Pneumatic tires

Abstract

To provide a pneumatic tire capable of suppressing an increase in mas while improving side cut resistance.SOLUTION: A pneumatic tire 1 is equipped with a tread portion 2, a pair of side wall portions 3, a pair of bead portions 4 respectively embedded with bead cores 5, and a toroidal carcass 6 disposed between the pair of bead portions 4. The carcass 6 includes a first ply 11 extending across the pair of bead portions 4, and a second ply 12 that is arranged on the outer side in a tire radial direction of the first ply 11 in the tread portion 2 and extends across the pair of the bead portion 4. The first ply 11 is made of a layer of first cords. The second ply 12 is made of a layer of second cords. The thickness of the second cord is 1.1 to 2.0 times that of the first cord.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a pneumatic tire. [Background technology]

[0002] The following Patent Document 1 describes a pneumatic tire including a first ply and a second ply disposed radially outward of the first ply. The second ply includes a pair of ply pieces each having a side portion extending radially inward from an inner end portion located in the tread portion and a rolled-up portion wound up by a pair of bead cores. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-100307 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned pneumatic tire, the modulus and breaking strength of the first ply are made lower than those of the pair of ply pieces of the second ply, thereby reducing the tire's weight; however, there is still room for improvement in terms of side cut resistance.

[0005] The present invention has been devised in consideration of the above-mentioned circumstances, and has as its main object to provide a pneumatic tire that can suppress an increase in mass while improving side cut resistance performance. [Means for solving the problem]

[0006] The present invention is a pneumatic tire comprising a tread portion, a pair of sidewall portions, a pair of bead portions each having a bead core embedded therein, and a toroidal carcass disposed between the pair of bead portions, the carcass including a first ply extending across the pair of bead portions, and a second ply disposed radially outward of the first ply in the tread portion and extending across the pair of bead portions, the first ply consisting of a layer of a first cord, the second ply consisting of a layer of a second cord, and a thickness of the second cord being 1.1 to 2.0 times that of the first cord.

[0007] In the pneumatic tire according to the present invention, the first ply may include a main body portion extending between the bead cores of the pair of bead portions, and a pair of turn-up portions that are folded back around the bead core from the inside to the outside in the tire axial direction in each of the pair of bead portions.

[0008] In the pneumatic tire according to the present invention, the second ply may include a main body portion extending between the bead cores of the pair of bead portions, and a pair of turn-up portions that are folded back around the bead core from the inside to the outside in the tire axial direction in each of the pair of bead portions.

[0009] In the pneumatic tire according to the present invention, the first cord and the second cord may be organic fiber cords.

[0010] In the pneumatic tire according to the present invention, the number of the second cords arranged per 5 cm of the width of the second ply, that is, second ends, may be less than or equal to the number of the first cords arranged per 5 cm of the width of the first ply, that is, first ends.

[0011] In the pneumatic tire according to the present invention, the second ends may be 0.75 times or more the first ends.

[0012] In the pneumatic tire according to the present invention, the second ends may be equal to the first ends. Effect of the Invention

[0013] By employing the above-described configuration, the pneumatic tire of the present invention can suppress an increase in mass while improving side cut resistance. [Brief description of the drawings]

[0014] [Figure 1] 1 is a tire meridian cross-sectional view including a rotation axis of a pneumatic tire of the present embodiment in a normal state. [Diagram 2] FIG. 2 is a development view of a carcass and a belt layer in a tread portion. [Diagram 3] FIG. 2 is a cross-sectional view taken along line A-A in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. It should be understood that the drawings include exaggerated expressions and expressions different from the dimensional ratio of the actual structure in order to help understand the contents of the invention. Furthermore, the same or common elements are given the same reference numerals throughout the embodiments, and duplicated explanations are omitted. Furthermore, the specific configurations shown in the embodiments and drawings are for understanding the contents of the present invention, and the present invention is not limited to the specific configurations shown in the drawings.

[0016] [Pneumatic tires] FIG. 1 is a tire meridian cross-sectional view including a rotation axis of a pneumatic tire (hereinafter sometimes simply referred to as "tire") 1 of this embodiment in a normal state. In FIG. 1, the dashed dotted line represents the tire equator (equatorial plane) C. The tire 1 of this embodiment is configured for passenger cars. Note that the tire 1 is not limited to passenger cars, and may be configured for heavy loads such as buses and trucks.

