JP2024061152A - Pneumatic tire - Google Patents

Abstract

To provide a pneumatic tire that can achieve both noise performance and low fuel consumption performance.SOLUTION: A pneumatic tire 1 comprises a tread portion 2, a pair of sidewall portions 3, a pair of bead portions 4, a carcass 6 extending between the pair of bead portions 4, and an inner rubber 10 extending between the pair of bead portions 4 on an inner side of the carcass 6. The inner rubber 10 comprises a first portion 11 extending in the tread portion 2 with a first thickness t1, and a second portion 12 extending in the pair of sidewall portions 3 with a second thickness t2. The first thickness t1 is greater than the second thickness t2. The tread portion 2 comprises a tread rubber 2G forming a ground contact surface 2s. The loss tangent tanδ1 of the first portion 11 at 70°C is greater than or equal to the loss tangent tanδ2 of the second portion 12 at 70°C, and less than or equal to the loss tangent tanδA of the tread rubber 2G at 30°C.SELECTED DRAWING: Figure 1

Description

The present invention relates to a pneumatic tire.

Various pneumatic tires capable of reducing road noise have been proposed in the past. For example, the following Patent Document 1 proposes a pneumatic tire that reduces road noise while minimizing the effect on rolling resistance by providing fillers that extend radially inward from the end of the belt along the carcass to suppress vibration at the end of the belt.

JP 2017-170968 A

However, in recent years, with the spread of electric vehicles and the like, the standards required for fuel efficiency and noise performance in pneumatic tires have increased, and further improvements have been demanded for the pneumatic tire of Patent Document 1.

The present invention was devised in consideration of the above-mentioned circumstances, and its main objective is to provide a pneumatic tire that can achieve both low fuel consumption and noise performance.

The present invention is a pneumatic tire including a tread portion, a pair of sidewall portions, a pair of bead portions, a carcass extending between the pair of bead portions, and an inner rubber extending between the pair of bead portions on the inside 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, the tread portion including a tread rubber constituting a contact surface, and a loss tangent tanδ1 of the first portion at 70°C being equal to or greater than a loss tangent tanδ2 of the second portion at 70°C and equal to or less than a loss tangent tanδA of the tread rubber at 30°C.

The pneumatic tire of the present invention has the above-mentioned configuration, and is therefore able to achieve both low fuel consumption and noise performance.

1 is a cross-sectional view showing one embodiment of a pneumatic tire of the present invention. FIG. FIG. 11 is an enlarged cross-sectional view of an inner rubber of the second embodiment. FIG. 11 is an enlarged cross-sectional view of an inner rubber of the third embodiment. FIG. 13 is an enlarged cross-sectional view of the inner rubber of the fourth embodiment.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
1 is a tire meridian cross-sectional view including a rotation axis showing a pneumatic tire 1 of the present embodiment in a normal state. Here, the "normal state" refers to a state in which the pneumatic tire 1 is mounted on a normal rim, and is adjusted to a normal internal pressure and unloaded. Hereinafter, unless otherwise specified, the dimensions of each part of the pneumatic tire 1 are values measured in this normal state.

A "genuine rim" is a rim that is determined for each tire by a standard system that includes the standard on which the pneumatic tire 1 is based, for example, a "standard rim" for JATMA, a "design rim" for TRA, and a "measuring rim" for ETRTO. If there is no standard system that includes the standard on which the pneumatic tire 1 is based, a "genuine rim" is a rim that can be assembled and does not leak air, and that has the smallest rim diameter and the smallest rim width among the rims that can be assembled and do not leak air.

"Normal internal pressure" is the air pressure set for each tire by a standard system that includes the standards on which the pneumatic tire 1 is based, such as the "maximum air pressure" for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and "INFLATION PRESSURE" for ETRTO. "Normal internal pressure" is the air pressure set for each tire by the manufacturer, etc., if there is no standard system that includes the standards on which the pneumatic tire 1 is based.

