Pneumatic tire

Abstract

To provide a pneumatic tire that is configured so that noise and resistance can suppressed during rolling thereof.SOLUTION: The pneumatic tire includes an inside rubber 10 extending between a pair of bead parts 4, inside a carcass 6. The inside rubber 10 includes a first portion 11 arranged in a tread part 2. The first portion 11 includes: a center portion 11c extending in a tire circumferential direction with a first thickness t1 on a tire equator C; a middle portion 11m extending in the tire circumferential direction with a second thickness t2, outside in a tire axial direction of the center portion 11c; and an outer portion 11o extending in the tire circumferential direction with a third thickness t3, outside in the tire axial direction of the middle portion 11m. The second thickness t2 is smaller than the first thickness t1 and the third thickness t3.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] BACKGROUND ART Conventionally, pneumatic tires have been known in which a thick portion is formed in the crown portion, the thickness from the outer peripheral surface of the carcass to the inner peripheral surface of the inner liner being thicker than other portions (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-120448 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the pneumatic tire disclosed in Patent Document 1, if the axial length of the thick portion is insufficient, noise generated when the tire rolls may not be sufficiently suppressed. On the other hand, if the axial length of the thick portion is set to be long, the weight of the tire increases, and the rolling resistance increases.

[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 suppress noise and resistance during rolling. [Means for solving the problem]

[0006] The present invention is a pneumatic tire, A tread portion; A pair of sidewall portions; a pair of bead portions; a carcass extending between the pair of bead portions; an inner rubber extending between the pair of bead portions on the inner side of the carcass, the inner rubber includes a first portion disposed in the tread portion, the first portion includes a center portion extending circumferentially on the tire equator at a first thickness, a middle portion extending circumferentially on at least one axially outer side of the center portion at a second thickness, and an outer portion extending circumferentially on the one axially outer side of the middle portion at a third thickness, The second thickness is less than the first thickness and the third thickness. [Effects of the Invention]

[0007] By adopting the above-described configuration, the pneumatic tire of the present invention can easily suppress noise and rolling resistance when the pneumatic tire rolls. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view showing an embodiment of a pneumatic tire of the present invention. [Figure 2] FIG. 2 is an enlarged cross-sectional view of the tread portion of FIG. 1. [Figure 3] FIG. 1 is a cross-sectional view conceptually showing standing waves generated in a tread portion at a resonance frequency of 315 Hz. [Figure 4] FIG. 1 is a side view showing a pneumatic tire during running. [Figure 5] FIG. 10 is an enlarged cross-sectional view of a first portion and a second portion of another embodiment of the present invention. [Figure 6] FIG. 10 is an enlarged cross-sectional view of a first portion and a second portion of yet another embodiment of the present invention. [Figure 7] FIG. 10 is an enlarged cross-sectional view of a sidewall portion according to yet another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of the present invention will now be described with reference to the drawings. FIG. 1 shows a cross-sectional view of a pneumatic tire 1 (hereinafter, sometimes simply referred to as "tire 1") illustrating one embodiment of the present invention. FIG. 1 is a cross-sectional view of a tire in a normal state, including the axis of rotation. As shown in FIG. 1, tire 1 of this embodiment is suitable for use as, for example, a pneumatic tire for passenger cars. However, the present invention is not limited to this embodiment and may be applied to, for example, a pneumatic tire for heavy loads.

[0010] "Normal condition" means, in the case of a pneumatic tire for which various standards are established, a state in which the tire is mounted on a normal rim, inflated 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 condition means 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 condition. Furthermore, for components that cannot be measured in the normal condition (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 condition.

[0011] 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."

[0012] "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."

