Crown Reinforcement of a Tire for a Heavy Construction Plant Vehicle

Abstract

A tire (1) for a heavy construction plant vehicle with satisfactory compromise between the breaking strength of its circumferential hoop reinforcement (7), having an axial width LF and having a circumferential hooping layer (71, 72) with elastic metallic reinforcers having a structural elongation AS and a force at break FR, and forming an angle at most equal to 5° with the circumferential direction (XX), and the endurance of its working reinforcement (6), formed by two working layers (61, 62) with inextensible metallic reinforcers, the mean angle AM of which with the circumferential direction (XX′) is at least equal to 15° and at most equal to 45°. The axial width LF, the structural elongation As, the force at break Fr and the mean angle AM satisfy the relationship:

Zn/Z0*(T0+(a1+a2*As)/AM+b*LF*(AM−A0)/A0+c*AM)<Fr/CS, where Zn is the nominal load, Z0=100 t, T0=7000 N, a1=−230,000 N*°, a2=−160,000 N*°/%, b=−34,000 N/m, A0=29°, c=550 N/°, CS>=1.

Claims

1. A tire for a heavy construction plant vehicle, intended to carry a nominal load Zn, comprising a crown reinforcement radially on the inside of a tread and radially on the outside of a carcass reinforcement: the crown reinforcement comprising a working reinforcement and a circumferential hoop reinforcement, the working reinforcement having an axial width LT and being formed by a first and a second working layer each comprising inextensible metallic reinforcers having a tensile elastic modulus of more than 150 GPa, coated with an elastomer-based material and mutually parallel, and one working layer crossing the next such that the mean angle AM of the metallic reinforcers of the working reinforcement, defined as the geometric mean of the respective angles formed by the reinforcers of the first and second working layers with a circumferential direction (XX′) tangential to the circumference of the tire, is at least equal to 15° and at most equal to 45°, the circumferential hoop reinforcement having an axial width LF at least equal to 0.3 times the axial width LT of the working reinforcement and comprising at least one circumferential hooping layer formed from elastic metallic reinforcers having a tensile elastic modulus of more than 150 GPa, coated with an elastomer-based material and mutually parallel, and forming with the circumferential direction (XX′) an angle at most equal to 5°, the elastic metallic reinforcers of the circumferential hoop reinforcement, removed from the tire with their coating of vulcanised elastomer-based material, having a structural elongation As at least equal to 0.5% and a force at break Fr, wherein the axial width LF of the circumferential hoop reinforcement, the structural elongation As and the force at break Fr of the elastic metallic reinforcers of the circumferential hoop reinforcement, and the mean angle AM of the inextensible metallic reinforcers of the working reinforcement, satisfy the relationship:
Zn/Z0*(T0+(a1+a2*As)/AM+b*LF*(AM−A0)/A0+c*AM)<Fr/CS where Zn: the nominal load (expressed in tonnes) applied to the tire, Z0: reference load equal to 100 tonnes, T0: reference tension equal to 7000 N,
a1=−230,000 N*°,
a2=−160,000 N*°/%,
b=−34,000 N/m, A0: mean reference angle of metallic reinforcers of the working reinforcement equal to 29°,
c=550 N/°, CS: safety coefficient at least equal to 1.

2. The tire for a heavy construction plant vehicle according to claim 1, wherein the elastic metallic reinforcers of each circumferential hooping layer form an angle equal to 0° with the circumferential direction (XX′).

3. The tire for a heavy construction plant vehicle according to claim 1, wherein the elastic metallic reinforcers of each circumferential hooping layer have a tensile elastic modulus at least equal to 40 GPa.

4. The tire for a heavy construction plant vehicle according to claim 1, wherein the elastic metallic reinforcers of each 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.

5. The tire for a heavy construction plant vehicle according to claim 4, wherein the single layer of N strands, wound in a helix, comprises N=3 or N=4 strands.

6. The tire for a heavy construction plant vehicle according to claim 4, 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 internal threads.

7. The tire for a heavy construction plant vehicle according to claim 4, 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.

8. The tire for a heavy construction plant vehicle according to claim 1, wherein the force at break Fr of each elastic metallic reinforcer of the circumferential hoop reinforcement is at least equal to 8000 N.

9. The tire for a heavy construction plant vehicle according to claim 1, wherein the circumferential hoop reinforcement has an axial width LF at most equal to 0.9 times the axial width LT of the working reinforcement.

10. The tire for a heavy construction plant vehicle according to claim 1, wherein the circumferential hoop reinforcement is positioned radially between the first working layer and the second working layer.

