Pneumatic tire

Abstract

To provide a pneumatic tire which can achieve improvement of noise performance while reducing increase of rolling performance to a low level.SOLUTION: A pneumatic tire 1 includes a belt layer 7 and inner rubber 10. The inner rubber 10 includes: a first portion 11 having a first thickness t1 and extending in a tread part 2; and a second portion 12 having a second thickness t2 and extending in a pair of side wall parts 3. The first thickness t1 is larger than a second thickness t2. The belt layer 7 includes an exterior belt ply 7A. A length La in a tire axial direction of the exterior belt ply 7A ranges from 83% to 88% of a nominal sectional width of the pneumatic tire 1. A length L1 in the tire axial direction of the first portion 11 ranges from 95% to 105% of a ground width TW.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pneumatic tire. [Background technology]

[0002] Patent Document 1 below describes a tire provided with a tread and a belt, in which the arrangement of the belt is specified for the purpose of reducing rolling resistance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-096309 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, there has been a demand for improved noise performance due to environmental considerations. One known method for improving noise performance is, for example, increasing the thickness of the rubber in the tread. However, simply increasing the rubber thickness of the tread has the problem of increasing rolling resistance due to the increased rubber volume.

[0005] The present invention has been devised in view of the above circumstances, and has as its main object to provide a pneumatic tire that can improve noise performance while minimizing an increase in rolling resistance. [Means for solving the problem]

[0006] The present invention is a pneumatic tire including a tread portion, a pair of sidewall portions extending radially inward from the tread portion, a pair of bead portions continuing radially inward from the pair of sidewall portions, a carcass extending between the pair of bead portions, a belt layer disposed radially outward from the carcass in the tread portion, and an inner rubber extending between the pair of bead portions on the inner side of the carcass, the inner rubber including a first portion extending through the tread portion with a first thickness and a second portion extending through the pair of sidewall portions with a second thickness, the first thickness being greater than the second thickness, and the belt layer The pneumatic tire has a plurality of belt plies overlapped in the tire radial direction, and when the pneumatic tire is mounted on a normal rim and adjusted to a normal internal pressure under no load, the axial length of the outer belt ply arranged on the outermost side in the tire radial direction among the plurality of belt plies is 83% to 88% of the nominal cross-sectional width of the pneumatic tire, and when the tire in the normal state is loaded with 80% of a normal load and the camber angle is 0° and the tire is brought into contact with a flat surface, the distance between both ends in the axial direction that come into contact with the flat surface is defined as the contact width, and the axial length of the first portion is 95% to 105% of the contact width. [Effects of the Invention]

[0007] By adopting the above-described configuration, the pneumatic tire of the present invention can improve noise performance while minimizing an increase in rolling resistance. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a tire meridian cross-sectional view of a pneumatic tire showing one embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged view of the tread portion of FIG. [Figure 3] FIG. 3 is an enlarged view of the left half of the tread portion of FIG. 2. [Figure 4] FIG. 10 is a cross-sectional view of the vicinity of the grounding end of another embodiment. [Figure 5] FIG. 10 is a cross-sectional view of the vicinity of the grounding end of yet another embodiment. [Figure 6] FIG. 10 is a cross-sectional view of a sidewall portion according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, one embodiment of the present invention will be described with reference to the drawings. The drawings include exaggerated representations and representations that differ from the dimensional ratios of the actual structure to facilitate understanding of the present invention. Furthermore, when there are multiple embodiments, the same or common elements are designated by the same reference numerals throughout the specification, and redundant explanations will be omitted.

[0010] FIG. 1 is a cross-sectional view of a pneumatic tire 1 (hereinafter sometimes simply referred to as "tire 1") according to one embodiment of the present invention, taken along the tire meridian including the tire rotation axis (not shown). The tire 1 of this embodiment is suitable for use as a tire for passenger cars, for example. However, the present invention may also be applied to tires for heavy loads, for example. FIG. 1 shows the tire 1 in its normal state.

[0011] In the case of a pneumatic tire for which various standards are established, the "normal state" refers to a state in which the tire is mounted on a normal rim, adjusted to the normal internal pressure, and no load is applied. In the case of a tire for which various standards are not established, the normal state refers to a standard use state according to the intended use of the tire, in which the tire is not mounted on a vehicle and no load is applied. In this specification, unless otherwise specified, the dimensions of each part of the tire are values ​​measured in the normal state. Furthermore, for components that cannot be measured in the normal state (for example, the internal materials of the tire 1), the values ​​are measured by placing the tire 1 in a state as close as possible to the normal state.

[0012] A "genuine rim" is a rim that is defined for each tire by the standard system that includes the standard on which the tire is based. For example, in the case of JATMA, it is called a "standard rim," in the case of TRA, it is called a "design rim," and in the case of ETRTO, it is called a "measuring rim."