[0013] The tire 1 includes a tread portion 2, a pair of sidewall portions 3, and a pair of bead portions 4. The sidewall portions 3 are connected to the axially outer side of the tread portion 2 and extend in the radial direction of the tire. The bead portions 4 are connected to the radially inner side of the sidewall portions 3. The tire 1 also includes a carcass 6 and an inner rubber 10. The carcass 6 extends between the pair of bead portions 4. In other words, the carcass 6 extends from one bead portion 4, through one sidewall portion 3, the tread portion 2, and the other sidewall portion 3, to the other bead portion 4. The inner rubber 10 is disposed inside the carcass 6 and extends between the pair of bead portions 4. As a result, the inner rubber 10 forms the tire cavity surface 1A. The inner rubber 10 is made of vulcanized rubber, and is significantly different in material and physical properties from puncture prevention sealant materials.

[0014] The carcass 6 is composed of, for example, one 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 two bead portions 4. The turned-up portion 6b is, for example, continuous with the main body portion 6a and turned up around the bead core 5 from the axially inner side to the axially outer side of the tire.

[0015] 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 such as aramid or rayon. The carcass cords are preferably arranged at an angle of 70 to 90 degrees with respect to the tire equator C.

[0016] FIG. 2 shows an enlarged cross-sectional view of the tread portion 2 of FIG. 1. As shown in FIG. 2, the tread portion 2 of this embodiment includes, for example, a belt layer 7 and a band layer 8 disposed radially outward of the carcass 6. However, the tread portion 2 is not limited to this configuration. The belt layer 7 includes a first belt ply 7A adjacent to the carcass 6 and a second belt ply 7B disposed radially outward of the first belt ply 7A. Each of the first belt ply 7A and the second 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 belt cords. The belt cords of the first belt ply 7A and the belt cords of the second belt ply 7B are inclined in opposite directions with respect to the tire circumferential direction. This effectively reinforces the tread portion 2.

[0017] The axial length of the second belt ply 7B is preferably shorter than the axial length of the first belt ply 7A, so that the axially outer end of the second belt ply 7B is located axially more inward than the axially outer end of the first belt ply 7A.

[0018] The band layer 8 is composed of, for example, one band ply 8 A. The band ply 8 A includes, for example, a band cord arranged at an angle of 5° or less with respect to the tire circumferential direction, and a topping rubber covering the band cord.

[0019] The band layer 8 of the present embodiment is arranged so as to cover the entire belt layer 7. The band layer 8 may be arranged so as to cover a part of the belt layer 7. For example, the band layer 8 may be arranged so as to locally cover the vicinity of the outer end of the belt layer 7 in the tire axial direction.

[0020] As shown in Fig. 1, the inner rubber 10 includes a first portion 11 disposed in the tread portion 2. The first portion 11 extends continuously in the tire circumferential direction.

[0021] As shown in Figures 1 and 2, the first portion 11 includes a center portion 11c located on the tire equator C, a middle portion 11m located axially outward of the center portion 11c, and an outer portion 11o located axially outward of the middle portion 11m.

[0022] The center portion 11c extends circumferentially on the tire equator C with a first thickness t1. The middle portion 11m extends circumferentially axially outward from the center portion 11c with a second thickness t2. In this embodiment, the middle portions 11m are disposed on both axially outer sides of the center portion 11c, but it is sufficient that they are disposed on at least one axially outer side.

[0023] In the present invention, the first thickness t1 of the center portion 11c is greater than the second thickness t2 of the middle portion 11m. In other words, the second thickness t2 is smaller than the first thickness t1. Here, the fact that the second thickness t2 is smaller than the first thickness t1 means that the average value of the second thickness t2 is smaller than the average value of the first thickness t1.

[0024] The average value of the first thickness t1 corresponds to the value obtained by dividing the cross-sectional area of ​​the center portion 11c in the tire meridian cross section by the length of the center portion 11c along the tire cavity surface 1A. The same applies to the average value of the second thickness t2. In the present embodiment, the above-mentioned thickness relationship is preferably maintained over the entire circumference of the tire. However, the present invention is not limited to this embodiment. The first thickness t1 and the second thickness t2 refer to the thickness from the inner surface 6i of the carcass 6 to the tire cavity surface 1A, and do not include the topping rubber of the carcass ply (the same applies to the third thickness t3 and thickness t4 described later).

