disposed between the ends of the working crown layers with tensile modulus of elasticity at 10% elongation substantially equivalent to those of the layer C according to the invention. invention, but maximum values of tan (δ), denoted tan (δ) _max , of the layer C greater than 0.130. Such more usual mixtures for this type of layer lead to better cohesion.

For the purposes of the invention, a cohesive rubbery mixture is a rubbery mixture particularly resistant to cracking. The cohesion of a mixture is thus evaluated by a fatigue cracking test carried out on a test piece "PS" (simple shear). It consists in determining, after notching the specimen, the crack propagation speed "Vp" (nm / cycle) as a function of the energy release rate "E" (J / m ² ). The experimental area covered by the measurement is in the range -20 ° C and + 150 ° C in temperature, with an air or nitrogen atmosphere. The biasing of the specimen is a dynamic displacement imposed amplitude ranging between 0.1mm and 10mm in the form of impulse-type stress (tangential "haversine" signal) with a rest time equal to the duration of the pulse; the frequency of the signal is of the order of 10 Hz on average.

The measurement comprises 3 parts:

• An accommodation of the "PS" test tube, from 1000 cycles to 27% deformation.

• an energetic characterization to determine the law "E" = f (deformation). The energy release rate "E" is equal to W0 * h0, with W0 = energy supplied to the material per cycle and per unit volume and hO = initial height of the test piece. The exploitation of acquisitions "force / displacement" thus gives the relation between "E" and the amplitude of the solicitation.

• The measurement of cracking, after notching of the "PS" test piece. The information collected leads to determining the propagation velocity of the crack "Vp" as a function of the imposed stress level "E". The inventors have demonstrated that the cohesion of the layer C according to the invention remains satisfactory.

The inventors have in particular demonstrated that the presence of at least one layer of circumferential reinforcing elements contributes to a lesser evolution of the cohesion of the layer C. In fact, the more usual tire designs comprising in particular layers of rubber mixture disposed between the ends of the working crown layers with values of tan (δ) _max greater than 0.130, lead to a change in the cohesion of said layers of rubber mixture disposed between the ends of the working crown layers, this one tending to weaken. The inventors find that the presence of at least one layer of circumferential reinforcing elements which limits the shear stresses between the ends of the working crown layers and furthermore limits the temperature increases leads to a slight change in the cohesion The inventors thus consider that the cohesion of the layer C, which is smaller than that which exists in the more usual tire designs, is satisfactory in the design of the tire according to the invention.

The inventors have thus been able to demonstrate that the presence of at least one layer of circumferential reinforcing elements makes it possible to maintain satisfactory performance, particularly in terms of endurance, with the combination of an elastic modulus under tension. 10% elongation of the layer C greater than 9 MPa and a value of tan (δ) _max of the layer C less than 0.100.

The inventors have further demonstrated that the choice of a first layer S having a complex shear modulus G *, measured at 10% and 60 ° C on the return cycle, greater than 1.35 MPa improves the dynamic properties and in particular properties of tire drift stiffness, especially when the tire is subjected to rolling conditions which are particularly penalizing in terms of cleavage of the rubber compounds. The inventors have indeed been able to highlight that despite the presence of a layer of circumferential reinforcing elements which nevertheless gives significant rigidity to the tire, more particularly to the crown reinforcement of this, the above stated characteristics of the first S layer makes a notable contribution to this property of drift rigidity.

Indeed, quite unexpectedly for the skilled person, the properties of the first layer S of polymeric mixture, said layer S being positioned in contact with the carcass reinforcement and at least one layer of the crown reinforcement, have a notable influence on drift rigidity properties. The presence of the layer of circumferential reinforcing elements seemed to be able to influence the properties of drift rigidity sufficiently and a priori optimally because of the rigidity it confers on the tire. The tests carried out have demonstrated that the properties of the first layer S have a significant effect on the drift rigidity properties of the tire and make it possible to improve them even in the presence of a layer of circumferential reinforcing elements. The inventors have further demonstrated that the choice of this first layer S of polymeric mixture does not degrade the performance relative to the stresses to which the tire is subjected when traveling in a straight line.

Advantageously according to the invention, the complex shear modulus G *, measured at 10% and 60 ° C on the return cycle, of the first layer S is less than 2 MPa, so that the thermal properties of the tire not too modified at the risk of degrading the endurance properties of the tire as well as its rolling resistance properties.

The inventors have also shown that the first layer S, consisting of a charged elastomer mixture having a macro dispersion Z score of greater than or equal to 65 and a maximum value of tan (δ), denoted tan (δ) max. , less than 0.100, has a sufficiently high cohesion to limit the propagation of cracks initiated when an object perforates the tread of the tire. The inventors thus highlight the achievement of a compromise of tire performance combining the dynamic properties, in particular the rigidity of drift, the rolling resistance and the endurance properties, including in the case stated above when an object pierces the tread of the tire. According to a preferred embodiment of the invention, the elastomeric mixture of the first layer S comprises, as reinforcing filler, at least one carbon black with a BET specific surface area greater than 90 m ² / g and preferably greater than or equal to 120 m ² / g, employed at a rate of between 10 and 50 phr. More preferably, the reinforcing filler of the elastomeric mixture of the first layer S comprises, as a reinforcing filler, a carbon black blend as described above and a white filler, the overall filler rate being between 10 and 60.degree. pce and the black carbon ratio on white charge being greater than 2.7.

The choice of fillers as described above still allows to confer cohesive properties of the second layer S satisfactory.

According to an advantageous variant of the invention, the tire comprises a second layer G of polymeric mixture radially between the carcass reinforcement and the layer of radially innermost reinforcing elements of the axial width vertex reinforcement. at least equal to 70% of the width of the radially innermost reinforcing element layer of the crown reinforcement, said second polymeric mixture layer G consisting of a charged elastomeric mixture having a macro dispersion grade Z greater than or equal to 65 and a maximum value of tan (δ), denoted tan (δ) max, less than 0.100 and the complex shear modulus G *, measured at 10% and 60 ° C on the return cycle, of the fourth layer G being greater than 1.35 MPa.

Advantageously according to the invention, the elastomer-charge bond of the second layer G of polymer mixture is characterized by a "bond rubber" rate, measured before crosslinking, greater than 35%.

