Pneumatic tire

Abstract

Provided is a pneumatic tire of which weight and rolling resistance can be reduced while any growth in the diameter of the tire is suppressed and the durability of a belt layer is satisfactorily maintained. A pneumatic tire comprising a tread part 1, a side wall part 2, and bead parts 3, the pneumatic tire being such that a carcass layer 4 is mounted between the pair of bead parts 3, a plurality of belt layers 7 are arranged on the outer-peripheral side of the carcass layer 4 in the tread part 1, and a belt cover layer 8 is arranged on the outer-peripheral side of the belt layer 7, wherein: steel cords having a 1×2 structure are used as belt cords of the belt layer 7; a steel cord amount A, which is calculated as the product of the cross-sectional area S of the steel cords (mm2 / cord) and the end count E of the steel cords per 50 mm width (cords / 50 mm), is within the range of 5.0-7.0; the thickness of the belt layer 7 at a tire central position CL is within the range of 0.8-1.0 mm; and the belt cover layer 8 is a single or double edge cover layer that locally covers the tire-width-direction edge parts of the belt layer 7.

Description

pneumatic tires

[0001] The present invention relates to a pneumatic tire having a belt layer and a belt cover layer in the tread portion, and more specifically to a pneumatic tire that enables weight reduction and reduced rolling resistance while suppressing radial growth of the tire and maintaining good durability of the belt layer.

[0002] A commonly known structure of a pneumatic tire is one in which a carcass layer is mounted between a pair of bead portions, multiple belt layers including belt cords inclined relative to the tire circumferential direction are arranged on the outer peripheral side of the carcass layer in the tread portion, and a belt cover layer including cover cords oriented in the tire circumferential direction is arranged on the outer peripheral side of the belt layers.

[0003] In the pneumatic tire described above, in order to reduce the weight and rolling resistance, it has been considered to make the belt layer thinner by making the belt cord thinner (see, for example, Patent Document 1). However, if the interlaminar rubber of the belt layer decreases as the gauge of the belt layer becomes thinner, separation of the belt layer becomes more likely to occur, and the durability of the belt layer decreases.

[0004] In addition, the belt cover layer is generally provided by combining a full cover layer that covers the entire width of the belt layer and an edge cover layer that locally covers the edge portion of the belt layer in the tire width direction, but for example, excluding the full cover layer is advantageous from the viewpoint of weight reduction. However, if there is no full cover layer that covers the center portion of the belt layer, there is a risk that radial growth will occur in the center portion of the tire as the tire runs.

[0005] Japanese Patent Application Publication No. 2013-39886

[0006] An object of the present invention is to provide a pneumatic tire that can suppress radial growth of the tire, maintain good durability of the belt layers, and achieve weight reduction and reduced rolling resistance.

[0007] In order to achieve the above object, the pneumatic tire of the present invention comprises a tread portion extending in the tire circumferential direction to form an annular shape, a pair of sidewall portions disposed on both sides of the tread portion, and a pair of bead portions disposed radially inward of the sidewall portions, a carcass layer is fitted between the pair of bead portions, a plurality of belt layers including belt cords inclined with respect to the tire circumferential direction are disposed on the outer peripheral side of the carcass layer in the tread portion, and a belt cover layer including cover cords oriented in the tire circumferential direction is disposed on the outer peripheral side of the belt layer, in which steel cords having a 1x2 structure are used as belt cords of the belt layer, and a cross-sectional area S (mm 2 a steel cord amount A calculated as the product of the steel cord count E (pieces / 50 mm) per 50 mm width in a direction perpendicular to the longitudinal direction of the steel cord and the steel cord length (pieces / 50 mm) is in the range of 5.0 to 7.0, the thickness of each belt layer at the tire center is in the range of 0.8 mm to 1.0 mm, and the belt cover layer is one or two edge cover layers that locally cover the edge portions of the belt layer in the tire width direction.

[0008] The inventors have found that steel cords with a tight twist and high tensile modulus, such as those in a 1x2 structure, are advantageous in reducing the gauge of the belt layer, and further found that by combining a belt layer using steel cords with a 1x2 structure with a belt cover layer consisting only of an edge cover layer, it is possible to maximize the advantages of both, which led to the present invention.

