JP7545034B2 - Pneumatic tires - Google Patents

Description

The present invention relates to a pneumatic tire in which a belt cover layer is arranged on the outer periphery of a belt layer, the belt cover layer being made of a strip material including a plurality of cover cords wound around the tire circumferential direction for a number of times. More specifically, the present invention relates to a pneumatic tire in which the strip material of the belt cover layer is arranged at intervals to reduce weight, suppress the occurrence of vulcanization failures caused by air pockets, and furthermore, to a tire that makes it possible to maintain good steering stability during high-speed driving.

In a pneumatic tire, multiple belt layers are arranged on the outer periphery of the carcass layer in the tread portion, and a belt cover layer is arranged on the outer periphery of the belt layer, the belt cover layer being made by winding a strip material including multiple cover cords around the tire circumferential direction multiple times (see, for example, Patent Document 1). By arranging such a belt cover layer on the outer periphery of the belt layer, tire characteristics such as high-speed durability can be improved.

In recent years, there has been a strong demand for lighter pneumatic tires, and there is also an increasing demand for a reduction in the mass of each component that constitutes a pneumatic tire. The belt cover layer is no exception, and for example, it has been proposed to reduce the weight by arranging strip materials at intervals (see, for example, Patent Document 2).

However, when the strips are spaced apart on the outer periphery of the belt layer, there is a drawback in that vulcanization failures are likely to occur due to air pockets between the spaced apart circumferential portions of the strips. Also, in high-performance tires, when the strips of the belt cover layer are spaced apart, there is a problem in that the handling stability during high-speed driving decreases.

JP 2011-156887 A JP 2017-7376 A

The object of the present invention is to provide a pneumatic tire that is lightweight by arranging the strips of material of the belt cover layer at intervals, suppresses the occurrence of vulcanization failures caused by air pockets, and furthermore, makes it possible to maintain good steering stability during high-speed driving.

In order to achieve the above object, a pneumatic tire of the present invention includes a plurality of belt layers disposed on an outer peripheral side of a carcass layer in a tread portion, and a belt cover layer disposed on the outer peripheral side of the belt layers, the belt cover layer being formed by winding a strip material including a plurality of cover cords around the tire circumferential direction in a plurality of turns,
When a region extending from the center position in the width direction of the belt layer to positions on both sides that are 25% of the width of the belt layer is defined as a center portion, the circumferential portions of the strip material are arranged to be spaced apart from each other in the center portion, and when a strip spacing of the strip material in the center portion is Wpc (mm) and a strip height of the strip material is Hc (mm), the relationship of 2.07×Hc ^-0.976 ≦(2×Hc+2×Wpc)/(Hc×Wpc)≦6.09×Hc ^-0.419 is satisfied,
a tensile stiffness of the cover cord in the center portion at 44 N is Sc (N/mm), a width of the center portion is Wb (mm), and a total number of the cover cords in the center portion is Eb (pieces), the relationship 100≦Sc×Eb×50/Wb≦1600 is satisfied,
The tread portion has a cap tread rubber layer and an undertread rubber layer, and the undertread rubber layer is characterized in that it is composed of a rubber composition in which 8 to 35 parts by weight of silica having a specific surface area in the range of 135 ^m2 /g to 215 ^m2 /g as measured by the CTAB adsorption method is compounded with 100 parts by weight of diene rubber.

In the present invention, in a pneumatic tire in which a belt cover layer is arranged on the outer periphery of a belt layer, the strip material including a plurality of cover cords is wound around the tire circumferential direction for a plurality of times, the strip material is arranged so that the winding portions are spaced apart from each other in the center portion, and when the strip spacing of the strip material in the center portion is Wpc (mm) and the strip height of the strip material is Hc (mm), the relationship of 2.07×Hc ^-0.976 ≦(2×Hc+2×Wpc)/(Hc×Wpc)≦6.09×Hc ^-0.419 is satisfied, the amount of strip material used can be reduced to reduce the weight, and the occurrence of vulcanization failure due to air pockets can be suppressed. In addition, by specifying the rigidity (Sc×Eb×50/Wb) of the belt cover layer per 50 mm width in the center portion and the compounding amount of silica in the undertread rubber layer, the steering stability during high-speed driving can be maintained well even when the strip material of the belt cover layer is spaced apart.

In the present invention, the shoulder portion is defined as the region from both ends of the outermost belt layer in the width direction toward the center in the width direction to a position that is 15% of the width of the belt layer, and the tensile stiffness of the cover cord in each shoulder portion at 44 N is Ss (N/mm), the width of each shoulder portion is Ws (mm), and the total number of the cover cords in each shoulder portion is Es (pieces). It is preferable to satisfy the relationship 0.25≦(Sc×Eb×Ws)/(Ss×Es×Wb)<1. In this way, by specifying the ratio of the stiffness of the belt cover layer per unit width in the center portion (Sc×Eb/Wb) to the stiffness per unit width in the shoulder portion (Ss×Es/Ws) within the above range, it is possible to achieve weight reduction while maintaining the required tire characteristics.

The strip height Hc of the strip material is preferably in the range of 0.5 mm ≦ Hc ≦ 1.3 mm. This allows high-speed durability and lightweight design based on the belt cover layer to be achieved at a higher level.

In addition, the shoulder portion is the region from both ends of the outermost belt layer in the width direction toward the center in the width direction to a position that is 15% of the width of the belt layer, and the strip spacing of the strip material in the shoulder portion is Wps (mm) and the strip width of the strip material is Wc (mm). It is preferable to satisfy the relationship 0≦Wps/Wc≦0.5. While achieving both weight reduction and air retention suppression effects in the center portion, satisfying the relationship 0≦Wps/Wc≦0.5 in the shoulder portion can sufficiently ensure the reinforcing effect based on the belt cover layer.

Furthermore, it is preferable that the total fineness of the cover cord is 1100 dtex or more and less than 6000 dtex. This allows high-speed durability and lightweight design based on the belt cover layer to be achieved at a higher level.

The cover cord contains aromatic polyamide fibers, and the content of aromatic polyamide fibers in the cover cord is preferably 65% by weight or more. By using a cover cord containing aromatic polyamide fibers in this way, it is possible to effectively improve steering stability during high-speed driving.

The rubber composition constituting the undertread rubber layer preferably contains 45 to 70 parts by weight of carbon black having a nitrogen adsorption specific surface area _N2SA in the range of ⁷⁰ to ¹⁵⁰ m2/g per 100 parts by weight of diene rubber, thereby making it possible to sufficiently ensure the reinforcing effect based on the undertread rubber layer while suppressing heat generation in the undertread rubber layer.

The rubber composition constituting the undertread rubber layer preferably contains 200 to 700 parts by weight of carbon black per 100 parts by weight of silica. This makes it possible to avoid deterioration of processability and vulcanization failures when obtaining the reinforcing effect based on the undertread rubber layer.

The present invention is applicable to pneumatic tires for various applications, but is particularly effective as a high-performance tire with a cap tread rubber layer and an under tread rubber layer in the tread portion. A high-performance tire is, for example, a tire with a speed range of W range or higher.

1 is a meridian cross-sectional view showing a pneumatic tire according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a belt layer and a belt cover layer of the pneumatic tire of FIG. 1 . 1 is a graph showing the relationship between strip height Hc of the strip material in the pneumatic tire of the present invention and (2Hc+2Wpc)/(Hc×Wpc).

The configuration of the present invention will be described in detail below with reference to the attached drawings. Figure 1 shows a pneumatic tire according to an embodiment of the present invention, and Figure 2 shows the belt layer and belt cover layer.

As shown in FIG. 1, the pneumatic tire of this embodiment has a tread portion 1 that extends in the circumferential direction of the tire to form an annular shape, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and a pair of bead portions 3 arranged on the radially inner side of the sidewall portions 2.

A carcass layer 4 including multiple carcass cords extending in the tire radial direction is mounted between a pair of bead portions 3, 3. The carcass cords constituting the carcass layer 4 are preferably made of organic fiber cords such as rayon, nylon, or polyester. The cord angle of the carcass layer 4 relative to the tire circumferential direction is set to a range of 75° to 90°, preferably 80° to 87°. The carcass layer 4 is wound around the bead core 5 from the inside to the outside of the tire. In other words, the carcass layer 4 is composed of a main body portion 4a and a wound portion 4b, which are bounded by the bead core 5.

In each bead portion 3, a bead filler 6 made of a rubber composition with a triangular cross section is disposed on the outer periphery of the bead core 5, and this bead filler 6 is sandwiched between the main body portion 4a and the turn-up portion 4b of the carcass layer 4. In addition, it is preferable that an organic fiber reinforcing layer 9 including organic fiber cords inclined in the tire circumferential direction is embedded in the bead portion 3 so as to encase the bead core 5 and the bead filler 6.

On the other hand, multiple belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. The belt layer 7 includes an inner belt layer 7A located on the inner side in the tire radial direction, and an outer belt layer 7B located on the outer side in the tire radial direction. The inner belt layer 7A is wider than the outer belt layer 7B. These belt layers 7 include multiple belt cords that are inclined with respect to the tire circumferential direction, and are arranged so that the belt cords cross each other between the layers. In the belt layer 7, the inclination angle of the belt cords with respect to the tire circumferential direction is set in the range of 10° to 40°, for example. Steel cords are preferably used as the belt cords of the belt layer 7.

On the outer periphery of the belt layer 7, a belt cover layer 8 is arranged in which cover cords are arranged at an angle of 5° or less with respect to the tire circumferential direction in order to improve high-speed durability. As shown in FIG. 2, the belt cover layer 8 has a jointless structure in which a strip material 80 made of a plurality of cover cords 81 aligned and rubber-coated is wound continuously around the tire circumferential direction for several turns. The strip material 80 constituting the belt cover layer 8 is arranged over the entire width of the belt layer 7, but as described later, its arrangement is optimized according to the position in the width direction of the belt layer 7. As the cover cords 81 of the belt cover layer 8, organic fiber cords such as nylon, polyester, aramid, or hybrid cords thereof are preferably used.

In addition, the tread portion 1 is provided with a cap tread rubber layer 1A exposed on the outer surface of the tire, and an undertread rubber layer 1B located between the cap tread rubber layer 1A and the belt cover layer 8. The tread portion 1, which has a laminated structure of the cap tread rubber layer 1A and the undertread rubber layer 1B, has a plurality of main grooves 10 formed therein that extend in the circumferential direction of the tire.

In the above pneumatic tire, as shown in FIG. 2, the region from the widthwise center position of the belt layer 7 to the positions of 25% of the width WB of the belt layer 7 on both sides is defined as the center portion Ce. Here, the widthwise center position of the belt layer 7 coincides with the tire center line CL. The width WB of the belt layer 7 is the width of the inner peripheral belt layer 7A, which is the widest. When the center portion Ce is defined in this way, the circumferential portions of the strip material 80 are arranged so as to be spaced apart from each other in the center portion Ce. When the strip spacing of the strip material 80 in the center portion Ce is Wpc and the strip height of the strip material 80 is Hc, the relationship of 2.07×Hc ^-0.976 ≦(2×Hc+2×Wpc)/(Hc×Wpc)≦6.09×Hc ^-0.419 is satisfied. The strip height Hc is the thickness of the strip material 80.

3 shows the relationship between the strip height Hc of the strip material 80 in the pneumatic tire of the present invention and (2Hc+2Wpc)/(Hc×Wpc), where the horizontal axis is the strip height Hc and the vertical axis is (2Hc+2Wpc)/(Hc×Wpc). In other words, as shown in FIG. 3, the strip height Hc of the strip material 80 is set to a value within the range between (2×Hc+2×Wpc)/(Hc×Wpc)=2.07×Hc ^-0.976 and (2×Hc+2×Wpc)/(Hc×Wpc)=6.09×Hc ^-0.419 .

In the above pneumatic tire, when the belt cover layer 8 is arranged on the outer periphery of the belt layer 7, the strip material 80 including the reinforcing cords 81 is wound around the tire circumferential direction for multiple times, the strip material 80 is arranged so that the turns are spaced apart from each other in the center part Ce, and the strip spacing Wpc and the strip height Hc of the strip material 80 in the center part Ce satisfy the above-mentioned relationship (for example, in the case of the embodiment shown by "○" in FIG. 3). This allows the undertread rubber layer 1B to flow smoothly between the spaced apart turns of the strip material 80, thereby reducing the amount of strip material 80 used and reducing the weight, while suppressing the occurrence of vulcanization failures due to air pockets.

Here, (2×Hc+2×Wpc) corresponds to the cross-sectional circumferential length of the gap formed between the winding portions of the strip material 80, and (Hc×Wpc) corresponds to the cross-sectional area of the gap formed between the winding portions of the strip material 80. By setting the ratio of the two as described above, it is possible to achieve both weight reduction and air retention suppression effects. If the value of (2×Hc+2×Wpc)/(Hc×Wpc) is smaller than 2.07×Hc ^-0.976 (for example, in the case of the comparative example shown by "△" in FIG. 3), the high-speed durability based on the belt cover layer 8 is reduced, and further, the steering stability during high-speed driving is deteriorated. On the other hand, if the value of (2×Hc+2×Wpc)/(Hc×Wpc) is larger than 6.09×Hc ^-0.419 (for example, in the case of the comparative example shown by "△" in FIG. 3), vulcanization failure due to air retention is likely to occur.

In addition, in the above pneumatic tire, when the tensile stiffness of the cover cord 81 in the center part Ce at 44 N is Sc (N/mm), the width of the center part Ce is Wb (mm), and the total number of the cover cords 81 in the center part Ce is Eb (pieces), the relationship of 100≦Sc×Eb×50/Wb≦1600 is satisfied. By specifying the stiffness (Sc×Eb×50/Wb) of the belt cover layer 8 per 50 mm width in the center part Ce in this way, even if the strip material 80 of the belt cover layer 8 is spaced apart, it is possible to maintain good steering stability during high-speed driving. Here, if the value of Sc×Eb×50/Wb is less than 100, it is not possible to maintain good steering stability during high-speed driving, and conversely, if it is greater than 1600, the weight reduction is insufficient.

Furthermore, in the above pneumatic tire, the undertread rubber layer 1B is composed of a rubber composition in which 8 to 35 parts by weight of silica having a specific surface area of 135 ^m2 /g to 215 ^m2 /g as measured by CTAB adsorption method is blended with 100 parts by weight of diene rubber. The specific surface area as measured by CTAB adsorption method is measured in accordance with JIS-K6430. By specifying the blending amount of silica in the undertread rubber layer 1B in this manner, good steering stability during high-speed running can be maintained even when the intervals between the strip materials 80 of the belt cover layer 8 are increased.

Here, if the specific surface area of silica measured by CTAB adsorption method is less than 135 ^m2 /g, the reinforcing effect becomes insufficient, whereas if it is more than 215 ^m2 /g, heat generation becomes easy and costs increase. Furthermore, if the amount of silica blended per 100 parts by weight of rubber in the rubber composition constituting the undertread rubber layer 1B is less than 8 parts by weight, the reinforcing effect becomes insufficient, whereas if it is more than 35 parts by weight, the processability of the rubber composition deteriorates (increased mixing time and vulcanization time).

The diene rubber used in the undertread rubber layer 1B is not particularly limited, but examples include natural rubber (NR), isoprene (IR), brazilian rubber (BR), styrene butadiene rubber (SBR), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), etc. For example, it is preferable to use a diene rubber containing 40% to 80% by weight of natural rubber.

In the above pneumatic tire, the shoulder portion Sh is the region from both ends of the outermost portion of the belt layer 7 in the width direction to a position of 15% of the width WB of the belt layer 7 toward the center in the width direction, the width of each shoulder portion Sh is Ws (mm), and the total number of cover cords 81 in each shoulder portion Sh is Es (pieces). It is preferable that the relationship of 0.25≦(Sc×Eb×Ws)/(Ss×Es×Wb)<1 is satisfied. In this way, by specifying the ratio of the stiffness of the belt cover layer 8 per unit width in the center portion Ce (Sc×Eb/Wb) to the stiffness of the belt cover layer 8 per unit width in the shoulder portion Sh (Ss×Es/Ws) within the above range, it is possible to achieve weight reduction while maintaining the required tire characteristics. Here, if the value of (Sc x Eb x Ws)/(Ss x Es x Wb) is less than 0.25, the rigidity of the center part Ce decreases, and the effect of improving steering stability during high-speed driving decreases, and conversely, if it is 1 or more, the effect of improving weight reduction decreases.

In the above pneumatic tire, the strip height Hc of the strip material 80 is preferably in the range of 0.5 mm≦Hc≦1.3 mm. This allows the belt cover layer 8 to achieve both high-speed durability and lightweight at a higher level. If the strip height Hc of the strip material 80 is smaller than 0.5 mm, the cover cord 81 becomes thinner, reducing high-speed durability, and conversely, if it is greater than 1.3 mm, the effect of improving the weight reduction is reduced.

In the above pneumatic tire, the shoulder portion Sh is the region from both ends of the outermost portion of the belt layer 7 in the width direction to a position that is 15% of the width WB of the belt layer 7 toward the center in the width direction, the strip spacing of the strip material 80 in the shoulder portion Sh is Wps (mm), and the strip width of the strip material 80 is Wc (mm). It is preferable that the relationship of 0≦Wps/Wc≦0.5 is satisfied. As described above, the center portion Ce is both lightweight and has an air retention suppression effect, while the shoulder portion Sh satisfies the relationship of 0≦Wps/Wc≦0.5, thereby sufficiently ensuring the reinforcing effect based on the belt cover layer 8. Here, if the value of Wps/Wc is greater than 0.5, the rigidity of the belt cover layer 8 in the shoulder portion Sh decreases, making it more susceptible to failures such as edge separation, and reducing durability.

In the above pneumatic tire, it is preferable that the total fineness of the cover cord 81 is 1100 dtex or more and less than 6000 dtex. This allows a higher level of compatibility between high-speed durability and lightweight due to the belt cover layer 8. Here, if the total fineness of the cover cord 81 is less than 1100 dtex, the reinforcing effect due to the belt cover layer 8 decreases, and conversely, if it is more than 6000 dtex, the thickness of the belt cover layer 8 becomes too large, resulting in increased weight.

In the above pneumatic tire, the cover cord 81 contains aromatic polyamide fiber, and the content of aromatic polyamide fiber in the cover cord 81 is preferably 65% by weight or more. By using the cover cord 81 containing aromatic polyamide fiber in this way, the steering stability during high-speed driving can be effectively improved. If the content of aromatic polyamide fiber in the cover cord 81 is less than 65% by weight, the effect of improving the steering stability during high-speed driving decreases. In addition, when the cover cord 81 contains aromatic polyamide fiber, a cord composed only of aromatic polyamide fiber, or a hybrid cord in which aromatic polyamide fiber yarn and low-elasticity fiber yarn made of nylon fiber or the like having a lower elastic modulus than aromatic polyamide fiber are twisted together can be used.

In the above pneumatic tire, the rubber composition constituting the undertread rubber layer 1B may contain 45 to 70 parts by weight of carbon black having a nitrogen adsorption specific surface area N ₂ SA in the range of 70 m ² /g to 150 m ² /g per 100 parts by weight of diene rubber. The nitrogen adsorption specific surface area N ₂ SA is measured in accordance with JIS-K6217-2. By specifying the amount of carbon black in the rubber composition constituting the undertread rubber layer 1B in this manner, it is possible to sufficiently ensure the reinforcing effect based on the undertread rubber layer 1B while suppressing heat generation in the undertread rubber layer 1B.

Here, if the nitrogen adsorption specific surface area _N2SA of carbon black is less than 70 ^m2 /g, the reinforcing effect becomes insufficient, whereas if it is more than 150 ^m2 /g, heat generation becomes likely and costs increase. Also, if the amount of carbon black blended per 100 parts by weight of rubber in the rubber composition constituting the undertread rubber layer 1B is less than 45 parts by weight, the reinforcing effect becomes insufficient, whereas if it is more than 70 parts by weight, heat generation becomes likely.

In the above pneumatic tire, the rubber composition constituting the undertread rubber layer 1B may preferably contain 200 to 700 parts by weight of carbon black per 100 parts by weight of silica. This makes it possible to avoid deterioration of processability and occurrence of vulcanization failure when obtaining the reinforcing effect based on the undertread rubber layer 1B. Here, if the amount of carbon black to be blended is less than 200 parts by weight per 100 parts by weight of silica, the processability of the rubber composition deteriorates, and conversely, if it is more than 700 parts by weight, it becomes difficult to suppress occurrence of vulcanization failure due to air pockets. At the upper limit of the amount of carbon black to be blended relative to silica (700 parts by weight), carbon black 45 phr = silica 6.8 phr, carbon black 70 phr = silica 10.5 phr. At the lower limit of the amount of carbon black to be blended relative to silica (200 parts by weight), carbon black 45 phr = silica 22.5 phr, carbon black 70 phr = silica 35 phr.

For a pneumatic tire with a tire size of 245/40R19, in which multiple belt layers are arranged on the outer periphery of the carcass layer in the tread portion, and a belt cover layer is arranged on the outer periphery of the belt layer, which is made by winding a strip material containing multiple reinforcing cords around the tire circumferential direction multiple times, tires were manufactured as Reference Examples 1-2, Examples 1-5, and Comparative Examples 1-5, with various different belt cover layer structures.

In Reference Examples 1 and 2, Examples 1 to 6, and Comparative Examples 1 to 5, the strip width Wc, strip interval Wpc, strip height Hc, (2Hc+2Wpc)/(Hc×Wpc), tensile stiffness Sc of the cover cord at 44 N, end count of the cover cord per 50 mm width when the strip material is rolled (end count of the cord during strip rolling), end count of the cover cord per 50 mm width of the belt cover layer (end count of the cord during tire molding=Eb×50/Wb), Sc×Eb×50/Wb; the strip width Wc, strip interval Wps, Wps/Wc, strip height Hc, (2Hc+2Wps)/(Hc×Wp s), tensile stiffness Ss of the cover cord at 44 N, number of cover cords per 50 mm width when rolling the strip material (number of cords per 50 mm width when rolling the strip), number of cover cords per 50 mm width of the belt cover layer (number of cords per 50 mm width when forming a tire=Es×50/Ws), Ss×Es×50/Ws; ratio of stiffness of the belt cover layer per unit width in the center portion to stiffness of the belt cover layer per unit width in the shoulder portion (Ss×Es/Ws) [(Sc×Eb×Ws)/(Ss×Es×Wb)]; amount of carbon black, amount of silica, and ratio of carbon black/silica in the rubber composition constituting the undertread rubber layer were set as shown in Table 1. The silica used had a specific surface area measured by the CTAB adsorption method in the range of 135 m ² /g to 215 m ² /g, and the carbon black used had a nitrogen adsorption specific surface area N ₂ SA in the range of 70 m ² /g to 150 m ² /g.

These test tires were evaluated for tire mass, amount of air pockets, high-speed driving stability, high-speed durability, and processability using the following evaluation methods, and the results are shown in Table 1.

Tire weight:
The mass of each test tire was measured. The evaluation results were expressed as an index with Reference Example 1 being 100. The smaller the index value, the lighter the tire.

Amount of air pockets:
Each test tire was disassembled after vulcanization to measure the amount of air pockets generated. The evaluation results were expressed as an index with Reference Example 1 being 100. The smaller the index value, the smaller the amount of air pockets generated.

High-speed handling stability:
Each test tire was mounted on a wheel with a rim size of 19×8 1/2J and mounted on a test vehicle, and the tire was air-pressurized to 230 kPa. A test driver performed a running test on a circuit course, and a sensory evaluation was performed on the steering stability during high-speed running. The evaluation results were expressed as an index with Reference Example 1 being 100. The higher the index value, the better the high-speed steering stability.

High Speed Durability:
Each test tire was mounted on a wheel with a rim size of 19 x 8 1/2J and attached to a drum durability tester, and a running test was started under the following conditions: air pressure: 220 kPa, load: 88% of the JATMA maximum load capacity, initial speed: 120 km/h, and the speed was increased by 10 km/h every 20 minutes, and the running distance until failure occurred in the tread was measured. The evaluation results were expressed as an index with Reference Example 1 being 100. The higher the index value, the better the high-speed durability.

Processability:
For each test tire, the sum of the kneading time and the vulcanization time of the undertread rubber layer was calculated. The evaluation results were expressed as an index with Reference Example 2 being 100. The smaller the index value, the more excellent the processability.

As can be seen from Table 1, the tire of Reference Example 2 is lighter than Reference Example 1 because the strip material of the belt cover layer is spaced apart, but as a result, the occurrence of air pockets increases and high-speed driving stability deteriorates. In contrast, the tires of Examples 1 to 5, while enjoying the effect of weight reduction, were able to suppress the occurrence of air pockets and improve high-speed driving stability compared to Reference Example 2.

On the other hand, the tire of Comparative Example 1 could not suppress the occurrence of air pockets because the value of (2Hc + 2Wpc) / (Hc x Wpc) in the center part was too large. The tire of Comparative Example 2 had a value of (2Hc + 2Wpc) / (Hc x Wpc) in the center part that was too small, so high-speed steering stability and high-speed durability were deteriorated. The tire of Comparative Example 3 had a value of (2Hc + 2Wpc) / (Hc x Wpc) in the center part that was too large and the value of Sc x Eb x 50 / Wb was too high, so air pockets were generated frequently and the tire mass was also increased. The tire of Comparative Example 4 had a value of (2Hc + 2Wpc) / (Hc x Wpc) in the center part that was too large and the amount of silica compounded in the rubber composition constituting the undertread rubber layer was too high, so air pockets were generated frequently and processability was also deteriorated. The tire of Comparative Example 5 had poor high-speed driving stability and high-speed durability because the value of Sc x Eb x 50/Wb was too small.

REFERENCE SIGNS LIST 1 Tread portion 1A Cap tread rubber layer 1B Under tread rubber layer 2 Sidewall portion 3 Bead portion 4 Carcass layer 5 Bead core 6 Bead filler 7 Belt layer 7A Inner circumferential belt layer 7B Outer circumferential belt layer 8 Belt cover layer 80 Strip material 81 Reinforcing cord

Claims (8)

A pneumatic tire having a plurality of belt layers disposed on an outer peripheral side of a carcass layer in a tread portion, and a belt cover layer formed by winding a strip material including a plurality of cover cords around the outer peripheral side of the belt layers in a tire circumferential direction,
When a region extending from the center position in the width direction of the belt layer to positions on both sides that are 25% of the width of the belt layer is defined as a center portion, the circumferential portions of the strip material are arranged to be spaced apart from each other in the center portion, and when a strip spacing of the strip material in the center portion is Wpc (mm) and a strip height of the strip material is Hc (mm), the relationship of 2.07×Hc ^-0.976 ≦(2×Hc+2×Wpc)/(Hc×Wpc)≦6.09×Hc ^-0.419 is satisfied,
a tensile stiffness of the cover cord in the center portion at 44 N is Sc (N/mm), a width of the center portion is Wb (mm), and a total number of the cover cords in the center portion is Eb (pieces), the relationship 100≦Sc×Eb×50/Wb≦1600 is satisfied,
The pneumatic tire is characterized in that the tread portion has a cap tread rubber layer and an under tread rubber layer, and the under tread rubber layer is composed of a rubber composition in which 8 to 35 parts by weight of silica having a specific surface area in the range of 135 ^m2 /g to 215 ^m2 /g as measured by the CTAB adsorption method is blended with 100 parts by weight of diene rubber. The pneumatic tire according to claim 1, characterized in that the shoulder portions are the regions from both ends of the outermost belt layer in the width direction toward the center in the width direction to a position that is 15% of the width of the belt layer, the tensile stiffness of the cover cord in each shoulder portion at 44 N is Ss (N/mm), the width of each shoulder portion is Ws (mm), and the total number of cover cords in each shoulder portion is Es (pieces), satisfying the relationship 0.25≦(Sc×Eb×Ws)/(Ss×Es×Wb)<1. The pneumatic tire according to claim 1 or 2, characterized in that the strip height Hc of the strip material is in the range of 0.5 mm ≦ Hc ≦ 1.3 mm. A pneumatic tire according to any one of claims 1 to 3, characterized in that the shoulder portions are the regions from both ends of the outermost belt layer in the width direction to the center in the width direction, each of which is 15% of the width of the belt layer, the strip spacing of the strip material in the shoulder portions is Wps (mm), and the strip width of the strip material is Wc (mm), satisfying the relationship 0≦Wps/Wc≦0.5. A pneumatic tire according to any one of claims 1 to 4, characterized in that the total fineness of the cover cord is 1100 dtex or more and less than 6000 dtex. A pneumatic tire according to any one of claims 1 to 5, characterized in that the cover cord contains aromatic polyamide fibers, and the content of the aromatic polyamide fibers in the cover cord is 65% by weight or more. The pneumatic tire according to any one of claims 1 to 6, characterized in that the rubber composition constituting the undertread rubber layer contains 45 to 70 parts by weight of carbon black having a nitrogen adsorption specific surface area _N2SA in the range of 70 ^m2 /g to 150 ^m2 /g per 100 parts by weight of diene rubber. The pneumatic tire according to any one of claims 1 to 7, characterized in that the rubber composition constituting the undertread rubber layer contains 200 to 700 parts by weight of carbon black per 100 parts by weight of silica.

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