According to a preferred embodiment of this variant of the invention, the axial width of said second layer G is at most equal to the width of the radially innermost reinforcing element layer of the crown reinforcement. and preferably at least 90% of the width of the radially innermost reinforcing layer of the crown reinforcement. Also preferably according to this variant of the invention, the thickness, measured in the radial direction, of said second layer G is greater than φ and preferably less than 3φ, φ being the diameter of the reinforcing elements of the crown reinforcement layer radially innermost. The inventors have further demonstrated that the second layer G of polymeric mixture thus defined further contributes to the improvement of the rigidity properties of the tire drift in addition to the layer of circumferential reinforcing elements and the first layer S of polymeric mixture.

Advantageously according to the invention, the complex shear modulus G *, measured at 10% and 60 ° C on the return cycle, of the second layer G is less than 2 MPa, so that the thermal properties of the tire not too modified at the risk of degrading the endurance properties of the tire as well as its rolling resistance properties.

According to a preferred embodiment of the invention, the elastomeric mixture of the second layer G comprises, as reinforcing filler, at least one carbon black with a BET specific surface area greater than 90 m ² / g and preferably greater than 120 m. ² / g, employed at a rate of between 10 and 50 phr.

More preferably, the reinforcing filler of the elastomeric mixture of the second layer G comprises, as a reinforcing filler, a carbon black blend as described above and a white filler, the overall filler rate being between 10 and 60.degree. pce and the black carbon ratio on white charge being greater than 2.7.

Advantageously, the polymer mixture constituting the second layer G is identical to the polymer mixture constituting the second layer S.

According to a preferred embodiment of the invention, said at least two working crown layers having unequal axial widths, the distance d between the end of the axially closest working layer and the working layer. separated from the axially narrowest working layer by the layer C of rubber mix is such that lo <d <2.20, where ø is the diameter of the reinforcing elements of said at least one layer of circumferential reinforcing elements and, in a meridian plane, the thickness of the layer C of rubber mixture being substantially constant over the axial width between the axially inner end of the layer C and the end of the axially narrowest working layer.

Within the meaning of the invention, the distance d is measured in a meridian plane of cable to cable, that is to say between the cable of a first working layer and the cable of a second layer of working in a direction substantially perpendicular to the surfaces of the layer C. In other words, this distance d includes the thickness of the first layer C and the respective thicknesses of the calendering rubber mixes, radially external to the cables of the layer of working radially inner and radially inner to the cables of the radially outer working layer.

Within the meaning of the invention, the thickness of the layer C of rubber mixture is measured between the two surfaces of said layer C according to the orthogonal projection of a point of a surface on the other surface.

Within the meaning of the invention, the thickness of the layer C rubbery mixture is substantially constant means that it does not vary more than 0.3 mm. These variations in thickness are due to creep phenomena during the manufacture and baking of the tire. The layer C in semi-finished form, that is to say as elements ready to be used for producing a tire, thus advantageously has a constant thickness. The various thickness measurements are made on a cross section of a tire, the tire is therefore in a non-inflated state.

The most common tire designs, provide layers of rubber mixture disposed between the ends of the working crown layers with greater thicknesses especially at the end of the narrowest working layer and with a profile. of inhomogeneous thickness when it is seen according to a meridian section of the tire to allow such a thickness and to avoid too much disturbing the environment of the end of the narrowest working layer. As explained above, the presence of this layer of rubber mix makes it possible in particular to limit the shear stresses between the ends of the working crown layers, the circumferential stiffnesses of said working crown layers being zero at their ends. The distance between the end of the axially narrowest working layer and the working layer separated from the axially narrowest working layer by the layer of rubber mix, measured according to the definition of d above, is usually greater than 3.3 mm. This corresponds to a thickness of the layer of rubber compound of at least 2.5 mm while, generally, its thickness tends at each of its ends to a value less than 0.5 mm.

The inventors have demonstrated that the presence of at least one layer of circumferential reinforcing elements makes it possible to maintain performance, particularly in terms of endurance but also in terms of satisfactory wear with a layer C of mixture. rubber-like material of substantially constant thickness over the axial width between the axially inner end of the layer C and the end of the axially narrowest working layer and such that the distance d is between 1. lo and 2.20. It seems indeed that the presence of the layer of circumferential reinforcing elements contributes sufficiently to the recovery of at least a portion of the circumferential tension, especially during the passage in the contact area to reduce the shear stresses between the ends of the working top layers.

In addition, the combination of the layer of circumferential reinforcing elements and the first layer S or even the second layer G, having a complex shear modulus G *, measured at 10% and 60 ° C. on the return cycle, greater than 1.35 MPa still makes it possible to maintain satisfactory tire drift rigidity properties when the layer C has a substantially constant thickness over the axial width between the axially inner end of the layer C and the end of the tire. the axially narrowest working layer and such that the distance d is between 1. lo and 2.20, such a characteristic relating to the thickness of the layer C being penalizing as regards the drift rigidity properties of the tire.

Furthermore, the layer C of rubber mix is thus advantageously in the semi-finished state in the form of a layer of constant thickness which is simple to manufacture and furthermore which can be stored simply. Indeed, the layers usually used as described above which have a sectional shape with thickness variations are on the one hand more difficult to achieve and on the other hand more difficult to store. Indeed, variations in thickness create storage problems, these semi-finished being most often stored as coil winding. The layer C according to the invention is in the state of semi-finished product with a section having a substantially flat profile compared to the layers usually used which are in the semi-finished product state with a section having a profile substantially round.

The manufacture and storage of the layer of rubber mixture according to the invention in the form of semi-finished being so simplified, it may result in lower costs for the manufacture of the tire, which may nevertheless include a layer of circumferential reinforcing elements in addition to a conventional tire.

According to an advantageous embodiment of the invention, the axially widest working crown layer is radially inside the other working crown layers. More preferably, the axial width D of the layer of rubber mix C between the axially innermost end of said layer of rubber mix C and the end of the working crown layer axially the less broad is such that:

3.φ ₂ ≤ϋ≤25.φ ₂ with φ2, diameter of the reinforcing elements of the axially least-wide working crown layer. Such a relationship defines a zone of engagement between the layer of rubbery mixture C and the axially-smaller working crown layer. Such an engagement below a value equal to three times the diameter of the reinforcing elements of the axially smaller working layer may not be sufficient to obtain a decoupling of the working crown layer, in particular to obtain attenuation of the stresses. at the end of the axially lower working crown layer. A value of this engagement greater than twenty times the diameter of the reinforcing elements of the axially narrower working layer can lead to an excessive reduction in the drift stiffness of the crown reinforcement of the tire. [0090] Preferably, the axial width D of the layer of rubber mix C between the axially innermost end of said layer of rubber mix C and the end of the working crown layer axially the least. wide is greater than 5 mm. The various thickness measurements are made on a cross section of a tire, the tire is therefore in a non-inflated state.

