Module Hooping Reinforcement for a Tire of a Heavy Duty Civil Engineering Vehicle

Abstract

A radial tire (1) for a heavy-duty vehicle of construction plant type, and aims to increase the rupture strength of the hoop reinforcement thereof having circumferential layers, ensuring satisfactory endurance of the crown reinforcement thereof. According to the invention, the at least one circumferential hooping layer (71, 72) comprises a median portion (711, 721) having a median width (L11, L21) and a median tensile elastic modulus (E11, E21), and two lateral portions (712, 722) that axially extend the median portion (711, 721) on either side and each have a lateral width (L12, L22) and a lateral tensile elastic modulus (E12, E22), the lateral width (L12, L22) is at least equal to 0.05 times the median width (L11, L21), and the lateral tensile elastic modulus (E12, E22) is at most equal to 0.9 times the median tensile elastic modulus (E11, E21).

Claims

1. A tire for a heavy-duty vehicle of construction plant type, comprising a crown reinforcement radially on the inside of a tread and radially on the outside of a carcass reinforcement, the crown reinforcement comprising, radially from the outside to the inside, a protective reinforcement and a working reinforcement, the protective reinforcement comprising at least one protective layer comprising elastic metal reinforcers having a tensile elastic modulus at most equal to 150 GPa, which are coated in an elastomeric material, are mutually parallel and form an angle at least equal to 10° with a circumferential direction (XX′) tangential to the circumference of the tire, the working reinforcement comprising two working layers that respectively comprise inextensible metal reinforcers having a tensile elastic modulus greater than 150 GPa and at most equal to 200 GPa, which are coated in an elastomeric material, are mutually parallel, form an angle at least equal to 15° and at most equal to 45° with the circumferential direction (XX′), and are crossed from one working layer to the next, the crown reinforcement also comprising, radially on the inside of the protective reinforcement, a circumferential hoop reinforcement, the circumferential hoop reinforcement comprising at least one circumferential hooping layer having an axial width (L1, L2) and comprising metal reinforcers which are coated in an elastomeric material, are mutually parallel and form an angle at most equal to 5° with the circumferential direction (XX′), wherein the at least one circumferential hooping layer comprises a median portion having a median width (L11, L21) and a median tensile elastic modulus (E11, E12), and two lateral portions that axially extend the median portion on either side and each have a lateral width (L12, L22) and a lateral tensile elastic modulus (E12, E22), in that the lateral width (L12, L22) is at least equal to 0.05 times the median width (L11, L21), and in that the lateral tensile elastic modulus (E12, E22) is at most equal to 0.9 times the median tensile elastic modulus (E11, E21).

2. The tire according to claim 1, wherein the lateral width (L12, L22) is at most equal to 0.5 times the median width (L11, L21).

3. The tire according to claim 1, wherein the lateral tensile elastic modulus (E12, E22) is at least equal to 0.3 times the median tensile elastic modulus (E11, E21).

4. The tire according to claim 1, wherein the working reinforcement has an axial width (LT), and wherein the axial width (L1, L2) of the at least one circumferential hooping layer is at least equal to 0.3 times and at most equal to 0.7 times the axial width (LT) of the working reinforcement.

5. The tire according to claim 1, wherein the median portion and the lateral portions of the at least one circumferential hooping layer respectively comprise elastic metal reinforcers having a tensile elastic modulus at most equal to 150 GPa.

6. The tire according to claim 5, wherein the median tensile elastic modulus (E11, E21) is at least equal to 110 GPa.

7. The tire according to claim 5, wherein the elastic metal reinforcers of the median portion and of the lateral portions of the at least one circumferential hooping layer are multistrand ropes of structure 1×N comprising a single layer of N strands wound in a helix, each strand comprising an internal layer of M internal threads wound in a helix and an external layer of K external threads wound in a helix around the internal layer.

8. The tire according to claim 7, wherein the single layer of N strands, wound in a helix, comprises N=3 or N=4 strands, preferably N=4 strands.

9. The tire according to claim 7, wherein the internal layer of M internal threads, wound in a helix, of each strand comprises M=3, 4, or 5 internal threads, preferably M=3 threads.

10. The tire according to claim 7, wherein the external layer of K external threads, wound in a helix around the internal layer of each strand, comprises K=7, 8, 9, 10 or 11 external threads, preferably K=8 external threads.

