pneumatic tires

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

Technical Field

[0001] The present invention relates to pneumatic tires.

Background Art

[0002] Conventionally, various pneumatic tires capable of reducing road noise have been proposed. For example, the following Patent Document 1 proposes a pneumatic tire that reduces road noise while suppressing the influence on rolling resistance by providing a filler that extends substantially inward in the radial direction along the carcass from the end of the belt to suppress the vibration of the belt end.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in recent years, with the spread of electric vehicles and the like, the levels of low fuel consumption performance and noise performance required for pneumatic tires have increased, and further improvement has been demanded for the pneumatic tire of Patent Document 1.

[0005] The present invention has been devised in view of the above actual situation, and the main object thereof is to provide a pneumatic tire capable of achieving both low fuel consumption performance and noise performance.

Means for Solving the Problems

[0006] The present invention relates to a pneumatic tire comprising 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 inside the carcass between the pair of bead portions, wherein the inner rubber comprises a first portion extending the tread portion with a first thickness and a second portion extending the pair of sidewall portions with a second thickness, the first thickness being greater than the second thickness, the tread portion comprising tread rubber constituting the contact surface, the loss tangent tanδ1 of the first portion at 70°C being greater than or equal to the loss tangent tanδ2 of the second portion at 70°C, and the loss tangent tanδA of the tread rubber at 30°C being less than or equal to the loss tangent tanδA of the tread rubber. [Effects of the Invention]

[0007] The pneumatic tire of the present invention, by having the above-described configuration, can achieve both low fuel consumption and low noise performance. [Brief explanation of the drawing]

[0008] [Figure 1] This is a cross-sectional view showing one embodiment of the pneumatic tire of the present invention. [Figure 2] This is a magnified cross-sectional view of the tread area. [Figure 3] This is an enlarged cross-sectional view of the inner rubber of the second embodiment. [Figure 4] This is an enlarged cross-sectional view of the inner rubber of the third embodiment. [Figure 5] This is an enlarged cross-sectional view of the inner rubber of the fourth embodiment. [Modes for carrying out the invention]

[0009] One embodiment of the present invention will be described in detail below with reference to the drawings. Figure 1 is a meridian cross-sectional view of the pneumatic tire 1 of this embodiment, including the axis of rotation in its normal state. Here, "normal state" refers to the unloaded state in which the pneumatic tire 1 is mounted on a normal rim and adjusted to the normal internal pressure. Unless otherwise specified, the dimensions of each part of the pneumatic tire 1 are values ​​measured in this normal state.

[0010] A "standard rim" is the rim specified for each tire by a standard that includes the standard on which the pneumatic tire 1 is based. For example, it is a "standard rim" for JATMA, a "design rim" for TRA, and a "measuring rim" for ETRTO. If there is no standard that includes the standard on which the pneumatic tire 1 is based, a "standard rim" is the rim with the smallest rim diameter and the smallest rim width among rims that can be mounted on and do not cause air leaks.

[0011] "Regular internal pressure" refers to the air pressure specified for each tire by each standard, if there is a standard system on which the pneumatic tire 1 is based. For example, it is the "maximum air pressure" for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and the "INFLATION PRESSURE" for ETRTO. If there is no standard system on which the pneumatic tire 1 is based, "regular internal pressure" refers to the air pressure specified for each tire by the manufacturer, etc.

[0012] As shown in Figure 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, an annularly extending bead core 5. The bead core 5 is formed from, for example, steel wire. The pneumatic tire 1 of this embodiment is suitably used as a passenger car tire. The pneumatic tire 1 is not limited to passenger car tires, but can be applied to various types of tires, such as heavy-duty tires, motorcycle tires, and industrial vehicle tires.

[0013] 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 inside the carcass 6 between the pair of bead portions 4. The inner rubber 10 of this embodiment constitutes the inner surface 1i of the tire.

[0014] The inner rubber 10 of this embodiment includes a first portion 11 extending from the tread portion 2 with a first thickness t1, and a second portion 12 extending from the pair of sidewall portions 3 with 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 inner surface 1i of the tire, and do not include the topping rubber of the carcass ply 6A, which will be described later.