As shown in FIG. 1, the pneumatic tire 1 of this embodiment includes a tread portion 2, a pair of sidewall portions 3, and a pair of bead portions 4. The bead portion 4 has, for example, a bead core 5 extending in an annular shape. The bead core 5 is formed, for example, from a steel wire. The pneumatic tire 1 of this embodiment is suitable for use as a passenger vehicle tire. The pneumatic tire 1 is not limited to passenger vehicle tires, and can be applied to various types of tires, such as heavy load tires, motorcycle tires, and industrial vehicle tires.

The pneumatic tire 1 of this embodiment includes a carcass 6 extending between a pair of bead portions 4, and an inner rubber 10 extending between the pair of bead portions 4 on the inside of the carcass 6. The inner rubber 10 of this embodiment forms the tire inner cavity surface 1i.

The inner rubber 10 of this embodiment includes a first portion 11 that extends through the tread portion 2 at a first thickness t1, and a second portion 12 that extends through a pair of sidewall portions 3 at a second thickness t2. Here, 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 inner surface 1i, and do not include the topping rubber of the carcass ply 6A described below.

The first thickness t1 of this embodiment is greater than the second thickness t2. It is desirable that the first thickness t1 be greater than the second thickness t2 over the entire circumference of the tire. Such an inner rubber 10 can achieve the same vibration reduction effect as increasing the thickness of the tread rubber 2G, which will be described later, with a small increase in weight. In addition, since the increase in weight on the inner side of the carcass 6 has little effect on rolling resistance, the pneumatic tire 1 of this embodiment can improve noise performance while maintaining good fuel efficiency performance.

Here, the first thickness t1 being greater than the second thickness t2 means that the average value of the first thickness t1 is greater than the average value of the second thickness t2. The average value of the first 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 of the first portion 11 along the tire cavity surface 1i. The same applies to the average value of the second thickness t2.

Figure 2 is an enlarged cross-sectional view of the tread portion 2. As shown in Figure 2, the tread portion 2 of this embodiment includes tread rubber 2G that constitutes the ground contact surface 2s. The tread portion 2 includes, for example, cap rubber 2A that constitutes the ground contact surface 2s and base rubber 2B arranged inside the cap rubber 2A in the tire radial direction. The tread portion 2 is not limited to this embodiment, and may be composed of, for example, one layer of rubber material, or three or more layers of rubber material. When the tread portion 2 is composed of multiple rubber materials, the tread rubber 2G is the rubber material that constitutes the ground contact surface 2s, for example, the cap rubber 2A.

In this embodiment, the loss tangent tanδ1 of the first portion 11 at 70°C is equal to or greater than the loss tangent tanδ2 of the second portion 12 at 70°C. Such a first portion 11 helps to suppress vibrations in the tread portion 2, thereby improving the noise performance of the pneumatic tire 1.

The loss tangent tanδ1 of the first portion 11 at 70°C is desirably equal to or less than the loss tangent tanδA of the tread rubber 2G at 30°C. The tread rubber 2G constituting the contact surface 2s is cooled by contact with the outside air, so the measurement temperature is set to 30°C. Such a first portion 11 can further reduce the effect on the rolling resistance in the tread portion 2, which helps to improve the fuel efficiency performance of the pneumatic tire 1. Therefore, the pneumatic tire 1 of this embodiment can achieve both fuel efficiency performance and noise performance.

Here, in this specification, the loss tangent tan δ is a value measured using a dynamic viscoelasticity measuring device under the following conditions in accordance with the provisions of JIS-K6394. A rubber sample used for measuring the loss tangent tan δ is, for example, taken from the 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 distortion: 5% (when the measurement temperature is 30°C) or 10% (when the measurement temperature is 70°C)
Dynamic strain amplitude: ±1%
Frequency: 10Hz
Deformation mode: Tensile Measurement temperature: 30°C or 70°C

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

Here, the loss tangent tanδ1 of the first portion 11 is the loss tangent tanδ1 of the rubber material when the first portion 11 is made of a single rubber material. When the first portion 11 is made of multiple rubber materials, the loss tangent tanδ1 of the first portion 11 is the average value calculated as a weighted average of the loss tangents tanδ1 of those rubber materials weighted by the cross-sectional area of each rubber material. The same applies to the other loss tangents tanδ.

