Run-flat tire

Abstract

To provide a run-flat tire which suppresses lowering of riding comfort.SOLUTION: In a run-flat tire, a bead filler is divided into a first bead filler and a second bead filler tire in a tire width direction, and a carcass folding part is folded to extend to pass through between the first bead filler and the second bead filler. An elastic modulus E1 of the first bead filler is larger than an elastic modulus E2 of the other part of a side reinforcement rubber; in a predetermined tire radial direction area, the one part of the side reinforcement rubber is a low elastic part lower than the other part; and an elastic modulus E3 of the low elastic part is 80% of the elastic modulus E2 or lower.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a run-flat tire.

Background Art

[0002] As a pneumatic tire, a run-flat tire having a side reinforcing rubber with a crescent-shaped cross section in the sidewall portion is known (for example, Patent Document 1). According to such a run-flat tire, even when the tire is punctured and the internal pressure is reduced, the side reinforcing rubber can substitute for the load, enabling running for a considerable distance.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Run-flat tires have a problem in that the placement of side reinforcing rubber leads to a deterioration in ride comfort due to an increase in the longitudinal spring constant.

[0005] Therefore, an object of the present invention is to provide a run-flat tire that suppresses a deterioration in ride comfort.

Means for Solving the Problems

[0006] The gist configuration of the present invention is as follows. (1) A tread portion, A pair of sidewall portions continuous with both sides of the tread portion, Bead portions continuous with the respective sidewall portions, Side reinforcing rubber with a crescent-shaped cross section disposed in the sidewall portion, A carcass spanning toroidally between a pair of the bead portions, A run-flat tire comprising: A pair of bead cores are embedded in the bead portion, and a bead filler is disposed radially outside the bead core in the tire radial direction. The bead filler is divided in the tire width direction into a first bead filler and a second bead filler disposed radially outside the first bead filler in the tire width direction. The carcass includes a carcass main body portion locked to the bead core and a carcass folded-back portion that is folded back from the carcass main body portion so as to extend between the first bead filler and the second bead filler. In a tire width direction cross section in a reference state where the run-flat tire is mounted on an application rim, filled with a specified internal pressure, and unloaded, the ratio A2 / A1 of the cross-sectional area A2 of the first bead filler to the cross-sectional area A1 of the bead core is 0.7 or more and 1.5 or less. In a tire radial direction region from the radially outer end of the first bead filler to a position radially outside the radially outer end by 40% of the tire cross-sectional height in the tire radial direction, a part of the side reinforcing rubber is a low elastic portion having a lower elastic modulus than other portions. The elastic modulus E1 of the first bead filler is greater than the elastic modulus E2 of the other portion of the side reinforcing rubber. A run-flat tire, characterized in that the elastic modulus E3 of the low elastic portion is 80% or less of the elastic modulus E2 of the other portion.

[0007] Here, the elastic modulus refers to the tensile elastic modulus at 25% elongation at 25°C (JIS K 6251:2017). The vulcanized rubber is processed into a dumbbell-shaped No. 8 test piece, and the tensile elastic modulus at 25% elongation at a measurement temperature of 25°C is meant. In addition, in this specification, the "applicable rim" refers to an industrial standard effective in the region where the tire is produced and used. In Japan, it is the JATMA YEAR BOOK of JATMA (Japan Automobile Tire Association); in Europe, it is the STANDARDS MANUAL of ETRTO (The European Tyre and Rim Technical Organisation); in the United States, it is the YEAR BOOK of TRA (The Tire and Rim Association, Inc.), etc. It refers to the standard rim (Measuring Rim in the STANDARDS MANUAL of ETRTO and Design Rim in the YEAR BOOK of TRA) for the applicable size described therein or to be described in the future (that is, the above-mentioned "rim" includes sizes that may be included in the above industrial standards in the future in addition to the current sizes. Examples of "sizes to be described in the future" include the sizes described as "FUTURE DEVELOPMENTS" in the 2013 edition of ETRTO). In the case of a size not described in the above industrial standards, it refers to a rim with a width corresponding to the bead width of the tire. Also, the "specified internal pressure" refers to the air pressure (maximum air pressure) corresponding to the maximum load capacity of a single wheel for the applicable size and ply rating described in the above JATMA, etc. In the case of a size not described in the above industrial standards, the "specified internal pressure" shall refer to the air pressure (maximum air pressure) corresponding to the maximum load capacity specified for each vehicle on which the tire is mounted.)