11. The tire fa a heavy construction plant vehicle according to claim 9, wherein the two waking layers of the working reinforcement come into contact with one another at their respective axial ends, so as to form a coupling zone axially inside a decoupling zone in which the axial ends are spaced apart from one another.

12. The tire fa a heavy construction plant vehicle according to claim 1, wherein the circumferential hoop reinforcement comprises at least two circumferential hooping layers.

13. The tire fa a heavy construction plant vehicle according to claim 1, wherein the crown reinforcement comprises, radially outermost, a protective reinforcement comprising at least one protective layer formed by elastic metallic reinforcers having a tensile elastic modulus at most equal to 150 GPa, coated with an elastomer-based material, mutually parallel and forming an angle at least equal to 10° with the circumferential direction (XX′) tangential to the circumference of the tire.

14. The tire for a heavy construction plant vehicle according to claim 13, wherein the protective reinforcement is formed by two protective layers the elastic metallic reinforcers of which form an angle at least equal to 15° with the circumferential direction (XX′).

15. The tire for a heavy construction plant vehicle according to claim 13, wherein the radially innermost protective layer is axially the widest of all layers of the crown reinforcement.

Description

[0061] The features of the invention are illustrated by the schematic FIGS. 1 to 5, which are not drawn to scale:

[0062] FIG. 1: A meridian half-section of a crown of a tire for a heavy construction plant vehicle according to the invention.

[0063] FIG. 2a: A developed schematic view of a circumferential hooping layer at rest.

[0064] FIG. 2b: A developed schematic view of a circumferential hooping layer under edgewise bending.

[0065] FIG. 3: A development of the maximum hooping reinforcer tension Tmax as a function of the structural elongation As of the elastic metallic reinforcers of the hoop reinforcement.

[0066] FIG. 4: A development of the maximum hooping reinforcer tension Tmax as a function of the axial width LF of the hoop reinforcement.

[0067] FIG. 5: A development of the maximum hooping reinforcer tension Tmax as a function of the mean angle AM of the inextensible metallic reinforcers of the working reinforcement.

[0068] FIG. 1 shows a meridian half-section, on a plane YZ, of a tire 1 for a heavy construction plant vehicle 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) each comprising elastic metallic reinforcers having a tensile elastic modulus at most equal to 150 GPa, which are coated in an elastomer-based material, are mutually parallel, and 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 has two working layers (61, 62) each comprising inextensible metallic reinforcers having a tensile elastic modulus of more than 150 GPa, coated with an elastomer-based material and mutually parallel, and one working layer crossing the next such that the mean angle AM of the metallic reinforcers of the working reinforcement (6), defined as the geometric mean of the respective angles formed by the reinforcers of the first and second working layers (61, 62) with the circumferential direction (XX′), is at least equal to 15° and at most equal to 45°. 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 a circumferential hoop reinforcement 7 positioned radially between the two working layers (61, 62) of the working reinforcement 6. The circumferential hoop reinforcement 7 has an axial width LF, defined as the greatest width of the hooping layer, at least equal to 0.3 times the axial width LT and comprises two circumferential hooping layers (71, 72) formed from elastic metallic reinforcers having a tensile elastic modulus of more than 150 GPa, coated with an elastomer-based material and mutually parallel, and forming with the circumferential direction XX′ an angle at most equal to 5°. The elastic metallic reinforcers of the circumferential hoop reinforcement 7, removed from the tire with their vulcanised elastomer-based material coating, have a structural elongation As at least equal to 0.5% and a force at break Fr at least equal to 9000 N. In view of the depiction of the invention on a meridian half-section which is symmetrical relative to the plane XZ, only the respective halves of the widths LF and LT are shown.

[0069] FIG. 2a shows a developed schematic view of a circumferential hooping layer (71, 72) at rest. The elastic metallic reinforcer (712, 722) designed to be under the most tension when the tire is subject to a transverse force FY during running, depending on the axial direction of the tire, equal to 0.7 times the nominal load Zn, is depicted in dotted lines while the other elastic metallic reinforcers (711, 712) are depicted in solid lines. At rest, all of these elastic metallic reinforcers, which are mutually parallel, are positioned in circumferential planes XZ.

[0070] FIG. 2b shows a developed schematic view of a circumferential hooping layer (71, 72) deformed by edgewise bending, when the tire is subjected to a transverse force FY, depending on the axial direction of the tire, equal to 0.7 times the nominal load Zn. The elastic metallic reinforcer (712, 722), positioned on the external fibre of the beam in extension constituted by the crown reinforcement, is under most tension while the other elastic metallic reinforcers (711, 721) are subjected to lower tensile forces.

