Tire for a civil engineering vehicle comprising first and second protective plies comprising different reinforcing elements

Abstract

The invention relates to a tire (1) for a civil engineering vehicle, the tire comprising: - a crown reinforcement, radially inside a tread (2) and radially outside a carcass reinforcement; - the crown reinforcement comprising, radially from the outside toward the inside, a protective reinforcement and a working reinforcement; - the protective reinforcement comprising first and second protective plies (311,312), the first ply (311) being arranged radially inside the second ply (312), wherein: - the force of the first protective ply (311) at 1% elongation, denoted E NSP1, is less than or equal to 500 daN / cm; - the force of the second protective ply (312) at 1% elongation, denoted E NSP2, is less than or equal to 100 daN / cm; and the ratio of the rigidities E NSP1 / E NSP2 is strictly greater than 3.0.

Description

Tire for construction equipment including first and second layers of protection comprising different reinforcement elements

[0001] The field of the present invention is that of tires for civil engineering type vehicles.

[0002] Prior art is known, notably from documents WO2016 / 131862 and W02020 / 161404, of a tire for construction vehicles with a radial carcass reinforcement comprising a tread, two inextensible beads, two sidewalls connecting the beads to the tread, and a crown reinforcement arranged circumferentially between the carcass reinforcement and the tread. This crown reinforcement comprises first and second protective plies, the first protective ply being arranged radially inside the second protective ply. The first and second protective plies include reinforcing elements, referred to as protective elements, comprising a 1x4 multi-strand structural cord.The cable comprises a single layer of 4 wound strands including an inner layer of 3 internal wires wound helically, an outer layer of 8 external wires wound helically around the inner layer, the wires having a diameter of 0.35mm.

[0003] We also know from the prior art, in particular from document WO2011134900, a tire in which the top reinforcement comprises a multi-strand cable of 1x4 structure. The cable comprises a single layer of 4 wound strands including an inner layer of 3 internal wires wound helically, an outer layer of 9 external wires wound helically around the inner layer, the wires having a diameter of 0.26 mm.

[0004] We also know from the prior art, in particular from document JP2010090509, a pneumatic system comprising cables of type 24.28 with a 4 x (1+5) structure. The cable comprises a single layer of 4 wound strands including an inner layer of 1 inner wire with a diameter of 0.22 mm and an infinite pitch, and an outer layer of 5 outer wires wound helically around the inner layer, the wires having a diameter of 0.28 mm.

[0005] On the one hand, it has been observed that when a tire passes over obstacles, such as pebbles, these obstacles can puncture the tire tread, reaching the crown reinforcement. These perforations allow corrosive agents to penetrate the crown reinforcement and reduce the tire's lifespan.

[0006] On the other hand, it has been observed that tires can experience ruptures resulting from deformations and relatively significant stresses exerted on the tire, particularly when the tire passes over obstacles.

[0007] The invention relates to a pneumatic device that reduces, or even eliminates the risk of tire puncture following tread damage when driving over sharp stones while reducing the mass of the crown reinforcement.

[0008] To this end, the invention relates to a tire for a construction vehicle comprising: - a crown reinforcement, radially internal to a tread and radially external to a carcass reinforcement, - the apex reinforcement comprising, radially from the outside in, a protective reinforcement and a working reinforcement, - the protective framework comprising first and second protective layers, with the first layer being radially 'inside' the second layer, - the first protective layer comprising at least one metallic multi-strand cable and the second protective layer comprising at least one metallic cable in which: - the effort of the first protective layer at 1% deformation noted E NSP1 is less than or equal to 500 daN / cm; - the effort of the second protective layer at 1% deformation noted E NSP2 is less than or equal to 100 daN / cm; and the ratio of the stiffnesses E NSP1 / E NSP2 is strictly greater than 3.0, the effort of the protective layer at 1% deformation being determined according to the ASTM D2969-04 standard of 2014, this effort corresponding to the value of the effort of the wire rope divided by the laying pitch of the wire rope in each protective layer at 1% deformation on the force-stretch curve.

[0009] The force-stretch measurement is carried out according to the ASTM D 2969 - 04 standard on a metal cable intended for tire reinforcement.

[0010] The measurement is performed on a tensile testing machine that allows the breaking force (Fm) of the wire rope to be reached, as well as the forces exerted during elongation. The elongation during the experiment is measured with a mechanical extensometer in contact with the wire rope.

