JP2021046054A - Pneumatic radial tire - Google Patents

Abstract

To provide a pneumatic radial tire which makes suppression of fatigue fracture of carcass cord possible even when a steal cord in which filaments of the outermost layer are not provided in the closest arrangement is used in a reinforcement layer of a bead part.SOLUTION: A reinforcement layer 9 which contains a plurality of steal cords 10 is arranged so as to abut on a carcass layer 4 on each bead part 3. Each of the steal cords 10 has at least two-layer twisted structure comprising a plurality of filaments 11. The number of filaments of the outer-most layer of the steal cords 10 is equal to or less than the number of filaments of a layer of the inner side thereof, and at the same time, when looking at the reinforcement layer 9 from the abutment surface side with the carcass layer 4, the steal cord 10 is arranged right downward while twisting direction of the filament 11 of the outermost layer of the steal cord 10 is Z-twisted or the steal cord 10 is arranged left downward while twisting direction of the filament 11 of the outermost layer of the steal cord 10 is S-twisted.SELECTED DRAWING: Figure 2

Description

The present invention relates to a pneumatic radial tire in which a reinforcing layer including a plurality of aligned steel cords is arranged in a bead portion, and more specifically, a steel cord in which the filament of the outermost layer is not arranged most densely is beaded. The present invention relates to a pneumatic radial tire that makes it possible to suppress fatigue fracture of a carcass cord even when it is used as a reinforcing layer of a portion.

In pneumatic radial tires for passenger cars, light trucks or trucks and buses, a reinforcing layer containing multiple aligned steel cords abuts against the carcass layer for the purpose of increasing the rigidity around the bead portion. (See, for example, Patent Documents 1 and 2).

As the steel cord of the reinforcing layer of the bead portion, a steel cord in which the filament of the outermost layer is not arranged most densely, such as a 2 + 2 structure or a 3 + 8 + 1 structure, is widely used. However, when the tire is running, fatigue fracture of the carcass cord may occur due to friction (fretting) between the filament of the outermost layer of the steel cord forming the reinforcing layer of the bead portion and the carcass cord. In particular, the steel cord in which the filaments in the outermost layer are not arranged in the closest pack has remarkable irregularities on the outer surface, so that the carcass cord is easily damaged.

Japanese Unexamined Patent Publication No. 2012-106568 Japanese Unexamined Patent Publication No. 2018-16156

An object of the present invention is to make it possible to suppress fatigue fracture of the carcass cord even when a steel cord in which the filament of the outermost layer is not closely arranged is used for the reinforcing layer of the bead portion. It is to provide radial tires.

In the pneumatic radial tire of the present invention for achieving the above object, a carcass layer is mounted between a pair of bead portions, and the carcass layer is wound around a bead core arranged in each bead portion. In the tire
A reinforcing layer containing a plurality of steel cords aligned with each of the bead portions is arranged so as to abut against the carcass layer, and each of the steel cords is twisted with at least two layers composed of a plurality of filaments. It has a structure, and the number of filaments in the outermost layer of the steel cord is equal to or less than the number of filaments in the inner layer.
When the reinforcing layer is viewed from the contact surface side with the carcass layer, the steel cord is arranged downward to the right, while the twist direction of the filament of the outermost layer of the steel cord is Z twist, or It is characterized in that the steel cord is arranged downward to the left, while the twisting direction of the filament in the outermost layer of the steel cord is S twist.

In the present invention, the bead portion is a reinforcing layer containing a steel cord in which the number of filaments in the outermost layer is equal to or less than the number of filaments in the inner layer, that is, a steel cord in which the filaments in the outermost layer are not arranged closest. When the reinforcing layer is viewed from the contact surface side with the carcass layer, the steel cord is arranged downward to the right, while the filament of the outermost layer of the steel cord is arranged so as to be in contact with the carcass layer. The outermost filaments are closest packed because the twisting direction is Z-twisted or the steel cord is arranged downward to the left while the outermost filament of the steel cord is twisted in S-twisted direction. Even when an unfinished steel cord is used for the reinforcing layer of the bead portion, the fatigue of the carcass cord due to friction (fretting) between the filament of the outermost layer of the steel cord constituting the reinforcing layer of the bead portion and the carcass cord. Breakage can be suppressed. Further, according to the above-mentioned arrangement, it is possible to obtain an effect of suppressing heat generation in the bead portion and preventing a separation failure in the bead portion.

