JP2024061154A - Pneumatic tires - Google Patents

Abstract

[Problem] To provide a pneumatic tire that can reduce interior noise without increasing rolling resistance. [Solution] A pneumatic tire (1) includes a tread portion (2), a sidewall portion (3), a bead portion (4), a carcass (6), and an inner rubber (10) extending inside the carcass (6). The inner rubber (10) 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 the sidewall portion (3) at a second thickness (t2). The first thickness (t1) is greater than the second thickness (t2). The carcass (6) includes carcass cords (6B), and the twist coefficient of the carcass cords (6B) is 2000 to 2500. [Selected Figure] Figure 1

Description

The present invention relates to a pneumatic tire.

Pneumatic tires have been proposed that aim to reduce passing noise while maintaining the necessary wet performance (see, for example, Patent Document 1).

JP 2022-096037 A

In recent years, there has been an increasing demand for quieter pneumatic tires. When a pneumatic tire is in motion, vibrations generated in the tread are transmitted to the rim and ultimately the vehicle body via the sidewall and bead portions, and are perceived by passengers as noise inside the vehicle.

Interior noise can be reduced, for example, by using tread rubber with a large loss tangent tan δ. However, this approach increases the rolling resistance of the pneumatic tires, worsening the fuel economy of the vehicle.

The present invention was devised in consideration of the above-mentioned circumstances, and its main objective is to provide a pneumatic tire that can reduce interior noise without increasing rolling resistance.

The present invention relates to
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 carcass includes a carcass cord,
The twist factor of the carcass cord is 2,000 to 2,500.

By adopting the above-mentioned configuration, the pneumatic tire of the present invention can reduce interior noise without increasing rolling resistance.

1 is a cross-sectional view showing one embodiment of a pneumatic tire of the present invention. FIG. 2 is an enlarged cross-sectional view of the tread portion of FIG. 1 . FIG. 2 is a development view of the ground contact surface of the tread portion of FIG. 1 . 2 is an enlarged cross-sectional view of a first end of the first portion of FIG. 1 . FIG. 2 is an enlarged cross-sectional view of a first portion and a second portion of another embodiment of the present invention. FIG. 11 is an enlarged cross-sectional view of a first portion and a second portion of yet another embodiment of the present invention. FIG. 11 is an enlarged cross-sectional view of a sidewall portion according to yet another embodiment of the present invention.

An embodiment of the present invention will be described below 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") showing one embodiment of the present invention. FIG. 1 is a cross-sectional view including the rotation axis of a tire in a normal state. As shown in FIG. 1, tire 1 of this embodiment is preferably used, for example, as a pneumatic tire for passenger cars. However, the present invention is not limited to such an embodiment, and may be applied, for example, to a pneumatic tire for heavy loads.

In the case of a pneumatic tire for which various standards are established, the "normal state" refers to a state in which the tire is mounted on a normal rim, inflated to the normal internal pressure, and unloaded. In the case of a tire for which various standards are not established, the normal state refers to a standard usage state according to the intended use of the tire, in which the tire is not mounted on a vehicle and is unloaded. In this specification, unless otherwise specified, the dimensions of each part of the tire are values measured in the normal state. In addition, components that cannot be measured in the normal state (for example, the internal materials of tire 1) are values measured with tire 1 in a state as close as possible to the normal state.

A "genuine rim" is a rim that is specified 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."

"Normal internal pressure" is the air pressure set for each tire by each standard in the standard system 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." For ETRTO, it is the "INFLATION PRESSURE."

The tire 1 includes a tread portion 2, a pair of sidewall portions 3, and a pair of bead portions 4. The sidewall portion 3 is connected to the axially outer side of the tread portion 2 and extends in the radial direction of the tire. The bead portion 4 is connected to the radially inner side of the sidewall portion 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 inner cavity surface 1A. The inner rubber 10 is made of vulcanized rubber 1.5 to 3.0, and is significantly different in material and physical properties from a sealant material for preventing punctures.

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 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 is folded back, for example, from the inside to the outside in the axial direction of the tire around the bead core 5.

The carcass ply 6A includes multiple carcass cords 6B and a topping rubber that covers them (not shown). The carcass cords 6B are made of organic fiber cords such as aramid or rayon. The carcass cords 6B are preferably arranged at an angle of 70 to 90 degrees with respect to the tire equator C.

