Pneumatic tire

Abstract

To provide a pneumatic tire which achieves improvement of noise performance while reducing deterioration of low rolling performance.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 average thickness t1 and extending in a tread part 2; and a second portion 12 having a second average thickness t2 and extending in a pair of side wall parts 3. The first average thickness t1 is larger than a second average 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 is equal to or shorter than 85% of a nominal sectional width of the pneumatic tire 1. A length L1 in the tire axial direction of the first portion 11 is larger than a length La in the tire axial direction of the exterior belt play 7A.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 in which a belt layer is arranged inside the tread portion. In this tire, the belt cords and topping rubber of the belt ply of the belt layer are specified for the purpose of improving noise performance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-070349 Summary of the Invention [Problem to be solved by the invention]

[0004] One known method for improving noise performance is to increase the axial length of the belt layer, but this method has the problem of deteriorating low rolling resistance, which is desirable from an environmental perspective.

[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 deterioration in low rolling resistance performance. [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, wherein the inner rubber has a first portion extending through the tread portion at a first average thickness and a second portion extending through the pair of sidewall portions at a second average thickness. and a second portion, wherein the first average thickness is greater than the second average thickness, the belt layer is formed by overlapping a plurality of belt plies in the tire radial direction, and when the pneumatic tire is mounted on a normal rim and in a normal, unloaded state adjusted to a normal internal pressure, the axial length of an outer belt ply disposed outermost in the tire radial direction among the plurality of belt plies is 85% or less of a nominal cross-sectional width of the pneumatic tire, and the axial length of the first portion is greater than the axial length of the outer belt ply. [Effects of the Invention]

[0007] By adopting the above-described configuration, the pneumatic tire of the present invention can improve noise performance while minimizing deterioration in low rolling resistance performance. [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 left half of the tread portion of another embodiment. [Figure 5] FIG. 10 is a cross-sectional view of the vicinity of the grounding end of another embodiment. [Figure 6] FIG. 10 is a cross-sectional view of the vicinity of the grounding end of yet another embodiment. [Figure 7] 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 (not shown), 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 the pair of bead portions 4. In this embodiment, the carcass 6 includes an inner surface 6i on the tire cavity surface 1A side that comes into contact with the inner rubber 10, and an outer surface 6j that faces opposite to the inner surface 6i and comes into contact with the belt layer 7.

[0016] The belt layer 7 is disposed on the radially outer side of the carcass 6 in the tread portion 2. The belt layer 7 is formed by overlapping 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 radially outermost side of the tire.

[0017] The axial length La of the outer belt ply 7A is set to a range of 85% or less of the nominal section width (not shown) of the pneumatic tire. Such an outer belt ply 7A can reduce rolling resistance and maintain high low rolling performance. The "nominal section width" is the "nominal section width" included in the "tire designation" specified in JIS D4202 "Automobile tires - Designation and specifications."

[0018] 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 running and can reduce road noise (low-frequency road noise) in the low-frequency range of about 1 to 100 Hz. Therefore, even when the outer belt ply 7A has the above-mentioned axial length La, noise performance can be improved. Furthermore, the inner side of the carcass 6 is a portion that experiences less strain during running than the contact patch 2s side of the tread portion 2. The inner rubber 10 suppresses heat generation during running, thereby suppressing an increase in rolling resistance and preventing a deterioration in low rolling performance.

[0019] 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 average thickness t1 (shown in FIG. 3). The second portion 12 extends through the pair of sidewall portions 3 with a second average thickness t2 (shown in FIG. 3). The first average thickness t1 is greater than the second average thickness t2. The first portion 11, which is relatively thick, effectively attenuates vibrations transmitted from the contact surface 2s of the tread portion 2 during running, thereby improving noise performance. The second portion 12, which is relatively thin, reduces the mass of the tire 1 and reduces rolling resistance.