[0015] In this embodiment, the first thickness t1 is greater than the second thickness t2. It is desirable that the first thickness t1 is greater than the second thickness t2 around the entire circumference of the tire. Such an inner rubber 10 can exert a vibration reduction effect similar to that of increasing the thickness of the tread rubber 2G, which will be described later, with a small increase in weight. Furthermore, since the increase in weight on the inside 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.

[0016] Here, the statement that the first thickness t1 is 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 section by the length of the first portion 11 along the inner surface 1i of the tire. The same applies to the average value of the second thickness t2.

[0017] FIG. 2 is an enlarged cross-sectional view of the tread portion 2. As shown in FIG. 2, the tread portion 2 of the present 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 disposed inside the cap rubber 2A in the tire radius direction. The tread portion 2 is not limited to such a mode. For example, it may be composed of a single layer of rubber material, or may be composed of three or more layers of rubber materials. When the tread portion 2 is composed of a plurality of rubber materials, the tread rubber 2G is the rubber material that constitutes the ground contact surface 2s, for example, the cap rubber 2A.

[0018] The loss tangent tanδ1 at 70°C of the first portion 11 of the present embodiment is not less than the loss tangent tanδ2 at 70°C of the second portion 12. Such a first portion 11 helps to suppress the vibration of the tread portion 2 and can improve the noise performance of the pneumatic tire 1.

[0019] The loss tangent tanδ1 at 70°C of the first portion 11 is preferably not more than the loss tangent tanδA at 30°C of the tread rubber 2G. Since the tread rubber 2G that constitutes the ground contact surface 2s is cooled by contact with the outside air, the measurement temperature is set to 30°C. Such a first portion 11 can further reduce the influence on the rolling resistance in the tread portion 2 and helps to improve the low fuel consumption performance of the pneumatic tire 1. Therefore, the pneumatic tire 1 of the present embodiment can achieve both low fuel consumption performance and noise performance.

[0020] Here, in this specification, the loss tangent tanδ is a value measured using a dynamic viscoelasticity measuring device under the following conditions in accordance with the provisions of JIS-K6394. The rubber sample when measuring the loss tangent tanδ is, for example, taken from the vulcanized pneumatic tire 1, and is taken so that the longitudinal direction of the sample coincides with the circumferential direction of the pneumatic tire 1. Initial strain: 5% (when the measurement temperature is 30°C) or 10% (when the measurement temperature is 70°C) Amplitude of dynamic strain: ±1% Frequency: 10 Hz Deformation mode: Tension Measurement temperature: 30 °C or 70 °C

[0021] Note that the loss tangent tanδ can be appropriately adjusted according to the glass transition point Tg of the rubber composition and the types and amounts of various compounding agents. Specifically, it is possible to increase the loss tangent tanδ by increasing the glass transition point Tg of the rubber composition, decreasing the average particle diameter of reinforcing agents such as carbon and silica, increasing the amount of the reinforcing agent, and decreasing the vulcanizing agent such as sulfur and accelerator.

[0022] Here, when the first part 11 is composed of a single rubber material, the loss tangent tanδ1 of the first part 11 is the loss tangent tanδ1 of that rubber material. Also, when the first part 11 is composed of a plurality of rubber materials, the loss tangent tanδ1 of the first part 11 is an average value obtained as a weighted average of the loss tangents tanδ1 of those rubber materials weighted by the cross-sectional area of each rubber material. Note that the same applies to other loss tangents tanδ.

[0023] As a more preferred embodiment, the loss tangent tanδ1 of the first part 11 is 1.0 to 2.0 times the loss tangent tanδ2 of the second part 12. By the loss tangent tanδ1 of the first part 11 being 1.0 times or more the loss tangent tanδ2 of the second part 12, the vibration suppression effect of the tread portion 2 can be surely achieved. From such a viewpoint, the loss tangent tanδ1 of the first part 11 is more preferably 1.1 times or more the loss tangent tanδ2 of the second part 12.

[0024] By the loss tangent tanδ1 of the first part 11 being 2.0 times or less the loss tangent tanδ2 of the second part 12, breakage such as peeling due to an excessive difference in physical properties can be suppressed, and the durability performance of the pneumatic tire 1 can be improved. From such a viewpoint, the loss tangent tanδ1 of the first part 11 is more preferably 1.5 times or less the loss tangent tanδ2 of the second part 12.

