Pneumatic tire

Abstract

To provide a pneumatic tire capable of reducing rolling resistance by weight reduction while excellently maintaining durability.SOLUTION: A pneumatic tire comprising a tread portion 1, sidewall portions 2, and bead portions 3, wherein a carcass layer 4 is mounted between the pair of bead portions 3, a plurality of belt layers 7 are disposed on an outer circumferential side of the carcass layer 4 in the tread portion 1, and a tread rubber layer 11 is disposed on an outer circumferential side of the belt layers 7 so as to abut against the belt layers 7, the cord count of the steel cords per widthwise 50mm in a direction orthogonal to the longitudinal direction of the steel cords is in a range of 35 cords / 50mm to 58 cords / 50mm, the interlayer rubber thickness Gc at the 2mm portion of the belt layer 7 is in a range of 0. 6mm to 0. 9mm, and the interlayer rubber thickness Ge at the edge portions of the belt layer 7 is greater than or equal to 0. center.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a pneumatic tire having a belt layer in the tread portion, and more particularly to a pneumatic tire that enables reduction in rolling resistance by reducing weight while maintaining good durability. [Background technology]

[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 order to reduce the weight and costs of pneumatic tires such as those described above, it has been considered to make the belt layers thinner by thinning the belt cords (see, for example, Patent Document 1). However, if the interlaminar rubber of the belt layers decreases as the belt layers are made thinner, separation of the belt layers becomes more likely to occur, resulting in a decrease in the durability of the pneumatic tire. In particular, in pneumatic tires that do not have a belt cover layer disposed on the outer periphery of the belt layers, the adverse effects of making the belt layers thinner are more pronounced. Furthermore, if there is no belt cover layer, there is also concern that the durability of the pneumatic tire will decrease due to radial growth. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-39886 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a pneumatic tire that can reduce rolling resistance by reducing weight while maintaining good durability. [Means for solving the problem]

[0006] 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 arranged on both sides of the tread portion, and a pair of bead portions arranged on the tire radially inward side of the sidewall portions, a carcass layer is mounted between the pair of bead portions, a plurality of belt layers including belt cords inclined with respect to the tire circumferential direction are arranged on the outer peripheral side of the carcass layer in the tread portion, and a tread rubber layer is arranged on the outer peripheral side of the belt layer so as to abut against the belt layer, The belt layer is characterized in that a steel cord having a 1x2 structure is used as the belt cord, the end count of the steel cord per 50 mm width in a direction perpendicular to the longitudinal direction of the steel cord is in the range of 35 / 50 mm to 58 / 50 mm, the interlayer rubber thickness at the center part of the belt layer is in the range of 0.2 mm to 0.6 mm, and the interlayer rubber thickness at the edge part of the belt layer is 0.9 mm or more. [Effects of the Invention]

[0007] The inventors have conducted extensive research into pneumatic tires that have a thin-gauge belt layer but no belt cover layer, and as a result have discovered that by optimizing the end count of the 1x2 steel cords that make up the belt layer and the thickness of the interlayer rubber in each part of the belt layer, it is possible to reduce weight and the rolling resistance while maintaining good durability, which led to the present invention.

[0008] That is, in the present invention, steel cords having a 1x2 structure are used as the belt cords of the belt layer, the end count of the steel cords is in the range of 35 cords / 50 mm to 58 cords / 50 mm, the interlayer rubber thickness at the center portion of the belt layer is in the range of 0.2 mm to 0.6 mm, and the interlayer rubber thickness at the edge portion of the belt layer is 0.9 mm or more, thereby making it possible to reduce rolling resistance by reducing the weight while maintaining good durability of the pneumatic tire.

[0009] In the present invention, it is preferable that the end count of the steel cords used in the belt layers is in the range of 43 / 50 mm to 58 / 50 mm, and the interlayer rubber thickness at the center of the belt layers is in the range of 0.2 mm to 0.4 mm, thereby achieving both durability and lightweight at a higher level.

[0010] In the present invention, the tensile strength of the steel cords used in the belt layer is preferably 3400 MPa or more, which allows the steel cords to have a smaller diameter and thus achieve further weight reduction.

