JP7699898B2 - Pneumatic tires - Google Patents

Description

The present invention relates to a pneumatic tire.

To improve the high-speed durability of tires, it is known to provide a belt reinforcing layer on the outer periphery of the 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).

JP 2005-239069 A JP 2005-75289 A JP 2003-237309 A JP 2017-81349 A

The belt layer is made of belt cords such as steel cords arranged at an angle to the tire circumferential direction, and the angle of the belt cords 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, it is possible to improve braking performance on wet road surfaces (wet braking performance) and steering stability. However, if the angle of the belt cords is made larger, the rigidity of the belt layer in the tire circumferential direction decreases, which deteriorates the ground contact shape, resulting in problems such as reduced high-speed durability, ride comfort, and rolling resistance.

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.

A pneumatic tire according to an embodiment of the present invention is a pneumatic tire having a belt layer in which belt cords are arranged at an angle 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 an angle of the belt cords with respect to the tire circumferential direction of the tire of more than 30 degrees and not more than 40 degrees, the organic fiber cords are double-twisted cords of yarn made of organic fibers, and the belt reinforcing layer is made of the organic fiber The fiber cord is covered with rubber, and the ratio (Sr/Sc) of the rubber cross-sectional area (Sr) to the cord cross-sectional area (Sc) is 1.0 to 1.5. The sum of the product (A) of the load at 5% elongation of the organic fiber cord (LASE5% (N)), the number of strands (strands/25 mm), and the number of belt reinforcing layers, the product (B) of the load at 0.5% elongation of the belt cord (N), cosθ where θ is the belt angle, the number of strands (strands/inch), and the number of belt layers, divided by 1000, is 8.7 or more.

The organic fiber cord may be a two-ply cord made of nylon 66 yarn.

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

According to an embodiment of the present invention, the angle of the belt cord is set to more than 30 degrees and less than 40 degrees, and high-speed durability, ride comfort, and rolling resistance can be improved while maintaining wet braking performance and handling stability.

1 is a half cross-sectional view of a pneumatic radial tire according to an embodiment. FIG. 2 is a schematic diagram showing a part of a cross section of a belt reinforcing layer according to an embodiment.

The following describes an embodiment of the present invention in detail.

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.

The belt layer is composed of at least one belt ply in which the belt cords are arranged at an angle to the circumferential direction of the tire on the outer peripheral side of the carcass layer in the tread (i.e., on the radially outer side of the tire).

The belt reinforcing layer is made of organic fiber cords arranged along the tire circumferential direction (equatorial plane) on the outer circumferential 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 a predetermined interval in the tire width direction. Such a belt reinforcing layer may be a cap ply that covers the entire width direction of the belt layer, or an edge ply that covers the belt ends.

Figure 1 is a half cross-sectional view of a pneumatic radial tire for passenger cars as an example of a pneumatic tire. This tire is composed of a pair of beads (1) and sidewalls (2) on the left and right, and a tread (3) provided between the two sidewalls (2), and a carcass layer (4) extending in a toroidal shape is provided between the pair of beads (1).

The carcass layer (4) runs from the tread (3) through the sidewall (2) and is secured to the bead (1) by folding back from the inside to the outside at the bead core (5). The carcass layer (4) is made of at least one ply of carcass cords made of organic fibers arranged substantially perpendicular to the circumferential direction of the tire.

A belt layer (7) is disposed on the outer periphery of the carcass layer (4) in the tread (3). The belt layer (7) is provided over the outer periphery of the crown of the carcass layer (4) and can be composed of one or more belt plies. In this example, it is composed of two layers, 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 covered with rubber, and the belt cords are inclined at a certain angle with respect to the tire circumferential direction and arranged at a certain interval in the tire width direction. Between the two belt plies (7A) and (7B), the belt cords are arranged so as to cross each other (i.e., so as to be inclined symmetrically with respect to the tire circumferential direction).

On the outer periphery of the belt layer (7), a belt reinforcing layer (9) is provided 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, and has a hoop effect that increases the rigidity and belt restraining force in the tire circumferential and radial directions, suppresses the belt from rising up or growing in diameter due to centrifugal force during high-speed driving, and distortion of the belt ends, improving durability performance and handling stability at high speeds.

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 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 of multiple belt plies, the belt angles of the multiple belt plies arranged so that the belt cords 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 be greater than 30 degrees, it is possible to improve wet braking performance and steering stability. By setting the belt angle to be not more than 40 degrees, it is possible to suppress the decrease in rigidity in the tire circumferential direction and suppress the 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.

