JP7595506B2 - Run-flat tires - Google Patents

Description

The present invention relates to run-flat tires.

Run-flat tires are known as pneumatic tires, and have sidewall reinforcing rubber with a crescent-shaped cross section (see, for example, Patent Document 1). With such run-flat tires, even if the tire is punctured and the internal pressure drops, the side reinforcing rubber can take on the load, allowing the tire to travel a considerable distance.

JP 2011-184000 A

While run-flat tires are required to have high durability when driving with run-flat tires, the problem is that the added weight of the side reinforcing rubber leads to increased rolling resistance. In particular, when driving with run-flat tires, the innermost part of the side reinforcing rubber is subject to high temperature and strain due to large deflections, which can cause cracks in the side reinforcing rubber and reduce run-flat durability.

The present invention aims to provide a run-flat tire that ensures run-flat durability while suppressing increases in rolling resistance.

The gist and configuration of the present invention are as follows.
(1) a tread portion;
A pair of sidewall portions connected to both sides of the tread portion;
a bead portion connected to each of the sidewall portions;
A side reinforcing rubber having a crescent-shaped cross section disposed on the sidewall portion;
a carcass extending in a toroidal shape between the pair of bead portions;
a belt consisting of one or more belt layers arranged on a radially outer side of the crown portion of the carcass,
An inner liner and an inner rubber layer are arranged on the inner surface of the tire,
an outer end of the inner liner in the tire width direction and an outer end of the inner layer rubber in the tire radial direction are disposed so as to abut against each other, or an outer end of the inner liner in the tire width direction and an outer end of the inner layer rubber in the tire radial direction overlap with an overlap width of 30 mm or less, and the outer end of the inner layer rubber in the tire radial direction is located closer to the inner surface of the tire than the outer end of the inner liner in the tire width direction,
In a standard state in which the run-flat tire is mounted on an applicable rim, inflated to a specified internal pressure, and unloaded, the width of the inner liner in the tire width direction is W1 (mm) and the width of the innermost belt layer in the tire radial direction among the one or more belt layers is W2 (mm), satisfying W2≦W1≦W2+20 (mm),
A run-flat tire, wherein a loss tangent tan δ1 of the inner layer rubber is 80% or less of a loss tangent tan δ2 of the inner liner.

In this specification, the term "applicable rim" refers to a standard rim for an applicable size that is an industrial standard effective in the region where the tire is manufactured and used, and is described or will be described in the future in the JATMA YEAR BOOK of the Japan Automobile Tire Manufacturers Association (JATMA), the STANDARDS MANUAL of the European Tire and Rim Technical Organization (ETRTO), the YEAR BOOK of the Tire and Rim Association, Inc. (TRA), and the like. "rim" refers to the rim width corresponding to the bead width of the tire (i.e., the above "rim" includes not only the current sizes but also sizes that may be included in the above industrial standard in the future. An example of "sizes to be described in the future" is the size described as "FUTURE DEVELOPMENTS" in the 2013 edition of ETRTO), but in the case of a size not described in the above industrial standard, it refers to a rim with a width corresponding to the bead width of the tire. Furthermore, "prescribed internal pressure" refers to the air pressure (maximum air pressure) corresponding to the maximum load capacity of a single wheel in the applicable size/ply rating described in the above JATMA etc., and in the case of a size not described in the above industrial standard, "prescribed internal pressure" refers to the air pressure (maximum air pressure) corresponding to the maximum load capacity specified for each vehicle on which the tire is mounted.
The term "loss tangent" refers to the ratio (E"/E') of the dynamic loss modulus E" to the dynamic storage modulus E' obtained using a dynamic tensile viscoelasticity measuring machine on a test piece of vulcanized rubber having a thickness of 2 mm, a width of 5 mm and a length of 20 mm under the conditions of a temperature of 60°C, a frequency of 52 Hz, an initial strain of 2% and a dynamic strain of 1%.

