Pneumatic tire

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 reinforcement layer 9 in which organic fiber cords are arrayed along a tire circumferential direction on an outer peripheral side of a belt layer 7. In the belt layer, an angle of 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. A ratio (Sr / Sc) of a rubber cross-sectional area to a cord cross-sectional area of the belt reinforcement layer satisfies 1.0-1.5. Further, in the pneumatic tire, a value obtained by dividing a sum of a product (A) of a load LASE5% (N) at 5% elongation of the organic fiber cords, the number of implantation (pieces / 25 mm) and the number of belt reinforcement layers, and a product (B) of a load (N) at 0.5% elongation of the belt cords, cosθ in which θ denotes a belt angle, the number of implantation (pieces / inch) and the number of belt layers, by 1000 is 8.7 or higher.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to pneumatic tires.

Background Art

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

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, the belt layer is formed by arranging belt cords such as steel cords in an inclined manner with respect to the tire circumferential direction, and the angle of the belt cords with respect to the tire circumferential direction is generally set to around 20 degrees. If such an angle of the belt cords is set larger than usual, for example, exceeding 30 degrees, the braking performance (wet braking performance) and handling stability on a wet road surface can be improved. However, when the angle of the belt cords is increased, the rigidity of the belt layer in the tire circumferential direction decreases, and as a result, the contact shape deteriorates, leading to problems such as a decrease in high-speed durability, riding comfort, and rolling resistance.

[0005] In view of the above, an embodiment of the present invention aims to provide a pneumatic tire capable of improving high-speed durability, riding comfort, and rolling resistance while maintaining wet braking performance and handling stability by increasing the angle of the belt cord.

Means for Solving the Problems

[0006] A pneumatic tire according to an embodiment of the present invention includes a belt layer in which belt cords are arranged obliquely with respect to the tire circumferential direction on the outer peripheral side of the carcass layer in the 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. In the pneumatic tire, the angle of the belt cord with respect to the tire circumferential direction in the belt layer is more than 30 degrees and 40 degrees or less, the organic fiber cord is a double-twist cord of yarn made of organic fiber, the belt reinforcing layer is formed by covering the organic fiber cord with rubber, the ratio (Sr / Sc) of the rubber cross-sectional area (Sr) to the cord cross-sectional area (Sc) satisfies 1.0 to 1.5, and the value obtained by dividing the sum of the product (A) of the load at 5% elongation LASE5% (N) of the organic fiber cord, the number of cords per 25 mm, and the number of belt reinforcing layers, the load at 0.5% elongation (N) of the belt cord, cosθ where θ is the belt angle, the number of cords per inch, and the number of belt layers by 1000 is 8.7 or more.

[0007] The organic fiber cord can be a double-twist cord of yarn made of nylon 66.

[0008] The product of the load at 5% elongation LASE5% (N) of the organic fiber cord and the number of cords per 25 mm can be 1000 (N / 25 mm) or more.

Advantages of the Invention

[0009] According to the embodiment of the present invention, by setting the angle of the belt cord to more than 30 degrees and 40 degrees or less, it is possible to improve high-speed durability, riding comfort, and rolling resistance while maintaining wet braking performance and handling stability.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described in detail.

[0012] The pneumatic tire according to this embodiment is characterized by the configuration of a belt layer and a belt reinforcing layer disposed on the outer peripheral side of the belt layer.

[0013] The belt layer is composed of at least one belt ply in which belt cords are arranged obliquely with respect to the tire circumferential direction on the outer peripheral side (i.e., the outer side in the tire radial direction) of the carcass layer in the tread.

[0014] The belt reinforcing layer is composed of organic fiber cords arranged along the tire circumferential direction (equatorial plane) on the outer peripheral 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, that is, at an angle of substantially 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 covering the entire width direction of the belt layer, or an edge ply covering the belt ends.

[0015] FIG. 1 is a semi - sectional view of a passenger car pneumatic radial tire as an example of a pneumatic tire. This tire is composed of a pair of left - and - right beads (1) and sidewalls (2), and a tread (3) provided between both sidewalls (2), and a toroidal - extending carcass layer (4) is provided between the pair of beads (1).

[0016] The carcass layer (4) is locked by being folded from the tread (3) through the sidewall (2) and then from the inside to the outside by the bead core (5) at the bead (1). The carcass layer (4) is composed of at least one ply formed by arranging carcass cords made of organic fibers substantially perpendicular to the tire circumferential direction.

[0017] 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 so as to overlap the outer periphery of the crown of the carcass layer (4), and can be composed of one or a plurality of belt plies. In this example, it is composed of two plies, an inner first belt ply (7A) and an outer second belt ply (7B). These belt plies are formed by coating a belt cord such as a steel cord with rubber. 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, and are arranged so that the belt cords cross each other (that is, are inclined symmetrically with respect to the tire circumferential direction) between the two belt plies (7A) and (7B).