[0020] The first average thickness t1 corresponds to the value obtained by dividing the cross-sectional area of ​​the first portion 11 in the tire meridian cross section by the length along the inner surface 6i of the carcass 6. Both axially outer ends 11e of the first portion 11 are the ends closest to the outer end 7e of the outer belt ply 7A among the bending points va where the thickness ta (shown in FIG. 3) of the inner rubber 10 decreases toward the outer side in the tire axial direction and the tire cavity surface 1A bends convexly outward in the tire radial direction. The second average thickness t2 corresponds to the value obtained by dividing the cross-sectional area of ​​the second portion 12 from the outer end 11e of the first portion 11 to the tire maximum width position M by the length along the inner surface 6i. The thickness ta (shown in FIG. 3) of the inner rubber 10 is the length in the normal direction of the inner surface 6i between the inner surface 6i of the carcass 6 and the tire cavity surface 1A. The tire maximum width position M is the position where the carcass ply 6A protrudes furthest outward in the tire axial direction.

[0021] The axial length L1 of the first portion 11 is greater than the length La of the outer belt ply 7A. Such a first portion 11 effectively damps the vibrations that pass axially outward of the outer belt ply 7A. Furthermore, the first portion 11 ensures a sufficient tread thickness at the axially outer end 7e of the outer belt ply 7A, thereby suppressing vibrations at the outer end 7e of the outer belt ply 7A, thereby reducing road noise in the mid-frequency range of about 250 to 350 Hz (mid-frequency road noise).

[0022] From the viewpoint of suppressing an increase in the mass of the tire 1, the length L1 of the first portion 11 is preferably 145% or less of the length La of the outer belt ply 7A, more preferably 140% or less, and even more preferably 135% or less. Also, from the viewpoint of further enhancing the vibration damping effect of the first portion 11 during running and the effect of suppressing vibration of the outer end 7e of the outer belt ply 7A, in combination with any of the above upper limit values, the length L1 of the first portion 11 is preferably 115% or more of the length La of the outer belt ply 7A, more preferably 120% or more, and even more preferably 125% or more. As an example, the length L1 of the first portion 11 is preferably 115% to 145%, further preferably 120% to 140%, and further preferably 125% to 135% of the length La of the outer belt ply 7A.

[0023] Furthermore, in order to maintain high low rolling resistance, the length La of the outer belt ply 7A is preferably 84% or less of the nominal cross-sectional width, more preferably 83% or less, and even more preferably 82% or less. If the length La of the outer belt ply 7A is excessively small, it may be impossible to suppress vibrations during running or vibrations of the outer end 7e of the outer belt ply 7A. From this perspective, in combination with any of the above upper limits, the length La of the outer belt ply 7A is preferably 75% or more of the nominal cross-sectional width, more preferably 77% or more, and even more preferably 79% or more. As an example, the length La of the outer belt ply 7A is preferably 75% to 82%, more preferably 77% to 83%, and even more preferably 79% to 84% of the nominal cross-sectional width.

[0024] The carcass 6 is made up of, for example, two carcass plies 6A, 6B. Each of the carcass plies 6A, 6B includes, for example, a main body portion 6a and a turned-up portion 6b. Each main body portion 6a extends, for example, between a pair of bead portions 4, 4. Each turned-up portion 6b is connected to, for example, the main body portion 6a and is turned up around the bead core 5 from the inside to the outside in the axial direction of the tire. Note that the carcass 6 may be made up of, for example, a single carcass ply.

[0025] Each of the carcass plies 6A, 6B includes a plurality of carcass cords and a topping rubber covering the cords (not shown). The carcass cords are made of organic fiber 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 Fig. 1. As shown in Fig. 2, in this embodiment, the band layer 8 is composed of a full band 8A that extends beyond both ground contact edges Te. The full band 8A extends 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.

[0028] In this specification, the contact edge Te is the axially outer contact position that comes into contact with a flat surface when the tire 1 in a normal state is placed on the flat surface with 70% of the normal load and a camber angle of 0°. The axial distance between the contact edges Te is the contact width TW. The axial center of the contact 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.

[0029] 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.

[0030] The full band 8A is composed 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.