[0025] When a large portion (e.g., 60% or more) of the center portion 11c is made up of a thick portion of substantially constant thickness, the thickness of the thick portion may be defined as the first thickness t1. The term "substantially constant thickness" refers to an allowance for unavoidable errors in rubber products such as tires, and includes, for example, a case where the difference between the maximum and minimum thickness values ​​is 5% or less of the maximum thickness.

[0026] Similarly, if most (e.g., 60% or more) of the middle portion 11m is made up of a thin portion of a substantially uniform thickness, the thickness of the thin portion may be set as the second thickness t2. In this case, the second thickness t2 of the thin portion of the middle portion 11m is smaller than the first thickness t1 of the thick portion of the center portion 11c.

[0027] The outer portion 11o extends circumferentially on the axially outer side of the middle portion 11m with a third thickness t3. The outer portion 11o extends circumferentially on the axially outer side of the middle portion 11m with a third thickness t3. In this embodiment, the outer portion 11o is disposed on both sides of the tire equator C, but it is sufficient if it is disposed on at least one side. In an embodiment in which the middle portion 11m is disposed on one axially outer side of the center portion 11c, it is desirable that the outer portion 11o be disposed further axially outward than the middle portion 11m on the side where the middle portion 11m is provided.

[0028] In the present invention, the third thickness t3 of the outer portion 11o is greater than the second thickness t2 of the middle portion 11m. In other words, the second thickness t2 of the middle portion 11m is smaller than the third thickness t3 of the outer portion 11o.

[0029] Here, the second thickness t2 being smaller than the third thickness t3 means that the average value of the second thickness t2 is smaller than the average value of the third thickness t3. The average value of the third thickness t3 corresponds to the value obtained by dividing the cross-sectional area of ​​the outer portion 11o in the tire meridian cross section by the length of the outer portion 11o along the tire cavity surface 1A. As a desirable aspect, in this embodiment, the above-mentioned thickness relationship is maintained over the entire circumference of the tire. However, the present invention is not limited to this aspect.

[0030] When a large portion (e.g., 60% or more) of the outer portion 11o is made up of a thick portion of a substantially constant thickness, the thickness of the thick portion may be defined as the third thickness t3. In this case, the second thickness t2 of the thin portion of the middle portion 11m is smaller than the third thickness t3 of the thick portion of the outer portion 11o.

[0031] In this embodiment, the center portion 11c and the outer portion 11o, which are relatively thicker than the middle portion 11m, function as mass dampers, reducing vibrations in the tread portion 2 and suppressing noise when the pneumatic tire 1 rolls. Meanwhile, the middle portion 11m, which is relatively thinner than the center portion 11c and the outer portion 11o, reduces the weight of the tread portion 2, making it possible to easily suppress the rolling resistance of the pneumatic tire 1. As a result, it is possible to easily suppress noise and rolling resistance when the pneumatic tire 1 rolls.

[0032] As shown in FIG. 2, the first portion 11 may be configured such that the thickness of the inner rubber 10 increases and decreases continuously along the tire cavity surface 1A, or may be configured such that the thickness increases and decreases in steps.

[0033] 3 conceptually shows a standing wave W generated in the tread portion 2 at a cross-sectional secondary resonance frequency of 315 Hz. As a result of extensive research, the inventors of the present application have found that in the tread portion 2, there are areas with large vibrations (i.e., vibration antinodes WP) near the tire equator C, and areas with small vibrations (i.e., vibration nodes WN) in the region from the tire equator C to the tread edge TE.

[0034] The inventors of the present application then considered that by positioning the relatively thin middle portion 11m at the node WN, the center portion 11c and outer portion 11o, which are relatively thick on both sides of the middle portion 11m in the tire axial direction, would be positioned at the antinodes WP. With this arrangement, the peak vibration of the antinodes WP is suppressed by the mass damper effect of the center portion 11c and outer portion 11o. Meanwhile, because the vibration of the node WN is relatively small, the impact of the relatively thin middle portion 11m on tire noise is suppressed. This makes it possible to easily suppress noise and rolling resistance during tire rotation of the pneumatic tire 1.

