Tire comprising a crown reinforcement

Abstract

The invention relates to a tire comprising a crown reinforcement formed of at least two working crown layers of reinforcing elements the ends of which are radially uncoupled by a polymer compound. According to the invention, the reinforcing elements of at least one working crown layer are metal cords with saturated layers, at least one internal layer being sheathed with a layer consisting of a polymer composition such as a rubber composition and in each of the shoulders of the tire, at least the uncoupling polymer compound in contact with the ends of at least two working crown layers exhibits, in the sorption test, a gas content lower than 0.06 m.sup.3.sub.STP/m.sup.3.sub.ML.

Claims

1. A tire with a radial carcass reinforcement, comprising at least one layer of reinforcing elements, the tire comprising a crown reinforcement formed of at least two working crown layers of reinforcing elements which are crossed from one layer to the other making with the circumferential direction angles of between 10 and 45 and the ends of which are radially uncoupled by a polymer compound, the crown reinforcement is capped radially by a tread, the tread being connected to two beads via two sidewalls, wherein the reinforcing elements of at least one working crown layer are metal cords with saturated layers, at least one internal layer being sheathed with a layer consisting of a polymer composition and wherein, in each of the shoulders of the tire, at least the uncoupling polymer compound in contact with the ends of at least two working crown layers exhibits, in the sorption test, a gas content lower than 0.06 m.sup.3.sub.STP/m.sup.3.sub.ML.

2. The tire according to claim 1, wherein the said reinforcing elements of at least one working crown layer are metal cords with layers of construction L+M comprising a first layer C1 of L threads of diameter d1 wound together in a helix at a pitch p1 with L ranging from 1 to 4, which is surrounded by an external layer C2 of M threads of diameter d2 wound together in a helix at a pitch p2 with M ranging from 3 to 12, and wherein a sheath constituted by a rubber composition that is non-crosslinkable, crosslinkable or crosslinked, based on at least one diene elastomer, covers said first layer C1.

3. The tire according to claim 2, wherein the diameter of the threads of the first layer C1 is between 0.10 and 0.5 mm and wherein the diameter of the threads of the layer C2 is between 0.10 and 0.5 mm.

4. The tire according to claim 2, wherein the rubber sheath has a mean thickness ranging from 0.010 mm to 0.040 mm.

5. The tire according to claim 1, wherein at least the uncoupling polymer compound in contact with the ends of at least two working crown layers is an elastomeric compound based on natural rubber or on synthetic polyisoprene containing a majority of cis-1,4 sequences and optionally on at least one other diene elastomer, the natural rubber or the synthetic polyisoprene in the case of a cut, being present in a predominant proportion in relation to the proportion of the other diene elastomer or elastomers used and of a reinforcing filler consisting: (i) carbon black with a BET specific surface area lower than 60 m.sup.2/g, used in a proportion comprised between 20 and 80 phr, (ii) a white filler of silica and/or alumina type containing SiOH and/or AlOH surface functions selected from the group consisting of precipitated or pyrogenated silicas, aluminas or alumino silicates or alternatively still carbon blacks modified during the course of or after synthesis with a specific surface comprised between 30 and 260 m.sup.2/g used at a proportion comprised between 20 and 80 phr, or (iii) a cut of carbon black described at (i) and a white filler described at (ii), in which cut the overall proportion of filler is between 20 and 80 phr.

6. The tire according to claim 1, wherein the crown reinforcement further comprises at least one layer of circumferential reinforcing elements.

7. The tire according to claim 1, wherein the reinforcing elements of at least one layer of the carcass reinforcement are metal cords exhibiting in what is known as the permeability test a flow rate lower than 20 cm.sup.3/min.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other details and advantageous features of the invention will emerge hereinafter from the description of some embodiments of the invention given with reference to FIGS. 1 to 3 which depict:

(2) FIG. 1: a meridian view of a diagram of a tire according to one embodiment of the invention;

(3) FIG. 2: a schematic depiction of a view in cross section of a first example of a working layer cord of the tire of FIG. 1;

(4) FIG. 3: a schematic depiction of a view in cross section of a second example of a working layer cord of the tire of FIG. 1.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

(5) In order to make them easier to understand, the figures have not been drawn to scale.

