Pneumatic tire

Abstract

To provide a pneumatic tire that can exert excellent steeling stability continuously during running at a high speed.SOLUTION: A pneumatic tire includes a ply 10 including a plurality of cords 11 and side wall rubbers 3G. In each of the cords 11, a plurality of filaments 14 having an outer diameter d are twisted. In each of the cords 11, a ratio D / d of an average diameter D of the cord to the outer diameter d of the filament 14 is 28 or more. The D / d and loss tangents tanδ of the side wall rubbers 3G satisfy the following formula (1): (tanδ) / (D / d)×1000≤5.5 (1).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to pneumatic tires.

Background Art

[0002] Conventionally, as a constituent member of a pneumatic tire, a ply including a plurality of cords has been used. Further, it is known that the cords affect various performances of the pneumatic tire. For example, Patent Document 1 below proposes a pneumatic tire capable of reducing rolling resistance by defining the intermediate elongation of carcass cords.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the tire rolls, the ply including a plurality of cords is repeatedly compressed and deformed, so that a plurality of filaments constituting the cords are gradually broken, and as a result, the rigidity of the ply may decrease. In particular, during high-speed driving, since the deformation frequency of the tire is high, there has been a problem that the handling stability is likely to decrease due to the decrease in the rigidity of the ply.

[0005] In view of the above actual situation, the present invention has been devised, and a main object thereof is to provide a pneumatic tire capable of continuously exhibiting excellent handling stability during high-speed driving.

Means for Solving the Problems

[0006] The present invention relates to a pneumatic tire, which includes a ply containing a plurality of cords and sidewall rubber. Each of the cords is formed by twisting a plurality of filaments having an outer diameter d. For each of the cords, the ratio D / d of the cord average diameter D to the outer diameter d of the filament is 28 or more, and the ratio D / d and the loss tangent tanδ of the sidewall rubber satisfy the following formula (1). (tanδ) / (D / d)×1000≦5.5 …(1)

[0007] In the pneumatic tire of the present invention, it is desirable that the ratio D / d is 32 or more.

[0008] In the pneumatic tire of the present invention, it is desirable that the ratio D / d is 35 or more.

[0009] The pneumatic tire of the present invention preferably satisfies the following formula (2). (tanδ) / (D / d)×1000≦2.0 …(2)

[0010] In the pneumatic tire of the present invention, it is desirable that the filaments of the cords contain polyester fibers.

[0011] In the pneumatic tire of the present invention, it is desirable that the heat shrinkage rate of the cords is 3.0% or less.

[0012] In the pneumatic tire of the present invention, it is desirable that the intermediate elongation of the cords is 6.5% or less.

[0013] In the pneumatic tire of the present invention, it is desirable that the ply includes a carcass ply.

[0014] In the pneumatic tire of the present invention, it is desirable that the ply includes a reinforcing ply for reinforcing the tread portion, the sidewall portion, and the bead portion.

[0015] In the pneumatic tire of the present invention, it is desirable that the cord is formed by twisting a plurality of lower-twisted yarns in which the plurality of filaments are twisted together.

[0016] In the pneumatic tire of the present invention, it is desirable that the lower-twisted yarn consists of two strands.

Effect of the Invention

[0017] By adopting the above configuration, the pneumatic tire of the present invention can continuously exhibit excellent handling stability during high-speed driving.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a meridian cross-sectional view of a pneumatic tire (hereinafter sometimes simply referred to as "tire") 1 of the present embodiment. FIG. 1 is a cross-sectional view including the rotation axis in the normal state of the tire 1. As shown in FIG. 1, the tire 1 of the present embodiment is a pneumatic tire for a passenger car. However, the present invention is not limited to such a mode, and the present invention may be applied to a heavy-duty tire or a tire for a motorcycle.

[0020] The "normal state" means that in the case of a tire with various standards, the tire is rim-mounted on a normal rim and filled with a normal internal pressure, and moreover, it is in a no-load state. In the case of a tire without various standards, the "normal state" means a standard use state according to the purpose of use of the tire, which means a state where the tire is not mounted on a vehicle and is in a no-load state. In this specification, unless otherwise specified, the dimensions and the like of each part of the tire are values measured in the normal state.

[0021] The "normal rim" is the rim defined for each tire in a standard system including the standards on which the tire is based. For example, in JATMA, it is the "standard rim", in TRA, it is the "Design Rim", and in ETRTO, it is the "Measuring Rim".

[0022] The "normal internal pressure" is the air pressure defined for each tire in a standard system including the standards on which the tire is based. In JATMA, it is the "maximum air pressure", in TRA, it is the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES", and in ETRTO, it is the "INFLATION PRESSURE".