[0025] 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 having the loss tangent tanδ1 of the first portion 11 be 0.4 times or more the loss tangent tanδA of the tread rubber 2G, vibration of the tread portion 2 can be reduced while maintaining the low fuel consumption performance of the pneumatic tire 1.

[0026] By ensuring that the loss tangent tanδ1 of the first part 11 is 0.7 times or less of the loss tangent tanδA of the tread rubber 2G, it is possible to reduce vibration of the tread section 2 while maintaining the handling stability performance of the pneumatic tire 1.

[0027] The loss tangent tanδ1 of the first portion 11 is preferably 0.14 or greater. A loss tangent tanδ1 of 0.14 or greater ensures reliable suppression of vibration in the tread portion 2 and reduces noise generation. From this perspective, the loss tangent tanδ1 of the first portion 11 is more preferably 0.15 or greater, and even more preferably 0.20 or greater.

[0028] The loss tangent tanδ2 of the second part 12 is preferably equal to the loss tangent tanδ1 of the first part 11. Such an inner rubber 10 allows the first part 11 and the second part 12 to be formed integrally, which helps to reduce the manufacturing cost of the pneumatic tire 1.

[0029] The loss tangent tanδA of the tread rubber 2G is preferably 0.30 or less. By having a loss tangent tanδA of 0.30 or less of the tread rubber 2G, rolling resistance can be reduced and the fuel efficiency performance of the pneumatic tire 1 can be improved. From this viewpoint, the loss tangent tanδA of the tread rubber 2G is more preferably 0.25 or less, and even more preferably 0.20 or less.

[0030] 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 equal to 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 the good handling stability of the pneumatic tire 1.

[0031] The loss tangent tanδB of the base rubber 2B is preferably 0.21 or less. Having a loss tangent tanδB of 0.21 or less of the base rubber 2B helps to suppress heat generation in the tread portion 2 during driving, and helps to maintain the good fuel efficiency performance of the pneumatic tire 1. From this viewpoint, the loss tangent tanδB of the base rubber 2B is more preferably 0.20 or less.

[0032] The complex modulus E*A of the tread rubber 2G at 30°C is preferably 7.8 MPa or higher. A complex modulus E*A of 7.8 MPa or higher of the tread rubber 2G helps to suppress vibrations of the tread portion 2 and improve the noise performance of the pneumatic tire 1. From this viewpoint, the complex modulus E*A of the tread rubber 2G is more preferably 8.0 MPa or higher, and even more preferably 9.0 MPa or higher. Note that when the tread rubber 2G is composed of multiple rubber materials, the complex modulus E*A is based on the rubber material constituting the contact surface 2s.

[0033] 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. The 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℃

[0034] Furthermore, the complex modulus of elasticity E* can be appropriately adjusted depending on the glass transition temperature Tg of the rubber composition and the type and amount of various compounding agents. Specifically, the complex modulus of elasticity E* can be increased by raising the glass transition temperature Tg of the rubber composition, reducing 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 vulcanizing agents such as sulfur and accelerators.

[0035] As shown in Figures 1 and 2, in this embodiment, the tread portion 2 has a belt layer 7 arranged on the radially outer side of the carcass 6. Preferably, the tread portion 2 has a band layer 8 arranged on the radially outer side of the belt layer 7.

[0036] The carcass 6 is composed of at least one carcass ply 6A, in this embodiment one carcass ply 6A. The carcass ply 6A includes, for example, a main body portion 6a and a folded portion 6b. The main body portion 6a extends, for example, between two bead portions 4. The folded portion 6b is, for example, connected to the main body portion 6a and folded back around the bead core 5 from the inside to the outside in the tire axial direction.

[0037] Although not shown in the diagram, the carcass ply 6A includes multiple carcass cords and a topping rubber covering them. The carcass cords are, for example, organic fiber cords such as aramid or rayon. The carcass cords are preferably arranged at an angle of 70 to 90° with respect to the tire equator C.

