JP7531315B2 - Pneumatic tires - Google Patents

Description

The present invention relates to a pneumatic tire.

In order to improve the functions of a rubber composition and a crosslinked rubber obtained by crosslinking the rubber composition, various components are also used as additives for the rubber composition.
For example, Patent Document 1 discloses a technology that achieves both abrasion resistance and wet performance and performance on ice by incorporating a diene rubber and silica having a glass transition point and a CTAB adsorption specific surface area defined within specific ranges.
However, the technology disclosed in Patent Document 1 does not provide sufficient effects in terms of cut resistance and abrasion resistance of the rubber composition after vulcanization because the rubber composition has low elasticity, and further improvements are desired.

In recent years, a new small shuttle bus has been proposed that focuses on transporting people and goods within cities. Although this small shuttle bus is small (approximately 5 meters in length and 2 meters in width), it is expected that the total vehicle weight may exceed 3 tons. Therefore, the pneumatic tires installed on such vehicles are required to have high load-bearing capacity and space-saving features, and there is a demand for technology development that will provide the above-mentioned cut resistance and wear resistance.

JP 2016-47888 A

Therefore, the object of the present invention is to provide a pneumatic tire that is excellent in cut resistance and abrasion resistance, and that combines high load capacity with space saving.

The pneumatic tire of the present invention is a pneumatic tire that includes a tread that contacts a road surface and a belt layer provided on the tire radially inner side of the tread, and is mounted on a vehicle,
an outer diameter of the pneumatic tire is 350 mm or more and 600 mm or less, and when a rim width of a rim wheel mounted on the pneumatic tire is RW and a tire cross-sectional width of the pneumatic tire is SW, the relationship of 0.78≦RW/SW≦0.88 is satisfied;
The rubber composition is characterized by using a rubber component containing natural rubber, and a cyclic polyol compound having a hydrocarbyl group and/or a linear polyhydric alcohol.
With the above-described configuration, the cut resistance and wear resistance of the pneumatic tire can be improved, and both a high load capacity and space saving can be achieved.

In addition, in the pneumatic tire of the present invention, it is preferable that the belt layer includes a sheath belt wound in a spiral shape along the tire circumferential direction. This is because the durability of the belt layer can be further improved.

Furthermore, in the pneumatic tire of the present invention, the content of the cyclic polyol compound is more preferably 0.1 to 6 parts by mass per 100 parts by mass of the rubber component. This allows for better cut resistance while maintaining good elongation fatigue properties.

［式中、Ａは炭素数６～３０のヒドロカルビルエステル基又は炭素数６～３０のヒドロカルビルエーテル基であり、Ｘ_１、Ｘ_２、Ｘ_３及びＸ_４はそれぞれ独立して－ＯＨ又は－Ｒ（ここで、－Ｒは－Ｈ又は－ＣＨ_２ＯＨである）であり、但し、Ｘ_１、Ｘ_２、Ｘ_３及びＸ_４のうち少なくとも３つは－ＯＨである］で表わされる化合物であることがより好ましく、式（１）中のＡのヒドロカルビル基部分の炭素数が１２～２４であることがより好ましい。より優れた伸長疲労性及び耐カット性を実現できるためである。 In the pneumatic tire of the present invention, the cyclic polyol compound having a hydrocarbyl group is represented by the following formula (1):

[wherein A is a hydrocarbyl ester group having 6 to 30 carbon atoms or a hydrocarbyl ether group having 6 to 30 carbon atoms, and X ₁ , X ₂ , X ₃ and X ₄ are each independently -OH or -R (wherein -R is -H or -CH ₂ OH), with the proviso that at least three of X ₁ , X ₂ , X ₃ and X ₄ are -OH] is more preferable, and it is more preferable that the hydrocarbyl group portion of A in formula (1) has 12 to 24 carbon atoms. This is because better elongation fatigue property and cut resistance can be realized.

Furthermore, in the pneumatic tire of the present invention, it is preferable that the melting point of the cyclic polyol compound having a hydrocarbyl group is 40 to 100°C. This is because it is possible to further improve cut resistance at high temperatures.

In addition, in the pneumatic tire of the present invention, it is preferable that the linear polyhydric alcohol has three or more hydroxyl groups. This is because better cut resistance can be achieved.

Furthermore, in the pneumatic tire of the present invention, it is preferable that the melting point of the linear polyhydric alcohol is less than 160°C. This is because it can improve solubility during the kneading and vulcanization reactions.

Furthermore, in the pneumatic tire of the present invention, it is preferable that the linear polyhydric alcohol is at least one selected from the group consisting of xylitol, sorbitol, mannitol, and galactitol. This is because better cut resistance can be achieved.

In addition, in the pneumatic tire of the present invention, the content of the linear polyhydric alcohol is preferably 0.1 to 6 parts by mass per 100 parts by mass of natural rubber in the rubber component. This is because it is possible to achieve excellent cut resistance while maintaining good performance such as low heat generation and elongation fatigue resistance.

Furthermore, in the pneumatic tire of the present invention, the content of natural rubber in the rubber component is preferably 70% by mass or more. This is because better cut resistance and abrasion resistance can be achieved.

Furthermore, in the pneumatic tire of the present invention, it is preferable that the rubber composition further contains a filler containing at least silica or carbon black, and it is more preferable that the content of the silica in the filler is 5 to 100 parts by mass per 100 parts by mass of the rubber component, and it is more preferable that the content of the carbon black in the filler is 5 to 100 parts by mass per 100 parts by mass of the rubber component. This is because it is possible to achieve better cut resistance and abrasion resistance without deteriorating processability.

In addition, in the pneumatic tire of the present invention, it is preferable that the rubber composition is used at least in the tread member, since this makes it possible to more significantly improve the wear resistance and reinforcement properties.

The present invention provides a pneumatic tire that is excellent in cut resistance and abrasion resistance, while also achieving both high load capacity and space saving.

1 is a schematic overall side view of a vehicle on which a tire is mounted. 1 is a cross-sectional view of a pneumatic tire and a rim wheel according to one embodiment of the present invention. 1 is a cross-sectional view in the tire width direction of a pneumatic tire according to one embodiment of the present invention. FIG. 4 is a perspective view of a belt layer during its manufacture. FIG. 2 is a perspective view of a belt layer after manufacture. FIG. 1 illustrates typical tire size positioning based on the combination of tire shape (tire outer diameter OD and tire width SW) and rim wheel shape (rim diameter RD and rim width RW).

The pneumatic tire of the present invention will be illustrated and described in detail with reference to the drawings.
(1) Schematic configuration of a vehicle on which a pneumatic tire is mounted Fig. 1 is a schematic overall side view of a vehicle on which a tire is mounted. As shown in Fig. 1, in this embodiment, the vehicle 1 is a four-wheeled automobile. Note that the vehicle 1 is not limited to a four-wheeled automobile, and may be a six-wheeled or eight-wheeled automobile.