[0023] As shown in FIG. 1, the tire 1 of the present embodiment has a carcass 6. The carcass 6 is composed of, for example, a single carcass ply 6A. The carcass ply 6A includes a plurality of carcass cords and a topping rubber covering them. The carcass cords are arranged, for example, at an angle of 75 to 90° with respect to the tire circumferential direction. For the carcass cords, organic fiber cords such as nylon, polyester, or rayon are preferably employed.

[0024] The carcass ply 6A has a main body portion 6a and a folded-back portion 6b. The main body portion 6a extends from one bead portion 4, passes through one sidewall portion 3, the tread portion 2, and the other sidewall portion 3, and reaches the other bead portion 4. The folded-back portion 6b is continuous with the main body portion 6a and is folded back from the inner side to the outer side in the tire axial direction around the bead core 5 and extends outward in the tire radial direction.

[0025] In the tread portion 2 of the present embodiment, a tread reinforcing layer 7 is provided. The tread reinforcing layer 7 includes, for example, a belt layer 8. The belt layer 8 includes, for example, two belt plies 8A and 8B. Each of the belt plies 8A and 8B includes, for example, a plurality of belt cords arranged obliquely with respect to the tire circumferential direction and a topping rubber covering them. Each belt cord is preferably inclined at an angle of 10 to 45° with respect to the tire circumferential direction.

[0026] The tread reinforcing layer 7 includes, for example, a band layer 9. The band layer 9 is composed of, for example, one band ply 9A. The band ply 9A is configured to include band cords arranged at an angle of 5° or less with respect to the tire circumferential direction. In a preferred embodiment, the band ply 9A is configured as a so-called jointless band in which one band cord is wound in the tire circumferential direction.

[0027] FIG. 2 shows an enlarged perspective view of the ply 10 included in the tire 1 of the present invention. As shown in FIG. 2, the tire of the present invention includes a ply 10 in which a plurality of cords 11 are covered with a topping rubber 12. The ply 10 is applied to at least one of the above-described carcass ply 6A, belt plies 8A and 8B, and band ply 9A.

[0028] FIG. 3 shows an enlarged cross-sectional view of one cord 11. As shown in FIG. 3, each of the cords 11 is formed by twisting a plurality of filaments 14 having an outer diameter d. As a preferred embodiment, the cord 11 of the present embodiment is formed by twisting a plurality of (two in the present embodiment) lower-twisted yarns 13 in which a plurality of filaments 14 are twisted together. Further, since two lower-twisted yarns 13 are twisted together in the cord 11 of the present invention, a part 13a of the outer surface of the lower-twisted yarn 13 (corresponding to the contact surface of the two lower-twisted yarns 13) is flattened. As a result, the cross-sectional shape of the cord 11 is substantially oval with a reduced cross-sectional width at the central portion. However, the cord of the present invention is not limited to such an embodiment.

[0029] Each of the cords 11 has a ratio D / d of the cord average diameter D to the outer diameter d of the filament 14 of 28 or more. Since such thin filaments 14 are densely twisted together, even when a large tensile stress repeatedly acts on the cord 11 during high-speed running, the deformation generated per filament 14 is small, and the stress that the cord 11 can exhibit can also be increased. For this reason, breakage of the filaments 14 inside the cord 11 is suppressed, and excellent handling stability can be continuously exhibited during high-speed running. Note that the cord 11 with the ratio D / d of 28 or more can be manufactured by appropriately combining known manufacturing methods.

[0030] The cord average diameter D is obtained by the simple average of the major axis D1 and the minor axis D2 in the cross section of the cord 11. The major axis D1 means the maximum diameter of the cord 11. The minor axis D2 means the maximum diameter among the diameters of the cord 11 in the direction orthogonal to the major axis D1. Although the cord 11 of the present embodiment extends in the length direction of the cord 11 with a constant cross-sectional shape, the cross-sectional shape and cross-sectional area of the cord 11 may change in the length direction of the cord 11. In this case, it is desirable that the cord average diameter D is measured at the position where the cross-sectional area of the cord 11 is the smallest. This is because the substantial tensile strength of the cord 11 depends on the configuration of the cord 11 at the position where the cross-sectional area of the cord 11 is the smallest.

[0031] Generally, when the ply 10 having the above-described cord 11 repeatedly undergoes compressive deformation when the tire rolls, a plurality of filaments 14 constituting the cord 11 may break little by little, and as a result, the rigidity of the ply 10 may decrease. Particularly during high-speed running, since the deformation frequency of the tire is high, the handling stability is likely to decrease due to the decrease in the rigidity of the ply 10.

