HOOPING REINFORCEMENT FOR A TIRE OF A HEAVY DUTY CIVIL ENGINEERING VEHICLE

Abstract

A hooping reinforcement of a tire for a heavy duty civil engineering type vehicle is disclosed. The crown reinforcement (3) of the tire (1), radially on the inside of a tread (2), comprises a protective reinforcement (6), a working reinforcement (5) and a hooping reinforcement (7). Said hooping reinforcement (7) has an axial width at most equal to the smallest axial width (L61, L62) of the two working layers (61, 62), and comprises at least two hooping layers (71, 72) that are formed from strips each made up of elastic metal reinforcers. Each hooping layer (71, 72) is made up of an axial juxtaposition of contiguous turns of the strip (8), which are circumferentially wound around the working layer (51). Each strip (8) is at least 35 mm and at most 250 mm thick, and its distributed breaking tension is at least equal to 100 daN/mm.

Claims

1.-10. (canceled)

11. A tire for a heavy duty civil engineering type vehicle, the tire comprising: a crown reinforcement, radially on an inside of a tread and radially on an outside of a carcass reinforcement, the crown reinforcement comprising a protective reinforcement, a working reinforcement and a hooping reinforcement, the protective reinforcement, which is radially outermost in the crown reinforcement, comprising at least one protective layer, the protective layer comprising metal reinforcers that form an angle at least equal to 10 with a circumferential direction tangential to a circumference of the tire, the working reinforcement comprising at least two working layers, each working layer comprising metal reinforcers that form an angle at least equal to 15 and at most equal to 45 with the circumferential direction and are crossed from one working layer to an adjacent working layer, the hooping reinforcement having an axial width at most equal to a smallest axial width of the at least two working layers, and comprising at least two hooping layers that are formed from strips each made of elastic metal reinforcers that form an angle at most equal to 2.5 with the circumferential direction, the strips having an axial width and a circumferential distributed breaking tension Nr, wherein each hooping layer is made of an axial juxtaposition of contiguous turns of a strip, which are circumferentially wound around a first working layer, radially innermost in the working reinforcement, wherein each strip comprises at least 8 and at most 30 parallel, consecutive, elastic metal reinforcers coated in an elastomeric compound, and wherein the distributed breaking tension Nr of each strip, in the circumferential direction, is at least equal to 100 daN/mm.

12. The tire for a heavy duty civil engineering type vehicle according to claim 10, wherein a width of each strip is at least equal to 35 mm and at most equal to 252 mm.

13. The tire for a heavy duty civil engineering type vehicle according to claim 10, wherein a diameter of the elastic metal reinforcers of each strip is at least equal to 1.9 mm.

14. The tire for a heavy duty civil engineering type vehicle according to claim 10, wherein a distance measured between two elastic metal reinforcers of each strip in a meridian section is at least equal to 2.5 mm.

15. The tire for a heavy duty civil engineering type vehicle according to claim 10, wherein the elastomeric compound coating the elastic metal reinforcers of each strip has viscoelastic loss Tg that is less than or equal to 0.09.

16. The tire for a heavy duty civil engineering type vehicle according to claim 10, wherein the elastic metal reinforcers of each strip are multistrand ropes of structure 1N, 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.

17. The tire for a heavy duty civil engineering type vehicle according to claim 16, wherein N=3 or N=4.

18. The tire for a heavy duty civil engineering type vehicle according to claim 16, wherein M=3, 4 or 5.

19. The tire for a heavy duty civil engineering type vehicle according to claim 16, wherein P=7, 8, 9, 10 or 11.

20. A method for manufacturing a tire according to claim 10, the method comprising: producing the hooping reinforcement by, for each hooping layer, performing a first complete circumferential winding turn of a strip at a first axial end of the hooping layer, then performing contiguous helical winding of the strip in the axial direction up to a second axial end of the hooping layer, and finally performing a final complete circumferential winding turn of the strip at the second axial end of the hooping layer.

Description

[0070] The invention is illustrated in FIGS. 1 to 4, which are not shown to scale for the sake of understanding.

[0071] FIG. 1 shows a cutaway perspective view of the crown of a tyre 1 according to the invention having: [0072] a tread 2 radially on the outside of a carcass reinforcement 4; [0073] the crown reinforcement 3 comprising a protective reinforcement 5, a working reinforcement 6 and a hooping reinforcement 7; [0074] the protective reinforcement 5, which is radially outermost in the crown reinforcement 3, comprising two protective layers (51, 52), each protective layer (51, 52) comprising metal reinforcers that form an angle at least equal to 10 with a circumferential direction (XX) tangential to the circumference of the tyre; [0075] the working reinforcement 6 comprising two working layers (61, 62), each working layer (61, 62) comprising metal reinforcers that 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; [0076] the hooping reinforcement (7) is made up of an axial juxtaposition of contiguous turns of the strip (8), which are circumferentially wound around the first working layer. In FIG. 1, the strips are separate, but in reality they are contiguous. The second layer 71 is overlaid on the second layer 72.