11. The tire according to claim 1, wherein the circumferential hoop reinforcement comprises at least two circumferential hooping layers.

12. The tire according to claim 11, wherein the respective axial widths (L1, L2) of the at least two circumferential hooping layers are the same.

13. The tire according to claim 1, wherein the circumferential hoop reinforcement is positioned radially between two working layers of the working reinforcement.

14. The tire according to claim 1, wherein the circumferential hoop reinforcement is positioned radially on the inside of the working reinforcement.

Description

[0053] The features of the invention are illustrated by the schematic FIGS. 1, 2A, 2B and 3, which are not drawn to scale.

[0054] FIG. 1: Meridian half-section of a crown of a tire for a heavy-duty vehicle of construction plant type according to the invention.

[0055] FIG. 2A: Schematic top view of a circumferential hooping layer at rest.

[0056] FIG. 2B: Schematic top view of a circumferential hooping layer under edgewise bending.

[0057] FIG. 3: Model tensile behaviour laws for a median portion and a lateral portion of a circumferential hooping layer.

[0058] FIG. 1 shows a meridian half-section, on a plane YZ, of a tire 1 for a heavy-duty vehicle of construction plant type according to the invention, comprising a crown reinforcement 3 radially on the inside of a tread 2 and radially on the outside of a carcass reinforcement 4. The crown reinforcement 3 comprises, radially from the outside to the inside, a protective reinforcement 5 and a working reinforcement 6. The protective reinforcement 5 comprises two protective layer (51, 52) comprising elastic metal reinforcers having a tensile elastic modulus at most equal to 150 GPa, which are coated in an elastomeric material, are mutually parallel, form an angle at least equal to 10° (not shown) with a circumferential direction XX′ tangential to the circumference of the tire, and are crossed from one protective layer to the next. The working reinforcement 6 comprises two working layers (61, 62) that respectively comprise inextensible metal reinforcers having a tensile elastic modulus greater than 150 GPa and at most equal to 200 GPa, which are coated in an elastomeric material, are mutually parallel, form an angle at least equal to 15° and at most equal to 45° (not shown) with the circumferential direction XX′, and are crossed from one working layer to the next. The working reinforcement 6 has an axial width LT defined as the width of the widest working layer, which, in the example shown, is the radially innermost working layer 61. The crown reinforcement 3 also comprises, radially on the inside of the protective reinforcement 5, a circumferential hoop reinforcement 7 positioned radially between the two working layers (61, 62) of the working reinforcement 6. The circumferential hoop reinforcement 7 comprises two circumferential hooping layers (71, 72) that respectively have an axial width (L1, L2) and comprise metal reinforcers which are coated in an elastomeric material, are mutually parallel and form an angle at most equal to 5° (not shown) with the circumferential direction XX′. In the example shown, the axial widths (L1, L2) of the two circumferential hooping layers (71, 72) are not the same. According to the invention, each circumferential hooping layer (71, 72) comprises a median portion (711, 721) having a median width (L11, L21) and a median tensile elastic modulus (E11, E21), and two lateral portions (712, 722) that axially extend the median portion (711, 721) on either side and each have a lateral width (L12, L22) and a lateral tensile elastic modulus (E12, E22). The lateral width (L12, L22) is at least equal to 0.05 times the median width (L11, L21) and the lateral tensile elastic modulus (E12, E22) is at most equal to 0.9 times the median tensile elastic modulus (E11, E21). Given that the invention is depicted in a meridian half-section, which is symmetric with respect to the plane XZ, only the respective halves of the widths L1, L11, L2, L21 and LT are shown and, likewise, only one lateral portion (712, 722) of each circumferential hooping layer (71, 72) is shown.

[0059] FIG. 2A shows a schematic top view of a circumferential hooping layer (71, 72) at rest. The elastic metal reinforcers of each lateral portion (712, 722) are shown using dashed lines, while those of each median portion (711, 721) are shown using solid lines. At rest, all of these metal reinforcers, which are mutually parallel, are positioned in circumferential planes XZ.