According to an alternative embodiment of the invention, the modulus of elasticity under tension at 10% elongation of at least one calender layer of at least one working crown layer is greater than 9 MPa and the maximum value of tan (δ), denoted tan (δ) _max , of said at least one calendering layer of at least one working crown layer is less than 0.100.

[0093] Usually, the values of tan (δ) _max of the calendering layers of the working crown layers are greater than 0.120 and the calendering layers have a better cohesion. As in the case of the layer C, the inventors have been able to demonstrate that the cohesion of the calendering layers of the working crown layers, when they have a modulus of elasticity under tension at 10% elongation. greater than 9 MPa and a value of tan (δ) _max less than 0.100 remains satisfactory.

The inventors have further demonstrated that the presence of at least one layer of circumferential reinforcing elements contributes to a lesser evolution of the cohesion of the calendering layers of the working crown layers. Indeed, the inventors have found that the presence of at least one layer of circumferential reinforcing elements which contributes to limiting the compression of the reinforcement elements of the working crown layers, especially when the vehicle follows a sinuous course and in Moreover, it limits the temperature increases and thus leads to a slight change in the cohesion of the layers of calendering. The inventors thus consider that the cohesion of the caliper layers of the working crown layers, which is lower than that which exists in the more usual tire designs, is satisfactory in the design of the tire according to the invention. As in the case of the layer of rubber mix C, the use of at least one calendering layer of at least one working crown layer whose modulus of elasticity is greater than or equal to 9 MPa and whose tan (δ) _{max value} is less than 0.100 will make it possible to improve the properties of the tire in terms of rolling resistance by maintaining satisfactory endurance properties.

According to a preferred embodiment of the invention, said at least one calendering layer of at least one working crown layer is an elastomeric mixture based on natural rubber or synthetic polyisoprene with a majority of cis-chains. - 1, 4 and possibly at least one other diene elastomer, the natural rubber or the synthetic polyisoprene in case of cutting being present at a majority rate relative to the rate of the other diene elastomer or other elastomers used and a reinforcing filler consisting of: a) carbon black with a BET specific surface area of less than 60 m ² / g, irrespective of its structural index, employed at a rate of between 40 and 100 phr, and preferably between 60 and 90 pce, b) by a white filler of silica and / or alumina type comprising SiOH and / or AlOH surface functional groups chosen from the group formed by precipitated or pyrogenic silicas, aluminas or alumino silicates or alternatively carbon blacks in progress or after the synthesis of BET specific surface area between 30 and 260 m ² / g employed at a rate of between 40 and 100 phr, and preferably between 60 and 90 phr, c) either by a carbon black cutting described in (a) and a white filler described in (b), in which the overall filler content is between 40 and 100 phr, and preferably between 60 and 90 phr; .

In the case of using clear charge or white charge, it is necessary to use a coupling agent and / or covering selected from agents known to those skilled in the art. As examples of preferential coupling agents, mention may be made of the sulphurised alkoxysilanes of the bis (3-trialkoxysilylpropyl) polysulfide type, and among these in particular bis (3-triethoxysilylpropyl) tetrasulfide marketed by the Company. DEGUSSA under the names Si69 for the pure liquid product and X50S for the solid product (50/50 by weight blend with N330 black). Examples of coating agents that may be mentioned include a fatty alcohol, an alkylalkoxysilane such as hexadecyltrimethoxy or triethoxysilane respectively marketed by DEGUSSA under the names Sil16 and Si216, diphenylguanidine, a polyethylene glycol, a silicone oil which may be modified with OH or alkoxy functions. The covering agent and / or coupling agent is used in a weight ratio relative to the filler> at 1/100 and ≤ at 20/100, and preferably between 2/100 and 15/100 when the clear filler represents the all of the reinforcing filler and between 1/100 and 20/100 when the reinforcing filler is constituted by a carbon black and clear charge cutting.

As other examples of reinforcing fillers having the morphology and SiOH and / or AlOH surface functions of the silica and / or alumina type materials previously described and which can be used according to the invention as partial or total replacement thereof. , the modified carbon blacks may be mentioned either during the synthesis by addition to the furnace feed oil of a silicon and / or aluminum compound or after the synthesis by adding, to an aqueous suspension of carbon black in a solution of silicate and / or sodium aluminate, an acid so as to at least partially cover the surface of the carbon black of SiOH and / or AlOH functions. As non-limiting examples of this type of carbonaceous feedstock with SiOH and / or AlOH functions at the surface, mention may be made of the CSDP type feeds described in Conference No. 24 of the ACS Meeting, Rubber Division, Anaheim, California, May 6-9. 1997 as well as those of the patent application EP-A-0 799 854.

When a clear filler is used as the only reinforcing filler, the hysteresis and cohesion properties are obtained using a precipitated or pyrogenic silica, or a precipitated alumina or even a BET surface area alumino-silicate between 30 and 260 m ² / g. As non-limiting examples of this type of filler, mention may be made of the silicas KS404 from Akzo, Ultrasil VN2 or VN3 and BV3370GR from Degussa, Zeopol 8745 from Huber, Zeosil 175MP or Zeosil 1165MP from Rhodia, HI -SIL 2000 of the PPG Company etc. Among the diene elastomers that can be used in a blend with natural rubber or a synthetic polyisoprene with a majority of cis-1,4 linkages, mention may be made of a polybutadiene (BR), preferably with a majority of cis-1 linkages, 4, a styrene-butadiene copolymer (SBR) solution or emulsion, a butadiene-isoprene copolymer (BIR) or even a styrene-butadiene-isoprene terpolymer (SBIR). These elastomers may be modified elastomers during polymerization or after polymerization by means of branching agents such as divinylbenzene or starch agents such as carbonates, halogenotins, halosilicons or else by means of functionalization leading to a grafting on the chain or at the end of the chain of oxygen functions carbonyl, carboxyl or an amino function such as for example by the action of dimethyl or diethylamino benzophenone. In the case of blends of natural rubber or synthetic polyisoprene with a majority of cis-1,4 linkages with one or more of the diene elastomers mentioned above, the natural rubber or the synthetic polyisoprene is preferably used at a majority rate. and more preferably at a rate greater than 70 phr.