The vehicle 1 is fitted with a predetermined number of pneumatic tires 10 depending on the wheel configuration. Specifically, the vehicle 1 is fitted with pneumatic tires 10 assembled to rim wheels 100 at predetermined positions.

Vehicle 1 belongs to a new type of small shuttle bus that is primarily intended for transporting people and goods within cities. In this embodiment, the new small shuttle bus is assumed to be a vehicle with an overall length of 4 to 7 m, an overall width of about 2 m, and a total vehicle weight of around 3 tons. However, the size and total vehicle weight are not necessarily limited to these ranges, and may deviate slightly from these ranges.

Furthermore, the small shuttle bus is not necessarily limited to being used for transporting people, but may also be used for transporting goods, as a mobile store, a mobile office, etc.
Furthermore, since the small shuttle bus is mainly intended for transporting people and goods within a city, it is assumed that the driving speed range is relatively low (maximum speed 70 km/h or less, average speed about 50 km/h). Therefore, it is not necessary to place importance on measures against hydroplaning.

In this embodiment, vehicle 1 is preferably an electric vehicle equipped with an autonomous driving function (assuming level 4 or higher), but the autonomous driving function is not essential, and the vehicle does not have to be an electric vehicle.

When the vehicle 1 is an electric vehicle, it is preferable to use an in-wheel motor (not shown) as the power unit. The in-wheel motor may be provided as a whole unit in the inner space of the rim wheel 100, or a part of the unit may be provided in the inner space of the rim wheel 100.
Furthermore, when using in-wheel motors, it is preferable that the vehicle 1 has an independent steering function that allows each wheel to be steered independently. This allows the vehicle 1 to turn around on the spot and move laterally, and also eliminates the need for a power transmission mechanism, thereby improving the space efficiency of the vehicle 1.

As such, high space efficiency is required for the vehicle 1. For this reason, it is preferable for the pneumatic tire 10 to have as small a diameter as possible.

On the other hand, since the vehicle 1 is to be mounted thereon with a total vehicle weight appropriate to the vehicle size and use, a high load-bearing capacity (maximum load capacity) is required.
Therefore, in order to satisfy such requirements, the pneumatic tire 10 has a small tire outer diameter OD (not shown in FIG. 1, see FIG. 2) while having a load-bearing capacity corresponding to the total vehicle weight of the vehicle 1.

(2) Structure of the Pneumatic Tire Fig. 2 is a cross-sectional view of the pneumatic tire 10 and the rim wheel 100. Specifically, Fig. 2 is a cross-sectional view along the tire width direction and tire radial direction of the pneumatic tire 10 mounted on the rim wheel 100. Note that hatching of the cross section is omitted in Fig. 2 (the same applies to Fig. 3 and subsequent Figs.).

The pneumatic tire 10 has a relatively small diameter, but is wide. Specifically, the rim diameter RD of the rim wheel 100 is preferably 12 inches or more and 17.5 inches or less. However, the rim diameter RD may be 10 inches or more and 22 inches or less as long as it satisfies other numerical ranges (the following (Formula 2) and (Formula 3)).
As shown in FIG. 2, the rim diameter RD is the outer diameter of the rim body portion of the rim wheel 100 and does not include the rim flange 110 portion.

The tire width SW of the pneumatic tire 10 is preferably 125 mm or more and 255 mm or less. As shown in FIG. 2, the tire width SW means the cross-sectional width of the pneumatic tire 10, and does not include the rim guard portion if the pneumatic tire 10 has a rim guard (not shown).

Furthermore, it is preferable that the aspect ratio of the pneumatic tire 10 is 35% or more and 75% or less. The aspect ratio is calculated using the following formula A.
Aspect ratio (%) = tire section height H / tire width SW (section width) × 100 (Formula A)
The pneumatic tire 10 has an outer tire diameter OD of 350 mm or more and 600 mm or less. The tire outer diameter OD is preferably 500 mm or less.

When the tire outer diameter OD is of this size and the rim width of the rim wheel 100 mounted to the pneumatic tire 10 is the rim width RW, the pneumatic tire 10 satisfies the relationships of (Equation B) and (Equation C).
0.78≦RW/SW≦0.88 (Formula B)
0.56≦RD/OD≦0.66 (Formula C)

The pneumatic tire 10 that satisfies such a relationship can ensure, even with a small diameter, the air volume necessary to support the total vehicle weight of the vehicle 1. Specifically, in consideration of the load support performance, the air volume is preferably 20,000 ^cm3 or more. In consideration of space saving, the air volume is preferably ^80,000 cm3 or less.
In place of RW, the tire width direction distance D between the bead heels is
0.78≦D/SW≦0.88
It is also possible to say this.

As long as the above relationship is satisfied, there are no particular limitations on the rim width RW, but from the perspective of ensuring sufficient air volume, it is preferable for it to be as wide as possible.

Also, from the perspective of ensuring air volume, it is preferable that the ratio of the rim diameter RD to the tire outer diameter OD is small, in other words, that the aspect ratio is high. However, as mentioned above, from the perspective of responsiveness, a low aspect ratio is preferable, and considering the space required to accommodate an in-wheel motor, etc., a large rim diameter RD is preferable, so the aspect ratio and rim diameter RD are in a trade-off relationship between air volume, responsiveness, and space required to accommodate an in-wheel motor, etc.

One example of a suitable size for the pneumatic tire 10 is 215/45R12. The appropriate rim width is about 7.0J.

Although not particularly limited, the set internal pressure (normal internal pressure) of the pneumatic tire 10 is assumed to be 400 to 1,100 kPa, and preferably 500 to 900 kPa. Note that normal internal pressure is, for example, the air pressure that corresponds to the maximum load capacity in the YearBook of the Japan Automobile Tire Manufacturers Association (JATMA) in Japan, ETRTO in Europe, TRA in the United States, and tire standards of other countries.

The load borne by the pneumatic tire 10 is preferably 500 to 1,500 kgf, for example, approximately 900 kgf.

Here, Fig. 3 is a cross-sectional view of the pneumatic tire 10. Specifically, Fig. 3 is a cross-sectional view of the pneumatic tire 10 taken along the tire width direction and the tire radial direction.
As shown in FIG. 3 , the pneumatic tire 10 includes a tread 20 , a tire side portion 30 , a carcass 40 , a belt layer 50 , a bead portion 60 , and a belt reinforcing layer 70 .

The tread 20 is a portion that comes into contact with the road surface. A pattern (not shown) is formed on the tread 20 according to the environment in which the pneumatic tire 10 is used and the type of vehicle on which the tire is to be mounted.
In this embodiment, the tread 20 is formed with a plurality of circumferential grooves including a circumferential main groove 21 and a circumferential main groove 22 extending in the tire circumferential direction.