[0017] The "normal state" refers to a state in which the tire 1 is mounted on a normal rim (not shown), inflated to normal internal pressure, and no load is applied. In this specification, unless otherwise specified, the dimensions of each part of the tire 1 are values ​​measured in this normal state.

[0018] A "genuine rim" is a rim that is defined for each tire by a standard system that includes the standard on which the tire 1 is based. A genuine rim is, for example, a "standard rim" for JATMA, a "Design Rim" for TRA, and a "Measuring Rim" for ETRTO.

[0019] "Normal internal pressure" is the air pressure that is determined for each tire by each standard in the standard system including the standard on which tire 1 is based. The normal internal pressure is the "maximum air pressure" in the case of JATMA, the maximum value listed in the table "TIRE LOAD LIMITSAT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and the "INFLATION PRESSURE" in the case of ETRTO.

[0020] The tire 1 of this embodiment comprises a tread portion 2, a pair of sidewall portions 3, a pair of bead portions 4 each having a bead core 5, 5 embedded therein, and a toroidal carcass 6 disposed between the pair of bead portions 4.

[0021] A bead apex rubber 8 extending radially outward from the bead core 5 is disposed in the bead portion 4. Furthermore, a belt layer 7 is disposed outside the carcass 6 in the tire radial direction and inside the tread portion 2. Fig. 2 is a development view of the carcass 6 and the belt layer 7 in the tread portion 2.

[0022] [Belt layer] As shown in Figs. 1 and 2, the belt layer 7 includes at least one, in this embodiment, two belt plies, an inner belt ply 7A and an outer belt ply 7B, disposed on the inner and outer sides in the radial direction of the tire.

[0023] 2, the inner belt ply 7A and the outer belt ply 7B are formed by, for example, covering an array of belt cords 7c with a topping rubber 7g. The angle θ3 of each belt cord 7c is set to, for example, 10 to 40 degrees with respect to the tire equator C. Although steel cords are used for the belt cords 7c in this embodiment, highly elastic organic fiber cords such as aromatic polyamide and rayon may also be used.

[0024] [Carcass] As shown in FIG. 1, the carcass 6 includes a first ply 11 and a second ply 12 disposed in the tread portion 2 on the outer side of the first ply 11 in the radial direction of the tire.

[0025] [First Ply] The first ply 11 extends so as to straddle between a pair of bead portions 4. The first ply 11 of the present embodiment includes a main body portion 11A and a pair of turned-up portions 11B.

[0026] The main body portion 11A extends between the bead cores 5 of the pair of bead portions 4. The pair of turn-up portions 11B are turned up around the bead cores 5 of the pair of bead portions 4 from the inside to the outside in the tire axial direction. Such a first ply 11 can increase the rigidity of the tire 1 from the tread portion 2 to the bead portions 4 (including the buttress portion 9 and the sidewall portion 3). Note that, although the first ply 11 of the present embodiment is exemplified as including the main body portion 11A and the pair of turn-up portions 11B, the first ply 11 is not limited to such an embodiment. For example, the first ply 11 may be composed of only the main body portion 11A.

[0027] 2, the first ply 11 is configured as a layer of first cords 11c. The first ply 11 of the present embodiment includes first cords 11c arranged in parallel and a topping rubber 11g that covers the first cords 11c. The first cords 11c are arranged at an angle θ1 of, for example, 75 to 90 degrees with respect to the tire equator C.

[0028] For example, an organic fiber cord or a steel cord may be appropriately used for the first cord 11c. The first cord 11c of the present embodiment is made of an organic fiber cord. For example, nylon, rayon, or aromatic polyamide (nylon in this example) may be used for the organic fiber cord. Such a first cord 11c is useful for improving side cut resistance.

[0029] 3 is a cross-sectional view taken along line A-A in FIG. 1. The first cord 11c of this embodiment is formed by twisting together a plurality of strands 13, 13. The first cord 11c of this embodiment is composed of two strands 13, 13, but may be composed of three or more strands. Each strand 13, 13 has a filament bundle that is first twisted. These strands 13, 13 are then second twisted to form one first cord 11c. The number of first twists and the number of second twists, etc., can be appropriately set in the same manner as in the past.

[0030] [Second Ply] 1, the second ply 12 extends so as to bridge between a pair of bead portions 4. The second ply 12 of the present embodiment includes a main body portion 12A and a pair of folded-up portions 12B.