[0031] The tread rubber 2G includes a cap rubber portion 2C that forms the ground contact surface 2s and a base rubber portion 2B that is disposed radially inward of the cap rubber portion 2C. Each of the cap rubber portion 2C and the base rubber portion 2B extends, for example, beyond both ground contact edges Te. In this embodiment, the cap rubber portion 2C extends axially outward beyond the outer end 7e of the outer belt ply 7A and further extends axially outward of the outer end 8e of the full band 8A. The base rubber portion 2B extends, for example, to the outer end 7e of the outer belt ply 7A.

[0032] The complex modulus Ec* of the cap rubber portion 2C is set to be larger than the complex modulus Eb* of the base rubber portion 2B. The complex modulus is a parameter that indicates the rigidity of each rubber portion 2C, 2B. By relatively increasing the complex modulus Ec* of the cap rubber portion 2C, the rigidity of the contact patch 2s can be increased, and high steering stability performance can be ensured. By relatively decreasing the complex modulus Eb* of the base rubber portion 2B, vibrations of the tread portion 2 can be effectively absorbed, and noise performance can be improved.

[0033] To effectively exert the above-mentioned effects, the complex elastic modulus Ec* of the cap rubber part 2C is preferably 5.1 MPa or more, more preferably 6.0 MPa or more, and preferably 13.0 MPa or less, and more preferably 12.0 MPa or less. The complex elastic modulus Eb* of the base rubber part 2B is preferably 3.2 MPa or more, more preferably 3.4 MPa or more, and preferably 4.6 MPa or less, and more preferably 4.2 MPa or less.

[0034] 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℃

[0035] Although not particularly limited, the rubber thickness d2 of the base rubber portion 2B is made smaller than the rubber thickness d1 of the cap rubber portion 2C. 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 2B is excessively small, noise performance may deteriorate. For this reason, the rubber thickness d2 of the base rubber portion 2B is preferably 7% or more of the rubber thickness d1 of the cap rubber portion 2C, more preferably 9% or more, more preferably 16% or less, and even more preferably 12% or less.

[0036] 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 low rolling performance is maintained. 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 2C and the rubber thickness d2 of the base rubber portion 2B 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.

[0037] The tread portion 2 of this embodiment is provided with a plurality of circumferential grooves 20. The circumferential grooves 20 are grooves 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.

[0038] The circumferential grooves 20 include a pair of crown circumferential grooves 21 arranged on both sides of the tire equator C, and a pair of shoulder circumferential grooves 22 arranged between each crown circumferential groove 21 and the ground contact edge Te. In this embodiment, the crown circumferential grooves 21 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] For example, the radially outer end 7i of the inner belt ply 7B is located more inward in the axial direction of the tire than the outer end 8e of the full band 8A, so that vibrations near the outer end 7i of the inner belt ply 7B are reduced by the full band 8A.

[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 axial length Lb of the inner belt ply 7B is, for example, greater than the length La (shown in FIG. 1) of the outer belt ply 7A. Such an inner belt ply 7B helps to reduce mid-frequency road noise. From the viewpoint of maintaining high low rolling performance while ensuring the effect of reducing mid-frequency road noise, the length Lb of the inner belt ply 7B is preferably 102% or more of the length La of the outer belt ply 7A, more preferably 105% or more, and more preferably 112% or less, and even more preferably 110% or less.

[0043] The inner rubber 10 constitutes the tire cavity surface 1A. 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 a pair of second portions 12 arranged on both sides of the first portion 11.

[0044] The first portion 11 includes a thick portion 13 having a large thickness and a thin portion 14 having a smaller thickness than the thick portion 13. The first portion 11 also includes a medium-thickness portion 15 having a smaller thickness than the thick portion 13 and a larger thickness than the thin portion 14. The thick portion 13 helps to reduce low-frequency road noise. The thin portion 14 prevents the first portion 11 from increasing in mass.

[0045] The thick portion 13 is located, for example, at an axially outer end 11e of the first portion 11. In this embodiment, the thick portion 13 is provided at each of the outer ends 11e of the first portion 11. Such thick portion 13 helps to more effectively damp vibrations that pass axially outer than the outer belt ply 7A during running.