Figure 2 shows an enlarged cross-sectional view of the tread portion 2 in Figure 1. As shown in Figure 2, the tread portion 2 of this embodiment includes, for example, a belt layer 7 and a band layer 8 arranged on the tire radially outer side of the carcass 6. However, the tread portion 2 is not limited to this form. The belt layer 7 includes a first belt ply 7A adjacent to the carcass 6 and a second belt ply 7B arranged on the tire radially outer side 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 that covers these. 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.

It is desirable that the axial length of the second belt ply 7B be smaller than the axial length of the first belt ply 7A. As a result, 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.

The band layer 8 is composed of, for example, one band ply 8A. 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. In this embodiment, the band layer 8 is arranged so as to cover the entire belt layer 7.

As shown in FIG. 1, the inner rubber 10 includes a first portion 11 and a second portion 12. The first portion 11 extends through the tread portion 2 with a first thickness t1. The second portion 12 extends through the pair of sidewall portions 3 with a second thickness t2. The first thickness t1 and the second thickness t2 refer to the thickness from the inner surface 6i of the carcass 6 to the tire inner surface 1A, and do not include the topping rubber of the carcass ply.

In the present invention, the first thickness t1 is greater than the second thickness t2. 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 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. 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 such an aspect.

In the tire 1 of the present invention, the twist coefficient K of the carcass cord 6B is 2000 to 2500. Here, when the number of twists per 100 mm is T and the total fineness of the carcass cord 6B is D (dtex), K is a coefficient expressed as T√D. Note that the twist coefficient K is the value for the carcass cord 6B after the dipping process.

If a cord with a small twist coefficient K is used as the carcass cord 6B, the cord fatigue resistance may deteriorate, which may affect the durability of the tire 1. In this tire 1, the twist coefficient of the carcass cord 6B is set to 2000 or more, so the cord fatigue resistance is good and the durability performance of the tire 1 is improved.

On the other hand, if a cord with a large twist coefficient K is used as the carcass cord 6B, good damping cannot be obtained from the sidewall portion 3 to the bead portion 4, which may affect the noise performance of the tire 1. Also, the deformation of the case structure including the carcass 6 from the sidewall portion 3 to the bead portion 4 increases, resulting in high rolling resistance. In this tire 1, the twist coefficient K of the carcass cord 6B is set to 2500 or less, so good damping is obtained from the sidewall portion 3 to the bead portion 4, improving the noise performance of the tire 1 and reducing interior noise. Also, because deformation of the case structure is suppressed, rolling resistance can be easily reduced.

In this tire 1, the first portion 11 of the inner rubber 10, which extends through the tread portion 2 with a first thickness t1 that is greater than the second thickness t2 of the second portion 12, functions as a mass damper and suppresses vibrations in the tread portion 2. Furthermore, the vibration energy of the tread portion 2 is damped by the viscoelastic properties of the rubber itself that is disposed in the first portion 11.

Therefore, compared to a conventional pneumatic tire that does not have the first portion 11, the tire 1 allows the use of cords with a large twist factor K as the carcass cords 6B. On the other hand, the increase in rolling resistance that is a concern due to the provision of the first portion 11 is easily suppressed by the carcass cords 6B, which have an upper limit of the twist factor K of 2500.

In other words, in the tire 1 of the present invention, the carcass cord 6B, in which the twist coefficient K is optimized according to the first thickness t1 of the first portion 11, makes it possible to reduce interior noise without increasing rolling resistance.

The tire 1 of this embodiment has a so-called high turn-up structure in which the tip of the folded portion 6b of the carcass 6 is positioned radially outward from the maximum width position of the tire 1. Such a carcass 6 makes it difficult for vibrations of the sidewall portion 3 to bead portion 4 to be transmitted, making it possible to reduce noise inside the vehicle. In addition, deformation of the case structure from the sidewall portion 3 to the bead portion 4 is suppressed, making it easy to reduce rolling resistance. The tire 1 of this embodiment may have a so-called ultra-high turn-up structure in which the tip of the folded portion 6b of the carcass 6 is positioned axially inward from the axial outer end of the belt layer 7.