[0031] The main body portion 12A extends between the bead cores 5 of the pair of bead portions 4. The pair of turn-up portions 12B are turned up around the bead cores 5 of each of the pair of bead portions 4 from the inside to the outside in the tire axial direction. Like the first ply 11, this second ply 12 can increase the rigidity of the tire 1 from the tread portion 2 to the bead portions 4 (including the buttress portions 9 and the sidewall portions 3). Note that, although the second ply 12 of the present embodiment includes the main body portion 12A and the pair of turn-up portions 12B as an example, it may also be composed of only the main body portion 12A.

[0032] It is desirable that the radially outer ends 12t of the pair of turned-up portions 12B are offset from the radially outer ends 11t of the pair of turned-up portions 11B of the first ply 11 in terms of the tire radius. This makes it possible to prevent a large rigidity step from being formed in the sidewall portion 3. The outer end 12t of the second ply 12 in this embodiment is disposed radially inward of the outer end 11t of the first ply 11.

[0033] 2, the second ply 12 is configured as a layer of second cords 12c. The second ply 12 of the present embodiment includes second cords 12c arranged in parallel and a topping rubber 12g that covers the second cords 12c. The second cords 12c are arranged at an angle θ2 of, for example, 75 to 90 degrees with respect to the tire equator C.

[0034] The second cord 12c may be appropriately configured, for example, of an organic fiber cord or a steel cord. The second cord 12c of this embodiment is configured of an organic fiber cord. The organic fiber cord constituting the second cord 12c of this embodiment is the same as the organic fiber cord constituting the first cord 11c. Such a second cord 12c is useful for improving side cut resistance. Note that the organic fiber cord constituting the second cord 12c may be an organic fiber cord different from the first cord 11c (for example, an organic fiber cord having a greater strength than the first cord).

[0035] As shown in FIG. 3, the second cord 12c of this embodiment is formed by twisting together a plurality of strands 14 (two in this example), similar to the first cord 11c.

[0036] The tire 1 of this embodiment can ensure the rigidity from the buttress portion 9 between the tread portion 2 and the sidewall portion 3 shown in FIG. 1 to the sidewall portion 3 by the first ply 11 and the second ply 12. Therefore, the tire 1 of this embodiment can improve the side cut resistance. Furthermore, the tire 1 of this embodiment can reduce the rubber thickness from the buttress portion 9 to the sidewall portion 3 by improving the side cut resistance. As a result, the tire 1 of this embodiment can suppress an increase in the mass of the tire 1 and reduce rolling resistance.

[0037] [Thickness of the first and second cords] In the tire 1 of the present embodiment, in order to further improve the side cut resistance performance, as shown in FIG. 3, the thickness T2 of the second cord 12c is set to 1.1 to 2.0 times the thickness T1 of the first cord 11c.

[0038] In this specification, the thicknesses T1 and T2 are defined as a total fineness (dtex) when the first cord 11c and the second cord 12c are organic fiber cords, whereas when the first cord 11c and the second cord 12c are metal cords (steel cords, etc.), the thicknesses T1 and T2 are defined as a diameter (mm) including the wire bundle.

[0039] In this embodiment, the thickness T2 of the second cord 12c is set to be 1.1 times or more the thickness T1 of the first cord 11c, thereby increasing the rigidity of the second ply 12, which receives a greater shock during running than the first ply 11. This allows the tire 1 to have improved side cut resistance.

[0040] On the other hand, by setting the thickness T2 of the second cord 12c to be 2.0 times or less the thickness T1 of the first cord 11c, it is possible to prevent an unnecessary increase in the mass of the second ply 12. As a result, in this embodiment, an increase in the mass of the tire 1 can be suppressed.

[0041] In this manner, in the tire 1 of the present embodiment, the thickness T2 of the second cord 12c is set to 1.1 to 2.0 times the thickness T1 of the first cord 11c, thereby making it possible to improve the side cut resistance performance and suppress an increase in mass. In order to effectively exert such an effect, the thickness T2 of the second cord 12c is preferably 1.3 times or more and preferably 1.8 times or less the thickness T1 of the first cord 11c.

[0042] The thickness (total fineness) T1 of the first cord 11c and the thickness (total fineness) T2 of the second cord 12c can be set appropriately as long as they satisfy the above-mentioned relationship.