The tire side portion 30 is connected to the tread 20 and is located on the radially inner side of the tread 20. The tire side portion 30 is the area from the outer end of the tread 20 in the tire width direction to the upper end of the bead portion 60. The tire side portion 30 is sometimes called a sidewall.

The carcass 40 forms the framework of the pneumatic tire 10. The carcass 40 has a radial structure in which carcass cords (not shown) arranged radially along the tire radial direction are covered with a rubber material. However, the carcass 40 is not limited to a radial structure, and may have a bias structure in which the carcass cords are arranged to cross each other in the tire radial direction.

The belt layer 50 is provided on the radially inner side of the tread 20. The belt layer 50 is composed of a core belt 51 and a sheath belt 52.

The core belt 51 is provided from one shoulder portion 26 of the tread 20 to the other shoulder portion 27 of the tread 20. The shoulder portion 26 is an area that is further outward in the tire width direction than the circumferential main groove 21, and the shoulder portion 27 is an area that is further outward in the tire width direction than the circumferential main groove 22. In other words, the shoulder portion 26 and the shoulder portion 27 are areas that are further outward in the tire width direction than the circumferential main groove that is formed on the outermost side in the tire width direction.

The core belt 51 is a belt in which a belt cord 51a (not shown in FIG. 3, see FIG. 4A) inclined at a low angle to the tire width direction is rubber-coated. The sheath belt 52 is a tape-like belt including a cord (not shown) and is wrapped around the entire circumference of the core belt 51. The belt layer 50 provides the same function as the intersecting belt layer. The configuration of the belt layer 50 will be described further below.

The bead portion 60 is connected to the tire side portion 30 and is located on the inner side of the tire side portion 30 in the tire radial direction. The bead portion 60 is engaged with the rim wheel 100 and has an annular bead core 61. The carcass 40 is folded back to the outer side in the tire width direction via the bead core 61.

The folded end 41 of the carcass 40 folded back at the bead portion 60 is wound around the bead core 61. The folded end 41 is in contact with the radially outer end of the bead core 61. Specifically, at the folded end 41 of the carcass 40, the carcass cord is wound around the radially outer end of the bead core 61.

In addition, the bead portion 60 may be provided with a bead filler on the radially outer side of the bead core, and a chafer may be provided to prevent the carcass 40, which is folded over at the bead portion 60, from rubbing against the rim wheel 100 and becoming worn.

(3) Configuration of the Belt Layer 50 Figures 4A and 4B show the configuration of the belt layer 50. Specifically, Figure 4A is a perspective view of the belt layer 50 alone during production, and Figure 4B is a perspective view of the belt layer 50 alone after production.

As described above, the belt layer 50 is composed of the core belt 51 and the sheath belt 52. As shown in FIG. 4A, the core belt 51 has belt cords 51a arranged along the tire width direction. The core belt 51 is an annular belt formed by rubber-coating multiple belt cords 51a.

As shown in FIG. 4A, it is preferable that the belt cord 51a is slightly inclined with respect to the tire width direction. Specifically, it is preferable that the belt cord 51a is inclined in the same direction as the inclination direction of the sheath belt 52 (upward to the left in FIG. 4A).

The sheath belt 52 is a tape-like belt with a width of about 1 cm, and is wound around the core belt 51 in a spiral shape along the tire circumferential direction. Specifically, the sheath belt 52 is wound around the core belt 51 in a spiral shape along the tire circumferential direction at a predetermined distance that is equal to or greater than the width of the sheath belt 52.

The sheath belt 52 is wound around the tire circumferential direction multiple times without overlapping with adjacent sheath belts 52, thereby covering the tire radial outer surface of the core belt 51 and the tire radial inner surface of the core belt 51.

Further, the longitudinal end portion (not shown) of the tape-shaped sheath belt 52 is wound around the core belt 51 so as not to be positioned in the shoulder portions 26, 27 and the center region (directly below the tire equator).
Furthermore, as shown in FIG. 4B, the sheath belt 52 is wound around the entire circumference of the annular core belt 51.

In this embodiment, the belt layer 50 is composed of only the core belt 51 and the sheath belt 52. As described above, the belt layer 50 provides the same function as the intersecting belt layer. In this embodiment, one belt reinforcing layer 70 is arranged on the tire radial outer side of the belt layer 50 consisting of the core belt 51 and the sheath belt 52 in the illustrated example. The belt reinforcing layer 70 can be, for example, one or more rubberized layers of cords extending in the tire circumferential direction. In the illustrated example, the width of the belt reinforcing layer 70 in the tire width direction is larger than the width of the belt layer 50 in the tire width direction, but it can be made equal to or smaller. When two or more belt reinforcing layers 70 are provided, a so-called cap and layer structure can be used, and the belt reinforcing layer on the tire radial outer side can be provided only in the shoulder parts of each half in the tire width direction.

The number of cords per end of the belt cord 51a in the core belt 51 is preferably 15 cords/50 mm or more and 30 cords/50 mm or less. The number of cords per end of the sheath belt 52 is preferably 10 cords/50 mm or more and 25 cords/50 mm or less. The number of cords per end of the belt cord 51a is preferably more than the number of cords per end of the sheath belt 52 (i.e., denser).

The angle that the belt cord 51a forms with the tire width direction is preferably 20 degrees or more and 60 degrees or less. The angle that the cord of the sheath belt 52 forms with the tire width direction is preferably 50 degrees or more and 80 degrees or less. In addition, the angle that the cord of the sheath belt 52 forms with the tire width direction is preferably larger than the angle that the belt cord 51a forms with the tire width direction.
In addition, the number of turns of the sheath belt 52 in the tire circumferential direction is preferably 3 to 6, in consideration of ensuring performance and productivity.

(3) Actions and Effects Next, a description will be given of the actions and effects of the above-mentioned pneumatic tire 10. Fig. 5 is a diagram showing the positioning of typical tire sizes based on the combination of the tire shape (tire outer diameter OD and tire width SW) and the rim wheel shape (rim diameter RD and rim width RW).

Specifically, the horizontal axis of the graph shown in Figure 5 indicates the ratio of the rim width RW to the tire width SW (RW/SW), and the vertical axis indicates the ratio of the rim diameter RD to the tire outer diameter OD (RD/OD). In Figure 5, the positions of typical tire sizes are plotted according to the values of RW/SW and RD/OD.

As shown in Figure 5, the area of truck and bus tires is low in both RW/SW and RD/OD. The area of passenger car or light truck tires is higher than that of truck and bus tires in both RW/SW and RD/OD.

215/45R12, an example of a suitable size for the pneumatic tire 10 described above, is included in region A1. As described above, region A1 is in the range of 0.78≦RW/SW≦0.88 and 0.56≦RD/OD≦0.66. Such region A1 is positioned as the region for tires for new small shuttle buses that are primarily intended for transporting people and goods within cities, such as the vehicle 1 described above.