[0011] In the present invention, the filament diameter of the steel cord used in the belt layer is preferably 0.22 mm or more, which allows the durability of the pneumatic tire to be maintained at a good level.

[0012] In the present invention, it is preferable that the ratio of the interlayer rubber thickness at the edge portions of the belt layers to the interlayer rubber thickness at the center portions of the belt layers is equal to or greater than 2. This makes it possible to achieve both durability and lightweight at a higher level. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a meridian cross-sectional view showing a pneumatic tire according to an embodiment of the present invention. [Figure 2] 2 is an enlarged cross-sectional view showing a main part of a belt layer of the pneumatic tire of FIG. 1. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings, in which: Figures 1 and 2 show a pneumatic tire according to an embodiment of the present invention.

[0015] 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 arranged on both sides of the tread portion 1, and a pair of bead portions 3, 3 arranged radially inward of the sidewall portions 2.

[0016] A carcass layer 4 is mounted between a 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.

[0017] Meanwhile, multiple belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. 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.

[0018] As shown in FIG. 2, 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 end count of the steel cord per 50 mm width in a direction perpendicular to the longitudinal direction of the steel cord used in the belt layer 7 is set to a range of 35 / 50 mm to 58 / 50 mm. This end count is applied to each belt layer 7. The interlayer rubber thickness Gc at the center of the belt layer 7 is set to a range of 0.2 mm to 0.6 mm, and the interlayer rubber thickness Ge at the edge of the belt layer 7 is set to 0.9 mm or more. To adjust the difference between the interlayer rubber thickness Gc at the center of the belt layer 7 and the interlayer rubber thickness Ge at the edge, an edge rubber layer 8 is inserted between the belt layers 7 at the edge of the belt layer 7. The interlayer rubber thicknesses Gc and Ge are the thicknesses of the rubber portions interposed between the belt cord C included in the belt layer 7A and the belt cord C included in the belt layer 7B. The average value of the interlayer rubber thickness Gc in the center portion corresponding to 80% of the central side of the maximum width Wb of the belt layer 7 satisfies the above range, and the maximum value of the interlayer rubber thickness Ge in the edge portion outside 80% of the central side of the maximum width Wb of the belt layer 7 satisfies the above range.

[0019] A tread rubber layer 11 is disposed on the outer peripheral side of the belt layer 7 so as to abut against the belt layer 7. That is, in this pneumatic tire, a belt cover layer including reinforcing cords is not disposed on the outer peripheral side of the belt layer 7. The tread rubber layer 11 may have a single layer structure made of a cap tread rubber layer, or may have a laminated structure including a cap tread rubber layer and an under tread rubber layer.

[0020] In the pneumatic tire described above, steel cords having a 1x2 structure are used as the belt cords C of the belt layer 7, the end count of the steel cords is in the range of 35 / 50mm to 58 / 50mm, the interlayer rubber thickness Gc at the center portion of the belt layer 7 is in the range of 0.2mm to 0.6mm, and the interlayer rubber thickness Ge at the edge portions of the belt layer 7 is 0.9mm or more. This makes it possible to reduce the weight and cost of the pneumatic tire while maintaining good durability, and also to reduce rolling resistance.

[0021] Here, if the end count of the steel cords used in the belt layer 7 is less than 35 cords / 50 mm, the reinforcing effect decreases, and the effect of suppressing outer diameter growth also decreases, resulting in insufficient durability. Conversely, if it is more than 58 cords / 50 mm, the weight of the belt layer 7 increases, and the effect of weight reduction becomes insufficient. In particular, it is desirable that the end count of the steel cords used in the belt layer 7 is in the range of 43 cords / 50 mm to 58 cords / 50 mm. This makes it possible to achieve both durability and weight reduction at a higher level.