[0035] From the above viewpoints, it is desirable that the middle portion 11m be disposed in an area that is 40% to 70% of the tread half width TW / 2 from the tire equator C. Here, the "tread half width TW / 2" is defined as the distance in the tire axial direction from the tire equator C to the tread edge TE on the side where the middle portion 11m is provided. The "tread edge" is defined as the outermost contact point in the tire axial direction when a pneumatic tire 1 in a normal state is placed on a flat surface with 70% of the normal load and a camber angle of 0 degrees.

[0036] "Normal load" refers to the load specified for each tire by the above standards, and is the maximum load capacity for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and "LOAD CAPACITY" for ETRTO. For tires for which no standards are specified, "normal load" refers to the maximum load that can be applied when using the tire in accordance with the above standards.

[0037] In the pneumatic tire 1 in which the middle portion 11m is disposed in the above-mentioned region, the middle portion 11m is positioned at the node WN, and the center portion 11c and the outer portion 11o are positioned at the antinode WP, which makes it possible to easily suppress noise and rolling resistance during tire rolling of the pneumatic tire 1.

[0038] To further enhance the above-mentioned effect, the middle portion 11m is preferably disposed in an area that is 45% or more, more preferably 50% or more, of the tread half width TW / 2 from the tire equator C. The middle portion 11m is preferably disposed in an area that is 65% or less, more preferably 60% or less, of the tread half width TW / 2 from the tire equator C. As an example, the middle portion 11m is preferably disposed in an area that is 45% to 65%, or even 50% to 60%, of the tread half width TW / 2 from the tire equator C.

[0039] The middle portion 11m is preferably disposed in an area 30% to 60% of the tire cross-sectional half width SW / 2 from the tire equator C. Here, the "tire cross-sectional half width SW / 2" is defined as the distance in the tire axial direction from the tire equator C to the maximum width position of the tire cross-sectional contour shape, excluding protruding parts such as patterns, letters, and rim protectors on the tire sidewall.

[0040] In the pneumatic tire 1 in which the middle portion 11m is disposed in the above-mentioned region, the middle portion 11m is positioned at the node WN, and the center portion 11c and the outer portion 11o are positioned at the antinode WP, which makes it possible to easily suppress noise and rolling resistance during tire rolling of the pneumatic tire 1.

[0041] To further enhance the above-mentioned effect, the middle portion 11m is preferably disposed in an area that is 35% or more, more preferably 40% or more, of the tread half width TW / 2 from the tire equator C. The middle portion 11m is preferably disposed in an area that is 55% or less, more preferably 50% or less, of the tread half width TW / 2 from the tire equator C. As an example, the middle portion 11m is preferably disposed in an area that is 35% to 55%, or even 40% to 50% of the tread half width TW / 2 from the tire equator C.

[0042] The first thickness t1 is preferably 4 to 9 times the second thickness t2. When the first thickness t1 is 4 times or more the second thickness t2, a significant mass damper effect is obtained by the center portion 11c, and noise generated when the pneumatic tire 1 rolls is easily suppressed. When the first thickness t1 is 9 times or less the second thickness t2, the weight of the tread portion 2 is reduced, and the rolling resistance of the pneumatic tire 1 is easily suppressed.

[0043] The third thickness t3 is preferably 4 to 9 times the second thickness t2. When the third thickness t3 is 4 times or more the second thickness t2, a significant mass damper effect is obtained by the outer portion 11o, and noise generated when the pneumatic tire 1 rolls is easily suppressed. When the third thickness t3 is 9 times or less the second thickness t2, the weight of the tread portion 2 is reduced, and the rolling resistance of the pneumatic tire 1 is easily suppressed.

[0044] As shown in Fig. 1, the inner rubber 10 includes second portions 12 disposed in the pair of sidewall portions 3. The second portions 12 extend continuously in the tire circumferential direction.