The RD/OD of the new small shuttle bus tire area is not significantly different from the RD/OD of the passenger car or small truck tire area, and there is some overlap. On the other hand, the RW/SW of the new small shuttle bus tire area is higher than the RW/SW of the passenger car or small truck tire area.

As described above, the tire outer diameter OD of the pneumatic tire 10 is 350 mm or more and 600 mm or less. Therefore, it is sufficiently small compared to the size of the vehicle 1, and can contribute to saving space on the vehicle 1.

In addition, according to the pneumatic tire 10 having a size included in the region A1,
0.78≦RW/SW≦0.88
In order to satisfy the above relationship, the rim width RW is wide relative to the tire width SW, i.e., a wide tire can be constructed, and it is easy to secure the air volume necessary to demonstrate a high load-bearing capacity. However, if the rim width RW becomes too wide, the tire width SW also widens, reducing the space efficiency and making it easier for the bead portion 60 to come off the rim wheel 100.

Furthermore, according to the pneumatic tire 10 having a size included in the region A1,
0.56≦RD/OD≦0.66
In order to satisfy the above relationship, the rim diameter RD is large relative to the tire outer diameter OD, making it easy to secure space to accommodate an in-wheel motor, etc. However, if the rim diameter RD becomes too small, the diameter size of the disc brake or drum brake becomes small. This reduces the effective brake contact area, making it difficult to secure the required braking performance.

In other words, the pneumatic tire 10 can achieve high space efficiency while having a higher load-bearing capacity when installed on new small shuttle buses and the like.

The rim diameter RD of the pneumatic tire 10 is preferably 12 inches or more and 17.5 inches or less. This allows the tire to maintain a small diameter while still ensuring a sufficient air volume and space to accommodate an in-wheel motor, etc. Braking and driving performance can also be ensured.

The tire width SW of the pneumatic tire 10 is preferably 125 mm or more and 255 mm or less. Furthermore, the aspect ratio of the pneumatic tire 10 is preferably 35% or more and 75% or less. This ensures a sufficient air volume and space to accommodate an in-wheel motor, etc.

Furthermore, in this embodiment, as described above, the belt layer 50 includes a core belt 51 provided from one shoulder portion 26 of the tread 20 to the other shoulder portion 27 of the tread 20, and a sheath belt 52 wound around the core belt 51 in a spiral shape along the tire circumferential direction.

Compared to typical intersecting belt layers, such belt layers 50 have high rigidity, particularly in the shoulder portions 26 and 27 of the tread 20, and can effectively suppress radial growth in the shoulder portions, which is a concern in small-diameter tires such as the pneumatic tire 10.

Specifically, because the tire outer diameter OD of the pneumatic tire 10 is small, assuming that the tension of the carcass 40 is constant, the tension of the belt layer 50 is relatively lower than that of a tire with a large tire outer diameter OD. For this reason, the tire diameter growth is particularly noticeable in the shoulder portion where the rigidity of the belt layer is low.

In addition, because the aspect ratio of the pneumatic tire 10 is low, the carcass 40 is pulled more strongly in the tire width direction and relatively less strongly in the tire radial direction. For this reason, the tire diameter growth is also significant in the shoulder area.

Furthermore, as mentioned above, the pneumatic tire 10 must support a large load and is set to a high internal pressure corresponding to the total vehicle weight, so there is concern that the durability of the belt layer may deteriorate.

In the pneumatic tire 10, the belt layer 50, which is composed of the core belt 51 and the sheath belt 52, suppresses radial growth in the shoulder portions 26 and 27 of the tread 20.

That is, the pneumatic tire 10 can achieve high load-bearing capacity and space saving while improving the durability of the belt (belt layer 50).
In addition, in this embodiment, the longitudinal ends of the sheath belt 52 wound in a spiral shape are not located in the shoulder regions 26, 27 (i.e., the regions that are outer in the tire width direction than the circumferential main grooves formed at the outermost positions in the tire radial direction) and in the center region (i.e., directly below the tire equator), so that the occurrence of distortion caused by the longitudinal ends of the sheath belt 52 can be suppressed.
Furthermore, in this embodiment, the belt cord 51a is inclined in the same direction as the inclination direction of the sheath belt 52. As a result, the core belt 51 and the sheath belt 52 have similar characteristics during deformation, and therefore the durability of the belt layer 50 is improved.

In this embodiment, the sheath belt 52 is a tape-shaped belt, and is wound around the core belt 51 in a spiral shape in the tire circumferential direction at a predetermined distance equal to or greater than the width of the sheath belt 52. The sheath belt 52 is wound around the core belt 51 multiple times in the tire circumferential direction to cover the outer side surface of the core belt 51 in the tire radial direction and the inner side surface of the core belt 51 in the tire radial direction.
Therefore, it is possible to provide the belt layer 50 having high rigidity over the entire circumference of the tire, particularly at the end portions in the tire width direction. This makes it possible to further improve the durability of the belt layer 50.

In this embodiment, the belt layer 50 is composed only of the core belt 51 and the sheath belt 52. As described above, the belt layer 50 composed of the core belt 51 and the sheath belt 52 can sufficiently suppress the radial growth in the shoulder portion 26 and the shoulder portion 27 of the tread 20, so there is no need to add a reinforcing belt or the like. This can improve the durability of the belt layer 50 while suppressing the weight increase of the pneumatic tire 10.

(4) Rubber Composition Constituting Pneumatic Tire In addition to the structural features described above, the present embodiment is characterized by the use of a rubber composition including a rubber component containing natural rubber, and a cyclic polyol compound having a hydrocarbyl group and/or a linear polyhydric alcohol.
By incorporating the above-mentioned cyclic polyol compound and/or linear polyhydric alcohol into a rubber composition containing natural rubber as a rubber component, it is possible to increase the strength of the rubber and improve its cut resistance and abrasion resistance.

The rubber component contained in the rubber composition contains natural rubber (NR). By containing a certain amount of natural rubber, excellent cut resistance, reinforcement, abrasion resistance, etc. can be obtained by using it together with a linear polyhydric alcohol or a cyclic polyol compound having a hydrocarbyl group, which will be described later.

Here, the content of natural rubber in the rubber component is not particularly limited, but is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more. By making the content of natural rubber in the rubber component 50% by mass or more, it is possible to more reliably improve cut resistance and abrasion resistance when used together with a linear polyhydric alcohol or a cyclic polyol compound having a hydrocarbyl group, which will be described later.

The rubber component may contain any synthetic rubber in addition to the natural rubber.
For example, from the viewpoint of obtaining excellent cut resistance and abrasion resistance, the rubber component preferably contains a diene-based synthetic rubber.

Examples of the diene synthetic rubber include synthetic polyisoprene (IR), styrene-butadiene copolymer rubber (SBR), polybutadiene rubber (BR), etc. The diene synthetic rubber in the rubber component may be contained alone or as a blend of two or more types. The rubber component may also contain non-diene synthetic rubber depending on the required performance.

