Run-flat pneumatic tires

Abstract

Run-flat pneumatic tires, comprising a carcass layer (4) arranged between a pair of left and right tire bead portions (3), a belt layer (8) arranged on an outer peripheral side of the carcass layer (4) in a tread portion (1), a belt cover layer (9) arranged on an outer peripheral side of the belt layer (8); and a reinforcing rubber layer (7) having a crescent-shaped cross-section and arranged on an inner side in the tire width direction of the carcass layer (4) in a sidewall portion (2); wherein in a tire meridian section, when a point at which a tire equator plane (E) contacts a tread surface is T0 and a point at which a straight line drawn parallel to the tire equator plane (E) from a position 40% of the total width SW of the tire measured from the point T0 meets the tread surface is T1, an angle θ formed by a straight line passing through the point T0 and the point T1 with respect to the tire width direction satisfies a relationship of (SH / SW×6+3)°≤θ≤(SH / SW×6+8)° with respect to the total width SW of the tire and a tire section height SH; a height H1 of an outer peripheral edge of the bead filler (6) from a bead heel is 30 to 50% of the tire section height SH; a height H2 of a position of the maximum thickness of the reinforcing rubber layer (7) from the bead heel is 35 to 55% of the tyre section height SH; and the belt cover layer (9) is formed from cord threads comprising organic fibers of a first type and organic fibers of a second type, wherein the organic fibers of the first type have a shrinkage that is greater than a shrinkage of the organic fibers of the second type, and wherein the organic fibers of the first type have an elasticity that is smaller than an elasticity of the organic fibers of the second type.

Description

Technical area

[0001] The present invention relates to a runflat pneumatic tire, and more particularly relates to a runflat pneumatic tire in which the tire weight can be reduced while maintaining runflat durability and is configured to improve ride comfort during regular driving. State of the art

[0002] For run-flat tires with a reinforcing rubber layer having a crescent-shaped cross-section on an inner surface side of a sidewall portion, prior art techniques such as increasing the thickness of the reinforcing rubber layer and using a rubber with higher hardness for the reinforcing rubber layer are used to ensure run-flat durability. However, tires whose run-flat durability has been improved in this way suffer from problems such as increased rolling resistance caused by the increased weight and deterioration in ride comfort during regular driving caused by increased lateral rigidity.

[0003] In the prior art, the use of a special rubber as the material of the reinforcing rubber layer and the blending of short fibers into the material of the reinforcing rubber layer have been proposed as measures to increase runflat durability while simultaneously improving ride comfort during regular driving (see JP 2005-343372 A). However, both of these proposals are insufficient in improving ride comfort during regular driving and reducing tire weight, and there is further room for improvement. Further prior art publications include JP 2006-182294 A, DE 60 2005 004 595 T2, JP 2005-297752 A, and US 2008 / 0 006 359 A1. Brief description of the invention

[0004] An object of the present invention is to solve the problems described above, and thus to provide a pneumatic run-flat tire in which the tire weight can be reduced while maintaining the run-flat durability and is configured to improve ride comfort during regular driving.

[0005] To achieve the above-described object, a runflat pneumatic tire according to the present invention includes a carcass layer disposed between a pair of left and right bead portions, a belt layer disposed on an outer peripheral side of the carcass layer in a tread portion, a belt cover layer disposed on an outer peripheral side of the belt layer, and a reinforcing rubber layer having a crescent-shaped cross section and disposed on an inner side of the carcass layer in a sidewall portion in the tire width direction. In a tire meridian cross section, a point at which the tire equatorial plane contacts the tread surface is T0, and a point at which a straight line drawn parallel to the tire equatorial plane from a position 40% of the total width SW measured from the point T0 meets the tread surface is T1.An angle θ formed by a straight line connecting point T0 and point T1 with respect to the tire width direction, with respect to the tire's overall width SW and a tire section height SH, satisfies a relationship of (SH / SW×6+3)°≤θ≤(SH / SW×6+8)°. A height H1 of an outer peripheral edge of the bead filler from a bead heel is 30 to 50% of the tire section height SH. A height H2 of a position of the maximum thickness of the reinforcing rubber layer from the bead heel is 35 to 55% of the tire section height SH. The belt cover layer is formed of cords comprising organic fibers of a first type and organic fibers of a second type, wherein the organic fibers of the first type have a shrinkage that is greater than a shrinkage of the organic fibers of the second type, and wherein the organic fibers of the first type have an elasticity that is smaller than an elasticity of the organic fibers of the second type. Effect of the invention