[0045] The first thickness t1 of the center portion 11c is preferably 2.0 to 4.5 times the thickness t4 of the second portion 12 of the sidewall portion 3. When the first thickness t1 is 2.0 times or more the thickness t4, a significant mass damper effect is obtained by the center portion 11c, and noise generated when the pneumatic tire 1 rolls is easily suppressed. When the first thickness t1 is 4.5 times or less the thickness t4, the weight of the tread portion 2 is reduced, and the rolling resistance of the pneumatic tire 1 is easily suppressed.

[0046] The second thickness t2 of the middle portion 11m is desirably 0.25 times or more the thickness t4 of the second portion 12 of the sidewall portion 3. When the second thickness t2 is 0.25 times or more the thickness t4, the internal pressure of the pneumatic tire 1 is well maintained.

[0047] Furthermore, it is desirable that the second thickness t2 be 0.75 times or less the thickness t4. By making the second thickness t2 0.75 times or less the thickness t4, the weight of the tread portion 2 is reduced, and the rolling resistance of the pneumatic tire 1 is easily suppressed.

[0048] The second thickness t2 is preferably 4.0% or more of the maximum depth d (see FIG. 2) of the plurality of circumferential grooves 20 described below. The "maximum depth d" refers to the largest depth among the depths of the first shoulder circumferential groove 21, the second shoulder circumferential groove 22, the first crown circumferential groove 23, and the second crown circumferential groove 24. When the second thickness t2 is 4.0% or more of the maximum depth d of the circumferential groove 20, the internal pressure of the pneumatic tire 1 is well maintained.

[0049] Moreover, it is desirable that the second thickness t2 be 8.0% or less of the maximum depth d of the plurality of circumferential grooves 20. By making the second thickness t2 8.0% or less of the maximum depth d of the circumferential groove 20, the weight of the tread portion 2 is reduced, and the rolling resistance of the pneumatic tire 1 is easily suppressed.

[0050] The third thickness t3 of the outer portion 11o is preferably 2.0 to 4.5 times the thickness t4 of the second portion 12 of the sidewall portion 3. When the third thickness t3 is 2.0 times or more the thickness t4, a significant mass damper effect is obtained by the outer portion 11o, and noise generated when the pneumatic tire 1 rolls is easily suppressed. When the third thickness t3 is 4.5 times or less the thickness t4, the weight of the tread portion 2 is reduced, and the rolling resistance of the pneumatic tire 1 is easily suppressed.

[0051] As shown in Fig. 1, the tread portion 2 has a plurality of circumferential grooves 20 that extend continuously in the tire circumferential direction. As shown in Fig. 2, in this embodiment, the tread portion 2 is divided into five land portions 25 (see Fig. 2) by four circumferential grooves 20. However, the present invention is not limited to this embodiment. In other words, it is sufficient that at least one circumferential groove 20 is formed in the tread portion 2.

[0052] As shown in FIG. 2 , the multiple circumferential grooves 20 include a first shoulder circumferential groove 21, a second shoulder circumferential groove 22, a first crown circumferential groove 23, and a second crown circumferential groove 24. The first shoulder circumferential groove 21 is provided between one tread edge TE and the tire equator C, and in the present embodiment, is disposed closest to the one tread edge TE among the multiple circumferential grooves 20. The second shoulder circumferential groove 22 is provided between the other tread edge TE and the tire equator C, and in the present embodiment, is disposed closest to the other tread edge TE among the multiple circumferential grooves 20. The first crown circumferential groove 23 is provided between the first shoulder circumferential groove 21 and the tire equator C. The second crown circumferential groove 24 is provided between the second shoulder circumferential groove 22 and the tire equator C.

[0053] Each circumferential groove 20 of this embodiment extends, for example, linearly in parallel to the tire circumferential direction. Each circumferential groove 20 may extend, for example, in a wavy shape.

