Carcass Reinforcement for a Tire of a Heavy Duty Civil Engineering Vehicle

Abstract

A tire design for a heavy-duty vehicle of construction plant type has a crown reinforcement (40) radially on the inside of a tread (10) and radially on the outside of a carcass reinforcement (70). The carcass reinforcement (70) has at least two carcass layers (50, 60) having metal reinforcers coated in an elastomer compound. The carcass layers (50, 60) have respective stiffnesses per unit width R1, R2. Metal reinforcers of a first carcass layer (50) form, with the circumferential direction (XX′), an angle A1, and those of the second carcass layer form an angle A2, such that the angles A1 and A2, and the stiffnesses R1 and R2, simultaneously satisfy the following three relationships: R1*sin 2(2*A1)+R2*sin 2(2*A2)≥(R1+R2)*) sin 2(30°), and ∥A1|-|A2∥<10°, and 0.7≤R1/R2≤1.3. The metal reinforcers have a critical compression buckling deformation DF at least equal to 2.5% and a compression elastic modulus MC at least equal to 10 GPa.

Claims

1. A tire for a heavy-duty vehicle of construction plant type, comprising: radially from the outside to the inside, a tread, a crown reinforcement and a carcass reinforcement, said crown reinforcement comprising at least one crown layer formed of elastic metal reinforcers coated in an elastomer compound making, with a circumferential direction (XX′), an angle A; said carcass reinforcement being made up of at least two carcass layers comprising metal reinforcers coated in an elastomer compound, said carcass layers having stiffnesses per unit width R1, R2, for the first and second layers, respectively, measured in the equatorial plane (XY), wherein the metal reinforcers of a first carcass layer form, with the circumferential direction (XX′), an angle A1, and the metal reinforcers of a second carcass layer form, with the circumferential direction (XX), an angle A2, such that the angles A1 and A2, and the stiffnesses R1 and R2, measured in the equatorial plane (XZ), simultaneously satisfy the following three relationships:
R1*sin 2(2*A1)+R2*sin 2(2*A2)(R1+R2)*sin 2(30°),  a)
∥A1|-|A2∥<10°,  b)
0.7≤R1/R2≤1.3,  c) and wherein the metal reinforcers (52, 62) of each carcass layer (50, 60) have a critical compression buckling deformation DF at least equal to 2.5% and a compression elastic modulus MC at least equal to 10 GPa.

2. The tire for a heavy-duty vehicle of construction plant type according to claim 1, wherein the angles A1 and A2 have opposite orientations, with respect to the circumferential direction (XX′).

3. The tire for a heavy-duty vehicle of construction plant type according to claim 1, wherein the angles A1 and A2 are angles, in terms of absolute value, with respect to the circumferential direction (XX′), which are comprised in the interval [15°; 75° ].

4. The tire for a heavy-duty vehicle of construction plant type according to claim 1, wherein the stiffnesses per unit width of layer R1, R2, for the first carcass layer and second carcass layer, respectively, are identical.

5. The tire for a heavy-duty vehicle of construction plant type according to claim 1, wherein the metal reinforcers of each carcass layer are multistrand rope cords 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 P external threads wound in a helix around the internal layer.

6. The tire for a heavy-duty vehicle of construction plant type according to claim 5, wherein N=3 or N=4.

7. The tire for a heavy-duty vehicle of construction plant type according to claim 5, wherein M=1, 3, or 4.

8. The tire for a heavy-duty vehicle of construction plant type according to claim 5, wherein P=5, 6, 8 or 9.

9. The tire for a heavy-duty vehicle of construction plant type according to claim 1, wherein an interior first carcass layer comprises a main part wrapped, within each bead, from the inside towards the outside of the tire, around a bead wire nucleus to form a turn-up, and an exterior second carcass layer comprises a main part wrapped, at least partially within each bead, from the outside towards the inside of the tire, around a bead wire nucleus.

10. The tire for a heavy-duty vehicle of construction plant type according to claim 1, wherein each carcass layer comprises a main part wrapped, within each bead, from the inside towards the outside of the tire, around a bead wire nucleus to form a turn-up (95, 85).

11. The tire according to claim 1, wherein the crown reinforcement is made up of at least one layer comprising metal reinforcers coated in an elastomer compound and forming, with the circumferential direction (XX′), an angle A at most equal to 2.5° in terms of absolute value.