In a more preferred embodiment, the loss tangent tanδ1 of the first portion 11 is 1.0 to 2.0 times the loss tangent tanδ2 of the second portion 12. By making the loss tangent tanδ1 of the first portion 11 1.0 or more times the loss tangent tanδ2 of the second portion 12, the vibration suppression effect of the tread portion 2 can be reliably achieved. From this perspective, the loss tangent tanδ1 of the first portion 11 is more preferably 1.1 or more times the loss tangent tanδ2 of the second portion 12.

By making the loss tangent tanδ1 of the first portion 11 2.0 times or less the loss tangent tanδ2 of the second portion 12, damage such as peeling caused by an excessive difference in physical properties can be suppressed, and the durability performance of the pneumatic tire 1 can be improved. From this perspective, the loss tangent tanδ1 of the first portion 11 is more preferably 1.5 times or less the loss tangent tanδ2 of the second portion 12.

The loss tangent tanδ1 of the first portion 11 is preferably 0.4 to 0.7 times the loss tangent tanδA of the tread rubber 2G. By making the loss tangent tanδ1 of the first portion 11 0.4 or more times the loss tangent tanδA of the tread rubber 2G, it is possible to reduce the vibration of the tread portion 2 while maintaining the fuel efficiency performance of the pneumatic tire 1.

By making the loss tangent tanδ1 of the first portion 11 0.7 times or less the loss tangent tanδA of the tread rubber 2G, it is possible to reduce the vibration of the tread portion 2 while maintaining the steering stability performance of the pneumatic tire 1.

The loss tangent tanδ1 of the first portion 11 is preferably 0.14 or more. By making the loss tangent tanδ1 of the first portion 11 0.14 or more, the vibration of the tread portion 2 can be reliably suppressed and the generation of noise can be reduced. From this perspective, the loss tangent tanδ1 of the first portion 11 is more preferably 0.15 or more, and even more preferably 0.20 or more.

It is desirable that the loss tangent tanδ2 of the second portion 12 is equal to the loss tangent tanδ1 of the first portion 11. Such an inner rubber 10 allows the first portion 11 and the second portion 12 to be integrally formed, which helps reduce the manufacturing costs of the pneumatic tire 1.

The loss tangent tan δA of the tread rubber 2G is preferably 0.30 or less. By making the loss tangent tan δA of the tread rubber 2G 0.30 or less, it is possible to reduce the rolling resistance and improve the fuel efficiency performance of the pneumatic tire 1. From this viewpoint, the loss tangent tan δA of the tread rubber 2G is more preferably 0.25 or less, and even more preferably 0.20 or less.

When the tread portion 2 is composed of a cap rubber 2A and a base rubber 2B, the loss tangent tanδA of the tread rubber 2G at 30°C is the loss tangent tanδA of the cap rubber 2A at 30°C. In this case, it is desirable that the loss tangent tanδB of the base rubber 2B at 70°C is smaller than the loss tangent tanδA of the cap rubber 2A at 30°C. Such a tread portion 2 helps to improve fuel efficiency while maintaining good steering stability of the pneumatic tire 1.

The loss tangent tan δB of the base rubber 2B is preferably 0.21 or less. Having a loss tangent tan δB of the base rubber 2B of 0.21 or less helps to suppress heat generation in the tread portion 2 during driving and maintain good fuel efficiency performance of the pneumatic tire 1. From this perspective, the loss tangent tan δB of the base rubber 2B is more preferably 0.20 or less.

The complex modulus E*A of the tread rubber 2G at 30°C is preferably 7.8 MPa or more. The complex modulus E*A of the tread rubber 2G of 7.8 MPa or more suppresses vibration of the tread portion 2 and helps improve the noise performance of the pneumatic tire 1. From this perspective, the complex modulus E*A of the tread rubber 2G is more preferably 8.0 MPa or more, and even more preferably 9.0 MPa or more. Note that the complex modulus E*A when the tread rubber 2G is made of multiple rubber materials is based on the rubber materials that make up the contact surface 2s.