[0043] The thickness (total fineness) T1 of the first cord 11c is desirably set to 2000 to 3200 dtex. By setting the thickness T1 to 2000 dtex or more, the rigidity of the first ply 11 can be maintained, and the side cut resistance performance can be improved. On the other hand, by setting the thickness T1 to 3200 dtex or less, it is possible to prevent the mass of the first ply 11 from increasing more than necessary. From this viewpoint, the thickness T1 is preferably 2200 dtex or more, and preferably 3000 dtex or less.

[0044] The thickness (total fineness) T2 of the second cord 12c is desirably set to 3000 to 4600 dtex. By setting the thickness T2 to 3000 dtex or more, the rigidity of the second ply 12 can be increased, and therefore the side cut resistance performance can be improved. On the other hand, by setting the thickness T2 to 4600 dtex or less, it is possible to prevent the mass of the second ply 12 from increasing more than necessary. From this viewpoint, the thickness T2 is preferably 3200 dtex or more, and preferably 4400 dtex or less.

[0045] [Ends of the 1st and 2nd plies] The first ends, which is the number of the first cords 11c arranged per 5 cm width of the first ply 11, and the second ends, which is the number of the second cords arranged per 5 cm width of the second ply 12, can be set appropriately. The width of the first ply 11 when specifying the ends is measured in a direction perpendicular to the longitudinal direction of the first cords 11c. The width of the second ply 12 when specifying the ends is measured in a direction perpendicular to the longitudinal direction of the second cords 12c.

[0046] If the second ends are larger than the first ends, the mass of the second ply 12 may increase more than necessary, and the mass of the tire 1 may increase. Furthermore, due to the flow of rubber during vulcanization, multiple second cords 12c tend to be inserted between adjacent first cords 11c, 11c in the tire circumferential direction. This reduces the rubber thickness between the first cords 11c and the second cords 12c, and there is a risk that the side cut resistance performance may not be sufficiently improved. From this perspective, it is preferable to set the second ends to be equal to or smaller than the first ends.

[0047] On the other hand, if the second ends are smaller than the first ends unnecessarily, the rigidity of the second ply 12 cannot be sufficiently increased, and the side cut resistance performance may not be sufficiently improved. Furthermore, due to the flow of rubber during vulcanization, multiple first cords 11c tend to be inserted between adjacent second cords 12c, 12c in the tire circumferential direction. This reduces the rubber thickness between the first cords 11c and the second cords 12c, and the side cut resistance performance may not be sufficiently improved. From this perspective, it is desirable to set the second ends to be 0.75 times or more the first ends.

[0048] In order to more effectively exert the above-mentioned action, it is desirable that the second ends are equal to the first ends. As a result, the tire 1 can alternately arrange the first cords 11c and the second cords 12c in the tire circumferential direction due to the rubber flow during vulcanization molding, and it is possible to prevent the rubber thickness between the first cords 11c and the second cords 12c from becoming small. Furthermore, it is possible to achieve a good balance between improving the rigidity of the second ply 12 and suppressing the increase in the mass of the second ply 12. Therefore, the tire 1 of this embodiment can suppress the increase in mass while improving the side cut resistance performance.

[0049] The first ends and the second ends are appropriately set. In this embodiment, the first ends and the second ends are set to 35 to 60 (pieces / 5 cm). By setting the first ends and the second ends to 35 (pieces / 5 cm) or more, the side cut resistance performance can be improved. On the other hand, by setting the first ends and the second ends to 60 (pieces / 5 cm) or less, an increase in the mass of the first ply 11 and the second ply 12 can be suppressed. From this viewpoint, the first ends and the second ends are preferably 40 (pieces / 5 cm) or more, and preferably 56 (pieces / 5 cm) or less.

[0050] In the tire 1 of this embodiment, the outer end 11t of the first ply 11 and the outer end 12t of the second ply 12 can be positioned radially inward of the tire maximum width position M due to the improved side cut resistance performance of the first ply 11 and the second ply 12. This makes it possible to suppress an unnecessary increase in the mass of the first ply 11 and the second ply 12, and therefore to suppress an increase in the mass of the tire 1.

