Tread for an aircraft tire

Abstract

Airplane tire tread (2), having an axial width L, comprises a middle part (3) having an axial width L.sub.C at least equal to 50% and at most equal to 80% of L and composed of a middle rubber composition, and two lateral parts (41, 42), positioned axially on either side of the middle part (3), each having an axial width (L.sub.S1, L.sub.S2) between 10% and 25% of L and each composed of a lateral rubber composition. The middle rubber composition comprises at least 50 phr of a first diene elastomer, a reinforcing filler and a crosslinking system, which first diene elastomer comprises ethylene units and diene units comprising a carbon-carbon double bond, which units are distributed randomly within the first diene elastomer, the ethylene units representing at least 50 mol % of all the monomer units of the first diene elastomer.

Claims

1. An aeroplane tire, comprising a tread having an axial width L, the tread comprising: a middle part having an axial width L.sub.C at least equal to 50% and at most equal to 80% of the axial width L of the tread and composed of a middle rubber composition, and two lateral parts positioned axially on either side of the middle part, each having an axial width at least equal to 10% and at most equal to 25% of the axial width L of the tread and each composed of a lateral rubber composition, wherein the middle rubber composition comprises at least 50 phr of a first diene elastomer, a reinforcing filler and a crosslinking system, which first diene elastomer comprises ethylene units and diene units comprising a carbon-carbon double bond, which units are distributed randomly within the first diene elastomer, the ethylene units representing at least 50 mol % of all the monomer units of the first diene elastomer, wherein the tire comprising a crown reinforcement radially inside the tread, wherein the tire comprises an interlayer composed of at least one rubber composition, in contact by a radially outer face with at least the middle part of the tread and by a radially inner face with the crown reinforcement, wherein the interlayer is composed of an elastomeric laminate comprising, radially from the outside to the inside, n layers Ci, n being an integer greater than or equal to 2 and i being an integer ranging from 1 to n, each composed of a diene rubber composition, the layer C1 comprising a diene elastomer E comprising ethylene units and diene units, the diene units representing more than 10% by weight of the monomer units of the diene elastomer E, the layer Cn comprising from 50 to less than 100 phr of a diene elastomer N having a content by weight of diene units of greater than 50%, the content expressed in phr of diene elastomer N being higher in the layer Cn than in the layer C1, the content expressed in phr of the diene elastomer E being higher in the layer C1 than in the layer Cn, the layers Ci, for the values of i ranging from 2 to n−1, where n is greater than 2, comprising a diene elastomer I selected from the group consisting of diene homopolymers and copolymers having more than 10% by weight of diene units.

2. The tire according to claim 1, wherein the middle rubber composition comprises at least 60 phr of the first diene elastomer.

3. The tire according to claim 1, wherein the first diene elastomer is a copolymer comprising ethylene units, butadiene units, and units of cyclical structure selected from the subunits of formula UD and of formula UE, ##STR00006##

4. The tire according to claim 1, wherein the first diene elastomer is a copolymer comprising the following units UA, UB, UC, UD, UE and UF, distributed randomly within the copolymer chain,
—CH.sub.2—CH.sub.2—  UA) according to a molar percentage of m %
—CH.sub.2R.sub.1C═CR.sub.2—CH.sub.2—  UB) according to a molar percentage of n % ##STR00007## according to a molar percentage of o % ##STR00008## according to a molar percentage of p % ##STR00009## according to a molar percentage of q % ##STR00010## according to a molar percentage of r % R.sub.1 and R.sub.2, which are identical or different, denoting a hydrogen atom, a methyl radical or a phenyl radical which is unsubstituted or substituted in the ortho, meta or para position by a methyl radical, R.sub.3 denoting an alkyl radical having from 1 to 4 carbon atoms or an aryl radical, m, n, o, p, q and r being numbers ranging from 0 to 100, m≥50 0<o+p≤25 o+p+q≥10 n+o>0 q≥0 0≤r≤25 the respective molar percentages of m, n, o, p, q and r being calculated on the basis of the sum of m+n+o+p+q+r, which is equal to 100.

5. The tire according to claim 4, wherein r is equal to 0.

6. The tire according to claim 4, wherein at least one of the two molar percentages p and q is different from 0.

7. The tire according to claim 4, wherein p is strictly greater than 0.

8. The tire according to claim 4, wherein the first diene elastomer meets at least one of the following criteria: m≥65 n+o+p+q≥15 10≥p+q≥2 1≥n/(o+p+q) when q is non-zero, 20≥p/q≥1.