Cyclic Polyol Compound Having a Hydrocarbyl Group The rubber composition may further contain a cyclic polyol compound having a hydrocarbyl group, in addition to the rubber component described above.
The cyclic polyol compound having a hydrocarbyl group contained in the rubber composition can greatly improve the cut resistance of the rubber composition (and thus the pneumatic tire). In addition, by increasing the interaction between the rubber molecules of the rubber component and the filler described below, the physical properties of the rubber after crosslinking can be homogenized, and as a result, the reinforcement and abrasion resistance can also be improved.
Furthermore, since the cyclic polyol compound having a hydrocarbyl group has fewer hydrophilic sites than compounds such as sorbitol, self-aggregation in the rubber composition can be suppressed, and as a result, deterioration of the elongation fatigue properties and low heat build-up properties of the rubber composition can be suppressed.

Here, the cyclic polyol compound having the hydrocarbyl group preferably has two or more hydroxyl groups, and more preferably has three or more hydroxyl groups. This is because having many hydroxyl groups leads to a stronger interaction between the rubber component and the additives, resulting in better cut resistance.

で表わされる化合物であることがより好ましい。 In order to realize better elongation fatigue resistance and cut resistance, the cyclic polyol compound having a hydrocarbyl group is represented by the following formula (1):

It is more preferable that the compound is represented by the following formula:

In the above formula (1), A is a hydrocarbyl ester group having 6 to 30 carbon atoms or a hydrocarbyl ether group having 6 to 30 carbon atoms, and the number of carbon atoms in the hydrocarbyl group portion of A is preferably 12 to 24. When the number of carbon atoms in the hydrocarbyl group portion of A in formula (1) is in the range of 12 to 24, cut resistance is further improved while maintaining good elongation fatigue properties.
In addition, it is preferable that A in formula (1) is an oxygen atom as the first atom from the ring portion (i.e., the atom bonded to the ring) or the second atom from the ring portion. Examples of A in which the first atom from the ring portion is an oxygen atom include groups represented by -O-A' and -O-CO-A'', and examples of A in which the second atom from the ring portion is an oxygen atom include groups represented by -CH ₂ -O-A'', and -CH ₂ -O-CO-A''', where A' is preferably a hydrocarbyl group having 6 to 30 carbon atoms, A'' is a hydrocarbyl group having 5 to 29 carbon atoms, and A''' is a hydrocarbyl group having 4 to 28 carbon atoms, and it is further preferable that A', A'' and A''' are hydrocarbyl groups having 12 to 24 carbon atoms.

In the above formula (1), X ₁ , X ₂ , X ₃ and X ₄ are each independently -OH or -R (wherein -R is -H or -CH ₂ OH), provided that at least three of X _{1 , X 2 , X 3 and X 4 are -OH. When three or more of X 1 , X 2 , X 3} and X ₄ are -OH, the cut resistance of the rubber composition is further improved.

で表わされる化合物が更に好ましく、上記式（２）で表わされる化合物が特に好ましい。
なお、式（２）及び式（３）中、ｎは自然数であり、１１～２３の範囲が好ましい。
前記変性環状ポリオール化合物として、上記式（２）又は式（３）で表わされる化合物を配合することで、良好な伸長疲労性を維持しつつ、耐カット性をより向上させることができる。 Furthermore, among the compounds represented by the above formula (1), compounds represented by the following formula (2) or (3):

More preferred is a compound represented by the formula (2) above.
In the formulas (2) and (3), n is a natural number, and is preferably in the range of 11 to 23.
By incorporating a compound represented by the above formula (2) or (3) as the modified cyclic polyol compound, it is possible to further improve cut resistance while maintaining good elongation fatigue properties.

The cyclic polyol compound having a hydrocarbyl group is not particularly limited, but can be obtained, for example, by reacting a polyol compound such as sorbitol, sorbitan, glucose, or fructose with an aliphatic alcohol such as octanol, decanol, dodecanol, tetradecanol, or hexadecanol, or an aliphatic carboxylic acid such as lauric acid, myristic acid, palmitic acid, stearic acid, or oleic acid.

Specific examples of the cyclic polyol compound having a hydrocarbyl group include ester compounds such as sorbitan monolaurate, sorbitan monomyristate, sorbitan monopalmitate, sorbitan monostearate, and sorbitan monooleate, and ether compounds such as octyl-β-D-glucopyranoside, decyl-β-D-glucopyranoside, dodecyl-β-D-glucopyranoside, tetradecyl-β-D-glucopyranoside, and hexadecyl-β-D-glucopyranoside. These compounds may be used alone or in combination of two or more.
Among these compounds, from the viewpoint of achieving both high levels of elongation fatigue resistance and cut resistance, the cyclic polyol compound having a hydrocarbyl group is preferably a sorbitan monoester.

Furthermore, the melting point of the cyclic polyol compound having a hydrocarbyl group is preferably 40 to 100°C, and more preferably 45 to 90°C. When the melting point of the cyclic polyol compound having a hydrocarbyl group is 100°C or lower, the solubility during the kneading and vulcanization reaction can be improved, and when it is 40°C or higher, the cut resistance at high temperatures can be improved.

Here, the content of the cyclic polyol compound having a hydrocarbyl group is preferably 0.1 to 6 parts by mass per 100 parts by mass of the natural rubber. If the amount of the cyclic polyol compound is less than 0.1 parts by mass per 100 parts by mass of the natural rubber, the amount of the cyclic polyol compound is so small that it is difficult to obtain a sufficient effect of improving cut resistance, and it is possible that a sufficient effect of improving elongation fatigue properties is also not obtained. On the other hand, if the content of the cyclic polyol compound having a hydrocarbyl group exceeds 6 parts by mass per 100 parts by mass of the natural rubber, the amount of the cyclic polyol compound becomes too large, which may cause self-aggregation in the rubber composition and lead to deterioration of elongation fatigue properties.
From the same viewpoint, the content of the hydrocarbyl group-containing cyclic polyol compound is preferably 0.1 to 4 parts by mass, and more preferably 0.3 to 2 parts by mass, per 100 parts by mass of the natural rubber.

Linear Polyhydric Alcohol The rubber composition may further contain a linear polyhydric alcohol in addition to the above-mentioned rubber component.
By further containing the linear polyhydric alcohol, the cut resistance of the rubber composition can be further improved.

Here, the linear polyhydric alcohol preferably has three or more hydroxyl groups, and more preferably has five or more hydroxyl groups. This is because having many hydroxyl groups in the linear polyhydric alcohol can achieve better cut resistance and abrasion resistance.

Furthermore, it is preferable that the melting point of the linear polyhydric alcohol is less than 170°C. This is because it is possible to improve the solubility during the kneading and vulcanization reactions. In addition, from the viewpoint of blocking properties, it is preferable that the melting point of the linear polyhydric alcohol is 40°C or higher.