[0018] A belt reinforcing layer (9) is provided between the belt layer (7) and the tread rubber (8) on the outer peripheral side of the belt layer (7). The belt reinforcing layer (9) is a cap ply that covers the entire width of the belt layer (7) in this example. The belt reinforcing layer (9) is composed of organic fiber cords arranged substantially parallel to the tire circumferential direction and coated with rubber. The belt reinforcing layer (9) tightens the belt layer (7) in the circumferential direction to obtain a tuck effect that increases the rigidity in the tire circumferential and radial directions and the belt restraint force, suppresses the lifting and radial growth of the belt and the distortion at the belt end due to the centrifugal force during high-speed running, and improves the durability performance and handling stability at high speeds.

[0019] 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 be more than 30 degrees and 40 degrees or less. That is, when the belt layer is composed of a single belt ply, the belt angle of the single belt ply is set to be more than 30 degrees and 40 degrees or less. When the belt layer is composed of a plurality of belt plies, the belt angles of the plurality of belt plies arranged such that the belt cords cross 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 be greater than 30 degrees, wet braking performance and handling stability can be improved. By setting the belt angle to be 40 degrees or less, a decrease in rigidity in the tire circumferential direction can be suppressed, and a decrease in high-speed durability can be suppressed. 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.

[0020] The load LASE0.5% (N) at 0.5% elongation of the belt cord is not particularly limited, and may be, for example, 100 to 400 N, or may be 150 to 400 N. The value of LASE0.5% can be adjusted, for example, by the number of filaments, the diameter of the filaments, the carbon content (mass%) of the filaments, and the like.

[0021] The number of belt cords E driven in is not particularly limited, and may be, for example, 10 to 30 cords / inch, may be 10 to 28 cords / inch, or may be 10 to 26 cords / inch.

[0022] Regarding the organic fiber cord used for the belt reinforcing layer of this embodiment, the type of organic fiber is not particularly limited, and various organic fibers such as nylon fiber, aramid fiber, polyester fiber, and rayon fiber can be used. Among these, nylon fiber is preferable. The twist structure of the cord may be a double-twist structure. When the twist structure of the cord is a double-twist structure, the convergence is high, and the filaments constituting the cord are less likely to locally buckle against compression and bending deformation, and the fatigue resistance is excellent.

[0023] Here, examples of the nylon fiber include nylon 6, nylon 66, nylon 46, etc. As for the aramid fiber, either para-type or meta-type may be used, and known aramid fibers can be employed.

[0024] The fineness D of the organic fiber cord is not particularly limited, and may be, for example, 1000 to 4000 dtex, may be 1500 to 3500 dtex, or may be 1800 to 3000 dtex. The twist number T is also not particularly limited, and may be, for example, 20 to 60 turns / 10 cm, or may be 25 to 55 turns / 10 cm. Regarding the lower twist number, it may be set to the same value as the upper twist number.

[0025] In this embodiment, for the belt reinforcing layer, it is preferable that the product of the load LASE5% (N) at 5% elongation of the organic fiber cord and the number of driven-in organic fiber cords E (pieces / 25 mm) (that is, LASE5% × E) is 1000 N or more, preferably 1100 N or more, and more preferably 1200 N or more. The upper limit is not particularly limited, but may be 2500 N or less, may be 2000 N or less, or may be 1500 N or less. When the product of LASE5% and the number of driven-in cords E is 1000 N or more, it is easy to enhance the belt restraint force and obtain excellent high-speed durability, handling stability, and rolling resistance.

[0026] The LASE5% of the 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 value of LASE5% can be adjusted, for example, by selecting the type of fiber constituting the organic fiber cord, the number of twists, the processing conditions of the cord, etc. For example, by reducing the number of twists, LASE5% can be increased. Further, as the processing conditions of the cord, there are conditions for dip treatment (resin liquid formulation, processing temperature, tension, time, etc.) in which the organic fiber cord is immersed in a resin liquid for adhesion treatment with rubber, and the physical properties of the organic fiber cord can be adjusted thereby. For example, when performing dip treatment using a resin liquid such as resorcinol-formalin-latex (RFL) or an aqueous solution of blocked isocyanate, by using a low-temperature bath and setting the tension applied to the organic fiber cord high, LASE5% can be increased. Here, LASE5% is measured in accordance with JIS L1017.

[0027] The number of organic fiber cords driven in (number of ends) E is not particularly limited and can be appropriately set so that the product with the value of LASE5% satisfies the above range. For example, it may be 15 to 50 cords / 25 mm, 20 to 40 cords / 25 mm, or 25 to 35 cords / 25 mm.