[0022] Furthermore, if the interlayer rubber thickness Gc at the center of the belt layer 7 is less than 0.2 mm, peeling of the rubber occurs during rolling of the belt member, which reduces durability. Conversely, if it is more than 0.6 mm, the weight reduction effect is insufficient. In particular, the interlayer rubber thickness Gc at the center of the belt layer 7 is preferably in the range of 0.2 mm to 0.4 mm. This allows for a higher level of both durability and weight reduction. On the other hand, if the interlayer rubber thickness Ge at the edge of the belt layer 7 is less than 0.9 mm, separation of the belt layer 7 is likely to occur, resulting in insufficient durability. In particular, the interlayer rubber thickness Ge at the edge of the belt layer 7 is preferably in the range of 0.9 mm to 1.5 mm. This allows for a higher level of both durability and weight reduction. In addition, the ratio (Ge / Gc) of the interlayer rubber thickness Ge at the edge of the belt layer 7 to the interlayer rubber thickness Gc at the center of the belt layer 7 is preferably 2 or more. Satisfying such a relationship is also effective in achieving both durability and lightweight design at a higher level.

[0023] In the above pneumatic tire, the tensile strength of the steel cords used in the belt layer 7 is preferably 3400 MPa or more. This allows the steel cords to be made thinner, thereby achieving further weight reduction. In particular, the tensile strength of the steel cords used in the belt layer 7 is preferably in the range of 3500 MPa to 4500 MPa. The tensile strength of the steel cord is the value obtained by dividing the strength at cord break by the cross-sectional area of ​​the steel cord.

[0024] In the above pneumatic tire, the filament diameter of the steel cord used in the belt layer 7 is preferably 0.22 mm or more. This allows the durability of the pneumatic tire to be maintained at a good level. In particular, the filament diameter of the steel cord used in the belt layer 7 is preferably in the range of 0.22 mm to 0.40 mm, and more preferably in the range of 0.22 mm to 0.35 mm. The upper limit of the filament diameter is limited from the viewpoint of weight reduction.

[0025] The above-described pneumatic tire has a structure including a thin-gauge belt layer 7 but excluding a belt cover layer, thereby reducing rolling resistance while maintaining good durability, and thus contributing greatly to the environment. To further enhance such environmental contribution, it is preferable to use electric furnace steel, rather than blast furnace steel, as the material for the steel cords used in the belt layer 7. Since electric furnace steel is made from recycled materials, the use of electric furnace steel can further reduce the burden on the environment. [Example]

[0026] In a pneumatic tire having a tire size of 195 / 70R14, which is provided with a tread portion, a pair of sidewall portions, and a pair of bead portions, a carcass layer is mounted between the pair of bead portions, and two belt layers are arranged on the outer peripheral side of the carcass layer in the tread portion, tires of a conventional example, comparative examples 1 to 3, and examples 1 to 9 were manufactured with the belt layer specifications (cord structure, cord count, interlayer rubber thickness Gc at the center portion, interlayer rubber thickness Ge at the edge portions, Ge / Gc, cord material, cord tensile strength) set as shown in Table 1.

[0027] These test tires were evaluated for durability, rolling resistance, and environmental friendliness using the following evaluation methods, and the results are shown in Table 1.

[0028] Durability: Each test tire was mounted on a 14x5.0J rim wheel, sealed with oxygen at 350 kPa, and stored in a chamber maintained at 80°C for five days. The oxygen was then released and the tire was filled with air at 200 kPa. Each pretreated test tire was mounted on a drum testing machine equipped with a 1707 mm diameter drum made of smooth steel and controlled at an ambient temperature of 38°C ± 3°C. The tire was run for 24 hours under conditions of 81 km / h speed and 79% of the JATMA maximum load. After the run, the speed was increased by 10 km / h and the tire was run for another 24 hours. This cycle of increasing speed and running for 24 hours was repeated without interruption, and the running distance until the tire failed was measured. The evaluation results were expressed as an index, with the conventional tire being set at 100. A higher index value indicates better durability.

[0029] Rolling resistance: In accordance with JIS-D4234, each test tire was mounted on a wheel with a rim size of 14 x 5.0J, the tire was inflated to 200 kPa, and the wheel was fitted to a drum testing machine equipped with a drum with 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 listed in the JATMA Yearbook was applied to the test tire, pressing it against the drum, while the tire was driven at a speed of 80 km / h, and 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 lower the rolling resistance.

[0030] Environmental contribution: Each test tire was evaluated for its overall environmental contribution on a scale of 1 to 5, taking into account the rolling resistance evaluation value and the steel cord material used in the belt layer. The higher the evaluation score, the greater the environmental contribution.

