Tire Reinforcement

Abstract

Hooping layer (71) of a passenger vehicle tire has a force at break FR per mm of axial width of the hooping layer at least equal to 35 daN/mm, an elongation at break AR at least equal to 5%, and a secant extension modulus MA at least equal to 250 daN/mm, for an applied force F equal to 15% of FR. Working reinforcement (6) comprises single working layer (61) the working reinforcers of which form, with circumferential direction (YY), an angle A.sub.T at least equal to 30 and at most equal to 50. The carcass reinforcers of at least one carcass layer (81) form, with circumferential direction (YY) and in equatorial plane (XZ), angle A.sub.C2 at least equal to 55 and at most equal to 80 and having an orientation opposite to angle A.sub.T of the working reinforcers so that the carcass reinforcers and the working reinforcers constitute a triangulation.

Claims

1. A tire for a passenger vehicle, comprising: a tread intended to come into contact with the ground and connected, at its axial ends, radially towards the inside, via two sidewalls, to two beads intended to come into contact with a rim; a working reinforcement, radially on the inside of the tread, and comprising at least one working layer comprising metal working reinforcers coated in an elastomeric material, the said working reinforcers forming, with a circumferential direction of the tire, an angle A.sub.T at least equal to 10; a hoop reinforcement, radially on the inside of the tread, and radially adjacent to the working reinforcement, and comprising a single hooping layer comprising hoop reinforcers coated in an elastomeric material, said hoop reinforcers forming, with the circumferential direction, an angle A.sub.F at most equal to 5; a carcass reinforcement, joining the two beads together, radially on the inside of the working reinforcement and of the hoop reinforcement, and comprising at least one carcass layer comprising textile carcass reinforcers coated in an elastomeric material, said carcass reinforcers forming, with the circumferential direction, at least partially in the sidewalls, an angle A.sub.C1 at least equal to 85; wherein the hooping layer has a force at break per mm of axial width of the hooping layer FR at least equal to 35 daN/mm, in that wherein the hooping layer (71) has an elongation at break AR at least equal to 5%, in that wherein the hooping layer has a secant extension modulus MA at least equal to 250 daN/mm, for an applied force F equal to 15% of the force at break FR of the said hooping layer, in that wherein the working reinforcement comprises a single working layer the working reinforcers of which form, with the circumferential direction, an angle A.sub.T at least equal to 30 and at most equal to 50, and in that wherein the carcass reinforcers of the at least one carcass layer form, with the circumferential direction and in the equatorial plane, an angle AC.sub.C2 at least equal to 55 and at most equal to 80 and having an orientation the opposite of that of the angle A.sub.T of the working reinforcers so that the carcass reinforcers and the working reinforcers constitute a triangulation.

2. The tire according to claim 1, wherein the hooping layer has a force at break per mm of axial width of the hooping layer FR at least equal to 45 daN/mm.

3. The tire according to claim 1, wherein the hooping layer has an elongation at break AR at least equal to 5.5%.

4. The tire according to claim 1, wherein the hooping layer has a secant extension modulus MA at least equal to 300 daN/mm, for an applied force F equal to 15% of the force at break FR of the said hooping layer.

5. The tire according to claim 1, wherein the hooping layer has a secant extension modulus MA at most equal to 900 daN/mm, for an applied force F equal to 15% of the force at break FR of the said hooping layer.

6. The tire according to claim 1, wherein the hooping layer has a secant extension modulus MA at most equal to 700 daN/mm, for an applied force F equal to 15% of the force at break FR of the said hooping layer.

7. The tire according to claim 1, the hooping layer comprising hoop reinforcers having a diameter D and spaced one from the next by an inter-reinforcer distance L, wherein the ratio D/L between the diameter D of a hoop reinforcer and the distance L separating two consecutive hoop reinforcers is at least equal to 1 and at most equal to 8.

8. The tire according to claim 1, the hooping layer comprising hoop reinforcers having a diameter D and spaced one from the next by an inter-reinforcer distance L, wherein the ratio D/L between the diameter D of a hoop reinforcer and the distance L separating two consecutive hoop reinforcers is at least equal to 2 and at most equal to 5.