In this embodiment, polyethylene terephthalate (PET) is used for the carcass cord 6B. The number of carcass plies 6A and the fineness of the carcass cord 6B are preferably as follows, depending on the load index of the tire 1. In a tire 1 with a load index of 90 or less, the carcass ply 6A is one ply, and the fineness of the carcass cord 6B is 1100 dtex/2. In a tire 1 with a load index of more than 90 and less than 100, the carcass ply 6A is one ply, and the fineness of the carcass cord 6B is 1440 dtex/2. In a tire 1 with a load index of more than 90 and less than 105, the carcass ply 6A is one ply, and the fineness of the carcass cord 6B is 1670 dtex/2. In a tire 1 with a load index of 110 or less, the carcass ply 6A is two plies, and the fineness of the carcass cord 6B is 1110 dtex/2. In a tire 1 with a load index of 115 or less, the carcass ply 6A is two plies, and the fineness of the carcass cord 6B is 1440 dtex/2. In a tire 1 with a load index of 115 or less, the carcass ply 6A is two plies, and the fineness of the carcass cord 6B may be 1670 dtex/2.

The tread portion 2 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, for example, composed of 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.

The loss tangent tan δ at 70°C of the first portion 11 of the inner rubber 10 is preferably equal to or less than the loss tangent tan δ at 30°C of the tread rubber 2G. Such a first portion 11 can reduce the effect on the rolling resistance in the tread portion 2, and is useful for improving the fuel efficiency performance of the tire 1. Therefore, the tire 1 of this embodiment can achieve both fuel efficiency performance and noise performance.

In this specification, the loss tangent tan δ is a value measured under the following conditions in accordance with the provisions of JIS-K6394. A viscoelasticity measurement sample of 20 mm length x 4 mm width x 1 mm thickness was taken from inside the rubber layer of the tread portion of each test tire, with the long side in the tire circumferential direction and the thickness direction in the tire radial direction, and the loss tangent tan δ was measured using a GABO Iplexer series at a temperature of 30°C or 70°C, an initial strain of 5%, a dynamic strain of 1%, a frequency of 10 Hz, and in elongation mode.

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 tanδ of the first portion 11 is the loss tangent tanδ 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 tanδ of the first portion 11 is the average value calculated as the weighted average of the loss tangents tanδ of those rubber materials weighted by the cross-sectional area of each rubber material. The same applies to the other loss tangents tanδ.

The loss tangent tan δ of the first portion 11 at 30°C is preferably 0.4 to 0.7 times the loss tangent tan δ of the tread rubber 2G at 30°C. When the loss tangent tan δ of the first portion 11 is 0.4 or more times the loss tangent tan δ of the tread rubber 2G, the vibration of the tread portion 2 can be reduced. When the loss tangent tan δ of the first portion 11 is 0.7 or less times the loss tangent tan δ of the tread rubber 2G, the rolling resistance of the tire 1 can be reduced.

In the tire 1 of the present invention, the synergistic effect of the carcass cord 6B, which has a twist coefficient K of 2000 to 2500, and the rubber of the first portion 11, which has the above-mentioned loss tangent tan δ, makes it easy to reduce interior noise without increasing rolling resistance.

The loss tangent tan δ of the first portion 11 at 30°C is preferably 0.4 to 0.7 times the loss tangent tan δ of the base rubber at 30°C. When the loss tangent tan δ of the first portion 11 is 0.4 or more times the loss tangent tan δ of the base rubber, the vibration of the tread portion 2 can be reduced. When the loss tangent tan δ of the first portion 11 is 0.7 or less times the loss tangent tan δ of the base rubber, the rolling resistance of the tire 1 can be reduced.

In the tire 1 of the present invention, the synergistic effect of the carcass cord 6B, which has a twist coefficient K of 2000 to 2500, and the rubber of the first portion 11, which has the above-mentioned loss tangent tan δ, makes it easier to reduce interior noise without increasing rolling resistance.

Figure 3 shows a development of the contact surface 2s of the tread portion 2 in Figure 1. The contact surface 2s of the tread portion 2 corresponds to the surface between the first tread edge T1 and the second tread edge T2 on the outer surface of the tread portion 2. The first tread edge T1 and the second tread edge T2 each correspond to the axially outermost contact positions when the tire 1 in the normal state is loaded with 70% of the normal load and the tread portion 2 contacts the ground on a flat surface with a camber angle of 0°.

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

As shown in FIG. 3, in the present invention, the land ratio of the tread portion 2 is 65% or more. In this specification, the "land ratio" is the ratio Sb/Sa of the actual total contact area Sb to the total area Sa of the virtual contact surface in which all the grooves and sipes arranged on the contact surface 2s of the tread portion 2 are filled.

By adopting the above configuration, the present invention can reduce both exterior and interior noise. The reasons for this are as follows.

