TIRE

Abstract

The present invention is directed to a tire comprising a tread, two sidewalls, a carcass and at least two belts arranged radially between the carcass and the tread in a crown area of the tire. The tread has at least one axially outer edge portion covering the axially outermost edge of at least one of the belts and comprising a different rubber composition than a portion of the tread neighboring the axially outer edge portion of the tread. Furthermore, one of the sidewalls at least partially covers and contacts the axially outer surface of the axially outer edge portion of the tread.

Claims

1. A tire comprising a tread, sidewalls, a carcass and at least two belts arranged radially between the carcass and the tread in a crown area of the tire, wherein the tread has at least one axially outer edge portion radially covering an axially outermost edge of at least one of the belts and comprising a different rubber composition than a neighboring portion of the tread, wherein the neighboring portion is adapted to be ground-contacting, and wherein one of the sidewalls at least partially covers and contacts an axially outer surface of the axially outer edge portion of the tread.

2. The tire according to claim 1, wherein the axially outer edge portion extends axially over 1% to 20% of the total width of the tread.

3. The tire according to claim 1, wherein the axially outer edge portion has an essentially triangular cross-section in a plane perpendicular to the equatorial plane of the tire, wherein a first side of the essentially triangular cross-section contacts the neighboring portion of the tread, a second side of the essentially triangular cross-section covers the axially outermost edge of at least one of the belts, and a third side of the essentially triangular cross-section contacts the sidewall.

4. The tire according to claim 3, wherein the second side further covers one or more of a portion of the carcass and at least one overlay covers the axially outermost edge of at least one of the belts.

5. The tire according to claim 1, wherein the axially outer edge portion comprises a rubber composition comprising at least 30 phr of polybutadiene rubber, at least 30 phr of polyisoprene rubber, and at least 20 phr of carbon black.

6. The tire according to claim 5, wherein the sidewall comprises a rubber composition comprising at least 30 phr of a polybutadiene rubber, at least 30 phr of polyisoprene rubber, and at least 20 phr of carbon black.

7. The tire according to claim 5, wherein the neighboring portion comprises a rubber composition comprising at least 50 phr of at least one styrene-butadiene rubber and at least 100 phr of filler.

8. The tire according to claim 1, wherein a rubber composition of at least one of (i) the sidewall and (ii) the axially outer edge portion has at least one of: (a) an elongation at break of at least 500%, and (b) an elongation at break which is at least 10% higher than the elongation at break of a rubber composition of the neighboring portion of the tread.

9. The tire according to claim 1, wherein a rubber composition of at least one of (i) the sidewall and (ii) the axially outer edge portion has at least one of: (a) a Shore A hardness of less than 55, and (b) a Shore A hardness which is at least 5% lower than the Shore A hardness of a rubber composition of the neighboring portion of the tread.

10. The tire according to claim 1, comprising one axially outer edge portion at each axial side of the tread, wherein each axially outer edge portion is covered by a respective sidewall.

11. The tire according to claim 10, wherein the axially outer edge portions do not touch each other and extend together over less than 20% of the total width of the tread.

12. The tire according to claim 1, wherein said belt edge is covered by at least one of an overlay and one or more overlay strips.

13. The tire according to claim 1, wherein the sidewall extends over at least 80% of the radial height of the axially outer edge portion.

14. The tire according to claim 12, wherein the axially outer edge portion covers (i) at least an axially outer edge of a radially inner belt, (ii) an axially outermost portion of the overlay or overlay strips, and optionally (iii) a carcass portion axially outwards the axially outermost portion of the overlay or overlay strips.

15. The tire according to claim 1, wherein the axially outer edge portion extends to a radially outermost position which is radially below the radially innermost surface of the tread in the equatorial plane of the tire.

16. The tire according to claim 1, wherein the axially outer edge portion tapers in an axially outer and radially inner direction.

17. The tire according to claim 1, wherein the sidewall tapers in its radially outermost portion and covers the majority of the axially outer surface of the axially outer edge portion.

18. The tire according to claim 1, wherein the sidewall contacts with its radially outermost portion the neighboring portion of the tread.

19. The tire according to claim 1, wherein a radially outer surface of the axially outer edge portion extends essentially in an axial direction.