[0038] The loss tangent tanδC of the topping rubber of the carcass ply 6A at 70°C is preferably 0.16 or less. Having a loss tangent tanδC of 0.16 or less suppresses heat generation in the carcass ply 6A, enabling both low fuel consumption and durability during high-speed driving of the pneumatic tire 1. From this viewpoint, the loss tangent tanδC of the topping rubber of the carcass ply 6A is more preferably 0.15 or less. Furthermore, from the viewpoint 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.

[0039] The belt layer 7 includes, for example, a first belt ply 7A adjacent to the carcass 6 and a second belt ply 7B positioned radially outside the first belt ply 7A. Each of the first belt ply 7A and the second belt ply 7B in this embodiment includes a plurality of belt cords arranged at an angle of 15 to 45° with respect to the circumferential direction of the tire, and a topping rubber covering them.

[0040] 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 with respect to the circumferential direction of the tire. Such a belt layer 7 can effectively reinforce the tread portion 2.

[0041] In this embodiment, the outer end 7b of the second belt ply 7B in the tire axial direction is located inward in the tire axial direction compared to the outer end 7a of the first belt ply 7A in the tire axial direction. As a result, the length of the second belt ply 7B in the tire axial direction is smaller than the length of the first belt ply 7A in the tire axial direction. Such a belt layer 7 can reinforce the tread portion 2 while suppressing the second belt ply 7B from becoming excessively large, thus helping to achieve both low fuel consumption and low noise performance for the pneumatic tire 1.

[0042] The loss tangent tanδD of the topping rubber of the first belt ply 7A at 70°C is preferably 0.16 or less. By having a loss tangent tanδD of the topping rubber of the first belt ply 7A of 0.16 or less, heat generation in the first belt ply 7A is suppressed, and both low fuel consumption performance and durability performance during high-speed driving of the pneumatic tire 1 can be achieved. From this viewpoint, the loss tangent tanδD of the topping rubber of the first belt ply 7A is more preferably 0.15 or less. Furthermore, from the viewpoint 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.

[0043] The loss tangent tanδE of the topping rubber of the second belt ply 7B at 70°C is preferably 0.16 or less. By having a loss tangent tanδE of the topping rubber of the second belt ply 7B of 0.16 or less, heat generation in the second belt ply 7B is suppressed, and both low fuel consumption performance and durability performance during high-speed driving of the pneumatic tire 1 can be achieved. From this viewpoint, the loss tangent tanδE of the topping rubber of the second belt ply 7B is more preferably 0.15 or less. Furthermore, from the viewpoint 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.

[0044] 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. Such a belt layer 7 allows for uniform control of the materials forming the first belt ply 7A and the second belt ply 7B, thereby reducing the manufacturing cost of the pneumatic tire 1.

[0045] The band layer 8 is composed of at least one band ply 8A, which in this embodiment is one band ply 8A. The band ply 8A includes, for example, band cords arranged at an angle of 5° or less with respect to the circumferential direction of the tire, and a topping rubber covering the band cords. The band layer 8 in this embodiment is arranged to cover the entire belt layer 7.

[0046] The loss tangent tanδF of the topping rubber of the band ply 8A at 70°C is preferably 0.16 or less. Having a loss tangent tanδF of 0.16 or less suppresses heat generation in the band ply 8A, enabling both low fuel consumption and durability during high-speed driving of the pneumatic tire 1. From this viewpoint, the loss tangent tanδF of the topping rubber of the band ply 8A is more preferably 0.15 or less. Furthermore, from the viewpoint 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.

[0047] The inner rubber 10 is preferably made of a rubber material that is impermeable to air. Examples of rubber materials include butyl-based or halogenated butyl-based rubber materials. In this embodiment, the inner rubber 10 is made of the same rubber material for both the first part 11 and the second part 12.

[0048] As shown in Figure 2, the first portion 11 of the inner rubber 10 in this embodiment includes a pair of outer ends 11A in the tire axial direction. It is desirable that the first thickness t1 of each of the pair of ends 11A decreases continuously toward the outer end 11a in the tire axial direction of the first portion 11. That is, the position where the decrease in the first thickness t1 ends corresponds to the outer end 11a in the tire axial direction of the first portion 11 in this embodiment. Such a first portion 11 helps to suppress stress concentration at the outer end 11a and improve the durability of the pneumatic tire 1.

