Tire for Passenger Vehicle

Abstract

A passenger vehicle tire having rolling resistance without negatively affecting the grip and behaviour. The tread (2) has a radial height H.sub.S between 5 mm and 8 mm, a volumetric void ratio T.sub.EV between 22% and 30%, a total volume V.sub.CP of the main voids (241) at least equal to 80% of the total volume V.sub.C of the voids (24), and comprises an elastomeric compound having a glass transition temperature T.sub.g between 22° C. and 5° C., a Shore A hardness between 45 and 65, and a dynamic loss tgδ at 23° C. at least equal to 0.13 and at most equal to 0.39. The metal reinforcers of the working layers (41, 42) are steel monofilaments having a cross section S with a smallest dimension Dmin between 0.20 mm and 0.50 mm. The monofilaments distributed at a density d.sub.T between 100 threads/dm 200 threads/dm, each working layer (41, 42) having a mean radial thickness E.sub.T between D+0.1 mm and D+0.6 mm.

Claims

1. A tire for a passenger vehicle, comprising: a tread that is intended to come into contact with the ground via a tread surface and comprises raised elements extending radially outwards from a bottom surface to the tread surface over a radial height H.sub.S, measured in an equatorial plane XZ of the tire, at most equal to 8 mm, the raised elements having a total volume V.sub.P and being separated by voids having a total volume V.sub.C, some of the voids being main voids, each having a mean width at least equal to 6 mm, and the set of main voids having a total volume V.sub.CP, the tread having a volumetric void ratio T.sub.EV, defined as being the ratio between the total volume V.sub.C of the voids and the sum of the total volume V.sub.C of the voids and the total volume V.sub.P of the raised elements, at least equal to 22% and at most equal to 30%, the tread also comprising at least one elastomeric compound having a glass transition temperature T.sub.g, a Shore A hardness and a dynamic loss tgδ at 23° C., a hoop reinforcement, radially on the inside of the tread, comprising at least one hooping layer comprising textile reinforcers that are coated in an elastomeric compound, are mutually parallel and form, with a circumferential direction XX′ of the tire, an angle A.sub.F, measured in the equatorial plane XZ of the tire, at most equal to 5° in terms of absolute value, a working reinforcement, radially on the inside of the hoop reinforcement, comprising at least two, radially superposed working layers comprising metal reinforcers that are coated in an elastomeric compound, are mutually parallel in each layer and are crossed from one layer to the next, forming, with the circumferential direction XX′ of the tire, an angle (A.sub.T1, A.sub.T2), measured in the equatorial plane XZ of the tire, with an absolute value at least equal to 20° and at most equal to 40°, a carcass reinforcement comprising at least one carcass layer comprising textile reinforcers that are coated in an elastomeric material, are mutually parallel and form, with the circumferential direction XX′ of the tire, an angle A.sub.C at least equal to 85° and at most equal to 95°, wherein the radial height H.sub.S of the raised elements of the tread is at least equal to 5.0 mm, in that the total volume V.sub.CP of the set of main voids in the tread is at least equal to 80% of the total volume V.sub.C of the voids in the tread, in that the at least one elastomeric compound that makes up the tread has a glass transition temperature T.sub.g at least equal to −22° C. and at most equal to −5° C., a Shore A hardness at least equal to 45 and at most equal to 65, and a dynamic loss tgδ at 23° C. at least equal to 0.13 and at most equal to 0.39, in that the metal reinforcers of each of the at least two working layers of the working reinforcement are steel monofilaments having a cross section S inscribed in a circle of diameter D, the smallest dimension Dmin of which is at least equal to 0.20 mm and at most equal to 0.5 mm, in that the metal reinforcers of each of the at least two working layers of the working reinforcement are distributed at a density d.sub.T at least equal to 100 threads/dm and at most equal to 200 threads/dm, and in that each working layer of the working reinforcement has a mean radial thickness E.sub.T at least equal to D+0.1 mm and at most equal to D+0.6 mm, where D is the diameter of the circle circumscribed on the cross section S of the monofilament-type metal reinforcer.

2. The tire according to claim 1, wherein the radial height H.sub.S of the raised elements of the tread is at least equal to 5.5 mm and at most equal to 7.5 mm.

3. The tire according to claim 1, wherein the volumetric void ratio T.sub.EV of the tread is at most equal to 28%.

4. The tire according to claim 1, wherein the volumetric void ratio T.sub.EV of the tread is at least equal to 25% and at most equal to 27%.