20. The tire according to claim 1, wherein an axially innermost end of the axially outer edge portion is situated between the axially outermost edge of the radially inner belt and the axially outermost edge of the radially outer belt.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0086] The structure, operation, and advantages of the invention will become more apparent upon contemplation of the following description taken in conjunction with the accompanying drawings, wherein

[0087] FIG. 1 is a schematic cross-section of a crown portion of a prior art tire; and wherein

[0088] FIG. 2 is a schematic cross-section of a crown portion of a tire in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0089] FIG. 1 is a schematic cross-section of a tire 1′ (not entirely in accordance with the present invention). The tire has a plurality of tire components including a tread 2′, two sidewalls 5′, a carcass 6′, two belts 9′, 10′ and two overlay layers or overlays 11′, 12′.

[0090] The tire 1′ depicted in FIG. 1 has two belts 9′, 10′ as for instance typically present in passenger cars. Usually, each belt 9′, 10′ has a metallic reinforcement. A radially inner belt 9′ is broader than the radially outer belt 10′, with respect to the axial direction (a) of the tire 1′.

[0091] A first radially inner overlay 12′ extends axially over an axial width covering the axial outer edges of the radially outer belt 10′ but not the edges of the radially inner belt 9′.

[0092] A second radially outer overlay 11′ extends over an axial width larger than that of the radially inner belt 9′ so as to cover the belt edge of the radially inner belt 9′ and also the belt edge of the radially outer belt 10′.

[0093] The tread 2′ comprises a so-called wing portion or axially outer edge portion 3′ which is attached to or in contact with a neighboring tread portion 4′. The tread 2′ has a total width w measured in the axial direction a, which is perpendicular to the equatorial plane (EP) of the tire 1′. The axially outer edge portion 3′ may help to improve the bond between sidewall 5′ and tread 2′, especially with the neighboring tread portion 4′. In particular, the sidewalls 5′ are laid over or cover the respective axially outer edge portion 3′ of the tread 2′. Moreover, the sidewalls 5′ cover the carcass 6′ at the axially outer sides of the tire 1′. Such a configuration is also sometimes referred to as sidewall over tread (SOT), in contrast to tread over sidewall (TOS). As visible in FIG. 1, the axially outer edge portion 3′ does not cover one or more of the belts 9′, 10′or is, in other words, axially spaced from the belts 9′, 10′. Rather the belts are completely covered below the neighboring tread portion 4′, which is a tread portion or tread cap portion that contacts also the ground or road when driving. In other words, the portion 4′ is intended to contact the road when driving, whereas the axially outer edge portion 3′ is not intended to contact the ground when driving.

[0094] The tread 2′ is schematically depicted without grooves but may have one or more circumferential grooves, e.g. delimiting one or more circumferential ribs or rows of tread blocks of the tire (not shown).

[0095] In general, a tire 1′ as depicted in FIG. 1 may have also two opposite bead portions, including apexes and potentially further components in the bead portions which are not depicted as they are not deemed relevant in the context of the present invention. In general such a tire may have further components not depicted herein.

[0096] The axial direction a, the radial direction r, and the circumferential direction c are shown for a better intelligibility in FIGS. 1 and 2. It is emphasized that the word direction is not limited as such to a certain orientation unless described otherwise herein.

[0097] One or more of the depicted components, such as the carcass, belts and overlays, may be fiber and/or fabric reinforced, either with metallic or textile reinforcements.

[0098] FIG. 2 depicts an embodiment of the present invention, in which different components are described with reference signs corresponding to those of FIG. 1. Thus, the tire 1 of FIG. 2 has also a tread 2 having axially outer edge portions 3 and a neighboring tread portion 4, two sidewalls 5, a carcass 6, two belts 9, 10 and two overlays 11, 12. The tread has the total axial width w measured between its actually outermost edges. It is noted that such a measurement can be carried out on a cross section of a tire along the axial direction. Axial direction is understood as directions in parallel to the direction of the axis of rotation of the tire. A radial direction is a direction perpendicular to the axis of rotation of the tire.