[0013] "Normal internal pressure" is the air pressure specified for each tire by each standard in the standard system, including the standard on which the tire is based. For JATMA, it is the "maximum air pressure," for TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO, it is the "INFLATION PRESSURE."

[0014] The tire 1 includes a tread portion 2, a pair of sidewall portions 3, and a pair of bead portions 4. The tread portion 2 includes a contact surface 2s that comes into contact with the road surface during running. Each sidewall portion 3 extends radially inward from the tread portion 2. Each bead portion 4 is continuous with the sidewall portion 3 on the radially inward side of the tire. A bead core 5 is embedded in each bead portion 4.

[0015] The tire 1 also includes a carcass 6, a belt layer 7, and an inner rubber 10. The carcass 6 extends between a pair of bead portions 4. The belt layer 7 is disposed in the tread portion 2 on the outer side of the carcass 6 in the tire radial direction.

[0016] The belt layer 7 is formed by stacking a plurality of belt plies in the radial direction of the tire. The plurality of belt plies includes an outer belt ply 7A disposed on the outermost side in the radial direction of the tire.

[0017] The axial length La of the outer belt ply 7A may be set within the range of 83% to 88% of the nominal section width (not shown) of the pneumatic tire. Because the length La is 83% or more of the nominal section width, the tread portion 2 is appropriately restrained, suppressing vibration during running, thereby reducing road noise (mid-frequency road noise) in the mid-frequency range of approximately 315 to 500 Hz. To effectively reduce mid-frequency road noise, the length La is preferably 84% or more of the nominal section width, and more preferably 85% or more. Because the length La is 88% or less of the nominal section width, the increase in mass of the tire 1 due to the provision of the inner rubber 10 can be suppressed, thereby minimizing the increase in rolling resistance. To further minimize the increase in rolling resistance, the length La is preferably 87% or less of the nominal section width, and more preferably 86% or less, in combination with any of the above lower limit values. As an example, the length La is preferably 84% to 87%, and more preferably 85% to 86% of the nominal cross-sectional width.

[0018] "Nominal section width" is the "nominal section width" included in the "tire designation" specified in JIS D4202 "Automobile tires - Designation and specifications."

[0019] The inner rubber 10 extends between the pair of bead portions 4 on the inner side of the carcass 6. The inner rubber 10 damps vibrations during driving and can reduce road noise (low-frequency road noise) in the low frequency range of about 70 to 100 Hz. Furthermore, the inner portion of the carcass 6 is a portion that experiences less distortion during driving than the contact patch 2s side of the tread portion 2. The inner rubber 10 arranged in this inner portion suppresses heat generation during driving, thereby suppressing an increase in rolling resistance.

[0020] The inner rubber 10 includes a first portion 11 and a second portion 12. The first portion 11 extends through the tread portion 2 with a first thickness t1. The second portion 12 extends through the pair of sidewall portions 3 with a second thickness t2. The first thickness t1 is greater than the second thickness t2. As such, the relatively thick first portion 11 is disposed in the tread portion 2, so that vibrations transmitted from the contact surface 2s of the tread portion 2 during running are effectively damped. In addition, the relatively thin second portion 12 suppresses excessive increase in mass of the tire 1 and helps maintain low rolling resistance.

[0021] The length L1 of the first portion 11 in the tire axial direction may be set within a range of 95% to 105% of the contact width TW. Such a first portion 11 can effectively attenuate vibrations transmitted from the contact patch 2s, improving noise performance, while maintaining the mass of the tire 1 and suppressing an increase in rolling resistance. To more effectively attenuate vibrations transmitted from the contact patch 2s, the length L1 is preferably 97% or more of the contact width TW, and more preferably 99% or more. To further suppress an increase in rolling resistance, the length L1, in combination with any of the above lower limit values, is preferably 103% or less of the contact width TW, and more preferably 101% or less. As an example, the length L1 is preferably 97% to 103%, and even more preferably 99% to 101% of the contact width TW.

[0022] In this specification, the contact patch width TW is the distance between the two outer ends of the tire in the axial direction that contact a flat surface when the tire 1 in the normal state is placed on the flat surface with 80% of the normal load and a camber angle of 0°. The outer ends are referred to as the contact edges Te. The axial center of the contact patch width TW is the tire equator C. The contact patch 2s includes the tire equator C and extends at least to the contact edges Te on both sides.

[0023] For pneumatic tires for which various standards are established, "normal load" refers to the load specified for each tire in the standard system including the standard on which the tire is based. For JATMA, this is "maximum load capacity," for TRA, this is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO, this is "LOAD CAPACITY." For tires for which various standards are not established, "normal load" refers to the maximum load that can be applied when using the tire in accordance with the above standards.