[0046] FIG. 3 is an enlarged view of the left half of the tread portion 2 in FIG. 2. As shown in FIG. 3, in this embodiment, the thick-walled portion 13 includes a gradually increasing portion 13a whose thickness increases axially outward, a constant-thickness portion 13b that extends at substantially the same thickness, and a gradually decreasing portion 13c whose thickness decreases axially outward. The constant-thickness portion 13b is, for example, located between the gradually increasing portion 13a and the gradually decreasing portion 13c. The gradually decreasing portion 13c is, for example, located axially outward of the constant-thickness portion 13b. Such a thick-walled portion 13 reduces the change in mass between the thick-walled portion 13 and the thin-walled portion 14 and between the thick-walled portion 13 and the second portion 12, thereby reducing distortion during running and suppressing heat generation. This suppresses an increase in rolling resistance. The term "substantially the same" means that inevitable variations in rubber products such as tires can be tolerated. In this embodiment, the axially outer end of the gradually tapering portion 13c is the outer end 11e of the first portion 11. Note that the thick portion 13 is not limited to this embodiment, and may be formed, for example, by only the constant thickness portion 13b.

[0047] The thickened portion 13 is preferably provided so that the outer end 7e of the outer belt ply 7A and the outer end 7i of the inner belt ply 7B are located radially outward of the tire. Such thickened portion 13 can suppress vibration of the outer end 7e of the outer belt ply 7A and the outer end 7i of the inner belt ply 7B, thereby further reducing mid-frequency road noise. The inner belt ply 7B is in contact with, for example, the outer surface 6j (shown in FIG. 1).

[0048] The length L6 of the constant thickness portion 13b along the inner surface 6i is preferably 45% or more, more preferably 50% or more, of the length L5 of the thick-walled portion 13 along the inner surface 6i. While not particularly limited, the length L6 of the constant thickness portion 13b is preferably 65% ​​or less, more preferably 60% or less, of the length L5 of the thick-walled portion 13. Such a constant thickness portion 13b enhances the effects of reducing distortion during running, damping vibration during running, and suppressing an increase in rolling resistance in a well-balanced manner. The length of the gradually increasing portion 13a along the inner surface 6i is, for example, shorter than the length of the gradually decreasing portion 13c along the inner surface 6i. The length of the gradually increasing portion 13a along the inner surface 6i may be the same as the length of the gradually decreasing portion 13c along the inner surface 6i.

[0049] In order to effectively suppress vibration of the outer end 7e of the outer belt ply 7A and vibration of the outer end 7i of the inner belt ply 7B, and to suppress an increase in the mass of the thick portion 13, the thickness tx of the thick portion 13 is preferably 2.0 mm or more, more preferably 2.5 mm or more, and is preferably 4.0 mm or less, and more preferably 3.5 mm or less.

[0050] The thickness tx of the thick portion 13 is preferably 120% or more of the thickness ty of the thin portion 14, more preferably 160% or more, even more preferably 200% or more, and preferably 600% or less, even more preferably 500% or less, and even more preferably 400% or less. This improves the effect of reducing low-frequency road noise and the effect of suppressing the mass of the first portion 11 in a well-balanced manner.

[0051] The thick portion 13 is a portion where the tire cavity surface 1A is bent convexly outward in the tire radial direction and is sandwiched between two bending points v, v (shown in FIG. 2) adjacent in the tire axial direction. The thickness tx of the thick portion 13 is the maximum value in the normal direction of the inner surface 6i between the inner surface 6i of the carcass 6 and the tire cavity surface 1A. The intermediate portion 15 is specified in the same manner as the thick portion 13. The thickness ty of the thin portion 14 and the thickness tz of the intermediate portion 15 are specified in the same manner as the thickness tx of the thick portion 13.