(2) The run-flat tire described in (1) above, in which the inner layer rubber is a test piece obtained by cutting out 1 mm from the center of a No. 8 dumbbell perpendicular to the direction of repeated tension of the test piece, and when repeated tension is applied at a frequency of 10 Hz under conditions of 150°C in accordance with JIS K6270:2001, the number of repetitions until the test piece breaks is at least twice as long as that of the side reinforcing rubber when the applied tensile strain is in the range of 10% to 30%.

(3) A run-flat tire as described in (2) above, in which the ratio T2/T1 of the thickness T2 of the inner layer rubber measured in the direction of a perpendicular line from the carcass to the maximum thickness T1 of the side reinforcement rubber when measured in the reference state is 0.05 to 0.30.

(4) The run-flat tire according to any one of (1) to (3) above, wherein the ratio of the elastic modulus of the inner layer rubber to the elastic modulus of the side reinforcing rubber is 0.75 or less.
Here, the "elastic modulus" refers to the tensile modulus at 25% elongation at 25°C when a vulcanized rubber is processed into a dumbbell-shaped No. 8 test piece and measured at 25% elongation at a measurement temperature of 25°C, based on the modulus of elasticity at 25% elongation at 25°C (JIS K 6251:2017).

The present invention provides a run-flat tire that ensures run-flat durability while suppressing increases in rolling resistance.

1 is a partial cross-sectional view in the tire width direction of a run-flat tire according to one embodiment of the present invention.

Figure 1 is a partial cross-sectional view in the tire width direction of a run-flat tire according to one embodiment of the present invention. Figure 1 shows a cross-section in the tire width direction of a run-flat tire in the above-mentioned reference state.

As shown in FIG. 1, this run-flat tire (hereinafter also simply referred to as a tire) 10 has a tread portion 1 made of tread rubber, a pair of sidewall portions 2 made of sidewall rubber continuing on both sides of the tread portion 1, and a bead portion 3 continuing to each sidewall portion 2.

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 on the radially outer side of the bead core 3a.

The tire 1 further includes a carcass 4 consisting of one or more carcass plies that span a pair of bead portions 3 in a toroidal shape. In this example, the carcass ply is made of organic fiber cords. The carcass 4 consists of a carcass main body 4a that is engaged with the bead core, and a carcass folded-back portion 4b that extends from the carcass main body 4a and is 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 than the belt end and terminates, forming a so-called envelope structure, but this is not limited to this example, and the end of the carcass folded-back portion 4b may be located, for example, radially inward from the maximum tire width position.

A belt 5 consisting of one or more belt layers 5a, 5b (two layers in the illustrated example) is disposed on the radially outer side 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 at an inclination angle of, for example, 30 to 60 degrees with respect to the tire circumferential direction. In this example, the belt cords are steel cords.

In addition, this tire 1 is provided with a side reinforcing rubber 6 with a crescent-shaped cross section on the sidewall portion 2. By providing such a side reinforcing rubber 6, the side reinforcing rubber 6, which contributes to supporting the vehicle weight, enables the vehicle to travel safely for a certain distance even in a state where the internal pressure of the tire has decreased due to a puncture or the like. In the illustrated example, the side reinforcing rubber 6 has a shape in which the thickness in the tire width direction gradually decreases from near the tire radial center position of the side reinforcing rubber 6 toward the tire radial inner and outer sides in the tire width direction in the tire width cross section, and protrudes convexly outward in the tire width direction.

As shown in FIG. 1, the tire 1 of this embodiment includes an inner liner 7 on the tire inner surface. In this example, the inner liner 7 is made of butyl rubber. In this tire 1, an inner layer rubber 8 is disposed on the tire inner surface . The inner layer rubber 8 is made of a test piece obtained by cutting out the center of a No. 8 dumbbell by 1 mm perpendicular to the direction of repeated tension of the test piece in accordance with JIS K6270:2001. When tension is repeatedly applied to the inner layer rubber 8 at a frequency of 10 Hz under conditions of 150° C., the number of repetitions until the test piece breaks is at least twice (preferably at least 10 times) that of the side reinforcing rubber 6 in the range of applied tensile strain of 10% to 30%. As for the material, the inner layer rubber 8 is made of a rubber that does not contain a copolymer of isobutylene and isoprene (for example, a rubber blended with butadiene rubber and natural rubber).