[0032] Regarding the cord 11 of ply 10 itself, various studies have been conducted conventionally. However, the relationship between the cord 11 and the rubber members constituting the tire 1 has not been paid much attention. The inventors focused on the relationship between the cord 11 of ply 10 constituting a pneumatic tire, which has not been much noticed conventionally, and the rubber members of the tire, and analyzed them in detail, thus completing the present invention.

[0033] As shown in FIG. 1, the tire 1 includes a sidewall rubber 3G. The sidewall rubber 3G is disposed, for example, on the outer side in the tire axial direction of the carcass 6 in the sidewall portion 3 and constitutes the outer surface of the sidewall portion 3. In the present invention, the ratio D / d and the loss tangent tanδ of the sidewall rubber 3G satisfy the following formula (1). (tanδ) / (D / d)×1000≦5.5 …(1)

[0034] The loss tangent tanδ of the sidewall rubber 3G is a value measured using a dynamic viscoelasticity measuring device (E-Plexor series) manufactured by GABO under the following conditions in accordance with the provisions of JIS-K6394. The test sample at the time of measurement is, for example, a rubber piece having a length of 20 mm in the tire circumferential direction, a width of 4 mm in the tire radial direction, and a thickness of 1 mm, collected from the sidewall rubber 3G. Initial strain: 5% Amplitude of dynamic strain: ±1% Frequency: 10 Hz Deformation mode: Extension Measurement temperature: 30°C

[0035] In the present invention, when the above formula (1) is satisfied, the calorific value of the sidewall rubber 3G decreases, and while the reduction in the rigidity of the sidewall portion 3 is suppressed, since the ratio D / d is defined to be sufficiently large with respect to the heat generation property of the sidewall rubber 3G, breakage of the filament 14 (shown in FIG. 3 and the same applies hereinafter) in the ply 10 (shown in FIG. 2 and the same applies hereinafter) is suppressed, and the reduction in the rigidity of the ply 10 is effectively suppressed. Further, since the reduction in the rigidity of the sidewall portion 3 and the ply 10 is suppressed, when a steering angle is applied to the tire 1, a cornering force is generated with good response. Due to such an action, it is considered that the tire 1 of the present invention can continuously exhibit excellent handling stability during high-speed driving.

[0036] Hereinafter, a more detailed configuration of the present embodiment will be described. Note that each configuration described below shows a specific aspect of the present embodiment. Therefore, it goes without saying that the present invention can exhibit the above-described effects even if it does not have the configurations described below. Further, even if any one of the configurations described below is applied alone to the tire of the present invention having the above-described features, an improvement in performance corresponding to each configuration can be expected. Furthermore, when some of the configurations described below are applied in combination, a combined improvement in performance corresponding to each configuration can be expected.

[0037] The ply 10 of the present invention can be applied to any of the carcass ply 6A, belt plies 8A and 8B, and band ply 9A. In the present embodiment, the above-described ply 10 is applied to the carcass ply 6A and the band ply 9A. By using the ply 10 as the carcass ply 6A and satisfying the above-described relationship, it is considered that in the side portion of the tire, while suppressing a reduction in rigidity, the reaction force of the ply 10 can be increased. Further, by using the ply 10 as the band ply 9A and satisfying the above-described relationship, it is possible to generate a large reaction force with the ply 10 in the tread portion and transmit the reaction force with good response in the side portion in a state of high rigidity. Therefore, it is considered that excellent handling stability can be continuously exhibited during high-speed driving.

[0038] The present invention is not limited to the above-described aspects. The above-described ply 10 may be applied to the belt plies 8A and 8B. Further, in another embodiment of the present invention, the above-described ply 10 may be applied to a reinforcing ply (not shown) for reinforcing the tread portion 2, the sidewall portion 3, and the bead portion 4. Such a reinforcing ply helps to further improve the handling stability during high-speed driving.

[0039] In a more desirable aspect, it is desirable to satisfy the following formula (2). Thereby, the above-described effects can be further enhanced. (tanδ) / (D / d)×1000≦2.0 …(2)

[0040] The loss tangent of the sidewall rubber 3G is desirably 0.05 or more, more desirably 0.07 or more, desirably 0.18 or less, and more desirably 0.16 or less. The sidewall rubber 3G can be manufactured by appropriately adjusting and combining known materials.

[0041] The above-described sidewall rubber 3G can be obtained by appropriately combining known materials. Examples of the rubber component of the sidewall rubber 3G include rubbers such as isoprene rubber, butadiene rubber (BR), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), and styrene-isoprene-butadiene copolymer rubber (SIBR). These may be used alone or in combination of two or more.