[0052] In this embodiment, the intermediate thickness portion 15 is disposed radially inward of the circumferential groove 20. Such intermediate thickness portion 15 effectively damps vibrations transmitted from the groove bottoms 20s of the circumferential grooves 20 during running, thereby reducing low-frequency road noise. Similar to the thick portion 13, the intermediate thickness portion 15 is formed of a gradually increasing portion 15a, a constant-width portion 15b, and a gradually decreasing portion 15c.

[0053] The intermediate thickness portion 15 has, for example, a length L7 along the inner surface 6i that is greater than the groove width Wg of the circumferential groove 20. An axially inner end 15i of the intermediate thickness portion 15 is, for example, located axially more inward than an axially inner end 20i of the circumferential groove 20. An axially outer end 15e of the intermediate thickness portion 15 is, for example, located axially more outward than an axially outer end 20e of the circumferential groove 20. Such an intermediate thickness portion 15 more effectively damps vibrations transmitted from the groove bottoms 20s of the circumferential grooves 20 during running. The intermediate thickness portion 15 is arranged radially inward of the crown circumferential grooves 21 and the shoulder circumferential grooves 22.

[0054] 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.

[0055] The complex elastic modulus Ea* of the first portion 11 is desirably smaller than the complex elastic modulus Ec* of the cap rubber portion 2C. This reduces the heat generated by the first portion 11, thereby maintaining high low rolling resistance. Here, if the first portion 11 is composed of a single element, the complex elastic modulus Ea* of the first portion 11 is the complex elastic modulus of that element. If the first portion 11 is composed of multiple elements, the complex elastic modulus Ea* of the first portion 11 is the maximum complex elastic modulus of the elements.

[0056] FIG. 4 is a cross-sectional view of the tread portion 2 of another embodiment near the ground contact edge Te. As shown in FIG. 4, in this embodiment, the thick portion 13 includes a gradually decreasing portion 13c having a relatively large length in the tire axial direction. The length L8 of the gradually decreasing portion 13c along the inner surface 6i is set to be 80% or more of the length L5 (shown in FIG. 3) of the thick portion 13. In this case, the thick portion 13 may be formed of the gradually decreasing portion 13c and a constant width portion (not shown) connected to the gradually decreasing portion 13c. Alternatively, the thick portion 13 may be formed of the gradually decreasing portion 13c and a gradually increasing portion (not shown) connected to the gradually decreasing portion 13c. The thick portion 13 of this embodiment is formed only by the gradually decreasing portion 13c. The thick portion 13 includes the outer end 11e of the first portion 11.

[0057] Fig. 5 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. 5, 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] Fig. 6 is a cross-sectional view of the vicinity of the ground contact edge Te of the tread portion 2 in yet another embodiment. As shown in Fig. 6, 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. 5 and 6, in these embodiments, the first average thickness t1 is a thickness including the inner liner layer 17 and the additional layer 18.

[0060] FIG. 7 is an enlarged cross-sectional view of the sidewall portion 3 of another embodiment of the present invention. As shown in FIG. 7, the second portion 12 of this embodiment includes an inner liner layer 17 made of a first rubber material having air impermeability 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. 5 and 6, for example. By including such an intermediate layer 19 in the second portion 12, transmission of the vibrations generated in the tread portion 2 to the vehicle side can be further suppressed. Note that 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 low rolling resistance and noise performance. The test method and common specifications for each test tire are as follows: Tire size: 225 / 45R17 Rim size: 17 x 7.0J Internal pressure: 250kPa First average thickness t1: 2.0 mm Second average thickness t2: 0.5 mm

[0064] <Low rolling performance> 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, and the smaller the rolling resistance, the larger the value. The value is expressed as an index with Comparative Example 1 being 100, and a value of 95 or higher is considered pass. Vertical load: 5.26kN Speed: 80km / h

[0065] <Noise performance> Each test tire was mounted on all wheels of the following vehicle. Then, a test driver drove the test vehicle on a road noise measurement road (rough asphalt road) at a speed of 60 km / h, and the interior noise was collected using a microphone installed near the driver's ear on the window side. Then, the peak sound pressure levels of low-frequency road noise from 1 to 100 Hz and mid-frequency road noise from 250 to 350 Hz were measured. The results were converted into an index, with each sound pressure level of Comparative Example 1 used as a reference, and the smaller the sound pressure level, the larger the numerical value. The numerical value was calculated by adding up each sound pressure level and displaying it as an index with Comparative Example 1 set to 100, with the larger the index, the better. Vehicle: Passenger car (2000cc displacement) The test results are shown in Tables 1 and 2.