It is generally known that as the land ratio of the tread portion decreases, pattern noise increases, and so does external vehicle noise. On the other hand, as the land ratio increases, pattern noise decreases, but vibrations from the road surface are more likely to be transmitted to the vehicle through the tire, which ultimately leads to increased interior vehicle noise. For this reason, conventional tires are often designed with a relatively small land ratio (less than 65%).

The tire 1 of the present invention has a land ratio of 65% or more, which reduces pattern noise and therefore reduces noise outside the vehicle. In addition, the tire 1 of the present invention has a large first thickness t1 (shown in FIG. 1) of the first portion 11 as described above, which allows the tread portion 2 to effectively absorb vibrations from the road surface, and can reliably reduce noise inside the vehicle even when the land ratio of the tread portion 2 is large. For these reasons, the present invention can reduce both noise outside the vehicle and noise inside the vehicle.

The following describes the configuration of this embodiment in more detail. Each of the configurations described below represents a specific aspect of this embodiment. Therefore, it goes without saying that the present invention can achieve the above-mentioned effects even if it does not have the configurations described below. Furthermore, even if any one of the configurations described below is applied alone to a tire of the present invention having the above-mentioned characteristics, an improvement in performance corresponding to each configuration can be expected. Furthermore, when several of the configurations described below are applied in combination, a composite improvement in performance corresponding to each configuration can be expected.

For example, the tire 1 of this embodiment has a specified orientation for mounting on a vehicle. As a result, the first tread edge T1 is located on the outer side of the vehicle when mounted on the vehicle. The second tread edge T2 is located on the inner side of the vehicle when mounted on the vehicle. The orientation for mounting on the vehicle is indicated, for example, by letters or symbols on the outer surface of the sidewall portion 3 (shown in FIG. 1). However, the tire 1 of the present invention is not limited to this aspect, and the orientation for mounting on a vehicle may not be specified.

As shown in FIG. 3, the tread portion 2 of the present invention includes a plurality of circumferential grooves 20 that extend continuously in the tire circumferential direction between the first tread edge T1 and the second tread edge T2, and a plurality of land portions 25 that are divided into the plurality of circumferential grooves 20. In the tire 1 of this embodiment, the tread portion 2 is divided into five land portions 25 by four circumferential grooves 20. However, the present invention is not limited to this aspect.

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 the first tread edge T1 and the tire equator C, and in this embodiment, is the most adjacent to the first tread edge T1 among the multiple circumferential grooves 20. The second shoulder circumferential groove 22 is provided between the second tread edge T2 and the tire equator C, and in this embodiment, is the most adjacent to the second tread edge T2 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.

The tire axial distance L1 from the tire equator C to the groove centerline of the first shoulder circumferential groove 21 or the second shoulder circumferential groove 22 is preferably, for example, 25% to 35% of the tread ground contact width TW. The tire axial distance L2 from the tire equator C to the groove centerline of the first crown circumferential groove 23 or the second crown circumferential groove 24 is preferably, for example, 5% to 15% of the tread ground contact width TW. The tread ground contact width TW is the tire axial distance from the first tread edge T1 to the second tread edge T2 in the normal state.

In this embodiment, each circumferential groove 20 extends, for example, linearly in parallel to the tire circumferential direction. Each circumferential groove 20 may extend, for example, in a wavy manner.

The groove width of each circumferential groove 20 is preferably at least 3 mm. The groove width of each circumferential groove 20 is preferably, for example, 4.0% to 8.5% of the tread contact width TW. The total groove width of the multiple circumferential grooves 20 is, for example, 20% to 30% of the tread contact width TW, and preferably 20% to 25%. This makes it possible to reduce external noise while improving steering stability on dry roads.

The groove width W3 of the first crown circumferential groove 23 is preferably larger than the groove width W1 of the first shoulder circumferential groove 21, for example. Specifically, the groove width W3 is 150% to 200% of the groove width W1. Also, the groove width W4 of the second crown circumferential groove 24 is preferably larger than the groove width W2 of the second shoulder circumferential groove 22, for example. Specifically, the groove width W4 is 140% or less of the groove width W2, and preferably 105% to 120%. Also, in a more desirable embodiment, the first shoulder circumferential groove 21 has the smallest groove width among the multiple circumferential grooves 20. This ensures wet performance while making it difficult for noise generated by each circumferential groove 20 to diffuse to the outside of the vehicle, thereby reducing exterior noise.

For pneumatic tires for passenger cars, the depth of each circumferential groove 20 is preferably, for example, 5 to 10 mm.