9. The tire according to claim 4, wherein the first diene elastomer contains, as monomer units, solely the units UA, UB, UC, UD and UE according to their respective molar percentages m, n, o, p and q.

10. The tire according to claim 4, wherein the first diene elastomer contains, as monomer units, solely the units UA, UB, UC and UD according to their respective molar percentages m, n, o, and p.

11. The tire according to claim 4, wherein R.sub.1 and R.sub.2 are identical and denote a hydrogen atom.

12. The tire according to claim 1, wherein the first diene elastomer is the only elastomer of the middle rubber composition.

13. The tire according to claim 1, wherein the middle rubber composition comprises a second elastomer.

14. The tire according to claim 13, wherein the second elastomer is a highly unsaturated diene elastomer selected from the group consisting of polybutadienes, polyisoprenes, butadiene copolymers, isoprene copolymers and the mixtures of these elastomers.

15. The tire according to claim 13, wherein the second elastomer is a ternary copolymer obtained by copolymerization of ethylene and of an α-olefin having from 3 to 6 carbon atoms with a non-conjugated diene monomer having from 6 to 12 carbon atoms.

16. The tire according to claim 1, wherein the content of reinforcing filler of the middle rubber composition is at least equal to 20 phr and at most equal to 70 phr.

17. The tire according to claim 1, wherein the middle rubber composition comprises 0 to 20 phr of a liquid plasticizer.

18. The tire according to claim 17, wherein the content of liquid plasticizer of the middle rubber composition is equal to 0.

19. The tire according to claim 1, wherein at least one lateral rubber composition is different from the middle rubber composition.

20. The tire according to claim 1, wherein at least one lateral rubber composition comprises a diene elastomer, a reinforcing filler and a crosslinking system, which diene elastomer is a highly unsaturated diene elastomer selected from the group consisting of polybutadienes, polyisoprenes, butadiene copolymers, isoprene copolymers and mixtures of these elastomers.

21. The tire according to claim 1, wherein at least one lateral rubber composition comprises at most 50 phr of the first diene elastomer.

22. The tire according to claim 1, wherein the two lateral parts, positioned axially on either side of the middle part, have identical axial widths (L.sub.S1, L.sub.S2) and are composed of identical lateral rubber compositions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The characteristics of the invention will be better understood by means of FIGS. 1 and 2, of results of measurements and tests carried out on rubber compositions as used in a tire according to the invention.

(2) FIG. 1 shows a view in cross-section in a meridian plane of the crown of an airplane tire according to an embodiment of the invention.

(3) FIG. 2 shows a view in cross-section in a meridian plane of the crown of an airplane tire according to another embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(4) FIG. 1, not shown to scale in order to facilitate the understanding thereof, presents a view in cross section in a meridian plane of the crown of an aeroplane tire according to the invention, comprising, radially from the outside to the inside, a tread 2, a crown reinforcement 5 and a carcass reinforcement 6. The tread 2, having an axial width L, comprises a middle part 3 having an axial width L.sub.C at least equal to 50% and at most equal to 80% of the axial width L of the tread and composed of a middle rubber composition, and two lateral parts (41, 42), positioned axially on either side of the middle part 3, each having an axial width (L.sub.S1, L.sub.S2) at least equal to 10% and at most equal to 25% of the axial width L of the tread and each composed of a lateral rubber composition.

(5) FIG. 2 presents a view in cross section in a meridian plane of the crown of an aeroplane tire according to a particular embodiment of the invention, wherein the tire 1 also comprises an interlayer 7 composed of a rubber composition, in contact by a radially outer face with the tread 2 and by a radially inner face with the crown reinforcement 5.

(6) The invention has more particularly been studied in the case of an aeroplane tire of dimension 46×17R20, intended to be fitted to the main landing gear of a commercial airliner. For such a tire, the inflation pressure is 15.3 bar, the static load is 21 tonnes and the maximum speed is 360 km/h.

(7) Laboratory tests and measurements were carried out on different rubber compositions comprising a first diene elastomer, a reinforcing filler and a crosslinking system, which first diene elastomer comprises ethylene units and diene units comprising a carbon-carbon double bond, which units are distributed randomly within the first diene elastomer, the ethylene units representing at least 50 mol % of all the monomer units of the first diene elastomer.

