Run-flat tire

Abstract

To provide a run-flat tire that suppresses decrease of ride comfort while ensuring run-flat durability.SOLUTION: A run-flat tire according to the present invention includes: a crescent-shaped cross-sectional side reinforcing rubber 6 disposed on a sidewall 2; and a carcass 4 toroidally shaped in a bead part 3. A part 6b of the side reinforcing rubber is a low elasticity part with a lower elastic modulus than the other part 6a, the low-elasticity part is equipped with a run-flat tire 10 on the applicable rim, the low-elasticity portion is located in a tire radial region of 50% or more and 80% or less of the tire cross-sectional height from a bead base line in a reference state in which a specified internal pressure is filled and no load is applied, and the elastic modulus of the low elastic part is less than 80% of the elastic modulus of the other part. When in the cross section in a tire width direction in the reference state, the maximum thickness of the low elasticity part when measured in a direction of the perpendicular line drawn down from the carcass to the inner surface of the tire is a maximum thickness t1, and the thickness of the other part when measured in the direction of the perpendicular ls t2, the ratio t1 / t2 is 0.2 or more and 3 or less.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 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 the vehicle to travel a considerable distance.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] While run-flat tires are required to have high durability in the run-flat state, the placement of side reinforcing rubber has a problem of causing 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 while ensuring run-flat durability.

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, A bead portion continuous with each sidewall portion, The side reinforcing rubber with a crescent cross-section disposed in the side wall portion, A run-flat tire comprising a carcass spanning toroidally between a pair of the bead portions, A part of the side reinforcing rubber is a low-elasticity portion having a lower elastic modulus than other portions, The low-elasticity portion is located in a tire radial direction region of 50% or more and 80% or less of the tire cross-sectional height from the bead base line in a reference state where the run-flat tire is mounted on an application rim, filled with a specified internal pressure, and unloaded, The elastic modulus of the low-elasticity portion is 80% or less of the elastic modulus of the other portions, In the tire width direction cross-section in the reference state, when the maximum thickness t1 at which the thickness of the low-elasticity portion measured in the direction of the perpendicular line dropped from the carcass to the tire inner surface is the maximum, and the thickness of the other portion measured in the direction of the perpendicular line is t2, the ratio t1 / t2 is 0.2 or more and 3 or less. A run-flat tire characterized by this.

[0007] Here, the elastic modulus is based on the 25% elongation modulus tensile elastic modulus at 25°C (JIS K 6251:2017). 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 referred to. 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 ETRTO STANDARDS MANUAL, Design Rim in the TRA YEAR BOOK) in the applicable size described or to be described in the future (that is, the above "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 in 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. Also, the "bead base line" refers to a virtual line passing through the bead base and parallel to the tire width direction in the above reference state.

[0008] (2) The low-elasticity part is located on the outer side in the tire width direction than the other parts in the tire radial direction region from 50% to 80% of the tire cross-sectional height from the bead base line, and is the run-flat tire described in the above (1).

[0009] (3) Only the other parts are located at the tire radial position where the maximum tire width position is reached, and it is the run-flat tire described in the above (1) or (2). Here, the "maximum tire width position" shall refer to the position where the width in the tire width direction of the run-flat tire is maximum in the above-mentioned reference state.

[0010] (4) The elastic modulus of the low-elasticity part is 50% or less of the elastic modulus of the other part, and the run-flat tire according to any one of (1) to (3) above.

[0011] (5) The elastic modulus of the low-elasticity part is 20% or less of the elastic modulus of the other part, and the run-flat tire according to (4) above.

[0012] (6) An inner liner is provided on the inner surface of the tire, An inner layer rubber is disposed between the side reinforcing rubber and the inner liner, The inner layer rubber is made of a rubber having no copolymer of isobutylene and isoprene, The ratio of the elastic modulus of the inner layer rubber to the elastic modulus of the other part of the side reinforcing rubber is 0.75 or less, In the reference state, the ratio of the thickness of the inner layer rubber measured in the direction of the perpendicular line to the maximum thickness at which the thickness of the side reinforcing rubber measured in the direction of the perpendicular line is maximum is 0.05 to 0.30, and the run-flat tire according to any one of (1) to (5) above.