[0051] Although a particularly preferred embodiment of the present invention has been described in detail above, the present invention is not limited to the illustrated embodiment and can be modified and carried out in various forms. EXAMPLES

[0052] [Example A] Pneumatic tires shown in FIG. 1 were prototyped based on the specifications in Table 1 (Examples 1 to 5, Comparative Examples 1 and 2). The side cut resistance and mass of each prototype tire were evaluated. The common specifications and test methods are as follows. The test results are shown in Table 1. Tire size: 265 / 65R18 Rim size: 18×8.0J Internal pressure: 250kPa Buttress thickness: 6.0mm Sidewall thickness: 3.0mm 1st Ply: 1st cord: Nylon (strands: 2) 1st Ends: 48 (pieces / 5cm) 2nd Ply: Second cord: Nylon (strands: 2) 2nd Ends: 48 (pieces / 5cm)

[0053] <Side cut resistance> Each prototype tire was mounted on the rim and inflated to the internal pressure. A pendulum with a weight attached to a wedge-shaped blade was allowed to fall freely onto the sidewall to apply impact, and the energy at which the sidewall was broken was calculated based on the weight's mass and the drop height. The results were expressed as an index, with the energy of Comparative Example 1 being set at 100. The higher the value, the better the result.

[0054] <Weight of tire> The mass of each prototype tire was measured. The results were expressed as an index with the mass of Comparative Example 1 being 100. The smaller the value, the lighter the tire is, and the more the increase in mass is suppressed.

[0055] [Table 1]

[0056] As a result of the test, the pneumatic tire of the example was able to suppress an increase in mass while improving the side cut resistance performance compared to the pneumatic tire of the comparative example.

[0057] [Example B] Pneumatic tires shown in FIG. 1 were prototyped based on the specifications in Table 2 (Example 1, Example 6 to Example 9). Each prototype tire was evaluated for side cut resistance, tire mass, and durability. Common specifications are as described in Example A, except for the specifications in Table 2 and the following specifications. Test methods are as described in Example A, except for the following durability performance. Thickness of the first cord T1 (total fiber count): 2200 (dtex) Thickness of the second cord T2 (total fiber count): 4400 (dtex)

[0058] <Durability> The tire was run under the following conditions using a drum durability tester. Then, based on the running distance until damage occurred to the sidewall, it was evaluated with an index of 100 for Example 1. The higher the value, the better. Note that an index of 90 or more indicates the durability required for a pneumatic tire. Speed: 60km / h Load: 14.35kN

[0059] [Table 2]

[0060] As a result of the test, the pneumatic tires of the examples were able to suppress the increase in mass while improving the side cut resistance performance. Furthermore, the examples 1, 7 and 8, which have a ratio of the first end to the second end within a preferable range, were able to improve the durability performance compared to the other examples. [Explanation of symbols]

[0061] 1. Pneumatic tires 2 Tread section 3 Sidewall 4 Bead section 5 Bead Core 6. Carcass 11 First Ply 12 2nd Ply

Claims

1. A pneumatic tire, A tread portion; A pair of sidewall portions; A pair of bead portions each having a bead core embedded therein; a toroidal carcass disposed between the pair of bead portions, The carcass is a first ply extending across the pair of bead portions; a second ply disposed on an outer side of the first ply in the tire radial direction in the tread portion and extending between the pair of bead portions, the first ply comprises a layer of a first cord; the second ply comprises a layer of a second cord; The thickness of the second cord is 1.1 to 2.0 times the thickness of the first cord, the first cord and the second cord are made of nylon, The number of the second cords arranged per 5 cm width of the second ply, that is, the second ends, is less than the number of the first cords arranged per 5 cm width of the first ply, that is, the first ends. Pneumatic tires.

2. 2. The pneumatic tire according to claim 1, wherein the first ply includes a main body portion extending between the bead cores of the pair of bead portions, and a pair of turn-up portions that are turned up around the bead cores in each of the pair of bead portions from the inside to the outside in the tire axial direction.

3. 3. The pneumatic tire according to claim 1, wherein the second ply includes a main body portion extending between the bead cores of the pair of bead portions, and a pair of turn-up portions that are turned back around the bead cores in each of the pair of bead portions from the inside to the outside in the tire axial direction.

4. A pneumatic tire as described in any one of claims 1 to 3, wherein the thickness of the second cord is 1.8 to 2.0 times the thickness of the first cord.

5. The thickness of the first cord is 2200 to 2300 dtex, The pneumatic tire according to any one of claims 1 to 4, wherein the second cord has a thickness of 4140 to 4600 dtex.

6. The pneumatic tire according to claim 5 , wherein the second ends are equal to or greater than 0.75 times the first ends.

7. The pneumatic tire described in any one of claims 1 to 5, which is a passenger car tire.

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