[0049] The outer end 11a of the first portion 11 of the inner rubber 10 in the tire axial direction is preferably at the same position as the outer end 7b of the second belt ply 7B in the tire axial direction, or it is preferably located inward in the tire axial direction from the outer end 7b of the second belt ply 7B and within 10 mm in the tire axial direction. In such an inner rubber 10, since the end 11A of the first portion 11 is located inward in the tire radial direction from the second belt ply 7B, changes in rigidity at the end 11A can be absorbed by the belt layer 7.

[0050] The tread portion 2 includes, for example, a plurality of circumferential grooves 20 that extend continuously in the circumferential direction of the tire. It is desirable that the outer end 11a of the first portion 11 of the inner rubber 10 in the tire axial direction is located outward in the tire axial direction from the outermost circumferential groove 20 in the tire axial direction.

[0051] In this embodiment, the entire end portion 11A of the first portion 11 is located outside the outermost circumferential groove 20 in the tire axial direction. In such an inner rubber 10, since the portion where the circumferential groove 20 is provided is the first portion 11, vibrations of the tread portion 2 associated with the circumferential groove 20 can be efficiently suppressed.

[0052] The first portion 11 extends between a 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, thereby achieving both low fuel consumption and noise performance for the pneumatic tire 1. Here, a constant first thickness t1 means that the difference between the maximum and minimum thickness is 5% or less of the maximum value.

[0053] 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 having an average value of 1.5 times or more the average value of the second thickness t2, vibrations of the tread portion 2 can be effectively suppressed, and the noise performance of the pneumatic tire 1 can be improved. From this viewpoint, 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.

[0054] By keeping the average value of the first thickness t1 at 3.5 times or less the average value of the second thickness t2, excessive weight increase can be suppressed, and the good fuel efficiency performance of the pneumatic tire 1 can be maintained. From this viewpoint, the average value of the first thickness t1 is more preferably 2.7 times or less the average value of the second thickness t2, and even more preferably 2.2 times or less.

[0055] The average value of the first thickness t1 is preferably 2.0 to 4.5 mm. An average value of 2.0 mm or more for the first thickness t1 effectively suppresses vibrations in the tread portion 2, thereby improving the noise performance of the pneumatic tire 1. From this perspective, the average value of the first thickness t1 is more preferably 2.5 mm or more.

[0056] By keeping the average value of the first thickness t1 at 4.5 mm or less, excessive weight increase can be suppressed, and the good fuel efficiency performance of the pneumatic tire 1 can be maintained. From this viewpoint, 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.

[0057] The average value of the second thickness t2 is preferably 0.5 to 2.0 mm. An average value of 0.5 mm or more for the second thickness t2 maintains good air impermeability, which helps improve the durability of the pneumatic tire 1. From this viewpoint, the average value of the second thickness t2 is more preferably 1.0 mm or more.

[0058] By keeping the average value of the second thickness t2 at 2.0 mm or less, excessive weight increase can be suppressed, and the good fuel efficiency performance of the pneumatic tire 1 can be maintained. From this viewpoint, the average value of the second thickness t2 is more preferably 1.5 mm or less.

[0059] In the above-described embodiment, the first portion 11 and the second portion 12 of the inner rubber 10 are shown to be formed from a single rubber material. However, the inner rubber 10 is not limited to this embodiment and may be formed from, for example, multiple rubber materials.

[0060] Figure 3 is an enlarged cross-sectional view of the inner rubber 10 of the second embodiment. Elements identical to those in the above-described embodiments are denoted by the same reference numerals, and their descriptions are omitted. As shown in Figure 3, the first portion 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 disposed between the inner liner layer 16 and the carcass 6.

[0061] In the second embodiment, the additional layer 17 is made of a different rubber material than 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 offers a wide variety of material choices for the additional layer 17 and is suitable for achieving various performance characteristics at low cost.