Advantages of the Invention

[0013] According to the present invention, it is possible to provide a run-flat tire that suppresses a decrease in riding comfort while ensuring run-flat durability.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be exemplified and described in detail with reference to the drawings.

[0016] 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 a cross-section in the tire width direction of the run-flat tire in the above reference state.

[0017] 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.

[0018] As shown in FIG. 1, a bead core 3a is embedded in each bead portion 3. Further, in this example, a bead filler 3b is disposed on the outer side in the tire radial direction of the bead core 3a.

[0019] This tire 1 further includes a carcass 4 composed of one or more carcass plies spanning toroidally between a pair of bead portions 3. The carcass ply is made of an organic fiber cord in this example. The carcass 4 includes a carcass main body portion 4a locked to the bead core and a carcass folded-back portion 4b extending from the carcass main body portion 4a and folded back around the bead core 3a. 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, but is not limited to this example. 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 tire maximum width position.

[0020] Further, a belt 5 composed of one or more (two layers in the illustrated example) belt layers 5a and 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.

[0021] Also, in this tire 1, side reinforcing rubber 6 having a cross-sectional crescent shape is disposed on the sidewall portion 2. By disposing such 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 running 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 toward the outer side in the tire width direction.

[0022] Here, in the tire of the present embodiment, a part of the side reinforcing rubber 6 is a low elastic portion 6b having a lower elastic modulus than the other part 6a. More specifically, the elastic modulus of the low elastic portion 6b is 80% or less of the elastic modulus of the other part 6a, preferably, the elastic modulus of the low elastic portion 6b is 50% or less of the elastic modulus of the other part 6a, and more preferably, the elastic modulus of the low elastic portion 6b is 20% or less of the elastic modulus of the other part 6a.

[0023] The low elastic portion 6b is located in the tire radial region of 50% or more and 80% or less of the tire cross-sectional height from the bead base line in the above reference state. In the illustrated example, the low elastic portion 6b (all or part of the low elastic portion 6b) is located on the outer side in the tire width direction than the other part 6a in the tire radial region of 50% or more and 80% or less of the tire cross-sectional height from the bead base line. Also, in the illustrated example, only the above other part 6a is located at the tire radial position that becomes the maximum tire width position (the low elastic portion 6b does not intersect with a line parallel to the tire width direction passing through the maximum tire width position).

[0024] Also, in the cross-section in the tire width direction in the reference state, when the maximum thickness of the low-elasticity portion 6b measured in the direction of the perpendicular line dropped from the carcass 4 to the inner surface of the tire is defined as t1, and the thickness of the other portion 6a measured in the direction of the perpendicular line is defined as t2, the ratio t1 / t2 is 0.2 or more and 3 or less (more preferably 0.5 or more and 1.5 or less). In the illustrated example, the low-elasticity portion 6b is located near the center along the carcass 4 where the thickness measured in the direction of the perpendicular line is the maximum, but the present invention is not limited to this case. Hereinafter, the operation and effect of the run-flat tire of the present embodiment will be described.

[0025] The present inventor has intensively studied to solve the above problems, and focused on the contribution of the side reinforcing rubber to load support during normal running and run-flat running of the run-flat tire. As a result, it was found that the contribution degree of the buttress portion to load support becomes larger during normal running compared to run-flat running. By providing a low-elasticity portion in which the buttress portion is made low-elastic and defining its elastic modulus and thickness in comparison with other portions, it was found that the riding comfort can be improved without impairing the durability during run-flat running.