Here, the type of the linear polyhydric alcohol is not particularly limited, and any known linear polyhydric alcohol can be used. For example, from the viewpoint of achieving better cut resistance, it is preferable to use at least one selected from the group consisting of xylitol, sorbitol, mannitol, and galactitol.

The content of the linear polyhydric alcohol is preferably 0.1 to 6 parts by mass, and more preferably 1 to 4 parts by mass, per 100 parts by mass of natural rubber in the rubber component. By having the content of the linear polyhydric alcohol be 0.1 parts by mass or more per 100 parts by mass of natural rubber, better cut resistance can be obtained, and by having the content be 6 parts by mass or less per 100 parts by mass of natural rubber, a decrease in elongation fatigue property caused by aggregation of the linear polyhydric alcohol can be suppressed.

In addition, the rubber composition can improve cut resistance and abrasion resistance by including at least one of the cyclic polyol compound and the linear polyhydric alcohol. However, from the viewpoint of further improving cut resistance and abrasion resistance while maintaining low heat buildup and elongation fatigue properties, it is preferable to include both the cyclic polyol compound and the linear polyhydric alcohol.

Filler The rubber composition preferably contains a filler containing at least silica or carbon black, in addition to the above-mentioned rubber component, and a cyclic polyol compound having a hydrocarbyl group and/or a linear polyhydric alcohol.
By including a filler containing silica together with the rubber component, properties such as low heat generation, low cut resistance, and abrasion resistance can be improved, and by including a filler containing carbon black together with the rubber component, properties such as low cut resistance and abrasion resistance can be improved.

Here, examples of the type of silica include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc., and among these, wet silica is preferred. These silicas may be used alone or in combination of two or more kinds.
The wet silica may be precipitated silica, which is obtained by growing primary silica particles by reacting a reaction solution at a relatively high temperature in a neutral to alkaline pH range in the early stages of production, and then aggregating the primary particles by controlling the reaction solution to an acidic pH range.

The silica is not particularly limited, but may have a CTAB specific surface area (cetyltrimethylammonium bromide adsorption specific surface area) of 70 m ² /g or more and 250 m ² /g or less. The CTAB specific surface area refers to a value measured in accordance with ASTM D3765-92. However, the adsorption cross-sectional area per molecule of cetyltrimethylammonium bromide on the silica surface is set to 0.35 nm ² , and the specific surface area (m ² /g) calculated from the amount of CTAB adsorbed is defined as the CTAB specific surface area.
The BET specific surface area of the silica can be 100 m ² /g or more and 250 m ² /g or less. The BET specific surface area is a specific surface area determined by a BET method, and in the present invention, it can be measured in accordance with ASTM D4820-93.

The content of the silica is preferably 5 to 100 parts by mass, and more preferably 10 to 50 parts by mass, per 100 parts by mass of the rubber component. If the content of the silica is 10 parts by mass or more per 100 parts by mass of the rubber component, cut resistance and handling stability can be further improved, and by making the content less than 50 parts by mass, deterioration of the processability and low rolling resistance of the rubber composition can be suppressed.

The carbon black is not particularly limited, and examples thereof include GPF, FEF, HAF, ISAF, and SAF grade carbon black, and carbon black having a nitrogen adsorption specific surface area (N ₂ SA, measured in accordance with JIS K 6217-2:2001) of 20 to 250 m ² /g can be used. Among these, ISAF and SAF grade carbon black are preferred from the viewpoint of improving the abrasion resistance of the rubber composition. These carbon blacks may be used alone or in combination of two or more.

Furthermore, the amount of carbon black is not particularly limited, but is preferably 5 to 100 parts by mass, and more preferably 10 to 50 parts by mass, per 100 parts by mass of the rubber component. If the amount of carbon black is 5 parts by mass or more per 100 parts by mass of the rubber component, cut resistance can be further improved, and if the amount is less than 50 parts by mass, heat buildup can be suppressed.

Furthermore, with regard to the content of the carbon black, the content of the carbon black relative to the content of the silica (carbon black content/silica content) is preferably 0.1 to 4 in mass ratio.
When the mass ratio of the carbon black to the silica content is 0.1 or more, better abrasion resistance and reinforcing properties can be obtained, and when the mass ratio of the carbon black to the silica content is 4 or less, better cut resistance can be obtained without deteriorating the low heat build-up properties.

In addition to the above-mentioned silica and carbon black, the filler may be a compound represented by the following general formula (XX):
nM・xSiO _y・zH ₂ O ... (XX)
[In the formula, M is at least one selected from a metal selected from the group consisting of aluminum, magnesium, titanium, calcium, and zirconium, an oxide or hydroxide of such a metal, and a hydrate thereof, or a carbonate of such a metal; and n, x, y, and z are integers of 1 to 5, integers of 0 to 10, integers of 2 to 5, and integers of 0 to 10, respectively].
Examples of the inorganic compound of the general formula (XX) include alumina (Al ₂ O ₃ ) such as γ-alumina and α-alumina, alumina monohydrate (Al ₂ O ₃ .H ₂ O) such as boehmite and diaspore, aluminum hydroxide [Al(OH) ₃ ] such as gibbsite and bayerite, aluminum carbonate [Al ₂ (CO ₃ ) ₃ ], magnesium hydroxide [Mg(OH) ₂ ], magnesium oxide (MgO), magnesium carbonate (MgCO ₃ ), talc (3MgO.4SiO _{2.H 2} O), attapulgite (5MgO.8SiO _{2.9H 2} O), titanium white (TiO ₂ ), titanium black (TiO _2n-1 ), calcium oxide (CaO), calcium hydroxide [Ca(OH) ₂ ], aluminum magnesium oxide (MgO.Al ₂ O ₃ ), clay (Al ₂ O _{3.2SiO 2} ), kaolin (Al ₂ O 3.2SiO _{2.2H 2} O), pyrophyllite (Al ₂ O 3.4SiO _2.H 2 O ₎ , bentonite (Al ₂ O 3.4SiO _{2.2H 2} O ₎ , aluminum silicate (Al ₂ SiO ₅ , Al 4.3SiO _{4.5H 2} O, etc.), magnesium silicate (Mg ₂ SiO ₄ , MgSiO ₃ , etc.), calcium silicate (Ca ₂ SiO ₄ , _etc. ), aluminum calcium silicate (Al ₂ O _{3.CaO.2SiO 2} , etc. ₎ , magnesium calcium silicate (CaMgSiO _{4 )} , calcium carbonate (CaCO ₃ ), zirconium oxide (ZrO ₂ ), zirconium hydroxide [ZrO(OH) _{2.nH 2} O], zirconium carbonate [Zr(CO ₃ ) ₂ ], and crystalline aluminosilicates containing hydrogen, alkali metals, or alkaline earth metals that compensate for the charge, such as various zeolites.
From the viewpoint of the balance between wear resistance and wet performance, the inorganic compound of the general formula (XX) preferably has an average particle size of 0.01 to 10 μm, and more preferably 0.05 to 5 μm.