[0006] As a result of diligent research on a runflat pneumatic tire having a reinforcing rubber layer having a crescent-shaped cross section and disposed on an inner side of the carcass layer in a sidewall portion in the tire width direction, the inventors of the present invention discovered that when the thickness of the reinforcing rubber layer is reduced, the sidewall portion deforms greatly in runflat running, and a position where the carcass layer expands most toward the outer side in the tire width direction (position of the maximum tire width) is the bending point, and therefore, collapse of the reinforcing rubber layer is increased.

[0007] Therefore, in the present invention, deformation in the vicinity of the tire bead portion is suppressed, and the bending points in the sidewall portion are shifted to the tread portion side in runflat running by configuring the height H1 of the outer peripheral edge of the bead filler to 30 to 50% of the tire section height SH and the height H2 of the position of the maximum thickness of the reinforcing rubber layer to 35 to 55% of the tire section height SH.

[0008] Furthermore, in the present invention, an angle θ formed by a straight line connecting a point T0 at which the tire equatorial plane touches a tread surface and a point T1 at which a straight line drawn parallel to the tire equatorial plane from a position 40% of the total width SW of the tire measured from the point T0 meets the tread surface, with respect to the tire width direction, satisfies a relationship of (SH / SW×6+3)°≤θ≤(SH / SW×6+8)° with respect to the total width SW of the tire and a tire section height SH. This configuration also contributes to shifting the bending points in the sidewall portion toward the tread portion side in runflat running.

[0009] Thus, according to the present invention, the arrangement of the bead filler and the reinforcing rubber layer is determined, and the tread pattern is optimized. Therefore, the bending points in the sidewall portion are shifted toward the tread portion side during runflat operation. Consequently, even when the reinforcing rubber layer is thinner than that of prior art tires, sagging of the reinforcing rubber layer can be prevented and runflat durability can be maintained. Therefore, it is possible to reduce tire weight while maintaining runflat durability and also improve ride comfort during regular driving.

[0010] Therefore, in the present invention, a tan δ at 60°C of the rubber constituting the reinforcing rubber layer is preferably in a range of 0.02 to 0.15, and a dynamic elastic modulus at 60°C is preferably in a range of 5 to 20 MPa. Consequently, runflat durability can be improved and ride comfort during regular driving can be improved.

[0011] In the present invention, a tan δ at 60°C of the rubber constituting the bead filler is preferably in a range of 0.05 to 0.25, and a dynamic elastic modulus at 60°C is preferably in a range of 5 to 20 MPa. Accordingly, ride comfort during regular driving can be improved while maintaining runflat durability.

[0012] In the present invention, a cross-sectional area of ​​the reinforcing rubber layer of a tire meridian cross section is preferably 190 to 270% of a cross-sectional area of ​​the bead filler. Consequently, ride comfort can be improved while maintaining runflat durability. Short description of the drawing Fig. 1 is a meridian cross-sectional view showing a pneumatic tire according to an embodiment of the present invention. Detailed description

[0013] Fig.1 illustrates a pneumatic runflat tire according to an embodiment of the present invention, where 1 is a tread portion, 2 is a sidewall portion, and 3 is a bead portion. A carcass layer 4 having a plurality of reinforcing cords extending in the tire radial direction is disposed between a pair of left and right bead portions 3. The ends of the carcass layer 4 are wound around the bead cores 5 from the tire inner side to the tire outer side. A bead filler 6 made of a rubber composition with a high degree of hardness is disposed at the edges of the bead cores 5, and the bead filler 6 is surrounded by the carcass layer 4.