As in the case of the layer C, the choice of the reinforcing filler involved in the rubber mixture constituting said at least one calendering layer of at least one working crown layer contributes both to obtaining the tensile modulus values at 10% elongation and tan (δ) _max values. However, within the aforementioned ranges of values for said reinforcing fillers, those skilled in the art will still be able to adapt the quantities of other usual constituents, such as vulcanizing agents or cobalt derivatives, or to adapt the mixing processes to obtain the above modulus of elasticity and tan (δ) _max values.

Advantageously again according to the invention, the difference between the tensile modulus of elasticity at 10% elongation of the layer C and the modulus of elasticity under tension at 10% elongation of said at least one layer of calendering at least one working crown layer is less than 2 MPa.

According to a first embodiment, the modulus of elasticity of the calendering of at least the narrower working crown layer is greater than that of said layer of rubber mix C so that the stack of said layers has a gradient of elastic modulus favorable to the fight against the crack initiation at the end of the narrower working crown layer.

According to a second embodiment, the elasticity moduli of the calendering of the working crown layers and that of said layer of rubber mix C are identical and advantageously the rubber compounds are the same to simplify the industrial conditions of manufacture of the tire.

According to an advantageous embodiment of the invention, said reinforcing elements of at least one working crown layer are saturated layer cables, at least one inner layer being sheathed with a layer consisting of a polymeric composition. such as a non-crosslinkable, crosslinkable or crosslinkable rubber composition, preferably based on at least one diene elastomer.

So-called "layered cords" or "multilayer" cables are cables consisting of a central core and one or more layers of strands or substantially concentric son disposed around this central core. For the purposes of the invention, a saturated layer of a layered cable is a layer consisting of wires in which there is not enough room to add at least one additional wire.

The inventors have demonstrated that the presence of the cables as just described as strengthening elements of the working crown layers can contribute to better performance in terms of endurance.

Indeed, it appears as explained above that the rubber mixes of the calenders of the working layers can reduce the rolling resistance of the tire. This results in lower temperatures of these rubber mixes, when using the tire, which can cause less protection of the reinforcing elements vis-à-vis the oxidation phenomena in some cases of use of the tire. Indeed, the properties of the rubber compounds related to the blocking of the oxygen decrease with the temperature and the presence of oxygen can lead to a progressive degeneration of the properties mechanical cables, for the most severe driving conditions, and can alter the service life of these cables.

The presence of the rubber sheath within the cables described above compensates for this potential risk of oxidation of the reinforcing elements, the sheath contributing to the blockage of oxygen.

By the expression "composition based on at least one diene elastomer", it is understood in known manner that the composition comprises in majority (i.e. in a mass fraction greater than 50%) this or these diene elastomers.

It will be noted that the sheath according to the invention extends in a continuous manner around the layer which it covers (that is to say that this sheath is continuous in the "orthoradial" direction of the cable which is perpendicular to its radius), so as to form a continuous sleeve of cross section which is preferably substantially circular.

It will also be noted that the rubber composition of this sheath may be crosslinkable or crosslinked, that is to say that it comprises by definition a crosslinking system adapted to allow the crosslinking of the composition during its baking ( ie, its hardening and not its fusion); thus, this rubber composition can be described as infusible, since it can not be melted by heating at any temperature.

By elastomer or "diene" rubber is meant in known manner an elastomer derived at least in part (i.e. a homopolymer or a copolymer) of monomers dienes (monomers bearing two carbon-carbon double bonds, conjugated or not).

Preferably, the crosslinking system of the rubber sheath is a so-called vulcanization system, that is to say based on sulfur (or a sulfur donor agent) and a primary accelerator of vulcanization. To this basic vulcanization system may be added various known secondary accelerators or vulcanization activators.

The rubber composition of the sheath according to the invention may comprise, in addition to said crosslinking system, all the usual ingredients that can be used in the rubber compositions for tires, such as reinforcing fillers based on carbon black and / or a reinforcing inorganic filler such as silica, anti-aging agents, for example antioxidants, extender oils, plasticizers or agents facilitating the use of the compositions in the green state, acceptors and donors of methylene, resins, bismaleimides, known adhesion promoter systems of the "RFS" type (resorcinol-formaldehyde-silica) or metal salts , especially cobalt salts.

[00118] Preferably, the composition of this sheath is chosen to be identical to the composition used for the calender layer of the working crown layer that the cables are intended to reinforce. Thus, there is no problem of possible incompatibility between the respective materials of the sheath and the rubber matrix.

According to a variant of the invention, said cables of at least one working crown layer are cables with building layers [L + M], comprising a first layer L to L son of diameter di wound together in propeller according to a pitch pi with L ranging from 1 to 4, surrounded by at least one intermediate layer C2 to M son of diameter d ₂ wound together helically in a pitch p ₂ with M ranging from 3 to 12, a sheath consisting of a non-crosslinkable, crosslinkable or crosslinked rubber composition based on at least one diene elastomer, covering, in the construction, said first layer C1.

Preferably, the diameter of the wires of the first layer of the inner layer (Cl) is between 0.10 and 0.5 mm and the diameter of the wires of the outer layer (C2) is between 0.10 and 0.5 mm.

[00121] More preferably, the winding pitch of said son of the outer layer (C2) is between 8 and 25 mm.

For the purposes of the invention, the pitch of the helix represents the length, measured parallel to the axis of the cable, at the end of which a wire having this pitch performs a complete revolution around the axis of the cable; thus, if the axis is divided by two planes perpendicular to said axis and separated by a length equal to the pitch of a wire of a constituent layer of the cable, the axis of this wire has in these two planes the same position on the two circles corresponding to the layer of the wire considered. Advantageously, the cable has one, and even more preferably all of the following characteristics which is verified (e):

the layer C2 is a saturated layer, that is to say that there is not enough room in this layer to add at least one (N + 1) th wire of diameter d ₂ , N representing then the maximum number of roll-up yarns in a layer around the layer C1;

the rubber sheath also covers the inner layer C1 and / or separates the adjacent two-to-two wires from the outer layer C2;

the rubber sheath substantially covers the radially inner half-circumference of each wire of the layer C2, so that it separates the adjacent two-to-two wires from this layer C2.

[00124] Preferably, the rubber sheath has an average thickness ranging from 0.010 mm to 0.040 mm.

In general, said cables according to the invention can be made with any type of metal son, in particular steel, for example carbon steel son and / or stainless steel son. Carbon steel is preferably used, but it is of course possible to use other steels or other alloys.