[0024] In this embodiment, the carcass 6 includes an inner surface 6i on the tire cavity surface 1A side that contacts the inner rubber 10, and an outer surface 6j that faces the opposite direction from the inner surface 6i and contacts the belt layer 7. The carcass 6 is configured, for example, with a single carcass ply 6A. The carcass ply 6A includes, for example, a main body portion 6a and a turned-up portion 6b. The main body portion 6a extends, for example, between the pair of bead portions 4, 4. The turned-up portion 6b is, for example, continuous with the main body portion 6a and is turned up around the bead core 5 from the inside to the outside in the tire axial direction.

[0025] The carcass ply 6A includes a plurality of carcass cords and a topping rubber covering the cords (not shown). The carcass cords are made of organic fiber cords such as aramid or rayon. The carcass cords are preferably arranged at an angle of 70 to 90 degrees relative to the tire circumferential direction.

[0026] The tread portion 2 of this embodiment includes a tread rubber 2G disposed on the outer side of the belt layer 7 in the tire radial direction, and a band layer 8 disposed between the belt layer 7 and the tread rubber 2G.

[0027] FIG. 2 is an enlarged view of the tread portion 2 of the tire 1 of FIG. 1. As shown in FIG. 2, in this embodiment, the band layer 8 includes a full band 8A extending beyond the gap between both ground contact edges Te and a pair of edge bands 8B arranged between the full band 8A and the outer belt ply 7A. In this embodiment, the edge bands 8B are spaced apart in the tire axial direction. The full band 8A and each edge band 8B extend so as to straddle the outer end 7e of the outer belt ply 7A. Such a band layer 8 suppresses vibration (movement) near the outer end 7e, thereby reducing mid-frequency road noise. The axially outer end 8e of the full band 8A and the axially outer end 8i of the edge band 8B are located, for example, axially outward of the ground contact edges Te. The outer ends 8e of the full band 8A and the outer ends 8i of the edge bands 8B are located at the same position in the tire axial direction.

[0028] The full band 8A and the edge band 8B are each made of a band ply including band cords (not shown) arranged at an angle of 5 degrees or less with respect to the tire circumferential direction and a topping rubber covering the band cords. The band cords are made of organic fibers such as nylon fibers, polyester fibers, and aramid fibers.

[0029] The tread rubber 2G includes a cap rubber portion 15 that forms the ground contact surface 2s and a base rubber portion 16 that is disposed radially inward of the cap rubber portion 15. Each of the cap rubber portion 15 and the base rubber portion 16 extends, for example, beyond both ground contact edges Te. In this embodiment, each of the cap rubber portion 15 and the base rubber portion 16 extends axially outward beyond the outer ends 8e of the full bands 8A and the outer ends 8i of the edge bands 8B.

[0030] The complex modulus of elasticity Ec* of the cap rubber portion 15 is set to be larger than the complex modulus of elasticity Eb* of the base rubber portion 16. The complex modulus of elasticity is a parameter that indicates the rigidity of each rubber portion 15, 16. By making the complex modulus of elasticity Ec* of the cap rubber portion 15 relatively larger, the rigidity of the contact patch 2s can be increased, and high steering stability performance can be ensured. By making the complex modulus of elasticity Eb* of the base rubber portion 16 relatively smaller, vibrations of the tread portion 2 can be effectively absorbed, and noise performance can be improved.

[0031] To effectively exert such effects, the complex elastic modulus Ec* of the cap rubber portion 15 is preferably 8.0 (MPa) or more, more preferably 9.0 (MPa) or more, and preferably 12.0 (MPa) or less, and more preferably 11.0 (MPa) or less. The complex elastic modulus Es* of the base rubber portion 16 is preferably 6.0 (MPa) or more, more preferably 6.5 (MPa) or more, and preferably 8.0 (MPa) or less, and more preferably 7.5 (MPa) or less.

[0032] In this specification, the complex modulus E* is a value measured in accordance with the provisions of JIS-K6394 using a dynamic viscoelasticity measuring device (Iplexer series) manufactured by GABO under the following conditions: A rubber sample used to measure the complex modulus E* is, for example, taken from a pneumatic tire 1 after vulcanization, and is taken so that the longitudinal direction of the sample coincides with the circumferential direction of the pneumatic tire 1. Initial strain: 5% Dynamic strain amplitude: ±1% Frequency: 10Hz Deformation mode: tension Measurement temperature: 30℃

[0033] Although not particularly limited, the rubber thickness d2 of the base rubber portion 16 is made smaller than the rubber thickness d1 of the cap rubber portion 15. This ensures the basic driving performance (steering stability and cornering performance) of the tire 1. If the rubber thickness d2 of the base rubber portion 16 is excessively small, noise performance may deteriorate. For this reason, the rubber thickness d2 of the base rubber portion 16 is preferably 7% or more of the rubber thickness d1 of the cap rubber portion 15, more preferably 9% or more, more preferably 16% or less, and even more preferably 12% or less.

[0034] Although not particularly limited, the rubber thickness dA of the tread rubber 2G is preferably 6% or more of the tire cross-sectional height Ha (shown in FIG. 1), more preferably 7% or more, more preferably 11% or less, and even more preferably 10% or less. Because the rubber thickness dA of the tread rubber 2G is 6% or more of the tire cross-sectional height Ha, the basic running performance of the tire 1 is ensured. Because the rubber thickness dA of the tread rubber 2G is 11% or less of the tire cross-sectional height Ha, the mass of the tire 1 is reduced, and rolling resistance is reduced. Furthermore, such a tire 1 has high cornering power and exhibits excellent steering stability. In this specification, the rubber thickness dA of the tread rubber 2G corresponds to the value obtained by dividing the cross-sectional area of ​​the tread rubber 2G between the contact edges Te by the contact width TW. The rubber thickness d1 of the cap rubber portion 15 and the rubber thickness d2 of the base rubber portion 16 are also defined in the same manner. Furthermore, the tire cross-sectional height Ha is the distance in the tire radial direction from the bead base line BL to the outermost position in the tire radial direction. The bead base line BL is a line in the tire axial direction that passes through the rim diameter position (see JATMA) determined by the standard to which the tire is based.

[0035] The tread portion 2 of this embodiment includes a crown land portion 21 that straddles the tire equator C, a middle land portion 22 that is adjacent to the crown land portion 21 in the tire axial direction, and a shoulder land portion 23 that includes a ground contact edge Te. The crown land portion 21, the middle land portion 22, and the shoulder land portion 23 are each defined by circumferential grooves 20 that extend continuously in the tire circumferential direction. In this specification, grooves including the circumferential grooves 20 refer to groove-like bodies with a width of 1.5 mm or more, and are clearly distinguished from notched sipes with a width of less than 1.5 mm.

[0036] The middle land portions 22 are arranged on both axial sides of the crown land portion 21. The shoulder land portions 23 are arranged axially outward of each middle land portion 22. The tread portion 2 of this embodiment has an axisymmetric shape with the tire equator C as the axis of symmetry.

[0037] Fig. 3 is an enlarged view of the left half of the tread portion 2 in Fig. 2. As shown in Fig. 2 or 3, the axial length Wc between the axially inner end 22i of the middle land portion 22 and the tire equator C is, for example, 8% to 16% of the contact patch width TW (shown in Fig. 1). Also, the axial length Wd between the axially outer end 22e of the middle land portion 22 and the tire equator C is, for example, 25% to 35% of the contact patch width TW.

[0038] The circumferential grooves 20 include a pair of crown circumferential grooves 24 arranged on both sides of the tire equator C, and a pair of shoulder circumferential grooves 25 arranged between each crown circumferential groove 24 and the ground contact edge Te. In this embodiment, the crown circumferential grooves 24 are provided at positions spaced apart from the tire equator C. As such, no grooves or sipes are provided on the tire equator C in this embodiment.

[0039] The plurality of belt plies includes, for example, an inner belt ply 7B disposed radially inward of the outer belt ply 7A. The plurality of belt plies in this embodiment is configured of two belt plies, the outer belt ply 7A and the inner belt ply 7B. The plurality of belt plies may be configured of three or more belt plies.

[0040] The radially outer end 7i of the inner belt ply 7B is disposed at the same position in the axial direction of the tire as the outer end 8e of the full band 8A and the outer end 8i of the edge band 8B, for example. Such a full band 8A and edge band 8B can suppress movement near the outer end 7i of the inner belt ply 7B.

[0041] Each of the outer belt ply 7A and the inner belt ply 7B includes a plurality of belt cords arranged at an angle of 15 to 45 degrees with respect to the tire circumferential direction and a topping rubber covering the cords (not shown). The belt cords may be, for example, steel cords or organic fiber cords such as aramid or rayon.

[0042] The length La of the outer belt ply 7A is preferably shorter than the axial length Lb of the inner belt ply 7B. Such an outer belt ply 7A suppresses excessive increase in the mass of the belt layer 7. From the viewpoint of achieving both the effect of reducing mid-frequency road noise and the effect of reducing rolling resistance, the length La of the outer belt ply 7A is preferably 80% or more of the axial length Lb of the inner belt ply 7B, more preferably 82% or more, and more preferably 90% or less, and even more preferably 88% or less.

[0043] The length La of the outer belt ply 7A is preferably smaller than the length L1 (shown in FIG. 1) of the first portion 11. Such an outer belt ply 7A keeps the tire mass small. In addition, the first portion 11 is highly effective in reducing low-frequency road noise.

[0044] From the viewpoint of preventing an excessive increase in mass due to the first portion 11 while achieving the effect of reducing mid-frequency road noise by the outer belt ply 7A, the length La of the outer belt ply 7A is preferably 80% or more, more preferably 82% or more, of the length L1 of the first portion 11. In addition, in combination with any of the above lower limit values, the length La of the outer belt ply 7A is preferably 90% or less, more preferably 88% or less, of the length L1 of the first portion 11. As an example, the length La of the outer belt ply 7A is preferably 80% to 90%, more preferably 82% to 88%, of the length L1 of the first portion 11.

[0045] The inner rubber 10 constitutes the tire cavity surface 1A. Such inner rubber 10 has little effect on reducing cornering power, and therefore maintains high steering stability. In this embodiment, the inner rubber 10 is made of vulcanized rubber and is different from a sealant material used to prevent punctures. The inner rubber 10 is formed, for example, by a first portion 11 and second portions 12 arranged on both sides of the first portion 11.

[0046] The first portion 11 includes end portions 14 on both outer sides in the tire axial direction. Each end portion 14 is, for example, a portion where the thickness ta of the inner rubber 10 continuously decreases toward the outer side in the tire axial direction. In this embodiment, the position where the decrease in the thickness ta ends corresponds to the outer end 11e of the first portion 11 in the tire axial direction. The outer end 11e is the end closest to the ground contact edge Te among the bending points where the thickness ta decreases toward the outer side in the tire axial direction and the tire cavity surface 1A bends convexly outward in the tire radial direction.

[0047] The outer end 11e of the first portion 11 of this embodiment is located axially outward of the crown circumferential groove 24 and further outward of the shoulder circumferential groove 25. This ensures a reduction in low-frequency road noise.

[0048] The length L6 of the end portion 14 in the tire axial direction is, for example, 2.0% to 4.0% of the contact width TW. This makes it possible to prevent a sudden change in the thickness ta of the inner rubber 10, and to suppress damage such as peeling of the inner rubber 10.

[0049] The first portion 11 includes a constant thickness portion 27 that extends at substantially the same thickness ta between the end portions 14 on both sides. The first portion 11 is formed, for example, by the constant thickness portion 27 and the end portions 14 arranged on both sides of the constant thickness portion 27. The constant thickness portion 27 is formed from the position of the tire equator C to a position on the ground contact edge Te side beyond the crown circumferential groove 24. In a desirable embodiment, the constant thickness portion 27 is formed from the position of the tire equator C to a position beyond the shoulder circumferential groove 25. Note that the term "substantially the same" means that inevitable errors in rubber products such as tires can be tolerated, and includes an embodiment in which the difference between the maximum and minimum values ​​of the thickness ta is 5% or less of the maximum value.

[0050] In this specification, the first thickness t1 of the first portion 11 and the second thickness t2 of the second portion 12 refer to the length from the inner surface 6i of the carcass 6 to the tire cavity surface 1A (the length in the normal direction to the inner surface 6i). The first thickness t1 and the second thickness t2 refer to the average thickness of the first portion 11 and the average thickness of the second portion 12, respectively. The average thickness of the first portion 11 corresponds to the value obtained by dividing the cross-sectional area of ​​the first portion 11 of the tread portion 2 in the tire meridian cross section by the length along the inner surface 6i of the carcass 6. The average thickness of the second portion 12 corresponds to the value obtained by dividing the cross-sectional area of ​​the second portion 12 from the axially outer end 11e of the first portion 11 to the tire maximum width position M (shown in FIG. 1) by the length along the inner surface 6i. The tire maximum width position M is the position of the carcass ply 6A that protrudes furthest outward in the tire axial direction. Preferably, in this embodiment, the above-described thickness relationship is maintained over the entire circumference of the tire. However, the present invention is not limited to such an embodiment.

[0051] The first thickness t1 is preferably 1.5 to 3.0 times the second thickness t2 (shown in FIG. 1). Specifically, the maximum value of the first thickness t1 is preferably 1.5 times or more, more preferably 1.8 times or more, and preferably 3.0 times or less, more preferably 2.5 times or less, and even more preferably 2.2 times or less, of the maximum value of the second thickness t2. This reliably reduces low-frequency road noise while suppressing an increase in tire mass.

[0052] From the same viewpoint, the first thickness t1 is preferably 2.0 mm or more, more preferably 2.5 mm or more, and preferably 4.5 mm or less, more preferably 4.0 mm or less, and even more preferably 3.5 mm or less. On the other hand, the second thickness t2 is, for example, greater than 0.5 mm and less than 2.0 mm. In a preferred embodiment, the second thickness t2 is 1.0 to 1.5 mm.

[0053] In this embodiment, the first portion 11 and the second portion 12 of the inner rubber 10 are made of an air-impermeable rubber material. For example, a butyl-based or halogenated butyl-based rubber material can be used as the rubber material. In this embodiment, the first portion 11 and the second portion 12 are made of the same rubber material.

[0054] The tread portion 2 of this embodiment also includes a first position A on the tire equator C, a second position H at the axially outer end 7e of the outer belt ply 7A, and a third position B at the middle 22c of the axial length of the middle land portion 22. The vicinity of the outer end 7e, which is the second position H, is a location where the movement of the outer belt ply 7A during running is likely to be large. The vicinity of the tire equator C, which is the first position A, and the middle 22c of the middle land portion 22, which is the third position B, are locations where relatively large ground contact pressure acts, significantly affecting low-frequency road noise.

[0055] When the rubber thickness of the tread rubber 2G at the first position A is Ta, the rubber thickness of the first portion 11 at the first position A is Fa, the rubber thickness of the tread rubber 2G at the second position H is Th, and the rubber thickness of the first portion 11 at the second position H is Fh, it is desirable to satisfy the following formula. (Th / (Th+Fh)) / (Ta / (Ta+Fa))=0.9~1.0 That is, the ratio of the rubber thickness Th of the tread rubber 2G to the sum of the rubber thicknesses of the tread rubber 2G and the first portion 11 at the second position H is 0.9 to 1 times the ratio of the rubber thickness Ta of the tread rubber 2G to the sum of the rubber thicknesses of the tread rubber 2G and the first portion 11 at the first position A. This effectively suppresses the movement of the outer end 7e of the outer belt ply 7A to reduce mid-frequency road noise, and also effectively reduces low-frequency road noise by the tread rubber 2G in the vicinity of the tire equator C.

[0056] Furthermore, when the rubber thickness Tb of the tread rubber 2G at the third position B and the rubber thickness Fb of the first portion 11 at the third position B are taken as Tb and Fb, respectively, it is desirable that the following formula be satisfied. (Th / (Th+Fh)) / (Tb / (Tb+Fb))=0.9~1.0 That is, the ratio of the rubber thickness Th of the tread rubber 2G at the second position H to the sum of the rubber thicknesses of the tread rubber 2G and the first portion 11 is 0.9 to 1 times the ratio of the rubber thickness Ta of the tread rubber 2G to the sum of the rubber thicknesses of the tread rubber 2G and the first portion 11 at the third position B. This effectively suppresses the movement of the outer end 7e of the outer belt ply 7A to reduce mid-frequency road noise, and also effectively reduces low-frequency road noise by the tread rubber 2G near the middle 22c of the middle land portion 22. The rubber thicknesses Th, Ta, and Tb of each tread rubber 2G are lengths normal to the contact patch 2s. The rubber thicknesses Fh, Fa, and Fb of each first portion 11 are lengths normal to the inner surface 6i.

[0057] Fig. 4 is a cross-sectional view of the vicinity of the ground-contact edge Te of the tread portion 2 of another embodiment. As shown in Fig. 4, the first portion 11 of the inner rubber 10 of this embodiment includes an inner liner layer 17 made of an air-impermeable rubber material (hereinafter referred to as the first rubber material), and an additional layer 18 disposed between the inner liner layer 17 and the carcass 6. This additional layer 18 is made of a second rubber material different from the first rubber material. For example, an air-permeable rubber material is used as the second rubber material. That is, the first portion 11 of this embodiment is formed by combining an air-impermeable rubber material and an air-permeable rubber material.

[0058] In this embodiment, the first portion 11 includes the additional layer 18, thereby improving various performances. For example, a rubber material having a higher complex modulus than the first rubber material forming the inner liner layer 17 can be used as the second rubber material forming the additional layer 18. In this case, the maximum value of the complex modulus Ea* of the first portion 11 is the complex modulus E* of the additional layer 18. The second portion 12 is formed of the inner liner layer 17. The inner liner layer 17 forms the tire cavity surface 1A.

[0059] The position of the additional layer 18 is not limited to the embodiment shown in Fig. 4. Fig. 5 is a cross-sectional view of the tread portion 2 in the vicinity of the ground contact edge Te in yet another embodiment. As shown in Fig. 5, the additional layer 18 may be disposed radially inward of the inner liner layer 17. The additional layer 18, for example, constitutes a part of the tire cavity surface 1A. Note that, as shown in Figs. 4 and 5, in these embodiments, the first thickness t1 is a thickness including the inner liner layer 17 and the additional layer 18.

[0060] FIG. 6 is an enlarged cross-sectional view of the sidewall portion 3 of another embodiment of the present invention. As shown in FIG. 6, the second portion 12 of this embodiment includes an inner liner layer 17 made of an air-impermeable first rubber material and an intermediate layer 19 disposed between the inner liner layer 17 and the carcass 6. The intermediate layer 19 is made of a rubber material different from the first rubber material. The intermediate layer 19 may be made of the same second rubber material as the additional layer 18 of the first portion 11 described in FIGS. 4 and 5, for example. The inclusion of such an intermediate layer 19 in the second portion 12 can further suppress transmission of the vibrations generated in the tread portion 2 to the vehicle side. The intermediate layer 19 may also be made of a rubber material different from the first rubber material and the second rubber material.

[0061] The intermediate layer 19 overlaps, for example, with the band layer 8 in the tire axial direction. In a desirable embodiment, the intermediate layer 19 overlaps with the belt layer 7 in the tire axial direction. The intermediate layer 19 may be continuous with the first portion 11 of the inner rubber 10. Also, it is desirable that the intermediate layer 19 extends radially inward in the tire than the radially outer end of the turned-up portion 6b of the carcass 6. In other words, in this embodiment, the intermediate layer 19 overlaps with the turned-up portion 6b in the tire radial direction. Such an intermediate layer 19 helps to further reduce low-frequency road noise or mid-frequency road noise.

[0062] Although a particularly preferred embodiment of the present invention has been described in detail above, the present invention is not limited to the illustrated embodiment and can be modified and implemented in various ways. [Example]

[0063] A pneumatic tire having the basic structure shown in Figure 1 was prototyped based on the specifications in Table 1. The test tires were then tested for noise performance and rolling resistance. The test method and common specifications for each test tire are as follows: Tire size: 205 / 55R16 Rim size: 16 x 6.5J Internal pressure: 210kPa t1:3.0mm t2:1.0mm

[0064] <Noise performance> Each test tire was mounted on all wheels of the following vehicle. A test driver drove the test vehicle on a test course, which was a circular course with a dry asphalt surface, and the loudness of noise audible inside the vehicle was evaluated by the test driver's senses. The noise performance results were expressed as a score with Comparative Example 1 being 100, with the higher the score, the better the performance. Vehicle: Passenger car (1800cc displacement)

[0065] <Rolling resistance> Each test tire was run on a rolling resistance tester under the following conditions, and its rolling resistance was measured. The results were converted into an index, with the rolling resistance of Comparative Example 1 used as the standard, with the smaller the rolling resistance, the larger the value. The results were expressed as an index with Comparative Example 1 set to 100, and a score of 98 or higher indicates a pass. Vertical load: 4.82kN Speed: 80km / h The test results are shown in Table 1.

[0066] [Table 1]

[0067] As a result of the test, the tire of the example improved noise performance by 2 points or more compared to the tire of comparative example 1, while suppressing the deterioration of rolling resistance by 2 points or less. Furthermore, the tire of the example had a higher total score for noise performance and rolling resistance compared to the tire of comparative example. Therefore, it can be understood that the tire of the example suppressed the increase in rolling resistance to a small extent and also improved noise performance compared to the tire of comparative example.

[0068] [Note] The present invention includes the following aspects.

[0069] [Invention 1] A pneumatic tire, A tread portion; a pair of sidewall portions extending radially inward from the tread portion; a pair of bead portions connected to the pair of sidewall portions on the inner side in the tire radial direction; a carcass extending between the pair of bead portions; a belt layer disposed radially outward of the carcass in the tread portion; an inner rubber extending between the pair of bead portions on the inner side of the carcass, the inner rubber includes a first portion extending through the tread portion at a first thickness and a second portion extending through the pair of sidewall portions at a second thickness, the first thickness is greater than the second thickness; The belt layer includes a plurality of belt plies superposed in the tire radial direction, When the pneumatic tire is mounted on a normal rim and is in a normal, unloaded state with the internal pressure adjusted to a normal level, the length in the tire axial direction of an outer belt ply disposed outermost in the tire radial direction among the plurality of belt plies is 83% to 88% of the nominal cross-sectional width of the pneumatic tire, When the tire in the normal state is loaded with 80% of the normal load and the camber angle is set to 0° and the tire is brought into contact with a flat surface, the distance between the two outer ends of the tire in the axial direction that come into contact with the flat surface is defined as the contact width. The length of the first portion in the tire axial direction is 95% to 105% of the contact width. Pneumatic tires. [Invention 2] The pneumatic tire according to invention 1, wherein the axial length of the outer belt ply is smaller than the axial length of the first portion. [Invention 3] The pneumatic tire according to invention 2, wherein the axial length of the outer belt ply is 80% to 90% of the axial length of the first portion. [Invention 4] the plurality of belt plies includes an inner belt ply disposed radially inward of the outer belt ply, The pneumatic tire according to any one of inventions 1 to 3, wherein the axial length of the outer belt ply is smaller than the axial length of the inner belt ply. [Invention 5] The pneumatic tire according to invention 4, wherein the length of the outer belt ply in the tire axial direction is 80% to 90% of the length of the inner belt ply in the tire axial direction. [Invention 6] the tread portion includes a tread rubber disposed on the outer side of the belt layer in the tire radial direction, A pneumatic tire according to any one of present inventions 1 to 5, wherein the following formula is satisfied when A is a first position on the tire equator, H is a second position at the outer end of the outer belt ply in the tire axial direction, Ta is a rubber thickness of the tread rubber at the first position A, Fa is a rubber thickness of the first portion at the first position A, Th is a rubber thickness of the tread rubber at the second position H, and Fh is a rubber thickness of the first portion at the second position H. (Th / (Th+Fh)) / (Ta / (Ta+Fa))=0.9~1.0 [Invention 7] The tread portion includes a crown land portion that straddles a tire equator C and a middle land portion that is adjacent to the crown land portion in the tire axial direction, A pneumatic tire according to invention 6, wherein the following formula is satisfied when a third position B is defined as a middle position in the axial length of the middle land portion, a rubber thickness Tb of the tread rubber at the third position B, and a rubber thickness Fb of the first portion at the third position B. (Th / (Th+Fh)) / (Tb / (Tb+Fb))=0.9~1.0 [Invention 8] the tread portion includes a tread rubber disposed on the outer side of the belt layer in the tire radial direction, The tread rubber includes a cap rubber portion that forms a contact surface of the tread portion, and a base rubber portion that is disposed radially inward of the cap rubber portion, 8. The pneumatic tire according to any one of claims 1 to 7, wherein the complex modulus of elasticity Ec* of the cap rubber portion is greater than the complex modulus of elasticity Eb* of the base rubber portion. [Invention 9] The complex elastic modulus Ec* of the cap rubber portion is 8.0 to 12.0 (MPa), 9. The pneumatic tire according to invention 8, wherein the complex modulus of elasticity Es* of the base rubber portion is 6.0 to 8.0 (MPa). [Explanation of symbols]

[0070] 1 pneumatic tire 2 Tread section 3 Sidewall 7 Belt Layer 7A Outer belt ply 10 Inner rubber 11 Part 1 12 Part 2 t1 First thickness t2 Second thickness

Claims

1. A pneumatic tire, A tread portion; a pair of sidewall portions extending radially inward from the tread portion; a pair of bead portions connected to the pair of sidewall portions on the inner side in the tire radial direction; a carcass extending between the pair of bead portions; a belt layer disposed radially outward of the carcass in the tread portion; an inner rubber extending between the pair of bead portions on the inner side of the carcass, the inner rubber includes a first portion extending through the tread portion at a first thickness and a second portion extending through the pair of sidewall portions at a second thickness, the first thickness is greater than the second thickness; The belt layer includes a plurality of belt plies superposed in the tire radial direction, When the pneumatic tire is mounted on a normal rim and is in a normal, no-load state with the internal pressure adjusted to a normal value, the length in the tire axial direction of an outer belt ply disposed outermost in the tire radial direction among the plurality of belt plies is 83% to 88% of the nominal cross-sectional width of the pneumatic tire, When the tire in the normal state is loaded with 80% of the normal load and the camber angle is set to 0°, and the tire is brought into contact with a flat surface, the distance between both outer ends of the tire in the axial direction that come into contact with the flat surface is defined as the contact width. The length of the first portion in the tire axial direction is 95% to 105% of the contact width. Pneumatic tires.

2. The pneumatic tire according to claim 1 , wherein the axial length of the outer belt ply is smaller than the axial length of the first portion.

3. The pneumatic tire according to claim 2, wherein the axial length of the outer belt ply is 80% to 90% of the axial length of the first portion.

4. the plurality of belt plies includes an inner belt ply disposed radially inward of the outer belt ply, The pneumatic tire according to claim 1 , wherein the axial length of the outer belt ply is smaller than the axial length of the inner belt ply.

5. The pneumatic tire according to claim 4, wherein the axial length of the outer belt ply is 80% to 90% of the axial length of the inner belt ply.

6. the tread portion includes a tread rubber disposed on the outer side of the belt layer in the tire radial direction, 6. The pneumatic tire according to claim 1, wherein the following formula is satisfied when a first position A on the tire equator, a second position H at the outer end of the outer belt ply in the tire axial direction, a rubber thickness Ta of the tread rubber at the first position A, a rubber thickness Fa of the first portion at the first position A, a rubber thickness Th of the tread rubber at the second position H, and a rubber thickness Fh of the first portion at the second position H are used: (Th / (Th+Fh)) / (Ta / (Ta+Fa))=0.9~1.0

7. the tread portion includes a crown land portion that straddles a tire equator C and a middle land portion that is adjacent to the crown land portion in the tire axial direction, 7. The pneumatic tire of claim 6, wherein the following formula is satisfied when a third position B is defined as a middle position in the tire axial length of the middle land portion, a rubber thickness Tb of the tread rubber at the third position B, and a rubber thickness Fb of the first portion at the third position B: (Th / (Th+Fh)) / (Tb / (Tb+Fb))=0.9 to 1.0

8. the tread portion includes a tread rubber disposed on the outer side of the belt layer in the tire radial direction, The tread rubber includes a cap rubber portion that forms a contact surface of the tread portion, and a base rubber portion that is disposed radially inward of the cap rubber portion, The pneumatic tire according to claim 1 , wherein the complex modulus of elasticity Ec* of the cap rubber portion is greater than the complex modulus of elasticity Eb* of the base rubber portion.

9. The complex elastic modulus Ec* of the cap rubber portion is 8.0 to 12.0 (MPa), The pneumatic tire according to claim 8, wherein the complex elastic modulus Es* of the base rubber portion is 6.0 to 8.0 (MPa).

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