[0014] A reinforcing rubber layer 7 having a crescent-shaped cross section and made of a rubber composition with a high degree of hardness is arranged on an inner side in the tire width direction of the carcass layer 4 in the sidewall portion 2. A thickness of the reinforcing rubber layer 7 is greatest at a center portion in the tire radial direction and gradually decreases toward the tire bead portion side and the tread portion side.

[0015] A plurality of layers of a belt layer 8 are embedded on an outer peripheral side of the carcass layer 4 in the tread portion 1. These belt layers 8 include a plurality of reinforcing cords inclined with respect to the tire circumferential direction, and the reinforcing cords are arranged between the layers so as to intersect each other. A belt cover layer 9 formed by winding reinforcing cords in the tire circumferential direction is arranged on an outer peripheral side of the belt layers 8.

[0016] When the tire weight is reduced and the ride comfort is improved by reducing a thickness of the reinforcing rubber layer 7, in a runflat pneumatic tire as described above, a shape of a tire meridian cross section according to the present invention is configured as described below in order to prevent the sidewall portion 2 from deforming greatly in runflat running because the reinforcing rubber layer 7 is thin, bending points are concentrated at a position of the maximum tire widths, and the reinforcing rubber layer 7 collapses due to a large amount of deformation.

[0017] As in Fig.As shown in Figure 1, in a tire meridian cross section, a point where the tire equatorial plane E touches the tread surface is T0, and a point where a straight line drawn parallel to the tire equatorial plane E from a position 40% of the total width SW of the tire, measured from the point T0, touches the tread surface is T1. Here, an angle θ formed by a straight line connecting the point T0 and the point T1 with respect to the tire width direction, with respect to the total width SW of the tire and a tire section height SH, satisfies a relationship of (SH / SW×6+3)°≤θ≤(SH / SW×6+8)°. In other words, the angle θ is defined by the flattening.Specifically, the angle θ is in a range of 4.5 to 9.5° when the flattening is 25% (SH / SW = 0.25), the angle θ is in a range of 4.8 to 9.8° when the flattening is 30% (SH / SW = 0.30), the angle θ is in a range of 5.1 to 10.1° when the flattening is 35% (SH / SW = 0.35), the angle θ is in a range of 5.4 to 10.4° when the flattening is 40% (SH / SW = 0.40), the angle θ is in a range of 5.7 to 10.7° when the flattening is 45% (SH / SW = 0.45), the angle θ is in a range of 6.0 to 11.0° when the flattening 50% (SH / SW = 0.50), and the angle θ ranges from 6.3 to 11.3° when the flattening is 55% (SH / SW = 0.55). In any case, the angle θ is larger than that of prior art tires. Consequently, belt flexion during runflat operation can be suppressed and runflat durability can be improved.If the angle θ is smaller than (SH / SW×6+3)°, belt flexion during runflat operation cannot be suppressed, and runflat durability decreases. If the angle θ exceeds (SH / SW×6+8)°, no significant improvement in runflat durability can be expected, and the tire is prone to uneven wear.

[0018] A height H1 of an outer peripheral edge 6a of the bead filler 6 from a bead heel 3a is 30 to 50% of the tire section height SH. By configuring the height of the outer peripheral edge 6a of the bead filler 6 to be larger than that of prior art tires as described above, ride comfort during regular driving can be improved while maintaining runflat durability. If the height H1 is less than 30% of the tire section height SH, the rigidity of the tire bead portion 3 is insufficient, and runflat durability decreases. If the height H1 exceeds 50% of the tire section height SH, ride comfort during regular driving decreases.

[0019] A height H2 of a position of the maximum thickness 7a of the reinforcing rubber layer 7 from the bead heel 3a is 35 to 55% of the tire section height SH. By configuring the height of the position of the maximum thickness 7a of the reinforcing rubber layer 7 to be smaller than that of prior art tires as described above, run-flat durability can be improved. If the height H2 is less than 35% of the tire section height SH, the rigidity of the sidewall portion 2 is insufficient, and run-flat durability decreases. If the height H2 exceeds 55% of the tire section height SH, ride comfort during regular driving decreases.