When carbon steel is used, its carbon content (% by weight of steel) is preferably between 0.1% and 1.2%, more preferably 0.4%> to 1, 0%; these grades represent a good compromise between the mechanical properties required for the tire and the feasibility of the wire. It should be noted that a carbon content of between 0.5% and 0.6% makes such steels ultimately less expensive because they are easier to draw. Another advantageous embodiment of the invention may also consist, depending on the applications concerned, of using steels with a low carbon content, for example between 0.2%> and 0.5%>, in particular because of lower cost and easier wire drawing.

Said cables according to the invention may be obtained according to various techniques known to those skilled in the art, for example in two stages, firstly by sheathing via an extrusion head of the core or layers Cl, step followed in a second step by a final wiring operation or twisting of the remaining M wires (layer C2) around of the Cl layer and sheathed. The problem of stickiness in the green state posed by the rubber sheath, during any intermediate operations of winding and uncoiling can be solved in a manner known to those skilled in the art, for example by the use of a spacer film. plastic material.

Such cables of at least one working crown layer are for example selected from the cables described in patent applications WO 2006/013077 and WO 2009/083212.

According to an advantageous embodiment of the invention, the layer of circumferential reinforcing elements has an axial width greater than 0.5xS.

[00130] S is the maximum axial width of the tire, when the latter is mounted on its service rim and inflated to its recommended pressure.

The axial widths of the reinforcing element layers are measured on a cross section of a tire, the tire therefore being in a non-inflated state.

According to a preferred embodiment of the invention, at least two working crown layers having different axial widths, the difference between the axial width of the axially widest working crown layer and the axial width of the layer. axially the least wide axially working vertex being between 10 and 30 mm.

According to a preferred embodiment of the invention, the layer of circumferential reinforcing elements is radially arranged between two working crown layers.

According to this embodiment of the invention, the layer of circumferential reinforcing elements makes it possible to limit more significantly the compression of the reinforcement elements of the carcass reinforcement than a similar layer placed in place. radially outside the working layers. It is preferably radially separated from the carcass reinforcement by at least one working layer so as to limit the stresses of said reinforcing elements and do not strain them too much. Advantageously again according to the invention, the axial widths of the working crown layers radially adjacent to the layer of circumferential reinforcement elements are greater than the axial width of said layer of circumferential reinforcing elements and preferably, said working crown layers adjacent to the layer of circumferential reinforcing elements are on either side of the equatorial plane and in the immediate axial extension of the layer of circumferential reinforcing elements coupled over an axial width, to be subsequently decoupled by said layer of rubber mixture C at least over the remainder of the width common to said two working layers. The presence of such couplings between the working crown layers adjacent to the layer of circumferential reinforcing elements makes it possible to reduce tension stresses acting on the axially outermost circumferential elements and located closest to the circumferential reinforcement elements. coupling.

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

According to a preferred embodiment, the secant modulus of the reinforcing elements at 0.7% elongation is less than 100 GPa and greater than 20 GPa, preferably between 30 and 90 GPa and more preferably less than 80 GPa. .

Also preferably, the maximum tangent modulus of the reinforcing elements is less than 130 GPa and more preferably less than 120 GPa.

The modules expressed above are measured on a tensile stress curve as a function of the elongation determined with a preload of 20 MPa brought back to the metal section of the reinforcing element, the tensile stress corresponding to a measured voltage brought back to the metal section of the reinforcing element.

The modules of the same reinforcing elements can be measured on a tensile stress curve as a function of the elongation determined with a prestressing of 10 MPa reduced to the overall section of the reinforcing element, the tensile stress corresponding to a measured voltage brought back to the overall section of the reinforcing element. The overall section of the reinforcing element is the section of a composite element made of metal and rubber, the latter having in particular penetrated the reinforcing element during the baking phase of the tire.

According to this formulation relating to the overall section of the reinforcing element, the reinforcing elements of the axially outer portions and of the central portion of at least one layer of circumferential reinforcing elements are metal reinforcing elements having a secant modulus at 0.7% elongation between 5 and 60 GPa and a maximum tangent modulus of less than 75 GPa.

According to a preferred embodiment, the secant modulus of the reinforcing elements at 0.7% elongation is less than 50 Gpa and greater than 10 GPa, preferably between 15 and 45 GPa and more preferably less than 40 GPa. .

[00144] Also preferably, the maximum tangent modulus of the reinforcing elements is less than 65 GPa and more preferably less than 60 GPa.

According to a preferred embodiment, the reinforcing elements of at least one layer of circumferential reinforcing elements are metal reinforcing elements having a tensile stress curve as a function of the relative elongation having slight slopes to the low elongations and a substantially constant and strong slope for the higher elongations. Such reinforcing elements of the additional ply are usually referred to as "bi-module" elements.

According to a preferred embodiment of the invention, the substantially constant and strong slope appears from a relative elongation of between 0.1% and 0.5%.

The various characteristics of the reinforcing elements mentioned above are measured on reinforcing elements taken from tires.

Reinforcing elements that are more particularly suitable for producing at least one layer of circumferential reinforcing elements according to the invention are, for example, assemblies of formula 21.23, the construction of which is 3x (0.26 + 6x0.23). 4.4 / 6.6 SS; this strand cable consists of 21 elementary wires of formula 3 x (1 + 6), with 3 twisted strands each consisting of 7 wires, a wire forming a central core of diameter equal to 26/100 mm and 6 coiled wires of diameter equal to 23/100 mm. Such a cable has a secant module at 0.7% equal to 45 GPa and a maximum tangent modulus equal to 98 GPa, measured on a tensile stress curve as a function of the elongation determined with a preload of 20 MPa brought back to the section. of the reinforcing element, the tensile stress corresponding to a measured voltage brought back to the metal section of the reinforcing element. On a tensile stress curve as a function of the elongation determined with a preload of 10 MPa brought back to the overall section of the reinforcing element, the tensile stress corresponding to a measured tension brought back to the overall section of the element of reinforcement, this cable of formula 21.23 has a secant module at 0.7% equal to 23 GPa and a maximum tangent modulus equal to 49 GPa.