[0026] That is, in the above reference state, by providing the low-elasticity portion 6b in the tire radial region that is 50% or more and 80% or less of the tire cross-sectional height from the bead base line, during normal driving, since the contribution of this region to load support is relatively large, the longitudinal spring coefficient is reduced due to the low elastic modulus of the low-elasticity portion 6b, and the ride comfort can be improved. On the other hand, during run-flat driving, since the contribution of this region to load support is relatively small, it is possible to suppress a decrease in durability during run-flat driving due to the low elastic modulus of the low-elasticity portion 6b. Here, if the elastic modulus of the low-elasticity portion 6b exceeds 80% of the elastic modulus of the other portion 6a, the effect of improving ride comfort during normal driving cannot be sufficiently obtained. Also, if the ratio t1 / t2 is less than 0.2, the effect of improving ride comfort during normal driving cannot be sufficiently obtained. On the other hand, if the ratio t1 / t2 exceeds 3, there is a risk of a decrease in durability during run-flat driving. Also, since making a part of the side reinforcing rubber 6 have low elasticity does not increase the weight, it does not impair the fuel efficiency. As described above, according to the run-flat tire of the present embodiment, while ensuring run-flat durability, it is possible to suppress a decrease in fuel efficiency and a decrease in ride comfort.

[0027] Here, the low-elasticity portion 6b is preferably located on the outer side in the tire width direction than the other portion 6a in the tire radial region that is 50% or more and 80% or less of the tire cross-sectional height from the bead base line. This is because it is possible to suppress rim detachment during run-flat driving.

[0028] Preferably, only the other portion 6a is located at the tire radial position that is the tire maximum width position. This is because the tire maximum width position contributes greatly to load support during run-flat driving, so the durability during run-flat driving can be further ensured.

[0029] The elastic modulus of the low-elasticity portion 6b is preferably 50% or less, and more preferably 20% or less, of the elastic modulus of the other portion 6a. This is because the ride comfort during normal driving can be further improved.

[0030] FIG. 2 is a partial cross-sectional view in the tire width direction of a run-flat tire according to another embodiment of the present invention. As shown in FIG. 2, the tire 11 of this embodiment includes an inner liner 7 on the inner surface of the tire. In this example, the inner liner 7 is made of butyl rubber. And in this tire 1, an inner layer rubber 8 is disposed between the side reinforcing rubber 6 and the inner liner 7. In the illustrated example, the inner layer rubber 8 is disposed over substantially the entire area of the region where the side reinforcing rubber 6 and the inner liner 7 are adjacent. In this example, the inner layer rubber 8 is a rubber having a peeling resistance of the interface of 1 N / mm or more when a precrack is formed on the rubber boundary line of a sample in which the side reinforcing rubber 6 and the inner layer rubber 8 are adhered and vulcanized and pulled in the direction of peeling the interface under room temperature conditions. As the material, the inner layer rubber 8 is made of a rubber having no copolymer of isobutylene and isoprene. Since the other configurations are the same as those in FIG. 1 except that the inner layer rubber 8 is disposed, the description of the other configurations is omitted.

[0031] Here, the ratio of the elastic modulus of the inner layer rubber 8 to the elastic modulus of the other portion 6a of the side reinforcing rubber 6 is 0.75 or less (preferably 0.6 or less). Further, in the above reference state, the ratio of the thickness of the inner layer rubber 8 measured in the direction of the perpendicular line dropped from the carcass 4 to the inner surface of the tire to the maximum thickness (including only the other portion 6a or the other portion 6a and the low elastic portion 6b) of the side reinforcing rubber 6 measured in the direction of the perpendicular line is 0.05 to 0.30.