The multiple land portions 25 include a crown land portion 30, a first middle land portion 28, a second middle land portion 29, a first shoulder land portion 26, and a second shoulder land portion 27. The crown land portion 30 is divided between the first crown circumferential groove 23 and the second crown circumferential groove 24. The first middle land portion 28 is divided between the first shoulder circumferential groove 21 and the first crown circumferential groove 23. As a result, the first middle land portion 28 is adjacent to the crown land portion 30 via the first crown circumferential groove 23. The second middle land portion 29 is divided between the second shoulder circumferential groove 22 and the second crown circumferential groove 24. As a result, the second middle land portion 29 is adjacent to the crown land portion 30 via the second crown circumferential groove 24.

The first shoulder land portion 26 includes the first tread edge T1 and is sectioned axially outward of the first shoulder circumferential groove 21. As a result, the first shoulder land portion 26 is adjacent to the first middle land portion 28 via the first shoulder circumferential groove 21. The second shoulder land portion 27 includes the second tread edge T2 and is sectioned axially outward of the second shoulder circumferential groove 22. As a result, the second shoulder land portion 27 is adjacent to the second middle land portion 29 via the second shoulder circumferential groove 22.

Each of these land portions 25 has a plurality of lateral grooves 31. Note that the arrangement of the lateral grooves 31 shown in FIG. 3 is merely an example, and the present invention is not limited to this arrangement.

It is desirable that the first middle land portion 28 is not divided in the circumferential direction of the tire by grooves having a groove width of 2 mm or more. Similarly, it is desirable that the crown land portion 30 and the second middle land portion 29 are not divided in the circumferential direction of the tire by grooves having a groove width of 2 mm or more. This reduces the pattern noise generated by these land portions, and can reduce external noise.

It is desirable that the land ratio Lac of the crown land portion 30 is larger than the land ratio Lam1 of the first middle land portion 28. Specifically, the land ratio Lac is larger than 105% of the land ratio Lam1, and is preferably 106% or more and less than 120%. This makes it possible to reduce the pattern noise generated by the crown land portion 30, and to improve the steering stability and wear resistance on dry road surfaces.

It is desirable that the land ratio Lam1 of the first middle land portion 28 is larger than the land ratio Las1 of the first shoulder land portion 26. Specifically, the land ratio Lam1 is larger than 105% of the land ratio Las1, specifically, 106% or more and less than 120%. This can further improve the steering stability and wear resistance on dry road surfaces.

From the same viewpoint, it is desirable that the land ratio Lam2 of the second middle land portion 29 is larger than the land ratio Las2 of the second shoulder land portion 27. Specifically, the land ratio Lam2 is larger than 105% of the land ratio Las2, specifically, 106% or more and less than 120%.

The average value of the first thickness t1 is preferably 1.5 to 3.5 times the average value of the second thickness t2 (shown in FIG. 1, and the same applies below). Specifically, the average value of the first thickness t1 is preferably 1.5 times or more, more preferably 1.75 times or more, and even more preferably 1.9 times or more, and preferably 3.5 times or less, more preferably 2.7 times or less, and even more preferably 2.2 times or less, of the average value of the second thickness t2. This makes it possible to reliably reduce interior noise while suppressing an increase in the weight of the tire 1.

From the same viewpoint, the average value of the first thickness t1 is preferably 2.0 mm or more, more preferably 2.5 mm or more, and preferably 4.5 mm or less, more preferably 4.0 mm or less, and even more preferably 3.5 mm or less. On the other hand, the average value of the second thickness t2 is, for example, greater than 0.5 mm and less than 2.0 mm. In a preferred embodiment, the average value of the second thickness t2 is 1.0 to 1.5 mm. In this embodiment, the second portion 12 is continuous with the first portion 11 and extends to the bead portion 4 (shown in FIG. 1), and the second thickness t2 is constant throughout the entire portion. However, the second portion 12 is not limited to this embodiment.

The inventors of the present application have confirmed that by setting the twist coefficient K of the carcass cord 6B to 2000 to 2500 and the first thickness t1 of the first portion 11 to 2.0 mm to 4.5 mm, noise inside the vehicle is reduced in the low frequency band below 160 Hz, the mid frequency band between 160 Hz and 350 Hz, and the high frequency band above 350 Hz.

The inventors of the present application have also confirmed that by setting the twist coefficient K of the carcass cord 6B to 2000 to 2500 and the first thickness t1 of the first portion 11 to 2.0 mm to 3.5 mm, there is no deterioration in rolling resistance.

