Tire comprising a tread made up of several elastomeric compounds

Abstract

A tire with a radial carcass reinforcement, having a crown reinforcement, itself capped radially by a tread connected to two beads by two sidewalls, having at least two radially superposed layers of elastomeric compounds; a first layer, forming the radially outer part of the tread, has a first elastomeric compound having a modulus G* greater than 1.8 MPa, a second layer of elastomeric compounds radially on the inside of and in contact with the said first layer of elastomeric compound has at least three parts, the axially outer parts having a second elastomeric compound having a maximum value of tan (), denoted tan () max, strictly less than 0.060, and at least a part of the second layer, axially in contact with at least an axially outer part having a third compound with modulus G* greater than 1.2 MPa and at least 5% less than the first elastomeric compound and a maximum value of tan (), tan ()max, between 0.060 and 0.120.

Claims

1. A tire with a radial carcass reinforcement, comprising: a crown reinforcement, a tread radially capping the crown reinforcement, and connected to two beads by two sidewalls, comprising at least two radially superposed layers of elastomeric compounds, wherein a first layer, forming the radially outer part of the tread, consists of a first elastomeric compound having a modulus G* greater than 1.8 MPa, wherein a second layer of elastomeric compounds radially on the inside of and in contact with the first layer of elastomeric compound, consists of at least three parts, wherein at least two of the parts of the second layer consist of different elastomeric compounds than one another and than the first elastomeric compound of the first layer, wherein axially outer parts of the second layer consist of a second elastomeric compound having a maximum value of tan (), denoted tan()max, strictly less than 0.060, wherein at least another part of the second layer, which is axially in contact with at least at least one of the axially outer parts consists of a third elastomeric compound having a value of the modulus G* greater than 1.2 MPa and at least 5% less than that of the first elastomeric compound and a maximum value of tan (), denoted tan ()max, of between 0.060 and 0.120 at 60 C., wherein the second elastomeric compound has a modulus G* which is less than the modulus G* of the first elastomeric compound and is less than the modulus G* of the third elastomeric compound.

2. The tire according to claim 1, wherein the second layer of elastomeric compound consists of at least five parts, wherein a central part consists of a fourth elastomeric compound having an electric resistivity per unit volume such that log() is less than 6, wherein the axially outer parts of the second layer consist of the second elastomeric compound, and wherein at least intermediate parts of the second layer axially in contact with the central part and axially outer parts consist of the third compound.

3. The tire according to claim 2, wherein the first elastomeric compound and the fourth elastomeric compound are identical.

4. The tire according to claim 1, wherein a ratio of a volume of the first layer of elastomeric compound to the sum of the first and second layers that make up the tread is between 50 and 85%.

5. The tire according to claim 1, wherein an axial width of a central part of the second layer is less than 10% of the axial width of the second layer.

6. The tire according to claim 1, wherein an axial width of an intermediate part of the second layer is between 65% and 95% of the axial width of the second layer.

7. The tire according to claim 1, wherein an axial width of an axially outer part of the second layer is greater than 5% of the axial width of the said second layer.

8. The tire according to claim 1, wherein the tire further comprises a third layer consisting of at least a fifth elastomeric compound radially on the inside of the second layer and in contact therewith, and wherein the fifth elastomeric compound has a maximum value of tan (), denoted tan ()max, strictly less than 0.060.

9. The tire according to claim 8, wherein a ratio of the volume of the fifth elastomeric compound to a sum of the volumes of the three layers of elastomeric compounds is between 5 and 15%.

10. The tire according to claim 2, wherein a ratio of a volume of the first layer of elastomeric compound to the sum of the first and second layers that make up the tread is between 50 and 85%.

11. The tire according to claim 2, wherein an axial width of a central part of the second layer is less than 10% of the axial width of the second layer.

12. The tire according to claim 2, wherein an axial width of an intermediate part of the second layer is between 65% and 95% of the axial width of the second layer.