[0011] Regarding the clamps used, they must allow for the extension of the metal cables until the sample breaks outside the gripping area of ​​the clamps.

[0012] Pliers with a gradual curvature are therefore preferentially used.

[0013] The test begins by loading the sample (called preload) corresponding to 1% of the estimated breaking force and allows the elongation measurement to be initiated (zeroing the deformation).

[0014] This preload is estimated beforehand based on 3 force measurements at the ruptures carried out with the same device.

[0015] The measurement involves recording the force-selongation curve of the cable until the break occurs.

[0016] The measurement is considered valid when the point of rupture is located in the area between the clamps, outside the gripping area of ​​the metal reinforcement.

[0017] The elongation measured at this point of rupture is called the total elongation at rupture, denoted "At", and is calculated as follows: Lt = Length between the arms of the extensometer at the time of rupture (mm) LO = Initial length between the arms of the extensometer after the extensometer has been put in place to perform the measurement (mm).

[0018] The result of the test is the value measured on a single test specimen.

[0019] To calculate the force at 1% of the web, we take the value of the force of the cable and divide by the spacing of the cable in the web.

[0020] By definition, the laying pitch is the average distance between the center of each cable in a plane perpendicular to the cable.

[0021] The expert observed that there was a need to optimize the protective layers to better withstand the stresses caused by wear and tear. He found that performance was improved by reducing the stiffness of the NSP2 layer to better withstand the deformation caused by the indenters. Therefore, a stiffness ratio of these layers (E NSP1 / E NSP2) strictly greater than 3 provided the best performance compromise.

[0022] According to the invention, the tire is for a construction vehicle. Thus, the tire has a dimension in which the diameter, in inches, of the seat of the rim on which the tire is intended to be mounted is greater than or equal to 25 inches.

[0023] Preferably, the ratio of stiffnesses E NSP1 / E NSP2 is greater than or equal to 3.2.

[0024] Advantageously, E NSP1 is less than or equal to 400 daN / cm.

[0025] The first protective layer retains good rigidity.

[0026] Advantageously, E NSP2 is less than or equal to 50 daN / cm.

[0027] The more flexible the second layer, the better the stiffness ratio E NSP1 / E NSP2.

[0028] Preferably, E NSP1 is strictly greater than 50 daN / cm and preferably greater than or equal to 100 daN / cm.

[0029] Advantageously, it is preferable to have a stiffness gradient between E NSP1 and E NSP2 to ensure good resistance to perforations.

[0030] Preferably, the multi-strand metallic cable of the first protective ribbon cable is of a 1xN structure comprising a single layer of N strands wound in a helix, each strand comprising: - an internal layer of M > 1 internal metallic wire elements, - an outer layer of P external metallic wire elements wound in a helix around the inner layer.

[0031] Advantageously, N= 3 or 4 and preferably N=4.

[0032] Preferably, M goes from 1 to 5, preferably M=1 or 3.

[0033] Preferably, P goes from 5 to 9, preferably P=5, 8 or 9.

[0034] In a first preferred embodiment, N= 4, M= 3 and P= 8.

[0035] In this first embodiment, the cable has a 1xN structure comprising a single layer of N strands wound in a helix, each strand comprising: - an inner layer of M internal wires (54) wound in a helix, - an outer layer of P external wires wound in a helix around the inner layer.

[0036] In a second preferred embodiment, N=4, M=4 and P=9.

[0037] In this second embodiment, the cable has a 1xN structure comprising a single layer of N strands wound in a helix, each strand comprising: - an inner layer of M internal metallic wire elements, - an outer layer of P external metallic wire elements wound in a helix around the inner layer.

[0038] In a third embodiment, N=4, M=1 and P=5.

[0039] Preferably, the pitch of the metal cables of the first protective layer should be from 2.5 to 5.0 mm.

[0040] Advantageously, the metallic cable of the second protective layer comprises a single layer consisting of T helically wound metallic wire elements, each metallic wire element of the layer describing, when the cable extends in a substantially straight direction, a helical path around a principal axis (A) substantially parallel to the substantially straight direction, the cable having a total elongation at break At > 10.00% as determined by ASTM D2969-04 of 2014.