The load LASE0.5% (N) of the belt cord at 0.5% elongation is not particularly limited and may be, for example, 100 to 400 N or 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, etc.

The number of strands E of the belt cord is not particularly limited, and may be, for example, 10 to 30 strands/inch, 10 to 28 strands/inch, or 10 to 26 strands/inch.

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, but nylon fiber is preferable. The twist structure of the cord may be a double twist structure, and the double twist structure of the cord provides high convergence, and the filaments that make up the cord are less likely to buckle locally when compressed or bent, resulting in excellent fatigue resistance.

Here, examples of nylon fibers include nylon 6, nylon 66, and nylon 46. Aramid fibers may be para- or meta-based, and known aramid fibers can be used.

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 first twists.

In this embodiment, the product of the load LASE5% (N) at 5% elongation of the organic fiber cord and the number of organic fiber cords E (strings/25 mm) (i.e., LASE5% x E) of the belt reinforcing layer is preferably 1000 N or more, more 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. When the product of LASE5% and the number of strings E is 1000 N or more, the belt restraining force is increased, and excellent high-speed durability, handling stability, and rolling resistance are likely to be obtained.

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

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

In this embodiment, the organic fiber cord obtained in this manner is 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) is 1.0 to 1.5. When this ratio is 1.0 or more, it is easy to obtain excellent high-speed durability. Also, when this ratio is 1.5 or less, it is easy to obtain excellent rolling resistance by suppressing the amount of rubber.

Here, 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) in a member width direction cross section obtained by cutting the belt reinforcing layer (9) along its width direction, as shown in Figure 2. The member width direction cross section is a cross section obtained by cutting the belt reinforcing layer (9) perpendicularly to the extension direction of the organic fiber cord (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 width of the belt reinforcement layer (9) is calculated from the number of organic fiber cords (10) and the cord diameter, the rubber cross-sectional area per 25 mm width is calculated from the cross-sectional area of the belt reinforcement layer calculated from the thickness (t) of the belt reinforcement layer (9) and the above-mentioned cord cross-sectional area, and the latter is divided by the former to calculate Sr/Sc per cord (Sr/Sc for each cord divided by dotted lines in Figure 2). When the number of organic fiber cords (10) is constant in the width direction of the belt reinforcement layer (9), this value per cord is taken as Sr/Sc of the belt reinforcement layer (9). When the number of organic fiber cords (10) varies in the width direction of the belt reinforcement layer (9), the average value of Sr/Sc of each cord calculated as above can be calculated.

In this embodiment, the belt layer and the belt reinforcing layer are set to a value obtained by dividing the sum of the product (A) of the load LASE 5% (N) at 5% elongation of the organic fiber cord, the number of strands (strands/25 mm), and the number of belt reinforcing layers, the product (B) of the load LASE 0.5% (N) at 0.5% elongation of the belt cord, cosθ where θ is the belt angle, the number of strands, and the number of belt layers by 1000, of 8.7 or more, preferably 8.9 or more, and more preferably 9.2 or more. The upper limit is not particularly limited, but may be 11.0 or less, or 10.5 or less. When this value is within the above range, the belt circumferential binding force is increased, the ground contact shape is improved, and excellent steering stability, wet braking performance, ride comfort, and rolling resistance are easily obtained.

A raw tire (green tire) is produced with the belt reinforcing layer wound around the outer periphery of the belt layer using the belt cord and organic fiber cord composed of the above, and the obtained raw tire is vulcanized to obtain a pneumatic tire. When forming the belt reinforcing layer on the belt layer, one or more of the above organic fiber cords are wound spirally on the belt layer of the raw tire, or a wide rubber-coated sheet with the organic fiber cords wound in parallel is wound once around the belt layer. The former spiral winding is preferable.

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

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

(Code Test Method)
Cord diameter: A single organic fiber cord is bent into four strands to prevent the twist from returning, and then these are aligned and arranged in parallel to prevent slack. The diameter is measured by dropping the legs from a height of approximately 6.5 mm using a specified dial gauge (leg (measuring probe) diameter 9.5±0.03 mm, load 1666±29.4 mN).

- Cord strength: For organic fiber cords, the load at which the sample breaks when a tensile test is performed at 20°C after leaving the organic fiber cord at constant temperature conditions of 20°C and 65% RH for 24 hours is determined in accordance with JIS L1017. For belt cords, the load at which the sample breaks is determined in accordance with JIS G3510 when a tensile test is performed.