[0028] In this embodiment, the organic fiber cord thus obtained is disposed 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. By this ratio being 1.0 or more, excellent high-speed durability is easily obtained. Further, by this ratio being 1.5 or less, it is easy to obtain excellent rolling resistance by suppressing the amount of rubber.

[0029] Here, as shown in FIG. 2, the cord cross-sectional area (Sc) and the rubber cross-sectional area (Sr) are the cross-sectional areas of the organic fiber cord (10) and the rubber (11), respectively, in the cross-section in the member width direction obtained by cutting the belt reinforcing layer (9) along its width direction. The cross-section in the member width direction is a cross-section obtained by cutting the belt reinforcing layer (9) perpendicularly to the extending direction of the organic fiber cord (10). Further, the ratio (Sr / Sc) can be obtained 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 width of the belt reinforcing layer (9) is calculated from the number of organic fiber cords (10) driven in and the cord diameter, and the rubber cross-sectional area per 25 mm 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 above cord cross-sectional area, and then the latter is divided by the former to calculate Sr / Sc per cord (Sr / Sc for each cord partitioned by the dotted line in FIG. 2). When the number of organic fiber cords (10) driven in is constant in the width direction of the belt reinforcing layer (9), this value per cord is taken as the Sr / Sc of the belt reinforcing layer (9). When the number of organic fiber cords (10) driven in varies in the width direction of the belt reinforcing layer (9), the average value of Sr / Sc of each cord calculated as described above may be calculated.

[0030] In the present embodiment, the value obtained by dividing the sum of the product (A) of the load LASE5% (N) at 5% elongation of the organic fiber cord, the number of cords driven in (number / 25 mm), and the number of belt reinforcing layers, and the product (B) of the load LASE0.5% (N) at 0.5% elongation of the belt cord, cosθ where the belt angle is θ, the number of cords driven in, and the number of belt layers by 1000 is set to be 8.7 or more, preferably 8.9 or more, and more preferably 9.2 or more. The upper limit is not particularly limited, but it may be 11.0 or less or 10.5 or less. When this value is within the above range, the restraint force in the belt circumferential direction is increased, the grounding shape is improved, and excellent handling stability, wet braking performance, riding comfort, and rolling resistance are easily obtained.

[0031] Using the belt cord and the organic fiber cord as described above, a green tire is produced with the belt reinforcing layer wound around the outer peripheral side of the belt layer, and an inflated tire is obtained by vulcanizing and molding the resulting green tire. When forming the belt reinforcing layer on the belt layer, one or a plurality of the above-described organic fiber cords aligned and rubber-coated are spirally wound around the belt layer of the green tire, or a wide rubber-coated sheet with the organic fiber cords aligned may be wound once around the belt layer. Preferably, it is the former, i.e., spirally winding.

Examples

[0032] Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited to these examples.

[0033] [Measurement method · Test method] The measurement methods and test methods in the examples are as follows.

[0034] (Cord test method) · Cord diameter: One organic fiber cord is bent into four pieces so that the twist does not return, aligned without sagging and arranged in parallel, and a predetermined dial gauge (the diameter of the legs (measuring elements) is 9.5 ± 0.03 mm, load 1666 ± 29.4 mN) is used to drop the legs from a height of about 6.5 mm for measurement.

[0035] · Cord strength: For the organic fiber cord, in accordance with JIS L1017, after leaving the organic fiber cord in a constant temperature condition of 20°C and 65% RH for 24 hours, the load at the time of cutting of the sample when a tensile test was conducted at 20°C was determined. For the belt cord, in accordance with JIS G3510, the load at the time of cutting of the sample when a tensile test was conducted was determined.

[0036] · LASE5%: In accordance with JIS L1017, after leaving the organic fiber cord in a constant temperature condition of 20°C and 65% RH for 24 hours, the load at 5% elongation when a tensile test was conducted at 20°C was determined.

[0037] · LASE 0.5%: The load at 0.5% elongation when conducting a tensile test was determined in accordance with JIS G3510.

[0038] (Tire Test Method) · Belt Angle: For a tire in an airless state, the angle of the belt cord with respect to the tire circumferential direction at the tire equator (center position in the width direction) of the tread was measured.

[0039] · Tire High-Speed Durability: Complies with FMVSS109 (UTQG). Using a drum tester made of steel with a smooth surface and a diameter of 1700 mm, with a tire internal pressure of 220 kPa and a load of 88% of the maximum load specified by JATMA. After a conditioning run at 80 km / h for 60 minutes and then cooling, the air pressure was adjusted again and then the main run was carried out. The main run started at 120 km / h and the speed was gradually increased by 8 km / h every 30 minutes until a failure occurred. The running distance until a failure occurred was expressed as an index with the tire of Comparative Example 1 taken as 100. The larger the number, the better the high-speed durability.