[0099] A main difference between the tire 1′ shown in FIG. 1 and the tire 1 shown in FIG. 2 consists in that the axially outer edge portion 3 of tire 1 covers the axially outer edge of one of the belts (i.e. herein the axially outer edge of the radially inner belt 9). In other words, the axially outer edge portion 3 of the tread 2 extends to an axially inner position which is axially closer to the equatorial plane EP of the tire 1 than the axially outer edge of the radially inner belt 9. At the same time, the axially outer edge portion 3 covers also the axially outer end of the radially outer overlay 12. In this non-limiting embodiment, the axially outer edge portion 3 may also be described as wedge-shaped portion or has in other words a wedge-shaped or essentially triangular cross-section in a plane perpendicular to the equatorial plane EP of the tire 1.

[0100] The sidewall 5 of the tire 1 covers the axially outer edge portion 3 of the tread 2 or is, in other words, laid upon or over the tread 2 and the axially outer edge portion 3.

[0101] The remaining components could have the shape, properties, or function as already described herein above in relation to FIG. 1.

[0102] In a preferred embodiment, the axially outer edge portion 3 of the tread 4 comprises a rubber composition which is similar to that of the sidewall. For instance it may comprise from 30 phr to 70 phr of polyisoprene, 30 phr to 70 phr of polybutadiene and from 30 phr to 80 phr of carbon black as filler material. This would typically not be a rubber composition which is used for a tread portion intended to contact a road. At the same time, the sidewall may comprise a rubber composition having the same or a similar rubber composition comprising from 30 phr to 70 phr of polyisoprene, 30 phr to 70 phr of polybutadiene and from 30 phr to 80 phr of carbon black as filler material.

[0103] The tread 2 is depicted with only 3 portions, i.e. two axially outer edge portions 3 and a central portion or in other words the neighboring portion 4. In principle, it is possible that the central portion comprises multiple tread portions such as in a (vertical) split tread design, i.e. having at least two strips comprising different rubber compounds axially beside one another, or in other words vertically split. It is also possible, in another embodiment, to provide a tread cap with multiple horizontal (or axial) splits, e.g. multiple tread cap layers arranged radially on top of each other. In such an embodiment (not shown), the neighboring portion would be the radially outermost portion or radially outermost layer of the tread or tread cap as it is intended to contact the road when driving. Preferably, as shown in FIG. 2, the neighboring portion 4 directly contacts the axially outer edge portion 3.

[0104] In an embodiment, a central tread portion and/or the neighboring portion 4 of the tread 2 may comprise a rubber composition comprising 100 phr of a diene-based elastomer and 100 phr to 250 phr of a filler, preferably comprising at least 40 phr of silica. Moreover, the rubber composition of the neighboring portion may comprise one or more traction resins or resins as listed already herein above. Preferably, the majority of the diene-based elastomer is at least one (preferably solution-polymerized) styrene-butadiene rubber, being optionally functionalized for the coupling to silica. The axially outer edge portion 3 has in the example a higher elongation at break than the neighboring portion of the tread 4 and preferably also a lower Shore A hardness and/or lower storage modulus G′ which can be considered as a stiffness indicator. This is considered to provide an improved flexibility in the area covering the belt edge, in particular the radially inner belt's edge.

[0105] The inventors have also carried out FEA simulations for tires having designs as shown in FIG. 1 and FIG. 2 which have shown an improved endurance of the design according to FIG. 2. In particular, the areas of the axially outermost belt edges did not heat up as much as in the design according to FIG. 1 when simulating the design of FIG. 2.

[0106] In particular, the present sidewall over tread construction according to FIG. 1 may result in a reduced endurance compared to a sidewall under tread construction as it has less flexible or soft material between the tread and the belt edge. According to a non-binding theory of the inventors, the enlarged axially outer edge portion 3 of the tread 2 according to FIG. 2 helps to exert less stress on the belt edges (compared to the design according to FIG. 1) which results in a reduced heat generation and limits the risk of failures.

[0107] Moreover, test tires have been built for each design as shown in FIG. 1 (prior art) and FIG. 2 (embodiment of the invention) in the size 255/35 ZR 20. An endurance test over more than ten thousand kilometers and under high load was run. This test confirmed the FEA results in that the design according to FIG. 2 did not show failures in the belt edge area.

[0108] While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention.