PNEUMATIC TIRE

Abstract

Pneumatic tire which has: a belt layer (7) in which a belt cord is arranged on an outer peripheral side of a carcass layer (4) in a tread (3) so as to be inclined with respect to a circumferential direction of the tire, and a belt reinforcing layer (9) in which a cord (10) of organic fibers is arranged along the circumferential direction of the tire on an outer circumferential side of the belt layer (7), wherein in the belt layer (7) an angle of the belt cord with respect to the circumferential direction of the tyre is more than 30 degrees and 40 degrees or less, the cord (10) made of organic fibres is a hybrid cord formed by twisting together an aramid yarn and a nylon yarn, the belt reinforcing layer (9) is formed by coating the cord (10) of organic fibers with a rubber (11), and a ratio (Sr / Sc) of a cross-sectional area of ​​the rubber (Sr) to a cross-sectional area of ​​the cord (Sc) is 1.5 to 2.0, and a value obtained by dividing a sum of a product (A) of a load LASE5% (N) at 5% elongation of the organic fiber cord (10), a cord number (per 25 mm), and the number of belt reinforcing layers (9) and a product (B) of a load (N) at 0.5% elongation of the belt cord, cosθ, where a belt angle is defined as θ, a cord number (per inch), and the number of belt layers (7) by 1000 is 11 or more.

Description

Background of the invention 1. Field of the invention

[0001] The present invention relates to a pneumatic tire. 2. Description of the state of the art

[0002] In order to improve the durability of a tire at high speeds, it is known that a belt reinforcing layer in which organic fiber cords such as nylon fiber cords are arranged substantially parallel to a circumferential direction of the tire is provided on an outer peripheral side of a belt layer (see JP 2005-239069 A, JP 2005-75289 A, JP 2003-237309 A and JP 2017-81349 A (Patent Documents 1 to 4)).

[0003] DE 10 2021 204 749 A1 relates to a pneumatic tire having a belt layer obtained by arranging a belt band obliquely with respect to a circumferential direction of the tire on the radially outer side of a carcass layer in a tread part, and having a belt reinforcing layer obtained by arranging an organic fiber band along the circumferential direction of the tire on the radially outer side of the belt layer. The belt layer is designed such that an angle of the belt band with respect to a circumferential direction of the tire is more than 30° and at most 40°. The organic fiber band of the belt reinforcing layer is designed such that when a number of twists per 10 cm of length is T (twists / 10 cm), a fineness is D (dtex), and a fiber density p (g / cm 3 ), a twist coefficient K, which is defined as T × (D / p) 1 / 2is 900 to 2,600 and the product of a load at 5% elongation LASE 5% (N) of the organic fiber sliver and a final number E (slivers / 25 mm) of the organic fiber sliver is 1,000 N or more.

[0004] JP 2016-060343 A relates to a pneumatic tire having a belt layer formed by arranging and inclining a cord in the tire circumferential direction on an outer peripheral side of a carcass layer on a tread portion, and having a belt reinforcing layer formed by arranging an organic fiber cord along the tire circumferential direction on the outer peripheral side of the belt layer. The organic fiber cord is a hybrid cord formed from aliphatic polyamide fibers and aramid fibers whose glass transition temperature is 90-170°C, with an intensity index M = LASE 2% × E / 100, determined from the product of a load LASE 2% (N) of the organic fiber cord during 2% elongation time and the implantation number E (pieces / 25 mm) of the organic fiber cord, being 3.0-6.0. This gives the pneumatic tire both resistance to the formation of flat spots and durability at high speeds.

[0005] JP 2020-093746 A relates to a pneumatic tire having a carcass and a belt layer in which a cord is arranged at an outer periphery of a crown portion of the carcass obliquely with respect to the tire circumferential direction, and having a belt reinforcing layer in which an organic fiber cord made of aromatic polyamide fibers is arranged at an outer periphery of the belt layer along the tire circumferential direction. A product of the load (N) at 2% elongation of the organic fiber cord, which is 100 N or less, and the number (pieces / 25 mm) of implantation pieces is 1,000-2,000. The pneumatic tire further includes a rubber plate between the belt layer and the belt reinforcing layer. This provides a pneumatic tire with reduced tire weight and improved driving stability and durability.US 2010 / 0300595 A1 relates to a pneumatic tire with a radial carcass, a tread portion arranged radially outwardly of the carcass, and a crown reinforcement structure arranged between the tread portion and the carcass in the circumferential direction of the carcass. The crown reinforcement structure comprises a belt arrangement with at least one belt ply with parallel reinforcing cords and a cover structure with a nylon-reinforced layer extending transversely across the belt arrangement and forming an angle between -5° and +5° with an equatorial plane of the tire. The nylon-reinforced layer comprises a nylon cord with a construction of 2,000-2,200 / 1 Dtex, 1-10 TPI, and a final density of 10-35 EPI. Summary of the invention

[0006] In the belt layer, belt cords, such as steel cords, are arranged at an angle relative to the tire's circumferential direction, and the angle of each belt cord relative to the tire's circumferential direction is generally set at about 20 degrees. When the belt cord angle is set larger than usual, for example, more than 30 degrees, wet braking performance and driving stability can be improved. However, when the belt cord angle is increased, the rigidity of the belt layer in the tire's circumferential direction decreases, causing the tire's ground contact shape to deteriorate, which may lead to a reduction in high-speed durability, ride comfort, and rolling resistance.

[0007] In view of the above points, an object of the invention is to provide a pneumatic tire in which high-speed durability, ride comfort and rolling resistance are improved while maintaining wet braking performance and driving stability by increasing the angle of a belt cord.

[0008] A pneumatic tire according to one aspect of the invention is a pneumatic tire comprising a belt layer in which a belt cord is arranged on an outer peripheral side of a carcass layer in a tread so as to be inclined with respect to a circumferential direction of the tire, and a belt reinforcing layer in which an organic fiber cord is arranged along the circumferential direction of the tire on an outer peripheral side of the belt layer, wherein, in the belt layer, an angle of the belt cord with respect to the circumferential direction of the tire is more than 30 degrees and 40 degrees or less, wherein the organic fiber cord is a hybrid cord formed by twisting an aramid yarn and a nylon yarn together, wherein the belt reinforcing layer is formed by coating the organic fiber cord with rubber,and wherein a ratio (Sr / Sc) of a cross-sectional area of ​​the rubber (Sr) to a cross-sectional area of ​​the cord (Sc) is 1.5 to 2.0, and wherein a value obtained by dividing a sum of a product (A) of a load LASE5% (N) at 5% elongation of the organic fiber cord, a cord number (per 25 mm), and the number of belt reinforcing layers and a product (B) of a load (N) at 0.5% elongation of the belt cord, cosθ, where a belt angle is defined as θ, a cord number (per inch), and the number of belt layers by 1000 is 11 or more.

[0009] The product of the load LASE5% (N) at 5% elongation of the organic fiber cord and the number of cords (per 25 mm) can be 2000 (N / 25 mm) or more.

[0010] The load LASE5% (N) at 5% elongation of the organic fiber cord can be 65 or more, and the cord count (per 25 mm) can be 23 to 40.

[0011] According to one aspect of the invention, by setting the angle of the belt cord to more than 30 degrees and 40 degrees or less, high-speed durability, ride comfort and rolling resistance can be improved while maintaining wet braking performance and driving stability. Short description of the drawings The Fig. 1 is a semi-cross-sectional view of a pneumatic radial tire according to an embodiment, and The Fig. 2 is a diagram schematically illustrating a part of a cross section of a belt reinforcing layer according to the embodiment. Description of the embodiments

[0012] An embodiment of the invention is described in detail below.

[0013] A pneumatic tire according to the present embodiment is characterized by having a belt layer and a belt reinforcing layer arranged on an outer peripheral side of the belt layer.

[0014] The belt layer includes at least one belt ply in which belt cords are arranged to be inclined with respect to a circumferential direction of the tire on an outer circumferential side (that is, an outer side in a radial direction of the tire) of a carcass layer in a tread.

[0015] The belt reinforcing layer is formed from organic fiber cords arranged along the tire circumferential direction (equatorial plane) on the outer circumferential side (i.e., the outer side in the tire radial direction) of the belt layer. The organic fiber cords of the belt reinforcing layer extend substantially parallel to the tire circumferential direction, i.e., at an angle of approximately 0 degrees (preferably, an angle of 5 degrees or less), and the cords are arranged at predetermined intervals in a tire width direction. Such a belt reinforcing layer may be a cap layer covering the entire belt layer in the width direction or an edge layer covering one end of the belt.

[0016] The Fig.Figure 1 is a semi-cross-sectional view of a pneumatic radial tire for a passenger car, which is an example of a pneumatic tire. The tire includes a pair of left and right beads (1) and a pair of left and right sidewalls (2), as well as a tread (3) provided between the two sidewalls (2), and a carcass layer (4) extending in a toroidal shape and provided between the pair of beads (1).

[0017] The carcass layer (4) extends from the tread (3) through the sidewalls (2) and is folded back from an inner side to an outer side to secure it to a bead core (5) of the bead (1). The carcass layer (4) is formed by at least one ply in which carcass cords made of organic fibers are arranged substantially perpendicular to the circumferential direction of the tire.

[0018] A belt layer (7) is arranged on an outer circumferential side of the carcass layer (4) in the tread (3). The belt layer (7) is provided so as to overlap an outer periphery of a crown of the carcass layer (4), and it may be constituted by one belt ply or a plurality of belt plies. In this example, the belt layer (7) is constituted by two belt plies, that is, a first belt ply (7A) on an inner side and a second belt ply (7B) on an outer side. These belt plies are formed by wrapping belt cords, such as steel cords, with rubber. The belt cords are each inclined at a constant angle to the circumferential direction of the tire and are arranged at predetermined intervals in the width direction of the tire.The belt cords are arranged between the two belt layers (7A) and (7B) in such a way that they overlap (i.e., they are inclined left-right symmetrically with respect to the circumferential direction of the tire).

[0019] On an outer circumferential side of the belt layer (7), a belt reinforcing layer (9) is provided between the belt layer (7) and a tread rubber (8). In this example, the belt reinforcing layer (9) is a cover layer extending across the entire width of the belt layer (7). The belt reinforcing layer (9) is formed from organic fiber cords arranged substantially parallel to the tire circumferential direction, and is formed by coating the organic fiber cords with rubber.The belt reinforcing layer (9) tightens the belt layer (7) in the circumferential direction of the tire to achieve a hoop effect to improve rigidity in the circumferential and radial directions of the tire and to improve the belt bonding force, thereby preventing belt lift-off, diameter increase, and belt edge deformation caused by centrifugal force during high-speed driving, thus improving durability and high-speed driving stability.

[0020] In the present embodiment, in the belt layer, the angle of the belt cord with respect to the tire circumferential direction (hereinafter also simply referred to as belt angle) is set to be more than 30 degrees and 40 degrees or less. That is, in a case where the belt layer is formed of one belt ply, a belt angle of the one belt ply is set to be more than 30 degrees and 40 degrees or less, and in a case where the belt layer is formed of a plurality of belt plies, the belt angles of the plurality of belt plies in which belt cords are arranged to intersect each other are all set to be more than 30 degrees and 40 degrees or less with respect to the tire circumferential direction. By setting the belt angle to more than 30 degrees, wet braking performance and driving stability can be improved.By setting the belt angle to 40 degrees or less, a decrease in tire circumferential rigidity and thus a decrease in high-speed durability can be prevented. The belt angle is preferably 31 degrees or more and 37 degrees or less, and more preferably 32 degrees or more and 35 degrees or less.

[0021] The load LASE0.5% (N) at 0.5% elongation of the belt cord is not particularly limited and can be, for example, 50 N to 400 N or 100 N to 300 N. The value of LASE0.5% can be adjusted, for example, by the number of filaments, the diameter of the filaments, and the carbon content (mass percent) of the filaments.

[0022] The number of cords E of the belt cord is not particularly limited and it can be, for example, 10 to 40 per inch, 15 to 35 per inch or 15 to 30 per inch.

[0023] The organic fiber cord used in the belt reinforcing layer according to the present embodiment is not particularly limited, as long as the organic fiber cord is a hybrid cord formed by twisting an aramid yarn and a nylon yarn together. By using such a hybrid cord, the bonding force in the tire circumferential direction can be improved.

[0024] Examples of the nylon fibers are nylon 6, nylon 66, and nylon 46. The aramid fiber may be a para-aramid fiber or a meta-aramid fiber, and yarn formed from a known aramid fiber may be used.

[0025] The fineness D of organic fiber cords is not particularly limited and can be, for example, 1000 dtex to 4000 dtex, 1500 dtex to 3500 dtex, or 1800 dtex to 3000 dtex. The twist ratio T of the organic fiber cord is also not particularly limited and can be, for example, 20 to 60 per 10 cm or 25 to 55 per 10 cm. The twist ratio of a primary twist can be set to the same value as the twist ratio of a secondary twist.

[0026] In the present embodiment, in the belt reinforcing layer, the product (i.e., LASE5% × E) of a load LASE5% (N) at 5% elongation of the organic fiber cord and the cord number E (per 25 mm) of the organic fiber cord is preferably 2000 N or more, and more preferably, it is 2100 N or more, and even more preferably, it is 2200 N or more. The upper limit thereof is not particularly limited, and it may be 5000 N or less, or it may be 4000 N or less. When the product of the LASE5% and the cord number E is 2000 N or more, the belt bonding force is improved, and excellent high-speed durability, excellent handling stability, and excellent rolling resistance are easily achieved.

[0027] The LASE5% value of the organic fiber cord can be, for example, 65 N to 200 N, 70 N to 180 N, or 80 N to 160 N. The LASE5% value can be adjusted, for example, by selecting the type of cord constituting the organic fiber cord and adjusting the twist ratio and cord treatment conditions. For example, the LASE5% value can be increased by decreasing the twist ratio. The cord treatment conditions also include the conditions of a dipping treatment in which the organic fiber cord is immersed in a resin solution to perform an adhesion treatment with rubber (formulation of the resin solution, treatment temperature, tension, time, and the like). Accordingly, the physical properties of the organic fiber cord can be adjusted.For example, if the dip treatment is performed with a resin solution such as resorcinol formaldehyde latex (RFL) or an aqueous solution containing blocked isocyanate, the LASE5% value can be increased by using a low-temperature bath and applying high tension to the organic fiber cord. Here, the LASE5% value is measured according to JIS L1017.

[0028] The cord count (final count) E of the organic fiber cord is not particularly limited and can be appropriately adjusted according to the LASE5% value so that the product of LASE5% and the cord count E falls within the above-mentioned range. For example, the cord count E can be in a range of 23 to 40 per 25 mm.

[0029] In the present embodiment, the thus-obtained organic fiber cord is arranged in the belt reinforcing layer in such a manner that the ratio (Sr / Sc) of the cross-sectional area of ​​the rubber (Sr) to the cross-sectional area of ​​the cord (Sc) is 1.5 to 2.0. When the ratio is 1.5 or more, excellent high-speed durability can be easily achieved. Furthermore, when the ratio is 2.0 or less, the amount of rubber is reduced and excellent rolling resistance is easily achieved.

[0030] Here are, as in the Fig.2, the cross-sectional area of ​​the cord (Sc) and the cross-sectional area of ​​the rubber (Sr) are the cross-sectional areas of an organic fiber cord (10) and a rubber (11), respectively, in a cross section in the component width direction, which are obtained by cutting the belt reinforcing layer (9) along its width direction. The cross section in the component width direction is a cross section obtained by cutting the belt reinforcing layer (9) perpendicular to an extending direction of the organic fiber cord (10). Furthermore, the ratio (Sr / Sc) can be obtained by dividing the cross-sectional area of ​​the rubber (Sr) by the cross-sectional area of ​​the cord (Sc). For example, the Sr / Sc per cord (Sr / Sc for each cord divided by dashed lines in the Fig.2) Calculated by calculating a cross-sectional area of ​​the cord per 25 mm width of the belt reinforcing layer (9) from a cord number and a cord diameter of the organic fiber cord (10), by calculating a cross-sectional area of ​​the rubber per 25 mm width from a cross-sectional area of ​​the belt reinforcing layer calculated from a thickness (t) of the belt reinforcing layer (9) and the cross-sectional area of ​​the cord, and by dividing the cross-sectional area of ​​the rubber by the cross-sectional area of ​​the cord. When the cord number of the organic fiber cord (10) is constant in the width direction of the belt reinforcing layer (9), the value per cord is used as the Sr / Sc of the belt reinforcing layer (9).When the cord number of the organic fiber cord (10) changes in the width direction of the belt reinforcing layer (9), an average value of the Sr / Sc of the respective cords can be calculated as described above.

[0031] In the present embodiment, the belt layer and the belt reinforcement layer are set in such a manner that a value obtained by dividing by 1000 a sum of a product (A) of the load LASE5% (N) at 5% elongation of the organic fiber cord, the number of cords (per 25 mm), and the number of belt reinforcement layers, and a product (B) of the load LASE0.5% (N) at 0.5% elongation of the belt cord, cosθ, where the belt angle is defined as θ, the number of cords, and the number of belt layers is 11 or more. The upper limit is not particularly limited, and it may be 15 or less, or it may be 14 or less.When this value is within the above range, the binding force in a circumferential direction of the belt is improved, and the shape of the ground contact is improved, and thus excellent driving stability, excellent wet braking performance, excellent ride comfort and excellent rolling resistance can be easily achieved.

[0032] Using the belt cord and the above-described organic fiber cord, a green tire (green tire) is manufactured in a state where the belt reinforcing layer is wound around the outer peripheral side of the belt layer, and the resulting green tire is vulcanized and molded to obtain a pneumatic tire. When the belt layer is formed on the carcass layer, a wide rubber-coated sheet in which the belt cords are aligned and arranged in an inclined manner may be wound once on the carcass layer.When the belt reinforcement layer is formed on the belt layer, one or more organic fiber cords may be aligned and covered with rubber, spirally wound on the belt layer of the green tire, or a wide rubber-coated sheet in which the organic fiber cords are aligned may be wound once on the belt layer. Preferably, the belt reinforcement layer is spirally wound in the former manner. [Examples]

[0033] The invention will now be described in more detail with reference to examples, although the invention is not limited to these examples. [Measurement and testing methods]

[0034] The measurement and testing methods in the examples are as follows. (Cord testing method) - Cord diameter: A cord made of organic fibers was bent into four sections in such a way that a twist thereof did not untwist, and the four sections were aligned so that they had not loosened and they were arranged in parallel, then a measurement was carried out using a predetermined fine indicator (a diameter of a leg (measuring element) was 9.5 ± 0.03 mm, a load was 1666 ± 29.4 mN) by dropping the leg from a height of about 6.5 mm. - Cord strength: The load at which a specimen fractured was determined for the organic fiber cord by allowing the organic fiber cord to stand for 24 hours at a constant temperature of 20°C and 65% relative humidity, followed by a tensile test at 20°C according to JIS L1017. For the belt cord, a load at which the specimen fractured was determined in a tensile test according to JIS G3510. - LASE5%: A load at 5% elongation was obtained when the organic fiber cord was left to stand for 24 hours at a constant temperature of 20°C and 65% relative humidity and then subjected to a tensile test at 20°C according to JIS L1017. - LASE0.5%: A load at 0.5% elongation was obtained when the belt cord was subjected to a tensile test according to JIS G3510. (Tire testing procedure) - Belt angle: The angle of the belt cord with respect to the circumferential direction of the tire on the tire equator (at the center of the tread in the width direction) was measured for a deflated tire. - Tire high-speed durability: The FMVSS 109 (UTQG) standard was applied. A smooth-surface steel drum tester with a diameter of 1700 mm was used. The tire inflation pressure was 220 kPa and the load was 88% of the maximum load specified by JATMA. After a 60-minute break-in period at 80 km / h, the tire was allowed to cool, and after the inflation pressure was readjusted, a formal test was conducted. The formal test began at 120 km / h, the speed was gradually increased by 8 km / h every 30 minutes, and the test continued until failure occurred. The test distance until failure occurred was expressed as an index, with a tire having a value of 100 for Comparative Example 1. A larger number indicates better high-speed durability. - Rolling resistance: The rolling resistance of the tire was measured with a rolling resistance meter under conditions of an internal tire pressure of 250 kPa, a rim size of 19 × 7.5 J, a load of 5.6 kN, and a speed of 80 km / h. The reciprocal of this value is expressed as an index, with a corresponding example receiving a value of 100, and a higher index indicates lower rolling resistance and better fuel consumption. - Driving comfort: Each tire was set to an internal pressure of 260 kPa using a standard JIS rim, four tires of the same type were placed on a 2000 cm 3-passenger cars from Japan, the ride comfort was sensorily evaluated by three test drivers on a test track with smooth and rough roads, and the evaluation was conducted based on Comparative Example 1. Those corresponding to Comparative Example 1 are marked "good," those with lower performance are marked "poor," and those with higher performance are marked "excellent." - Actual vehicle driving stability: Test tires, each mounted at an internal pressure of 260 kPa, were mounted on a 2000 cc test vehicle and driven on a test track by three trained test drivers for sensory evaluation. Scores were rated on a scale of 1 to 10, and a relative comparison was conducted. The tire of Comparative Example 1 received a score of 6, and the average score of the three test drivers was expressed as an index, with the tire of Comparative Example 1 receiving a score of 100. A higher index indicates better driving stability. - Wet braking performance: Test tires, each mounted at an internal pressure of 260 kPa, were mounted on a test vehicle with a displacement of 2000 cc, and the water depth on the road surface was set to 1 mm. The distance between the brake pedal being depressed at a speed of 100 km / h and the vehicle coming to a standstill was measured, and the reciprocal of this value was expressed as an index, with the tire of Comparative Example 1 having a value of 100. A larger index indicates better wet braking performance. [Examples and comparative examples]

[0035] A pneumatic radial tire of a passenger car, which has a tire size of 225 / 45ZR19 96Y and which has the Fig.A tire containing the belt reinforcing layer (9) shown in Figure 1 was experimentally prepared. The belt angle of a belt layer and the configuration of the organic fiber cords constituting the belt reinforcing layer (cover layer) were as shown in Table 1 below for each of the tires in the Examples and Comparative Examples, and the other configurations were the same for all the tires.

[0036] Specifically, as the belt layer, two steel cords of 2 + 2 × 0.25 mm were arranged at the belt angle shown in Table 1 and with the number of cords shown in Table 1.

[0037] With respect to a cord structure, "1100 dtex / 1 + 940 dtex / 1" means a double-twisted structure obtained by twisting together a yarn made of aramid fibers with a nominal fineness of 1100 dtex and a yarn made of nylon fibers with a nominal fineness of 940 dtex. "1670 dtex / 1 + 940 dtex / 1" means a double-twisted structure obtained by twisting together a yarn made of aramid fibers with a nominal fineness of 1670 dtex and a yarn made of nylon fibers with a nominal fineness of 940 dtex.

[0038] The resulting tires were used to evaluate high-speed durability, rolling resistance, ride comfort, handling stability, and wet braking performance. The results are shown in Table 1. [Table 1] Comparison example 1 Example 1 Example 2 Example 3 Example 4 Comparison example 2 Comparison example 3 Comparison example 4 Comparison example 5 Belt reinforcement layer Cord material nylon Aramid / Nylon Aramid / Nylon Aramid / Nylon Aramid / Nylon Aramid / Nylon Aramid / Nylon Aramid / Nylon Aramid / Nylon Corduroy structure 1400 dtex / 2 1100 dtex / 1 + 940 dtex / 1 1100 dtex / 1 + 940 dtex / 1 1100 dtex / 1 + 940 dtex / 1 1670 dtex / 1 + 940 dtex / 1 1100 dtex / 1 + 940 dtex / 1 1100 dtex / 1 + 940 dtex / 1 1100 dtex / 1 + 940 dtex / 1 1100 dtex / 1 + 940 dtex / 1 Nominal fineness (dtex) 2800 2040 2040 2040 2610 2040 2040 2040 2040 Final twist degree (per 10 cm) 38 36 36 36 30 36 36 36 57 Cord diameter (mm) 0,67 0,55 0,55 0,55 0,65 0,55 0,55 0,55 0,59 Cord thickness (N) 220 216 216 216 340 216 216 216 156 Modulus at 5% elongation (LASE5%) (N) 30.0 73.0 73.0 73.0 149.6 73.0 73.0 73.0 57.9 LASE5% × number of cords (N / 25 mm) 915 2592 2592 2592 3741 2592 2592 2592 2057 Component thickness of the belt reinforcement layer (mm) 1,00 1,00 0,85 0,85 0,95 1,10 0,80 1,00 1,00 Number of cords (per 25 mm) 30,5 35,5 35,5 35,5 25,0 35,5 35,5 35,5 35,5 Ratio (Sr / Sc) of the cross-sectional area of ​​the rubber (Sr) to the cross-sectional area of ​​the cord ((Sc) 1,32 1,96 1,52 1,52 1,86 2,26 1,37 1,96 1,58 Number of belt reinforcement layers 2 2 2 2 2 2 2 2 2 Belt layer Belt angle (°) 33 33 33 39 33 33 33 41 40 Cord thickness (N) 617 617 617 617 617 617 617 617 617 Modulus at 0.5% strain (LASE0.5%) (N) 180 180 180 180 180 180 180 180 180 Number of belt reinforcement layers 2 2 2 2 2 2 2 2 2 Number of cords (per inch) 21 21 21 21 21 21 21 21 21 LASE0.5% × cos[belt angle] × number of cords (N / inch) 3170 3170 3170 2938 3170 3170 3170 2853 2896 (A+B) / 1000A = LASE5% × number of cords × number of belt reinforcement layersB = LASE0.5% × cos[belt angle] × number of cords × number of belt layers 8,2 11,5 11,5 11,1 13,8 11,5 11,5 10,9 9,9 Durability at high speeds 100 109 103 103 110 105 98 101 101 Rolling resistance 100 106 108 108 108 98 108 99 98 Driving comfort good excellent excellent excellent excellent excellent excellent excellent excellent Actual driving stability of the vehicle 100 128 128 128 133 116 122 106 106 Braking performance in wet conditions 100 106 107 105 108 102 104 100 100

[0039] As shown in Table 1, Comparative Example 2 is an example in which the ratio (Sr / Sc) of the cross-sectional area of ​​the rubber (Sr) to the cross-sectional area of ​​the cord (Sc) exceeds the upper limit and in which the rolling resistance is worse than that of Comparative Example 1.

[0040] Comparative Example 3 is an example in which the ratio (Sr / Sc) of the cross-sectional area of ​​the rubber (Sr) to the cross-sectional area of ​​the cord (Sc) is smaller than the lower limit, and its high-speed durability is inferior to that of Comparative Example 1.

[0041] Comparative Example 4 is an example where the belt angle exceeds the upper limit. Compared with Comparative Example 1, Comparative Example 4 has poorer rolling resistance and its wet braking performance is not improved.

[0042] Comparative Example 5 is an example where the value of (A+B) / 1000 is smaller than the lower limit, compared with Comparative Example 1, Comparative Example 5 has worse rolling resistance and its wet braking performance is not improved.

[0043] Although specific embodiments of the invention have been described above, these embodiments have been presented only as examples and are not intended to limit the scope of the invention. These embodiments may be implemented in various other forms, and various omissions, substitutions, and changes may be made without departing from the spirit of the invention. These embodiments and their omissions, substitutions, and changes are included in the invention described in the claims and their equivalents, as well as within the scope and spirit of the invention. [Industrial applicability]

[0044] The embodiment of the invention can be suitably used for various pneumatic tires, such as a passenger car tire. List of reference symbols 1 bead 2 side wall 3 Tread 4 carcass layers 5 Bead core 7 belt layer 8 Tread rubber 9 Belt reinforcement layer 10 Cord made of organic fibers 11 Rubber

Claims

[1] Pneumatic tire which has: a belt layer (7) in which a belt cord is arranged on an outer peripheral side of a carcass layer (4) in a tread (3) so as to be inclined with respect to a circumferential direction of the tire, and a belt reinforcing layer (9) in which a cord (10) of organic fibers is arranged along the circumferential direction of the tire on an outer circumferential side of the belt layer (7), wherein in the belt layer (7) an angle of the belt cord with respect to the circumferential direction of the tyre is more than 30 degrees and 40 degrees or less, the cord (10) made of organic fibres is a hybrid cord formed by twisting together an aramid yarn and a nylon yarn, the belt reinforcing layer (9) is formed by coating the cord (10) of organic fibers with a rubber (11), and a ratio (Sr / Sc) of a cross-sectional area of ​​the rubber (Sr) to a cross-sectional area of ​​the cord (Sc) is 1.5 to 2.0, and a value obtained by dividing a sum of a product (A) of a load LASE5% (N) at 5% elongation of the organic fiber cord (10), a cord number (per 25 mm), and the number of belt reinforcing layers (9) and a product (B) of a load (N) at 0.5% elongation of the belt cord, cosθ, where a belt angle is defined as θ, a cord number (per inch), and the number of belt layers (7) by 1000 is 11 or more. [2] A pneumatic tire according to claim 1, wherein the product of the load LASE5% (N) at 5% elongation of the organic fiber cord (10) and the cord number (per 25 mm) is 2000 (N / 25 mm) or more. [3] Pneumatic tire according to claim 1, wherein the load LASE5% (N) at 5% elongation of the organic fibre cord (10) is 65 or more, and the number of cords (per 25 mm) is 23 to 40. [4] Pneumatic tire according to claim 2, wherein the load LASE5% (N) at 5% elongation of the organic fibre cord (10) is 65 or more, and the number of cords (per 25 mm) is 23 to 40.

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