In the present invention, the number of filaments in the outermost layer of the steel cord is preferably 1 to 2. Since such a steel cord tends to cause fatigue fracture of the carcass cord, a remarkable effect can be expected by adopting the above-mentioned arrangement.

Further, the reinforcing layer defined by A = S × E based on the cross-sectional area S (mm ² / piece) of the steel cord constituting the reinforcing layer and the driving density E (piece / 50 mm) of the steel cord in the reinforcing layer. The amount of steel cord A is preferably in the range of 6.0 to 10.0. As a result, fatigue fracture of the carcass cord can be effectively suppressed while sufficiently ensuring the reinforcing effect based on the reinforcing layer.

It is a meridian cross-sectional view which shows the pneumatic radial tire which concerns on embodiment of this invention. It is a side view which shows an example of the reinforcing layer of a bead part. It is a side view which shows another example of the reinforcing layer of a bead part. It is sectional drawing which shows an example of the steel cord used for the reinforcing layer of a bead part. It is sectional drawing which shows the other example of the steel cord used for the reinforcing layer of a bead part. It is sectional drawing which shows the other example of the steel cord used for the reinforcing layer of a bead part.

Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows a pneumatic radial tire according to an embodiment of the present invention, FIGS. 2 and 3 show a reinforcing layer of a bead portion, and FIGS. 4 to 6 show a steel cord used for the reinforcing layer of the bead portion, respectively. Is shown.

As shown in FIG. 1, the pneumatic radial tire of the present embodiment includes a tread portion 1 extending in the tire circumferential direction to form an annular shape, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and a pair of sidewall portions 2. It includes a pair of bead portions 3 arranged inside the sidewall portion 2 in the tire radial direction.

A carcass layer 4 including a plurality of carcass cords C (see FIG. 2) extending in the tire radial direction is mounted between the pair of bead portions 3 and 3. An annular bead core 5 is embedded in each bead portion 3, and a bead filler 6 made of a rubber composition having a triangular cross section is arranged on the outer periphery of the bead core 5. Then, the carcass layer 4 is wound around the bead core 5 from the inside to the outside of the tire. The carcass layer 4 has a main body portion 4A and a winding portion 4B which are separated by the bead core 5 as a boundary. As the carcass cord C of the carcass layer 4, an organic fiber cord such as a polyester cord is preferably used.

On the other hand, on the outer peripheral side of the carcass layer 4 in the tread portion 1, a plurality of belt layers 7 are embedded over the entire circumference of the tire. These belt layers 7 include a plurality of belt cords that are inclined with respect to the tire circumferential direction, and are arranged so that the belt cords intersect each other between the layers. In the belt layer 7, the inclination angle of the belt cord with respect to the tire circumferential direction is set in the range of, for example, 10 ° to 40 °. As the belt cord of the belt layer 7, for example, a steel cord is preferably used.

At least one belt cover layer 8 formed by arranging band cords at an angle of 5 ° or less with respect to the tire circumferential direction on the outer peripheral side of the belt layer 7 for the purpose of improving high-speed durability and reducing road noise. Is arranged so as to cover the entire area of the belt layer 7. The belt cover layer 8 may be only a full cover that covers the entire area of the belt layer 7, or may be a combination of a full cover that covers the entire area of the belt layer 7 and an edge cover that covers only both edges of the belt layer 7. There may be. It is desirable that the belt cover layer 8 has a jointless structure in which at least one band cord is aligned and a strip formed by rubber coating is spirally wound in the tire circumferential direction.

In the pneumatic radial tire, a reinforcing layer 9 including a plurality of aligned steel cords 10 (see FIG. 2) is arranged in each of the bead portions 3 so as to abut against the carcass layer 4. .. More specifically, the reinforcing layer 9 is arranged between the bead filler 6 and the winding portion 4B of the carcass layer 4. Each of the steel cords 10 has a twisted structure of at least two layers composed of a plurality of filaments 11 (see FIGS. 4 to 6), and the number of filaments in the outermost layer of the steel cord 10 is Nout and the number of filaments in the inner layer thereof. Nin and Nin satisfy the relationship of Nout ≤ Nin.