The total content of the filler is not particularly limited, but is preferably 20 to 150 parts by mass, more preferably 30 to 120 parts by mass, and particularly preferably 40 to 100 parts by mass, per 100 parts by mass of the rubber component. By optimizing the amount of the filler, tire properties such as cut resistance, low loss, and abrasion resistance can be further improved.

Other Components The rubber composition may contain, in addition to the above-mentioned rubber component, linear polyhydric alcohol, cyclic polyol compound having a hydrocarbyl group, and filler, compounding agents that are commonly used in the rubber industry as other components.
Other components may be appropriately selected and included within the scope not impairing the object of the present invention, such as silane coupling agents, crosslinking agents, vulcanization accelerators, polyethylene glycols, softeners, resins, antioxidants, zinc oxide, etc. Commercially available products may be suitably used as these compounding agents.

In addition, when silica is contained as the filler, it is preferable to further contain a silane coupling agent. This is because it can further improve the effects of cut resistance, reinforcing property, and low loss property due to silica. In addition, the silane coupling agent can be appropriately used from known ones.
Examples of the silane coupling agent include bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide, 3-triethoxysilylpropyl Examples of the silane coupling agent include -N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropyl benzothiazolyl tetrasulfide, 3-triethoxysilylpropyl benzothiazolyl tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, bis(3-diethoxymethylsilylpropyl)tetrasulfide, 3-mercaptopropyldimethoxymethylsilane, dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, dimethoxymethylsilylpropyl benzothiazolyl tetrasulfide, etc. These silane coupling agents may be used alone or in combination of two or more.

Furthermore, the content of the silane coupling agent varies depending on the type of silane coupling agent, but is preferably 0.2 or less in mass ratio to the content of the silica, and more preferably 0.1 or less. This is because by reducing the content of the silane coupling agent to 0.2 or less in mass ratio to the content of the silica, the cut resistance of the rubber composition can be further improved.

The crosslinking agent is not particularly limited and can be appropriately selected depending on the purpose. Examples of the crosslinking agent include sulfur-based crosslinking agents, organic peroxide-based crosslinking agents, inorganic crosslinking agents, polyamine crosslinking agents, resin crosslinking agents, sulfur compound-based crosslinking agents, and oxime-nitrosamine-based crosslinking agents. Among these crosslinking agents, sulfur-based crosslinking agents (vulcanizing agents) are more preferable for rubber compositions for tires.
The content of the crosslinking agent is not particularly limited and can be appropriately selected depending on the purpose, but it is preferably 0.1 to 20 parts by mass based on 100 parts by mass of the rubber component.

In addition, when sulfur is used as the crosslinking agent, it is preferable to include a vulcanization accelerator. The vulcanization accelerator may be any conventionally known one, and is not particularly limited. Examples of the vulcanization accelerator include sulfenamide-based vulcanization accelerators such as CBS (N-cyclohexyl-2-benzothiazylsulfenamide), TBBS (N-t-butyl-2-benzothiazylsulfenamide), and TBSI (N-t-butyl-2-benzothiazylsulfenimide); guanidine-based vulcanization accelerators such as DPG (diphenylguanidine); thiuram-based vulcanization accelerators such as tetraoctylthiuram disulfide and tetrabenzylthiuram disulfide; and zinc dialkyldithiophosphate. The content is preferably less than the content of sulfur, and more preferably about 1 to 10 parts by mass per 100 parts by mass of the rubber component.

In addition, it is preferable that the rubber composition further contains glycerol monostearate, since this can further improve workability, such as shortening the scorch time and increasing the vulcanization speed during tire manufacturing.

The content of the glycerol monostearate is 0.1 parts by mass or more, preferably 0.3 parts by mass or more, and more preferably 0.5 parts by mass or more, per 100 parts by mass of the rubber component. If the content is less than 0.1 parts by mass, the effects of the present invention may not be obtained satisfactorily. The content is 3.5 parts by mass or less, preferably 3 parts by mass or less, and more preferably 2.5 parts by mass or less. If the content exceeds 3.5 parts by mass, the scorch time tends to be too short.

Furthermore, the rubber composition may contain a softener in order to increase the flexibility of the rubber and realize better wet performance and ice performance. The softener may be any softener known in the art, and is not particularly limited. Examples of the softener include petroleum-based softeners such as aroma oil, paraffin oil, naphthenic oil, and plant-based softeners such as palm oil, castor oil, cottonseed oil, and soybean oil. When used, one or more of these may be appropriately selected and used.
When the softener is contained, from the viewpoint of ease of handling, it is preferable to contain, among the above-mentioned softeners, one that is liquid at room temperature such as 25° C., for example, a petroleum-based softener such as aroma oil, paraffin oil, or naphthenic oil.

The rubber composition may further contain a resin, which enhances the flexibility of the rubber and achieves better wet and ice performance. As the resin, various natural and synthetic resins may be used, and specifically, it is preferable to use rosin-based resins, terpene-based resins, petroleum-based resins, phenol-based resins, coal-based resins, xylene-based resins, etc. These resins may be used alone or in combination of two or more types.

The method for producing the rubber composition is not particularly limited. For example, the rubber composition can be obtained by blending and kneading the above-mentioned rubber component, linear polyhydric alcohol, cyclic polyol compound having a hydrocarbyl group, filler, and other components that are optionally blended, by a known method.

The pneumatic tire of the present invention uses the above-mentioned rubber composition, but there is no particular limitation on the portion to which the rubber composition is applied.
For example, it can be used in at least one of the tread portion, shoulder portion, sidewall portion, bead portion, belt layer (belt coating rubber), and carcass (ply coating rubber). Among these portions, it is preferably used in the tread portion. By applying the rubber composition to the tire tread portion, it is possible to realize excellent cut resistance while maintaining performance such as low rolling resistance and elongation fatigue resistance.

(5) Other Embodiments Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments.

For example, in the above embodiment, the pneumatic tire 10 satisfies the relationship 0.56≦RD/OD≦0.66, but this relationship does not necessarily have to be satisfied. In addition, in the above embodiment, the folded end 41 of the carcass 40 is provided so as to be wound along the bead core 61, but the folded end 41 does not necessarily have to be wound along the bead core 61. Furthermore, in the above embodiment, the sheath belt 52 is wound around the core belt 51 in a spiral shape along the tire circumferential direction at a predetermined distance equal to or greater than the width of the sheath belt 52, and covers the tire radial outer side surface of the core belt 51 and the tire radial inner side surface of the core belt 51, but the sheath belt 52 does not necessarily have to be configured in this way. For example, the sheath belt 52 may be simply wound around the core belt 51 in a spiral shape along the tire circumferential direction without a predetermined distance, and the tire radial outer side surface of the core belt 51 and the tire radial inner side surface of the core belt 51 may not be completely covered. Moreover, the core belt 51 does not necessarily have to be provided. In other words, the sheath belt 52 may simply be wound spirally around the core belt 51 in the tire circumferential direction without covering the core belt 51.
The tire of the present invention can be molded by steam vulcanization or electric vulcanization.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

<Examples 1-1 to 3-3, Comparative Examples 1 to 3>
Rubber composition samples were prepared by compounding and kneading in a conventional manner according to the formulation shown in Table 1. The compounding amounts shown in Table 1 are the compounding amounts (parts by mass) per 100 parts by mass of the rubber component.
The following evaluations were carried out for each of the obtained samples.