2, the first portion 11 includes a first end 13 on the first tread edge T1 side and a second end 14 on the second tread edge T2 side. The first end 13 has a first thickness t1 that decreases continuously toward the outer end 11a on the first tread edge T1 side of the first portion 11. The second end 14 has a first thickness that decreases continuously toward the outer end 11b on the second tread edge T2 side of the first portion 11. In this embodiment, the position where the reduction in the first thickness t1 ends corresponds to the axially outer end 11a of the first portion 11.

From the viewpoint of reliably reducing interior noise, the outer end 11a of the first portion 11 on the first tread end T1 side of the present embodiment is, for example, located closer to the first tread end T1 than the first crown circumferential groove 23, and more desirably, located closer to the first tread end T1 than the first shoulder circumferential groove 21.

Figure 4 shows an enlarged cross-sectional view of the first end 13 of the first portion 11. As shown in Figure 4, the outer end 11a of the first portion 11 on the first tread end T1 side is preferably at the same position in the tire axial direction as the outer end 7b of the second belt ply 7B in the tire axial direction, or is preferably located axially inward of the outer end 7b of the second belt ply 7B. In a more preferable embodiment, the tire axial distance L3 between the outer end 11a of the first portion 11 and the outer end 7b of the second belt ply 7B is set to 10 mm or less. This allows the belt layer 7 to suppress deformation around the outer end 11a of the first portion 11 during tire running while ensuring a sufficient tire axial length of the first portion 11, and thus suppresses peeling of the inner rubber 10 around the outer end 11a.

The first end 13 is connected to a portion extending at a constant first thickness t1 on the tire equator C side. The axial length L4 of the first end 13 is 2.0% to 4.0% of the tread width TW. This makes it possible to prevent a sudden change in thickness of the inner rubber 10, and suppress damage such as peeling of the inner rubber 10.

2, the first portion 11 has the same configuration on the second tread edge T2 side as on the first tread edge T1 side. That is, the outer end 11b on the second tread edge T2 side of the first portion 11 is located, for example, closer to the second tread edge T2 side than the second crown circumferential groove 24, and more preferably, closer to the second tread edge T2 side than the second shoulder circumferential groove 22. Also, it is preferable that the outer end 11b on the second tread edge T2 side of the first portion 11 is in the same position in the tire axial direction as the outer end 7b of the second belt ply 7B in the tire axial direction, or is located axially inside the outer end 7b of the second belt ply 7B. Also, the axial distance between the outer end 11b of the first portion 11 and the outer end 7b of the second belt ply 7B is 10 mm or less. Also, the second end 14 has the same configuration as the first end 13.

By arranging the outer ends 11a, 11b of the first portion 11 as described above, it is desirable that the axial length L5 of the first portion 11 in this embodiment is 90% to 110% of the tread width TW. This makes it possible to reliably reduce interior noise while suppressing an increase in tire weight.

In this embodiment, the first portion 11 has a first length L6 from the tire equator C to the outer end 11a on the first tread edge T1 side and a second length L7 from the tire equator C to the outer end 11b on the second tread edge T2 side that are substantially the same. More specifically, the difference between the first length L6 and the second length L7 is 5% or less of the first length L6. This improves the uniformity of the tire. In another embodiment, for example, the second length L7 may be greater than the first length L6. Specifically, the second length L7 is 105% to 110% of the first length L6. In this embodiment, the length of the first portion 11 is sufficiently secured on the second tread edge T2 side, which is on the inside of the vehicle when mounted on the vehicle, thereby reducing interior noise.

The first portion 11 extends between the first end 13 and the second end 14 with a constant first thickness t1. As a result, the first thickness t1 is substantially the same at the tire equator C and at a position on the first tread edge T1 side of the first shoulder circumferential groove 21. In a desirable embodiment, the first thickness t1 is substantially the same from the tire equator C to a position beyond the first shoulder circumferential groove 21. Note that "substantially the same" means that unavoidable errors in rubber products such as tires can be tolerated, and includes an embodiment in which the difference between the maximum and minimum thickness values is 5% or less of the maximum thickness.

The first portion 11 may have a region extending with a constant first thickness t1 to the first tread edge T1. In other words, the first thickness t1 may be substantially the same from the position of the tire equator C to the position of the first tread edge T1 (an imaginary line passing through the first tread edge T1 and extending parallel to the tire radial direction). In this case, the outer end 11a of the first portion 11 is located axially outboard of the first tread edge T1. Such an embodiment can further reduce interior noise.