[0060] FIG. 2B shows a schematic top view of a circumferential hooping layer (71, 72) deformed under edgewise bending, when the tire is subjected to a cornering angle about a radial direction ZZ′. The elastic metal reinforcers of the lateral portion (712, 722) under tension are more flexible than those of the median portion (711, 721), since, according to the invention, the lateral tensile elastic modulus (E12, E22) is at most equal to 0.9 times the median tensile elastic modulus (E11, E21), and therefore have an elongation capacity that makes it possible to limit the tensile stress to which they are subjected.

[0061] FIG. 3 shows model tensile behaviour laws for the constituent metal reinforcers of a median portion and the constituent metal reinforcers of a lateral portion, respectively, of a circumferential hooping layer. For the median portion and each lateral portion, respectively, the tensile stress (S11, S12), expressed in MPa, defined as the ratio between the tensile load, expressed in N, and the reinforcer section, expressed in mm, is shown as a function of the tensile deformation (D11, D12), that is to say the corresponding relative elongation, expressed in %. For each of the behaviour laws shown, the tensile stress (S11, S12) varies very little up to a first value of tensile deformation corresponding to the structural elongation (AS11, AS12) of the respective elastic metal reinforcers of the median portion and lateral portion, and then increases with a gradient corresponding to the tensile elastic modulus (E11, E12) up to a tensile deformation at break (AR11, AR12). This graph shows that the lateral tensile elastic modulus E12 is at most equal to 0.9 times the median tensile elastic modulus E11.

[0062] The inventors compared two tires I1 and I2 according to the invention against a reference tire R, for the tire size 59/80 R 63.

[0063] The reference tire R and the tires I1 and I2 according to the invention all have a crown reinforcement 3 having the same radial stack of crown layers. The crown reinforcement 3 comprises, radially from the outside to the inside, a protective reinforcement 5 having two protective layers (51, 52), the respective elastic metal reinforcers of which, which are crossed from one layer to the next, form an angle equal to 33° with the circumferential direction XX′, and a working reinforcement 6 having two working layers (61, 62), the respective inextensible metal reinforcers of which, which are crossed from one layer to the next, form an angle equal to 33° with the circumferential direction XX′. The crown reinforcement 3 also comprises, radially interposed between the working layers (61, 62) of the working reinforcement 6, a circumferential hoop reinforcement 7 having two circumferential hooping layers (71, 72), the respective elastic metal reinforcers of which form an angle substantially equal to 0° with the circumferential direction.

[0064] For the reference tire R, the two circumferential hooping layers (71, 72), which have an axial width L1 equal to 520 mm and an axial width L2 equal to 520 mm, respectively, comprise elastic metal reinforcers of the multistrand rope type of structure 44.35=4*(3+8)*35, that is to say made up of N=4 strands, each strand comprising an internal layer of M=3 internal threads and an external layer of K=8 external threads wound in a helix around the internal layer, the threads having a section of diameter d=0.35 mm, in a variant referred to as V1. For the variant V1 of rope 44.35 in question, the reinforcers have a tensile elastic modulus E.sub.R equal to 130 GPa, a diameter D equal to 3.8 mm, and are distributed axially at an axial spacing P equal to 4.4 mm, resulting in a tensile elastic modulus of each hooping layer equal to E.sub.R*(Π*D)/(4*P)=130*(Π*3.8)/(4*4.4)=88 GPa.