[0008] (2) The run-flat tire according to claim 1, wherein the hardness of the first bead filler is the same as the hardness of the second bead filler. Here, the "hardness" refers to the hardness measured at a temperature of 20°C using a JIS K6253 type A durometer.

[0009] (3) The first bead filler is adjacent to the bead core and has a substantially triangular cross-sectional shape in which the width in the tire width direction gradually increases from the outer side in the tire radial direction toward the inner side in the tire radial direction. The second bead filler has a substantially triangular cross-sectional shape in which the width in the tire width direction gradually increases from the outer side in the tire radial direction toward the central portion in the tire radial direction, and the width in the tire width direction gradually decreases from the central portion in the tire radial direction toward the inner side in the tire radial direction. The run-flat tire according to (1) or (2) above, wherein the hypotenuse on the outer side in the tire width direction of the first bead filler and the hypotenuse located on the inner side in the tire radial direction among the two hypotenuses on the inner side in the tire width direction of the second bead filler are adjacent to each other.

[0010] (4) The run-flat tire according to any one of (1) to (3) above, wherein the ratio E1 / E2 is 1.2 to 3. [Effect of the Invention]

[0011] According to the present invention, it is possible to provide a run-flat tire that suppresses a decrease in riding comfort. [Brief Description of the Drawings]

[0012]

Figure 1

Figure 2A

Figure 2B

Figure 2C

[0013] Hereinafter, embodiments of the present invention will be exemplified and described in detail with reference to the drawings.

[0014] FIG. 1 is a partial cross-sectional view in the tire width direction of a run-flat tire according to an embodiment of the present invention. FIG. 1 shows the cross-section in the tire width direction of the run-flat tire in the above reference state.

[0015] As shown in Fig. 1, this run-flat tire (hereinafter also simply referred to as a tire) 10 includes a tread portion 1 made of tread rubber, a sidewall portion 2 made of a pair of sidewall rubbers continuous on both sides of the tread portion 1, and a bead portion 3 continuous with each sidewall portion 2.

[0016] As shown in Fig. 1, a bead core 3a is embedded in each bead portion 3. In this example, a bead filler 3b is disposed outside the bead core 3a in the tire radial direction. The bead filler 3b is divided in the tire width direction into a first bead filler 31 and a second bead filler 32 disposed outside the first bead filler 31 in the tire width direction. The first bead filler 31 and the second bead filler 32 are made of the same material and thus have the same hardness and the like. The first bead filler 31 is adjacent to the bead core 3a and has a substantially triangular cross-sectional shape in which the width in the tire width direction gradually increases from the outside in the tire radial direction toward the inside in the tire radial direction. The second bead filler 32 has a substantially triangular cross-sectional shape in which the width in the tire width direction gradually increases from the outside in the tire radial direction toward the central portion in the tire radial direction (near the outer end of the first bead filler 31 in the tire radial direction) and gradually decreases from the central portion in the tire radial direction toward the inside in the tire radial direction. Among the hypotenuse on the outside in the tire width direction of the first bead filler 31 and the two hypotenuses on the inside in the tire width direction of the second bead filler 32, the hypotenuse located on the inside in the tire radial direction is adjacent. When viewed in the overall shape of the combined first bead filler 31 and second bead filler 32, it has a substantially triangular cross-sectional shape in which the width in the tire width direction gradually increases from the outside in the tire radial direction toward the inside in the tire radial direction.

[0017] This tire 1 further includes a carcass 4 composed of one or more carcass plies extending in a toroidal shape between a pair of bead portions 3. The carcass ply is composed of organic fiber cords in this example. The carcass 4 includes a carcass main body portion 4a locked to a bead core, and a carcass folded-back portion 4b formed by folding back from the carcass main body portion 4a so as to extend between a first bead filler 31 and a second bead filler 32. In the illustrated example, the carcass folded-back portion 4b extends to the inner side in the tire width direction from the belt end and terminates, having a so-called envelope structure. However, the present invention is not limited to this example, and the end of the carcass folded-back portion 4b may be located, for example, on the inner side in the tire radial direction from the maximum tire width position.

[0018] Further, a belt 5 composed of one or more (two layers in the illustrated example) belt layers 5a, 5b is disposed on the outer side in the tire radial direction of the crown portion of the carcass 4. The belt cords of the two belt layers extend so as to cross each other between the layers, and the belt cords can extend inclined at an inclination angle of, for example, 30 to 60° with respect to the tire circumferential direction. The belt cords are steel cords in this example.