- LASE 5%: According to 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.

- LASE 0.5%: The load at 0.5% elongation was determined in a tensile test in accordance with JIS G3510.

(Tire Test Method)
Belt angle: For an uninflated tire, the angle of the belt cord with respect to the circumferential direction of the tire was measured at the tire equator (center position in the width direction) of the tread.

- High-speed tire durability: Compliant with FMVSS109 (UTQG). A drum tester with a diameter of 1,700 mm and a smooth steel surface was used, with the tire internal pressure at 220 kPa and a load of 88% of the maximum load specified by JATMA. After a 60-minute break-in run at 80 km/h, the tire was allowed to cool, and the air pressure was adjusted again before the actual run. The actual run started at 120 km/h, and the speed was increased in stages by 8 km/h every 30 minutes until a failure occurred. The run distance until a failure occurred was expressed as an index, with the tire of Comparative Example 1 set at 100. The higher the number, the better the high-speed durability.

- Rolling resistance: Using a rolling resistance tester, the rolling resistance of the tire 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 set at 100, and the higher the index, the lower the rolling resistance and the better the fuel efficiency.

- Ride comfort: Each tire was adjusted to an internal pressure of 260 kPa using a standard rim of the JIS standard, and four tires of the same type were mounted on a 2000cc domestic passenger car. The ride comfort was evaluated by three test drivers on a test course with good and bad roads, and was evaluated using Comparative Example 1 as the standard. Those equivalent to Comparative Example 1 are indicated with "○", those inferior with "×", and those superior with "◎".

- Actual vehicle handling stability: Test tires assembled with 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 done 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.

- Wet braking performance: A test tire assembled 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 stepping on the brake pedal at a speed of 100 km/h, and the reciprocal of the 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.

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

In detail, the belt layer consisted of two sheets of 2+2 x 0.25 mm steel cord arranged at the belt angle and number of strands as shown in Table 1.

Regarding the cord structure, "1400 dtex/2" means that it is a two-ply structure obtained by twisting together two first-twisted yarns with a nominal fineness of 1400 dtex.

Each of the resulting tires was evaluated for high-speed tire durability, rolling resistance, ride comfort, actual vehicle handling stability, and wet braking performance. The results are shown in Table 1.

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.

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 the high-speed durability was inferior to that of Comparative Example 1.

Comparative Example 4 is an example in which the belt angle exceeds the upper limit, and compared to Comparative Example 1, the high-speed durability and wet braking performance are inferior, and there is no improvement in rolling resistance or actual vehicle handling stability.

Comparative examples 5 and 6 are examples in which the value of (A+B)/1000 is below the lower limit, and none of the evaluations were improved compared to comparative example 1.

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 gist of the invention. These embodiments and their omissions, substitutions, modifications, etc. are included within the scope and gist of the invention as well as the invention and its equivalents as set forth in the claims.

Embodiments of the present invention can be suitably used for various pneumatic tires, including passenger vehicle tires.

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 (3)

A pneumatic tire including a belt layer in which belt cords are arranged at an angle to the circumferential direction of the tire on an outer peripheral side of a carcass layer in a tread, and a belt reinforcing layer in which organic fiber cords are arranged along the circumferential direction of the tire on an outer peripheral side of the belt layer,
The belt layer has a belt cord angle of more than 30 degrees and not more than 40 degrees with respect to the tire circumferential direction,
the organic fiber cord is a two-ply cord made of yarn made of organic fiber,
the belt reinforcing layer is formed by covering the organic fiber cord with rubber, and a ratio (Sr/Sc) of a rubber cross-sectional area (Sr) to a cord cross-sectional area (Sc) satisfies 1.0 to 1.5;
a product (A) of a load at 5% elongation (LASE5% (N) of the organic fiber cord, the end count (correspondence/25 mm), and the number of belt reinforcing layers, a product (B) of a load at 0.5% elongation (N) of the belt cord, cos θ where θ is a belt angle, the end count (correspondence/inch), and the number of belt layers, divided by 1000, the value is 8.7 or more. The pneumatic tire according to claim 1, wherein the organic fiber cord is a two-ply cord made of yarn made of nylon 66. The pneumatic tire according to claim 1 or 2, wherein the product of the load at 5% elongation LASE5% (N) of the organic fiber cord and the number of cords (cords/25 mm) is 1000 (N/25 mm) or more.

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