Here, in this specification, the complex modulus E* is a value measured using a dynamic viscoelasticity measuring device under the following conditions in accordance with the provisions of JIS-K6394. A rubber sample used for measuring the complex modulus E* is, for example, taken from the 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 distortion: 5%
Dynamic strain amplitude: ±1%
Frequency: 10Hz
Deformation mode: Tensile Measurement temperature: 30°C

The complex modulus E* can be adjusted as appropriate by adjusting the glass transition temperature Tg of the rubber composition and the types and amounts of various compounding agents. Specifically, the complex modulus E* can be increased by increasing the glass transition temperature Tg of the rubber composition, decreasing the average particle size of reinforcing agents such as carbon and silica, increasing the amount of reinforcing agents, decreasing the total amount of plasticizers, and increasing the amount of vulcanizing agents such as sulfur and accelerators.

As shown in Figures 1 and 2, in the tread portion 2 of this embodiment, a belt layer 7 is arranged on the radially outer side of the carcass 6. It is preferable that a band layer 8 is arranged on the radially outer side of the belt layer 7 in the tread portion 2.

The carcass 6 is composed of at least one carcass ply 6A, one in this embodiment. The carcass ply 6A includes, for example, a main body portion 6a and a folded-up portion 6b. The main body portion 6a extends, for example, between two bead portions 4. The folded-up portion 6b is connected to the main body portion 6a and folded back, for example, from the inside to the outside in the axial direction of the tire around the bead core 5.

Although not shown in the figure, the carcass ply 6A includes multiple carcass cords and a topping rubber that covers them. 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 with respect to the tire equator C.

The loss tangent tanδC of the topping rubber of the carcass ply 6A at 70°C is preferably 0.16 or less. By making the loss tangent tanδC of the topping rubber of the carcass ply 6A 0.16 or less, heat generation in the carcass ply 6A can be suppressed, and the pneumatic tire 1 can achieve both low fuel consumption performance and durability performance during high-speed driving. From this perspective, the loss tangent tanδC of the topping rubber of the carcass ply 6A is more preferably 0.15 or less. Note that, from the perspective of improving the noise performance of the pneumatic tire 1, it is desirable to make the loss tangent tanδ1 of the first portion 11 larger than the loss tangent tanδC of the topping rubber of the carcass ply 6A.

The belt layer 7 includes, for example, a first belt ply 7A adjacent to the carcass 6 and a second belt ply 7B arranged radially outward of the first belt ply 7A. In this embodiment, 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 relative to the tire circumferential direction, and a topping rubber that covers these.

It is desirable that the belt cords of the first belt ply 7A and the belt cords of the second belt ply 7B are inclined in opposite directions relative to the tire circumferential direction. Such a belt layer 7 can effectively reinforce the tread portion 2.

In this embodiment, the axially outer end 7b of the second belt ply 7B is located axially inward of the axially outer end 7a of the first belt ply 7A. As a result, the axial length of the second belt ply 7B is smaller than the axial length of the first belt ply 7A. Such a belt layer 7 can reinforce the tread portion 2 while preventing the second belt ply 7B from becoming excessively large, which helps to achieve both low fuel consumption performance and noise performance of the pneumatic tire 1.

The loss tangent tanδD of the topping rubber of the first belt ply 7A at 70°C is preferably 0.16 or less. By making the loss tangent tanδD of the topping rubber of the first belt ply 7A 0.16 or less, heat generation in the first belt ply 7A can be suppressed, and the pneumatic tire 1 can achieve both low fuel consumption performance and durability performance during high-speed driving. From this perspective, the loss tangent tanδD of the topping rubber of the first belt ply 7A is more preferably 0.15 or less. Note that, from the perspective of improving the noise performance of the pneumatic tire 1, it is desirable to make the loss tangent tanδ1 of the first portion 11 larger than the loss tangent tanδD of the topping rubber of the first belt ply 7A.