[0019] Further, a side reinforcing rubber 6 having a crescent cross section is disposed on the sidewall portion 2 of this tire 1. By disposing such a side reinforcing rubber 6, even in a state where the internal pressure of the tire has decreased due to a puncture or the like, the side reinforcing rubber 6 that contributes to supporting the vehicle body weight enables safe driving for a certain distance. In the illustrated example, the side reinforcing rubber 6 has a shape in which the thickness in the tire width direction gradually decreases from the vicinity of the central position in the tire radial direction of the side reinforcing rubber 6 toward the inner and outer sides in the tire radial direction and protrudes convexly to the outer side in the tire width direction. An inner liner 7 is disposed on the inner surface of the tire.

[0020] Here, in the tire of the present embodiment, in the tire radial direction region from the outer end of the first bead filler 31 in the tire radial direction to the position separated by 40% of the tire section height radially outward from the outer end of the first bead filler 31 in the tire radial direction, a part of the side reinforcing rubber 6 is a low elastic part 6b having a lower elastic modulus than the other part 6a. More specifically, the elastic modulus E3 of the low elastic part 6b is 80% or less of the elastic modulus E2 of the other part 6a, preferably, the elastic modulus E3 of the low elastic part 6b is 50% or less of the elastic modulus E2 of the other part 6a, and more preferably, the elastic modulus E3 of the low elastic part 6b is 20% or less of the elastic modulus E2 of the other part 6a.

[0021] In the illustrated example, the entire low elastic part 6b is located in the tire radial direction region. It is preferable that 80% or more of the low elastic part 6b is located in the tire radial direction region.

[0022] Here, in the tire width direction cross section in the reference state, the ratio A2 / A1 of the cross sectional area A2 of the first bead filler 31 to the cross sectional area A1 of the bead core 3a is 0.7 or more and 1.5 or less.

[0023] Also, the elastic modulus E1 of the first bead filler 31 is larger than the elastic modulus E2 of the other part 6a of the side reinforcing rubber 6.

[0024] Furthermore, as described above, the elastic modulus E3 of the low elastic part 6b is 80% or less of the elastic modulus E2 of the other part 6a. Hereinafter, the operation and effect of the run-flat tire of the present embodiment will be described.

[0025] According to the run-flat tire of the present embodiment, first, since the side reinforcing rubber 6 is disposed in the sidewall portion, run-flat durability can be ensured. Here, as schematically shown in FIG. 2A, when the bead filler is not divided and the carcass turn-up portion extends along the outer side of the bead filler in the tire width direction, the entire bead filler is surrounded by the carcass main body portion and the carcass turn-up portion. As a result, the rigidity of the portion where the bead filler is disposed becomes high, and it is difficult for bending deformation to occur during normal running. Bending deformation is less likely to occur in the portion of the side reinforcing rubber located in the tire radial region inside the tire radial direction than the outer end position of the bead filler in the tire radial direction, the longitudinal spring constant increases, and the riding comfort deteriorates. Therefore, as in the present embodiment, the bead filler 3b is divided in the tire width direction into a first bead filler 31 and a second bead filler 32 disposed outside the first bead filler 31 in the tire width direction, and the carcass turn-up portion 4b is folded so as to extend between the first bead filler 31 and the second bead filler 32. By adopting such a configuration, only the first bead filler 31 is surrounded by the carcass main body portion 4a and the carcass turn-up portion 4b, and the second bead filler 32 can be disposed outside the carcass turn-up portion 4b in the tire width direction. As a result, bending deformation is more likely to occur in the region outside the tire radial direction than the outer end position of the first bead filler 31 in the tire radial direction, as compared with the case shown in FIG. 2A. In this way, by securing a large tire radial region where bending deformation is likely to occur, bending deformation in the portion of the side reinforcing rubber located in the region can be made to occur moderately easily, the longitudinal spring constant can be reduced, and a decrease in riding comfort can be suppressed. Therefore, as schematically shown in FIG. 2B, in the tire radial region from the outer end of the first bead filler 31 in the tire radial direction to a position 40% of the tire cross-sectional height away from the outer end of the first bead filler 31 in the tire radial direction toward the outer side in the tire radial direction, a part of the side reinforcing rubber 6 is made into a low-elasticity part 6b having a lower elastic modulus than the other part 6a (as described above, the elastic modulus E3 of the low-elasticity part 6b is less than 80% of the elastic modulus E2 of the other part 6a). Thus, compared with the configuration without the low-elasticity part as shown in FIG. 2C, the second bead filler 32, which is a part of the bead filler, is positioned on the outer side in the tire width direction of the carcass, making it easier to cause bending deformation in the region outside the outer end position of the first bead filler 31 in the tire radial direction. Combined with the effect of moderately reducing the rigidity by the low-elasticity part 6b, the longitudinal spring coefficient can be reduced and a decrease in ride comfort can be suppressed. Also, in the present embodiment, in the tire width direction cross-section in the reference state, the ratio A2 / A1 of the cross-sectional area A2 of the first bead filler 31 to the cross-sectional area A1 of the bead core 3a is set to be 0.7 or more and 1.5 or less. If the ratio A2 / A1 exceeds 1.5, the effect of sufficiently securing a region in the tire radial direction where bending deformation easily occurs cannot be obtained, and a decrease in ride comfort cannot be sufficiently suppressed. On the other hand, if the ratio A2 / A1 is less than 0.7, the rigidity of the bead part cannot be sufficiently secured, leading to a decrease in handling stability and the like. Also, in the present embodiment, the elastic modulus E1 of the first bead filler 31 is larger than the elastic modulus E2 of the other part 6a of the side reinforcing rubber 6. Thereby, it is possible to achieve both ensuring the rigidity of the bead part and suppressing a decrease in ride comfort at a higher level.

