TIRE COMPRISING A CARCASS REINFORCEMENT MADE UP OF TWO LAYERS

Abstract

Each of at least two layers of a carcass reinforcement has a breaking force per unit width higher than 2250 daN/dm. The minimum strength per unit width, measured for an elongation of less than 10%, of a second layer of carcass reinforcement is strictly greater than a value equal to 20% of the minimum strength per unit width, measured for an elongation of less than 10%, of a first layer of carcass reinforcement. The reinforcing elements of the two layers of carcass reinforcement have a thread count of less than 750 tex. The elongation of the reinforcing elements of the second layer of carcass reinforcement is greater than 4% under a force of 20 daN, and the secant elastic modulus values under tension at 10% elongation, Mt, Mj, satisfy the relationship Mt/Mj≧1.

Claims

1. A tire with a radial carcass reinforcement and having an inflation pressure of which is greater than or equal to 6 bar, said tire comprising: a crown reinforcement that is capped radially by a tread, said tread being connected to two beads, each of said beads comprising a bead wire, by two sidewalls, said carcass reinforcement being made up of two layers of textile reinforcing elements, a first layer of carcass reinforcement being turned up around the bead wire in each of the beads, the ends of the said first layer of carcass reinforcement being radially on the outside of the radially outermost point of the bead wire in each bead and the second layer of carcass reinforcement extending from one bead to the other without any turnup around the bead wire in each of the beads, its ends being axially on the outside of the axially outermost point of the bead wire in each bead, said tire comprising in each sidewall a first filling element, axially on the inside of the exterior surface of a sidewall and axially on the outside of the turnup of the first layer of carcass reinforcement, and made of a rubber compound having a secant elastic modulus under tension at 10% elongation of Mj, each bead comprising a second filling element made of a rubber compound having a secant elastic modulus under tension at 10% elongation of Mt, extending the bead wire core radially towards the outside, wherein each of the layers of carcass reinforcement has a breaking force per unit width higher than 2250 daN/dm, wherein the minimum strength per unit width, measured for an elongation of less than 10%, of the second layer of carcass reinforcement is strictly greater than a value equal to 20% of the minimum strength per unit width, measured for an elongation of less than 10%, of the first layer of carcass reinforcement, wherein the reinforcing elements of the two layers of carcass reinforcement have a thread count of less than 750 tex, wherein the elongation of the reinforcing elements of the second layer of carcass reinforcement is greater than 4% under a force of 20 daN and wherein the secant elastic modulus values under tension at 10% elongation, Mt, Mj, satisfy the relationship Mt/Mj≦1.

2. The tire according to claim 1, wherein, in a meridean plane, a single layer of reinforcing elements is present axially between the exterior surface of the tire and the turnup of the first layer of carcass reinforcement in a zone delimited radially towards the outside by the axial direction passing through the end of the turnup of the first layer of carcass reinforcement and radially towards the inside by the axial direction passing through the intersection of the straight line passing through center O of curvature of the zone of the tire that comes to bear on the rim flange, intended to accept the tire, and making an angle of 45° with the axial direction and the turnup of the first layer of carcass reinforcement.

3. The tire according to claim 1, wherein each of the layers of carcass reinforcement has a breaking force per unit width greater than 2900 daN/dm.

4.The tire according to claim 1, wherein the reinforcing elements of the first layer of carcass reinforcement have a thread count higher than 300 tex and preferably higher than 400 tex.

5. The tire according to claim 1, wherein it has a load index strictly higher than 99.

6. The tire according to claim 1, wherein the second layer of carcass reinforcement is made up of reinforcing elements between two skim layers formed of rubber compound having a secant elastic modulus under tension at 10% elongation of Mc.sub.2, and wherein the secant elastic modulus values under tension at 10% elongation, Mc.sub.2, Mj, satisfy the relationship 0.6≦Mc.sub.2/Mj ≦4.

7. The tire according to claim 1, wherein the layers of carcass reinforcement that are made up of reinforcing elements between two skim layers formed of rubber compound have a secant elastic modulus under tension at 10% elongation, denoted Mc.sub.1 for the first layer of carcass reinforcement and Mc.sub.2 for the second layer of carcass reinforcement respectively, and wherein the secant elastic modulus values under tension at 10% elongation Mc.sub.1, Mc.sub.2 satisfy the relationship Mc.sub.2/Mc1≦4.6.

