CROWN REINFORCEMENT FOR A TIRE OF A TRACTOR-TYPE AGRICULTURAL VEHICLE

Abstract

A tire (1) for an agricultural vehicle comprises a working reinforcement (2), radially on the inside of a tread (3) and radially on the outside of a carcass reinforcement (4), the working reinforcement (2) comprising a multilayer component made up of a radial stack of at least two working layers (21, 22), and aims to improve the endurance thereof. The working reinforcement (2) is made up of a circumferential spiral winding of at least one turn of the multilayer component, the first and second circumferential ends (211, 221; 212, 222) of each working layer (21, 22) are circumferentially offset from one another, and the respective first circumferential ends (211, 221) of two consecutive working layers (21, 22) are likewise circumferentially offset from one another.

Claims

1.-12. (canceled)

13. A tire for an agricultural vehicle: the tire comprising a working reinforcement, radially on an inside of a tread and radially on an outside of a carcass reinforcement; the working reinforcement comprising a multilayer component made up of a radial stack of at least two working layers, each working layer of the multilayer component extending circumferentially from a first circumferential end to a second circumferential end and being made up of reinforcers that are coated in an elastomeric compound, are mutually parallel and are oriented at an angle A relative to a circumferential direction tangential to the tread; the working reinforcement being made up of a circumferential spiral winding of at least one turn of the multilayer component about the carcass reinforcement, the first and second circumferential ends of each working layer of the multilayer component being circumferentially offset from one another by an angle B; the respective first circumferential ends of two consecutive working layers of the multilayer component being circumferentially offset from one another by an angle C, wherein the first and second circumferential ends of the set of working layers are regularly distributed circumferentially.

14. The tire according to claim 13, wherein the first and second circumferential ends of each working layer of the multilayer component are circumferentially offset from one another by an angle B at least equal to 38.

15. The tire according to claim 13, wherein the first and second circumferential ends of each working layer are circumferentially offset from one another by an identical angle B for each working layer.

16. The tire according to claim 13, wherein respective first circumferential ends of two consecutive working layers are circumferentially offset from one another by a distance at least equal to a product of a maximum axial width of the working layers multiplied by a cotangent of a cutting angle of the working layers.

17. The tire according to claim 13, wherein respective first circumferential ends of two consecutive working layers are circumferentially offset from one another by an identical angle C for each pair of two consecutive working layers.

18. The tire according to claim 13, wherein the first and second circumferential ends of the set of working layers form, with respect to the circumferential direction, an angle D at least equal to 30.

19. The tire according to claim 13, wherein the reinforcers of each working layer form an angle A at least equal to 10 and at most equal to 40 relative to the circumferential direction.

20. The tire according to claim 13, wherein the reinforcers of each working layer form an identical angle A, relative to the circumferential direction, for each working layer.

21. The tire according to claim 13, wherein respective reinforcers of two consecutive working layers are crossed from one working layer to the next.

22. The tire according to claim 13, wherein the reinforcers of the working layers are made up of spun textile filaments.

23. The tire according to claim 13, wherein the reinforcers of the working layers are metal cords made up of at least one steel thread.

24. The tire according to claim 13, wherein each working layer, reinforced with textile reinforcers, has a radial thickness at most equal to 1.5 mm.

Description

[0072] The invention is illustrated in FIGS. 1 to 3, which are not shown to scale in order to make them easier to understand.

[0073] FIG. 1 depicts a meridian section through a tyre according to the invention, comprising: [0074] A tread 1 that is intended to be in contact with the ground; [0075] A working reinforcement 2 radially on the inside of the tread 1, made up of a stack of six working layers C.sub.1 to C.sub.6. Each working layer has its own mechanical properties such as the angle of the reinforcers with respect to the circumferential direction XX. This stack of layers is obtained by spirally winding a multilayer component of working layers radially on the outside of the carcass reinforcement 4, comprising three radial carcass layers NC.sub.1, NC.sub.2, and NC.sub.3.