[0009] That is, in the present invention, steel cords having a 1x2 structure are used as the belt cords of the belt layer, and the steel cord amount A is set in the range of 5.0 to 7.0. Therefore, even if the belt layer is made thinner, separation is unlikely to occur in the belt layer, and the durability of the belt layer can be maintained at a good level. Furthermore, even if a belt cover layer consisting only of an edge cover layer is adopted, the steel cords having a 1x2 structure used in the belt layer have a high tensile modulus, so tire radial growth can be suppressed. As a result, the combination of a thin-gauge belt layer and a belt cover layer consisting only of an edge cover layer makes it possible to reduce the weight of a pneumatic tire and its rolling resistance. Moreover, by having the steel cord amount A in the above range, sufficient plunger strength can be ensured. Plunger strength refers to the strength measured in a plunger test (see, for example, JIS-D4230 (1998): Section 6.1 "Tire Strength (Fracture Energy) Test"), in which a plunger of a predetermined size is pressed against the center of the tread to measure the fracture energy when the tire breaks.

[0010] In the present invention, the breaking stress of the steel cords used in the belt layer is preferably 3500 MPa or more. When the breaking stress of the steel cords is in the above range, the plunger strength can be increased.

[0011] In the present invention, the filament diameter of the steel cord used in the belt layer is preferably in the range of 0.25 mm to 0.30 mm, which allows the belt layer to be made thinner in gauge while ensuring sufficient plunger strength, thereby achieving weight reduction and reduced rolling resistance.

[0012] Fig. 1 is a meridian cross-sectional view showing a pneumatic tire according to an embodiment of the present invention. Fig. 2 is a plan view showing a belt layer and a belt cover layer of the pneumatic tire of Fig. 1. Fig. 3 is an enlarged cross-sectional view showing the belt layer of the pneumatic tire of Fig. 1.

[0013] The present invention will be described in detail below with reference to the accompanying drawings. Figures 1 to 3 show a pneumatic tire according to an embodiment of the present invention. In Figure 1, CL indicates the tire center position.

[0014] As shown in FIG. 1, the pneumatic tire of this embodiment includes a tread portion 1 extending circumferentially in a ring shape, a pair of sidewall portions 2, 2 disposed on both sides of the tread portion 1, and a pair of bead portions 3, 3 disposed radially inward of the sidewall portions 2.

[0015] A carcass layer 4 is mounted between the pair of bead portions 3, 3. This carcass layer 4 includes a plurality of carcass cords extending in the tire radial direction, and is folded back from the inside to the outside of the tire around a bead core 5 disposed in each bead portion 3. Organic fiber cords such as polyester are preferably used as the carcass cords of the carcass layer 4. A bead filler 6 made of a rubber composition and having a triangular cross section is disposed on the outer periphery of the bead core 5.

[0016] Meanwhile, multiple belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1 (see FIG. 2). These belt layers 7 include multiple belt cords that are inclined with respect to the tire circumferential direction, and are arranged so that the belt cords cross each other between the layers. The multiple belt layers 7 include a belt layer 7A located on the innermost side in the tire radial direction and a belt layer 7B located outside the belt layer 7A, and the width of the belt layer 7A is wider than the width of the belt layer 7B. In the belt layers 7, the inclination angle of the belt cords with respect to the tire circumferential direction is set to be in the range of 10° to 40°, for example.

[0017] As shown in FIG. 3, a steel cord having a 1x2 structure is used as the belt cord C of the belt layer 7. A steel cord having a 1x2 structure has two filaments tightly twisted together. The cross-sectional area S (mm 2The steel cord amount A (A=S×E) calculated as the product of the number of steel cords per 50 mm width E (pieces / 50 mm) in the direction perpendicular to the longitudinal direction of the steel cord is 5.0 to 7.0 (mm 2 / 50 mm). This steel cord amount A is applied to each of the belt layers 7. The thickness Gc of each belt layer 7 at the tire center position CL is set to a range of 0.8 mm to 1.0 mm.

[0018] A belt cover layer 8 is disposed on the outer periphery of the belt layer 7, with the aim of improving high-speed durability. The belt cover layer 8 does not include a full cover layer that covers the entire width of the belt layer 7, but includes only one or two edge cover layers that locally cover the edge portions of the belt layer 7 in the tire width direction. The edge cover layers cover the edge portions of all belt layers on each side of the tire center position CL. In the illustrated example, the outer end of the edge cover layer is located outward in the tire width direction from the edge of the belt layer 7A, and the inner end of the edge cover layer is located inward in the tire width direction from the edge of the belt layer 7B. The belt cover layer 8 can be formed, for example, by spirally winding a strip material in the tire circumferential direction, in which at least one cover cord is aligned and coated with coating rubber. Organic fiber cords such as nylon and polyester are preferably used as the cover cord of the belt cover layer 8.