(6) In FIG. 1, the tire 1, of size 315/80 R 22.5, comprises a radial carcass reinforcement 2 anchored in two beads 3. The carcass reinforcement 2 is formed of a single layer of metal cords wound around a bead wire 4 to form a turn-up 5. The carcass reinforcement 2 is wrapped by a crown reinforcement 6 itself capped by a tread 7. The crown reinforcement 6 is formed radially from the inside to the outside: of a first working layer 61 formed of 3+90.30 unwrapped inextensible metal cords according to the invention, continuous across the entire width of the ply, and oriented at an angle equal to 18, of a second working layer 62 formed of 3+90.30 unwrapped inextensible metal cords according to the invention, continuous across the entire width of the ply, oriented at an angle equal to 18 and crossed with the metal cords of the first working layer, of a protective layer 63 formed of 320.35 elastic metal cords.

(7) The carcass reinforcing layer 2 is wound around a bead wire 4 to form a turn-up 5.

(8) The ends of the working layers 61 and 62 are uncoupled by profiled elements of rubber compound 8.

(9) According to embodiments of the invention, the profiled elements of rubber compound 8 have the following composition:

(10) TABLE-US-00001 COMPOSITION (in parts per 100 rubber) Natural rubber 100 Black N683 56 Cobalt abietate 4.5 Antioxidant (6PPD) 1.8 Stearic acid/zinc oxide 0.6/7.5 Sulphur/accelerant (DCBS) 5.6/0.8 Critical pressure 0.75 bar

(11) The black N683 has a BET specific surface area equal to 37 m.sup.2/g. The reference for the black corresponds to an ASTM grade.

(12) The table above also indicates the critical pressure of the rubber compound 8 which is indicative of the amount of gas contained in the compound.

(13) The profiled elements of rubber compound 8 exhibit, on the sorption test, a gas content equal to 0.045 m.sup.3.sub.STP/m.sup.3.sub.ML.

(14) FIG. 2 is a schematic depiction of the cross section of a cord 21 of a working layer of the crown reinforcement that can be used in a tire according to an embodiment of the invention. This cord 21 is an unwrapped layered cord of 3+9 structure made up of a central core formed of a cord made up of three threads 22 twisted together and of an external layer formed of nine threads 23.

(15) It has the following characteristics (with d and p in mm):

(16) structure 3+9;

(17) d.sub.1=0.30 (mm);

(18) p.sub.1=15.4 (mm)

(19) (d.sub.1/d.sub.2)=1;

(20) d.sub.2=0.30 (mm);

(21) p.sub.2=15.4 (mm),

(22) where d.sub.1, p.sub.1 are respectively the diameter and the helix pitch of the threads of the central core and d.sub.2 and p.sub.2 are respectively the diameter and the helix pitch of the threads of the external layer.

(23) The central core consisting of a cord formed of the three threads 22 was sheathed with a rubber composition 24 based on a diene elastomer which was unvulcanized (in the raw state). Sheathing was performed using an extrusion head of the cord 22, followed by a final operation of cabling the 9 threads 23 around the core thus sheathed.

(24) The penetrability of the cord 31, as measured using the method described hereinabove, is equal to 95%.

(25) FIG. 3 is a schematic depiction of the cross section of another cord 31 of a working layer of the crown reinforcement that can be used in a tire according to the invention. This cord 31 is an unwrapped layered cord of 1+6 structure, consisting of a central core formed of one thread 32 and of an external layer formed of six threads 33.

(26) It has the following characteristics (with d and p in mm):

(27) structure 1+6;

(28) d.sub.1=0.35 (mm);

(29) (d.sub.1/d.sub.2)=1;

(30) d.sub.2=0.35 (mm);

(31) p.sub.2=15.4 (mm),

(32) where d.sub.1 is the diameter of the core and d.sub.2 and p.sub.2 are respectively the diameter and the helix pitch of the threads of the external layer.