The loss tangent tanδE of the topping rubber of the second belt ply 7B at 70°C is preferably 0.16 or less. By making the loss tangent tanδE of the topping rubber of the second belt ply 7B 0.16 or less, heat generation in the second belt ply 7B can be suppressed, and the pneumatic tire 1 can achieve both low fuel consumption performance and durability performance during high-speed driving. From this perspective, the loss tangent tanδE of the topping rubber of the second belt ply 7B is more preferably 0.15 or less. Note that, from the perspective of improving the noise performance of the pneumatic tire 1, it is desirable to make the loss tangent tanδ1 of the first portion 11 larger than the loss tangent tanδE of the topping rubber of the second belt ply 7B.

In this embodiment, the loss tangent tanδE of the second belt ply 7B is equal to the loss tangent tanδD of the first belt ply 7A. With this type of belt layer 7, the materials forming the first belt ply 7A and the second belt ply 7B can be uniformly managed, and the manufacturing costs of the pneumatic tire 1 can be reduced.

The band layer 8 is composed of at least one band ply 8A, one in this embodiment. The band ply 8A 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 that covers the band cord. The band layer 8 in this embodiment is arranged so as to cover the entire belt layer 7.

The loss tangent tanδF of the topping rubber of the band ply 8A at 70°C is preferably 0.16 or less. By making the loss tangent tanδF of the topping rubber of the band ply 8A 0.16 or less, heat generation in the band ply 8A can be suppressed, and the pneumatic tire 1 can achieve both low fuel consumption performance and durability performance during high-speed driving. From this perspective, the loss tangent tanδF of the topping rubber of the band ply 8A is more preferably 0.15 or less. Note that, from the perspective of improving the noise performance of the pneumatic tire 1, it is desirable to make the loss tangent tanδ1 of the first portion 11 larger than the loss tangent tanδF of the topping rubber of the band ply 8A.

The inner rubber 10 is desirably formed of an air-impermeable rubber material. Examples of rubber materials include butyl-based or halogenated butyl-based rubber materials. In this embodiment, the first portion 11 and the second portion 12 of the inner rubber 10 are formed of the same rubber material.

As shown in FIG. 2, the first portion 11 of the inner rubber 10 of this embodiment includes a pair of axially outer ends 11A. It is desirable that the first thickness t1 of each of the pair of ends 11A continuously decreases toward the axially outer end 11a of the first portion 11. In other words, the position where the decrease in the first thickness t1 ends corresponds to the axially outer end 11a of the first portion 11 of this embodiment. Such a first portion 11 suppresses stress concentration at the outer end 11a and helps improve the durability of the pneumatic tire 1.

The axially outer end 11a of the first portion 11 of the inner rubber 10 is preferably located at the same position as the axially outer end 7b of the second belt ply 7B, or is located axially inward of the axially outer end 7b of the second belt ply 7B and within 10 mm of the axially inner end 7b of the second belt ply 7B. In this type of inner rubber 10, the end 11A of the first portion 11 is located radially inward of the second belt ply 7B, so that the change in stiffness at the end 11A can be absorbed by the belt layer 7.

The tread portion 2 includes, for example, a plurality of circumferential grooves 20 that extend continuously in the tire circumferential direction. It is desirable that the axially outer end 11a of the first portion 11 of the inner rubber 10 is located axially outboard of the axially outermost circumferential groove 20.

In this embodiment, the entire end 11A of the first portion 11 is located axially outboard of the axially outermost circumferential groove 20. In this type of inner rubber 10, the portion where the circumferential grooves 20 are provided is the first portion 11, so vibrations of the tread portion 2 associated with the circumferential grooves 20 can be efficiently suppressed.

The first portion 11 extends between the pair of ends 11A with a constant first thickness t1. Such a first portion 11 can suppress vibration of the tread portion 2 while suppressing excessive weight increase, and can achieve both low fuel consumption performance and noise performance of the pneumatic tire 1. Here, the constant first thickness t1 means that the difference between the maximum and minimum thickness values is 5% or less of the maximum value.