In addition, in the above-mentioned standard state, the ratio T2/T1 of the thickness T2 of the inner layer rubber when measured in the direction of a perpendicular line from the carcass 4 to the maximum thickness T1 of the side reinforcing rubber 6 when measured in the direction of the perpendicular line is 0.05 to 0.30.

In addition, in this tire 10, the outer end of the inner liner 7 in the tire width direction and the outer end of the inner layer rubber 8 in the tire radial direction are arranged to abut against each other, or as shown in the figure, the outer end of the inner liner 7 in the tire width direction and the outer end of the inner layer rubber 8 in the tire radial direction overlap with an overlap width of 30 mm or less. Note that in the example shown, the inner liner 7 overlaps so as to be located outside the inner layer rubber 8 in the tire radial direction, but this is not limited to this case, and the inner liner 7 may overlap so as to be located inside the inner layer rubber 8 in the tire radial direction.
Furthermore, in the above-mentioned reference state, when the width in the tire width direction of the inner liner 7 is W1 (mm) and the width in the tire width direction of the innermost belt layer 5a in the tire radial direction among the one or more belt layers is W2 (mm), W2≦W1≦W2+20 (mm) is satisfied.

Further, the loss tangent tan δ1 of the inner layer rubber 8 is 80% or less of the loss tangent tan δ2 of the inner liner 7, preferably 70% or less, and more preferably 60% or less.
The effects of the run-flat tire of this embodiment will be described below.

The inventors of the present invention noticed that in a run-flat tire, since the side reinforcing rubber 6 is arranged in the sidewall portion and the side reinforcing rubber 6 suppresses air permeation, it is not necessary to arrange the inner liner 7, and came up with the idea that the rolling resistance can be reduced by removing the inner liner with a large loss tangent in the sidewall portion. On the other hand, if the side reinforcing rubber 6 is exposed on the innermost surface of the tire, the run-flat durability may be reduced, and the inventors found that by arranging an inner layer rubber having a loss tangent smaller than that of the inner liner, the reduction in run-flat durability can be suppressed without significantly losing the above-mentioned effect of reducing rolling resistance.
Specifically, in the tire of this embodiment, the outer end of the inner liner 7 in the tire width direction and the outer end of the inner layer rubber 8 in the tire radial direction are arranged to butt against each other, or as shown in the illustrated example, the outer end of the inner liner 7 in the tire width direction and the outer end of the inner layer rubber 8 in the tire radial direction overlap with an overlap width of 30 mm or less. In addition, in the above-mentioned reference state, when the width of the inner liner 7 in the tire width direction is W1 (mm) and the width of the innermost belt layer 5a in the tire radial direction among one or more belt layers is W2 (mm), W2≦W1≦W2+20 (mm) is satisfied. In this way, the rolling resistance can be reduced by reducing the amount of the inner liner 7. That is, if the overlap width is more than 30 mm, the effect of reducing the rolling resistance cannot be sufficiently obtained. Also, even if W1>W2+20 (mm), the effect of reducing the rolling resistance cannot be sufficiently obtained. Note that, if W2>W1, the occurrence of failure near the belt end due to the intrusion of air near the belt end cannot be sufficiently suppressed. In addition, since the inner liner 7 itself is a heat source, by reducing the amount of the inner liner 7 disposed as described above, it is also possible to improve run-flat durability.
Furthermore, in this embodiment, the inner layer rubber 8 is disposed on the inner surface of the side reinforcing rubber 6 that is not covered by the inner liner 7, thereby making it possible to suppress a decrease in run-flat durability compared to a case in which the side reinforcing rubber 6 is exposed on the innermost surface of the tire. Furthermore, since the loss tangent tanδ1 of such an inner layer rubber 8 is 80% or less of the loss tangent tanδ2 of the inner liner 7, it is possible to reduce rolling resistance compared to a case in which the inner liner 7 is disposed on the entire inner surface of the tire.
As described above, according to the run-flat tire of the present embodiment, it is possible to suppress an increase in rolling resistance while ensuring run-flat durability.