In the example of FIG. 2, when the reinforcing layer 9 of the bead portion 3 is viewed from the contact surface side with the carcass layer 4 (that is, the outside in the tire width direction), the carcass cord C extends in the tire radial direction. On the other hand, the steel cord 10 is arranged downward to the left, and the twist direction of the filament 11 in the outermost layer of the steel cord 10 is S twist. Further, in the example of FIG. 3, when the reinforcing layer 9 of the bead portion 3 is viewed from the contact surface side with the carcass layer 4 (that is, the outside in the tire width direction), the carcass cord C extends in the tire radial direction. On the other hand, the steel cord 10 is arranged downward to the right, and the twist direction of the filament in the outermost layer of the steel cord 10 is Z twist. Here, it is desirable that the inclination angle of the steel cord 10 of the reinforcing layer 9 with respect to the tire radial direction is set in the range of 65 ° to 75 °.

As shown in FIG. 4, the steel cord 10 can have an N + W structure (N = 2-4, W = 1-2). In FIG. 4, a 2 + 2 structure is depicted as a typical example, but the structure is not limited to this. Further, as shown in FIG. 5, the steel cord 10 can have an N + M + W structure (N = 2-4, M = 5-9, W = 1-2). In FIG. 5, a 3 + 8 + 1 structure is depicted as a typical example, but the structure is not limited to this. Further, as shown in FIG. 6, the steel cord 10 can have an N + M + L + W structure (N = 2-4, M = 5-9, L = 10-15, W = 1-2). In FIG. 6, a 3 + 9 + 15 + 1 structure is depicted as a typical example, but the structure is not limited to this. In either case, the diameter of the filament 11 is preferably in the range of 0.15 mm to 0.35 mm.

In the above-mentioned pneumatic radial tire, the steel cord 10 in which the number of filaments Nout in the outermost layer is equal to or less than the number Nin in the number of filaments in the inner layer, that is, the steel in which the filaments 11 in the outermost layer are not closely arranged. When arranging the reinforcing layer 9 including the cord 10 so as to abut against the carcass layer 4 in the bead portion 3, the inclination direction of the steel cord 10 constituting the reinforcing layer 9 and the twist of the filament 11 of the outermost layer of the steel cord 10 The direction is optimized. That is, when the reinforcing layer 9 is viewed from the contact surface side with the carcass layer 4, the steel cord 10 is arranged downward to the left, while the twist direction of the filament 11 of the outermost layer of the steel cord 10 is S twist. The structure of FIG. 2 or the structure of FIG. 3 in which the twist direction of the filament 11 of the outermost layer of the steel cord 10 is Z-twisted while the steel cord 10 is arranged downward to the right is adopted.

As a result, even when the steel cord 10 in which the filament 11 of the outermost layer is not closely arranged is used for the reinforcing layer 9 of the bead portion 3, the steel cord 10 constituting the reinforcing layer 9 of the bead portion 3 Fatigue fracture of the carcass cord C due to friction (fretting) between the filament 11 of the outermost layer and the carcass cord C included in the winding portion 4B of the carcass layer 4 can be suppressed. Further, according to the above-mentioned arrangement, it is possible to obtain an effect of suppressing heat generation of the bead portion 3 due to fretting and preventing a separation failure in the bead portion 3.

In the pneumatic tire, the number of filaments Nout of the outermost layer of the steel cord 10 is preferably 1 to 2. For example, a steel having a structure in which two sheath filaments are wound around two core filaments as shown in FIG. 4 and a structure in which one wrapping filament is wound around the outermost layer as shown in FIGS. 5 and 6. Since the cord 10 has remarkable irregularities on the outer surface, the carcass cord C is easily damaged, and therefore, fatigue fracture of the carcass cord C is likely to occur. However, by adopting the arrangement as shown in FIGS. 2 and 3, it is possible to effectively suppress fatigue fracture of the carcass cord C while fully enjoying the reinforcing effect of the reinforcing layer 9.

^{Further, in the pneumatic tire, A = based on the cross-sectional area S (mm 2} / piece) of the steel cord 10 constituting the reinforcing layer 9 and the driving density E (piece / 50 mm) of the steel cord 10 in the reinforcing layer 9. steel cord amount a of the reinforcing layer 9, which is defined by ^{S × E (mm 2 / 50mm} ) is may be in the range of 6.0 to 10.0. The driving density E of the steel cord 10 is the number of driving of the steel cord 10 per 50 mm width measured in the direction orthogonal to the longitudinal direction of the steel cord 10.