The average value of the first thickness t1 is preferably 1.5 to 3.5 times the average value of the second thickness t2. By making the average value of the first thickness t1 1.5 times or more the average value of the second thickness t2, vibration of the tread portion 2 can be effectively suppressed, and the noise performance of the pneumatic tire 1 can be improved. From this perspective, the average value of the first thickness t1 is more preferably 1.75 times or more the average value of the second thickness t2, and even more preferably 1.9 times or more.

By making the average value of the first thickness t1 3.5 times or less than the average value of the second thickness t2, excessive weight increase can be suppressed and good fuel efficiency performance of the pneumatic tire 1 can be maintained. From this perspective, the average value of the first thickness t1 is more preferably 2.7 times or less than the average value of the second thickness t2, and even more preferably 2.2 times or less.

The average value of the first thickness t1 is preferably 2.0 to 4.5 mm. By making the average value of the first thickness t1 2.0 mm or more, vibrations in the tread portion 2 can be effectively suppressed, and the noise performance of the pneumatic tire 1 can be improved. From this perspective, the average value of the first thickness t1 is more preferably 2.5 mm or more.

By having the average value of the first thickness t1 be 4.5 mm or less, excessive weight increase can be suppressed and good fuel efficiency performance of the pneumatic tire 1 can be maintained. From this perspective, the average value of the first thickness t1 is more preferably 4.0 mm or less, and even more preferably 3.5 mm or less.

The average value of the second thickness t2 is preferably 0.5 to 2.0 mm. By making the average value of the second thickness t2 0.5 mm or more, good air impermeability can be maintained, which helps to improve the durability performance of the pneumatic tire 1. From this perspective, the average value of the second thickness t2 is more preferably 1.0 mm or more.

By making the average value of the second thickness t2 2.0 mm or less, excessive weight increase can be suppressed and good fuel efficiency performance of the pneumatic tire 1 can be maintained. From this perspective, the average value of the second thickness t2 is more preferably 1.5 mm or less.

In the above embodiment, the first portion 11 and the second portion 12 of the inner rubber 10 are formed from a single rubber material, but the inner rubber 10 is not limited to this configuration and may be formed from, for example, multiple rubber materials.

Figure 3 is an enlarged cross-sectional view of the inner rubber 10 of the second embodiment. The same elements as those of the above-mentioned embodiment are given the same reference numerals, and their explanations are omitted. As shown in Figure 3, the first part 11 of the inner rubber 10 of the second embodiment includes an inner liner layer 16 made of an air-impermeable rubber material, and an additional layer 17 arranged between the inner liner layer 16 and the carcass 6.

The additional layer 17 of the second embodiment is made of a rubber material different from that of the inner liner layer 16. The additional layer 17 may be made of, for example, an air-permeable rubber material. Such an inner rubber 10 has a wide variety of materials to choose from for the additional layer 17, and is suitable for achieving a variety of performances at low cost.

For example, the additional layer 17 may be made of a rubber material having a loss tangent tan δ at 70°C greater than that of the inner liner layer 16. In this case, the loss tangent tan δ1 of the first portion 11 is the average value of the loss tangent tan δ of the inner liner layer 16 and the loss tangent tan δ of the additional layer 17 weighted by the cross-sectional area. The loss tangent tan δ2 of the second portion 12 corresponds to the loss tangent tan δ of the inner liner layer 16. Such an additional layer 17 can more reliably reduce vibrations in the tread portion 2, improving the noise performance of the pneumatic tire 1.

Figure 4 is an enlarged cross-sectional view of the inner rubber 10 of the third embodiment. The same elements as those of the above-mentioned embodiment are given the same reference numerals, and their description is omitted. As shown in Figure 4, the additional layer 17 may be arranged, for example, on the inner side of the inner liner layer 16 in the tire radial direction. In this case, the additional layer 17 constitutes a part of the tire cavity surface 1i. As with the inner rubber 10 of the second embodiment, the inner rubber 10 of the third embodiment also has a wide variety of materials to choose from for the additional layer 17, and is suitable for achieving various performances at low cost.

