TIRE FOR A VEHICLE

Abstract

Breaking energy test performance of lightweight tyres that have a good performance in terms of rolling resistance is increased. These tyres comprise two thin and lightened working layers (41, 42) comprising metal reinforcing elements (411, 421) having a linear breaking strength Rct at most equal to 400 daN/cm, and a single carcass layer (6) radially on the inside of the working layers. In order to successfully undergo the breaking energy test, this carcass layer comprises textile reinforcing elements that have an elongation at break Acc at least equal to 15%, the carcass layer having a linear breaking strength Rcc at least equal to 0.55 times the linear breaking strength of the working layers.

Claims

1.-12. (canceled)

13. A tire for a vehicle comprising: a tread; a crown reinforcement radially on the inside of the tread and comprising at least one working reinforcement, the at least one working reinforcement comprising at least two working layers, each working layer comprising metal reinforcing elements, the metal reinforcing elements of the working layers comprising individual metal threads or monofilaments, and each working layer having a linear breaking strength Rct defined by Rct=Fr*d, where Fr is the tensile breaking force of the metal reinforcing elements, and d is the density of the metal reinforcing elements, measured around the radially outermost point of each working layer; and a single carcass layer that is radially on the inside of the crown reinforcement and connects together two beads that are intended to come into contact with a rim and comprise textile reinforcing elements, the single carcass layer having a linear breaking strength Rcc defined by Rcc=Fr*d, where Fr is the tensile breaking force of the textile reinforcing elements, and d is the density of the textile reinforcing elements, measured around the radially outermost point of the single carcass layer, wherein the linear breaking strength Rct of each working layer is at least equal to 300 daN/cm and at most equal to 400 daN/cm, wherein elongation at break Acc of the textile reinforcing elements of the single carcass layer is at least equal to 15%, and wherein, when the tire has a nominal width at least equal to 135 mm, the linear breaking strength Rcc of the single carcass layer is at least equal to 0.55 times the linear breaking strength Rct of the at least two working layers, and, when the tire has a nominal width at least equal to 245 mm, the linear breaking strength Rcc of the single carcass layer is at least equal to 0.65 times the linear breaking strength Rct of the at least two working layers.

14. The tire according to claim 13, wherein the single carcass layer has a linear breaking strength Rcc at least equal to 190 daN/cm.

15. The tire according to claim 13, wherein the textile reinforcing elements of the single carcass layer have an elongation at break Acc at least equal to 20%.

16. The tire according to claim 13, wherein the textile reinforcing elements of the single carcass layer are made of spun elementary filaments subjected to torsion, and wherein the torsion in the spun elementary filaments is at least equal to 185 t/m and at most equal to 420 t/m.

17. The tire according to claim 13, wherein the textile reinforcing elements of the single carcass layer are made of polyethylene terephthalate, rayon, a combination of aliphatic polyamide and aromatic polyamide, or a combination of polyethylene terephthalate and aromatic polyamide.

18. The tire according to claim 13, wherein the metal reinforcing elements of at least one working layer are made of individual metal threads or monofilaments having a section of which the smallest dimension is at most equal to 0.40 mm.

19. The tire according to claim 13, wherein each working layer comprises metal reinforcing elements that form, with a circumferential direction of the tire, an angle at least equal to 20 and at most equal to 45.

20. The tire according to claim 13, wherein each working layer comprises metal reinforcing elements that form, with a circumferential direction of the tire, an angle at least equal to 23 and at most equal to 35.

21. The tire according to claim 13, wherein the metal reinforcing elements of the working layers are made of carbon steel.

22. The tire according to claim 13, wherein the density of metal reinforcing elements in a single working layer is at least equal to 100 monofilaments per dm and at most equal to 200 monofilaments per dm.

23. The tire according to claim 13, wherein the density of the textile reinforcing elements in the single carcass layer, measured in the vicinity of the radially outermost point of the carcass layer, is at least equal to 40 reinforcing elements per dm and preferably at least equal to 50 reinforcing elements per dm.

24. The tire according to claim 13, further comprising at least one hooping layer, wherein reinforcing elements in the at least one hooping layer are made of textile.

25. The tire according to claim 24, wherein the textile is selected from the group consisting of polyethylene terephthalate, aliphatic polyamide, combination of aliphatic polyamide and aromatic polyamide, and combination of polyethylene terephthalate and aromatic polyamide type.

Description

DESCRIPTION OF THE DRAWINGS

[0059] The features and other advantages of the invention will be understood better with the aid of FIG. 1, which shows a meridional cross section of the crown of a tyre according to the invention.

[0060] The tyre has a tread 2 intended to come into contact with the ground via a tread surface 21. The tyre also comprises a crown reinforcement 3 radially on the inside of the tread 2 and comprising a working reinforcement 4 and a hoop reinforcement 5. The working reinforcement comprises two working layers 41 and 42 each comprising mutually parallel reinforcing elements 411, 412 that respectively form, with a circumferential direction (XX) of the tyre, an oriented angle A1, A2 at least equal to 20 and at most equal to 50, in terms of absolute value, and of opposite sign from one layer to the next. The tyre likewise comprises a single carcass layer 6 radially on the inside of the crown reinforcement.

[0061] The inventors carried out calculations on the basis of the invention for a tyre of size 225/55 R16, with a nominal width of 225 mm, comprising two working layers and one carcass layer.