[0032] According to this configuration, since the inner layer rubber 8 is made of a rubber having no copolymer of isobutylene and isoprene, the adhesiveness to the side reinforcing rubber 6 and the inner liner 7 is high in comparison with butyl rubber or the like, and even during run-flat driving in which a high temperature and a large compressive strain occur, peeling between the side reinforcing rubber 6 and the inner liner 7 hardly occurs. Therefore, the state in which the side reinforcing rubber 6 and the inner liner 7 are adhered via the inner layer rubber 8 can be maintained. Thereby, it is possible to suppress a decrease in load support capacity due to a decrease in bending rigidity of the sidewall portion 2 caused by peeling between the side reinforcing rubber 6 and the inner liner 7. Furthermore, the inner rubber 8 as described above is less likely to develop cracks compared to butyl rubber or the like. Therefore, it is less likely to generate crack nuclei that may spread to the side reinforcing rubber 6, and also, since cracks generated in the inner liner 7 are less likely to spread to the inner rubber 8, the spread of cracks from the inner liner 7 to the side reinforcing rubber 6 can be suppressed. As a result, it is possible to suppress a decrease in the load support capacity due to cracks occurring in the side reinforcing rubber 6 that plays a role in load support during run-flat driving. In addition, since the ratio of the elastic modulus of the inner rubber 8 to the elastic modulus of the other part 6a of the side reinforcing rubber 6 is 0.75 or less, it is also possible to prevent the ride comfort during normal driving from deteriorating.

[0033] In the above reference state, by setting the ratio of the thickness of the inner rubber 8 measured in the direction of the perpendicular line dropped from the carcass 4 to the inner surface of the tire to the maximum thickness of the side reinforcing rubber 6 measured in the direction of the perpendicular line to be 0.05 or more, the effect of suppressing the decrease in the above load support capacity can be obtained more effectively. On the other hand, in the above reference state, by setting the ratio of the thickness of the inner rubber 8 measured in the direction of the perpendicular line dropped from the carcass 4 to the inner surface of the tire to the maximum thickness of the side reinforcing rubber 6 measured in the direction of the perpendicular line to be 0.30 or less, the weight increase due to the addition of the inner rubber 8 can be suppressed as much as possible.

[0034] FIG. 3 is a diagram showing a modified example of the bead portion. As shown in FIG. 3, in this modified example, the bead filler 3b is divided into a first bead filler 31 and a second bead filler 32. 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 outer side in the tire diameter direction toward the inner side in the tire diameter 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 outer side in the tire diameter direction toward the center in the tire diameter direction (near the outer end in the tire diameter direction of the first bead filler 31), and the width in the tire width direction gradually decreases from the center in the tire diameter direction toward the inner side in the tire diameter direction. The hypotenuse on the outer side in the tire width direction of the first bead filler 31 and the hypotenuse on the inner side in the tire width direction of the second bead filler 32 (the hypotenuse on the inner side in the tire diameter direction from the center in the tire diameter direction) are adjacent to each other. When viewed in terms of 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 outer side in the tire diameter direction toward the inner side in the tire diameter direction (the same as the bead filler 3b in FIG. 1 except that it is divided into the first bead filler 31 and the second bead filler 32).

[0035] Here, as shown in FIG. 2, the carcass turn-up portion 4b is sandwiched between the first bead filler 31 and the second bead filler 32. Although not shown in the figure, the carcass turn-up portion 4b extends to the inner side in the tire width direction from the belt end and terminates in the same manner as in FIG. 1.

[0036] Here, if the entire bead filler 3b is located between the carcass main body portion 4a and the carcass folded-back portion 4b, since the rigidity of the bead filler 3b is high, the bead portion 3 is difficult to bend and deform, the longitudinal spring coefficient increases, the riding comfort deteriorates, and there is a case where the desired bending deformation cannot be achieved and the rolling resistance increases. On the other hand, as shown in FIG. 3, by dividing the bead filler 3b into a first bead filler 31 and a second bead filler 32 and sandwiching the carcass folded-back portion 4b between the first bead filler 31 and the second bead filler 32, the bead filler 3b can be appropriately bent easily on the outside of the carcass 4. Thereby, a decrease in riding comfort and an increase in rolling resistance can be suppressed.