Description

[0069] The features of the invention will be better understood with the aid of the description of the attached FIGS. 1, 2, 3 and 4. FIGS. 1, 2 and 3 are described in relation to a crown reinforcement comprising at least two crown layers:

[0070] FIG. 1 depicts an exploded view in section on a meridian plane of a tire for a heavy-duty vehicle of construction plant type according to the invention, with one single carcass layer turned up around the bead wire. The second carcass layer has no turn-up;

[0071] FIG. 2 depicts an exploded view in section on a meridian plane of a tire for a heavy-duty vehicle of construction plant type according to the invention, with both carcass layers turned up around the bead wire;

[0072] FIG. 3 depicts a perspective view of the cutaway of FIG. 2 of a tire for a heavy-duty vehicle of construction plant type, according to the invention;

[0073] FIG. 4 depicts a reinforcer of the carcass layers in the form of the cord comprising four strands.

[0074] [FIG. 1] FIG. 1 shows, in a meridian plane of a tire 1 of the invention: [0075] a tread 10 intended to be in contact with the ground, radially on the outside of a crown reinforcement 40 formed of two composite layers 20 and 30 comprising metal reinforcers coated in an elastomer compound. The crown reinforcement is itself radially on the outside of a carcass reinforcement 70. [0076] the carcass reinforcement 70 comprises a first carcass layer 60, radially innermost beneath the tread, having a main part 80 wrapped, within each bead, from the inside towards the outside of the tire, around a bead wire nucleus 100 to form a turn-up 85. The carcass reinforcement is supplemented by a second carcass layer 50, radially on the outside of the first carcass layer 60 and in contact therewith. It comprises a main part wrapped, at least in part within each bead, from the outside towards the inside of the tire, around the bead wire nucleus 100. The two carcass layers (50, 60) are made up of reinforcers (52, 62) coated in an elastomer compound (51, 61). The first carcass layer 60 is said to be turned up around the bead wire 100.

[0077] FIG. 2 shows another tire 1 according to the invention: [0078] a tread 10 intended to be in contact with the ground, radially on the outside of a crown reinforcement 40 formed of four crown layers comprising metal reinforcers coated in an elastomer compound. These crown layers are grouped into a hoop reinforcement 30 with the hooping layers (31, 32), and into a protective reinforcement 20 with the protective layers (21, 22). The crown reinforcement is itself radially on the outside of a carcass reinforcement 70; [0079] The carcass reinforcement 70 comprises two carcass layers 50 and 60, the carcass layer 60 being the radially innermost one, each carcass layer (50, 60) respectively having a main part (90, 80) wrapped within each bead, from the inside to the outside of the tire, around a bead wire nucleus 100, to form a turn-up (95, 85). The two carcass layers (50, 60) comprise metal reinforcers (52, 62) coated in an elastomer compound (51, 61).

[0080] [FIG. 3] FIG. 3 depicts a perspective view of the tire of FIG. 2 of the invention, showing the stack of layers of the carcass 70, hoop 30 and protective 20 reinforcements capped by the tread 10.

[0081] [FIG. 4] FIG. 4 depicts an example of cords formed of four strands 200. Each strand 200 comprises an internal layer 220 of M threads, and an external layer 230 of P threads. Thus, in FIG. 4, the number N of strands is equal to 4, the number M of threads in the internal layer is equal to 1, and finally the number of threads in the external layer is equal to 5. This cord is designated: 4×(1+5)×0.26, where 0.26 represents the diameter of each thread in millimetres.

[0082] The 24.00R35 size of tire was designed according to the invention, as depicted in FIG. 1. These results were compared against those of a reference tire as defined hereinbelow.

[0083] The reference tire comprises, radially from the inside towards the outside: [0084] a carcass reinforcement having a single carcass layer formed of 49 threads each measuring 23 hundredths of a millimetre in diameter. The angle made by the reinforcers with the circumferential direction is 90°. This is a radial carcass reinforcement turned up around the bead wire; [0085] a hoop reinforcement with two superposed hooping layers each comprising reinforcers made up of a collection of 26 threads each measuring 30 hundredths of a millimetre in diameter. The hooping layers are crossed with angles of ±8°; [0086] a working reinforcement with two crossed layers making angles of 19°/−33°, formed of reinforcers made up of a collection of 26 threads each measuring 30 hundredths of a millimetre in diameter; [0087] a protective reinforcement with two crossed layers making angles of ±24°, formed of reinforcers made up of a collection of 24 threads each measuring 26 hundredths of a millimetre in diameter.

