Belt layer for a vehicle tire

Abstract

Belt ply for a pneumatic vehicle tire, in particular for a commercial vehicle tire, wherein the belt ply comprises steel cords of construction 1+N, with N=4 or N=5 with a single core filament (1) and four or five layer filaments (2), wherein the layer filaments (2) all touch the core filament (1) on the outside and have the same diameter (D2), wherein the cord construction is an open cord construction, characterized in that the ratio of the breaking energy of the core filament (1) to the breaking energy of a layer filament (2) corresponds to 1.1 to 1.5.

Description

[0001] The invention relates to a belt ply for a pneumatic vehicle tire, in particular for a commercial vehicle tire, wherein the belt ply comprises steel cords of construction 1+N, with N=4 or N=5 with a single core filament and four or five ply filaments, wherein the ply filaments all contact the core filament on the outside and have the same diameter, wherein the cord construction is an open cord construction.

[0002] The belt cords in the belt plies of pneumatic vehicle tires are subject to stringent requirements, which are closely related to certain properties of the belt cords – the steel cords in the belt plies. These requirements include sufficiently high tensile and flexural rigidity, high strength, good fatigue resistance, good corrosion resistance, stability against displacement of the individual cord components, good adhesion to the surrounding rubber compound, and moderate manufacturing costs. Conflicting objectives now exist primarily between abrasion life, belt edge durability, belt robustness, and also the manufacturing costs of the belt package consisting of several belt plies.

[0003] The service life of a pneumatic vehicle tire, determined by tread wear, is significantly influenced by the belt cords. Greater stiffness of the belt layers and thus of the entire belt package results in a longer abrasion life. The abrasion life can be positively influenced by using stiffer steel cords in the belt layers. For belt durability, it is advantageous to select steel cords with a larger cord diameter and a lower cord density, thus providing a larger, clear cord spacing. Greater steel cord strength and a relatively close spacing between the steel cords in the belt layers promote the robustness of the belt package and protect it from external damage.

[0004] A steel cord structure that is as compact as possible is advantageous for achieving high cord stiffness in relation to cost. High steel cord stiffness and larger cord spacing therefore reduce costs. Steel cord designs with a larger cord diameter and the same stiffness, while maintaining the same cord density in the belt layers, prove to be disadvantageous in terms of belt durability and result in higher costs due to the greater thickness of the belt layers and the associated larger volume of rubber lining.

[0005] Steel cords of the type mentioned above are known in various embodiments from the prior art. For example, a commercial vehicle tire is known whose belt plies contain a steel cord of the 1+6×0.34 construction. The six ply filaments are pre-formed; without pre-forming, they would completely or almost completely envelop the core filament, making it almost impossible for rubber material to penetrate the interfilament spaces. Due to the pre-forming of the ply filaments, the steel cord is overall less compact and has a larger outer diameter. As a result, the clear cord spacing is reduced at a certain cord density, which is detrimental to belt durability. This known steel cord construction requires a certain thickness of the belt plies and thus a larger volume of rubber compound, which increases costs.

[0006] A belt ply of the type mentioned above is known, for example, from EP 0 849 098 A1. Disclosed is, in principle, a pneumatic vehicle tire with carcass plies comprising metallic cords made of filaments with a diameter of 0.10 mm to 0.45 mm and a breaking strength of -2000 × D + 4400 MPa, where D is the filament diameter in millimeters. In connection with one exemplary embodiment, a steel cord of the construction 1 + 5 × 0.18 is disclosed for a carcass ply or a belt ply, the cord construction being an open cord construction. A pneumatic vehicle tire with such carcass plies and / or such belt plies is intended, among other things, to have low rolling resistance.

[0007] JP H09 31874 A discloses a steel cord of the 1+N construction, where N = 1 to 8, i.e., a steel cord with a single core filament and five to eight layer filaments. The diameter of the core filament is 1.1 to 1.3 times the diameter of the layer filaments. Furthermore, the tensile strength (breaking strength) of the core filament is 1.07 to 1.20 times the tensile strength of the layer filaments. Such a steel cord should be able to be embedded in a rubber compound without twisting, so that during vulcanization, the rubber compound can flow easily into the interstices of the steel cord, thus improving the adhesion between the steel cord and the forming rubber material. Consequently, any problems that may arise due to twisting of the steel cord during vulcanization should be avoided.