9. The tire according to claim 1, wherein the hoop reinforcers comprise a textile material such as an aromatic polyamide or aramid, an aliphatic polyamide or nylon, a polyester such as a polyethylene terephthalate (PET), a polyethylene naphthenate (PEN), a polyketone or a textile material comprising cellulose fibres such as rayon or lyocell.

10. The tire according to claim 9, wherein the hoop reinforcers comprise a combination of at least two distinct textile materials.

11. The tire according to claim 10, wherein the hoop reinforcers are made of the combination of an aromatic polyamide or aramid and of a polyethylene terephthalate (PET).

12. The tire according to claim 1, the hooping and working layers respectively having an axial width L.sub.F and L.sub.T, in which wherein the hooping layer has an axial width L.sub.F less than the axial width L.sub.T of the working layer.

13. The tire according to claim 1, wherein the working reinforcers of the working layer form, with the circumferential direction, an angle A.sub.T at least equal to 35 and at most equal to 45.

14. The tire according to claim 1, wherein the carcass reinforcers of the at least one carcass layer form, with the circumferential direction and in the equatorial plane, an angle A.sub.C2 at least equal to 60 and at most equal to 70.

15. The tire according to claim 1, the hooping and working layers respectively having an axial width L.sub.F and L.sub.T, wherein the hooping layer has an axial width L.sub.F less than the axial width L.sub.T of the working layer when the hooping layer is radially on the outside of the working layer.

Description

[0054] In what follows, the invention is described with the aid of the attached FIGS. 1 to 3 and of the examples described in Tables 1 to 5, all given by way of illustration.

[0055] FIG. 1 schematically shows the cross section of half a tire according to the invention, in a radial plane. As FIG. 1 shows, the tire 1 according to the invention comprises a tread 2, intended to come into contact with the ground and connected, at its axial ends 21, radially towards the inside, via two sidewalls 3, to two beads 4 intended to come into contact with a rim 5. The working reinforcement 6, radially on the inside of the tread 2, comprises a working layer 61 comprising metal working reinforcers (not depicted) coated in an elastomeric material, the said working reinforcers forming, with the circumferential direction YY of the tire, an angle A.sub.T at least equal to 10. The hoop reinforcement 7, radially on the inside of the tread 2, and radially on the outside of the working reinforcement 6, comprises a single hooping layer 71 comprising hoop reinforcers coated in an elastomeric material, the said hoop reinforcers forming, with the circumferential direction YY, an angle A.sub.F at most equal to 5. The carcass reinforcement 8, joining the two beads 4 together, radially on the inside of the working reinforcement 6 and of the hoop reinforcement 7, comprises at least one carcass layer 81 comprising textile carcass reinforcers (not depicted) coated in an elastomeric material, the said carcass reinforcers forming, with the circumferential direction YY, at least partially in the sidewalls 3, an angle A.sub.C2 at least equal to 85.

[0056] FIG. 2 shows a curve of the typical behaviour of a hooping layer, representing the tensile force F applied to the hooping layer, expressed in daN/mm, namely in daN per mm of axial width of the hooping layer, as a function of its deformation in extension DX/X. FIG. 2 in particular indicates the breaking force FR of the hooping layer and the secant extension modulus MA, measured at a force F equal to 0.15 times the breaking force FR and in a standardized manner characterizing the tensile stiffness of the hooping layer.

[0057] FIG. 3 shows various curves of the tensile behaviour of a hooping layer, showing the variation in the tensile force per mm of axial width of the hooping layer F, expressed in daN/mm, as a function of its deformation in extension DX/X, for various types of hoop reinforcers.

[0058] The curves in FIG. 3 were established for a hooping layer of a passenger vehicle tire of size 205/55 R 16, intended to be mounted on a 6.5J16 rim and to be inflated to a nominal pressure of 2.5 bar under normal load and 2.9 bar under extra load, in accordance with the ETRTO (European Tire and Rim Technical Organisation) standard. Curve S1 is the tensile curve for a hooping layer the hoop reinforcers of which are made up of 3, 440-tex strands (440/3) of PET with a balanced twist of 160 turns per metre (160 tpm), the pitch P of the reinforcers being equal to 1.31 mm Curve S2 is the tensile curve for a hooping layer the hoop reinforcers of which are of hybrid type and made up of a combination of a 334 tex PET and a 330 tex aramid, twisted together with a balanced twist of 270 turns per metre (270 tpm), the pitch P of the reinforcers being equal to 0.8 mm Curve S3 is the tensile curve for a hooping layer the hoop reinforcers of which are of hybrid type and made up of a combination of a 334 tex PET and a 330 tex aramid, twisted together with a balanced twist of 210 turns per metre (210 tpm), the pitch P of the reinforcers being equal to 1.23 mm Curve S4 is the tensile curve for a hooping layer the hoop reinforcers of which are made up of 2, 167-tex strands (167/2) of aramid, with a twist of 440 turns per metre (440 tpm), the pitch P of the reinforcers being equal to 0.87 mm Curve E1 is the tensile curve for a hooping layer the hoop reinforcers of which are made up of 2, 167-tex strands (167/2) of aramid, with a twist of 315 turns per metre (315 tpm), the pitch P of the reinforcers being equal to 0.87 mm Curve E2 is the tensile curve for a hooping layer the hoop reinforcers of which are made of metal cords made of steel made up of an assembly of 3 metal threads of diameter 0.26 mm, the pitch P of the reinforcers being equal to 0.85 mm The segment with an arrow in FIG. 3 indicates the specified minimum elongation at break of 5% beyond which the elongation at break of any hooping layer falling within the scope of the invention needs to lie. Curves S1, S2, S3 and S4 correspond to hooping layers that fall within the scope of the invention, whereas curves E1 and E2 correspond to comparative examples which do not fall within the scope of the invention.

[0059] The invention was studied more particularly for a passenger vehicle tire of size 205/55 R 16, intended to be mounted on a 6.5J16 rim and to be inflated to a nominal pressure of 2.5 bar under normal load and 2.9 bar under extra load, in accordance with the ETRTO (European Tire and Rim Technical Organisation) standard. Four alternative forms of embodiment of the invention, S1, S2, S3, S4, and two comparative examples El and E2 not falling within the scope of the invention, were compared.

[0060] Table 1 below shows the characteristics of the hooping layers of the two comparative examples E1 and E2 that do not fall within the scope of the invention and of the four alternative forms of embodiment of the invention S 1, S2, S3, S4, for a tire of size 205/55R16:

TABLE-US-00001 TABLE 1 Characteristics of the hooping layers in 205/55R16 Force at break per De- Secant Reinforcer Reinforcer Reinforcer mm of axial width of 15% formation modulus MA Elongation Hoop Force at diameter pitch P Ratio the hooping layer FR of FR at 15% at 15% of FR at break reinforcer break (daN) D (mm) (mm) D/L (daN/mm) (daN/mm) of FR (%) (daN/mm) layer AR(%) Alternative PET 440/3 83.5 1.29 1.69 3.2 49.4 7.4 2.15 345 11.6 form S1 160 tpm Alternative Aramid 330 + 62.0 1.00 1.31 3.2 47.2 7.1 2.05 345 9.4 form S2 PET 334 270/270 tpm Alternative Aramid 330 + 71.5 0.94 1.23 3.2 58.0 8.7 1.45 600 6.3 form S3 PET 334 210/210 tpm Alternative Aramid 167/2 48.5 0.66 0.87 3.2 56.0 8.4 1.16 724 5.4 form S4 440 tpm Comparative Aramid 167/2 60.0 0.66 0.87 3.2 69.4 10.4 1.05 991 5.0 example E1 315 tpm Comparative Metal cord 3.26 47.5 0.60 0.85 2.4 55.9 8.4 0.53 1582 3.6 example E2

[0061] It should be noted that the inter-reinforcer distance L in the formula D/L is equal to the difference between the pitch P spacing between the reinforcers, measured between the axes of two consecutive reinforcers, and the diameter D of a reinforcer. This ratio is equal to 3.2 in all the cases studied, except for comparative example E2 where it is equal to 2.4.