In the same way, another example of reinforcing elements is an assembly of formula 21.28, the construction of which is 3x (0.32 + 6x0.28) 6.2 / 9.3 SS. This cable has a secant module at 0.7% equal to 56 GPa and a maximum tangent modulus equal to 102 GPa, measured on a tensile stress curve as a function of the elongation determined with a preload of 20 MPa brought to the cross section. metal of the reinforcing element, the tensile stress corresponding to a measured voltage brought back to the metal section of the reinforcing element. On a tensile stress curve as a function of the elongation determined with a preload of 10 MPa brought back to the overall section of the reinforcing element, the tensile stress corresponding to a measured tension brought back to the overall section of the element of reinforcement, this cable of formula 21.28 has a secant module at 0.7% equal to 27 GPa and a maximum tangent modulus equal to 49 GPa.

The use of such reinforcing elements in at least one layer of circumferential reinforcing elements makes it possible in particular to maintain satisfactory layer stiffnesses even after the conformation and firing steps in usual manufacturing processes. According to a second embodiment of the invention, the circumferential reinforcing elements may be formed of inextensible metal elements and cut to form sections of length much shorter than the circumference of the least long layer, but preferably greater than 0.1 times said circumference, the cuts between sections being axially offset with respect to each other. More 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 crown layer. Such an embodiment makes it possible to confer, in a simple manner, on the layer of circumferential reinforcement elements a module which can easily be adjusted (by the choice of intervals between sections of the same row), but in all cases weaker. the module of the layer consisting of the same metallic elements but continuous, the module of the additional layer being measured on a vulcanized layer of cut elements, taken from the tire.

According to a third embodiment of the invention, the circumferential reinforcing elements are corrugated metal elements, the ratio a / λ of the waviness amplitude over the wavelength being at most equal to 0, 09. Preferably, the tensile modulus of elasticity per unit width of the additional layer is smaller than the tensile modulus of elasticity, measured under the same conditions, of the most extensible working crown layer.

The metal elements are preferably steel cables. According to a preferred embodiment of the invention, the reinforcing elements of the working crown layers are inextensible metal cables.

The invention further advantageously provides for decreasing the tension stresses acting on the axially outermost circumferential elements that the angle formed with the circumferential direction by the reinforcement elements of the working crown layers is less than 30 ° and preferably less than 25 °.

A preferred embodiment of the invention further provides that the crown reinforcement is completed radially outside by at least one additional layer, called protective layer, of so-called elastic reinforcing elements, oriented with respect to the circumferential direction with an angle between 10 ° and 45 ° and in the same direction as the angle formed by the elements of the working layer which is radially adjacent thereto.

The protective layer may have an axial width smaller than the axial width of the least wide working layer. Said protective layer may also have an axial width greater than the axial width of the narrower working layer, such that it covers the edges of the narrower working layer and, in the case of the radially upper layer, being the smallest, as coupled, in the axial extension of the additional reinforcement, with the widest working crown layer over an axial width, to be subsequently, axially outside, decoupled from said widest working layer with profiles at least 2 mm thick. The protective layer formed of elastic reinforcing elements may, in the case mentioned above, be on the one hand possibly decoupled from the edges of said least wide working layer by profiles of thickness substantially less than the thickness. profiles separating the edges of the two working layers, and have on the other hand an axial width less than or greater than the axial width of the widest vertex layer.

According to any one of the embodiments of the invention mentioned above, the crown reinforcement may be further completed, radially inwardly between the carcass reinforcement and the nearest radially inner working layer. of said carcass reinforcement, by a triangulation layer of steel non-extensible reinforcing elements making, with the circumferential direction, an angle greater than 60 ° and in the same direction as that of the angle formed by the reinforcing elements of the layer radially closest to the carcass reinforcement.

The tire according to the invention as it has just been described thus has improved rolling resistance compared to conventional tires and improved drift stiffness properties and therefore improved endurance performance, whatever it may be. are the driving conditions.

Other details and advantageous features of the invention will emerge below from the description of the exemplary embodiments of the invention with reference to FIGS. 1 to 3 which represent: FIG. 1, a meridian view of a diagram of a tire according to one embodiment of the invention, FIG. 2, a meridian view of a diagram of a tire according to a second embodiment of the invention; Figure 3, a meridian view of a diagram of a tire according to a third embodiment of the invention.

The figures are not represented to scale for simplicity of understanding. The figures represent only a half-view of a tire which extends symmetrically with respect to the axis XX 'which represents the circumferential median plane, or equatorial plane, of a tire.

In FIG. 1, the tire 1, of dimension 315/70 R 22.5, has an aspect ratio H / S equal to 0.70, H being the height of the tire 1 on its mounting rim and S its width. axial axis. Said tire 1 comprises a radial carcass reinforcement 2 anchored in two beads, not shown in the figure. The carcass reinforcement is formed of a single layer of metal cables. This carcass reinforcement 2 is fretted by a crown reinforcement 4, formed radially from the inside to the outside: of a first working layer 41 formed of unstretchable, inextensible metal cords 9.28, continuous over the entire width of the web , oriented at an angle equal to 24 °, a layer of circumferential reinforcing elements 42 formed of 21x23 steel cables, of the "bi-module" type, of a second working layer 43 formed of metal cables Inextensibles 9.28 not fretted, continuous over the entire width of the web, oriented at an angle equal to 24 ° and crossed with the metal cables of the layer 41, a protective layer 44 formed of elastic metal cables 6.35. The crown reinforcement is itself capped with a tread 5. [00164] The maximum axial width S of the tire is equal to 317 mm. The axial width L of the first working layer 41 is equal to 252 mm. The axial width L ₄₃ of the second working layer 43 is equal to 232 mm.

As for the axial width L ₄₂ of the layer of circumferential reinforcing elements 42, it is equal to 194 mm.

The last crown ply 44, called the protection ply, has a width L ₄₄ equal to 124 mm.

According to the invention, a layer of rubbery mixture C decouples the ends of the working crown layers 41 and 43.

The zone of engagement of the layer C between the two working crown layers 41 and 43 is defined by its thickness or more precisely the radial distance d between the end of the layer 43 and the layer 41 and by the axial width D of the layer C between the axially inner end of said layer C and the end of the radially outer working crown layer 43. The radial distance d is 3.5 mm. The axial distance D is equal to 20 mm.

According to the invention, a first layer S of rubber mixture is placed between the carcass reinforcement 2 and the first working layer 41.

In FIG. 2, the tire 1 differs from that shown in FIG. 1 in that a second layer G axially extends the first layer S, radially between the carcass reinforcement 2 and the first working layer 41.