5. The tire according to claim 1, wherein the total volume V.sub.CP of the set of main voids in the tread is at least equal to 85%, preferably at least equal to 88%, of the total volume V.sub.C of the voids in the tread.

6. The tire according to claim 1, wherein the at least one elastomeric compound that makes up the tread has a glass transition temperature T.sub.g at least equal to −16° C. and at most equal to −8° C.

7. The tire according to claim 1, wherein the at least one elastomeric compound that makes up the tread has a Shore A hardness at least equal to 50 and at most equal to 63.

8. The tire according to claim 1, wherein the at least one elastomeric compound that makes up the tread has a Shore A hardness at least equal to 52 and at most equal to 57.

9. The tire according to claim 1, wherein the at least one elastomeric compound that makes up the tread has a dynamic loss tgδ at 23° C. at most equal to 0.27.

10. The tire according to claim 1, wherein the textile reinforcers of the at least one hooping layer of the hoop reinforcement comprise an aromatic polyamide, such as aramid.

11. The tire according to claim 10, wherein the textile reinforcers of the at least one hooping layer of the hoop reinforcement comprise a combination of an aromatic polyamide, such as aramid, and an aliphatic polyamide, such as nylon.

12. The tire according to claim 10, wherein the textile reinforcers of the at least one hooping layer of the hoop reinforcement comprise a combination of an aromatic polyamide, such as aramid, and a polyester, such as polyethylene terephthalate (PET).

13. The tire according to claim 1, wherein the metal reinforcers of each of the at least two working layers of the working reinforcement form, with the circumferential direction XX′ of the tire, an angle (A.sub.T1, A.sub.T2), measured in the equatorial plane XZ of the tire, with an absolute value at most equal to 30°.

14. The tire according to claim 1, wherein the metal reinforcers of each of the at least two working layers of the working reinforcement are monofilaments having a cross section S, the smallest dimension Dmin of which is at least equal to 0.30 mm and at most equal to 0.4 mm.

15. The tire according to claim 1, wherein the metal reinforcers of each of the at least two working layers of the working reinforcement are steel monofilaments, the ultimate tensile strength Rm of which is at least equal to 3000 MPa.

16. The tire according to claim 1, wherein the metal reinforcers of each of the at least two working layers of the working reinforcement are distributed at a density d.sub.T at least equal to 120 threads/dm and at most equal to 180 threads/dm.

17. The tire according to claim 1, wherein each working layer of the working reinforcement has a mean radial thickness E.sub.T at least equal to D+0.3 mm and at most equal to D+0.5 mm, where D is the diameter of the circle circumscribed on the cross section S of the monofilament-type metal reinforcer.

18. The tire according to claim 1, wherein an intermediate layer comprising at least one elastomeric compound is positioned radially on the inside of the tread and radially on the outside of the hoop reinforcement.

19. The tire according to claim 1 claim 18, wherein the intermediate layer advantageously has a radial thickness E at least equal to 0.3 mm and at most equal to 4.0 mm.

20. The tire according to claim 18, wherein the at least one elastomeric compound that makes up the intermediate layer has a Shore A hardness at least equal to 59 and at most equal to 69 and a dynamic loss tgδ at 23° C. at least equal to 0.08 and at most equal to 0.20.

21. (canceled)

Description

[0076] The invention is illustrated in FIGS. 1 to 3, which are not to scale and are described below:

[0077] FIG. 1 shows a meridian half-section through a tire according to the invention.

[0078] FIG. 2 shows a perspective cross section through a tire according to the invention.

[0079] FIG. 3 shows a standard tread of a tire according to the invention.