[0008] DE 30 06 488 A1 discloses a steel cord which, when used in belt plies of pneumatic vehicle tires for passenger cars, has a core filament with a diameter of 0.138 mm or 0.15 mm and ply filaments with diameters of 0.23 mm or 0.25 mm. For use of this steel cord in belt plies of commercial vehicle tires, the diameter of the core filament should be between 0.18 mm and 0.21 mm, and that of the ply filaments between 0.30 mm and 0.35 mm. The ply filaments should be made of a carbon steel wire with a tensile strength of at least 2250 to 1130 log(d) N / mm 2 where d is the wire diameter in millimeters, the core filament shall be made of a carbon steel wire with a tensile strength of less than 2250 to 1130 log(d) N / mm 2 consist.

[0009] Another two-ply steel cord construction is known from JP 60-038208 A. A 1+5 cord construction with a maximum filament diameter of 0.342 mm is disclosed. To ensure sufficient tensile stiffness of the belt layers, especially in commercial vehicle tires, these steel cords would have to be arranged with a relatively high cord density, which, as mentioned above, is detrimental to belt edge durability.

[0010] DE 10 2010 036 809 A discloses a steel cord of construction 1+N with N > 3, whose core filament should have a diameter of 0.30 mm to 0.45 mm and whose ply filaments should have a diameter of 0.35 mm to 0.50 mm. The ratio of the diameter of the core filament to the diameter of the ply filaments should be between 0.7 and 1.1, and the number of ply filaments should in particular be four to six. The steel cords known from this prior art are particularly advantageous for use in the belt layers of pneumatic vehicle tires designed for higher loads, i.e., in particular, truck tires and bus tires.

[0011] A further requirement for the belt plies of commercial vehicle tires is that the belt cords are designed in such a way that the tread is sufficiently strong to prevent the penetration of foreign objects. In some countries, the responsible authorities have set minimum standards in defined test procedures in which the energy absorption of the tire structure before failure is assessed (e.g. in the USA by the Department of Transportation). The test prescribed in the USA is referred to below as the "plunger test". The belt plies known to date from the state of the art need to be improved with regard to passing the plunger test. The plunger test, also called the "strength test", is carried out in accordance with FMVSS 119. For light truck tires, the strength test is carried out in accordance with FMVSS 139.

[0012] The invention is therefore based on the object of providing a belt ply with steel cords of the type mentioned above, which is particularly well suited for use in radial commercial vehicle tires, such as van tires or light truck tires, truck tires, and bus tires. The belt ply should be optimized with regard to the aforementioned trade-offs between abrasion life, belt edge durability, belt robustness, and manufacturing costs, or should be able to resolve these trade-offs significantly better than known designs. Furthermore, the belt ply should pass the plunger test significantly better due to the steel cord arranged in this belt ply.

[0013] The stated object is achieved according to the invention in that the ratio of the breaking energy of the inner filament to the breaking energy of a layer filament is 1.1 to 1.5. No filaments of the steel cord are pre-formed.

[0014] In a belt layer constructed according to the invention, the steel cord is open, with an openness of between 10% and 20%. This means that the diameters of the core filament and the layer filaments are matched to ensure good penetration of the rubber material of the belt rubber lining into the spaces between the layer filaments. This effectively secures the core filament against displacement, and the risk of corrosion is reduced. The fact that the core filament has a higher breaking energy than any of the layer filaments surrounding it positively influences the plunger test result. It is assumed that this positive result is achieved due to the higher breaking energy and thus greater durability of the core filament.As a result, the core filament is not brought to its load limit earlier than the layer filaments during the plunger test and thus no longer breaks as the first filament of the steel cord and does not initiate subsequent breakage of the layer filaments surrounding the core filament.

[0015] “Fracture strength” means the maximum force measured when the strength member is stretched to the point of fracture.

[0016] “Fracture energy” means the integral of the force measured when the strength member is stretched to the point of fracture.

[0017] The openness O of the outer filaments is determined according to the relationship O[%]=N×ANM / π×D0 determined, where A NMis the arithmetic mean of the smallest mutual distances between the layer filaments and D0 is the diameter of the circle in which the smallest mutual distances between the layer filaments form chords. The diameter of this circle is determined according to the relationship D0=(D1+D2)×cos(360° / 8) determined.