[0054] In this embodiment, it is desirable that at least one of the circumferential grooves 20 is arranged so as to overlap with the middle portion 11m in the tire axial direction. For example, it is sufficient that at least a portion of the first shoulder circumferential groove 21 and the second shoulder circumferential groove 22 overlap with at least a portion of the middle portion 11m in the tire axial direction. With this configuration, the first shoulder circumferential groove 21 and the second shoulder circumferential groove 22 are arranged at or near the vibration node WN, thereby further suppressing vibration of the tread portion 2 near the first shoulder circumferential groove 21 and the second shoulder circumferential groove 22.

[0055] It is known that the air trapped between the circumferential groove 20 and the road surface vibrates, becoming a noise source. In a pneumatic tire 1 in which the total groove width Wall of the circumferential grooves 20 is large relative to the tread width TW, the impact on the tire noise performance becomes significant.

[0056] In particular, in a pneumatic tire 1 in which the total groove width Wall of the circumferential grooves 20 measured in the normal state is 25% or more of the tread width TW, the influence of the circumferential grooves 20 on the noise performance of the tire becomes significant. In this embodiment, even in a pneumatic tire 1 in which the total groove width Wall of the circumferential grooves 20 is large, the second thickness t2 of the middle portion 11m is configured to be smaller than the first thickness t1 of the center portion 11c and the third thickness t3 of the outer portion 11o, so that vibration of the tread portion 2 is small and the influence on the noise performance of the tire can be suppressed.

[0057] As shown in FIG. 2, the "total groove width Wall of the circumferential grooves 20" is calculated as W1+W2+W3+W4, where W1 is the axial width of the first shoulder circumferential groove 21 measured in the normal state, W2 is the axial width of the second shoulder circumferential groove 22, W3 is the axial width of the first crown circumferential groove 23, and W4 is the axial width of the second crown circumferential groove 24.

[0058] Furthermore, in the pneumatic tire 1, it is desirable that the total groove width of the circumferential grooves 20 be 30% or less. By having the total groove width of the circumferential grooves 20 be 30% or less, the noise source is reduced and the function of the tread portion 2 as a mass damper is strengthened, thereby suppressing the effect on the noise performance of the tire.

[0059] FIG. 4 shows how a pneumatic tire 1 generates noise while running. It is known that the sound generated at the contact surface of a pneumatic tire while running is also amplified by the horn formed by the tread surface and the road surface, which is called the horn effect. A pneumatic tire 1 with a large tire outer diameter has a small angle α between the tread surface 2s of the tread 2 and the road surface G, and the horn effect has a significant effect on the tire's noise performance. Furthermore, a pneumatic tire 1 with a tire section width of 225 mm or more has a significant effect on the tire's noise performance.

[0060] In particular, the influence of the horn effect on tire noise performance becomes significant in a pneumatic tire 1 having a tire outer diameter DM of 660 mm or more and a tire section width SW of 225 mm or more, measured under the above-mentioned normal condition. In this embodiment, even in such a large-diameter, wide pneumatic tire 1, the second thickness t2 of the middle portion 11m is configured to be smaller than the first thickness t1 of the center portion 11c and the third thickness t3 of the outer portion 11o, so that vibration of the tread portion 2 is small and the horn effect can be suppressed.

[0061] As shown in Fig. 1, 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.

[0062] However, the present invention is not limited to this embodiment. Fig. 5 shows an enlarged cross-sectional view of the vicinity of the tire equator C of the tread portion 2 of another embodiment of the present invention. As shown in Fig. 5, the first portion 11 of the inner rubber 10 of this embodiment includes an inner liner layer 16 made of an air-impermeable rubber material (hereinafter referred to as the first rubber material), and an additional layer 17 disposed between the inner liner layer 16 and the carcass 6. This additional layer 17 is made of a second rubber material different from the first rubber material, for example, a rubber material that has excellent adhesion to the carcass 6. Such additional layer 17 prevents contact between the carcass 6 and the inner liner layer 16, improving the durability of the tire 1. 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 laminating an air-impermeable rubber material and an air-permeable rubber material.