[0080] FIG. 1 shows a meridian half-section, in a meridian plane YZ, through a tire 1 for a passenger vehicle according to the invention. The tire 1 comprises, radially outermost, a tread 2 that is intended to come into contact with the ground via a tread surface 21 and comprises raised elements 22 extending radially outwards from a bottom surface 23 to the tread surface 21 over a radial height H.sub.S, measured in an equatorial plane XZ of the tire, at least equal to 5 mm and at most equal to 8 mm. The raised elements 22 have a total volume V.sub.P and are separated by voids 24 having a total volume V.sub.C. Some of the voids 24 are main voids 214, which each have a mean width at least equal to 6 mm, the set of main voids 241 having a total volume V.sub.CP at least equal to 80% of the total volume V.sub.C of the voids 24 in the tread 2. The tread 2 has a volumetric void ratio T.sub.EV, defined as being the ratio between the total volume V.sub.C of the voids 24 and the sum of the total volume V.sub.C of the voids 24 and the total volume V.sub.P of the raised elements 22, at least equal to 22% and at most equal to 30%. The tread 2 is made up of an elastomeric compound having a glass transition temperature T.sub.g at least equal to −22° C. and at most equal to −5° C., a Shore A hardness at least equal to 45 and at most equal to 65, and a dynamic loss tgδ at 23° C. at least equal to 0.13 and at most equal to 0.39. The tire 1 further comprises, according to a particular embodiment of the invention, an intermediate layer 6 that comprises an elastomeric compound and is positioned radially on the inside of the tread 2. The tire 1 also comprises a hoop reinforcement 3, which is radially inside the intermediate layer 6 and comprises a hooping layer 31, a working reinforcement 4, which is radially inside the hoop reinforcement 3 and comprises two, radially superposed working layers (41, 42), and, finally, a carcass reinforcement 5 comprising a carcass layer 51.

[0081] FIG. 2 shows a perspective cross section through a tire according to the invention.

[0082] The hooping layer 31 comprises textile reinforcers 311 that are coated in an elastomeric compound, are mutually parallel and form, with a circumferential direction XX′ of the tire, an angle A.sub.F, measured in the equatorial plane XZ of the tire, at most equal to 5° in terms of absolute value. The two working layers (41, 42) each comprise metal reinforcers (411, 421) that are coated in an elastomeric compound, are mutually parallel in each layer and are crossed from one layer to the next, forming, with the circumferential direction XX′ of the tire, an angle (A.sub.T1, A.sub.T2), measured in the equatorial plane XZ of the tire, with an absolute value at least equal to 20° and at most equal to 40°. The carcass layer 51 comprises textile reinforcers 511 that are coated in an elastomeric material, are mutually parallel and form, with the circumferential direction XX′ of the tire, an angle A.sub.C at least equal to 85° and at most equal to 95°.

[0083] FIG. 3 shows a top view of a tread of a tire according to the invention. The tread 2, which is intended to come into contact with the ground via a tread surface 21, comprises raised elements 22, having a total volume V.sub.P, which are separated by voids 24, having a total volume V.sub.C. Some of the voids are main voids 241, each having a mean width at least equal to 6 mm, the set of main voids 241 having a total volume V.sub.CP. In the case shown, the main voids 241 are circumferential. The tread 2 has a volumetric void ratio T.sub.EV, defined as being the ratio between the total volume V.sub.C of the voids 24 and the sum of the total volume V.sub.C of the voids 24 and the total volume V.sub.P of the raised elements 22, at least equal to 22% and at most equal to 30%. In addition, the total volume V.sub.CP of the set of main voids 241 in the tread 2 is at least equal to 80% of the total volume V.sub.C of the voids 24 in the tread 2.

[0084] The invention has been studied more particularly in the case of a passenger vehicle tire of size 225/45R17. A first reference tire R1 was compared with a first tire I1 according to the invention, and a second reference tire R2 was compared with a first tire I2 according to the invention.

[0085] The tread of the first reference tire R1 comprises raised elements extending radially over a radial height H.sub.S equal to 7.5 mm. The volumetric void ratio T.sub.EV of the tread is equal to 23%. The elastomeric compound that makes up the tread has a glass transition temperature T.sub.g equal to −5° C., a Shore A hardness equal to 67, and a dynamic loss tgδ at 23° C. equal to 0.44. The first reference tire R1 also comprises an intermediate layer radially on the inside of the tread and radially on the outside of the hoop reinforcement, said intermediate layer being made up of an elastomeric compound having a Shore A hardness equal to 66 and a dynamic loss tgδ at 23° C. equal to 0.13. The hoop reinforcement comprises a hooping layer, the textile reinforcers of which are made of nylon with a titre of 140/2 (assembly of 2 strands of 140 tex each, 1 tex being the mass in g of 1000 m of thread) and are distributed in the hooping layer at a density of 98 threads/dm. The working reinforcement comprises two, radially superposed working layers. The metal reinforcers of formulation 2.30 (twisted assembly of two metal threads that each have a diameter equal to 0.30 mm) of the radially innermost working layer and of the radially outermost working layer are distributed at a spacing equal to 1.05 mm and form, with the circumferential direction XX′ of the tire, an angle (A.sub.T1, A.sub.T2), measured in the equatorial plane XZ of the tire, equal to +25° and −25°, respectively. The mean radial thickness E.sub.T of each working layer is equal to 0.9 mm. The carcass reinforcement is made up of a carcass layer, the textile reinforcers of which are made of polyethylene terephthalate (PET) with a titre of 334/2 (assembly of 2 strands of 334 tex each), with a twist of 270 turns/m, and are distributed in the carcass layer at a density of 80 threads/dm.

[0086] The tread of the first tire II according to the invention comprises raised elements extending radially over a radial height H.sub.s equal to 7 mm. The volumetric void ratio T.sub.EV of the tread is equal to 26.5%. The total volume V.sub.CP of the set of main voids in the tread is equal to 81% of the total volume V.sub.C of the voids in the tread. The elastomeric compound that makes up the tread has a glass transition temperature T.sub.g equal to −12° C., a Shore A hardness equal to 63.5, and a dynamic loss tgδ at 23° C. equal to 0.38. The first tire I1 according to the invention also comprises an intermediate layer radially on the inside of the tread and radially on the outside of the hoop reinforcement, said intermediate layer being made up of an elastomeric compound having a Shore A hardness equal to 63 and a dynamic loss tgδ at 23° C. equal to 0.15. The hoop reinforcement comprises a hooping layer, the textile reinforcers of which are made of nylon with a titre of 140/2 (assembly of 2 strands of 140 tex each, 1 tex being the mass in g of 1000 m of thread) and are distributed in the hooping layer at a density of 98 threads/dm. The working reinforcement comprises two, radially superposed working layers. The metal reinforcers of formulation 1.32 (monofilament having in each case a diameter equal to 0.32 mm) of the radially innermost working layer and of the radially outermost working layer are distributed at a spacing equal to 0.70 mm and form, with the circumferential direction XX′ of the tire, an angle (A.sub.T1, A.sub.T2), measured in the equatorial plane XZ of the tire, equal to +25° and −25°, respectively. The mean radial thickness E.sub.T of each working layer is equal to 0.83 mm. The spacing between two consecutive monofilaments, that is to say the distance between their respective mean lines, is equal to 0.70 mm, and so the density of monofilaments is equal to 1/0.70=1.42 reinforcer/mm, i.e. 142 reinforcers/dm. The carcass reinforcement is made up of a carcass layer, the textile reinforcers of which are made of polyethylene terephthalate (PET) with a titre of 334/2 (assembly of 2 strands of 334 tex each), with a twist of 270 turns/m, and are distributed in the carcass layer at a density of 80 threads/dm.

[0087] The tread of the second reference tire R2 comprises raised elements extending radially over a radial height H.sub.s equal to 7.5 mm. The volumetric void ratio T.sub.EV of the tread is equal to 23%. The elastomeric compound that makes up the tread has a glass transition temperature T.sub.g equal to −9° C., a Shore A hardness equal to 65, and a dynamic loss tgδ at 23° C. equal to 0.32. The second reference tire R2 also comprises an intermediate layer radially on the inside of the tread and radially on the outside of the hoop reinforcement, said intermediate layer being made up of an elastomeric compound having a Shore A hardness equal to 65 and a dynamic loss tgδ at 23° C. equal to 0.11. The hoop reinforcement comprises a hooping layer, the textile reinforcers of which are made of nylon with a titre of 140/2 (assembly of 2 strands of 140 tex each, 1 tex being the mass in g of 1000 m of thread) and are distributed in the hooping layer at a density of 98 threads/dm. The working reinforcement comprises two, radially superposed working layers. The metal reinforcers of formulation 2.30 (twisted assembly of two metal threads that each have a diameter equal to 0.30 mm) of the radially innermost working layer and of the radially outermost working layer are distributed at a spacing equal to 1.05 mm and form, with the circumferential direction XX′ of the tire, an angle (A.sub.T1, A.sub.T2), measured in the equatorial plane XZ of the tire, equal to +25° and −25° , respectively. The mean radial thickness E.sub.T of each working layer is equal to 0.90 mm. The carcass reinforcement is made up of a carcass layer, the textile reinforcers of which are made of polyethylene terephthalate (PET) with a titre of 334/2 (assembly of 2 strands of 334 tex each), with a twist of 270 turns/m, and are distributed in the carcass layer at a density of 80 threads/dm.

