Tire comprising a tread made up of several elastomeric compounds

Abstract

A tire with radial carcass reinforcement comprising a crown reinforcement itself capped radially with a tread of which the tread pattern comprises at least two circumferential grooves. The tread is made up of at least three layers, a first layer forming the radially outer part of the tread of a first compound having an electrical resistivity per unit volume .sub.1 such that log(.sub.1) is less than 6, a second layer radially on the inside of at least three parts, at least the axially outer parts of a second compound having an electrical resistivity per unit volume .sub.2 such that log(.sub.2) is greater than 10, and at least part, radially extending the at least first elastomeric compound of the first layer, of a third elastomeric compound having an electrical resistivity per unit volume .sub.3 such that log(.sub.3) is less than 6, a third layer radially furthest towards the inside of at least five parts, at least the axially outer parts of a third elastomeric compound having a maximum value of tan(), denoted tan()max, of less than 0.080, at least two parts of the second compound, and at least part of the third layer, that radially extends the at least one part of the second layer of the third elastomeric compound.

Claims

1. A tire with radial carcass reinforcement comprising a crown reinforcement itself capped radially with a tread of which the tread pattern comprises at least two circumferential grooves, which is connected to two beads via two sidewalls, the tread comprising at least three layers (C1, C2, C3) of elastomeric compounds which are radially superposed, wherein a first layer (C1) forming the radially outer part of the tread is made up of at least one first elastomeric compound having an electrical resistivity per unit volume .sub.1 such that log(.sub.1) is less than 6, wherein a second layer (C2) of elastomeric compounds radially on the inside of and in contact with the first layer (C1) of elastomeric compound is made up of at least three parts, wherein at least axially outer parts of the second layer (C2) are made up of a second elastomeric compound having an electrical resistivity per unit volume .sub.2 such that log(.sub.2) is greater than 10, wherein at least part of the second layer, which extends radially from and is in direct contact with the at least one first elastomeric compound of the said first layer, is made up of a third elastomeric compound having an electrical resistivity per unit volume .sub.3 such that log(.sub.3) is less than 6, wherein a third layer (C3) of elastomeric compounds radially furthest towards the inside is made up of at least five parts, wherein at least axially outer parts of the third layer (C3) are made up of a fourth elastomeric compound having a maximum value of tan(d), denoted tan(d)max, of less than 0.080, wherein at least two parts of the third layer (C3), which are axially in contact with at least one axially outer part of the third layer (C3), are made up of the second elastomeric compound, and wherein at least one part of the third layer (C3), which extends radially and is in direct contact with the at least one part of the said second layer (C2) made up of the third elastomeric compound, is made up of the third elastomeric compound.

2. The tire according to claim 1, wherein the distance between a point on the wall forming a groove and the fourth elastomeric compound is greater than 1 mm.

3. The tire according to claim 1, wherein the at least two parts of the third layer (C3) that are made up of the second elastomeric compound are axially centered on a circumferential plane passing through one of the at least two circumferential grooves.

4. The tire according to claim 1, wherein the tread pattern comprises an even number of circumferential grooves wherein the second layer comprises an odd number of parts made up of the third elastomeric compound.

5. The tire according to claim 4, wherein the third layer (C3) of elastomeric compounds comprises an even number of parts made up of the second elastomeric compound.

6. The tire according to claim 1, wherein the tread pattern comprises an odd number of circumferential grooves, wherein the second layer of elastomeric compounds is made up of at least five parts, and wherein the second layer (C2) comprises an even number of parts made up of the third elastomeric compound.

7. The tire according to claim 6, wherein the said third layer (C3) of elastomeric compounds comprises an odd number of parts made up of the second elastomeric compound.

8. The tire according to claim 1, wherein the ratio of the volume of the first elastomeric compound to the sum of the volumes of the four elastomeric compounds is between 25 and 70%.

9. The tire according to claim 1, wherein the ratio of the volume of the third elastomeric compound to the sum of the volumes of the four elastomeric compounds is between 5 and 10%.

10. The tire according to claim 1, wherein the ratio of the volume of the second elastomeric compound to the sum of the volumes of the four elastomeric compounds is between 10 and 40%.

11. The tire according to claim 1, wherein the ratio of the volume of the fourth elastomeric compound to the sum of the volumes of the four elastomeric compounds is less than 25%.

12. The tire according to claim 1, wherein the third elastomeric compound present in the second and third layers (C2, C3) is identical to the first elastomeric compound.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) Other details and advantageous features of embodiments of the invention will become apparent hereinafter from the description of exemplary embodiments of the invention which are given with reference to FIGS. 1 to 4, which depict:

(2) in FIG. 1, a meridian view of a tire layout according to a first embodiment of the invention,

(3) in FIG. 2, a meridian view of a tread layout of the tire according to a first embodiment of the invention,

(4) in FIG. 3, a meridian view of a tread layout of the tire according to a second embodiment of the invention,

(5) in FIG. 4, a meridian view of a tread layout of the tire according to a third embodiment of the invention.

(6) The figures are not represented to scale in order to make them easier to understand.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

(7) FIG. 1 depicts just half a view of a tire which continues symmetrically about the axis XX which represents the circumferential mid-plane or equatorial plane of a tire.

(8) In FIG. 1, the tire 1, of size 275/70 R 22.5, comprises a radial carcass reinforcement 2 anchored in two beads around bead wires, not depicted in the drawings. The carcass reinforcement 2 is formed of a single layer of metal cords. The carcass reinforcement 2 is hooped by a crown reinforcement 5, itself capped by a tread 6. The tread comprises grooves 3 forming ribs 4.

(9) The low regions and the beads of the tire 1 are notably not depicted in the figures.

(10) In FIG. 1, the crown reinforcement 5 is formed radially from the inside to the outside: of a triangulation layer 51 formed of non-wrapped inextensible 9.28 metal cords which are continuous across the entire width of the ply and oriented at an angle of 65, of a first working layer 52 formed of non-wrapped inextensible 11.35 metal cords which are continuous across the entire width of the ply, oriented at an angle of 26, of a second working layer 53 formed of non-wrapped inextensible 11.35 metal cords which are continuous across the entire width of the ply, oriented at an angle of 18 and crossed with the metal cords of the first working layer, of a protective layer 54 formed of non-wrapped elastic 18.23 metal cords which are continuous across the entire width of the ply, oriented at an angle of 18 in the same direction as the metal cords of the working layer 53.

(11) According to an embodiment of the invention, the tread 6 is made up of a first layer C1 consisting of a first elastomeric compound 61, radially on the outside which comes into contact with the ground, of a second layer C2, radially in contact with the first layer, made up of the first compound 61 and of a second elastomeric compound 62, and of a third layer C3, radially furthest towards the inside, formed of a combination of the first compound 61, of the second compound 62 and of the fourth compound 63.

(12) According to an embodiment of the invention, the first elastomeric compound 61 has an electric resistivity per unit volume such that log(.sub.1) is equal to 3 and therefore less than 6.

(13) The second elastomeric compound 62 that forms at least the axially outer parts of the layer C2 has an electrical resistivity per unit volume such that log(.sub.2) is equal to 10 and therefore greater than 8.

(14) The fourth elastomeric compound 63 forming at least the axially outer parts of the layer C3 has a maximum value of tan (), denoted tan()max, equal to 0.045 and therefore less than 0.080.

(15) FIG. 2 very schematically illustrates a partial meridian view of the tread 6 of a tire 1 according to a first embodiment of the invention.

(16) According to this first embodiment of the invention, the tread comprises two circumferential grooves 3, thus forming three ribs 4.

(17) The layer C2 comprises a part formed of the first elastomeric compound 61 and two parts formed of the second elastomeric compound 62. The part formed of the first elastomeric compound 61 is centred on the circumferential mid-plane of the tire.

(18) The layer C3 comprises a part formed of the first elastomeric compound 61 radially extending the part of the layer C2 formed of the same compound 61; these two parts made up of the elastomeric compound 61 thus form a conductive path from the reinforcement to the surface of the tread.

(19) The layer C3 comprises two parts formed of the second elastomeric compound 62, the said parts being centered respectively on circumferential planes passing through each of the grooves 3.

(20) The layer C3 also comprises four parts formed of the fourth compound 63 axially in contact on either side with the parts formed of the compound 62.

(21) The ratio of the volume of the first elastomeric compound 61 to the sum of the volumes of the three compounds 61, 62 and 63 is equal to 64%.

(22) The ratio of the volume of the second elastomeric compound 62 to the sum of the volumes of the three compounds 61, 62 and 63 is equal to 19%.

(23) The ratio of the volume of the fourth elastomeric compound 63 to the sum of the volumes of the three compounds 61, 62 and 63 is equal to 17%.

(24) FIG. 3 very schematically illustrates a partial meridian view of the tread 6 of a tire 1 according to a second embodiment of the invention.

(25) According to this second embodiment of the invention, the tread comprises three circumferential grooves 3, thus forming four ribs 4.

(26) The layer C2 comprises two parts formed of the first elastomeric compound 61 and three parts formed of the second elastomeric compound 62. The two parts formed of the first elastomeric compound 61 are axially distributed on each side of the groove 3 centered on the circumferential mid-plane of the tire. The electrically conductive path consisting of the parts formed of the first elastomeric compound 61 is thus centered on a circumferential plane that does not pass through a groove 3 thus optimizing the area of conduction with the ground.