[0019] In the pneumatic tire described above, steel cords having a 1x2 structure are used as the belt cords C of the belt layer 7, and the steel cord amount A is set in the range of 5.0 to 7.0. Therefore, even if the interlayer rubber thickness Gi (see FIG. 3) of the belt layer 7 decreases as the gauge of the belt layer 7 becomes thinner, separation is unlikely to occur in the belt layer 7, and the durability of the belt layer 7 can be maintained at a high level. Furthermore, even if a belt cover layer 8 consisting only of an edge cover layer is adopted, the steel cords having a 1x2 structure used in the belt layer 7 have a high tensile modulus, which can suppress tire radial growth. As a result, the combination of a thin-gauge belt layer 7 and a belt cover layer 8 consisting only of an edge cover layer can reduce the weight of the pneumatic tire and its rolling resistance. Furthermore, by setting the steel cord amount A within the above range, sufficient plunger strength can be ensured.

[0020] Here, if the steel cord amount A of the belt layer 7 is less than 5.0 mm, the durability of the belt layer 7 is improved, but the insufficient rigidity of the belt layer 7 results in increased radial growth of the tire and reduced plunger strength. Conversely, if the steel cord amount A of the belt layer 7 is greater than 7.0 mm, radial growth is suppressed and plunger strength is increased, but the durability of the belt layer 7 is reduced and the weight reduction effect is reduced. Furthermore, if the thickness Gc of the belt layer 7 at the tire center position CL is less than 0.8 mm, the rigidity of the belt layer 7 is increased and radial growth is suppressed, but the durability of the belt layer 7 is reduced. Conversely, if the thickness Gc of the belt layer 7 at the tire center position CL is greater than 1.0 mm, the durability of the belt layer 7 is improved, but the weight reduction effect is reduced.

[0021] In the above pneumatic tire, the breaking stress of the steel cords used in the belt layer 7 is preferably 3500 MPa or more. Having the breaking stress of the steel cords in the above range can increase plunger strength. In particular, it is desirable that the breaking stress of the steel cords used in the belt layer 7 be in the range of 3500 MPa to 4000 MPa. The breaking stress of the steel cord is the value obtained by dividing the strength at cord break by the cross-sectional area of ​​the steel cord.

[0022] In the pneumatic tire, the filament diameter of the steel cord used in the belt layer 7 is preferably in the range of 0.25 mm to 0.30 mm. This allows the belt layer 7 to have a thin gauge while ensuring sufficient plunger strength, thereby reducing weight and rolling resistance.

[0023] In a pneumatic tire having a tire size of 195 / 65R15 and including a tread portion, a pair of sidewall portions, and a pair of bead portions, with a carcass layer mounted between the pair of bead portions, with multiple belt layers disposed on the outer peripheral side of the carcass layer in the tread portion, and a belt cover layer disposed on the outer peripheral side of the belt layer, tires were manufactured as a conventional example, comparative examples 1 to 8, and examples 1 to 7, with the belt layer specifications (cord structure, cord diameter, cord cross-sectional area S, thickness at the tire center Gc, interlayer rubber thickness Gi, cord end count E, steel wire amount A, cord breaking stress, total cord strength) and the belt cover layer specifications (presence or absence of full cover layer, presence or absence of edge cover layer) set as shown in Tables 1 and 2. In Tables 1 and 2, the total cord strength of the belt layer is an index value with the conventional example being 100.

[0024] These test tires were evaluated for weight, rolling resistance, diameter growth, plunger strength, and durability of the belt layer by the following evaluation methods. The results are shown in Tables 1 and 2.

[0025] Weight: For each test tire, the weight of five tires was measured and the average value was calculated. The evaluation results were expressed as an index with the conventional tire being set at 100. The smaller the index value, the lighter the tire.

[0026] Rolling resistance: Each test tire was mounted on a wheel with a rim size of 15x6J, and the tire was inflated to 200 kPa. The tire was mounted on a drum testing machine equipped with a drum having a smooth steel surface and a diameter of 1707 mm. A load equivalent to 85% of the maximum load capacity at the above air pressure as listed in the 1998 edition of the JATMA Yearbook was applied to the test tire, and the tire was pressed against the drum. The tire was then run at a speed of 80 km / h, and the rolling resistance was measured. The evaluation results were expressed as an index, with the conventional example being set at 100. The smaller the index value, the smaller the rolling resistance.

[0027] Diameter growth: Each test tire was mounted on a wheel with a rim size of 15x6J, inflated to 200 kPa, and mounted on a drum testing machine equipped with a drum having a smooth steel surface and a diameter of 1707 mm. A load equivalent to 88% of the maximum load capacity at the above air pressure as stated in the 1998 edition of the JATMA Yearbook was applied to the test tire, and the tire was pressed against the drum. The tire was then run for 20,000 km at a speed of 120 km / h. After that, the tire outer diameter and remaining groove depth at the tire equator were measured, and the diameter growth at the groove bottom was calculated. The evaluation results were expressed as an index, with the conventional example being set at 100. The smaller the index value, the smaller the diameter growth.