[0063] The loss tangent tan δ of the air-impermeable rubber material at 70° C. is preferably 0.14 or more.

[0064] In this specification, the loss tangent tanδ is a value measured under the following conditions in accordance with the provisions of JIS-K6394: A viscoelasticity measurement sample, 20 mm long, 4 mm wide, and 1 mm thick, was taken from inside the rubber layer of the tread portion of each test tire, with the long side aligned in the tire circumferential direction and the thickness direction aligned in the tire radial direction, and the loss tangent tanδ was measured using an Iplexer series manufactured by GABO under the conditions of a temperature of 70°C, an initial strain of 5%, a dynamic strain of 1%, a frequency of 10 Hz, and an extension mode, and the average value was calculated.

[0065] The loss tangent tanδ can be adjusted appropriately by adjusting the glass transition temperature Tg of the rubber composition and the types and amounts of various compounding agents. Specifically, the loss tangent tanδ can be increased by increasing the glass transition temperature Tg of the rubber composition, reducing the average particle size of reinforcing agents such as carbon and silica, increasing the compounding amount of reinforcing agents, reducing the amount of vulcanizing agents such as sulfur and accelerators, etc.

[0066] When the loss tangent tan δ at 70° C. of the air-impermeable rubber material is 0.14 or more, vibration of the tread portion 2 is further suppressed.

[0067] 5, various performances can be improved by including the additional layer 17 in the first portion 11. For example, a rubber material having a loss tangent tanδ greater than that of the first rubber material constituting the inner liner layer 16 can be used as the second rubber material constituting the additional layer 17. In such an embodiment, the tread portion 2 can further absorb vibrations from the road surface, thereby further reducing noise.

[0068] The position of the additional layer 17 is not limited to the embodiment shown in Fig. 5. Fig. 6 shows an enlarged cross-sectional view of the vicinity of the tire equator C of the tread portion 2 according to yet another embodiment of the present invention. As shown in Fig. 6, the additional layer 17 may be disposed radially inward of the inner liner layer 16. The additional layer 17 may also constitute a part of the tire cavity surface 1A.

[0069] As shown in Figures 5 and 6, even in an embodiment in which the additional layer 17 is included in the first portion 11 of the inner rubber 10, the first thickness t1 corresponds to the thickness from the inner surface 6i of the carcass 6 in the tread portion 2 to the tire cavity surface 1A.

[0070] FIG. 7 shows 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 16 made of a first rubber material having air impermeability and an intermediate layer 18 disposed between the inner liner layer 16 and the carcass 6. In FIG. 7, the intermediate layer 18 is dotted. The intermediate layer 18 is made of a rubber material different from the first rubber material, for example, a rubber material that has excellent adhesion to the carcass 6. Such an intermediate layer 18 prevents contact between the carcass 6 and the inner liner layer 16, improving the durability of the tire 1. The intermediate layer 18 may be made of, for example, the same second rubber material as the additional layer 17 of the first portion 11 described in FIGS. 5 and 6. Including such an intermediate layer 18 in the second portion 12 can further suppress transmission of vibrations generated in the tread portion 2 to the vehicle side. Note that the intermediate layer 18 may be made of a rubber material different from the first rubber material and the second rubber material.

[0071] Although the tire 1 of the present invention has been described in detail above, the present invention is not limited to the specific embodiment described above, and can be modified and practiced in various aspects.

