Tire for a Heavy-Duty Vehicle of Construction Plant Type, Provided with a Protective Reinforcement Having Three Differentiated Layers

Abstract

A radial tire (1) for a heavy-duty vehicle of construction plant type, and to reduce the risk of tire tread separation when running over sharp stones, while at the same time ensuring that the crown reinforcement exhibits good resistance to cracking. The tire (1) has a protective reinforcement (50) having three protective layers (51, 52, 53), comprising metal reinforcers that respectively have a diameter (D1, D2, D3) and are distributed at an axial spacing (P1, P2, P3). According to the invention, with Alpha1, Alpha2 and Alpha3 being the angles of the reinforcers of the respective layers (51, 52, 53) with the circumferential direction, the following relationships are satisfied:

15°≤|Alpha1|≤40°

15°≤|Alpha2|≤40°

Alpha1*Alpha2≤0

35°≤|Alpha3|≤75°

As regards the differences between the angles of the reinforcers of the protective layers, the following relationship in terms of absolute values applies:

|(Alpha1−Alpha3)|≥10°

|(Alpha2−Alpha3)|≥10°

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; said protective reinforcement comprising at least two protective layers: a first, radially innermost protective layer, of axial width LP1, 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 Alpha1 with a circumferential direction (XX′) tangential to the circumference of the tire, said reinforcers having a diameter D1 and being distributed at an axial spacing P1; a second, radially outermost protective layer of axial width LP2, 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 Alpha2 with a circumferential direction (XX′) tangential to the circumference of the tire, said reinforcers having a diameter D2 and being distributed at an axial spacing P2; the working reinforcement comprising two working layers respectively comprising metal reinforcers that 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; wherein a third protective layer, referred to as intermediate protective layer, of axial width LP3, is interposed between the radially innermost protective layer and radially outermost protective layer and is in contact therewith, said intermediate 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 Alpha3 with a circumferential direction (XX′) tangential to the circumference of the tire, said reinforcers having a diameter D3 and being distributed at an axial spacing P3; in that the angles Alpha1, Alpha2, Alpha3 of the radially innermost protective layer-the radially outermost protective layer and the intermediate protective layer, respectively, satisfy the following relationships:
15°≤|Alpha1|≤40°
15°≤|Alpha2|≤40°
Alpha1*Alpha2≤0
35°≤|Alpha3|≤75° and in that the differences between angles of the elastic metal reinforcers of the protective layers with the circumferential direction XX′ in terms of absolute values satisfy the following relationships:
|(Alpha1−Alpha3)|≥10°
|(Alpha2−Alpha3)|≥10°

2. The tire for a heavy-duty vehicle of construction plant type according to claim 1, wherein the distributed breaking tension in extension of each protective layer is greater than or equal to 100 daN/mm.

3. The tire for a heavy-duty vehicle of construction plant type according claim 1, wherein the reinforcers of the protective layer interposed between the two other protective layers are identical to those of the radially outermost protective layer.

4. The tire for a heavy-duty vehicle of construction plant type according to claim 1, wherein the angle Alpha3 of the reinforcers of the intermediate protective layer with the circumferential direction (XX′) is equal to −45°.

5. The tire for a heavy-duty vehicle of construction plant type according to claim 4, wherein the values of the angles Alpha1 and Alpha2 are 33° and −33°, respectively.

6. The tire for a heavy-duty vehicle of construction plant type according to claim 1, wherein the axial width LP3 of the intermediate protective layer is such that LP3≤Min (LP1, LP2).

7. The tire for a heavy-duty vehicle of construction plant type according to claim 1, wherein the respective axial distances LP1, LP2, LP3 of the respective protective layers the relationship LP2≤LP3≤LP1.

8. The tire for a heavy-duty vehicle of construction plant type according to claim 1, wherein the radially innermost protective layer has an axial width LP1 at least equal to 1.05 times and at most equal to 1.25 times the axial width LT1 of the radially innermost working layer.

9. The tire for a heavy-duty vehicle of construction plant type according to claim 1, wherein the elastic metal reinforcers of the radially innermost protective layer and radially outermost protective layer, respectively, satisfy the following relationships:
D1≥D2
P1≥P2
P1≥1.2*D1 and P2≥1.2*D2
2.4≤(D1*P1)/(D2*P2)≤5

10. The tire for a heavy-duty vehicle of construction plant type according to claim 1, wherein the elastic metal reinforcers of the radially innermost protective layer have a diameter D1 at least equal to 3 mm.

11. The tire for a heavy-duty vehicle of construction plant type according to claim 1, wherein the elastic metal reinforcers of the radially outermost protective layer have a diameter D2 at most equal to 2.5 mm.

12. The tire for a heavy-duty vehicle of construction plant type according to claim 1, wherein the crown reinforcement comprises a hoop reinforcement comprising two hooping layers, the metal reinforcers of which, which are coated in an elastomeric material and are mutually parallel, form an angle at most equal to 10° with the circumferential direction (XX′).