[0028] Plunger strength: A plunger test was carried out on each test tire in accordance with JIS-D4230 (1998): Section 6.1 "Tire strength (breaking energy) test." The evaluation results were indicated as "OK" when the plunger strength was equal to or greater than the specified value, and as "NG" when the plunger strength was less than the specified value.

[0029] Durability of Belt Layer: Each test tire was mounted on a wheel with a rim size of 15x6J, and the internal pressure was 280 kPa and oxygen was sealed in. Each test tire was stored in a chamber maintained at 70°C for two weeks, after which the internal oxygen was released and air was filled to 170 kPa. Each pretreated test tire was mounted on a drum testing machine equipped with a 1707 mm diameter drum made of smooth steel with a drum surface. The ambient temperature was controlled to 38°C ± 3°C, the speed was set to 50 km / h, the slip angle was set to 0° ± 3°, and the load was set to 70% ± 40% of the JATMA maximum load. The load and slip angle were fluctuated with a 0.83 Hz square wave. After running, each test tire was cut open, and the widthwise length of separation occurring at the widthwise end of the belt layer was measured. The evaluation results were shown in three stages: "good" when the amount of separation was 3 mm or less, "passable" when the amount of separation was more than 3 mm and 5 mm or less, and "poor" when the amount of separation was more than 5 mm. An evaluation result of "good" or "passable" means that sufficient durability was obtained, and "good" means that particularly excellent durability was exhibited.

[0030]

[0031]

[0032] As can be seen from Tables 1 and 2, compared to the conventional tires, the tires of Examples 1 to 7 were able to suppress radial growth and maintain good durability of the belt layer while achieving weight reduction and reduced rolling resistance. On the other hand, in the tires of Comparative Examples 1 to 3, the belt cover layer was composed only of an edge cover layer, and steel cords having a 2+2 structure were used in the belt layer, so the effects of weight reduction and reduced rolling resistance were small and the radial growth was large. In the tire of Comparative Example 4, the thickness Gc of the belt layer at the tire center was too large, so the effects of weight reduction and reduced rolling resistance were not necessarily sufficient. In the tire of Comparative Example 5, the thickness Gc of the belt layer at the tire center was too small, so the durability of the belt layer was reduced. In the tire of Comparative Example 6, the steel cord amount A was too small, so the rigidity of the belt layer was insufficient, resulting in large radial growth of the tire and reduced plunger strength. In the tire of Comparative Example 7, the steel cord amount A was too large, so the durability of the belt layer was reduced. In the tire of Comparative Example 8, the durability of the belt layer was reduced because the tire did not have a belt cover layer.

[0033] REFERENCE SIGNS LIST 1 tread portion 2 sidewall portion 3 bead portion 4 carcass layer 5 bead core 6 bead filler 7, 7A, 7B belt layer 8 belt cover layer CL tire center position (tire equator)

Claims

1. A pneumatic tire comprising a tread portion extending in the circumferential direction of the tire and forming an annular shape, a pair of sidewall portions disposed on both sides of the tread portion, and a pair of bead portions disposed radially inward of the sidewall portions, with a carcass layer mounted between the pair of bead portions, with multiple belt layers including belt cords inclined relative to the circumferential direction of the tire disposed on the outer circumferential side of the carcass layer in the tread portion, and a belt cover layer including cover cords oriented in the circumferential direction of the tire disposed on the outer circumferential side of the belt layer, wherein steel cords having a 1x2 structure are used as the belt cords of the belt layer, and the cross-sectional area S (mm 2 a steel cord amount A calculated as the product of the number of steel cords (number of steel cords per 50 mm) and the end count E (number of steel cords / 50 mm) of the steel cords per 50 mm width in a direction perpendicular to the longitudinal direction of the steel cords is in the range of 5.0 to 7.0, the thickness of each of the belt layers at the tire center is in the range of 0.8 mm to 1.0 mm, and the belt cover layer is a single-layer or double-layer edge cover layer that locally covers the edge portions of the belt layer in the tire width direction.

2. The pneumatic tire according to claim 1, wherein the steel cord used in the belt layer has a breaking stress of 3500 MPa or more.

3. A pneumatic tire according to claim 1 or 2, characterized in that the filament diameter of the steel cord used in the belt layer is in the range of 0.25 mm to 0.30 mm.

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