[0026] Here, the ratio A2 / A1 is preferably 0.8 or more and 1.2 or less. By setting the ratio A2 / A1 to be 0.8 or more, the rigidity of the bead part can be increased by twisting to further improve handling stability. On the other hand, by setting the ratio A2 / A1 to be 1.2 or less, a decrease in ride comfort can be further suppressed.

[0027] Also, the ratio E1 / E2 is preferably 1.2 to 3. By setting the ratio E1 / E2 to 1.2 or more, it is possible to further achieve both ensuring the rigidity of the bead portion and suppressing the deterioration of the riding comfort at a higher level. On the other hand, by setting the ratio E1 / E2 to 3 or less, it is possible to ensure the rigidity of the side reinforcing rubber and prevent the run-flat durability from deteriorating.

[0028] Also, the ratio E3 / E2 is preferably 70% or less, more preferably 60% or less. This is because it is possible to further achieve both ensuring the rigidity of the bead portion and suppressing the deterioration of the riding comfort at a higher level. On the other hand, in order to prevent the rigidity difference between the low-elasticity portion and other portions from becoming too large, the ratio E3 / E2 is preferably 50% or more.

[0029] Here, in the illustrated example, the low-elasticity portion 6b is disposed adjacent to the inner surface side of the tire. Among the bending deformations of the tire, compressive bending stress is applied on the inner surface side of the tire, and tensile bending stress is applied on the outer side of the tire. However, reducing the rigidity against compressive bending is relatively more effective in reducing the vertical spring coefficient than reducing the rigidity against tensile bending. Therefore, by disposing the low-elasticity portion 6b adjacent to the inner surface side of the tire, it is possible to further reduce the vertical spring coefficient and further suppress the deterioration of the riding comfort. For the same reason, if the cross-sectional area of the same low-elasticity portion 6b is the same, having a longer extension range in the tire radial direction and being located on the inner surface side of the tire can effectively improve the riding comfort. From such a perspective, the low-elasticity portion 6b preferably extends over 80% or more of the tire radial region from the outer end in the tire radial direction of the first bead filler 31 to a position 40% of the tire cross-sectional height away from the outer end in the tire radial direction of the first bead filler 31 in the tire radial outer direction, and / or 80% or more of the cross-sectional area of the low-elasticity portion is preferably located on the inner side in the tire width direction with respect to the center line in the width direction of the side reinforcing rubber (a virtual line connecting the midpoints in the width direction at each tire radial position).