[0040] · Rolling Resistance: Using a rolling resistance tester, the rolling resistance of the tire was measured under the conditions of a tire internal pressure of 250 KPa, a rim size of 19×7.5J, a load of 5.6 kN, and a speed of 80 km / h. The reciprocal was expressed as an index with the conventional example taken as 100. The larger the index, the smaller the rolling resistance and the better the low fuel consumption performance.

[0041] · Ride Comfort: Each tire was adjusted to an internal pressure of 260 kPa using a JIS standard rim, and four tires of the same type were installed on a 2000 cc domestic passenger car. The ride comfort was subjectively evaluated by three test drivers on test courses for good roads and bad roads and evaluated based on Comparative Example 1. Those equivalent to Comparative Example 1 were indicated by "○", those inferior by "×", and those superior by "◎".

[0042] ·On-vehicle handling stability: The test tire installed at an internal pressure of 260 kPa was mounted on a test vehicle with a displacement of 2000 cc, and three trained test drivers drove on a test course for sensory evaluation. The scoring was based on a 10-point scale, with the tire of Comparative Example 1 set at 6 points for relative comparison, and the average score of the three was expressed as an index with the tire of Comparative Example 1 set at 100. A larger number indicates better handling stability.

[0043] ·Wet braking performance: The test tire installed at an internal pressure of 260 kPa was 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 was measured when the vehicle stopped after stepping on the brake pedal at a speed of 100 km / h, and the reciprocal was expressed as an index with the tire of Comparative Example 1 set at 100. A larger number indicates better wet braking performance.

[0044] [Examples and Comparative Examples] A passenger car pneumatic radial tire with a tire size of 225 / 45ZR19 96Y and having a belt reinforcing layer (9) as shown in Fig. 1 was prototyped. The belt angle of the belt layer and the configuration of the organic fiber cords constituting the belt reinforcing layer (cap ply) are as shown in Table 1 below for each tire of the examples and comparative examples, and the other configurations were all common configurations.

[0045] Specifically, two belt layers were installed with 2 + 2 × 0.25 mm steel cords arranged at the belt angles and number of plies described in Table 1.

[0046] Regarding the cord structure, "1400 dtex / 2" means a double-twist structure obtained by twisting two single-twisted yarns with a nominal fineness of 1400 dtex.

[0047] Using each of the obtained tires, the high-speed durability, rolling resistance, ride comfort, on-vehicle handling stability, and wet braking performance of the tires were evaluated. The results are shown in Table 1.

[0048]

Table 1

[0049] As shown in Table 1, Comparative Example 2 is an example where the ratio (Sr / Sc) of the rubber cross-sectional area (Sr) to the cord cross-sectional area (Sc) exceeds the upper limit value, and the rolling resistance was inferior compared to Comparative Example 1.

[0050] Comparative Example 3 is an example where the ratio (Sr / Sc) of the rubber cross-sectional area (Sr) to the cord cross-sectional area (Sc) is less than the lower limit value, and the high-speed durability was inferior compared to Comparative Example 1.

[0051] Comparative Example 4 is an example where the belt angle exceeds the upper limit value. Compared to Comparative Example 1, the high-speed durability and wet braking performance were inferior, and also the rolling resistance and the actual vehicle handling stability did not improve.

[0052] Comparative Examples 5 and 6 are examples where the value of (A + B) / 1000 is less than the lower limit value, and none of the evaluations improved compared to Comparative Example 1.

[0053] As described above, some embodiments of the present invention have been explained. However, 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, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their omissions, replacements, changes, etc. are included in the scope and gist of the invention, and are also included in the invention described in the claims and its equivalent scope.

Industrial Applicability

[0054] The embodiments of the present invention can be suitably used for various pneumatic tires including passenger car tires.

Explanation of Signs

[0055] 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. In a pneumatic tire comprising a belt layer in which belt cords are arranged obliquely in the tire circumferential direction on the outer peripheral side of the carcass layer in the 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, in the belt layer, the angle of the belt cords with respect to the tire circumferential direction is more than 30 degrees and 40 degrees or less, the organic fiber cords are double-twist cords of yarns made of organic fibers, the belt reinforcing layer is formed by covering 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, a pneumatic tire, wherein a value obtained by dividing the sum of the product (A) of the 5% elongation load LASE5% (N) of the organic fiber cords, the number of cords per 25 mm, and the number of layers of the belt reinforcing layer, the 0.5% elongation load (N) of the belt cords, cosθ where θ is the belt angle, the number of cords per inch, and the number of layers of the belt layer by 1000 is 8.7 or more.

2. The pneumatic tire according to claim 1, wherein the organic fiber cords are double-twist cords of yarns made of nylon 66.

3. The pneumatic tire according to claim 1 or 2, wherein the product of the 5% elongation load LASE5% (N) of the organic fiber cords and the number of cords per 25 mm is 1000 (N / 25 mm) or more.

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