TIRE FOR A HEAVY CIVIL-ENGINEERING VEHICLE WITH A SIMPLIFIED CROWN REINFORCEMENT

Abstract

A tire for a heavy-duty vehicle of construction plant type comprises a crown reinforcement (35) radially on the inside of a tread (10) and radially on the outside of a carcass reinforcement (50). The crown reinforcement (35) comprises: at least one “low-modulus” layer (20) formed of elastic metal reinforcers having a structural elongation at least equal to 0.4%, and a total elongation at break at least equal to 3%, and a tensile elastic modulus of between 40 GPa and 130 GPa; at least one “rigid” layer (30) formed of rigid metal reinforcers, the structural elongation of which is less than or equal to 0.2% and the tensile elastic modulus of which is between 140 GPa and 200 GPa. The ratio of the breaking tension of the rigid layer to that of the low-modulus layer is greater than or equal to 1.2.

Claims

1.-10. (canceled)

11. A tire for a heavy-duty vehicle of construction plant type, having a nominal section B within the meaning of the European Tyre and Rim Technical Organisation (ETRTO) standard and comprising a crown reinforcement, radially on an inside of a tread and radially on an outside of a carcass reinforcement, the crown reinforcement comprising: at least one low-modulus layer, formed of low-modulus elastic metal reinforcers, which are coated in an elastomeric material, are mutually parallel and form an angle Alpha1 with a circumferential direction tangential to a circumference of the tire, the low-modulus reinforcers having a structural elongation at least equal to 0.4% and a total elongation at break at least equal to 3%, and the tensile elastic modulus of the low-modulus reinforcers being between 40 GPa and 130 GPa; and at least one rigid layer, formed of rigid metal reinforcers, which are coated in an elastomeric material, are mutually parallel and form an angle Alpha2 with the circumferential direction tangential to the circumference of the tire, the structural elongation of the rigid metal reinforcers being less than or equal to 0.2%, and the tensile elastic modulus of the rigid reinforcers being between 140 GPa and 200 GPa, wherein a breaking tension of the at least one rigid layer is greater than or equal to 120 daN/mm, wherein a ratio of the breaking tension of the at least one rigid layer to that of the at least one low-modulus layer is greater than or equal to 1.2, wherein the breaking tension of the at least one low-modulus layer is greater than or equal to 80 daN/mm, and wherein at least one low-modulus layer is in contact with at least one rigid layer over an axial width W at least equal to 20% of the nominal section B of the tire.

12. The tire according to claim 11, wherein the at least one rigid layer comprises reinforcers provided with a wrapping thread of small diameter, between 0.10 mm and 0.3 mm, wound in a helix on an external surface of the reinforcers.

13. The tire according to claim 12, wherein the at least one low-modulus layer is positioned on an outside of the at least one rigid layer in a radial direction.

14. The tire according to claim 11, wherein an axial width of the at least one low-modulus layer is greater than an axial width of the at least one rigid layer by a distance DNT at least equal to 10 mm at each axial end.

15. The tire according to claim 11, wherein an additional triangulation layer, comprising metal reinforcers, which are coated in an elastomeric material, are mutually parallel and form an angle Beta with the circumferential direction tangential to the circumference of the tire, is positioned on an inside of the at least one rigid layer and in contact therewith in the radial direction, the angle Beta being greater than or equal to 50° in terms of absolute value, and in the same direction as the adjacent rigid layer.

16. The tire according to claim 15, wherein an axial width of the additional triangulation layer, measured in a meridian cross section of the tire, is less than that of the at least one low-modulus layer and greater than that of the at least one rigid layer.

17. The tire according to claim 11, wherein an absolute value of the angle Alpha1 of the reinforcers of the at least one low-modulus layer is greater than or equal to an absolute value of the angle Alpha2 of the at least one rigid layer.

18. The tire according to claim 11, wherein the crown reinforcement comprises at least one layer formed of elastic metal reinforcers, an angle of which with the circumferential direction of the tire is less than or equal to 10°.