It is desirable that the first portion 11 has a similar configuration to that described above between the tire equator C and the second tread edge T2. That is, the first thickness t1 is substantially the same at the position of the tire equator C and at a position on the second tread edge T2 side of the second shoulder circumferential groove 22. In a desirable aspect, the first thickness t1 is substantially the same from the position of the tire equator C to a position beyond the second shoulder circumferential groove 22. In another embodiment, the first portion 11 may have a region extending with a constant first thickness t1 extending to the second tread edge T2.

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 may 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.

However, the present invention is not limited to such an embodiment. FIG. 5 shows an enlarged cross-sectional view 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 arranged between the inner liner layer 16 and the carcass 6. This additional layer 17 is composed 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 an 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.

The loss tangent tanδ of the air-impermeable rubber material at 70°C is desirably 0.14 or more. The loss tangent tanδ of the air-impermeable rubber material can be measured as described above.

The loss tangent tanδ of the air-impermeable rubber material at 70°C is 0.14 or more, which further suppresses vibrations in the tread portion 2.

In the embodiment shown in FIG. 5, the first portion 11 includes the additional layer 17, thereby improving various performances. For example, a rubber material having a loss tangent tanδ greater than that of the first rubber material constituting the inner liner layer 16 may be used as the second rubber material constituting the additional layer 17. In this case, the loss tangent tanδ of the first portion 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 the cross-sectional area. In addition, the loss tangent tanδ2 of the second portion 12 corresponds to the loss tangent tanδ of the inner liner layer 16. In such an embodiment, the tread portion 2 can further absorb vibrations from the road surface, and the noise inside the vehicle can be further reduced.

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 tire equator C of the tread portion 2 in 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.

As shown in Figures 5 and 6, even if the first portion 11 of the inner rubber 10 includes an additional layer 17, 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.

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 arranged 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 having 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 the same second rubber material as the additional layer 17 of the first portion 11 described in FIG. 5 and FIG. 6. By including such an intermediate layer 18 in the second portion 12, it is possible to further suppress the transmission of vibrations generated in the tread portion 2 to the vehicle side. In addition, the intermediate layer 18 may be made of a rubber material further different from the first rubber material and the second rubber material.

The tire 1 according to one embodiment of the present invention has been described in detail above, but the present invention is not limited to the specific embodiment described above and can be modified and implemented in various ways.

The tire 1 of the present invention has been described in detail above, but the present invention is not limited to the specific embodiment described above and can be modified and implemented in various forms.

[Additional Notes]
The present invention includes the following aspects.

[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 carcass includes a carcass cord,
The twist coefficient of the carcass cord is 2000 to 2500.
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 carcass has a main body portion extending between a pair of bead portions, and a turn-up portion connected to the main body portion and turned up around the bead core from the inside to the outside in the tire axial direction,
3. The pneumatic tire according to claim 1, wherein a tip of the folded-back portion is positioned radially outward of a maximum width position of the main body portion.
[Invention 5]
The tread portion includes a tread rubber that forms a ground contact surface,
The pneumatic tire according to the first or second aspect of the present invention, wherein a loss tangent tan δ of the first portion at 70° C. is equal to or less than a loss tangent tan δ of the tread rubber at 30° C.
[Invention 6]
The pneumatic tire according to claim 5, wherein the loss tangent tan δ of the first portion is 0.4 to 0.7 times the loss tangent tan δ of the tread rubber.
[Invention 7]
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 5, wherein the loss tangent tan δ of the first portion is 0.4 to 0.7 times the loss tangent tan δ of the base rubber at 70° C.
[The present invention 8]
The plurality of circumferential grooves include a shoulder circumferential groove extending closest to a first tread end side of the tread portion,
The pneumatic tire according to claim 1 or 2, wherein an outer end of the first portion on the first tread end side in the tire axial direction is positioned between a first shoulder circumferential groove and the first tread end.
[The present invention 9]
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 on an outer side of the first belt ply in the tire radial direction,
On the side of the first tread edge, an outer end of the second belt ply in the tire axial direction is located axially more inward than an outer end of the first belt ply in the tire axial direction,
The pneumatic tire according to claim 8, wherein the outer end of the first portion 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.
[The present invention 10]
A pneumatic tire according to claim 9, wherein the first portion includes a portion in which the first thickness continuously decreases toward the outer end.
[Invention 11]
The plurality of circumferential grooves include a shoulder circumferential groove extending axially outermost of the tread portion,
The pneumatic tire according to claim 8, wherein the first thickness is substantially uniform at a position of the tire equator and at a position on the first tread end side of the first shoulder circumferential groove.
[Invention 12]
12. The pneumatic tire according to claim 11, wherein the first thickness is substantially uniform from a position at the tire equator to a position beyond the first shoulder circumferential groove.
[The present invention 13]
13. The pneumatic tire of claim 12, wherein the first thickness is substantially the same from the tire equator to the first tread edge.
[The present invention 14]
A pneumatic tire according to claim 9, wherein the axially outer end of the first portion on the side of the first tread end is positioned axially outboard of the first tread end.
[The present invention 15]
The pneumatic tire according to claim 1, wherein the first portion is formed of an air-impermeable rubber material.
[The present invention 16]
The pneumatic tire according to claim 1, wherein the first portion is formed by combining an air-impermeable rubber material and an air-permeable rubber material.