[0020] It should be noted that in the present invention, the tire dimensions are measured according to methods for measuring tire dimensions prescribed by the standard on which the pneumatic tire is based (e.g., JATMA, ETRTO, or TRA).

[0021] In the present invention, a tan δ at 60°C of the rubber constituting the reinforcing rubber layer 7 is preferably in a range of 0.02 to 0.15, and more preferably in a range of 0.02 to 0.10. This can improve runflat durability. If the tan δ of the reinforcing rubber layer 7 is less than 0.02, practical manufacturing is difficult. If the tan δ of the reinforcing rubber layer 7 is over 0.15, the runflat durability cannot be sufficiently improved.

[0022] Furthermore, the dynamic elastic modulus E1 at 60°C of the rubber constituting the reinforcing rubber layer 7 is preferably in a range of 5 to 20 MPa, and more preferably in a range of 5 to 15 MPa. This can enhance ride comfort during regular driving. If the dynamic elastic modulus E1 is less than 5 MPa, runflat durability cannot be sufficiently improved. If the dynamic elastic modulus E1 is greater than 20 MPa, ride comfort during regular driving decreases.

[0023] In the present invention, a tan δ at 60°C of the rubber constituting the bead filler 6 is preferably in a range of 0.05 to 0.25, and more preferably in a range of 0.02 to 0.20. This can improve runflat durability. If the tan δ of the bead filler 6 is less than 0.02, practical manufacturing is difficult. If the tan δ of the bead filler 6 is over 0.25, the runflat durability cannot be sufficiently improved.

[0024] Furthermore, the dynamic elastic modulus E2 at 60°C of the rubber constituting the bead filler 6 is preferably in a range of 5 to 20 MPa, and more preferably in a range of 5 to 15 MPa. This can improve ride comfort during regular driving. If the dynamic elastic modulus E2 is less than 5 MPa, runflat durability cannot be sufficiently improved. If the dynamic elastic modulus E2 is over 20 MPa, ride comfort during regular driving decreases.

[0025] In the present invention, "tanδ" refers to a tanδ measured with a viscoelasticity spectrometer (manufactured by Toyo Seiki Seisaku-sho, Ltd.) under the following conditions: initial strain 10%; amplitude 2%; and frequency 20 Hz. "Dynamic elastic moduli E1 and E2" refer to moduli measured with a viscoelasticity spectrometer (manufactured by Toyo Seiki Seisaku-sho, Ltd.) under the following conditions: static strain 10%; dynamic strain ±2%; and frequency 20 Hz.

[0026] In the present invention, the dynamic elastic modulus E1 at 60 °C of the rubber constituting the reinforcing rubber layer 7 and the dynamic elastic modulus E2 at 60 °C of the rubber constituting the bead filler 6 preferably satisfy a relationship E1 <E2. Demzufolge weist eine Innenumfangsseite des Reifens eine größere Steifigkeit als eine Außenumfangsseite des Reifens im Seitenwandabschnitt 2 auf, die Biegepunkte können zur Außenumfangsseite des Reifens verschoben werden, und die Notlauf-Haltbarkeit kann verbessert werden. Wenn das Größenverhältnis der dynamischen Elastizitätsmoduln E1 und E2 E1> E2, an outer peripheral side of the tire has greater rigidity than an inner peripheral side of the tire in the sidewall portion 2, and the runflat durability cannot be sufficiently improved.

[0027] In the present invention, a cross-sectional area of ​​the reinforcing rubber layer 7 in a tire meridian cross section is preferably 190 to 270%, and more preferably 200 to 250%, of a cross-sectional area of ​​the bead filler 6. This can improve ride comfort while maintaining runflat durability. If the cross-sectional area of ​​the reinforcing rubber layer 7 is less than 190% of the cross-sectional area of ​​the bead filler 6, runflat durability decreases. If the cross-sectional area of ​​the reinforcing rubber layer 7 exceeds 270% of the cross-sectional area of ​​the bead filler 6, ride comfort during regular driving decreases.