[0065] For the tire I1 according to the invention, the two circumferential hooping layers (71, 72) have an axial width L1 equal to 520 mm and an axial width L2 equal to 520 mm, respectively. The two circumferential hooping layers (71, 72) each comprise a median portion (711, 721), having a median width (L11, L21) equal to 410 mm and a median tensile elastic modulus (E11, E21) equal to 88 GPa, and two lateral portions (712, 722) that axially extend the median portion (711, 721) on either side, each lateral portion (712, 722) having a lateral width (L12, L22) equal to 55 mm and a lateral tensile elastic modulus (E12, E22) equal to 79 GPa. In the present case, the lateral width (L12, L22) is equal to 410/520=0.13 times the median width (L11, L21) and therefore at least equal to 0.05 times the median width (L11, L21). The lateral tensile elastic modulus (E12, E22) is equal to 79/88=0.9 times the median tensile elastic modulus (E11, E21). The median tensile elastic modulus (E11, E21) of the median portion (711, 721) results from the use of elastic metal reinforcers of the multistrand rope type of structure 44.35=4*(3+8)*35, that is to say made up of N=4 strands, each strand comprising an internal layer of M=3 internal threads and an external layer of K=8 external threads wound in a helix around the internal layer, the threads having a section of diameter d=0.35 mm, in a variant referred to as V1. For the variant V1 of rope 44.35 in question, the reinforcers have a tensile elastic modulus E.sub.R equal to 130 GPa, a diameter D equal to 3.8 mm, and are distributed axially at an axial spacing P equal to 4.4 mm, resulting in a median tensile elastic modulus (E11, E21) equal to E.sub.R*(Π*D)/(4*P)=130*(Π*3.8)/(4*4.4)=88 GPa. The lateral tensile elastic modulus (E12, E22) of the lateral portion (712, 722) results from the use of elastic metal reinforcers of the multistrand rope type of structure 44.35=4*(3+8)35, that is to say made up of N=4 strands, each strand comprising an internal layer of M=3 internal threads and an external layer of K=8 external threads wound in a helix around the internal layer, the threads having a section of diameter d=0.35 mm, but in a variant referred to as V2. For the variant V2 of rope 44.35 in question, the reinforcers have a tensile elastic modulus E.sub.R equal to 117 GPa, a diameter D equal to 3.8 mm, and are distributed axially at an axial spacing P equal to 4.4 mm, resulting in a lateral tensile elastic modulus (E12, E22) equal to E.sub.R*(Π*D)/(4*P)=117*(Π*3.8)/(4*4.4)=79 GPa.

[0066] The tire I2 according to the invention differs from the tire I1 only by the nature of the elastic metal reinforcers of the lateral portions (712, 722) of the circumferential hooping layers (71, 72). In this case, the lateral tensile elastic modulus (E12, E22) is equal to 46 GPa, i.e. 46/88=0.52 times the median tensile elastic modulus (E11, E21) equal to 88 GPa, and therefore at most equal to 0.9 times the median tensile elastic modulus (E11, E21). The lateral tensile elastic modulus (E12, E22) of the lateral portion (712, 722) results from the use of elastic metal reinforcers of the multistrand rope type of structure 52.26=4*(5+8)*26, that is to say made up of N=4 strands, each strand comprising an internal layer of M=5 internal threads and an external layer of K=8 external threads wound in a helix around the internal layer, the threads having a section of diameter d=0.26 mm These reinforcers have a tensile elastic modulus E.sub.R equal to 70 GPa, a diameter D equal to 3.1 mm, and are axially distributed at an axial spacing P equal to 3.7 mm, resulting in a lateral tensile elastic modulus (E12, E22) equal to E.sub.R*(Π*D)/(4*P)=70*(Π*3.1)/(4*3.7)=46 GPa.

[0067] The respective technical features of the tires R, I1 and I2, set out above, are summarized in Table 1 below:

TABLE-US-00001 TABLE 1 Tire I1 according Tire I2 according Size 59/80R63 Reference tire R to the invention to the invention Axial width L1 520 mm 520 mm 520 mm Median width L11 N/A 410 mm 410 mm Lateral width L12 N/A 55 mm 55 mm Axial width L2 520 mm 520 mm 520 mm Median width L21 N/A 410 mm 410 mm Lateral width L22 N/A 55 mm 55 mm Type of layer 71 (72) reinforcer 44.35 V1 = N/A N/A 4*(3 + 8)*35 Tensile elastic modulus E.sub.R of a layer 130 GPa N/A N/A 71 (72) reinforcer Diameter D of a layer 71 (72) reinforcer 3.8 mm N/A N/A Axial spacing P of the layer 71 (72) 4.4 mm N/A N/A reinforcers Tensile elastic modulus E1 (E2) of a layer 88 GPa N/A N/A 71 (72) (=E.sub.R*(II*D/(4*P)) Type of median portion reinforcer of layer N/A 44.35 V1 = 44.35 V1 = 711 (721) 4*(3 + 8)*35 4*(3 + 8)*35 Tensile elastic modulus E.sub.R of a median N/A 130 GPa 130 GPa portion reinforcer of layer 711 (721) Diameter D of a median portion reinforcer of N/A 3.8 mm 3.8 mm layer 711 (721) Axial spacing P of the median portion N/A 4.4 mm 4.4 mm reinforcers of layer 711 (721) Median tensile elastic modulus E11 (E21) of N/A 88 GPa 88 GPa a median portion of layer 711 (721) (=E.sub.R*(II*D/(4*P)) Type of lateral portion reinforcer of layer N/A 44.35 V2 = 52.26 = 712 (722) 4*(3 + 8)*35 4*(5 + 8)*26 Tensile elastic modulus E.sub.R of a lateral N/A 117 GPa 70 GPa portion reinforcer of layer 712 (722) Diameter D of a lateral portion reinforcer N/A 3.8 mm 3.1 mm of layer 712 (722) Axial spacing P of the lateral portion N/A 4.4 mm 3.7 mm reinforcers of layer 712 (722) Lateral tensile elastic modulus E12 (E22) N/A 79 GPa 46 GPa of a lateral portion reinforcer of layer 712 (722) (=E.sub.R*(II*D/(4*P))