[0077] FIG. 2 shows a view in the meridian plane that identifies the widths of the layers. In particular, the width of the second working layer that corresponds to the maximum width of the hooping layer.

[0078] FIG. 3 shows the strip identifying the diameter of the reinforcer, the pitch P of the reinforcers, as well as the thickness h of the coating rubber, which is greater than or equal to 0.6 mm. The diameter 1 of the reinforcers varies from 1.9 mm to 3.8 mm. The width L8 of the strip depends on the diameter and on the pitch of the reinforcers, which is the distance P between two consecutive reinforcers. Typically, the width L8 is defined for a number of reinforcers ranging from 8 to 30, and the pitch ranges from 2.5 mm to 4.4 mm. In FIG. 3, the strip is shown with 8 reinforcers. The width of the strip can vary from 35 mm to 252 mm.

[0079] FIG. 4 shows a reinforcer of the strip made up of 4 strands (100) each formed by an internal layer of 3 threads and by an external layer of 8 threads (110).

[0080] The invention was implemented on a 59/80R63 sized tyre for a heavy duty civil engineering type vehicle. The tyre according to the invention differs from the reference tyre by the production of the hooping reinforcement. For the reference tyre, the hooping reinforcement was obtained by continuously winding a metal ply on two turns around the first working layer. For the invention, the hooping is made up of an axial juxtaposition of contiguous turns of a strip (8), which are circumferentially wound around the first working layer.

[0081] Among other things, the invention differs from the prior art through the use of strips formed by elastic metal reinforcers with large diameters ranging from 1.9 mm to 3.8 mm, with a breaking force that ranges from 250 daN to 850 daN.

[0082] The elastomeric coating compound of the reinforcers of the strip typically, but not exclusively, have the following composition, consolidated in table 1:

TABLE-US-00001 TABLE 1 NR (Natural Carbon OPF Rubber) black Stearic Epoxy Cobalt Composition Elastomer N326 Antioxidant ZnO acid Sulphur DCBS resin salt CTP Elastomeric 100 47 1.5 7.5 0.9 5.63 0.8 0.5 1.5 0.15 compound of the strip

[0083] The mechanical properties consolidated into table 2 below correspond to this composition of the coating compound:

TABLE-US-00002 TABLE 2 Elastomeric coating Results compound of the strip Shore A 67 Ma10 5.2 MPa MA100 2.6 MPa Tg () 0.09 G (10%) 2.12 MPa

[0084] The thickness of the strip can vary from 3.1 mm to 5 mm. The thickness of the coating compound on the back of the reinforcers can reach 0.6 mm. For a hooping reinforcement with two layers, the cumulative thickness of the compound on the back of the reinforcers can be greater than 2.4 mm. The dimensions of the tyres affected by the invention have a rim diameter that can be up to 63 inches. It is possible to deduce that the volume of the coating compound becomes high and that therefore its selection must be optimized with respect to its hysteresis, its shore A hardness and its stiffness.

[0085] The static stiffness modulus of the coating compound of the strip has a value of 5.2 MPa at 10% deformation and a value of 2.6 MPa at 100% deformation. Dynamically, at 10% deformation, the dynamic stiffness modulus has a value of 2.12 MPa.

[0086] The endurance of a tyre for civil engineering is directly correlated with the operating temperature caused by the viscoelastic loss of the elastomeric compounds. The inventors have established that the viscoelastic loss of the coating compound of the strip must have a level of Tg that is approximately equal to 0.09 for correct operation of the invention.

[0087] Another advantage of the invention relates to the industrial manufacturing cost, which is substantially lower for a hooping reinforcement laid as a strip compared to the reference configuration using plies. The cycle for manufacturing the hooping reinforcement with a strip is shorter, and the loss of material associated with losses is lower. However, another method gain appears with respect to the flexibility provided by this solution, with respect to the width of the crown to be hooped and the control of the level of tightening of the hoop. The width limitations associated with the upstream methods for obtaining plies are removed when manufacturing with a strip.

[0088] The invention also relates to an improvement of the endurance of the tyre. The separation of the working layers (61, 62) from the crown reinforcement (3) is one of the common failure modes of these types of tyres. When the shearing forces in the circumferential planes and in the meridian planes are too high, cracks begin to appear, then spread until the plies separate, which leads to the sudden failure of the tyre. The following result shows that hooping with the use of the strip allows a wider hoop to be provided, accompanied by a 14% reduction of the shearing level in the coating compound of the working layers:

TABLE-US-00003 TABLE No 2 Circumferential Hooped width elongation Hooping with plies 520 mm 100 Hooping with strip 740 mm 114

[0089] Another improvement of the invention relates to the thrust forces of the tyre on a curved path. The cornering stiffness is associated with the thrust forces generated by the tyre in corners. Here again, hooping with strips provides a significant improvement of approximately 17% gains relative to the reference tyre hooped with a ply, as shown in table No 3:

TABLE-US-00004 TABLE No 3 Cornering stiffness Cornering Variant (daNP/ cornering) stiffness (base 100) Hooping with plies 9335 100 Hooping with strip 10958 117