13. The tire according to claim 2, wherein an axial width of an axially outer part of the second layer is greater than 5% of the axial width of the said second layer.

14. The tire according to claim 2, wherein the tire further comprises a third layer consisting of at least a fifth elastomeric compound radially on the inside of the second layer and in contact therewith, and wherein the fifth elastomeric compound has a maximum value of tan (), denoted tan ()max, strictly less than 0.060.

15. The tire according to claim 14, wherein a ratio of the volume of the fifth elastomeric compound to a sum of the volumes of the three layers of elastomeric compounds is between 5 and 15%.

16. A tire with a radial carcass reinforcement, comprising: a crown reinforcement, a tread radially capping the crown reinforcement, and connected to two beads by two sidewalls, comprising at least two radially superposed layers of elastomeric compounds, wherein a first layer, forming the radially outer part of the tread, consists of a first elastomeric compound having a modulus G* greater than 1.8 MPa, wherein a second layer of elastomeric compounds radially on the inside of and in contact with the first layer of elastomeric compound, consists of at least three parts, wherein at least two of the parts of the second layer consist of different elastomeric compounds than one another and than the first elastomeric compound of the first layer, wherein axially outer parts of the second layer consist of a second elastomeric compound having a maximum value of tan (), denoted tan()max, strictly less than 0.060, wherein at least another part of the second layer, which is axially in contact with at least at least one of the axially outer parts consists of a third elastomeric compound having a value of the modulus G* greater than 1.2 MPa and at least 5% less than that of the first elastomeric compound and a maximum value of tan (), denoted tan ()max, of between 0.060 and 0.120 at 60 C., and wherein the axially outer parts of the second layer are recessed relative to the remainder of the second layer such that the axially outer arts of the second layer do not come into contact with the ground during the life of the tire.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) Other details and advantageous features of embodiments of the invention will become apparent hereinafter from the description of some exemplary embodiments of the invention which are given with reference to FIGS. 1 and 2, 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 tire layout according to a second embodiment of the invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

(4) The figures are not represented to scale in order to make them easier to understand. The figures represent only a half-view of a tire, which extends symmetrically with respect to the axis XX, which represents the circumferential median plane, or equatorial plane, of a tire.

(5) In FIG. 1, the tire 1, of size 315/70 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 faulted 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.

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

(7) 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 9.35 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 18, 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 6.35 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.

(8) According to the invention, the tread 6 is made up of a radially outer first layer 61 which comes into contact with the ground and of a radially inner layer 62.

(9) The layer 61 is made up of the first elastomeric compound having a modulus G* equal to 2 MPa.

(10) The layer 62, radially on the inside of the layer 61, is made up of three elastomeric compounds.

(11) The second elastomeric compound forming the axially outer parts 621 has a maximum value of tan (), denoted tan()max, equal to 0.045.

(12) The third elastomeric compound forming the axially intermediate parts 622 has a modulus G* equal to 1.65 MPa and a maximum value of tan (), denoted tan () max, equal to 0.080.

(13) The central part 623 of the layer 62 is made up of the first elastomeric compound and has an electrical resistivity such that log() is equal to 3.

(14) The ratio of the volume of the layer 61 of the first elastomeric compound to the sum of the volumes of the layers 61 and 62 is equal to 70%.

(15) The axial width L.sub.623 of the central part 623 of the second layer 62 is equal to 5% of the axial width L.sub.62 of the said second layer.

(16) The axial width L.sub.622 of an intermediate part 622 is equal to 75% of the axial width L.sub.62 of the said second layer 62.

(17) The axial width L.sub.621 of an axially outer part 621 of the second layer 62 is equal to 20% of the axial width L.sub.62 of the said second layer 62.