As shown in Figures 3 and 4, even when the first portion 11 of the inner rubber 10 includes an additional layer 17, the first thickness t1 is the thickness from the inner surface 6i of the carcass 6 in the tread portion 2 to the tire cavity surface 1i, and does not include the topping rubber of the carcass ply 6A.

Figure 5 is an enlarged cross-sectional view of the inner rubber 10 of the fourth embodiment. The same elements as those of the above-mentioned embodiment are given the same reference numerals, and their explanations are omitted. As shown in Figure 5, the second part 12 of the inner rubber 10 of the fourth embodiment includes an inner liner layer 16 made of an air-impermeable rubber material, and an intermediate layer 18 disposed between the inner liner layer 16 and the carcass 6.

The intermediate layer 18 of the fourth embodiment is made of a rubber material different from that of the inner liner layer 16. The intermediate layer 18 may be made of the same rubber material as the additional layer 17 (shown in Figures 3 and 4), for example, or may be made of a rubber material different from that of the additional layer 17. This type of inner rubber 10 has a wide variety of materials to choose from for the intermediate layer 18, and is suitable for achieving a variety of performances at low cost.

The intermediate layer 18 overlaps, for example, with the band layer 8 in the tire axial direction. The intermediate layer 18 of the fourth embodiment overlaps with the belt layer 7 in the tire axial direction. The intermediate layer 18 may be continuous with the first portion 11 of the inner rubber 10, for example. It is desirable for the intermediate layer 18 to overlap with the folded portion 6b of the carcass 6 in the tire radial direction. Such an intermediate layer 18 helps to suppress vibrations of the sidewall portion 3, and can improve the noise performance of the pneumatic tire 1.

Even if the second portion 12 of the inner rubber 10 includes an intermediate layer 18, the second thickness t2 is the thickness from the inner surface 6i of the carcass 6 in the sidewall portion 3 to the tire inner cavity surface 1i, not including the topping rubber of the carcass ply 6A.

The above describes in detail a particularly preferred embodiment of the present invention, but the present invention is not limited to the above-described embodiment and can be modified in various ways.

A pneumatic tire with the basic structure shown in Figure 1 was prototyped based on the specifications in Table 1. The prototype tire was used to test fuel economy and noise performance. The main common specifications and test methods are as follows:

<Common specifications>
Tire size: 205/55R16
Air pressure: 230kPa
Load: 4.2 kN
Loss tangent tan δ2 of the second portion: 0.14

<Low fuel consumption performance>
The prototype tire was mounted on a rolling resistance tester, and the rolling resistance was measured when the tire was driven at a speed of 50 km/h. The rolling resistance was converted into an index, with the comparative example being set at 100, and the higher the index, the lower the rolling resistance and the better the fuel economy.

<Noise performance>
The prototype tire was mounted on an anechoic bench noise tester, and the sound pressure was measured when the tire was driven at a speed of 50 km/h. The sound pressure was converted into an index, with the comparative example being set at 100, and the larger the index, the smaller the sound pressure and the better the noise performance.

The results of the tests are shown in Table 1.

As a result of the test, the pneumatic tire of the embodiment exhibited fuel efficiency performance equal to or greater than that of the comparative example, while improving noise performance. The overall performance represented by the sum of these was also excellent, confirming that the tire achieved both fuel efficiency performance and noise performance.

[Additional Notes]
The present invention is as follows.

[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 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 tread portion includes a tread rubber that forms a ground contact surface,
The loss tangent tanδ1 at 70 ° C. of the first portion is equal to or greater than the loss tangent tanδ2 at 70 ° C. of the second portion and equal to or less than the loss tangent tanδA at 30 ° C. of the tread rubber.
Pneumatic tires.

[Invention 2]
The pneumatic tire according to claim 1, wherein the first thickness is 1.5 to 3.5 times the second thickness.

[The present invention 3]
3. The pneumatic tire according to claim 1 or 2, wherein the first thickness is 2.0 to 4.5 mm.