[0062] According to Table 1, the forces at break per mm of axial width of the hooping layer FR of the hooping layers are respectively equal to 69.4 daN/mm and 55.9 daN/mm for comparative examples E1 and E2 outside of the scope of the invention and respectively equal to 49.4 daN/mm, 47.2 daN/mm, 58 daN/mm and 56 daN/mm for alternative forms of embodiment S1, S2, S3, S4, so they are all higher than the specified minimum force at break of 35 daN/mm, and even a higher than the 45 daN/mm specified preferred value for the minimum force at break. The elongations at break AR of the hooping layers are respectively equal to 5% and 3.6% for comparative examples E1 and E2 outside of the scope of the invention and respectively equal to 11.8% , 9.4%, 6.3% and 5.4% for alternative forms of embodiment S1, S2, S3, S4, so only alternative forms of embodiment S1, S2, S3, S4 exhibit deformations at break at least equal to the 5.5% specified preferred value for the elongation at break. Finally, the secant extension modulus values at 15% of the force at break of the hooping layer FR are respectively equal to 991 daN/mm and 1582 daN/mm for comparative examples E1 and E2 outside of the scope of the invention and respectively equal to 345 daN/mm, 606 daN/mm, 600 daN/mm and 724 daN/mm for alternative forms of embodiment S1, S2, S3, S4, so only alternative forms of embodiment S1, S2, S3, S4 exhibit secant modulus values comprised between the 300 daN/mm and 900 daN/mm specified preferred values for the secant extension modulus at 15% of the force at break.

[0063] Table 2 below shows the types of reinforcers and the angles, formed by the said reinforcers, for the carcass, working and hoop reinforcements, for a passenger vehicle tire of size 205/55R16, for the two comparative examples E1 and E2 not falling within the scope of the invention and the four alternative forms of embodiment of the invention S1, S2, S3, S4:

TABLE-US-00002 TABLE 2 Types and angles of the reinforcers of carcass, working and hoop reinforcements in 205/55R16 Angle A.sub.C2 in the Type of Angle A.sub.T in the Angle A.sub.F in the Type of carcass equatorial working equatorial Type of hoop equatorial reinforcer plane () reinforcer plane () reinforcer plane () Reference of PET 144/2 90 Steel 2.30 +/25 Nylon N140/2 0 the prior art R 290 tpm P = 1.2 mm 250/250 tpm Alternative PET 144/2 67 Steel 2.30 40 PET 440/3 0 form S1 290 tpm P = 0.9 mm 160 tpm Alternative PET 144/2 67 Steel 2.30 40 Aramid 330 + 0 form S2 290 tpm P = 0.9 mm PET 334 270/270 tpm Alternative PET 144/2 67 Steel 2.30 40 Aramid 330 + 0 form S3 290 tpm P = 0.9 mm PET 334 210/210 tpm Alternative PET 144/2 67 Steel 2.30 40 Aramid 167/2 0 form S4 290 tpm P = 0.9 mm 440 tpm Comparative PET 144/2 67 Steel 2.30 40 Aramid 167/2 0 example E1 290 tpm P = 0.9 mm 315 tpm Comparative PET 144/2 67 Steel 2.30 40 Metal cord 3.26 0 example E2 290 tpm P = 0.9 mm

[0064] According to Table 2, the carcass reinforcement, in all configurations, is made up of a single carcass layer the carcass reinforcers of which are made up of 2, 144-tex strands (144/2) of PET with a twist of 290 turns per metre (290 tpm). For the reference of the prior art R, the carcass reinforcers of the carcass layer form, with the circumferential direction and in the equatorial plane, an angle A.sub.C2 equal to 90. For all the other configurations, the carcass reinforcers of the carcass layer form, with the circumferential direction and in the equatorial plane, an angle A.sub.C2 equal to 67.