[0076] FIG. 2 is a circumferential cross section in the equatorial plane (XZ), showing the multilayer component formed of two working layers, before winding onto the carcass reinforcement. In order to obtain the crown in FIG. 1, it is therefore necessary, during the phase of assembling the tyre, to effect a winding of three turns about the finishing drum: [0077] The first, radially inner working layer 21 is delimited circumferentially by its starting end or first circumferential end 211, and its finishing end or second circumferential end 212. The angle B1 is formed between this starting end 211 and finishing end 212; [0078] The second working layer 22 is laid with a circumferential offset radially on the outside of the first working layer, from its starting end or first circumferential end 221 to its finishing end or second circumferential end 222. The starting end 211 of the first working layer 21 and the starting end 221 of the second working layer 22 form an angle C.sub.1 between one another. In the same way, the finishing end 212 of the first working layer 21 and the finishing end 222 of the second working layer 22 form an angle C.sub.2 between one another.

[0079] FIG. 3 shows a cutaway view of the crown of the tyre, showing: [0080] a tread 1 that is intended to be in contact with the ground; [0081] a working reinforcement 2 having of a stack of six working layers C.sub.1 to C.sub.6.
In the case shown in FIG. 3, the working layers are grouped in pairs of the same length (C.sub.1, C.sub.2; C.sub.3, C.sub.4; C.sub.5, C.sub.6), and thus only three layers are shown; [0082] a carcass reinforcement 4 having three carcass layers that are each oriented at an angle of 90 with respect to the circumferential direction (XX).

[0083] The invention was studied more particularly in the case of a radial tyre for an agricultural vehicle, of size 650/65 R38 157D. According to the ETRTO standard, this tyre can bear a load of index 157, which corresponds to a mass of 4125 kg, and can be subjected to a maximum speed of rating D, i.e. 65 km/h, for a nominal pressure of 160 kPa.

[0084] It is known that, simply on account of the radial profile of this tyre, pressurizing to 160 kPa generates distributed circumferential and meridian tensile forces. It is necessary to determine the reinforcers so as to take up these distributed tensile forces plus a safety factor.

[0085] The inventors examined the reinforcers defined in Table 1 below:

TABLE-US-00001 TABLE 1 Rein- Rein- Rein- Rein- forcer 1 forcer 2 forcer 3 forcer 4 Designation PET PET PET R244/3.sup.(2) J144/2.sup.(1) J220/2 J334/2 Titre (tex) 144 220 334 244 Assembly 144/2 220/2 334/2 244/3 Twist (t/m) 290/290 240/240 270/270 330/330 Helix angle () 18.4 18.8 25.2 28.9 Breaking 18.5 28.5 40 28 strength (daN) Standard 0.80% 0.80% 0.90% / contraction Tenacity (cN/tex) 60.3 57.9 53.3 35.2 Elastic modulus 5.20% 4.50% 2.60% 2.70% (elongation at 7 daN) Adhesion, 76 86 92 105 pull- out force .sup.(3) N/thread HMLS yes yes yes NA Nature of the Polyester Polyester Polyester Rayon thread .sup.(1)the letter J indicates an HMLS (High Modulus Low Shrinkage) polyester terephthalate (PET) having a high modulus and low standard contraction; .sup.(2)the letter R indicates a cord made of rayon. .sup.(3) pull-out test as described in paragraph [0017].

[0086] The inventors have summarized, in Table 1, the physical characteristics and mechanical properties associated with four kinds of reinforcer. The first three examples of reinforcers are made of HMLS polyester with respective titres of 144 tex, 220 tex and 334 tex. The fourth example of a reinforcer is made of rayon with a titre of 244 tex. The first three examples of reinforcers are cords obtained by twisting two spun textile filaments, the twists of which in turns per metre are indicated in the table. The fourth reinforcer made of rayon is obtained by twisting three spun textile filaments of 334 tex, each with 330 turns per metre.

[0087] The inventors showed that, for proper operation of the invention, the tenacity of the polyester textile reinforcers needs to be greater than 60 cN/tex, and that the tenacity of the rayon reinforcers needs to be greater than or equal to 35 cN/tex. The textile cords need to be sufficiently strong to undergo all the steps of the method for manufacturing the tyre, in particular the shaping phases, during which they are subjected to significant deformation without being damaged.

[0088] The temperature-sensitive textile reinforcers made of PET exhibit a standard contraction of between 0.8% and 1%. The twists applied to the polyester spun yarns have an amplitude greater than 240 turns per metre and less than 270 turns per metre. The helix angle during the application of the twist about the axis of the spun yarn is less than or equal to 25.2 in terms of amplitude.