[0062] The additional layer 17 can be made of a rubber material that has a larger loss tangent tanδ at 70°C than the inner liner layer 16. In this case, the loss tangent tanδ1 of the first part 11 is the average value obtained by weighting the loss tangent tanδ of the inner liner layer 16 and the loss tangent tanδ of the additional layer 17 by their cross-sectional area. The loss tangent tanδ2 of the second part 12 corresponds to the loss tangent tanδ of the inner liner layer 16. Such an additional layer 17 can more reliably reduce vibrations in the tread portion 2 and improve the noise performance of the pneumatic tire 1.

[0063] Figure 4 is an enlarged cross-sectional view of the inner rubber 10 of the third embodiment. The same reference numerals are used for elements identical to those in the embodiments described above, and their descriptions are omitted. As shown in Figure 4, the additional layer 17 may be located, for example, radially inward of the inner liner layer 16. In this case, the additional layer 17 constitutes a part of the inner surface 1i of the tire. The inner rubber 10 of the third embodiment, like the inner rubber 10 of the second embodiment, offers a wide variety of material choices for the additional layer 17 and is suitable for achieving various performance characteristics at low cost.

[0064] As shown in Figures 3 and 4, even when an additional layer 17 is included in the first portion 11 of the inner rubber 10, the first thickness t1 is the thickness from the inner surface 6i of the carcass 6 in the tread portion 2 to the inner surface 1i of the tire, and does not include the thickness of the topping rubber of the carcass ply 6A.

[0065] Figure 5 is an enlarged cross-sectional view of the inner rubber 10 of the fourth embodiment. The same reference numerals are used for elements identical to those in the embodiments described above, and their descriptions are omitted. As shown in Figure 5, the second portion 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.

[0066] The intermediate layer 18 of the fourth embodiment is made of a different rubber material than 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), or it may be made of a different rubber material than the additional layer 17. Such an inner rubber 10 offers a wide variety of material choices for the intermediate layer 18 and is suitable for achieving various performance characteristics at low cost.

[0067] The intermediate layer 18 overlaps, for example, with the band layer 8 in the tire axial direction. In the fourth embodiment, the intermediate layer 18 overlaps with the belt layer 7 in the tire axial direction. The intermediate layer 18 may, for example, be connected to the first portion 11 of the inner rubber 10. It is desirable that the intermediate layer 18 overlaps 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.

[0068] Even when 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 inner surface 1i of the tire, and does not include the thickness of the topping rubber of the carcass ply 6A.

[0069] Although particularly preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above and can be implemented in various modified forms. [Examples]

[0070] 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 its fuel efficiency and noise performance. The main common specifications and test methods are as follows:

[0071] <Common Specifications> Tire size: 205 / 55R16 Air pressure: 230kPa Load capacity: 4.2kN Loss tangent for the second part tanδ²: 0.14

[0072] <Fuel efficiency> The prototype tires were mounted on a rolling resistance testing machine, and their rolling resistance was measured when driven at 50 km / h. The results were converted into an index where lower rolling resistance corresponds to higher values. The results are expressed as an index with the comparative example set to 100, and a higher value indicates lower rolling resistance and superior fuel efficiency.

[0073] <Noise performance> The prototype tire was mounted on an anechoic chamber noise tester, and the sound pressure was measured when it was driven at 50 km / h. The sound pressure was converted into an index where lower sound pressure corresponds to a higher numerical value. The results are expressed as an index with the comparative example set to 100, and a higher numerical value indicates lower sound pressure and superior noise performance.

[0074] The test results are shown in Table 1. [Table 1]

[0075] The test results showed that the pneumatic tire in the example demonstrated fuel efficiency equal to or better than the comparative example, while also improving noise performance. The overall performance, represented by the sum of these factors, was also superior, confirming that it achieved a balance between fuel efficiency and noise performance.

[0076] [Note] The present invention is as follows:

[0077] [Invention 1] It is a pneumatic tire, The tread section and, A pair of sidewall sections, A pair of bead sections, A carcass extending between the pair of bead portions, The carcass includes an inner rubber extending between the pair of bead portions inside the carcass, The inner rubber includes a first portion extending the tread portion with a first thickness and a second portion extending the pair of sidewall portions with a second thickness. The first thickness is greater than the second thickness. The tread portion includes tread rubber that constitutes the contact surface. The loss tangent tanδ1 of the first portion at 70°C is greater than or equal to the loss tangent tanδ2 of the second portion at 70°C, and less than or equal to the loss tangent tanδA of the tread rubber at 30°C. Pneumatic tires.