[0088] By way of example, two crossed layers at 19°/−33° means that with respect to the radial direction from the outside towards the inside of the tire, the reinforcers of the first layer encountered make angles of 19° with the circumferential direction XX′, and the reinforcers of the second layer make angles of −33°.

[0089] The carcass reinforcement of the reference tire is made up of a single carcass layer comprising reinforcers in the form of compact wrapped cable cords within the meaning of the definition given in standard ISO 17893:2004. The stack of layers of the reference tire comprises, in addition to the carcass reinforcement, the working layers, the hooping layers and the protective layers, the characteristics of which are defined in the table which follows. The angles and the pitch spacings were measured at the crown of the tire:

TABLE-US-00001 TABLE 1 Angle of Pitch spacing reinforcers wrt Breaking of reinforcers Assembly of XX' at centre strength of within the Tire design reinforcers of crown reinforcers (N) layer (mm) 2. Protective 4 × (1 + 5) × 0.26 24°/−24° 2650 2.5 layers 2 Working layers 3 + (9 + 14 × 0.30)FR 19°/−33° 6000 3.4 2 Hooping layers 3 + (9 + 14 × 0.30)FR 8°/−8° 6000 3.5 Carcass layer (1 + 6) × (1 + 6) × 0.23FR 90° 5400 6.2

[0090] For the control tire, the reinforcers of the carcass layer have a compression modulus of 75 GPa and a critical buckling deformation of 0.4%

[0091] The inflation pressure is 725 kPa for a load of 20 000 kg to be carried.

[0092] The tire of the invention is the same size as the reference tire, 24.00R35, and comprises, radially from the inside to the outside: [0093] a carcass reinforcement with two carcass layers each comprising reinforcers of 24 threads each measuring 26 hundredths of a millimetre in diameter. This is a multistrand rope cord, with 4 strands assembled in two layers: an internal layer of one thread and an external layer of 5 threads. The two carcass layers are not radial, and so this is a bias-belted carcass reinforcement; [0094] two layers with reinforcers making angles smaller than 2.5° in terms of absolute value, in order to perform both the protective and hooping functions.

[0095] The table which follows summarizes the design choices for the tire according to the invention and depicted in FIG. 1:

TABLE-US-00002 TABLE 2 Angle of Breaking Pitch spacing reinforcers at strength of of reinforcers Assembly of centre of reinforcers within the Tire design reinforcers crown (°) (N) layer (mm) 2 Protective/ 4 × (4 + 9) × 0° 6000 3.7 hooping layers 0.26 2 Carcass 4 × (1 + 5) × 65°/−65° 2650 5.5 layers 0.26

[0096] For the tire of the invention, the reinforcers of the carcass layer have a compression modulus of 45 GPa and a critical buckling deformation of 4%.

[0097] The design of the tire of the invention is simplified by comparison with the reference in so far as the working layers have been omitted and the carcass layers combine both the functions of load-bearing and of guiding the vehicle under cornering.

[0098] In this example, the protective reinforcement comprises a single layer, and likewise the hoop reinforcement comprises just a single hooping layer. The protective and hooping layers have the same coating compound, and the angles that the reinforcers make with the circumferential direction XX′ are equal to 0° for both layers.

[0099] The carcass reinforcement comprises two layers, of which the radially innermost is turned up around the bead wire. The reinforcers of each carcass layer make, with the circumferential direction (XX′) an angle, in terms of absolute value, of 65° measured at the crown of the tire.

[0100] Finite-element calculation simulations were carried out on the reference tire and the tire of the invention, respectively. The values observed were: [0101] the radial stiffness of the tire of the invention capable of carrying 15% more load than the reference tire; [0102] the indentation stiffnesses; [0103] the cornering stiffnesses associated with the guiding of the vehicle.

[0104] These results are collated in the following table:

TABLE-US-00003 TABLE 3 Radial Indentation Cornering stiffnesses stiffness stiffness (N/m) (N/m) N/° Reference tire 1.9E+06 1.6E+06 2E+04 Tire of the 2.3E+06 1.2E+06 2E+04 invention

[0105] A 20% increase in radial stiffness may be seen for the tire of the invention, confirming its ability to carry 15% more load.

[0106] The 25% drop in indentation stiffness confirms the improved ability of the tire of the invention to run over indenting features.

[0107] The cornering stiffnesses remain the same between the control and the tire of the invention. The ability of the tire of the invention to guide the vehicle is not impaired.

[0108] The results confirm that the compromise sought by the inventors, to improve the load-bearing capability of the tire without impairing its ability to run over obstacles, has been achieved.