8. The tire according to claim 1, wherein, in a meridian plane, in each bead, the tire comprises a layer of reinforcing elements made of aromatic polyamide in contact with said first layer of carcass reinforcement over the entire length thereof, at least a part being radially on the inside of the bead wire and of which the ends are radially on the outside of the geometric center of the bead wire and wherein said first layer of carcass reinforcement is interposed between the bead wire and the layer of reinforcing elements made of aromatic polyamide.

9. The tire according to claim 1, wherein, in any meridian plane, in each bead, the tire comprises a retention reinforcement surrounding the bead wire and a volume of rubber compound directly in contact with the bead wire.

10. The tire according to claim 1, the first layer of carcass reinforcement forming a main part between the two bead wires and a turnup in each of the beads, and wherein, in any meridian plane, in each bead, the turnup of the first layer of carcass reinforcement is distant from the main part by a distanced of between 0.5 and 3.2 mm over a length L of at least 15 mm.

11. The tire according to claim 1, wherein the reinforcing elements of the first layer of carcass reinforcement are identical to those of the second layer of carcass reinforcement.

12. The tire according to claim 8, wherein the direction passing through the center O of curvature of the zone of the tire that comes to bear against the flange of the rim intended to accept the tire, and the axially external end of the layer of reinforcing elements made of aromatic polyamide makes an angle α of between 0 and 45° with the axial direction.

13. The tire according to claim 8 wherein the direction passing through the center O of curvature of the zone of the tire that comes to bear against the flange of the rim intended to accept the tire and the axially interior end of the layer of reinforcing elements made of aromatic polyamide makes an angle β of between 0 and 20° with the axial direction.

14. The tire according to claim 1, wherein the direction passing through the geometric center of the bead wire and the end of the second layer of carcass reinforcement makes an angle θ of less than 50° with the axial direction.

15. The tire according to claim 8, wherein the distance between the end of the second layer of carcass reinforcement and the axially outermost end of the layer of reinforcing elements made of aromatic polyamide is greater than 5 mm.

16. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Further details and advantageous features of the disclosure will become apparent hereinafter from the description of some exemplary embodiments of the invention making reference to FIGS. 1 to 4 which depict:

[0062] FIG. 1 a schematic depiction of a view in cross section of a bead according to a first alternative form of embodiment of a tire according to the disclosure,

[0063] FIG. 2 a schematic depiction of a view in cross section of a bead according to a second alternative form of embodiment of a tire according to the disclosure,

[0064] FIG. 3 a schematic depiction of a view in cross section of a bead according to a third alternative form of embodiment of a tire according to the disclosure,

[0065] FIG. 4 a schematic depiction of a view in cross section of a bead according to a fourth alternative form of embodiment of a tire according to the disclosure.

DETAILED DESCRIPTION OF THE ENABLING EMBODIMENTS

[0066] In order to make them easier to understand, the figures have not been drawn to scale.

[0067] FIG. 1 is a schematic depiction in cross section of a bead 1 of a tire of light truck type of size 7.50R16. At this bead 1 of the tire there is part of the first layer of carcass reinforcement 2 wound around a bead wire 3 to form a turnup 4 having an end 5. Also depicted is part of the second layer of carcass reinforcement 6 the end 7 of which is axially on the outside of the geometric center 8 of the bead wire 3.

[0068] The angle θ formed by the direction 9, passing through the geometric center of the bead wire and the end of the second layer of carcass reinforcement, and the axial direction A is equal to 30° and therefore less than 50°.

[0069] The layers of carcass reinforcement 2 and 6 are made up of reinforcing elements between two skim layers made of rubber compound having secant elastic modulus values under tension at 10% elongation of Mc.sub.1 for the first layer of carcass reinforcement and Mc.sub.2 for the second layer of carcass reinforcement, respectively.

[0070] The secant elastic modulus under tension at 10% elongation, Mc.sub.1, of the first layer of carcass reinforcement 2 is equal to 3.3 MPa.

[0071] The secant elastic modulus under tension at 10% elongation, Mc.sub.2, of the second layer of carcass reinforcement 6 is equal to 12.5 MPa.