[0078] [Invention 2] The pneumatic tire according to the present invention 1, wherein the first thickness is 1.5 to 3.5 times the second thickness.

[0079] [Invention 3] The pneumatic tire according to invention 1 or 2, wherein the first thickness is 2.0 to 4.5 mm.

[0080] [4th Invention] The pneumatic tire according to any one of inventions 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.

[0081] [5th ​​Invention] The pneumatic tire according to any one of inventions 1 to 4, wherein the loss tangent tanδ1 of the first portion is 0.4 to 0.7 times the loss tangent tanδA of the tread rubber.

[0082] [Invention 6] A pneumatic tire according to any one of inventions 1 to 5, wherein the loss tangent tanδ1 of the first portion is 0.15 or greater.

[0083] [7th Invention] A pneumatic tire according to any one of claims 1 to 6 of the present invention, wherein the loss tangent tanδA of the tread rubber is 0.30 or less.

[0084] [8th Invention] The tread portion includes a cap rubber that constitutes the contact surface and a base rubber positioned inside the cap rubber in the tire radial direction. A pneumatic tire according to any one of inventions 1 to 7, wherein the loss tangent tanδB of the base rubber at 70°C is 0.20 or less.

[0085] [Invention 9] A pneumatic tire according to any one of inventions 1 to 8, wherein the complex modulus of elasticity E*A of the tread rubber at 30°C is 8.0 MPa or higher.

[0086] [Invention 10] The tread portion has a belt layer arranged 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 positioned outside the first belt ply in the tire radial direction. The outer end of the second belt ply in the tire axial direction is located inward in the tire axial direction compared to the outer end of the first belt ply in the tire axial direction. The pneumatic tire according to any one of inventions 1 to 9, wherein the outer end of the first portion of the inner rubber in the tire axial direction is at the same position as the outer end of the second belt ply in the tire axial direction, or is located inward in the tire axial direction from the outer end of the second belt ply and within 10 mm in the tire axial direction. [Explanation of Symbols]

[0087] 1. Pneumatic tire 2 Tread section 2G Tread Rubber 2s ground plane 3. Sidewall section 4. Bead section 6 Carcass 10 Inner rubber 11 Part 1 12 Part 2

Claims

1. It is a pneumatic tire, The tread section and A pair of sidewall sections, A pair of bead sections, A carcass extending between the pair of bead portions, The carcass includes an inner rubber extending between the pair of bead portions inside the carcass, The inner rubber includes a first portion extending the tread portion with a first thickness and a second portion extending the pair of sidewall portions with a second thickness. The first thickness is greater than the second thickness. The tread portion includes tread rubber that constitutes the contact surface. The loss tangent tanδ1 of the first portion at 70°C is greater than or equal to the loss tangent tanδ2 of the second portion at 70°C, and less than or equal to the loss tangent tanδA of the tread rubber at 30°C. Pneumatic tires.

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

3. The pneumatic tire according to claim 1, wherein the first thickness is 2.0 to 4.5 mm.

4. 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.

5. 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.

6. 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.

7. 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.

8. The tread portion includes a cap rubber that constitutes the contact surface and a base rubber positioned inside the cap rubber in the tire radial direction. The pneumatic tire according to any one of claims 1 to 3, wherein the loss tangent tanδB of the base rubber at 70°C is 0.20 or less.

9. 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.

10. The tread portion has a belt layer arranged 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 positioned outside the first belt ply in the tire radial direction. The outer end of the second belt ply in the tire axial direction is located inward in the tire axial direction compared to the outer end of the first belt ply in the tire axial direction. The pneumatic tire according to any one of claims 1 to 3, wherein the outer end of the first portion of the inner rubber in the tire axial direction is at the same position as the outer end of the second belt ply in the tire axial direction, or is located inward in the tire axial direction from the outer end of the second belt ply and within 10 mm in the tire axial direction.

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