In Figure 3, the tire 1 differs from that of Figure 1 by the shape of the layer C which is substantially flat. The radial distance d is equal to 2 mm, which corresponds to a thickness of the layer C equal to 1.2 mm. According to the variant of the invention shown in this FIG. 2, the thickness of the layer C is substantially identical in a meridian view on the axial width lying between the axially inner end of the layer C and the end of the layer. working axially the narrowest.

The diameter of the circumferential reinforcing elements of the layer 42 is equal to 1.35 mm. The distance d is equal to 1.48 times the diameter ø of these elements. Tests have been made with different tires made according to the invention in accordance with the representations of Figures 1 and 3 and with reference tires.

In particular, tests are carried out by varying the characteristics of the mixtures of the layer C, in particular their modulus of elasticity under tension at 10% elongation and the value tan (δ) _max and the characteristics of the mixtures of the layer. S, in particular the complex dynamic shear modulus G ^* , measured at 10% and 60 ° C on the return cycle.

[00177] Other tests are also carried out with tires by also varying the characteristics of the calendering mixture mixtures of the working layers 41 and 43, in particular their tensile modulus of elasticity at 10% elongation and the tan value ( δ) _max , in accordance with the invention.

[00178] Other tests are still carried out by varying the shape and the dimensions of the layer C.

The various mixtures used are listed below.

Mixture RI Mixture R2 Mixture R3 Mixture 1 Mixture 2

N 100 100 100 100 100

Black N347 52 50

Black N683 63

Black N330 35

Black N234 35

165G Silica 5

Antioxidant (6PPD) 1 1.8 0.7 1 1.7

Stearic acid 0.65 0.6 1.4 0.65 0.5

Zinc oxide 9.3 9.3 2.1 9.3 5

Cobalt Salt (AcacCo) 1.12 1.12

Cobalt Salt (AbietateCo) 4.5 sulfur 6.1 5.6 2.15 6.1 3.13

DCBS 0.93 0.8 0.93 accelerator

Accelerator CBS 1 1.10

PTC Delay (PVI) 0.25 0.08 0.25

MA ₁₀ (MPa) 10.4 8.5 3.4 10.03 3.5 tan (6) ~ "0.130 0.141 0.074 0.092 0.080

P60 (%) 22.9 24.5 11.3 17.4 12

G * 10% at 60 ° C (cycle 1.25

1.43

return)

Note Z 60 65

Bound rubber 27.5 48.1

The values of the constituents are expressed in phr (parts by weight per hundred parts of elastomers).

Different reference tires were tested.

The first reference tires T1 have a first layer C consisting of the mixture R2, as shown in FIG. 1 and having a distance d equal to 3.5 mm and a profile of its rounded section, the calendering of the working layers being consisting of the mixture RI and the first layer S of the mixture R3

Second reference tires T2 have a first layer C consisting of the mixture 1, as shown in FIG. 1 and having a distance d equal to 3.5 mm and a profile of its rounded section, the calendering of the working layers being consisting of the mixture RI and the first layer S of the mixture R3.

Third reference tires T3 have a first layer C consisting of the mixture 1, as shown in FIG. 3, the calendars of the working layers consisting of the mixture R1 and the first layer S of the mixture R3. Fourth reference tires T4 have a first layer C consisting of the mixture 1, as shown in FIG. 3, the calendars of the working layers consisting of the mixture and the first layer S of the mixture R3. Different tires according to the invention were tested.

The first tires SI according to the invention have a first layer C consisting of the mixture 1, as shown in Figure 1 and having a distance d equal to 3.5 mm and a profile of its rounded section, the layers of the diapers working consisting of the mixture RI and the first layer S of the mixture 2.

Second tires S2 according to the invention have a first layer C consisting of the mixture 1, as shown in FIG. 3, the calenders of the working layers consisting of the mixture R1 and the first layer S of the mixture 2. Third tires S2 according to the invention have a first layer C consisting of the mixture 1, as shown in FIG. 3, the calendars of the working layers consisting of the mixture 1 and the first layer S of the mixture 2.

[00190] First endurance tests were performed on a test machine requiring each tire to run a straight line at a speed equal to the maximum speed index prescribed for said tire (speed index) under an initial load of 4000 Kg gradually increased to reduce the duration of the test.

It turns out that all the tires tested shows substantially comparable results. Other endurance tests were performed on a test machine imposing cyclically a transverse force and a dynamic overload to the tires. The tests were carried out for the tires according to the invention with conditions identical to those applied to the reference tires.

The distances traveled vary from one type of tire to another, the lapses appearing due to a degradation of the rubber compounds at the ends of the working layers. The results are expressed in the table which follows with reference to a base 100 fixed for the reference tire T1. Pneumatic Tl Pneumatic T2 Pneumatic Τ3 Pneumatic Τ4 Pneumatic SI Pneumatic S2 Pneumatic S3

100 110 90 105 130 110 125

In addition, rolling resistance measurements have been made. These measurements relate to all the tires described above.

The results of the measurements are presented in the following table; they are expressed in Kg / t, a value of 100 being attributed to the tire T1.

Pneumatic Tl Pneumatic T2 Pneumatic T3 Pneumatic T4 Pneumatic SI Pneumatic S2 Pneumatic S3

100 98 97 95 98 97 95

Claims

1 - Radial carcass reinforcement tire comprising a crown reinforcement formed of at least two reinforcing element working crown layers, crossed from one layer to the other by making with the circumferential direction angles between 10 And 45 °, a layer C of rubber mixture being disposed between at least the ends of said at least two working crown layers, a first layer S of polymeric mixture being in contact with at least one working crown layer and at least contact of the carcass reinforcement, said first polymeric mixture layer S extending axially to at least the axial end of the tread, said tread capping the crown reinforcement and being joined to two beads by the intermediate of two sidewalls, the crown reinforcement having at least one layer of circumferential reinforcing elements, characterized in that the elastic modulus under tension at 10% elongation of layer C is greater than 9 MPa, in that the maximum value of tan (δ), denoted tan (δ) _max , of layer C is less than 0.100, in that said first layer S of polymeric mixture mixture consists of a charged elastomeric mixture having a macro dispersion Z of greater than or equal to 65 and a maximum value of tan (δ), noted tan (δ) max, less than 0.100 and that the complex modulus of dynamic shear G *, measured at 10% and 60 ° C on the return cycle, of said first layer S of polymeric mixture is greater than 1.35 MPa. 2 - A tire according to claim 1, characterized in that the complex shear modulus G *, measured at 10% and 60 ° C on the return cycle, of the first layer S is less than 2 MPa.