[0028] In the present invention, an upwardly bent edge 4a of the carcass layer 4 is preferably disposed between the belt layer 8 and the carcass layer 4. If the upwardly bent edge 4a of the carcass layer 4 is disposed in the sidewall portion 2, there is a risk of breakage from the upwardly bent edge 4a during runflat running. Therefore, instead of being disposed in the sidewall portion 2, the carcass layer 4 is extended, and the upwardly bent edge 4a is disposed between the belt layer 8 and the carcass layer 4 of the tread portion 1. This can further improve runflat durability.

[0029] By forming the belt cover layer 9 from cords having two types of organic fibers with different properties, while forming a belt cover layer 9 having the high shrinkage and low elasticity characteristics of the organic fibers during regular running, sagging of the tread portion during runflat running due to the low shrinkage and high elasticity characteristics of the organic fibers can be effectively suppressed; and runflat durability, steering stability, and ride comfort can be improved. Examples of the high shrinkage and low elasticity organic fibers described above include nylon, polyester, and the like; and examples of the low shrinkage and high elasticity organic fibers include aramid, polyolefin ketone, and the like. Examples

[0030] For a prior art example, Comparative Examples 1 to 4, and Working Examples 1 to 5, ten types of tires with a typical tire size of 255 / 40RF19 were manufactured. Tire cross-sectional shapes and specifications of the bead filler and reinforcing rubber layer were configured as shown in Table 1.

[0031] The prior art example is an example where the angle θ and the height of the bead filler are smaller, and the height of the reinforcing rubber layer is larger, than the ranges specified in the present invention. Comparative Examples 1 and 2 are examples where the height of the bead filler is outside the range of the present invention. Comparative Example 3 is an example where the height of the reinforcing rubber layer is outside the range of the present invention. Comparative Example 4 is an example where the angle θ is outside the range of the present invention.

[0032] Working Examples 1 to 5 are all examples in which the tire cross-sectional shape was within the range specified in the present invention. The dynamic elastic modulus and tanδ at 60°C of the bead filler and the reinforcing rubber layer, and the cross-sectional area of ​​the bead filler and the reinforcing rubber layer were varied in each of Working Examples 1 to 5.

[0033] It should be noted that in each of Comparative Examples 1 to 3 and Working Examples 1 to 5, a reinforcing rubber layer having a maximum thickness 3 mm thinner than that used in the Prior Art Example was used as the reinforcing rubber layer.

[0034] Tire weight, runflat durability, and ride comfort were evaluated for each of the 10 tire types according to the procedures described below. The results are shown in Table 1. Tire weight

[0035] The weight of the test tires was measured. The results were indexed, with the comparison samples assigned an index value of 100. Lower index values ​​indicate lower tire weights and thus better results. Emergency running durability

[0036] Each test tire was mounted on a 19×9J wheel and installed on a 2.5L-class passenger car. A load equivalent to four passengers was applied, and the valve core was removed. The car was driven for 80 km in this condition. After driving, the tire's external appearance and inner tire surface were visually inspected. Tires that showed no serious damage were marked with a "◯," tires that showed serious damage were marked with a "△," and tires that could not complete the 80 km drive and showed damage near the tire bead portion were marked with an "×." Driving comfort