From the viewpoint of reducing the amount of inner liner 7 as much as possible and obtaining the above-mentioned effect of reducing rolling resistance and improving run-flat durability by reducing the amount of heat generated, it is preferable for the overlap width to be small, and it is more preferable for the tire width direction outer end of the inner liner and the tire radial direction outer end of the inner layer rubber to be arranged abutting each other.
From the same viewpoint, it is more preferable to satisfy W1≦W2+10 (mm).
From the viewpoint of suppressing air leakage, it is preferable that there is no gap between the outer end of the inner liner in the tire width direction and the outer end of the inner layer rubber in the tire radial direction.

From the viewpoint of suppressing an increase in rolling resistance, the loss tangent tanδ1 of the inner layer rubber 8 is preferably 70% or less of the loss tangent tanδ2 of the inner liner 7, and more preferably 60% or less.

During run-flat driving, the innermost part of the side reinforcing rubber is exposed to high temperatures and high strain due to large deflection, so the side reinforcing rubber is required to have the function of supporting the load in the run-flat state as well as the function of being resistant to fracture under high temperatures and high strain.
Therefore, in accordance with JIS K6270:2001, when a test specimen is prepared by cutting out the center of a No. 8 dumbbell by 1 mm perpendicular to the direction of repeated tension of the test specimen and tension is repeatedly applied to the inner layer rubber 8 at a frequency of 10 Hz under conditions of 150°C, it is preferable that the number of repetitions until the test specimen breaks is at least twice (more preferably at least 10 times) that of the side reinforcing rubber 6, in the range of applied tensile strain of 10% to 30%. Such a rubber has high peeling resistance. This allows the side reinforcing rubber 6 to support the load, while the inner layer rubber 8 can suppress destruction from the tire inner surface side, further improving run-flat durability. Also, the inner layer rubber 8 is preferably such that, in accordance with JIS K6270:2001, a test piece is used in which the center of a No. 8 dumbbell is notched by 1 mm perpendicular to the direction of repeated tensile tests, and the number of repetitions until the test piece is destroyed is 70,000 or more when repeated tension is applied at a strain of 30% and a frequency of 10 Hz under conditions of 150°C. By using such an inner layer rubber 8, it is possible to further increase peel resistance and further improve run-flat durability.

When using an inner layer rubber 8 having high peel resistance as described above, in the above-mentioned standard state, the ratio T2/T1 of the thickness T2 of the inner layer rubber 8 when measured in the direction of a perpendicular line extending from the carcass to the inner surface of the tire to the maximum thickness T1 at which the thickness of the side reinforcing rubber 6 is at its maximum when measured in the direction of the perpendicular line is preferably 0.05 to 0.30.
This can further improve run-flat durability. That is, by making the ratio T2/T1 0.30 or less, the volume of the side reinforcing rubber 6 can be secured, and the load support capacity can be made even more sufficient. On the other hand, by making the ratio T2/T1 0.05 or more, the volume of the inner layer rubber 8, which has high peel resistance, can be secured, and the fracture resistance under high temperature and high strain conditions can be secured sufficiently.

Here, it is preferable that the ratio of the elastic modulus of the inner layer rubber 8 to the elastic modulus of the side reinforcing rubber 6 is 0.75 or less (preferably 0.6 or less) because this can prevent a decrease in ride comfort.