[0071] FIG. 3 shows the development of the maximum hooping reinforcer tension Tmax as a function of the structural elongation As of the elastic metallic reinforcers of the hoop reinforcement. The maximum hooping reinforcer tension Tmax is the tension of the elastic metallic reinforcer of the hoop reinforcement which is under most tension when the tire is subject to a transverse force FY, depending on its axial direction, equal to 0.7 times the nominal load Zn, leading to a deformation of the hoop reinforcement by edgewise bending. FIG. 3 shows as a solid line a first maximum limit corresponding to the force at break Fr of a reinforcer, and as a broken line a second permitted limit corresponding to the force at break Fr of a reinforcer divided by a safety coefficient CS equal to 1.2. The straight dotted line T1 and broken line T2 show the development of Tmax as a function of As for a mean angle AM respectively equal to 25° and 35°, and for an axial width LF of the hoop reinforcement equal to 0.52 m. In both cases, Tmax reduces when As increases, with a smaller reduction when AM is higher. The straight line T1 lies fully within the permitted range since Tmax remains lower than the permitted limit Fr/CS. However, the straight line T2 is fully outside the permitted range since Tmax remains greater than the permitted limit Fr/CS, but has a portion passing below the maximum limit Fr.

[0072] FIG. 4 shows the development of the maximum hooping reinforcer tension Tmax as a function of the axial width LF of the hoop reinforcement. FIG. 4 shows as a solid line a first maximum limit corresponding to the force at break Fr of a reinforcer, and as a broken line a second permitted limit corresponding to the force at break Fr of a reinforcer divided by a safety coefficient CS equal to 1.2. The straight lines T1 and T2 show the development of Tmax as a function of LF for a mean angle AM respectively equal to 25° and 35°, and a structural elongation As equal to 1.1%. In the case of the dotted straight line T1, Tmax increases when the axial width LF of the hoop reinforcement increases, since the mean angle AM equal to 25° is smaller than the reference mean angle A0 equal to 29°. The straight line T1 lies fully within the permitted range since Tmax remains lower than the permitted limit Fr/CS. In the case of the broken straight line T2, Tmax reduces when the axial width LF of the hoop reinforcement increases, since the mean angle AM equal to 35° is larger than the reference mean angle A0 equal to 29°. However, the straight line T2 is fully outside the permitted range since Tmax remains greater than the permitted limit Fr/CS, but has a portion passing below the maximum limit Fr.

[0073] FIG. 5 shows the development of the maximum hooping reinforcer tension Tmax as a function of the mean angle AM of the elastic metallic reinforcers of the hoop reinforcement. FIG. 5 shows as a solid line a first maximum limit corresponding to the force at break Fr of a reinforcer, and as a broken line a second permitted limit corresponding to the force at break Fr of a reinforcer divided by a safety coefficient CS equal to 1.2. The curves T1 and T2 show the development of Tmax as a function of AM for an axial width LF of the hoop reinforcement respectively equal to 0.52 m and 0.80 m, and a structural elongation As equal to 1.1%. In the case of the dotted curve T1, Tmax increases continuously, passing the permitted limit and then the maximum limit. In the case of the broken curve T2, Tmax increases, passes through a maximum and then reduces, while remaining below the permitted limit. This curve T2 allows definition of an optimum mean angle AM for a given axial width LF and given structural elongation As, which can guarantee the breaking strength of the hoop reinforcement and an optimum endurance of the working reinforcement with respect to splitting.

[0074] The inventors have assessed the invention in two dimensions of tires for construction plant vehicles, respectively 40.00R57 and 53/80R63, for which the characteristics verifying the criteria of the invention are shown in table 1 below:

TABLE-US-00001 TABLE 1 Dimension 40.00R57 53/80R63 Nominal load Zn applied to 60,000 kg (ETRTO) 82,500 kg (TRA) the tire (reference standard) Axial width LF of 0.35 m 0.52 m circumferential hoop reinforcement Force at break Fr of elastic 9000N 9000N metallic reinforcers of circumferential hoop reinforcement Structural elongation AS of 0.7% 1.1% elastic metallic reinforcers of circumferential hoop reinforcement Mean angle AM of 33° 29° inextensible metallic reinforcers of working reinforcement Maximum hooping tension 7887N 7384N Tmax (in reinforcer under most tension)

[0075] The inventors have been able to verify by experiment, using the two examples above, a satisfactory compromise between the breaking strength of the hoop reinforcement and the endurance of the working reinforcement during running of the tire, in particular during cornering.