[0018] In a particular embodiment of the invention, the core filament and the layer filaments have the same diameter.

[0019] In the above-mentioned embodiment, the ratio of the breaking energy of the inner filament to the breaking energy of a layer filament corresponds to 1.10 to 1.25.

[0020] It is particularly advantageous if the core filament is made of steel of strength class ST or UT and the layer filaments are made of steel of strength class HT. This combination of steel strength classes has proven particularly suitable for successful performance in the plunger test.

[0021] It is particularly advantageous if the steel cord has the construction 0.40 ST + 5 × 0.40 HT or 0.40 UT + 5 × 0.40 HT.

[0022] In another advantageous embodiment of the invention, the core filament has a smaller diameter than that of the layer filaments.

[0023] In the above-mentioned embodiment, the ratio of the breaking energy of the inner filament to the breaking energy of a layer filament corresponds to 1.10 to 1.25 .

[0024] It is particularly advantageous if the core filament is made of steel of strength class HT or ST, and if the layer filaments are made of steel of strength class HT. It has been shown that filaments with a smaller diameter within a steel strength class have a higher breaking energy than filaments with a larger diameter of the same steel strength class. Therefore, in a design where the core filament has a smaller diameter than the layer filaments, both the core filament and the layer filaments can be made of steel of the same strength class. However, it is essential that the aforementioned ratio of the breaking strengths of the inner core filament to the outer layer filaments is maintained.

[0025] It is particularly advantageous if the steel cord has the construction 0.25 HT + 4 × 0.40 HT or 0.25 ST + 4 × 0.40 HT.

[0026] The invention also relates to a pneumatic vehicle tire of radial design with a belt assembly comprising a plurality of belt layers, which contains at least one belt layer according to an aforementioned embodiment.

[0027] The diameters of the steel filaments of certain steel strength classes mentioned in relation to the invention have the breaking strengths listed in the following table: Table Filament diameter / steel strength class Breaking strength [N / mm 2 ] 0.25 / HT 3300 + / - 5% 0.25 / ST 3600 + / - 5% 0.40 / HT 2975 + / - 5% 0.40 / ST 3300 + / - 5% 0.40 / UT 3600 + / - 5%

[0028] The determination of the breaking strength is carried out according to a method well known to the person skilled in the art.

[0029] Further features, advantages and details of the invention are described in more detail with reference to the drawing, which shows a schematic embodiment. Fig. 1 a cross section through a steel cord of construction 1+4 of a belt layer according to the invention.

[0030] The Fig.Figure 1 shows a cross-section through a steel cord of construction 1+4, comprising a core filament 1 with a diameter of 0.25 mm and four layer filaments 2 with a diameter of 0.40 mm in contact with the outer surface. The layer filaments 2 are twisted together around the core filament 1 in a known manner. The twist pitch of the layer filaments 2 is from 10 mm to 25 mm, preferably in the order of 17.5 mm.

[0031] The core filament 1 is made of steel of strength class HT, whereby the core filament with a diameter of 0.25 mm has a tensile strength of approx. 3300 N / mm 2 Each layer filament 2 is a steel filament of strength class HT, whereby for each layer filament with a diameter of 0.40 mm a tensile strength of approximately 2975 N / mm 2 The ratio of the breaking energy of core filament to layer filament is 1.11.

[0032] The core filament 1 and the layer filaments 2 are not pre-formed and can therefore be viewed as circles in cross-section. The core filament 1 has a diameter D1 of 0.25 mm. The layer filaments 2 all have matching diameters D2 of 0.40 mm. With regard to the diameter ratios D1:D2, the layer filaments 2 and the core filament 1 are matched to one another such that the diameter D1 of the core filament 1 is 57.5% to 67.5%, in particular 62.5%, of the diameter D2 of the layer filaments 2. The cord diameter D K should be 0.98 mm to 1.1 mm, especially 1.05 mm.

