pneumatic tires

Abstract

To improve high speed durability, riding comfort, and rolling resistance, while maintaining wet braking performance and steering stability due to an incremented angle of a belt cord.SOLUTION: A pneumatic tire comprises: a belt layer in which belt cords are arranged in an inclined manner relative to a tire circumferential direction on an outer peripheral side of a carcass layer on a tread; and a belt reinforcement layer in which organic fiber cords are arrayed along the tire circumferential direction on an outer peripheral side of the belt layer. In the belt layer, an angle of the belt cords to the tire circumferential direction is larger than 30 degrees but equal to 40 degrees or less. The organic fiber cords are double-twisted cords of yarn made of organic fibers. Further, in the pneumatic tire, a product of a load LASE5% (N) at 5% elongation of the organic fiber cords, and the number of implantation (pieces / 25 mm) is 1000 (N / 25 mm) or more. In the belt reinforcement layer, the organic fiber cords are covered by rubber, and a ratio (Sr / Sc) of a rubber cross-sectional area (Sr) to a cord cross-sectional area (Sc) satisfies 1.0-1.5.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pneumatic tire. [Background technology]

[0002] For the purpose of improving the high-speed durability of tires, it is known to provide a belt reinforcing layer on the outer circumferential side of a belt layer, in which organic fiber cords such as nylon fiber cords are arranged substantially parallel to the tire circumferential direction (see Patent Documents 1 to 4). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-239069 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-75289 [Patent Document 3] Japanese Patent Application Laid-Open No. 2003-237309 [Patent Document 4] Japanese Patent Application Laid-Open No. 2017-81349 Summary of the Invention [Problem to be solved by the invention]

[0004] The belt layer is formed by arranging belt cords such as steel cords at an angle relative to the tire circumferential direction, and the angle of the belt cords relative to the tire circumferential direction is generally set to about 20 degrees. If the angle of the belt cords is set larger than usual, for example, to more than 30 degrees, braking performance on wet roads (wet braking performance) and handling stability can be improved. However, if the angle of the belt cords is increased, the rigidity of the belt layer in the tire circumferential direction decreases, which deteriorates the contact shape, resulting in problems such as reduced high-speed durability, ride comfort, and rolling resistance.

[0005] In view of the above, an embodiment of the present invention aims to provide a pneumatic tire that can improve high-speed durability, ride comfort, and rolling resistance while maintaining wet braking performance and handling stability achieved by increasing the angle of the belt cord. [Means for solving the problem]

[0006] A pneumatic tire according to an embodiment of the present invention comprises a belt layer in the tread, on the outer peripheral side of a carcass layer, in which belt cords are arranged at an angle with respect to the tire circumferential direction, and a belt reinforcing layer on the outer peripheral side of the belt layer, in which organic fiber cords are arranged along the tire circumferential direction, wherein the angle of the belt cords in the belt layer with respect to the tire circumferential direction is more than 30 degrees and not more than 40 degrees, the organic fiber cords are double-twisted cords of yarn made of organic fiber, the product of the load at 5% elongation (LASE5%) of the organic fiber cords and the end count (cords / 25mm) is 1000 (N / 25mm) or more, and the belt reinforcing layer is formed by coating the organic fiber cords with rubber, and the ratio (Sr / Sc) of the rubber cross-sectional area (Sr) to the cord cross-sectional area (Sc) satisfies 1.0 to 1.5.

[0007] The organic fiber cord may be a two-twisted cord of nylon 66 yarn. [Effects of the Invention]

[0008] According to an embodiment of the present invention, the angle of the belt cord is set to more than 30 degrees and not more than 40 degrees, and high-speed durability, ride comfort, and rolling resistance can be improved while maintaining wet braking performance and handling stability. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a half cross-sectional view of a pneumatic radial tire according to an embodiment. [Figure 2] FIG. 3 is a diagram schematically illustrating a part of a cross section of a belt reinforcing layer according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail.

[0011] The pneumatic tire according to this embodiment is characterized by the configuration of the belt layer and the belt reinforcing layer disposed on the outer peripheral side of the belt layer.

[0012] The belt layer is formed on the outer peripheral side of the carcass layer in the tread (that is, on the outer side in the tire radial direction) and is composed of at least one belt ply in which belt cords are arranged at an angle with respect to the tire circumferential direction.

[0013] The belt reinforcing layer is made of organic fiber cords arranged along the tire circumferential direction (equatorial plane) on the outer peripheral side of the belt layer (i.e., on the outer side in the tire radial direction). 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° (preferably an angle of 5° or less), and the cords are arranged at predetermined intervals in the tire width direction. Such a belt reinforcing layer may be a cap ply that covers the entire belt layer in the width direction, or an edge ply that covers the belt ends.

[0014] 1 is a half cross-sectional view of a pneumatic radial tire for passenger cars as an example of a pneumatic tire. The tire is configured with a pair of left and right beads 1 and sidewalls 2, a tread 3 provided between the sidewalls 2, and a carcass layer 4 extending toroidally between the pair of beads 1.

[0015] The carcass layer (4) runs from the tread (3) through the sidewalls (2) and is anchored by folding back from the inside to the outside at the bead cores (5) in the beads (1). The carcass layer (4) is composed of at least one ply of carcass cords made of organic fibers arranged substantially perpendicular to the circumferential direction of the tire.

[0016] A belt layer 7 is disposed on the outer peripheral side of the carcass layer 4 in the tread 3. The belt layer 7 is provided overlying the outer periphery of the crown of the carcass layer 4 and can be constituted by one or more belt plies. In this example, the belt layer 7 is constituted by two belt plies: an inner first belt ply 7A and an outer second belt ply 7B. These belt plies are made of belt cords such as steel cords coated with rubber, and the belt cords are inclined at a certain angle with respect to the tire circumferential direction and arranged at predetermined intervals in the tire width direction. The belt cords are disposed between the two belt plies 7A and 7B so as to cross each other (i.e., so as to be inclined symmetrically with respect to the tire circumferential direction).

[0017] A belt reinforcing layer (9) is provided on the outer circumferential side of the belt layer (7) between the belt layer (7) and the tread rubber (8). In this example, the belt reinforcing layer (9) is a cap ply that covers the entire width of the belt layer (7). The belt reinforcing layer (9) is made of organic fiber cords arranged substantially parallel to the tire circumferential direction, and the organic fiber cords are coated with rubber. The belt reinforcing layer (9) tightens the belt layer (7) in the circumferential direction, providing a hoop effect that increases the tire circumferential and radial rigidity and belt restraint force. This suppresses belt lift and radial growth and belt end distortion due to centrifugal force during high-speed driving, improving durability and handling stability at high speeds.

[0018] In this embodiment, in the belt layer, the angle of the belt cord with respect to the tire circumferential direction (hereinafter also simply referred to as the belt angle) is set to more than 30 degrees and not more than 40 degrees. That is, when the belt layer is made up of one belt ply, the belt angle of the one belt ply is set to more than 30 degrees and not more than 40 degrees, and when the belt layer is made up of multiple belt plies, the belt angles of the multiple belt plies, in which the belt cords are arranged so as to cross each other, are all set to more than 30 degrees and not more than 40 degrees with respect to the tire circumferential direction. By setting the belt angle to more than 30 degrees, it is possible to improve wet braking performance and handling stability. By setting the belt angle to not more than 40 degrees, it is possible to suppress a decrease in rigidity in the tire circumferential direction and suppress a decrease in high-speed durability. The belt angle is more preferably 31 degrees or more and 37 degrees or less, and even more preferably 32 degrees or more and 35 degrees or less.

[0019] The type of organic fiber used in the belt reinforcing layer of this embodiment is not particularly limited, and various organic fibers such as nylon fiber, aramid fiber, polyester fiber, and rayon fiber can be used, with nylon fiber being preferred. The twist structure of the cord may be a two-twist structure, and the two-twist structure of the cord provides high convergence, making the filaments that make up the cord less likely to buckle locally when compressed or bent, and providing excellent fatigue resistance.

[0020] Examples of nylon fibers include nylon 6, nylon 66, and nylon 46. Aramid fibers may be either para-type or meta-type, and known aramid fibers can be used.

[0021] The fineness D of the organic fiber cord is not particularly limited and may be, for example, 1000 to 4000 dtex, 1500 to 3500 dtex, or 1800 to 3000 dtex. The number of twists T is also not particularly limited and may be, for example, 20 to 60 turns / 10 cm or 25 to 55 turns / 10 cm. The number of first twists may be set to the same value as the number of final twists.

[0022] In this embodiment, the belt reinforcing layer is set so that the product of the load LASE5% (N) at 5% elongation of the organic fiber cord and the end count E of the organic fiber cord (lines / 25 mm) (i.e., LASE5% x E) is 1000 N or more. By setting the product of LASE5% and the end count E to 1000 N or more, the belt restraining force can be increased, thereby improving high-speed durability, handling stability, and rolling resistance. The product of LASE5% and the end count E is preferably 1100 N or more, and more preferably 1200 N or more. There is no particular upper limit, but it may be 2500 N or less, 2000 N or less, or 1500 N or less.

[0023] The LASE5% of an organic fiber cord is not particularly limited and may be, for example, 30 to 100 N, 35 to 90 N, or 40 to 80 N. The LASE5% value can be adjusted by, for example, selecting the type of fiber constituting the organic fiber cord, adjusting the number of twists, and cord processing conditions. For example, LASE5% can be increased by reducing the number of twists. Cord processing conditions include the conditions of the dip treatment in which the organic fiber cord is immersed in a resin liquid for adhesive treatment with rubber (resin liquid formulation, treatment temperature, tension, time, etc.), which can adjust the physical properties of the organic fiber cord. For example, when performing dip treatment using a resin liquid such as resorcinol-formalin-latex (RFL) or a blocked isocyanate aqueous solution, using a low-temperature bath and setting a high tension on the organic fiber cord can increase LASE5%. Here, LASE5% is measured in accordance with JIS L1017.

[0024] The number of ends (E) of the organic fiber cords is not particularly limited and can be appropriately set according to the value of LASE5% so that the product thereof satisfies the above range, and may be, for example, 15 to 50 cords / 25 mm, 20 to 40 cords / 25 mm, or 25 to 35 cords / 25 mm.

[0025] In this embodiment, the organic fiber cords thus obtained are arranged in the belt reinforcing layer so that the ratio (Sr / Sc) of the rubber cross-sectional area (Sr) to the cord cross-sectional area (Sc) satisfies 1.0 to 1.5. When this ratio is 1.0 or more, excellent high-speed durability is likely to be obtained. Furthermore, when this ratio is 1.5 or less, the amount of rubber can be reduced and excellent rolling resistance is likely to be obtained.

[0026] Here, the cord cross-sectional area (Sc) and the rubber cross-sectional area (Sr) are the cross-sectional areas of the organic fiber cords (10) and the rubber (11) in a cross-section of the belt reinforcing layer (9) in the width direction of the member, as shown in FIG. 2. The cross-section of the member in the width direction is a cross-section of the belt reinforcing layer (9) cut perpendicular to the extending direction of the organic fiber cords (10). The ratio (Sr / Sc) can be calculated by dividing the rubber cross-sectional area (Sr) by the cord cross-sectional area (Sc). For example, the cord cross-sectional area per 25 mm of the belt reinforcing layer (9) is calculated from the end count and cord diameter of the organic fiber cords (10), and the rubber cross-sectional area per 25 mm of the width is calculated from the cross-sectional area of ​​the belt reinforcing layer calculated from the thickness (t) of the belt reinforcing layer (9) and the cord cross-sectional area. The Sr / Sc per cord is calculated by dividing the latter by the former (Sr / Sc for each cord divided by the dotted line in FIG. 2). When the end count of the organic fiber cords 10 is constant across the width of the belt reinforcing layer 9, the value per cord is taken as the Sr / Sc of the belt reinforcing layer 9. When the end count of the organic fiber cords 10 varies across the width of the belt reinforcing layer 9, the average value of the Sr / Sc of each cord calculated as above can be calculated.

[0027] A green tire is produced using the organic fiber cords described above with a belt reinforcing layer wound around the outer periphery of the belt layer, and the resulting green tire is vulcanized to produce a pneumatic tire. When forming the belt reinforcing layer on the belt layer, one or more of the organic fiber cords described above, which are aligned and coated with rubber, may be wound spirally around the belt layer of the green tire, or a wide rubberized sheet made of aligned organic fiber cords may be wound around the belt layer once. The former spiral winding is preferred. [Example]

[0028] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0029] [Measurement and test methods] The measurement and test methods used in the examples are as follows.

[0030] (Code Test Method) Cord diameter: One organic fiber cord is bent into four strands to prevent the twist from returning, and then pulled together and arranged in parallel to prevent slack. Using a specified dial gauge (diameter of the legs (measuring probe) 9.5±0.03mm, load 1666±29.4mN), the legs are dropped from a height of approximately 6.5mm to measure.

[0031] Cord strength: In accordance with JIS L1017, an organic fiber cord was left at constant temperatures of 20°C and 65% RH for 24 hours, and then subjected to a tensile test at 20°C to determine the load at which the sample broke.

[0032] LASE 5%: In accordance with JIS L1017, the load at 5% elongation was determined when an organic fiber cord was left at constant temperature conditions of 20°C and 65% RH for 24 hours and then subjected to a tensile test at 20°C.

[0033] (Tire Testing Methods) Belt angle: For uninflated tires, the angle of the belt cord relative to the tire circumferential direction was measured at the tire equator (center position in the width direction) of the tread.

[0034] Tire high-speed durability: Compliant with FMVSS109 (UTQG). A 1700mm diameter drum tester with a smooth steel surface was used, with the tire internal pressure at 220kPa and a load of 88% of the maximum load specified by JATMA. After a 60-minute break-in run at 80km / h, the tire was allowed to cool, the air pressure was readjusted, and then the actual run began. The actual run began at 120km / h, and the speed was increased in steps of 8km / h every 30 minutes until failure occurred. The run distance until failure occurred was expressed as an index, with the tire of Comparative Example 1 set at 100. A higher number indicates better high-speed durability.

[0035] Rolling resistance: Using a rolling resistance tester, tire rolling resistance was measured under the following conditions: tire internal pressure 250 kPa, rim size 19 x 7.5 J, load 5.6 kN, and speed 80 km / h. The reciprocal of the rolling resistance was expressed as an index, with the conventional example being set at 100. The higher the index, the lower the rolling resistance and the better the fuel efficiency.

[0036] Ride comfort: Each tire was adjusted to an internal pressure of 260 kPa using a standard JIS rim, and four tires of the same type were mounted on a 2000 cc domestic passenger car. Three test drivers then conducted a sensory evaluation of the ride comfort on a test course with good and bad roads, with the evaluation being based on Comparative Example 1. Results equivalent to Comparative Example 1 are indicated by "○", results inferior by "×", and results superior by "◎".

[0037] Actual vehicle handling stability: Test tires mounted at an internal pressure of 260 kPa were mounted on a test vehicle with an engine displacement of 2000 cc, and three trained test drivers drove the vehicle on a test course and performed a sensory evaluation. Scoring was performed on a 10-point scale, with the tire of Comparative Example 1 given a score of 6, and the average score of the three drivers was expressed as an index, with the tire of Comparative Example 1 given a score of 100. The higher the number, the better the handling stability.

[0038] Wet braking performance: A test tire with an internal pressure of 260 kPa was mounted on a test vehicle with an engine displacement of 2000 cc, and the water depth on the road surface was set to 1 mm. The vehicle was stopped by pressing the brake pedal at a speed of 100 km / h, and the distance traveled was measured. The reciprocal of this distance was expressed as an index, with the tire of Comparative Example 1 set at 100. The larger the number, the better the wet braking performance.

[0039] [Examples and Comparative Examples] A pneumatic radial tire for a passenger car was produced as a prototype, having a tire size of 225 / 45ZR19 96Y and including a belt reinforcing layer (9) as shown in Fig. 1. The belt angle of the belt layer and the configuration of the organic fiber cords constituting the belt reinforcing layer (cap ply) were as shown in Table 1 below for each tire of the example and comparative example, and the other configurations were the same for all tires.

[0040] Specifically, two belt layers each having 2+2×0.25 mm steel cords arranged at the belt angle and end count shown in Table 1 were installed.

[0041] The number of plies in the belt reinforcing layer was set to two for all the tires of the examples and comparative examples.

[0042] Regarding the cord structure, "1400 dtex / 2" means that the cord has a two-ply structure obtained by twisting together two first-twisted yarns having a nominal fineness of 1400 dtex.

[0043] Using each of the resulting tires, the tire high-speed durability, rolling resistance, ride comfort, actual vehicle handling stability, and wet braking performance were evaluated. The results are shown in Table 1.

[0044] [Table 1]

[0045] As shown in Table 1, Comparative Example 2 is an example in which the ratio (Sr / Sc) of the rubber cross-sectional area (Sr) to the cord cross-sectional area (Sc) exceeds the upper limit, and the rolling resistance is inferior to that of Comparative Example 1.

[0046] Comparative Example 3 is an example in which the ratio (Sr / Sc) of the rubber cross-sectional area (Sr) to the cord cross-sectional area (Sc) is less than the lower limit, and was inferior to Comparative Example 1 in high-speed durability.

[0047] Comparative Example 4 is an example in which the belt angle exceeds the upper limit, and compared to Comparative Example 1, high-speed durability and wet braking performance were inferior, and rolling resistance and actual vehicle handling stability were not improved.

[0048] Comparative Example 5 is an example in which the product of LASE5% (N) and the number of threads driven (threads / 25 mm) is less than the lower limit, and compared to Comparative Example 1, no improvement was observed in any of the evaluations.

[0049] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their omissions, substitutions, modifications, etc. are included within the scope and spirit of the invention, as well as within the scope of the invention described in the claims and their equivalents. [Industrial Applicability]

[0050] The embodiment of the present invention can be suitably used for various pneumatic tires including tires for passenger cars. [Explanation of symbols]

[0051] 1... bead, 2... sidewall, 3... tread, 4... carcass layer, 5... bead core, 7... belt layer, 8... tread rubber, 9... belt reinforcing layer, 10... organic fiber cord, 11... rubber

Claims

1. A pneumatic tire including: a belt layer in which belt cords are arranged at an angle with respect to the tire circumferential direction on the outer peripheral side of a carcass layer in a tread; and a belt reinforcing layer in which organic fiber cords are arranged along the tire circumferential direction on the outer peripheral side of the belt layer, the belt layer has a belt cord whose angle with respect to the tire circumferential direction is more than 30 degrees and not more than 40 degrees, the organic fiber cord is a two-twisted cord of yarn made of organic fiber, the organic fiber cord has a load at 5% elongation (LASE5% (N)) of 30 to 100 N; the product of the load at 5% elongation (LASE5% (N)) of the organic fiber cord and the end count (cords / 25 mm) is 1440 to 2000 (N / 25 mm), The belt reinforcing layer is formed by coating the organic fiber cord with rubber, and the ratio (Sr / Sc) of the rubber cross-sectional area (Sr) to the cord cross-sectional area (Sc) satisfies 1.0 to 1.

5.

2. 2. The pneumatic tire according to claim 1, wherein the organic fiber cord is a two-ply cord of yarn made of nylon 66.

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