[0068] The inventors carried out, for the tires R, I1 and I2, running finite-element numerical simulations, the tire being inflated to a pressure P equal to 7 bar, compressed under a radial load Z equal to 102 024 daN (104 tonnes), and subjected to a lateral drift thrust Fy equal to 25% of the radial load Z. They thus determined the maximum tensile loads in the circumferential hooping layers and/or in the respective median and lateral portions thereof, presented in Table 2 below.

TABLE-US-00002 TABLE 2 Tire I1 according to Tire I2 according to the invention: - the invention: - median portion median portion Reference reinforcers of type reinforcers of type tire R: - 44.35 V1 - lateral 44.35 V1 - lateral reinforcers portion reinforcers portion reinforcers of type of type of type 44.35 V1 44.35 V2 52.26 Tensile load T max in the layer 71 418 daN reinforcers (daN) Tensile load T max in the layer 72 348 daN reinforcers (daN) Tensile load T max in the median 296 daN 293 daN portion 711 reinforcers of layer 71 (daN) Tensile load T max in the lateral 331 daN 263 daN portion 712 reinforcers of layer 71 (daN) Tensile load T max in the median 230 daN 228 daN portion 721 reinforcers of layer 72 (daN) Tensile load T max in the lateral 276 daN 228 daN portion 722 reinforcers of layer 72 (daN)

[0069] Table 2 shows, compared with the reference tire R: [0070] For the tire I1: a reduction in the maximum tensile loads equal to (331−418)*100/418=−21% for the reinforcers of the lateral portion 712 of the radially inner layer 71, and equal to (276−348)*100/348=−21% for the reinforcers of the lateral portion 722 of the radially outer layer 72. [0071] For the tire I2: a reduction in the maximum tensile loads equal to (263−418)*100/418=−37% for the reinforcers of the lateral portion 712 of the radially inner layer 71, and equal to (228-348)*100/348=−35% for the reinforcers of the lateral portion 722 of the radially outer layer 72.

[0072] This significant reduction in the maximum tensile loads in the lateral portion reinforcers of the circumferential hooping layer causes a significant increase in the rupture strength of the hoop reinforcement, at the axial ends thereof.

[0073] The inventors furthermore determined the maximum amplitudes of shear deformations, as the wheel turns, in the elastomeric compounds, positioned radially on the inside and on the outside of the axial end portions of the radially outermost working layer 72, this criterion being considered relevant as regards the endurance of the crown with regard to cleavage. These maximum amplitudes of shear deformations are presented in Table 3 below:

TABLE-US-00003 TABLE 3 Tire I1 according Tire I2 according to the invention: - to the invention: - median portion median portion Reference reinforcers of type reinforcers of type tire R: - 44.35 V1 - lateral 44.35 V1 - lateral reinforcers portion reinforcers portion reinforcers of type of type of type 44.35 V1 44.35 V2 52.26 Maximum amplitude of shear elongation 0.80 rad 0.81 rad 0.81 rad radially on the outside of the working layer 72 Maximum amplitude of shear elongation 0.62 rad 0.63 rad 0.63 rad radially on the inside of the working layer 72

[0074] According to Table 3, the maximum amplitudes of shear elongation remain substantially at the same level between the tires R, I1 and I2, resulting in performance aspects in terms of endurance with regard to cleavage of the crown that are substantially identical between the reference tire and the tires according to the invention.