19. The tire according to claim 11, wherein a layer of elastomeric compound is positioned toward an inside in a radial direction beneath the at least one low-modulus layer and in contact with the at least one low-modulus layer vertically in line with the end of the at least one rigid layer.

20. The tire according to claim 19, wherein the layer of elastomeric compound has a tensile stiffness modulus less than or equal to 4.5 MPa.

Description

[0073] The features of the invention are illustrated in the schematic FIGS. 1 and 2, which are not to scale, with reference to a tyre of size 29.5R25:

[0074] FIG. 1: meridian cross section through the crown of the tyre according to the invention;

[0075] FIG. 2: portion of a meridian cross section through said crown;

[0076] FIG. 3: illustration of the assembly of a cable as used in the invention.

[0077] FIG. 1 shows a tyre 1 for a heavy-duty vehicle of construction plant type, comprising a crown reinforcement 35 radially on the inside of a tread 10 and radially on the outside of a carcass reinforcement 50. The crown reinforcement 35 comprises at least one layer 20, known as the “low-modulus layer”, and at least one layer 30, known as the “rigid layer”. A layer of elastomeric compound 25 is positioned radially on the interior side of the low-modulus layer. The radially innermost crown reinforcement layer 40, in contact with the carcass reinforcement 50, is known as the triangulation layer. The ends of the layers 20, 30 and 40 are embedded in an elastomeric edging compound 110. The rigid crown layer 30 and low-modulus crown layer 20 are separated at their axial ends by a decoupling compound 90.

[0078] FIG. 2 shows the crown reinforcement 35 with its characteristic dimensions. The rigid layer has an axial width LNT1 and the low-modulus layer has a width LNT2. The width LNT2 is greater than LNT1 such that the low-modulus layer extends beyond the ends of the rigid layer on both sides. The axial ends of the triangulation layer of width LNTS are interposed between the axial ends of the low-modulus layer and rigid layer. In order to avoid coincidence of the axial ends of the crown layers, an offset of at least 10 mm is provided between two consecutive layers. LCOUP is the coupling distance for achieving the maximum level of tension in the reinforcers of the crown layers.

[0079] FIG. 3 shows an example of low-modulus reinforcers used for the low-modulus layer. The cable 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.

[0080] The inventors compared a tyre I according to the invention against a reference tyre R of the same size 29.5R25. The reference tyre is a conventional prior art solution, the description of which is summarized in Table 1 below:

TABLE-US-00001 TABLE 1 Crown reinforcement of the reference tyre Reinforcers Assembly Angle Protective Layer 1 E18.23 3 × (1 + 5) × 0.23 −24° reinforcement Layer 2 E18.23 3 × (1 + 5) × 0.23  24° Working Layer 3 13.30 FR (4 + 9) × 0.30 −24° reinforcement Layer 4 13.30 FR (4 + 9) × 0.30  24° Triangulation layer Layer 5 13.30 FR (4 + 9) × 0.30 −65°

[0081] Table 1 describes the layers that make up the crown of the reference tyre. The reinforcers of the layers are cables, the assembly of which is mentioned for each layer. The angles that the reinforcers make with the circumferential direction of the tyre are also mentioned.

[0082] The formulations of the assemblies of the cables that end in FR mean that the cables are wrapped. The cables are provided with a wrapping thread of small diameter, between 0.10 mm and 0.3 mm, wound in a helix on the external surface of the cable. For example, the cable 13.30 FR has a wrap with a diameter of 0.18 mm.