Description

[0063] The features of the invention are illustrated in the schematic FIGS. 1 and 2, which are not to scale, with reference to a tire of size 53/80R63:

[0064] FIG. 1 is a meridian cross section through a crown of a tire for a heavy-duty vehicle of dumper type according to the invention;

[0065] FIG. 2 is a meridian cross section through a portion of a protective reinforcement according to the invention;

[0066] FIG. 3 is an illustration of the assembly of a rope as used in the invention.

[0067] FIG. 1 shows a meridian cross section through a tire 1 for a heavy-duty vehicle of construction plant type of size 53/80R63, comprising a crown reinforcement 30 radially on the inside of a tread 10 and radially on the outside of a carcass reinforcement 40. The crown reinforcement 30 comprises, radially from the outside to the inside, a protective reinforcement 50, a working reinforcement 60 and a hoop reinforcement 70. The protective reinforcement 50 comprises three protective layers (51, 52, 53), respectively, containing elastic metal reinforcers that are coated in an elastomeric material, are mutually parallel and form angles Alpha1, Alpha2, Alpha3, respectively, with a circumferential direction (XX′) tangential to the circumference of the tire. In the case illustrated here, the angles have the respective values (33°, −33°, −45°). The working reinforcement 60 comprises two working layers (61, 62), the respective metal reinforcers of which, which are inextensible, are coated in an elastomeric material, are mutually parallel and form angles respectively equal to 24°, in the case of the radially innermost working layer 61, and −24°, in the case of the radially outermost working layer 62, with the circumferential direction (XX′). The radially innermost protective layer 51 protrudes axially with respect to the radially innermost working layer 61, meaning that the radially innermost protective layer 51 has an axial width LP1 greater than the axial width LT1 of the radially innermost working layer 61. The intermediate protective layer has a width LP3 less than or equal to (LP1 −7 mm) in the case considered here, and the radially outermost protective layer 52 has an axial width LP2 less than or equal to the axial width (LP3 −7 mm). The hoop reinforcement 7 comprises two hooping layers (71, 72), the respective metal reinforcers of which, which are coated in an elastomeric material, are mutually parallel and form an angle of between 6° and 10° with the circumferential direction XX′, are crossed from one hooping layer to the next.

[0068] FIG. 2 shows a meridian cross section through the protective layer 51, or (52, 53), respectively, having reinforcers with a diameter D1, or (D2, D3), respectively, and a spacing P1, or (P2, P3), respectively. The radially innermost protective layer 51 comprises large elastic metal reinforcers having a large diameter D1, advantageously at least equal to 3 mm, which are distributed axially at an axial spacing P1 at least equal to 1.2*D1, the axial spacing being the axial distance between the respective centres of the circular cross sections of two consecutive reinforcers. The radially outermost protective layer 52 comprises small elastic metal reinforcers having a small diameter D2, advantageously at most equal to 2.5 mm, which are distributed axially at an axial spacing P2 at least equal to 1.2*D1. The inter-reinforcer sections of the radially innermost protective layer 51 and of the radially outermost protective layer, respectively, are respectively equal to D1*P1, D1 being the radial thickness and P1 being the axial width of the section, and to D2*P2, D2 being the radial thickness and P2 being the axial width of the section. The intermediate protective layer 53, interposed between the radially innermost protective layer 51 and the radially outermost protective layer 52, has the same reinforcers as the radially outermost protective layer 52. There is therefore D3, which is equal to D2, and P3, which is equal to P2. The angles of the reinforcers of the layers 52 and 53 with the circumferential direction (XX′) are different, as are their axial widths LP2 and LP3.

[0069] FIG. 3 shows the assembly of a rope as used in the invention for producing the protective layers. The rope comprises 4 strands 200 wound in a helix, each strand being made up of an internal layer 220 of one thread, surrounded by an external layer 230 formed of 4 threads 210 wound around the internal layer.

[0070] The inventors compared a tire I according to the invention against a reference tire R of the same size 53/80R63. The reference tire is a conventional solution in the prior art with a protective reinforcement comprising two protective layers, while the tire of the invention has a protective reinforcement that comprises three protective layers, the angles of which are distributed as claimed in the invention.

[0071] Table 1 below gives the technical characteristics of the reference tire R and of the tire I according to the invention, respectively, of the size 53/80R63 studied:

TABLE-US-00001 TABLE 1 Crown layers for the size Tire I according 53/80R63 Characteristics Reference tire R to the invention Radially Type of reinforcer 52.26 = 4*(4 + 9)*26 52.26 = 4*(4 + 9)*26 innermost R1 protective Tensile elastic 67 GPa 67 GPa layer 51 modulus Ml of a reinforcer Force at break 605 daN 605 daN Fm1 of a reinforcer Diameter D1 of a 3.1 mm 3.1 mm reinforcer Axial spacing P1 3.7 mm 3.7 mm between reinforcers Angle Alpha1 of 33° 33° the reinforcers, with respect to XX′ Force at break 1635 N/mm 1635 N/mm Rm1 of the protective layer Axial width LP1 1190 mm 1190 mm of the protective layer Radially Type of reinforcer 24.26 = 4*(1 + 5)*26 24.26 = 4*(1 + 5)*26 outermost R2 protective Tensile elastic 77 GPa 77 GPa layer 52 modulus M2 of a reinforcer Force at break 255 daN 255 daN Fm2 of a reinforcer Diameter D2 of a 1.9 mm 1.9 mm reinforcer Axial spacing P2 2.5 mm 2.5 mm between reinforcers Angle Alpha2 of −33° −33° the reinforcers, with respect to XX′ Force at break 1060 N/mm 1060 N/mm Rm2 of the protective layer Axial width LP2 956 mm 956 mm of the protective layer Protective Ratio of the inter- 3.1*3.7/1.9*2.5 = 2.41 3.1*3.7/1.9*2.5 = 2.41 reinforcement reinforcer 50 sections D1*P1/D2*P2 Third protective Alpha 3 N/A −45° layer 53, interposed between 51 and 52 Working Axial width LT1 1060 mm 1060 mm reinforcement of the radially 60 innermost working layer 61

[0072] The tire of the invention differs from the reference tire by the presence of the third protective layer interposed between the first, radially innermost protective layer and the second, radially outermost protective layer, and also by the relationships between the angles of the reinforcers of each layer with the circumferential direction. The third protective layer uses reinforcers identical to those of the radially outermost protective layer, but the width of the third layer and the orientation of these reinforcers with the circumferential direction may be different from those of the second protective layer.

[0073] The characteristics of the tire according to the invention clearly meet the essential conditions of the invention with the combination of the following angles:

Alpha1=33°

Alpha2=−33°

Alpha3=−45°

Hence:

[0074]
15°≤|Alpha1|≤40°

15°≤|Alpha2|≤40°

Alpha1*Alpha2≤0

35°≤|Alpha3|≤75°

And in respect of the differences between angles of the reinforcers of the protective layers with a circumferential direction, the relationship in terms of absolute values is also satisfied:

|(Alpha1−Alpha3)|≥10°

|(Alpha2−Alpha3)|≥10°.

[0075] More specifically, for the tire according to the invention, the radially innermost protective layer has an axial width LP1 equal to 1190 mm, 130 mm greater than the axial width LT1 of the radially innermost working layer. The elastic metal reinforcers of the radially innermost protective layer are multistrand ropes with a 4×(4+9)×0.26 assembly, meaning that they are made up of 4 strands, each strand comprising an internal layer of 4 internal threads and an external layer of 9 external threads wound in a helix around the internal layer, the threads having a section of diameter d=0.26 mm.

[0076] In addition, the elastic metal reinforcers of the radially innermost protective layer have a tensile elastic modulus equal to 67 GPa, a force at break equal to 605 daN, a diameter D1 equal to 3.1 mm, and are axially distributed at an axial spacing P1 equal to 3.7 mm, and form an angle Alphal equal to 33° with the circumferential direction XX′.

[0077] The elastic metal reinforcers of the radially outermost protective layer are multistrand ropes with a 4×(1+5)×0.26 structure, meaning that they are made up of 4 strands, each strand comprising an internal layer of 1 internal thread and an external layer of 5 external threads wound in a helix around the internal layer, the threads having a section of diameter 0.26 mm.

[0078] The elastic metal reinforcers of the radially outermost protective layer have a tensile elastic modulus equal to 77 GPa, a force at break equal to 255 daN, a diameter D2 equal to 1.9 mm, and are axially distributed at an axial spacing P2 equal to 2.5 mm, and form an angle Alpha2 of −33° with the circumferential direction XX′.

[0079] Still for the tire of the invention, the intermediate protective layer 53 has the same reinforcers as the radially outermost protective layer, i.e. multistrand ropes with a 4×(1+5)×0.26 structure, made up of 4 strands, each strand comprising an internal layer of 1 internal thread and an external layer of 5 external threads wound in a helix around the internal layer, the threads having a section of diameter 0.26 mm. By contrast, these reinforcers make an angle Alpha3 of −45° with the circumferential direction XX′.

[0080] The inventors have shown, by way of finite-element calculations, that the resistance of the tire to tread separation following cuts to the tread has been improved. The addition of the third protective layer with elastic reinforcers contributes to defining a protective reinforcement that is deformable so as to absorb the obstacles on tracks run on, without severing the reinforcers. Furthermore, the appropriate choice of the reinforcers makes it possible to arrive at a balanced compromise between the indentation stiffnesses and radial stiffnesses in order to carry more loads with increased endurance, without tread separation.

[0081] The inventors simulated the test of pressing the polar into the crown of the tire as described in paragraph [0024]. The depth of indentation upon breakage of the first protective layer was compared between the reference tire and the tire of the invention. The improvement in the depth of indentation is 12% better with the tire of the invention.

[0082] Cleavage shear in the meridian and circumferential planes is substantially at the same level for the reference tire and the tire of the invention. The additional protective layer has therefore not brought about any worsening of shear at the axial ends of the crown and protective layers.