[Invention 4]
The pneumatic tire according to any one of claims 1 to 3, wherein the loss tangent tan δ1 of the first portion is 1.0 to 2.0 times the loss tangent tan δ2 of the second portion.

[Invention 5]
The pneumatic tire according to any one of claims 1 to 4, wherein the loss tangent tan δ1 of the first portion is 0.4 to 0.7 times the loss tangent tan δA of the tread rubber.

[Invention 6]
The pneumatic tire according to any one of claims 1 to 5, wherein the loss tangent tan δ1 of the first portion is 0.15 or more.

[Invention 7]
The pneumatic tire according to any one of claims 1 to 6, wherein the loss tangent tan δA of the tread rubber is 0.30 or less.

[The present invention 8]
The tread portion includes a cap rubber constituting the ground contact surface and a base rubber disposed on the inner side of the cap rubber in the tire radial direction,
The pneumatic tire according to any one of claims 1 to 7, wherein the base rubber has a loss tangent tan δB at 70°C of 0.20 or less.

[The present invention 9]
9. The pneumatic tire according to any one of claims 1 to 8, wherein the tread rubber has a complex modulus E*A at 30°C of 8.0 MPa or more.

[Invention 10]
A belt layer is disposed on the tread portion on the outer side of the carcass in the tire radial direction,
The belt layer includes a first belt ply and a second belt ply disposed outside the first belt ply in the tire radial direction,
an axially outer end of the second belt ply is located axially more inward than an axially outer end of the first belt ply,
A pneumatic tire according to any one of claims 1 to 9, wherein an axially outer end of the first portion of the inner rubber is located at the same position in the tire axial direction as the outer end of the second belt ply, or is located axially inward of the outer end of the second belt ply and within 10 mm in the tire axial direction.

Reference Signs List 1 Pneumatic tire 2 Tread portion 2G Tread rubber 2s Ground contact surface 3 Sidewall portion 4 Bead portion 6 Carcass 10 Inner rubber 11 First portion 12 Second portion

Claims (10)

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 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 tread portion includes a tread rubber that forms a ground contact surface,
The loss tangent tanδ1 at 70 ° C. of the first portion is equal to or greater than the loss tangent tanδ2 at 70 ° C. of the second portion and equal to or less than the loss tangent tanδA at 30 ° C. of the tread rubber.
Pneumatic tires. The pneumatic tire of claim 1, wherein the first thickness is 1.5 to 3.5 times the second thickness. The pneumatic tire according to claim 1, wherein the first thickness is 2.0 to 4.5 mm. The pneumatic tire according to any one of claims 1 to 3, wherein the loss tangent tanδ1 of the first portion is 1.0 to 2.0 times the loss tangent tanδ2 of the second portion. The pneumatic tire according to any one of claims 1 to 3, wherein the loss tangent tanδ1 of the first portion is 0.4 to 0.7 times the loss tangent tanδA of the tread rubber. The pneumatic tire according to any one of claims 1 to 3, wherein the loss tangent tanδ1 of the first portion is 0.15 or more. The pneumatic tire according to any one of claims 1 to 3, wherein the loss tangent tanδA of the tread rubber is 0.30 or less. The tread portion includes a cap rubber constituting the ground contact surface and a base rubber disposed on the inner side of the cap rubber in the tire radial direction,
The pneumatic tire according to claim 1 , wherein the base rubber has a loss tangent tan δB at 70° C. of 0.20 or less. The pneumatic tire according to any one of claims 1 to 3, wherein the complex modulus E*A of the tread rubber at 30°C is 8.0 MPa or more. A belt layer is disposed on the tread portion on the outer side of the carcass in the tire radial direction,
The belt layer includes a first belt ply and a second belt ply disposed outside the first belt ply in the tire radial direction,
an axially outer end of the second belt ply is located axially more inward than an axially outer end of the first belt ply,
4. The pneumatic tire according to claim 1, wherein an axially outer end of the first portion of the inner rubber is located at the same position in the tire axial direction as the outer end of the second belt ply, or is located axially inward of the outer end of the second belt ply and within 10 mm in the tire axial direction.

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