[0083] The tyre according to the invention comprises the components described in Table 2 below:

TABLE-US-00002 TABLE 2 Crown reinforcement of the tyre according to the invention Elastic Reinforcers Assembly Angle ER TR moduli Spacing Low-modulus Layer 1 E24.26 4 × (1 + 5) × 0.26  24° 2600N 1060 N/mm  42 GPa 2.5 mm layer Rigid layer Layer 2 26.30 FR 3 × 0.35 + (4 + 14) × 0.30 −20° 6200N 1800 N/mm 144 GPa   2 mm Triangulation Layer 3 13.30 FR (4 + 9) × 0.30 −65° 3000N 1500 N/mm 174 GPa 3.4 mm layer

[0084] Table 2 describes the layers that make up the simplified crown of the tyre according to the invention. Indicated are the cables used as reinforcers, their assembly, and the angles that they make with the circumferential direction of the tyre. Mechanical properties of the layers are mentioned: the breaking force of the cables, the breaking tension of the layers and the axial spacing of the reinforcers for each layer.

[0085] The tyre according to the invention, in the configuration tested here, differs from the reference tyre by the elimination of layers of the crown reinforcement so as to be limited to a radially innermost triangulation layer, followed by a rigid layer formed of reinforcers wrapped with 26 metal threads each measuring 30 hundredths of a millimetre, and a low-modulus layer formed of 24 metal threads each having a diameter of 26 hundredths of a millimetre.

[0086] The assembly of the reinforcers in the low-modulus layer has the formulation 4×(1+5)×0.26, meaning that the reinforcers are multistrand ropes 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 with a diameter of 0.26 mm.

[0087] The reinforcers of the low-modulus layer have a tensile elastic modulus equal to 42 GPa, a force at break equal to 260 daN, are axially distributed at a spacing equal to 2.5 mm, and form an angle Alpha1 of 24° with the circumferential direction XX′. The breaking tension of the low-modulus layer is 106 daN/mm.

[0088] As regards the rigid layer, the reinforcers are cables having three layers of threads, assembled according to the formulation 3×0.35+(4+14)×0.30. The first layer comprises 3 threads with a diameter of 0.35 mm, followed by the second with 4 threads with a diameter of 0.30 mm, and the third layer comprises 14 threads with a diameter of 0.30 mm. The reinforcers thus defined have a force at break equal to 620 daN, are axially distributed at a spacing equal to 3.4 mm, and form an angle Alpha1 of −20° with the circumferential direction XX′. The breaking tension of the rigid layer is 176 daN/mm.

[0089] The triangulation layer comprises reinforcers which are cables having two layers of threads, assembled according to the formulation (4+9)×0.30. The first layer comprises 4 threads with a diameter of 0.30 mm, followed by the second layer with 9 threads with a diameter of 0.30 mm. The reinforcers thus defined have a force at break equal to 300 daN, are axially distributed at a spacing equal to 2.0 mm, and form an angle Alpha1 of −65° with the circumferential direction XX′. The breaking tension of the triangulation layer is 140 daN/mm.

[0090] The above-described tyre according to the invention clearly meets the objective of the claimed patent. The intended objective of a saving in the industrial manufacturing cost is achieved with a weight of the tyre according to the invention that is lower than that of the reference tyre by 7%. The saving of weight results from the elimination, in the reference tyre, of a protective layer and a working layer.

[0091] The strength of the crown of the tyre according to the invention when passing over obstacles on the road is at a level comparable to that of the reference tyre. The low-modulus layer, which is formed of elastic E24.26 multistrand ropes, also has a protective function with a performance level sufficient to replace the two layers of the E18.23 protective reinforcement of the crown of the reference tyre.

[0092] The endurance was evaluated by way of finite-element calculations on the reference tyre and the tyre according to the invention, making it possible to calculate the tensions in the carcass layer and the shear stresses at the ends of the layers of the crown reinforcement.

[0093] To evaluate these performance aspects, the tyre was subjected to calculations with a vertical load of 14 000 kg, a drift thrust of 6000 daN, and an inflation pressure of 450 kPa.

[0094] In the version of the tyre with the triangulation layer, the carcass layer is still under relative tension, thereby obviating the risk of buckling. The shear stresses at the ends of the layers of the crown are sufficiently low as to not have a negative effect on endurance.

[0095] The invention makes it possible to lighten the tyre while making it possible to transmit the forces for guiding the vehicle without impairing the integrity of the compounds at the axial ends of the layers.