[0037] The first bead filler 31 and the second bead filler 32 can be obtained by dividing a normal bead filler, and those of a normal material can be used. In the tire width direction cross section, the ratio of the area of the second bead filler to the area of the first bead filler is preferably 1.0 to 6.0. By setting it to 1.0 or more, the region radially outside the rim separation point can be easily bent. On the other hand, by setting it to 6.0 or less, it is possible to suppress the deterioration of the durability of the bead portion due to an increase in the tilting deformation of the bead portion in the rim flange direction on the radially inner side of the rim separation point. Since the bending deformation of the bead portion 3 occurs on the radially outer side of the tire diameter from the rim separation point, in the tire width direction cross section, it is preferable that 50% or more of the area of the second bead filler 32 is located on the radially outer side of the tire diameter from the rim separation point.

Example

[0038] (Example) In order to confirm the effects of the present invention, tires according to the inventive example and the comparative example of the tire size PSR 275 / 35F21 were prototyped and a test was conducted to evaluate the tire performance. Inventive Example: A structure is adopted in which a low-elasticity part having an elastic modulus of 56% is arranged in the range of 61% to 73% of the tire cross-sectional height from the bead base line in the tire radial direction, and the ratio of the low-elasticity part gauge to the rubber gauge of other parts is 0.5 at the thickest part of the low-elasticity part gauge. Comparative Example: The side reinforcing rubber is made of one type of rubber. Other aspects are the same as in Inventive Example 1.

[0039] <Run-flat Durability> Under the rim, internal pressure, and load conditions compliant with ISO standards, the run-flat durability was evaluated. The results of the comparative example are shown as an index with 100 as the reference, and the larger the index, the better the performance. <Vertical Spring Constant> The vertical spring constant was calculated when the tire was mounted on a rim compliant with JATMA, filled with an internal pressure of 230 kPa, and loaded with a load of 5320 N. The results of the comparative example are shown as 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.

[0040]

Table 1

Explanation of Symbols

[0041] 10: Run-flat tire, 11: Run-flat tire, 1: Tread part, 2: Sidewall part, 3: Bead part, 4: Carcass, 5: Belt, 6: Side reinforcing rubber, 7: Inner liner, 8: Inner layer rubber

Claims

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 having a crescent cross section disposed on the sidewall portion, A run-flat tire comprising a carcass spanning toroidally between a pair of the bead portions, wherein A part of the side reinforcing rubber is a low elastic portion having a lower elastic modulus than other portions, The low elastic portion is located only in a tire radial direction region of 50% or more and 80% or less of the tire section height from the bead base line in a reference state where the run-flat tire is mounted on an application rim, filled with a specified internal pressure, and unloaded, The elastic modulus of the low elastic portion is 80% or less of the elastic modulus of the other portions, In the tire width direction cross section in the reference state, when the maximum thickness t1 of the low elastic portion measured in the direction of the perpendicular line dropped from the carcass to the tire inner surface is the maximum, and the thickness of the other portion measured in the direction of the perpendicular line is t2, the ratio t1 / t2 is 0.2 or more and 3 or less, The low elastic portion is located outside the tire width direction of the other portions in a tire radial direction region of 50% or more and 80% or less of the tire section height from the bead base line, A run-flat tire, characterized in that only the other portions are located at the tire radial position where the maximum tire width position is reached.

2. The run-flat tire according to claim 1, wherein the elastic modulus of the low elastic portion is 50% or less of the elastic modulus of the other portions.

3. The run-flat tire according to claim 2, wherein the elastic modulus of the low elastic portion is 20% or less of the elastic modulus of the other portions.

4. An inner liner is provided on the tire inner surface, An inner layer rubber is disposed between the side reinforcing rubber and the inner liner, The inner layer rubber is made of a rubber having no copolymer of isobutylene and isoprene, The ratio of the elastic modulus of the inner layer rubber to the elastic modulus of the other portions of the side reinforcing rubber is 0.75 or less, The run-flat tire according to any one of claims 1 to 3, wherein the ratio of the thickness of the inner layer rubber measured in the direction of the perpendicular line to the maximum thickness of the side reinforcing rubber measured in the direction of the perpendicular line in the reference state is 0.05 to 0.30.

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