[0037] Each test tire was mounted on a 19×9J wheel and installed on a 2.5-liter passenger car. The tires were inflated to an air pressure of 250 kPa, and ride comfort on a test track was rated on a five-point scale (sensory evaluation). The comparison tire was assigned a score of 3. Higher scores indicate better ride comfort. Table 1 Comparison example Example of the state of the art 1 2 3 4 Angle θ1 ° 5,0 6,9 6,9 6,9 4,5 Bead filler Height H1 % 30 20 60 40 40 Dynamic elastic modulus E1 MPa 13,8 13,8 13,8 13,8 13,8 tanδ 0,18 0,18 0,18 0,18 0,18 Reinforcing rubber layer Height H2 % 60 45 45 70 45 Dynamic elastic modulus E2 MPa 14,1 14,1 14,1 14,1 14,1 tanδ 0 05 0,05 0,05 0,05 0,05 cross-sectional area % 300 290 170 230 230 Driving comfort 3 4 2+ 3+ 3+ Tire weight index 100 93 98 95 95 Emergency running durability index ◯ × △ △ × Table 1 (continued) Example 1 2 3 4 5 Angle θ1 ° 6,9 6,9 6,9 6,9 6,9 Bead filler Height H1 % 40 40 40 45 35 Dynamic elastic modulus E1 MPa 13,8 30 13,8 13,8 13,8 tanδ 0,18 0,27 0,18 0,18 0,18 Reinforcing rubber layer Height H2 % 45 45 45 45 45 Dynamic elastic modulus E2 MPa 14,1 14,1 30 14,1 14,1 tanδ 0,05 0,05 0,20 0,05 0,05 cross-sectional area % 230 230 230 190 270 Driving comfort 4- 3+ 3+ 4 3+ Tire weight index 95 95 95 95 95 Emergency running durability index ◯ ◯ ◯ ◯ ◯

[0038] As shown in Table 1, compared to the prior art example, in each of Examples 1 to 5, tire weight was reduced and ride comfort was improved while maintaining runflat durability. Furthermore, these performance characteristics were exhibited at a high level. On the other hand, in Comparative Examples 1 to 4, the improvements in runflat durability, tire weight, and ride comfort were insufficient. REFERENCE SYMBOL: 1 tread section 2 side wall section 3 Tire bead section 4 carcass layers 5 tire bead core 6 bead fillers 7 Reinforcing rubber layer 8 Belt layer 9 Belt cover layer E Tire equator plane SW Total width of the tire SH tire section height

Claims

[1] Run-flat pneumatic tires, comprising a carcass layer (4) arranged between a pair of left and right tire bead portions (3), a belt layer (8) arranged on an outer peripheral side of the carcass layer (4) in a tread portion (1), a belt cover layer (9) arranged on an outer peripheral side of the belt layer (8); and a reinforcing rubber layer (7) having a crescent-shaped cross-section and arranged on an inner side in the tire width direction of the carcass layer (4) in a sidewall portion (2); wherein in a tire meridian section, when a point at which a tire equator plane (E) contacts a tread surface is T0 and a point at which a straight line drawn parallel to the tire equator plane (E) from a position 40% of the total width SW of the tire measured from the point T0 meets the tread surface is T1, an angle θ formed by a straight line passing through the point T0 and the point T1 with respect to the tire width direction satisfies a relationship of (SH / SW×6+3)°≤θ≤(SH / SW×6+8)° with respect to the total width SW of the tire and a tire section height SH; a height H1 of an outer peripheral edge of the bead filler (6) from a bead heel is 30 to 50% of the tire section height SH; a height H2 of a position of the maximum thickness of the reinforcing rubber layer (7) from the bead heel is 35 to 55% of the tyre section height SH; and the belt cover layer (9) is formed from cord threads comprising organic fibers of a first type and organic fibers of a second type, wherein the organic fibers of the first type have a shrinkage that is greater than a shrinkage of the organic fibers of the second type, and wherein the organic fibers of the first type have an elasticity that is smaller than an elasticity of the organic fibers of the second type. [2] Runflat pneumatic tire according to claim 1, wherein a tanδ at 60 °C of the rubber constituting the reinforcing rubber layer (7) is in a range of 0.02 to 0.15 and a dynamic elastic modulus at 60 °C is in a range of 5 to 20 MPa. [3] Runflat pneumatic tire according to claim 1 or 2, wherein a tanδ at 60 °C of the rubber constituting the bead filler (6) is in a range of 0.05 to 0.25 and a dynamic elastic modulus at 60 °C is in a range of 5 to 20 MPa. [4] Run-flat pneumatic tire according to claim 1, 2 or 3, wherein a cross-sectional area of ​​the reinforcing rubber layer (7) in a tire meridian cross-section is in a range of 190 to 270% of a cross-sectional area of ​​the bead filler (6).

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