3 - tire according to one of the preceding claims, characterized in that the elastomeric mixture of the first layer S comprises as reinforcing filler at least carbon black employed at a rate of between 10 and 50 phr, and in that the black carbon has a BET specific surface area greater than 90 m ² / g and preferably greater than or equal to 120 m ² / g.

4 - tire according to one of the preceding claims, characterized in that the elastomeric mixture of the first layer S comprises a carbon black cut, BET specific surface area greater than 90 m ² / g and preferably greater than or equal to 120 m ² / g, and of a white charge, in that the reinforcing filler is used at a rate of between 10 and 60 phr, and in that the ratio of carbon black on white charge is greater than 2.7.

5 - A tire according to one of the preceding claims, characterized in that the layer C rubbery mixture is an elastomeric mixture based on natural rubber or synthetic polyisoprene predominantly cis-1,4 linkages and possibly at least another diene elastomer, the natural rubber or the synthetic polyisoprene in case of cutting being present at a majority rate relative to the rate of the other or other diene elastomers used and a reinforcing filler constituted: a) by black with a BET surface area of less than 60 m ² / g, irrespective of its structural index, employed at a level of between 40 and 100 phr, and preferably between 60 and 90 phr, or with a white charge of silica and / or alumina type having SiOH and / or AlOH surface functions chosen from the group formed by precipitated or pyrogenic silicas, aluminas or alumino silicates or in addition, the modified carbon blacks in progress or after the BET specific surface area synthesis of between 30 and 260 m ² / g employed at a level of between 40 and 100 phr, and preferably between 60 and 90 phr, c) either by a carbon black blend described in (a) and a white filler described in (b), wherein the overall filler rate is between 40 and 100 phr, and preferably between 60 and 90 phr.

6 - A tire according to one of the preceding claims, said tire comprising a second layer G of polymeric mixture axially in contact with the first layer S of polymeric mixture radially between the carcass reinforcement and the layer of reinforcing elements radially most interior of the crown reinforcement, characterized in that said second layer G of polymeric mixture consists of a charged elastomeric mixture having a macro dispersion Z of greater than or equal to 65 and a maximum value of tan (δ), noted tan (δ) max, less than 0.100 and in that the dynamic shear complex modulus G ^* , measured at 10% and 60 ° C on the return cycle, of said second G layer of polymer mixture is greater than 1.35 MPa. 7 - A tire according to claim 6, characterized in that the complex shear modulus G *, measured at 10% and 60 ° C on the return cycle, of the second layer G is less than 2 MPa.

8 - A tire according to one of claims 6 or 7, characterized in that the elastomeric mixture of the second layer G comprises as reinforcing filler at least carbon black employed at a rate of between 10 and 50 phr, and in that the carbon black has a BET specific surface area greater than 90 m ² / g and preferably greater than or equal to 120 m ² / g.

9 - A tire according to one of claims 6 or 7, characterized in that the elastomeric mixture of the second layer G comprises as a carbon black cut, BET specific surface area greater than 90 m ² / g and preferably greater than or equal to 120 m ² / g, and a white filler, in that the reinforcing filler is used at a rate of between

10 and 60 phr, and in that the ratio of carbon black on white charge is greater than 2.7.

Tire according to one of the preceding claims, said at least two working crown layers having unequal axial widths, characterized in that the distance d between the end of the axially narrowest working layer and the Separate working of the axially narrowest working layer by the layer C of rubber mix is such that lo <d <2.20, ø being the diameter of the reinforcing elements of said at least one layer of circumferential reinforcing elements and in that, in a meridian plane, the thickness of the layer C of rubbery mixture is substantially constant over the axial width between the axially inner end of the layer C and the end of the axially narrowest working layer.

11 - tire according to one of the preceding claims, said at least two working crown layers being each formed of reinforcing elements inserted between two layers of calendering rubber mix, characterized in that the modulus of elasticity under tension at 10% of elongation of at least one calendering layer of at least one working crown layer is greater than 9 MPa and in that the maximum value of tan (δ), denoted tan (δ) max, of said at least one calendering layer of at least one working crown layer is less than 0.100. 12 - A tire according to claim 11, characterized in that said at least one calender layer of at least one working crown layer is an elastomeric mixture based on natural rubber or synthetic polyisoprene predominantly with cis-1 linkages. , 4 and optionally at least one other diene elastomer, the natural rubber or the synthetic polyisoprene in the case of cutting being present at a majority rate relative to the rate of the other diene elastomer (s) used and a reinforcing filler consisting of: a) carbon black with a BET specific surface area of less than 60 m ² / g, irrespective of its structural index, employed at a level of between 40 and 100 phr, and preferably between 60 and 90 phr, b) either with a white filler of silica and / or alumina type comprising SiOH and / or AlOH surface functional groups chosen from the group formed by precipitated or pyrogenic silicas, aluminas or aluminosilicates or alternatively modified carbon blacks in progress or after the BET surface area synthesis of between 30 and 260 m ² / g employed at a level of between 40 and 100 phr, and preferably between 60 and 90 phr, c) either by a carbon black cutting described in (a) and a white filler described in (b), in which the overall filler content is between 40 and 100 phr, and preferably between 60 and 90 phr; .

13 - tire according to one of the preceding claims, characterized in that the difference between the tensile modulus of elasticity at 10% elongation of the layer C and the modulus of elasticity under tension at 10% elongation of said at least one calendering layer of at least one working crown layer is less than 2 MPa.

14 - A tire according to one of the preceding claims, characterized in that the layer of circumferential reinforcing elements is radially disposed between two working crown layers.

15 - A tire according to one of the preceding claims, characterized in that the reinforcing elements of at least one layer of circumferential reinforcing elements are metal reinforcing elements having a secant modulus at 0.7% an elongation of between 10 and 120 GPa and a maximum tangent modulus of less than 150 GPa.

16 - tire according to one of the preceding claims, characterized in that the reinforcing elements of the working crown layers are inextensible.

17 - tire according to one of the preceding claims, characterized in that the crown reinforcement is completed radially outwardly by at least one additional sheet, said protective, of so-called elastic reinforcing elements, oriented relative to the circumferential direction with an angle between 10 ° and 45 ° and in the same direction as the angle formed by the elements of the working ply which is radially adjacent thereto.

18 - A tire according to one of the preceding claims, characterized in that the crown reinforcement further comprises a triangulation layer formed of metal reinforcing elements making with the circumferential direction angles greater than 60 °.