(27) The layer C3 comprises two parts formed of the first elastomeric compound 61 radially extending the two parts of the layer C2 which are formed of the same compound 61; these parts made up of the elastomeric compound 61 thus form a conductive path from the reinforcement to the surface of the tread.

(28) The layer C3 comprises three parts formed of the second elastomeric compound 62, the said parts being centered respectively on circumferential planes passing through each of the grooves 3.

(29) The layer C3 also comprises six parts formed of the fourth compound 63 axially in contact on either side with the parts formed of the compound 62.

(30) The ratio of the volume of the first elastomeric compound 61 to the sum of the volumes of the three compounds 61, 62 and 63 is equal to 68%.

(31) The ratio of the volume of the second elastomeric compound 62 to the sum of the volumes of the three compounds 61, 62 and 63 is equal to 19%.

(32) The ratio of the volume of the third elastomeric compound 63 to the sum of the volumes of the three compounds 61, 62 and 63 is equal to 13%.

(33) FIG. 4 very schematically illustrates a partial meridian view of the tread 6 of a tire 1 according to a third embodiment of the invention. This is in fact an alternative form of the second embodiment illustrated in FIG. 3.

(34) According to this third embodiment of the invention, the tread also comprises three circumferential grooves 3, and only the third layer C3 is different.

(35) The layer C3 comprises just two parts formed of the fourth elastomeric compound 63 forming the axially outer parts of the third layer.

(36) The ratio of the volume of the first elastomeric compound 61 to the sum of the volumes of the three compounds 61, 62 and 63 is equal to 68%.

(37) The ratio of the volume of the second elastomeric compound 62 to the sum of the volumes of the three compounds 61, 62 and 63 is equal to 25%.

(38) The ratio of the volume of the third elastomeric compound 63 to the sum of the volumes of the three compounds 61, 62 and 63 is equal to 7%.

(39) Compared with the tire illustrated in FIG. 3, the tire of FIG. 4 does not perform as well in terms of rolling resistance.

(40) Two tires were produced based on the three elastomeric compounds described hereinbelow with some of their properties.

(41) TABLE-US-00001 Compound A Compound B Compound C NR 80 100 100 BR 20 N234 48 N683 35 Silica (165) m2/G 50 10 N330/Coupling agent 5/5 1/1 Covering agent Antioxidant 3 2.5 1 PARAFFIN 1 1 STEARIC ACID 2 2.5 1.5 ZnO 3 3 4.5 SULPHUR 1.5 1.5 1.5 Accelerator (CBS) 0.9 1.8 1.4 tan().sub.max 0.135 0.080 0.045 Resistivity - log() 3.8 10.4 10

(42) The first tire is a reference tire R produced to a configuration corresponding to conventional productions as described hereinabove, consisting of two radially superposed layers, the radially inner layer being formed of a single elastomeric compound. It combines a compound A present radially on the outer side of the tread and a radially inside compound C. The volume of compound C is defined in the conventional way by a person skilled in the art so that the operating temperature of the tire corresponds to the driving envisaged with such a tire. In this particular instance, the volume of compound C represents 17% of the sum of the volumes of compounds A and C.

(43) The second tire T according to the invention and more particularly to the scenario of FIGS. 1 and 3 combines, in order to form the tread, compound A, which corresponds to compound 61, compound B, which corresponds to compound 62, and compound C, which corresponds to compound 63.

(44) In order to make a comparison, similar tests were run with the two tires.

(45) The first tests involved evaluating the distance covered by the tires before they needed to be retreaded.

(46) The tests are carried out under defined load and speed conditions to lead to tread wear and tread attack of the reference tire R that allow it to be retreaded after a certain distance, assigned the value 100, covered under the said conditions of this test. The wearing performance is evaluated on a heavy vehicle when driving on an open road over routes representative of the usage to which heavy vehicles are conventionally put. Values lower than 100 express inferior wear performance.

(47) The results obtained are given in the following table:

(48) TABLE-US-00002 Tire R Tire T Wear 100 95

(49) These results show that the tire according to the invention allows running that is substantially equivalent to the distance covered by the reference tire before retreading is needed.

(50) Rolling resistance measurements were also carried out on each of the tires under identical running conditions. The results of the measurements are shown in the following table; they are expressed in kg/t, with a value of 100 assigned to tire R. Values below 100 express superior performance in terms of rolling resistance.

(51) TABLE-US-00003 Tire R Tire T 100 90

(52) These results show that the tire according to the invention offers performance in terms of rolling resistance which is superior to the reference tire.

(53) These results show that combining three layers to form the tread makes it possible for example to offset the compromise between wearing performance and rolling resistance.

(54) Moreover, according to the invention, the presence of the electrically conductive paths through the radially innermost layers makes it possible to ensure that electrostatic charge is discharged more effectively than in the reference tire.