(18) FIG. 2, according to an alternative form of embodiment of the invention, shows a tire 1 similar to that of FIG. 1 and which differs therefrom through the presence of a third layer 63. This layer 63 is placed in contact with the crown reinforcement and radially on the inside of the layer 62. The thickness of this layer 63 positioned notably radially under the grooves to is sufficiently insignificant to allow grooving steps before having to envisage the steps of retreading in order to recreate the tread pattern without the risk of revealing the layer 63 at the surface of the tread. The layer 63 is interrupted at the equatorial plane by the presence of the first compound in order to create continuity in the radial direction with the central part 623 of the layer 62 from the crown reinforcement as far as the surface of the tread.

(19) The layer 63 is made up of the second elastomeric compound and therefore has a maximum value of tan (), denoted tan()max, equal to 0.045.

(20) The ratio of the volume of the layer 63 to the sum of the volumes of the three layers 61, 62 and 63 is equal to 10%.

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

(22) TABLE-US-00001 Compound A Compound B Compound C NR 60 100 100 BR 40 N234 54 N683 35 Silica (165) m2/G 50 10 N330/Coupling agent 5/5 1/1 Resin/hardener 0.25/0.3 Anti Oxidant 2 2.5 1 Processing agent 3 PARAFFIN 1 1 STEARIC ACID 1.5 2.5 1.5 ZnO 3 3 4.5 SULPHUR 1.1 1.5 1.5 Accelerator (CBS) 1.1 1.8 1.4 G*50% cc/60 2 1.65 1.4 C./10 Hz (MPa) tan().sub.max 0.180 0.080 0.045 Resistivity - log() 3 10.4 10 T95 at 150 C. 11 19.7 9

(23) The first tire is a reference tire R produced to a configuration close to the depiction of FIG. 1 but corresponding to conventional productions as described hereinabove, 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 15% of the sum of the volumes of compounds A and C.

(24) A first tire T.sub.1 according to an embodiment of the invention and, more particularly, in the case of FIG. 1, combines, to foul the tread, the compound A which forms the radially outer part and therefore the layer 61 and the central part 623 of the radially inner layer 62, compound B, which forms the axially intermediate parts 622 of the radially inner layer 62 and compound C which forms the axially outer parts 621 of the radially inner layer 62.

(25) The ratio of the volume of compound B to the sum of the volumes of compounds A, B and C is equal to 17%.

(26) The ratio of the volume of compound C to the sum of the volumes of the three compounds A, B and C is equal to 13%.

(27) The second tire T.sub.2 produced according to an embodiment of the invention can be likened to that of FIG. 2. The tread of the tire T.sub.2 is similar to that of the tire T.sub.1 and further comprises a layer 63 consisting of compound C and compound A around the circumferential plane.

(28) The ratio of the volume of compound B to the sum of the volumes of compounds A, B and C is equal to 12%.

(29) The ratio of the volume of compound C to the sum of the volumes of three compounds A, B and C is equal to 18%.

(30) In order to make a comparison, similar tests were run with all three tires.

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

(32) The tests are carried out under defined load and speed conditions to lead to tread wear and tread attack of the reference tire R1 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 paths representative of the usage to which heavy vehicles are conventionally put. Values lower than 100 express inferior wear performance.

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

(34) TABLE-US-00002 Tire R1 Tire T1 Tire T2 Wear 100 99 98

(35) These results show that the tires according to the invention allow running that is substantially equivalent to the reference tire before retreading is needed.

(36) 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.

(37) TABLE-US-00003 Tire R Tire T1 Tire T2 100 92 89

(38) These values demonstrate the benefit of using the compound B to limit the rolling resistance of the tire.

(39) Comparing tires T1 and T2 shows that the presence of a layer 63 may have a significant benefit in teens of rolling resistance while at the same time maintaining satisfactory properties in terms of wear and attack.

(40) Furthermore, because the layer 63 has a small thickness at least under the grooves, it is possible to carry out a step of regrooving in order to recreate grooves before having to envisage the step of retreading. From this standpoint, the presence of the layer of compound 63 therefore does not penalize the tire T2 in comparison with the tire T1.