[0088] The tread of the second tire I2 according to the invention comprises raised elements extending radially over a radial height H.sub.S equal to 7 mm. The volumetric void ratio T.sub.EV of the tread is equal to 26.5%. The total volume V.sub.CP of the set of main voids in the tread is equal to 90% of the total volume V.sub.C of the voids in the tread. The elastomeric compound that makes up the tread has a glass transition temperature T.sub.g equal to −14° C., a Shore A hardness equal to 52, and a dynamic loss tgδ at 23° C. equal to 0.18. The second tire I2 according to the invention also comprises an intermediate layer radially on the inside of the tread and radially on the outside of the hoop reinforcement, said intermediate layer being made up of an elastomeric compound having a Shore A hardness equal to 60 and a dynamic loss tgδ at 23° C. equal to 0.10. The hoop reinforcement comprises a hooping layer, the textile reinforcers of which comprise a combination of aramid threads and nylon threads with a titre of A167/N140 (assembly of one strand of aramid of 167 tex and one strand of nylon of 140 tex) with a twist of 290 turns/m, and are distributed in the carcass layer at a density of 98 threads/dm. The working reinforcement comprises two, radially superposed working layers. The metal reinforcers of formulation 1.32 (monofilament having in each case a diameter equal to 0.32 mm) of the radially innermost working layer and of the radially outermost working layer are distributed at a spacing equal to 0.70 mm and form, with the circumferential direction XX′ of the tire, an angle (A.sub.T1, A.sub.T2), measured in the equatorial plane XZ of the tire, equal to +25° and −25° , respectively. The mean radial thickness E.sub.T of each working layer is equal to 0.83 mm. The spacing between two consecutive monofilaments, that is to say the distance between their respective mean lines, is equal to 0.70 mm, and so the density of monofilaments is equal to 1/0.70=1.42 reinforcer/mm, i.e. 142 reinforcers/dm. The carcass reinforcement is made up of a carcass layer, the textile reinforcers of which are made of polyethylene terephthalate (PET) with a titre of 334/2 (assembly of 2 strands of 334 tex each), with a twist of 270 turns/m, and are distributed in the carcass layer at a density of 80 threads/dm.

[0089] The mass of the first reference tire R1 is equal to 9.1 kg, and the mass of the first tire I1 according to the invention is equal to 8.5 kg. The mass of the second reference tire R2 is equal to 9.1 kg, and the mass of the second tire I2 according to the invention is equal to 8.5 kg.

[0090] The tires I1 and R1, for the one part, and I2 and R2, for the other part, were subjected to a variety of tests and comparative measurements. The results, which are presented in Table 1 below, are expressed respectively for I1 with respect to R1 (reference or base 100), and for I2 with respect to R2 (reference or base 100):

TABLE-US-00001 TABLE 1 Difference in Difference in performance of performance of Performance tire I1/tire R1 tire I2/tire R2 Rolling resistance −1.2 kg/t −1.3 kg/t Longitudinal grip (braking distance) 111 100  on wet ground (base 100) Longitudinal grip (braking distance) 102 99 on dry ground (base 100) Transverse grip (time to carry out a −1.3 s +5 s circuit lap) on wet ground Lateral stiffness at low acceleration  89 96 (or cornering stiffness) (base 100) Mass −0.6 kg −0.6 kg

[0091] Compared with the prior art tire R1 taken as a reference, the tire I1 according to the invention exhibits a reduction in rolling resistance of 1.2 kg/t, an improvement in longitudinal grip (significant on wet ground but less so on dry ground), an improved performance in terms of transverse grip on wet ground (with a time to carry out a circuit lap reduced by 1.3 s, for a reference lap time equal to 103 s), and a reduction in lateral rigidity at low acceleration implying a slight worsening in behaviour. An improvement in mass performance, that is to say a reduction in mass equal to 0.6 kg for the tire I1 compared with the tire R1 is also noted.

[0092] Compared with the prior art tire R2 taken as a reference, the tire I2 according to the invention exhibits a reduction in rolling resistance of 1.3 kg/t, an equivalent performance in terms of longitudinal grip on wet ground and on dry ground, a slightly worse performance in terms of transverse grip on wet ground (with a time to carry out a circuit lap increased by 5 s, for a reference lap time equal to 103 s), and a slight reduction in lateral rigidity at low acceleration implying substantially equivalent behaviour. An improvement in mass performance, that is to say a reduction in mass equal to 0.6 kg for the tire I2 compared with the tire R2 is also noted.