[0066] [Table 1]

[0067] [Table 2]

[0068] As a result of the test, it can be seen that the tires of the example have significantly improved noise performance while minimizing deterioration in low rolling resistance performance compared to the tires of the comparative example.

[0069] [Note] The present invention includes the following aspects.

[0070] [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 average thickness and a second portion extending through the pair of sidewall portions at a second average thickness, the first average thickness is greater than the second average 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 state with no load and adjusted to a normal internal pressure, 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 85% or less of a nominal cross-sectional width of the pneumatic tire, The length of the first portion in the tire axial direction is greater than the length of the outer belt ply in the tire axial direction. Pneumatic tires. [Invention 2] The pneumatic tire according to invention 1, wherein the axial length of the first portion is 115% to 145% of the axial length of the outer belt ply. [Invention 3] The pneumatic tire according to invention 2, wherein the axial length of the first portion is 125% to 135% of the axial length of the outer belt ply. [Invention 4] The pneumatic tire according to any one of claims 1 to 3, wherein the first portion includes a thick portion having a large thickness and a thin portion having a smaller thickness than the thick portion. [Invention 5] 5. The pneumatic tire according to claim 4, wherein the thick portion has a thickness that is 120% to 600% of the thickness of the thin portion. [Invention 6] 6. The pneumatic tire according to claim 5, wherein the thickness of the thick portion is 200% to 400% of the thickness of the thin portion. [Invention 7] 7. The pneumatic tire according to any one of claims 4 to 6, wherein the thick portion has a thickness of 2.0 to 4.0 mm. [Invention 8] The pneumatic tire according to any one of inventions 4 to 7, wherein the thick portion is located at an outer end of the first portion in the tire axial direction. [Invention 9] 9. The pneumatic tire according to any one of aspects 4 to 8, wherein the thick-walled portion has a thickness that continuously decreases toward the outside in the tire axial direction. [Invention 10] 10. The pneumatic tire according to any one of claims 4 to 9, wherein the first portion includes a medium-thickness portion that is thinner than the thick portion and thicker than the thin portion. [Explanation of symbols]

[0071] 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 average thickness t2 Second average 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 average thickness and a second portion extending through the pair of sidewall portions at a second average thickness, the first average thickness is greater than the second average 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 state with no load and adjusted to a normal internal pressure, 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 85% or less of a nominal cross-sectional width of the pneumatic tire, The axial length of the first portion is greater than the axial length of the outer belt ply. Pneumatic tires.

2. The pneumatic tire according to claim 1, wherein the axial length of the first portion is 115% to 145% of the axial length of the outer belt ply.

3. The pneumatic tire according to claim 2, wherein the axial length of the first portion is 125% to 135% of the axial length of the outer belt ply.

4. The pneumatic tire according to claim 1 , wherein the first portion includes a thick portion having a large thickness and a thin portion having a smaller thickness than the thick portion.

5. The pneumatic tire according to claim 4, wherein the thickness of the thick portion is 120% to 600% of the thickness of the thin portion.

6. The pneumatic tire according to claim 5, wherein the thickness of the thick portion is 200% to 400% of the thickness of the thin portion.

7. The pneumatic tire according to claim 4, wherein the thick portion has a thickness of 2.0 to 4.0 mm.

8. The pneumatic tire according to claim 4 , wherein the thick portion is located at an outer end of the first portion in the tire axial direction.

9. The pneumatic tire according to claim 8 , wherein the thick-walled portion has a thickness that continuously decreases toward an outer side in the tire axial direction.

10. The pneumatic tire according to claim 4 , wherein the first portion includes a medium-thickness portion that is thinner than the thick portion and thicker than the thin portion.

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