(8) The rubber compositions according to the invention and of the prior art were prepared according to the process described below. The diene elastomers, the reinforcing fillers and also the various other ingredients, with the exception of the vulcanization system, are successively introduced into an internal mixer (final degree of filling: approximately 70% by volume), the initial vessel temperature of which is approximately 80° C. Thermomechanical working (non-productive phase) is then carried out in one step, which lasts in total approximately 3 to 4 min, until a maximum “dropping” temperature of 165° C. is reached. The mixture thus obtained is recovered and cooled and then sulfur and an accelerator of sulfamide type are incorporated on a mixer (homofinisher) at 70° C., everything being mixed (productive phase) for an appropriate time (for example approximately ten minutes). The compositions thus obtained are subsequently calendered, either in the form of slabs (thickness of 2 to 3 mm) or of thin sheets of rubber, for the measurement of their physical or mechanical properties, or extruded in the form of an aeroplane tire tread.

(9) The wear resistance of the rubber compositions defined above was evaluated on samples, in particular by a high-speed abrasion test, representative of the landing conditions of an aeroplane tire, combined with a measurement of loss in weight and by a measurement of breaking strength.

(10) Regarding the loss in weight, a sample of rubber composition is subjected to an abrasion test on a high-speed abrasion tester. The high-speed abrasion test is carried out according to the principle described in the paper by S. K. Clark, “Touchdown dynamics”, Precision Measurement Company, Ann Arbor, Mich., NASA, Langley Research Center, Computational Modeling of Tires, pages 9-19, published in August 1995. The tread material rubs over a surface, such as a Norton Vulcan A30S-BF42 disc. The linear speed during contact is 70 m/s with a mean contact pressure of 15 to 20 bar. The device is designed to rub until exhausting of the energy from 10 to 20 MJ/m.sup.2 of contact surface. The loss in weight performance is evaluated on the basis of the loss in weight according to the following formula: Loss in weight performance=loss in weight control/loss in weight sample. The results are expressed in base 100. A loss in weight performance for the sample of greater than 100 is regarded as better than the control.

(11) Table I below describes a rubber composition T1 of the prior art, used as reference, and a rubber composition C1 according to the invention. The rubber composition T1 comprises 100 phr of natural rubber: it is a composition based on natural rubber, commonly used by those skilled in the art to manufacture an aeroplane tire tread. The rubber composition C1 comprises 100 phr of a diene elastomer E1 comprising, in accordance with the invention, ethylene units and diene units comprising a carbon-carbon double bond, which units are distributed randomly within the first diene elastomer, the ethylene units representing at least 50 mol % of all the monomer units of the first diene elastomer. This diene elastomer E1 is a copolymer comprising units UA, UB, UC, UD at molar percentages as defined by table II below: 71% of subunit UA, 8% of subunit UB, 14% of subunit UC and 7% of subunit UD.

(12) TABLE-US-00001 TABLE I Composition T1 C1 NR (1) 100 — Elastomer E1 — 100 Carbon black (2) 30 30 Antioxidant (3) 1.5 1.5 Stearic acid (4) 2.5 2.5 Zinc oxide (5) 3 3 Accelerator (6) 2.0 2.0 Sulfur 0.8 1.5 (1) Natural rubber (2) N234 according to Standard ASTM D-1765 (3) N-(1,3-Dimethylbutyl)-N-phenyl-para-phenylenediamine, Santoflex 6-PPD from Flexsys (4) Stearin, Pristerene 4931 from Uniqema (5) Zinc oxide of industrial grade from Umicore (6) N-Cyclohexyl-2-benzothiazolesulfenamide, Santocure CBS from Flexsys

(13) TABLE-US-00002 TABLE II Subunit UA 71 Subunit UB 8 Subunit UC 14 Subunit UD 7

(14) Table III below presents the loss in weight performance of the rubber compositions T1 and C1, respectively, following laboratory abrasion tests on a high-speed abrasion tester, as described above. The loss in weight performance of the rubber composition C1 is virtually double (180%) that of the rubber composition T1.

(15) TABLE-US-00003 TABLE III Composition T1 C1 Loss in weight performance (%) 100 180

(16) Consequently, an aeroplane tire, the tread of which comprises, in the middle part, a rubber composition C1, will have better resistance to touch wear and may, at an equivalent rate of wear, perform a greater number of landings than an aeroplane tire, the tread of which comprises, in the middle part, a composition T1 based on natural rubber.

(17) The scope of protection of the invention is not limited to the examples given hereinabove. The invention is embodied in each novel characteristic and each combination of characteristics, which includes every combination of any features which are stated in the claims, even if this feature or combination of features is not explicitly stated in the examples.