[0031] [Table 1]

[0032] As can be seen from Table 1, the tires of Examples 1 to 9 were able to reduce rolling resistance by reducing weight while maintaining good durability compared to conventional tires. Furthermore, the tires of Examples 1 to 7 were also preferable from the perspective of environmental contribution. On the other hand, the tire of Comparative Example 1 had insufficient durability because the interlayer rubber thickness Gc at the center portion of the belt layer was too small. The tire of Comparative Example 2 had an excessively large end count of steel cords used in the belt layer, resulting in poor rolling resistance. The tire of Comparative Example 3 had insufficient durability because the interlayer rubber thickness Ge at the edge portion of the belt layer was too small.

[0033] The present disclosure includes the following inventions [1] to [5]. Invention [1] is a pneumatic tire comprising a tread portion extending in the tire circumferential direction and forming an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and a pair of bead portions arranged on the tire radially inward side of these sidewall portions, a carcass layer mounted between the pair of bead portions, a plurality of belt layers including belt cords inclined with respect to the tire circumferential direction arranged on the outer peripheral side of the carcass layer in the tread portion, and a tread rubber layer arranged on the outer peripheral side of the belt layer so as to abut against the belt layer, The pneumatic tire is characterized in that steel cords having a 1x2 structure are used as belt cords of the belt layer, the end count 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 35 / 50 mm to 58 / 50 mm, the interlayer rubber thickness at the center part of the belt layer is in the range of 0.2 mm to 0.6 mm, and the interlayer rubber thickness at the edge part of the belt layer is 0.9 mm or more. Invention [2] is the pneumatic tire according to invention [1], characterized in that the end count of the steel cords used in the belt layer is in the range of 43 / 50 mm to 58 / 50 mm, and the interlayer rubber thickness at the center of the belt layer is in the range of 0.2 mm to 0.4 mm. Invention [3] is the pneumatic tire according to invention [1] or [2], characterized in that the tensile strength of the steel cord used in the belt layer is 3400 MPa or more. Invention [4] is the pneumatic tire according to any one of inventions [1] to [3], characterized in that the filament diameter of the steel cord used in the belt layer is 0.22 mm or more. Invention [5] is a pneumatic tire according to any one of inventions [1] to [4], characterized in that the ratio of the interlayer rubber thickness at the edge portion of the belt layer to the interlayer rubber thickness at the center portion of the belt layer is 2 or more. [Explanation of symbols]

[0034] 1 Tread section 2 Sidewall 3 Bead section 4 carcass layers 5 bead core 6 Bead filler 7, 7A, 7B belt layers 8 Edge rubber layer 11 Tread rubber layer

Claims

1. A pneumatic tire comprising a tread portion extending in the tire circumferential direction 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, a carcass layer mounted between the pair of bead portions, a plurality of belt layers including belt cords inclined with respect to the tire circumferential direction disposed on the outer peripheral side of the carcass layer in the tread portion, and a tread rubber layer disposed on the outer peripheral side of the belt layer so as to abut against the belt layer, a steel cord having a 1x2 structure is used as the belt cord of the belt layer, the end count of the steel cord per 50 mm width in a direction perpendicular to the longitudinal direction of the steel cord is in the range of 35 cords / 50 mm to 58 cords / 50 mm, the interlayer rubber thickness at a center portion of the belt layer is in the range of 0.2 mm to 0.6 mm, and the interlayer rubber thickness at an edge portion of the belt layer is 0.9 mm or more.

2. The pneumatic tire according to claim 1, characterized in that the end count of the steel cords used in the belt layer is in the range of 43 cords / 50 mm to 58 cords / 50 mm, and the interlayer rubber thickness at a center portion of the belt layer is in the range of 0.2 mm to 0.4 mm.

3. 3. The pneumatic tire according to claim 1, wherein the steel cords used in the belt layer have a tensile strength of 3,400 MPa or more.

4. 3. The pneumatic tire according to claim 1, wherein the filament diameter of the steel cord used in the belt layer is 0.22 mm or more.

5. 3. The pneumatic tire according to claim 1, wherein a ratio of the interlayer rubber thickness at the edge portions of the belt layers to the interlayer rubber thickness at the center portions of the belt layers is 2 or more.

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