[0072] The ratio Mc.sub.2/Mc.sub.1 is equal to 3.8 and therefore well below 4.6.

[0073] This FIG. 1 also shows a first filling element 10, axially on the inside, of the sidewall and axially on the outside of the turnup of the first layer of carcass reinforcement 4, made of a rubber compound having a secant elastic modulus under tension at 10% elongation, Mj, equal to 7.8 MPa.

[0074] The ratio Mc.sub.2/Mj is equal to 1.6 and therefore indeed comprised between 0.6 and 4.

[0075] The bead 1 also comprises a second filling element 11 extending the bead wire core radially towards the outside and made of a rubber compound having a secant elastic modulus under tension at 10% elongation, Mt, equal to 7.8 MPa. The second filling element 11, has, in any meridian plane, a substantially triangular cross section.

[0076] The ratio Mt/Mj is equal to 1 and therefore indeed greater than or equal to 1.

[0077] FIG. 2 illustrates a schematic depiction of a view in cross section of a bead 1 according to a second alternative form of embodiment of a tire according to the disclosure. This second alternative form differs from the first alternative form illustrated in FIG. 1 through the presence of a layer 12 of reinforcing elements made of aromatic polyamide. This layer 12 of reinforcing elements made of aromatic polyamide is arranged over its entire length in contact with the said first layer of carcass reinforcement 2 so that at least part of the layer 12 is radially on the inside of the bead wire 3 and so that the ends 13, 14 of the layer 12 are radially on the outside of the geometric centre of the bead wire. The positioning of the layer 12 is such that the first layer of carcass reinforcement 2 is interposed between the bead wire 3 and the layer 12 of reinforcing elements made of aromatic polyamide.

[0078] The angle α formed by the direction 15, passing through the center O of the curvature of the flange of the rim intended to accept the tire and the axially outer end 13 of the layer 12 of reinforcing elements made of aromatic polyamide, and the axial direction A is equal to 20°. The angle a is therefore comprised between 0 and 45°.

[0079] The angle β formed by the direction 16 passing through the center O of the curvature of the flange of the rim intended to accept the tire and the axially inner end 14 of the layer 12 of reinforcing elements made of aromatic polyamide, and the axial direction A is equal to 10°. The angle θ is therefore comprised between 0 and 20°.

[0080] FIG. 3 illustrates a schematic depiction of a view in cross section of a bead 1 according to a third alternative form of embodiment of a tire according to the disclosure. This third alternative form differs from the second alternative form illustrated in FIG. 2 through the presence in each bead of a retaining reinforcement 17 surrounding the bead wire 3 and a volume of rubber compound 18 directly in contact with the bead wire.

[0081] FIG. 4 illustrates a schematic depiction of a view in cross section of a bead 1 according to a fourth alternative form of embodiment of a tire according to the disclosure. This fourth alternative form differs from the third alternative form illustrated in FIG. 3 by one end 5 of the turnup 4 of the first layer of carcass reinforcement 2 that is radially further away from the bead wire. Furthermore, according to this fourth alternative form of the disclosure, the turnup 4 of the first layer of carcass reinforcement 2 is pressed firmly against the main part of the first layer of carcass reinforcement 2. This firm pressing results in a distance d at most equal to 1.9 mm over a length L equal to 20 mm. Over this length of 20 mm, the distance d varies between 1.2 and 1.9 mm.

[0082] The distance d is measured between the generatrix of a reinforcing element of the main part of the first layer of carcass reinforcement 2 and the generatrix of a reinforcing element of the turnup 4 of the first layer of carcass reinforcement 2 in a direction normal to the skim surfaces of the turnup 4 and of the main part of the first layer of carcass reinforcement 2.

[0083] According to any one of these alternative forms of embodiment of the disclosure or any other configuration in accordance with the disclosure, according to a first embodiment, the reinforcing elements of the first layer of carcass reinforcement 2 are identical to those of the second layer of carcass reinforcement 6.

[0084] Tires according to this first alternative were produced using PET (polyethylene terephthalate) cords of count 334/2.

[0085] The elongation of the PET (polyethylene terephthalate) cords of count 334/2 is equal to 9.6% and therefore greater than 4% under a force of 20 daN.