Example

[0030] In the following examples, the data is simulated data. (Example) To confirm the effects of the present invention, a test was conducted to evaluate the tire performance of the inventive example of tire size PSR 235 / 40F19 and Comparative Examples 1 and 2. Inventive example: The bead filler is divided in the tire width direction into a first bead filler and a second bead filler disposed outside the first bead filler in the tire width direction. The carcass includes a carcass main body portion locked to the bead core and a carcass folded-back portion that is folded back from the carcass main body portion so as to extend through the space between the first bead filler and the second bead filler. The ratio A2 / A1 was set to 1.0. In the tire radial region from the outer end of the first bead filler in the tire radial direction to the position 40% of the tire cross-sectional height away from the outer end of the tire in the tire radial direction, a part of the side reinforcing rubber was made into a low-elasticity portion having a lower elastic modulus than other portions. E3 was set to 75% of E2. Comparative Example 1: The ratio A2 / A1 was set to 2.0. Also, it was made to have no low-elasticity portion. Otherwise, it was the same as the inventive example. Comparative Example 2: The ratio A2 / A1 was set to 1.0. It was made to have no low-elasticity portion. Otherwise, it was the same as the inventive example. Also, for each tire, E1>E2 (E1 / E2 = 1.3) was made common.

[0031] <Run-flat durability> The run-flat durability was evaluated under the rim, internal pressure, and load conditions conforming to the ISO standard. The results of Comparative Example 1 were shown in an index with 100 as the reference, and the larger the index, the better the performance. <Vertical spring constant> The rim was assembled to a rim conforming to JATMA, filled with an internal pressure of 230 kPa, and the vertical spring constant when a load of 4320 N was applied was calculated. The results of Comparative Example 1 were shown in an index with 100 as the reference, and the smaller the index, the better the performance. The evaluation results are shown in Table 1 below.

[0032]

Table 1

Explanation of Symbols

[0033] 10: Run-flat tire, 1: Tread portion, 2: Sidewall portion, 3: Bead portion, 3a: Bead core, 3b: Bead filler, 31: First bead filler, 32: Second bead filler, 4: Carcass, 5: Belt, 6: Side reinforcement rubber, 7: Inner liner

Claims

1. A tread portion, A pair of sidewall portions continuous with both sides of the tread portion, A bead portion continuous with each sidewall portion, Side reinforcing rubber having a crescent cross-section disposed on the sidewall portion, A carcass spanning toroidally between a pair of the bead portions, A run-flat tire comprising: A pair of bead cores are embedded in the bead portion, and a bead filler is disposed outside the bead core in the tire radial direction, The bead filler is divided in the tire width direction into a first bead filler and a second bead filler disposed outside the first bead filler in the tire width direction, The carcass includes a carcass main body portion locked to the bead core, and a carcass folded-back portion folded back from the carcass main body portion so as to extend through between the first bead filler and the second bead filler, In a tire width direction cross-section in a reference state where the run-flat tire is mounted on an application rim, filled with a specified internal pressure, and unloaded, the ratio A2 / A1 of the cross-sectional area A2 of the first bead filler to the cross-sectional area A1 of the bead core is 0.7 or more and 1.5 or less, In a tire radial region from the outer end of the first bead filler in the tire radial direction to a position 40% of the tire cross-sectional height away from the outer end of the tire in the tire radial direction, a part of the side reinforcing rubber is a low elastic portion having a lower elastic modulus than other portions, The entire low elastic portion is located in the tire radial region, The entire low elastic portion is located only inside the tire radial direction from the tire maximum width position, The elastic modulus E1 of the first bead filler is greater than the elastic modulus E2 of the other portion of the side reinforcing rubber, A run-flat tire, characterized in that the elastic modulus E3 of the low elastic portion is 80% or less of the elastic modulus E2 of the other portion.

2. The run-flat tire according to claim 1, wherein the hardness of the first bead filler and the hardness of the second bead filler are the same.

3. The first bead filler has a substantially triangular cross-sectional shape adjacent to the bead core and having a width that gradually increases in the tire width direction from the outside in the tire radial direction toward the inside in the tire radial direction. The second bead filler has a substantially triangular cross-sectional shape in which the width in the tire width direction gradually increases from the outer side in the tire radial direction toward the central portion in the tire radial direction, and the width in the tire width direction gradually decreases from the central portion in the tire radial direction toward the inner side in the tire radial direction. The run-flat tire according to claim 1 or 2, wherein the hypotenuse on the outer side in the tire width direction of the first bead filler and the hypotenuse located on the inner side in the tire radial direction among the two hypotenuses on the inner side in the tire width direction of the second bead filler are adjacent to each other.

4. The run-flat tire according to any one of claims 1 to 3, wherein the ratio E1 / E2 is 1.2 to 3.

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