[0042] In addition, fillers such as carbon black and silica, plasticizers such as oil and resin, processing aids such as fatty acids, vulcanizing agents such as sulfur, vulcanization accelerators, etc. can be appropriately added to the rubber component described above. Further, the loss tangent tanδ of the sidewall rubber 3G of the present embodiment can be adjusted by appropriately changing, for example, the glass transition point of the rubber component, and the types and amounts of the filler, plasticizer, vulcanizing agent, and vulcanization accelerator. In particular, compared with conventional rubber materials, by relatively reducing the filler and plasticizer and relatively increasing the vulcanizing agent and vulcanization accelerator, the loss tangent tanδ of the sidewall rubber 3G can be made within the above range.

[0043] As shown in FIG. 2, the cord 11 included in the ply 10 is an organic fiber cord. The filament 14 of the cord 11 of the present embodiment includes polyester fiber. Such a cord 11 helps to reduce the manufacturing cost of the tire. However, the material applied to the cord 11 is not limited to such a mode, and various materials such as nylon, rayon, or aramid are applicable.

[0044] The ends, which are the number of cords 11 included per 5 cm width of the ply 10, are, for example, 40 to 60, preferably 45 to 55. Further, the fineness of one cord 11 is desirably 2000 dtex or more, more desirably 2500 dtex or more, still more desirably 3000 dtex or more, and desirably 7000 dtex or less, more desirably 6500 dtex or less, still more desirably <6000 dtex or less. In the present embodiment, one cord 11 is composed of two lower-twisted yarns 13. The fineness of one lower-twisted yarn 13 is desirably 1000 dtex or more, more desirably 1500 dtex or more, and desirably 3500 dtex or less, more desirably 3000 dtex or less.

[0045] As shown in FIG. 3, in order to further enhance the above-described effects, the ratio D / d of the cord 11 is desirably 33 or more, more desirably 36 or more. On the other hand, when the ratio D / d is excessively large, the manufacturing cost of the cord 11 tends to increase. For this reason, the ratio D / d is desirably 40 or less, more desirably 38 or less.

[0046] As shown in FIG. 3, the average cord diameter D of the cord 11 is, for example, 0.50 to 0.90 mm, desirably 0.58 to 0.78 mm. The outer diameter d of the filament 14 is, for example, 15.0 to 30.0 μm, desirably 20.0 to 25.0 μm. However, the cord 11 and the filament 14 are not limited to such dimensions.

[0047] The heat shrinkage rate of the cord 11 is desirably small. For this reason, the heat shrinkage rate of the cord 11 is desirably 5.0% or less, more desirably 4.0% or less, and even more desirably 3.0% or less. Such a cord 11 does not shrink excessively even during high-speed driving, and can further enhance the handling stability.

[0048] The "heat shrinkage rate" means the dry heat shrinkage rate after heating according to paragraph 8.10(b) of JIS-L1017, "Dry heat shrinkage rate (Method B)" after heating the cord at a temperature of 180°C for 5 minutes in a no-load state.

[0049] The intermediate elongation of the cord 11 is desirably 6.5% or less, more desirably 5.0% or less, and even more desirably 4.5% or less. Such a cord 11 can continuously exhibit excellent handling stability. In this specification, the "intermediate elongation" means the elongation (%) when a constant load defined by the standard is applied in accordance with the test method for chemical fiber tire cords of JIS L1017.

[0050] All of the above-described compositions of the cord 11 are applied to the composition of the cord collected from the new and unused tire 1.

[0051] As described above, the particularly preferred embodiments of the present invention have been described in detail. However, the present invention is not limited to the above-described embodiments and can be implemented in various forms.

Example

[0052] A pneumatic tire of size 215 / 60R16 that meets the invention-specific matters of the present invention was prototyped based on the specifications in Tables 1 to 3. As Comparative Examples 1 to 4, pneumatic tires that do not meet the invention-specific matters of the present invention were prototyped. The tires of Comparative Examples 1 to 4 have substantially the same configuration as the tires of the examples except for the specifications shown in Tables 1 to 3. For each test tire, the handling stability during high-speed driving (when the tire is new and in the later stage of tire use) was tested. The common specifications and test methods of the test tires are as follows. Mounting rim: 16×6.5J Inner pressure: 210 kPa Displacement of the test vehicle: 2000 cc Drive method: FF Test tire mounting position: All wheels

[0053] <Handling stability during high-speed driving (when the tire is new and in the later stage of tire use)> The handling stability when driving at high speed with the above test vehicle was evaluated by the driver's sensory perception. In the table, "handling stability when the tire is new" is the evaluation of the handling stability of a new test tire after running-in. "Handling stability in the later stage of tire use" is the evaluation of the handling stability of the test tire after traveling 3000 km on ordinary roads. The results are in a score with the handling stability of Comparative Example 1 being 100, and the larger the numerical value, the better the handling stability during high-speed driving. The test results are shown in Tables 1 to 3.