[0041] The cable according to the invention lacks a central metallic core. It is also referred to as a 1xT structure cable, where T is the number of metallic wire elements, or as an open-cord cable. In the cable according to the invention defined above, the internal core is hollow and therefore devoid of any filling material, in particular, any elastomeric composition. This is referred to as a cable without filling material.

[0042] A wire element is defined as an element extending longitudinally along a principal axis and having a cross-section perpendicular to the principal axis, the largest of which The dimension G is relatively small compared to the dimension L along the principal axis. By relatively small, we mean that L / G is greater than or equal to 100, preferably greater than or equal to 1000. This definition covers both wire elements with a circular cross-section and wire elements with a non-circular cross-section, for example, polygonal or oblong cross-sections. Preferably, each metallic wire element has a circular cross-section.

[0043] By definition, a metallic element is understood to be a wire element composed mainly (i.e., for more than 50% of its mass) or entirely (for 100% of its mass) of a metallic material. Each metallic wire element is preferably made of steel, more preferably of pearlitic or ferritic-pearlitic carbon steel, commonly referred to by those skilled in the art as carbon steel, or of stainless steel (by definition, steel containing at least 10.5% chromium).

[0044] Preferably, the metal wires do not undergo pre-forming. In other words, the cable is obtained by a process without individual pre-forming steps for each of the metal wire elements.

[0045] As described above, the cable according to the invention is manufactured according to a process and using an installation described in documents WO2016083265 and WO2016083267. This process includes a step of assembling X metallic wire elements together in a layer of X metallic wire elements around a transient core to form a transient assembly, and a step of splitting the transient assembly into at least two assemblies of X1 metallic wire elements and X2 metallic wire elements and the transient core. At least one of the first and second assemblies then forms the cable according to the invention, i.e., X1=Y and / or X2=Y.

[0046] Advantageously, in a first embodiment, the transient assembly splitting step includes a step of separating the transient core from the first and second assemblies. In this embodiment, the first assembly consists of M1 metallic wire elements wound together and arranged in a single layer around the axis of the first assembly. Similarly, the second assembly in this embodiment consists of X2 metallic wire elements wound together and arranged in a single layer around the axis of the second assembly. In other words, in this first embodiment, since the transient core comprises at least one wire element, each wire element of the transient core does not belong to the first and second assemblies of X1 metallic wire elements and X2 metallic wire elements. Therefore, X1 + X2 = X.

[0047] In a first preferred variant of this first embodiment, during the splitting step, the first assembly is separated from a transient set formed by the second assembly and the transient nucleus, then the second assembly and the transient nucleus are separated from each other. In a second variant, during the splitting step, the transient nucleus, the first assembly and the second assembly are simultaneously separated two by two from each other.

[0048] Advantageously, the process includes a transient core recycling step during which: the transient core is recovered downstream of the splitting step, and the previously recovered transient core is introduced upstream of the assembly step.

[0049] In a preferred embodiment, the transient nucleus recycling step can be continuous, meaning that the transient nucleus exiting the separation step is reintroduced into the assembly step without an intermediate storage step. In another embodiment, the transient nucleus recycling step is discontinuous, meaning it includes an intermediate storage step for the transient nucleus.

[0050] Preferably, a textile transitional core is used.

[0051] In a second embodiment, the transient assembly splitting step includes a step of splitting the transient core between at least the first and second assemblies. Thus, in this second embodiment, two assemblies of metallic wire elements are obtained, each comprising a layer of P1 and P2 metallic wire elements wound together in a helix, respectively, and for at least one of the assemblies, a central core comprising or consisting of at least a portion of the transient core around which the metallic wire elements of the layer are wound. In other words, in this second embodiment, the transient core comprising K metallic wire element(s), at least one of the K metallic wire element(s) of the transient core belongs to at least one of the first and second assemblies of M1 and M2 metallic wire elements.

[0052] Advantageously, during the fractionation step, at least a first part of the transient core is fractionated with first metallic wire elements of the transient assembly so as to form the first assembly.

[0053] Thus, the first assembly comprises a layer of P1 metallic wire elements wound together in a helix and a central core comprising or constituted by a first part (K1 wire element(s)) of the K metallic wire elements of the transient core and around which the P1 metallic wire elements are wound together in a helix. We have P1+K1=M1.

[0054] Advantageously, during the splitting step, at least one second part of the transient core with second metallic wire elements of the transient assembly so as to form the second assembly.