[0086] The breaking force per unit width of the layers of carcass reinforcement is equal to 3280 daN/dm and therefore greater than 2250 daN/dm. It is determined by the product of the density of reinforcing elements equal to 80 threads/dm, and of the breaking force of one reinforcing element, equal to 41 daN.

[0087] The minimum stiffness per unit width, measured for an elongation of less than 10%, of the layers of carcass reinforcement is equal to 123 daN/dm/%. It is determined as the product of the density of reinforcing elements, equal to 80 threads/dm, and of the minimum stiffness of one reinforcing element, equal to 1.54 daN/%.

[0088] According to a second embodiment, the reinforcing elements of the first layer of carcass reinforcement 2 are different from those of the second layer of carcass reinforcement 6.

[0089] Tires according to this second embodiment were produced using PET (polyethylene terephthalate) cords of count 334/2 for the first layer of carcass reinforcement 2 and cords of aromatic polyamide of count 210/3 for the second layer of carcass reinforcement.

[0090] The elongation of the cords made of aliphatic polyamide of count 210/3 is equal to 14.5% and therefore greater than 4% under a force of 20 daN.

[0091] The breaking force per unit width of the second layer of carcass reinforcement is equal to 4028 daN/dm and therefore greater than 2250 daN/dm. It is determined by the product of the density of reinforcing elements, equal to 75 threads/dm, and of the breaking force of one reinforcing element, equal to 53.7 daN.

[0092] The minimum stiffness per unit width, measured for an elongation of less than 10%, of the first layer of carcass reinforcement is equal to 123 daN/dm/%. It is determined as the product of the density of reinforcing elements, equal to 80 threads/dm, and of the minimum stiffness of one reinforcing element, equal to 1.54 daN/%.

[0093] The minimum stiffness per unit width, measured for an elongation of less than 10%, of the second layer of carcass reinforcement is equal to 55 daN/dm/%. It is determined as the product of the density of reinforcing elements, equal to 75 threads/dm, and of the minimum stiffness of one reinforcing element, equal to 0.73 daN/%.

[0094] The minimum stiffness per unit width, measured for an elongation less than 10%, of the second layer of carcass reinforcement is therefore equal to 45% of the minimum rigidity per unit width, measured for an elongation less than 10%, of the first layer of carcass reinforcement and therefore strictly greater than a value equal to 20% of the minimum rigidity per unit width, measured for an elongation of less 10%, of the first layer of carcass reinforcement.

[0095] Tests were performed using tires produced according to the disclosure and others using tires referred to as reference tires.

[0096] The tires according to the disclosure which were tested are in accordance with the depiction of FIG. 1.

[0097] A first series of tires according to the disclosure is produced according to the first embodiment set out hereinabove and the cords of the layers of carcass reinforcement are PET (polyethylene terephthalate) cords of count 334/2.

[0098] A second series of tires according to the disclosure is produced according to the second embodiment set out hereinabove and the cords are PET cords of count 334/2 for the first layer of carcass reinforcement 2 and cords made of aliphatic polyamide of count 210/3 for the second layer of carcass reinforcement.

[0099] The reference tires are standard tires of the same size comprising a single layer of carcass reinforcement turned up around a bead wire similar to the first layer of carcass reinforcement 2 depicted in FIG. 1 and comprising metal cords of type 12.18.

[0100] Endurance tests were carried out on a test machine that forced each of the tires to run in a straight line at a speed varying from 50 to 110 km/h (the recommended speed rating for the tire is 120 km/h) under a load varying between the nominal load and 1.9 times the nominal load and at inflation pressures varying between 0.7 times and 1.1 times the nominal pressure.

[0101] A threshold level for the distance covered is defined in order to be able to consider the tires as being sufficiently durable.

[0102] All of the tires tested passed this test by exceeding the set threshold.

[0103] The tires according to the disclosure therefore lead to satisfactory performance notably in terms of endurance.

[0104] The mass of the reference tire is 21.9 kg.

[0105] The mass of the tire according to the disclosure of the first series (cords in the two layers of carcass reinforcement identical) is equal to 19.7 kg.

[0106] The mass of the tire according to the disclosure for the second series (different cords in the two layers of carcass reinforcement) is equal 19.7 kg.