(33) The central core consisting of the thread 32 was sheathed with a rubber composition 34 based on a diene elastomer which was unvulcanized (in the raw state). Sheathing was performed via an extrusion head of the thread 32, followed by a final operation of cabling the 6 threads 33 around the core thus sheathed.

(34) The penetrability of the cord 31, as measured using the method described hereinabove, is equal to 95%.

(35) Tests were carried out using tires produced according to embodiments of the invention in accordance with the depiction of FIGS. 1 and 2 and other tests were carried out using tires referred to as reference tires.

(36) The first reference tires differ from the tires according to embodiments of the invention by a crown reinforcement in which the reinforcing elements of the working layers are unwrapped 11.35 metal cords which have no sheathing layer. Unlike the cords according to the invention, these cords contain air.

(37) First reference tires R1 also differ from the tires according to embodiments of the invention by profiled elements of rubber compound 8 having the following composition:

(38) TABLE-US-00002 COMPOSITION (in parts per 100 rubber) Natural rubber 100 Black N347 50 Cobalt abietate 4.5 Antioxidant (6PPD) 1.8 Stearic acid/zinc oxide 0.6/7.5 Sulphur/accelerant (DCBS) 5.6/0.8 Critical pressure 1.5 bar

(39) The black N347 has a BET specific surface area equal to 90 m.sup.2/g.

(40) The profiled elements of rubber compound 8 exhibit, on the sorption test, a gas content equal to 0.075 m.sup.3.sub.STP/m.sup.3.sub.ML.

(41) The second reference tires R2 differ from the tires according to embodiments of the invention by profiled elements of rubber compound 8 having a composition identical to that of the first reference tires.

(42) The reinforcing elements of the working layers of these second reference tires are metal cords identical to those of the tires produced according to embodiments of the invention.

(43) Curing tests on the various tires were carried out in order to determine the minimum possible length of time without bubbles appearing within the rubber compounds at the ends of the working layers.

(44) The results are given in the following table:

(45) TABLE-US-00003 Curing time Tires (in minutes) R1 40.5 R2 36 Invention 34.5

(46) It is evident from this example that the savings made according to embodiments of the invention, which combines firstly the characteristic relating to the reinforcing elements of the working crown layers as being metal cords with saturated layers, at least one internal layer being sheathed with a layer consisting of a polymer composition such as a rubber composition and, on the other hand, the characteristic whereby in each of the shoulders of the tire at least one polymer compound in contact with the ends of at least two working crown layers which, on the sorption test, exhibits a gas content lower than 0.06 m.sup.3.sub.STP/m.sup.3.sub.ML, make it possible to reduce the curing time of the tires by the order of 15% by comparison with conventional tires corresponding to the reference tires R1 without any bubble being seen to appear within the said polymer compounds near the ends of the said working crown layers.

(47) Moreover, it should be noted that in the case of the reference tires R2, if the curing time is reduced below 36 minutes, a significant number of bubbles appear within the polymer compounds, the mean diameter of which bubbles is smaller than that of the bubbles that appear in the case of the reference tire R1 when the curing time is reduced below 40.5 minutes.

(48) Endurance testing was carried out on a test machine that made each of the tires run in a straight line at a speed equal to the maximum speed index of the said tire under an initial load of 4000 kg, which was increased progressively in order to shorten the duration of the test.

(49) The tests were carried out on the tires according to the invention with conditions identical to those applied to the reference tires R1.

(50) The tests carried out lead, for the tires R1, to performance that established the base 100. The tests were stopped when tire degradation became apparent.

(51) The results are given in the following table:

(52) TABLE-US-00004 Distance covered Tire (in km) R1 100 Invention 109

(53) These results show that the tires according to the invention are at least as good as, if not slightly better than, the reference tires.

(54) Rolling resistance measurements showed that the tires according to the invention lead, by comparison with the reference tires RE to an improvement of the order of 0.4 kg/T.

(55) The measurements taken are summarized in the following table:

(56) TABLE-US-00005 Tire Rolling resistance R1 5.92 kg/T Invention 5.55 kg/T