<Evaluation>
(1) Cut Resistance After each sample in the Examples and Comparative Examples was subjected to a vulcanization treatment, a pure shear type test piece was prepared, and a tensile testing device (Shimadzu Corporation) was used to make an incision in the test piece while the test piece was being pulled. The progress of the crack was observed, and the energy release rate (transition energy) at which the crack growth rate discontinuously increased was measured.
The evaluation was carried out by calculating the reciprocal of the transition energy of each measured sample, and the evaluation was expressed as an index value when the reciprocal of the transition energy of the sample of Comparative Example 1 was set to 100 for Examples 1-1 and 1-2, an index value when the reciprocal of the transition energy of the sample of Comparative Example 2 was set to 100 for Examples 2-1 and 2-2, and an index value when the reciprocal of the transition energy of the sample of Comparative Example 3 was set to 100 for Examples 3-1 to 3-3. Note that the larger the index value in Table 1, the better the cut resistance.

(2) Elongation fatigue property After vulcanization, each sample of the examples and comparative examples was subjected to a tensile test using a tensile tester (Shimadzu Corporation) to repeatedly tensile a 6 mm wide dumbbell-shaped test piece with a 0.5 mm wide cut at 5 Hz. For evaluation, the number of breaks was measured when the common logarithm of the energy release rate was 4.3. For evaluation, the index for Examples 1-1 and 1-2 was calculated as 100 for the number of breaks in Comparative Example 1, the index for Examples 2-1 and 2-2 was calculated as 100 for the number of breaks in Comparative Example 2, and the index for Examples 3-1 to 3-3 was calculated as 100 for the number of breaks in Comparative Example 3, and these are shown in Table 1. Note that the larger the index value in Table 1, the better the elongation fatigue property.

*1 Natural rubber: RSS#3
*2 Sorbitan monoester: Sorbitan monostearate, manufactured by Kao Corporation, "Rheodol AS-10V", hydroxyl group number 3
*3 Sorbitol: Kanto Chemical Co., Ltd., hydroxyl group number 6
* 4 Carbon black: N234, manufactured by Mitsubishi Chemical Corporation, "DIABLACK N234"
*5 Silica: "NIPSIL AQ" manufactured by Tosoh Silica Corporation
*6 Antioxidant: N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., "Nocrac 6C"
* 7 Silane coupling agent: bistriethoxysilylpropyl polysulfide, manufactured by Shin-Etsu Chemical Co., Ltd. * 8 Vulcanization accelerator: N-cyclohexyl-2-benzothiazole sulfenamide, manufactured by Sanshin Chemical Industry Co., Ltd., "Suncerer CM-G" * 9 Styrene butadiene rubber: manufactured by Asahi Kasei Corporation, "Tufden 2

From the results in Table 1, it can be seen that the rubber compositions of each Example all achieved excellent results in terms of cut resistance while maintaining good elongation fatigue properties. On the other hand, it can be seen that the rubber compositions of the Comparative Examples achieved the same elongation fatigue properties as the Examples, but showed inferior results in terms of cut resistance compared to the Examples, among the evaluation items.

The present invention provides a pneumatic tire that is excellent in cut resistance and abrasion resistance, while also achieving both high load capacity and space saving.

1: Vehicle 10: Pneumatic tire 20: Tread 21, 22: Circumferential main grooves 26, 27: Shoulder portion 30: Tire side portion 40: Carcass 41: Turn-up end portion

Claims (11)

A pneumatic tire to be mounted on a vehicle includes a tread that contacts a road surface and a belt layer provided on a radially inner side of the tread,
The outer diameter of the pneumatic tire is 350 mm or more and 600 mm or less,
When the rim width of the rim wheel to be mounted on the pneumatic tire is RW and the tire cross-sectional width of the pneumatic tire is SW,
0.78≦RW/SW≦0.88
Fulfilling the relationship,
A rubber composition including a rubber component containing natural rubber and a cyclic polyol compound and/or a linear polyhydric alcohol having a hydrocarbyl group is used for at least a tread member ,
The hydrocarbyl group-containing cyclic polyol compound is represented by the following formula (1):

[wherein A is a hydrocarbyl ester group having 6 to 30 carbon atoms or a hydrocarbyl ether group having 6 to 30 carbon atoms, and X ₁ , X ₂ , X ₃ and X ₄ are each independently -OH or -R (wherein -R is -H or -CH ₂ OH), with the proviso that at least three of X ₁ , X ₂ , X ₃ and X ₄ are -OH],
The linear polyhydric alcohol has three or more hydroxyl groups,
The pneumatic tire, wherein the belt layer includes a sheath belt wound spirally along a circumferential direction of the tire. The pneumatic tire according to claim 1, characterized in that the content of the cyclic polyol compound is 0.1 to 6 parts by mass per 100 parts by mass of the rubber component. The pneumatic tire according to claim 1 or 2, characterized in that the hydrocarbyl group-containing cyclic polyol compound has a hydrocarbyl group moiety of A in formula (1) with a carbon number of 12 to 24. The pneumatic tire according to any one of claims 1 to 3, characterized in that the melting point of the cyclic polyol compound having a hydrocarbyl group is 40 to 100°C. The pneumatic tire according to any one of claims 1 to 4, characterized in that the melting point of the linear polyhydric alcohol is less than 160°C. The pneumatic tire according to any one of claims 1 to 5, characterized in that the linear polyhydric alcohol is at least one selected from the group consisting of xylitol, sorbitol, mannitol, and galactitol. The pneumatic tire according to any one of claims 1 to 6, characterized in that the content of the linear polyhydric alcohol is 0.1 to 6 parts by mass per 100 parts by mass of natural rubber in the rubber component. The pneumatic tire according to any one of claims 1 to 7, characterized in that the content of natural rubber in the rubber component is 70% by mass or more. The pneumatic tire according to any one of claims 1 to 8, characterized in that the rubber composition further contains a filler containing at least silica or carbon black. The pneumatic tire according to claim 9, characterized in that the content of the silica in the filler is 5 to 100 parts by mass per 100 parts by mass of the rubber component. The pneumatic tire according to claim 9 or 10, characterized in that the content of the carbon black in the filler is 5 to 100 parts by mass per 100 parts by mass of the rubber component.

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