[0089] The reinforcers have adhesion properties that are reflected by results of the pull-out test of between 76 newtons per thread and 92 newtons per thread for the polyester cords; for rayon, the pull-out force is equal to 105 newtons per thread.

[0090] The secant moduli of the textile reinforcers at 7% deformation are in the range from 2.6 daN/mm.sup.2 to 5.2 daN/mm.sup.2.

[0091] The coating compounds are compositions of compounds as defined in Table 2 below:

TABLE-US-00002 TABLE 2 Constituents Per hundred rubber (phr) Natural rubber 40 SBR Ref 1 (1) 25 SBR Ref 2 (2) 35 Carbon black N550 (3) 60 Oil (4) 2 Tackifying resin (5) 5 Zinc oxide 3 Stearic acid 1.5 Antioxidant 1 (6) 1.5 Antioxidant 2 (7) 1 Sulfur 2 Sulfenamide (8) 0.5 (1): SBR Solution of Tg 48 C., % Styrene 27, % Vinyl 24, % Trans 46 (2): SBR Solution of Tg 54 C., % Styrene 26, % Vinyl 24, % Trans 47 (3): Carbon black N550 (4): Oil of MES type (5): Tackifying resin of TAC OPF type (6): Antioxidant of phenylenediamine type (7): Antioxidant of acetone aniline (TMQ) type (8): Sulfenamide of tert-butyl benzothiazolesulfenamide (TBBS)

[0092] Starting from the reinforcers and the coating compound described in Tables 1 and 2 above, the inventors defined the following working layers for studying the optimal combination for proper operation of the invention.

TABLE-US-00003 TABLE 3 Total Tensile Examples Nature.sup.(2) Reinforcer.sup.(3) Twist.sup.(4) thickness Density.sup.(1) strength Example 1 J J 220/2 240/240 1.4 mm 87 t/dm 24.8 daN/mm Example 2 J J 144/2 290/290 0.97 mm 104 t/dm 19.2 daN/mm Example 3 J J 144/2 290/290 0.97 mm 90 t/dm 16.6 daN/mm Example 4 R R 244/3 330/330 1.25 mm 79 t/dm 31.6 daN/mm Example 5 J J 334/2 270/270 1.44 mm 74 t/dm 20.7 daN/mm .sup.(1)The density is the number of threads per decimetre (t/dm) .sup.(2)Nature of the reinforcers: J for HMLS PET and R for rayon .sup.(3)Assembly of the strands to obtain cords. Example: J114/2 signifies a cord made up of the assembly of two strands of 144 tex each .sup.(4)Torsion applied to the strands (in turns per metre) to obtain the cord

[0093] The inventors used Example 1 to produce the working reinforcement of the tyre. This choice represents the best technical and economical compromise. The working reinforcement therefore comprises six working layers reinforced with textile PET reinforcers of the type J220/2. Each working layer has a density of 87 reinforcers per decimetre. The coating compound is the one described in Table 2.

[0094] The stack of six working layers is obtained by three turns of spiral winding of the multilayer component made up of two working layers, as shown in FIG. 2, radially on the outside of the carcass reinforcement.

[0095] The tests that make it possible to quantify the performance aspects of a tyre according to the invention relate to endurance and industrial production cost.

[0096] By taking as reference a conventionally manufactured tyre having six successively laid textile layers, each comprising a weld that spreads over an overlap length of 8 mm, the following results in Table 4 are obtained, with reference to a base 100 reference:

TABLE-US-00004 TABLE 4 Endurance Industrial (Running hours) manufacturing cost Working layers with welds 100 100 (Reference) Working layers without welds 131 91 (Invention)

[0097] The endurance result was obtained according to the test described in paragraph [022]. The tyre of the invention has a more than 31% longer running life compared with the reference. Moreover, the novel spiral laying method has a cycle time reduced by 9% compared with the conventional method of laying layers with a weld for each layer.

[0098] The tyre of the invention exhibits better performance aspects than those of the reference tyre and therefore meets the initial objective of the inventors.

[0099] The invention has been described for a tyre for equipping agricultural vehicles, but it can also apply to any type of tyre.