[0054]

Table 1

[0055]

Table 2

[0056]

Table 3

[0057] Note that the formulations A to C of the sidewall rubber described in Tables 1 to 3 are as shown in Table 4 below.

[0058]

Table 4

[0059] In addition, as an index for the comprehensive evaluation of the handling stability during high-speed driving, the total score of the handling stability ratings of the tire when new and in the later stage of tire use shown in Tables 1 to 3 may be used.

[0060] As shown in Tables 1 to 3, it was confirmed that the tires of the examples continuously exhibited excellent handling stability during high-speed driving.

Explanation of Signs

[0061] 3 Sidewall rubber 10 Ply 11 Cord 14 Filament D Cord average diameter d Outer diameter of filament

Claims

1. A pneumatic tire comprising a ply containing a plurality of cords and sidewall rubber, wherein each of the cords is formed by twisting a plurality of filaments having an outer diameter d, wherein for each of the cords, the ratio D / d of the average cord diameter D to the outer diameter d of the filaments is 28 or more, wherein the ratio D / d and the loss tangent tanδ of the sidewall rubber satisfy the following formula (1): A pneumatic tire. (tanδ) / (D / d)×1000 ≤ 5.5 …(1)

2. The pneumatic tire according to claim 1, wherein the ratio D / d is 32 or more.

3. The pneumatic tire according to claim 1, wherein the ratio D / d is 35 or more.

4. The pneumatic tire according to any one of claims 1 to 3, which satisfies the following formula (2): (tanδ) / (D / d)×1000 ≤ 2.0 …(2)

5. The pneumatic tire according to any one of claims 1 to 4, wherein the filaments of the cords contain polyester fibers.

6. The pneumatic tire according to any one of claims 1 to 5, wherein the heat shrinkage rate of the cords is 3.0% or less.

7. The pneumatic tire according to any one of claims 1 to 6, wherein the intermediate elongation of the cords is 6.5% or less.

8. The pneumatic tire according to any one of claims 1 to 7, wherein the ply includes a carcass ply.

9. The pneumatic tire according to any one of claims 1 to 8, wherein the ply includes a reinforcing ply for reinforcing a tread portion, a sidewall portion, and a bead portion.

10. The pneumatic tire according to any one of claims 1 to 9, wherein the cord is formed by twisting a plurality of lower-twisted yarns in which a plurality of filaments having an outer diameter d are twisted together.

11. The pneumatic tire according to claim 10, wherein the lower-twisted yarns are two in number.

12. A pneumatic tire comprising a ply containing a plurality of cords and sidewall rubber, wherein each of the cords is formed by twisting a plurality of filaments having an outer diameter d, wherein the cord is formed by twisting a plurality of lower-twisted yarns in which a plurality of filaments having an outer diameter d are twisted together, wherein the cross-section of the cord includes a major axis D1 which is the maximum diameter of the cord and a minor axis D2 which is the maximum of the cord diameters in a direction orthogonal to the major axis D1. ​ ​ The cord average diameter D is obtained by the simple average of the major diameter D1 and the minor diameter D2, for each of the cords, the ratio D / d of the cord average diameter D to the outer diameter d of the filament is 28 or more, the ratio D / d and the loss tangent tanδ of the sidewall rubber satisfy the following formula (1), Pneumatic tire. (tanδ) / (D / d)×1000 ≤ 5.5 …(1)

13. A pneumatic tire, including a ply containing a plurality of cords and sidewall rubber, each of the cords is formed by twisting a plurality of filaments having an outer diameter d, the cord is formed by twisting a plurality of lower-twisted yarns in which the plurality of filaments are twisted together, the cross-section of the cord includes a major diameter D1 which is the maximum diameter of the cord and a minor diameter D2 which is the maximum of the cord diameters in a direction orthogonal to the major diameter D1, the cord average diameter D is obtained by the simple average of the major diameter D1 and the minor diameter D2, the minor diameter D2 is the same as the diameter of the lower-twisted yarn, for each of the cords, the ratio D / d of the cord average diameter D to the outer diameter d of the filament is 28 or more, the ratio D / d and the loss tangent tanδ of the sidewall rubber satisfy the following formula (1), Pneumatic tire. (tanδ) / (D / d)×1000 ≤ 5.5 …(1)

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