[0062] The control tyre TA of conventional non-inventive design comprises: [0063] two working layers comprising reinforcing elements made up of cords of two threads with a diameter of 0.3 mm at a density of 95 reinforcing elements per decimetre for a linear breaking strength Rct equal to 420 daN/cm, [0064] a carcass layer made of polyethylene terephthalate comprising two strands of 220 tex at a density of 63 reinforcing elements per dm for a linear breaking strength of 180 daN/cm, the reinforcing elements having an elongation at break of 19%. The ratio of the linear breaking strengths of the carcass layer and the working layers is equal to 0.43.

[0065] This design makes it possible to have a sufficient performance in the breaking energy test of more than 680 J as opposed to an admissible limit of 588 J according to the standard.

[0066] The need for savings in mass and improvements in rolling resistance has led the inventors to the use of working layers comprising steel monofilaments.

[0067] In line with the prior art, a tyre TA2 was designed by the inventors in which the carcass layer remains unchanged. The saving in mass for this design is thus 200 g and the improvement in rolling resistance is close to 0.15 kg/t. This non-inventive tyre comprises: [0068] two working layers comprising reinforcing elements made up of HT (High Tensile) steel monofilaments with a diameter of 0.32 mm, distributed at a density of 143 monofilaments per decimetre for a linear breaking strength Rct equal to 350 daN/cm, and the ratio of the linear breaking strengths of the carcass layer and of the working layer is then equal to 0.51.

[0069] However, this tyre TA2 exhibits an unsatisfactory performance in the breaking energy test of 610 j, i.e. barely 3% above the regulation value, this considerably limiting the number of markets on which it could be sold.

[0070] The invention consists in modifying the reinforcing elements of the carcass layer to design the tyre A. The tyre A, according to the invention, comprises: [0071] two working layers, identical to those of TA2 since they are innovative, allowing the saving in mass and improvement in rolling resistance, comprising reinforcing elements made up of HT (High Tensile) steel monofilaments with a diameter of 0.32 mm, distributed at a density of 143 monofilaments per decimetre for a linear breaking strength Rct equal to 350 daN/cm, [0072] a carcass layer made of polyethylene terephthalate comprising two strands of 344 tex at a density of 53 reinforcing elements per dm for a linear breaking strength of 214 daN/cm, the reinforcing elements having an elongation at break of 19%, and the ratio of the linear breaking strengths of the carcass layer and of the working layer is then equal to 0.61.

[0073] The saving in mass for this design is then 200 g and the improvement in rolling resistance is close to 0.15 kg/t compared with the initial tyre TA, and its breaking energy performance is 960 J, i.e. greater than the value set by the regulations.

[0074] For all of the tyres described, the angles A1 and A2 of the reinforcing elements of the working layers are respectively equal to +25 and 25.

[0075] The inventors carried out a second set of tests on the basis of the invention for a tyre of size 255/55 R18, with a nominal width of 255 mm, comprising two working layers and one carcass layer.

[0076] The control tyre TB of conventional non-inventive design comprises: [0077] two working layers comprising reinforcing elements made up of cords of four threads with a diameter of 0.26 mm at a density of 80 reinforcing elements per decimetre for a linear breaking strength Rct equal to 480 daN/cm, [0078] a carcass layer made of polyethylene terephthalate comprising two strands of 334 tex at a density of 52 reinforcing elements per dm for a linear breaking strength of 212 daN/cm, the reinforcing elements having an elongation at break of 19%. The ratio of the linear breaking strengths of the carcass layer and the working layer is then equal to 0.44.

[0079] This design makes it possible to have a sufficient performance in the breaking energy test of more than 790 J as opposed to an admissible limit of 588 J according to the regulations.

[0080] The need for savings in mass and improvements in rolling resistance has led the inventors to the use of working layers comprising steel monofilaments.

[0081] In line with the prior art, a tyre TB2 was designed by the inventors in which the carcass layer remains unchanged. The saving in mass for this design is thus 650 g and the improvement in rolling resistance is close to 0.15 kg/t. This non-inventive tyre comprises: [0082] two working layers comprising reinforcing elements made up of HT (High Tensile) steel monofilaments with a diameter of 0.32 mm, distributed at a density of 143 monofilaments per decimetre for a linear breaking strength Rct equal to 350 daN/cm. The ratio of the linear breaking strengths of the carcass layer and the working layer is then equal to 0.605.

[0083] However, this tyre TB2 exhibits an unsatisfactory performance in the breaking energy test of 500 j, i.e. below the regulation value, this considerably limiting the number of markets on which it could be sold.

[0084] The invention consists in modifying the reinforcing elements of the carcass layer to design the tyre B. The tyre B, according to the invention, comprises: [0085] two working layers comprising reinforcing elements made up of HT (High Tensile) steel monofilaments with a diameter of 0.32 mm, distributed at a density of 143 monofilaments per decimetre for a linear breaking strength Rct equal to 350 daN/cm, [0086] a carcass layer made of nylon comprising three strands of 210 tex at a density of 52 reinforcing elements per dm for a linear breaking strength of 234 daN/cm, the reinforcing elements having an elongation at break of 27%. The ratio of the linear breaking strengths of the carcass layer and the working layer is then equal to 0.67.

[0087] The saving in mass for this design is then 650 g and the improvement in rolling resistance is close to 0.15 kg/t compared with the initial tyre TB, and its breaking energy performance is 937 J, i.e. much greater than the value set by the regulations.

[0088] For all of the tyres described, the angles A1 and A2 of the reinforcing elements of the working layers are respectively equal to +25 and 25.