[0055] Thus, the second assembly comprises a layer of P2 metallic wire elements wound together in a helix and a central core comprising or constituted by a second part (K2 wire element(s)) of the K wire elements of the transient core and around which the P2 metallic wire elements are wound together in a helix. We have P2+K2=M2.

[0056] Preferably, the first and second assemblies are formed simultaneously.

[0057] Preferably, before the splitting step, the first and second parts of the transient kernel constitute the transient kernel. Thus, the first and second parts of the transient kernel are complementary. Therefore, K1 + K2 = K. In a variant, we could have K1 + K2 <K.

[0058] In one variant, the first assembly comprises a layer of P1 metallic wire elements wound together in a helix around a central core comprising or constituted by the transient core and the second assembly comprises a layer of P2=M2 metallic wire elements wound together in a helix and lacking a central core.

[0059] In one embodiment, the assembly step is performed by twisting. In this case, the metal wire elements undergo both collective and individual twisting around their own axis, generating a detorsion torque on each wire element. In another embodiment, the assembly step is performed by wiring. In this case, the metal wire elements do not undergo twisting around their own axis due to synchronous rotation before and after the assembly point.

[0060] Preferably, in the case of a twisting assembly step, the process includes a balancing step of the transient assembly. Thus, since the balancing step is performed on the assembly consisting of the M metallic wire elements and the transient core, the balancing step is implicitly performed upstream of the splitting step.

[0061] Advantageously, the process includes a balancing step of at least one of the first and second assemblies after the splitting step.

[0062] Advantageously, the process includes a step to maintain the rotation of the first and second assemblies around their respective direction of travel. This step is performed after the splitting step and before the balancing step of at least one of the first and second assemblies.

[0063] Advantageously, T ranges from 4 to 9 and preferably from 5 to 7.

[0064] Preferably, the spacing of the metal cables of the second protective layer will from 2.0 to 4.0 mm.

[0065] Advantageously, the diameter D of the cable is such that and preferably 1.40 mm < D < 2.20 mm.

[0066] The apparent diameter, denoted D, is measured using a thickness gauge with a probe diameter at least 1.5 times the winding pitch P of the wire elements (for example, the KAEFER JD50 model, which achieves an accuracy of 1 / 100 of a millimeter, is equipped with type a probes, and has a contact pressure close to 0.6 N). The measurement protocol consists of three repetitions of a series of three measurements (taken perpendicular to the cable axis and under zero tension), the second and third of which are performed in a direction angularly offset from the previous one by one-third of a turn, by rotating the measurement direction around the cable axis.

[0067] Advantageously, the metal mass of the metallic cables of the two protective layers is greater than or equal to 5.0 kg / m 3 , preferably greater than or equal to 6.5 kg / m 3and more preferably greater than or equal to 8.0 kg / m³ 3 .

[0068] For a given mass of metal at the level of the protective layers, the ratio of the stiffnesses E NSP1 / E NSP2 allows to optimize the performance to better resist the problems of aggression.

[0069] In a first embodiment, the metal mass of the metallic cables of the two protective layers is greater than or equal to 5.0 kg / m 3 which allows coverage of tires with a size less than or equal to 35 inches.

[0070] In a second embodiment, the metal mass of the metallic cables of the two protective layers is greater than or equal to 6.5 kg / m 3 which allows it to cover tires with dimensions ranging from 33 to 49 inches.

[0071] In a third embodiment, the metal mass of the metallic cables of the two protective layers is greater than or equal to 8.0 kg / m3 which allows coverage for tires with a size greater than or equal to 39 inches.

[0072] The optional features described below may be combined with each other to the extent that such combinations are technically compatible.

[0073] Advantageously, the tire has a thickness ep_NSP1 + ep_NSP2 of the first and second protective plies measured along a direction (Y) perpendicular to the main direction (X) such that ep_NSP1 + ep_NSP2 goes from 5 to 10 mm.

[0074] The invention will be better understood upon reading the following examples, given solely as non-limiting examples and made with reference to the drawings in which: - Figure 1 is a detailed cross-sectional view perpendicular to the circumferential direction of a pneumatic tire according to the invention; - Figure 2 is a cross-sectional view of the first and second protective layers according to the invention; - Figure 3 is a cross-sectional view perpendicular to its axis of a 50 cable (assumed to be straight and at rest); - Figure 4 is a cross-sectional view perpendicular to its axis of a 60 cable (assumed to be straight and at rest); - Figure 5 is a cross-sectional view perpendicular to its axis of a 60' cable (assumed to be straight and at rest); - Figure 6 is a cross-sectional view perpendicular to its axis of a 60” cable (assumed to be straight and at rest); and - Figure 7 is a photograph of the stacking of the cables with 50 and 60 cables according to the invention.