[0065] The working reinforcement, for the reference of the prior art, is made up of two working layers the working reinforcers of which are metal cords made of steel containing 0.7% carbon, made up of 2 threads having a diameter equal to 0.30 mm, and laid at a pitch P equal to 1.2 mm, the said working reinforcers forming, with the circumferential direction, an angle equal to 25 and crossed from one working layer to the next. The working reinforcement, for all the other configurations studied, is made up of a single working layer the working reinforcers of which are metal cords made of steel containing 0.7% carbon, made up of 2 threads having a diameter equal to 0.30 mm, and laid at a pitch P equal to 0.9 mm, the said working reinforcers forming, with the circumferential direction, an angle equal to 40.

[0066] Table 3 hereinbelow presents theoretical results relating to the radial Rxx and shear

[0067] Gxy stiffnesses, derived from analytical calculations, and theoretical burst pressures for a tire of size 205/55R16:

TABLE-US-00003 TABLE 3 Stiffnesses and burst pressures calculated on 205/55R16 Radial stiffness Shear stiffness Burst pressure Rxx as a Gxy as a as a relative value relative value relative value (%) (%) (%) Reference of the 100 100 100 prior art R Alternative 80 14 82 form S1 Alternative 52 13 76 form S2 Alternative 82 14 91 form S3 Alternative 90 15 90 form S4 Comparative 113 15 110 example E1 Comparative 1001 18 85 example E2

[0068] The radial stiffness Rxx, expressed in daN/mm, is the radial force that needs to be applied to the tire in order to obtain a 1 mm radial displacement of its crown. The shear stiffness Gxy, expressed in daN/mm, is the axial force that needs to be applied to the tire in order to obtain a 1 mm axial displacement of its crown. The theoretical burst pressure of the tire, expressed in bar, is a characteristic of the ability of the tire to withstand pressure. The radial stiffness Rxx and shear stiffness Gxy characteristics, and the burst pressure, are expressed in the form of a relative value with respect to the corresponding characteristics of the prior-art reference R, considered as the base 100.

[0069] According to Table 3, the alternative forms S1, S3 and S4 exhibit values of radial stiffness Rxx and of burst pressure which are close to the values obtained for the prior-art reference R. By contrast, the shear stiffnesses Gxy are very much lower than the reference R, which is to be expected given the fact that the working reinforcement comprises just one working layer.

[0070] Table 4 hereinbelow shows the results of measurements and tests relating to the various tire designs studied, for a tire of size 205/55 R16:

TABLE-US-00004 TABLE 4 Cornering stiffnesses, breaking energy and burst pressures measured on 205/55R16 Burst pressure Cornering Breaking energy of the tire stiffness as a (J) for an inflated relative value inflation pressure with water (%) of 2.2 bar (bar) Reference of the 100 >588 J >16 bar prior art R Alternative form S1 98 >588 J >16 bar Alternative form S2 >588 J >16 bar Alternative form S3 110 >588 J >16 bar Alternative form S4 >588 J >16 bar Comparative 110 >588 J >16 bar example E1 Comparative 107 >588 J >16 bar example E2

[0071] The cornering stiffness Dz of a tire is the axial force applied to the tire in order to generate a 1 rotation of the tire about a radial direction. In Table 4, the cornering stiffness is expressed in the form of a relative value, namely as a percentage of the prior-art reference considered as base 100, for a tire of size 205/55R16, subjected to a load equal to 0.8 times its nominal load, within the meaning of the ETRTO standard, the said nominal load being equal to 4826 N.

[0072] The perforation energy or breaking energy is measured by indentation by a cylindrical or polar obstacle having a diameter of 19 mm, the tire being inflated to a pressure equal to 2.2 bar (extraload condition). During the course of this test, the energy is measured at the moment that the polar perforates the crown and is compared against a minimum threshold value. For a tire of this size, the minimum threshold value that is to be respected to meet the so-called Extraload requirement of the standard cover is equal to 588 J.

[0073] The burst-pressure test on the tire is carried out on a tire inflated with water. The minimum threshold value adapted to guarantee the tire's ability to withstand the pressure with a satisfactory margin of safety is taken as 16 bar.

[0074] According to Table 4, in comparison with the results obtained for the reference R, the alternative forms of the invention S1 and S3 and comparative examples E1 and E2 exhibit a cornering stiffness Dz at the same level as the reference (between 98% and 110%). In addition, all the configurations tested have a breaking energy value higher than the minimum threshold value of 588 J and a burst pressure higher than the minimum threshold value of 16 bar. It should be noted that these results are obtained for lightened tire structures comprising just one working layer rather than two working layers that are crossed with respect to one another in the case of the reference R.

[0075] Table 5 hereinbelow presents the results of tests of running over cobbles, aimed at quantifying the fatigue strength of the hoop reinforcers under conditions of severe hammering of the tread. More specifically, for each configuration tested, the number of zones in which the hooping layer has broken is counted after the tire has been de-capped.

[0076] Table 5, for the hooping layer of each of the configurations tested, gives a reminder of the secant extension modulus MA, for an applied force F equal to 15% of the breaking force FR, the elongation at break AR and shows the corresponding number of breakage zones, for a tire of size 205/55R16.

TABLE-US-00005 TABLE 5 Number of zones of breakage of the hooping layer, after test of running over cobbles, on 205/55R16 Number of zones of breakage of Secant extension the hooping modulus MA Elongation layer, after at 15% FR at break AR test of running (daN/mm) (%) over cobbles Reference of the 10 prior art R Alternative form S1 345 11.60 0 Alternative form S2 606 9.40 0 Alternative form S3 600 6.26 2 Alternative form S4 724 5.39 29 Comparative 991 4.96 49 example E1 Comparative 1582 3.60 120 example E2

[0077] According to Table 5, the prior-art reference R exhibits 10 zones of breakage of the hooping layer. The best configurations as regards the test of running over cobbles are the alternative forms of embodiment S1, S2 and S3, because the number of zones of breakage of the hooping layer is zero or near-zero. These 3 alternative forms of embodiment S1, S2 and S3 have in common a secant extension modulus MA, for an applied force F equal to 15% of the force at break FR, comprised between 300 daN/mm and 700 daN/mm, and an elongation at break AR greater than 5.5%. The alternative form of embodiment S4, with a secant extension modulus MA, for an applied force F equal to 15% of the force at break FR, comprised between 700 daN/mm and 900 daN/mm and an elongation at break AR comprised between 5% and 5.5%, is not as good as the previous ones, because the number of breakage zones in its hooping layer rises to 29. Finally, comparative examples E1 and E2, with a secant extension modulus MA, for an applied force F equal to 15% of the force at break FR, greater than 900 daN/mm and an elongation at break AR less than 5%, exhibit a number of hooping layer breakage zones respectively equal to 49 and to 120, which is a performance that is appreciably downgraded by comparison with the prior art R.

[0078] In the field of passenger vehicle tires, the invention is not restricted to the carcass reinforcers and to the working reinforcers described hereinabove. The carcass reinforcers may be made of any type of textile material such as, for example and non-exhaustively, PET, aramid, nylon or any combination of these materials. Working reinforcers are metal cords which may be of various assemblies such as, for example and non-exhaustively, cords of formula 3.26 (assembly of 3 threads, 0.26 mm in diameter), 3.18 (assembly of 3 threads, 0.18 mm in diameter), 2.30 (assembly of 2 threads, 0.30 mm in diameter, with a helix pitch of 14 mm) or mono-filaments 0.40 mm in diameter.

[0079] The invention is not restricted to a tire for a passenger vehicle but may be extended, non-exhaustively, to tires intended to be fitted to 2-wheeled vehicles such as motorbikes, vehicles of the heavy duty or construction plant type.