[0033] The steel cord has an open construction in which the layer filaments 2 are in contact with the core filament 1, but ideally do not touch each other. The layer filaments 2 can therefore all be spaced apart by a certain distance, but it is also possible for some of the intended layer filaments 2, for example, two layer filaments 2, to touch each other. Fig. 1 are the mutual distances A N1 to A N4 of the layer filaments 2, which are determined at those points where the mutual distance between the adjacent layer filaments 2 is the smallest. The mutual distances A N1 to A N4 can be of different sizes. At the mentioned points with the smallest mutual distance A N1 to A N4straight lines drawn in the cord cross-section can be considered as chords of a circle of diameter D0, where D0 is determined according to equation I below as follows: D0=(D1+D2)×cos(360° / 2N)=(D1+D2)×cos(360° / 8) with D1: diameter of the core filament, D2: Diameter of the layer filaments and N = 4.

[0034] The average distance A, calculated as an arithmetic mean NM of the layer filaments 2 can be determined according to equation II: ANM=avg(AN1,…AN4)=[(D1+D2)×sin(360° / 8)]−D2

[0035] Equations I and II are only valid for a uniform arrangement of the layer filaments 2 around the core filament 1, but for an uneven arrangement with different mutual distances A N1 to A N4 , as in Fig.1, there is a slight inaccuracy which can, however, be ignored.

[0036] A certain openness O of the second layer, the layer filaments 2, i.e., an arrangement of as many layer filaments 2 as possible at certain mutual distances, is important to ensure good penetration of the rubber material into the spaces between the layer filaments 2, thus fixing the core filament 1 against displacement. In this context, an openness O of the layer filaments 2 is defined, which is determined from equation III: O[%]=N×ANM / π×D0=4×ANM / π×D0

[0037] The openness O for steel cords designed according to the invention should be between 10% and 25%. If the openness O is below 10%, sufficient rubber penetration between the layer filaments 2, which is necessary for good fixation of the core filament 1, is not possible. This creates a risk of displacement of the core filament 1 and increases the susceptibility of the steel cord to corrosion. If the openness exceeds 25%, the cord stiffness relative to the outer diameter deteriorates for a constant number of cords per decimeter (epdm, "ends per decimeter") in a belt ply. This impairs the abrasion performance of the tire tread. If, as a countermeasure, the number of cords per decimeter of the belt ply were to be increased, i.e., the cord spacing were to be reduced, the belt durability would be reduced. List of reference numbers 1 core filament 2 layer filament A N1 Distance A N2 Distance A N3 Distance A N4 Distance D0 diameter D1 diameter D2 diameter D K Cord diameter O openness

Claims

[1] Belt ply for a pneumatic vehicle tire, in particular for a commercial vehicle tire, wherein the belt ply comprises steel cords of construction 1+N, with N=4 or N=5 with a single core filament (1) and four or five layer filaments (2), wherein the layer filaments (2) all touch the core filament (1) on the outside and have the same diameter (D2), wherein the cord construction is an open cord construction, characterized by that the ratio of the breaking energy of the core filament (1) to the breaking energy of a layer filament (2) corresponds to 1.1 to 1.

5. [2] Belt layer according to claim 1, characterized by that the core filament (1) and the layer filaments (2) have the same diameter. [3] Belt layer according to claim 1 or 2, characterized by that the ratio of the breaking energy of the core filament (1) to the breaking energy of a layer filament (2) is 1.10 to 1.

25. [4] Belt layer according to one or more of the preceding claims, characterized bythat the core filament (1) is made of steel of strength class ST or UT and that the layer filaments (2) are made of steel of strength class HT. [5] Belt layer according to claim 4, characterized by that the steel cord has the construction 0.40 ST + 5 × 0.40 HT or 0.40 UT + 5 × 0.40 HT. [6] Belt layer according to claim 1, characterized by that the core filament (1) has a smaller diameter (D1) than the layer filaments (2). [7] Belt layer according to claim 6, characterized by that the ratio of the breaking energy of the core filament (1) to the breaking energy of a layer filament (2) is 1.10 to 1.

25. [8] Belt layer according to claim 6 or 7, characterized by that the core filament (1) is made of steel of strength class HT or ST and that the layer filaments (2) are made of steel of strength class HT. [9] Belt layer according to claim 8, characterized bythat the steel cord has the construction 0.25 HT + 4 × 0.40 HT or 0.25 ST + 4 × 0.40 HT. [10] Pneumatic vehicle tire of radial design with a belt assembly comprising a plurality of belt layers, which contains at least one belt layer according to one or more of claims 1 to 9.

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