[0075] EXAMPLE OF A PNEUMATIC TIRE ACCORDING TO THE INVENTION

[0076] Figure 1 shows a cross-section of a heavy-duty construction vehicle tire 1 comprising a crown reinforcement radially internal to a tread 2 and radially external to a carcass reinforcement 4. The crown reinforcement comprises, radially from the outside in, a protective reinforcement, a working reinforcement, and a reinforcing reinforcement. The protective reinforcement comprises two protective layers 311 and 312, each consisting of parallel metallic reinforcements 50 and 60 respectively, embedded in an elastomeric material, forming an angle of 24°, with a circumferential direction tangent to the circumference of the tire, the respective metallic reinforcements of each protective layer being crossed from one protective layer to the next.

[0077] The working reinforcement comprises two working layers 321 and 322, whose respective non-extensible metallic reinforcements, embedded in an elastomeric material, are parallel to each other and form, with the circumferential direction, angles of 33° for the innermost radially facing working layer 321 and 19° for the outermost radially facing working layer 322, respectively, and are intersected from one working layer to the next. The innermost radially facing protective layer 311 is axially overhanging with respect to the working layer of greatest axial width, here the innermost radially facing working layer 321.

[0078] The shrink-fitting reinforcement comprises two shrink-fitting layers 331, 332 whose respective metallic reinforcements, embedded in an elastomeric material, parallel to each other and forming, with the circumferential direction, an angle between 5° and 10°, are crossed from one shrink-fitting layer to the next.

[0079] EXAMPLE OF PROTECTIVE SHEETS ACCORDING TO THE INVENTION

[0080] Figure 2 shows the protective layers according to the invention, and the photograph in Figure 7 shows an example of a stack of layers according to the invention. The thickness of the protective layers is represented by ep NSP1+NSP2. It is measured along a direction (Y) perpendicular to the principal direction (X).

[0081] EXAMPLE OF A FIRST PROTECTIVE LAYER ACCORDING TO THE INVENTION

[0082] Figure 2 shows the protective layers according to the invention and the first protective layer designated by the general reference 311. The first protective layer comprises at least one cable 60, in this case several cables 60, embedded in the polymeric matrix Ma.

[0083] Here, the polymeric matrix Ma is an elastomeric matrix based on an elastomeric composition.

[0084] The cable laying pitch is 60 VA from 4.0 to 6.0 mm.

[0085] EXAMPLE OF A SECOND PROTECTIVE LAYER ACCORDING TO THE INVENTION

[0086] Figure 2 shows the protective layers according to the invention and the second protective layer designated by the general reference 312. The second protective layer comprises at least one cable 50, in this case several cables 50, embedded in the polymeric matrix Ma.

[0087] Here, the polymeric matrix Ma is an elastomeric matrix based on an elastomeric composition.

[0088] The cable installation pitch is 50 VA from 2.0 to 3.5 mm.

[0089] CABLES OF THE FIRST PROTECTIVE LAYER ACCORDING TO THE INVENTION

[0090] Figures 4, 5 and 6 show cables according to first, second and third embodiments of the invention.

[0091] Cable 60 according to a first embodiment of the invention

[0092] Figure 4 shows cable 60 according to a first embodiment of the invention.

[0093] The 60 multistrand cable has a 1xN structure. The 60 cable comprises a single layer 70 of N strands 62 wound helically with a pitch p3. The N strands 62 are wound in a Z or S direction.

[0094] Each strand 62 comprises an inner layer Cl of M inner yarns 72 wound helically with a pitch p1 and an outer layer CE of P outer yarns 74 wound helically around the inner layer 52 with a pitch p2. In this case, each strand 62 consists of the inner layer Cl and the outer layer CE. Each strand 62 is thus devoid of a binding yarn.

[0095] Each internal 72 and external 74 wire has a diameter ranging from 0.12 mm to 0.50 mm, preferably from 0.25 mm to 0.45 mm and more preferably from 0.30 to 0.40 mm and Here, the diameter is equal to 0.35 mm. Each inner wire 72 and outer wire 74 is metallic, here made of HT (High Tensile) grade steel with a tensile strength of 2765 MPa. Other grades of steel can, of course, be used. In other embodiments, the diameter of the inner wires 72 may differ from the diameter of the outer wires 74.

[0096] The outer CE layer of each 62 strand is non-compact and unsaturated.

[0097] The winding pitch p1 of the internal M wires 72 ranges from 3 to 11 mm, preferably from 5 to 9 mm, and is here equal to 6.7 mm. The winding pitch p2 of the external P wires 74 ranges from 6 to 14 mm, preferably from 8 to 12 mm, and is here equal to 10 mm. Finally, the winding pitch p3 of the N strands 62 ranges from 10 to 30 mm, preferably from 15 to 25 mm, and is here equal to 20 mm.

[0098] The inner wires 72, the outer wires 74 and the N strands are wound in the same direction, Z or S.

[0099] The diameter D60 of the 60 cable is such that D60 < 5.0 mm and preferably 1.40 mm < D60 < 4.5 mm. Here D60 = 3.80 mm.

[0100] In the first embodiment illustrated in Figure 4, N=3 or N=4, and here N=4. M also ranges from 1 to 5, preferably M=1 or 3, and here M=3. Finally, P ranges from 5 to 9, preferably P=5, 8, or 9, and here P=8. This cable is a 4 x (3+8) construction cable, commonly called 44.35.

[0101] 60' cable according to a second embodiment of the invention

[0102] Figure 5 shows the 60' cable according to a second embodiment of the invention.

[0103] The 60' multi-strand cable has a 1xN structure. The 60' cable comprises a single layer of 70 N strands of 62 wound helically with a pitch of p3. The N strands of 62 are wound in a Z or S direction.

[0104] Each strand 62 comprises an inner layer Cl of M inner yarns 72 wound helically with a pitch p1 and an outer layer CE of P outer yarns 74 wound helically around the inner layer 52 with a pitch p2. In this case, each strand 62 consists of the inner layer Cl and the outer layer CE. Each strand 62 is thus devoid of a binding yarn.

[0105] Each internal wire 72 and external wire 74 has a diameter ranging from 0.12 mm to 0.50 mm, preferably from 0.20 mm to 0.45 mm and here equal to 0.26 mm.

[0106] In other embodiments, the diameter of the internal wires 72 may be different from the diameter of the external wires 74.

[0107] The outer CE layer of each 62 strand is non-compact and unsaturated.

[0108] The winding pitch p1 of the internal M wires 72 ranges from 3 to 11 mm, preferably from 5 to 9 mm, and is here equal to 5.1 mm. The winding pitch p2 of the external P wires 74 ranges from 6 to 14 mm, preferably from 7 to 12 mm, and is here equal to 7.5 mm. Finally, the winding pitch p3 of the N strands 62 ranges from 10 to 30 mm, preferably from 15 to 25 mm, and is here equal to 15 mm.

[0109] The inner wires 72, the outer wires 74 and the N strands are wound in the same direction, Z or S.

[0110] The diameter D60' of the 60' cable is such that D60' < 5.0 mm and preferably 2.40 mm < D60' < 4.5 mm. Here D60 - 3.10 mm.

[0111] In the second embodiment illustrated in Figure 5, we have N=3 or N=4, and here N=4. We also have M ranging from 1 to 5, and here M=4. Finally, we have P ranging from 5 to 9, preferably P=5, 8, or 9, and here P=9. This cable is a 4 x (4+9) construction cable, commonly called 52.26.

[0112] 60” cable according to a third embodiment of the invention

[0113] Figure 6 shows the 60” cable according to a third embodiment of the invention.

[0114] The 60” multi-strand cable has a 1xN structure. The 60” cable comprises a single layer of 70 N strands of 62 wound helically with a p3 pitch. The N strands of 62 are wound in a Z or S direction.

[0115] Each strand 62 comprises an inner layer Cl of one inner wire 72 wound helically with a pitch p1 and an outer layer CE of P outer wires 74 wound helically around the inner layer 52 with a pitch p2. In this case, each strand 62 consists of the inner layer Cl and the outer layer CE. Each strand 62 is thus devoid of a binding wire.

[0116] Each internal wire 72 and external wire 74 has a diameter ranging from 0.12 mm to 0.50 mm, preferably from 0.20 mm to 0.45 mm and here the diameter of the internal wire is equal to 0.26 mm and the diameter of the external wires is equal to 0.26 mm.

[0117] The outer CE layer of each 62 strand is non-compact and unsaturated.

[0118] The winding pitch p1 of the inner wire is infinite. The winding pitch p2 of the outer wires 74 ranges from 4 to 14 mm, preferably from 5 to 12 mm, and is here equal to 5 mm. Finally, the winding pitch p3 of the strands 62 ranges from 6 to 30 mm, preferably from 7 to 20 mm, and is here equal to 8 mm.

[0119] The diameter D60” of the 60” cable is such that D60” < 5.0 mm and preferably 1.40 mm < D60” < 4.5 mm. Here D60” = 1.91 mm.

[0120] The outer 74 wires and the N strands are wound in the same direction, Z or S.

[0121] In the third embodiment illustrated in Figure 6, we have N=3 or N=4, and here N=4. We also have M ranging from 1 to 5, and here M=1. Finally, we have P ranging from 5 to 9, preferably P=5, 8, or 9, and here P=5. This cable is a 4 x (1+5) construction cable, commonly called 24.26.

[0122] CABLE OF THE SECOND PROTECTIVE LAYER ACCORDING TO THE INVENTION

[0123] The cable 50 according to the embodiment of the invention is shown in Figure 3.

[0124] Cable 50 comprises a single layer 52 of T = 5 metallic wire elements 54 wound in a helix around a main axis A extending substantially parallel to the direction in which the cable extends along its greatest length.

[0125] In the illustrated embodiment, each wire element 54 comprises a single metal monofilament. Each wire element 54 also includes a layer (not shown) of a metallic coating comprising copper, zinc, tin, cobalt, or an alloy of these metals, in this case, brass. Each metal monofilament 56 is made of carbon steel and has a mechanical strength of 3100 MPa.

[0126] Each metallic wire element is wound at a pitch P such that 3 mm < P < 15 mm, preferably 7 mm < P < 12 mm. Here P = 9 mm.

[0127] The diameter D50 of the 50 cable is such that D50 < 2.50 mm and preferably 1.40 mm < D50 < 2.20 mm. Here D50 = 1.91 mm.

[0128] This cable is commonly referred to as 5.35.

[0129] COMPARATIVE TESTS

[0130] The stress-stretch curve of the different configurations of protective mats noted below 31-1 to 31-5 was plotted, applying the ASTM D2969-04 standard of 2014, this stress corresponding to the value of the force of each cable 50, 60, 60', 60" of the mat divided respectively by the pitch of each cable 50, 60, 60', 60" in the mat and the stiffness of the protective mat was determined for an elongation of 1%. The same procedure was followed for the state-of-the-art protective mats EDT1 from document WO2016 / 131862 or W02020 / 161404, EDT2 from document W02011134900 and EDT3 from document JP 2010090509 and a control mat T1 and the values ​​were reported in Table 1 below.

[0131] Table 2 also shows the performance of the tires designated below as P_31-1 and P_31-4 according to the invention, comprising respectively the protective plies 31-1 and 31-4, compared to the P4 tire, which comprises the EDT4 plies. The puncture resistance of the tire following tread damage was simulated by calculating the contact pressure exerted on the tire by an indenter at the same depth of indentation. The results are shown in Table 2 below: [Table 1] 0132] [Table 2]

[0133] Tables 1 and 2 show that the protective plies designated below as 31-1 to 31-4 according to the invention have a stiffness ratio E_NSP1 / E_NSP2 strictly greater than 3 compared to the prior art protective plies EDT 1 to EDT4 and the reference ply T1. The plies of tires P_31-1 and P_31-4 provide a better performance compromise, particularly compared to tire P4. It can be seen that a more flexible NSP2 protective ply (31-1 and 31-4) reduces the pressure at the indenter contact point compared to the EDT4 plies. Thus, with a more flexible NSP2 protective ply, the risk of tire punctures resulting from tread damage is further reduced, or even eliminated.

[0134] Table 3 shows, on a base of 100, the reduction in mass of the tires according to the invention compared to the P2 tire of the prior art EDT2 from document WO2011134900.