[0072] [Note] [Invention 1] A pneumatic tire, A tread portion; A pair of sidewall portions; a pair of bead portions; a carcass extending between the pair of bead portions; an inner rubber extending between the pair of bead portions on the inner side of the carcass, the inner rubber includes a first portion disposed in the tread portion, the first portion includes a center portion extending circumferentially on the tire equator at a first thickness, a middle portion extending circumferentially on at least one axially outer side of the center portion at a second thickness, and an outer portion extending circumferentially on the one axially outer side of the middle portion at a third thickness, the second thickness is less than the first thickness and the third thickness; Pneumatic tires. [Invention 2] The pneumatic tire according to invention 1, wherein the middle portion is disposed in an area of ​​40% to 70% of the half width of the tread from the tire equator. [Invention 3] 3. The pneumatic tire according to claim 1 or 2, wherein the middle portion is disposed in a region of 30% to 60% of the tire cross-sectional half width from the tire equator. [Invention 4] 4. The pneumatic tire according to claim 1, wherein the first thickness is 4 to 9 times the second thickness. [Invention 5] The pneumatic tire according to any one of inventions 1 and 4, wherein the third thickness is 4 to 9 times the second thickness. [Invention 6] the inner rubber includes a second portion disposed in the sidewall portion, 6. The pneumatic tire according to claim 1, wherein the first thickness is 2.0 to 4.5 times the thickness of the second portion. [Invention 7] the inner rubber includes a second portion disposed in the sidewall portion, 6. The pneumatic tire according to claim 1, wherein the third thickness is 2.0 to 4.5 times the thickness of the second portion. [Invention 8] At least one circumferential groove extending in the tire circumferential direction is formed in the tread portion, The pneumatic tire according to any one of inventions 1 and 7, wherein the circumferential groove is arranged so as to overlap with the middle portion in the tire axial direction. [Invention 9] 9. The pneumatic tire according to invention 8, wherein the total groove width of the circumferential grooves is 25% to 30% of the tread width. [Invention 10] 10. The pneumatic tire according to any one of inventions 1 or 9, having a tire outer diameter of 660 mm or more and a tire section width of 225 mm or more. [Explanation of symbols]

[0073] 1: Pneumatic tires 2: Tread area 3: Sidewall 4: Bead part 6: Carcass 10: Inner rubber 11: 1st part 11c: Center part 11m: Middle section 11o: Outer part 12:Second part 20: Circumferential groove C: Tire equator DM: Tire outer diameter t1: First thickness t2: Second thickness t3: Third thickness t4: thickness TW: Tread width

Claims

1. A pneumatic tire, A tread portion; A pair of sidewall portions; a pair of bead portions; a carcass extending between the pair of bead portions; an inner rubber extending between the pair of bead portions on the inner side of the carcass, the inner rubber includes a first portion disposed in the tread portion, the first portion includes a center portion extending circumferentially on the tire equator at a first thickness, a middle portion extending circumferentially on at least one axially outer side of the center portion at a second thickness, and an outer portion extending circumferentially on the one axially outer side of the middle portion at a third thickness, the second thickness is less than the first thickness and the third thickness; Pneumatic tires.

2. 2. The pneumatic tire according to claim 1, wherein the middle portion is disposed in an area from the tire equator to 40% to 70% of a half width of the tread.

3. 3. The pneumatic tire according to claim 1, wherein the middle portion is disposed in an area ranging from the tire equator to 30% to 60% of the half width of the tire cross section.

4. The pneumatic tire according to claim 1, wherein the first thickness is 4 to 9 times the second thickness.

5. The pneumatic tire according to claim 1, wherein the third thickness is 4 to 9 times the second thickness.

6. the inner rubber includes a second portion disposed in the sidewall portion, The pneumatic tire according to claim 1, wherein the first thickness is 2.0 to 4.5 times the thickness of the second portion.

7. the inner rubber includes a second portion disposed in the sidewall portion, The pneumatic tire according to claim 1, wherein the third thickness is 2.0 to 4.5 times the thickness of the second portion.

8. At least one circumferential groove extending in the tire circumferential direction is formed in the tread portion, The pneumatic tire according to claim 1 , wherein the circumferential groove is arranged so as to overlap with the middle portion in the tire axial direction.

9. The pneumatic tire according to claim 8, wherein the total groove width of the circumferential grooves is 25% to 30% of the tread width.

10. 2. The pneumatic tire according to claim 1, wherein the tire outer diameter is 660 mm or more and the tire section width is 225 mm or more.

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