In order to confirm the effect of the present invention, Example 1 of the tire size PSR 235/60F18 was used.
Tires according to the above No. 1, No. 2 and Comparative Example were produced as prototypes, and tests were carried out to evaluate the tire performance.
Comparative Example: The side reinforcing rubber was made of one type of rubber.
Invention Example 1: An inner layer rubber having an elastic modulus of 35% compared to the side reinforcing rubber was arranged so that the gauge ratio of the inner layer rubber/the side reinforcing rubber was 0.09 at the thickest part of the side reinforcing rubber gauge. In addition, at the overlapping part between the inner liner and the inner layer rubber, the inner layer rubber was closer to the side reinforcing rubber than the inner liner. The other configurations were the same as those of the comparative example.
Invention Example 2: The inner layer rubber having an elastic modulus of 31% compared to the side reinforcing rubber was arranged so that the gauge ratio of the inner layer rubber/the side reinforcing rubber was 0.09 at the thickest part of the side reinforcing rubber gauge. In addition, at the overlapping part between the inner liner and the inner layer rubber, the inner liner was closer to the side reinforcing rubber than the inner layer rubber. The other configurations were the same as those of the comparative example.

<Run-flat durability>
Run-flat durability was evaluated under rim, internal pressure, and load conditions conforming to ISO standards. The results of the comparative example were expressed as an index, with the result being 100, and the higher the index, the better the performance.
<Rolling resistance>
Each tire was freely rotated on a drum at an air pressure of 210 kPa, a speed of 80 km/h, and a load of 6890 N to measure the rolling resistance. The results of the comparative example were expressed as an index of 100, with a smaller index indicating better performance.
<Vertical spring coefficient>
The tire was assembled on a rim conforming to JATMA standards, filled with an internal pressure of 230 kPa, and the vertical spring coefficient was calculated when a load of 6010 N was applied. The results of the comparative example are expressed as an index of 100, with a smaller index indicating better performance.
The evaluation results are shown in Table 1 below.

10: Run-flat tires,
1: tread portion,
2: Sidewall portion,
3: bead portion,
4: Carcass,
5: Belt,
6: Side reinforcement rubber,
7: inner liner,
8: Inner layer rubber

Claims (3)

A tread portion;
A pair of sidewall portions connected to both sides of the tread portion;
a bead portion connected to each of the sidewall portions;
A side reinforcing rubber having a crescent-shaped cross section disposed on the sidewall portion;
a carcass extending in a toroidal shape between the pair of bead portions;
a belt consisting of one or more belt layers arranged on a radially outer side of a crown portion of the carcass,
An inner liner and an inner rubber layer are arranged on the inner surface of the tire,
an outer end of the inner liner in the tire width direction and an outer end of the inner layer rubber in the tire radial direction are disposed so as to abut against each other, or an outer end of the inner liner in the tire width direction and an outer end of the inner layer rubber in the tire radial direction overlap with an overlap width of 30 mm or less, and the outer end of the inner layer rubber in the tire radial direction is located closer to the inner surface of the tire than the outer end of the inner liner in the tire width direction,
In a standard state in which the run-flat tire is mounted on an applicable rim, inflated to a specified internal pressure, and unloaded, the width of the inner liner in the tire width direction is W1 (mm) and the width of the innermost belt layer in the tire radial direction among the one or more belt layers is W2 (mm), satisfying W2≦W1≦W2+20 (mm),
a loss tangent tanδ1 of the inner layer rubber is 80% or less of a loss tangent tanδ2 of the inner liner,
The inner layer rubber 8 is a run-flat tire characterized in that, in accordance with JIS K6270:2001, a test specimen is prepared by cutting out the center of a No. 8 dumbbell by 1 mm perpendicular to the direction of repeated tension of the test specimen, and when repeated tension is applied at a frequency of 10 Hz under conditions of 150°C, the number of repetitions until the test specimen breaks is at least twice as long as that of the side reinforcing rubber, in the range of applied tensile strain of 10% to 30% . 2. The run-flat tire according to claim 1, wherein a ratio T2/T1 of a thickness T2 of the inner layer rubber measured in a perpendicular direction to a maximum thickness T1 at which the thickness of the side reinforcing rubber is maximum when measured in the perpendicular direction from the carcass to the inner surface of the tire in the reference state is 0.05 to 0.30. 3. The run-flat tire according to claim 1, wherein a ratio of an elastic modulus of said inner layer rubber to an elastic modulus of said side reinforcing rubber is 0.75 or less.

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