[0135] [Table 3]

[0136] The plies 31-1 to 31-4 respectively of the P_31-1 to P_31-4 tires make it possible to considerably reduce the mass of the tire compared to the P2 tire of the prior art while maintaining a breaking strength sufficient to resist perforations.

[0137] Thus, the tires according to the invention make it possible to solve the problems mentioned in the preamble.

[0138] The invention is not limited to the embodiments described above.

Claims

DEMANDS 1. Pneumatic (1) for a civil engineering vehicle comprising: - a crown reinforcement, radially internal to a tread (2) and radially external to a carcass reinforcement (4), - the apex reinforcement comprising, radially from the outside in, a protective reinforcement and a working reinforcement, - the protective frame comprising first and second protective layers (311, 312) with the first layer (311) being radially internal to the second layer (312), - the first protective layer comprising at least one metallic multi-strand cable (60; 60'; 60") and the second protective layer comprising at least one metallic cable (50) characterized in that: - the effort of the first protective layer (311) at 1% deformation noted E NSP1 is less than or equal to 500 daN / cm; - the effort of the second protective layer (312) at 1% strain noted E NSP2 is less than or equal to 100 daN / cm; and the ratio of the stiffnesses E NSP1 / E NSP2 is strictly greater than 3.0, the effort of the protective layer at 1% strain being determined according to the ASTM D2969-04 of 2014, this effort corresponding to the value of the effort of the wire rope divided by the laying pitch of the wire rope (50; 60, 60', 60") in each protective layer (311; 312) at 1% strain on the force-stretch curve.

2. Pneumatic (1) according to the preceding claim, wherein the ratio of stiffnesses E NSP1 / E NSP2 is greater than or equal to 3.

2.

3. Pneumatic (1) according to any one of the preceding claims, wherein E NSP1 is less than or equal to 400 daN / cm.

4. Pneumatic (1) according to any one of the preceding claims, wherein E NSP2 is less than or equal to 50 daN / cm.

5. Pneumatic (1) according to any one of the preceding claims, wherein E NSP1 is strictly greater than 50 daN / cm and preferably greater than or equal to 100 daN / cm.

6. Pneumatic (1) according to any one of the preceding claims, wherein the metallic multi-strand cable (60; 60'; 60") of the first protective layer (311) has a 1xN structure comprising a single layer (70) of N strands (62) wound helically, each strand (62) comprising: - an internal layer (Cl) of M > 1 internal metallic wire elements (72), - an outer layer (CE) of P external metallic wire elements (74) wound in a helix around the inner layer (Cl).

7. Pneumatic (1) according to the preceding claim, wherein N= 3 or 4 and preferably N=4.

8. Pneumatic (1) according to claim 6 or 7, wherein M goes from 1 to 5, preferably M=1 or 3.

9. Pneumatic (1) according to any one of claims 6 to 8, wherein P goes from 5 to 9, preferably P=5, 8 or 9.

10. Pneumatic (1) according to any one of claims 6 to 9, wherein the pitch of the metal cables (60; 60'; 60") of the first protective layer (311) ranges from 2.5 to 5.0 mm.

11. Pneumatic (1) according to any one of the preceding claims, wherein the wire rope (50) of the second protective layer (312) comprises a single layer (52) consisting of helically wound metal wire elements (54), each metal wire element (54) of the layer (52) describing, when the rope (50) extends in a substantially straight direction, a helical path around a principal axis (A) substantially parallel to the substantially straight direction, the rope (50) having a total elongation at break At > 10.00% as determined by ASTM D2969-04 of 2014.

12. Pneumatic (1) according to the preceding claim, in which T goes from 4 to 9 and preferably from 5 to 7.

13. Pneumatic (1) according to claim 11 or 12, wherein the pitch of the metal cables (50) of the second protective layer (312) goes from 2.0 to 4.0 mm.

14. Pneumatic (1) according to any one of claims 6 to 13, wherein the metal mass of the wire ropes (50; 60; 60'; 60") of the two protective layers (311, 312) is greater than or equal to 5.0 kg / m 3 , preferably greater than or equal to 6.5 kg / m 3 and more preferably greater than or equal to 8.0 kg / m³ 3 .

15. Pneumatic (1) according to any one of the preceding claims, having a thickness ep_NSP1 + ep_NSP2 of the first and second protective layers (311, 312) measured along a direction (Y) perpendicular to the main direction (X) such that ep_NSP1 + ep_NSP2 goes from 5 to 10 mm.

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