Reference Signs List 1: Pneumatic tire 2: Tread portion 2G: Tread rubber 2s: Ground contact surface 3: Sidewall portion 4: Bead portion 5: Bead core 6: Carcass 6B: Carcass cord 6a: Main body portion 6b: Turn-up portion 7: Belt layer 7A: First belt ply 7B: Second belt ply 7a: Outer end 7b: Outer end 10: Inner rubber 11: First portion 11a: Outer end 11b: Outer end 12: Second portion 20: Circumferential groove 21: First shoulder circumferential groove C: Tire equator K: Twist factor

Claims (16)

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 carcass includes a carcass cord,
The twist coefficient of the carcass cord is 2000 to 2500.
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 or 2, wherein the first thickness is 2.0 to 4.5 mm. the carcass has a main body portion extending between a pair of bead portions, and a turn-up portion connected to the main body portion and turned up around the bead core from the inside to the outside in the tire axial direction,
The pneumatic tire according to claim 1 , wherein a tip of the folded-back portion is positioned radially outward of a maximum width position of the main body portion. The tread portion includes a tread rubber that forms a ground contact surface,
The pneumatic tire according to claim 1 or 2, wherein a loss tangent tan δ of the first portion at 70° C. is equal to or less than a loss tangent tan δ of the tread rubber at 30° C. The pneumatic tire according to claim 5, wherein the loss tangent tanδ of the first portion is 0.4 to 0.7 times the loss tangent tanδ of the tread rubber. 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 5, wherein the loss tangent tan δ of the first portion is 0.4 to 0.7 times the loss tangent tan δB of the base rubber at 70°C. The plurality of circumferential grooves include a shoulder circumferential groove extending closest to a first tread end side of the tread portion,
The pneumatic tire according to claim 1 , wherein an outer end of the first portion on a side of the first tread end in the tire axial direction is positioned between a first shoulder circumferential groove and the first tread end. 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 on an outer side of the first belt ply in the tire radial direction,
On the side of the first tread edge, an outer end of the second belt ply in the tire axial direction is located axially more inward than an outer end of the first belt ply in the tire axial direction,
9. The pneumatic tire according to claim 8, wherein the outer end of the first portion is at the same position as the outer end of the second belt ply in the tire axial direction, or is located axially inward of the outer end of the second belt ply and within 10 mm in the tire axial direction. The pneumatic tire according to claim 9, wherein the first portion includes a portion in which the first thickness continuously decreases toward the outer end. The plurality of circumferential grooves include a shoulder circumferential groove extending axially outermost of the tread portion,
The pneumatic tire according to claim 8 , wherein the first thickness is substantially uniform at a position of a tire equator and at a position on a side of the first tread end relative to the first shoulder circumferential groove. The pneumatic tire of claim 11, wherein the first thickness is substantially the same from the tire equator to a position beyond the first shoulder circumferential groove. The pneumatic tire of claim 12, wherein the first thickness is substantially the same from the tire equator to the first tread edge. The pneumatic tire according to claim 9, wherein the outer end of the first portion on the side of the first tread end in the tire axial direction is located axially outboard of the first tread end. The pneumatic tire according to claim 1, wherein the first portion is formed of an air-impermeable rubber material. The pneumatic tire according to claim 1, wherein the first portion is formed by laminating an air-impermeable rubber material layer and an air-permeable rubber material layer.

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