By setting the amount of steel cord A of the reinforcing layer 9 in the above range, fatigue fracture of the carcass cord C can be effectively suppressed while sufficiently ensuring the reinforcing effect based on the reinforcing layer 9. Here, if the steel cord amount A of the reinforcing layer 9 is smaller than 6.0, the rigidity around the bead portion 3 becomes insufficient, and conversely, if it is larger than 10.0, the steel cord 10 and the carcass of the reinforcing layer 9 are insufficient. The influence of fretting generated between the layer 4 and the carcass cord C becomes large, the effect of suppressing fatigue fracture of the carcass cord C decreases, and the effect of preventing separation failure in the bead portion 3 decreases.

In the above-described embodiment, the case where the reinforcing layer 9 is arranged between the bead filler 6 and the winding portion 4B of the carcass layer 4 has been described, but in the present invention, the reinforcing layer 9 is the main body of the bead filler 6 and the carcass layer 4. It is possible to arrange it between the portion 4A and the reinforcing layer 9 outside the winding portion 4B of the carcass layer 4 in the tire width direction.

Further, in the above-described embodiment, the case of a pneumatic radial tire for a passenger car has been described, but the present invention can also be applied to a pneumatic radial tire for a light truck or a truck / bus.

In a pneumatic radial tire in which the tire size is 225 / 60R15 or 11R22.5, a carcass layer is mounted between a pair of bead portions, and the carcus layer is wound around a bead core arranged in each bead portion. A reinforcing layer containing a plurality of steel cords aligned is arranged between the bead filler and the winding portion of the carcass layer, and the inclination direction of the steel cord when the reinforcing layer is viewed from the contact surface side with the carcass layer. , The tires of Comparative Examples 1 to 12 and Examples 1 to 12 in which the cord structure of the steel cord, the twisting direction of the outermost filament of the steel cord, and the amount of steel cord A of the reinforcing layer were set as shown in Tables 1 and 2 were manufactured. did. Comparative Examples 1 to 6 and Examples 1 to 6 are truck and bus tires, and Comparative Examples 7 to 12 and Examples 7 to 12 are passenger car tires.

For these test tires, the durability of the bead portion and the rigidity around the bead portion were evaluated by the following evaluation methods, and the results are shown in Tables 1 and 2.

Durability of bead part:
(Truck / bus tires)
Each test tire is assembled on a wheel with a rim size of 22.5 x 8.25J, mounted on a drum tester equipped with a drum made of steel with a smooth surface and a diameter of 1707 mm, and the ambient temperature is controlled to 38 ± 3 ° C to a maximum. The air pressure is set to correspond to the load capacity (single wheel), the speed is set to 50 km / h, and the vehicle is run under the conditions specified by JIS-D4230. After completing the race, continue to increase the load by 17% and run for 8 hours. In this way, the load increase and the running for 8 hours were repeated without interruption, and the test was continued until the tire broke due to the fatigue fracture of the carcass cord in the bead portion, and the mileage was measured. The evaluation results are shown in Table 1 by an index with Comparative Example 1 as 100. The larger the index value, the better the durability of the bead portion.
(Passenger car tires)
Each test tire is assembled on a wheel with a rim size of 15 x 6.5J, mounted on a drum tester equipped with a drum made of steel with a smooth surface and a diameter of 1707 mm, the ambient temperature is controlled to 38 ± 3 ° C, and the air pressure is 180 kPa. The vehicle is run for 2 hours under the conditions that the speed is 80 km / h and the load is 88% of the maximum load of JATTA. After completing the race, continue to increase the load by 13% and run for 2 hours. In this way, the load increase and the running for 2 hours were repeated without interruption, and the test was continued until the tire broke due to the fatigue fracture of the carcass cord in the bead portion, and the mileage was measured. The evaluation results are shown in Table 2 with an index of Comparative Example 7 as 100. The larger the index value, the better the durability of the bead portion.

Rigidity around the bead:
For each test tire, the rigidity around the bead portion was evaluated based on the steel cord amount A. That is, it was evaluated as "large", "medium", and "small" in descending order of rigidity around the bead portion.

As can be seen from Tables 1 and 2, the tires of Examples 1 to 12 are less likely to cause fatigue fracture of the carcass cord in the bead portion in comparison with the reference Comparative Examples 1 and 7, respectively, and the durability of the bead portion. Was excellent. On the other hand, Comparative Examples 2 to 6 had an insufficient effect of improving the durability of the bead portion in comparison with Comparative Example 1. Further, Comparative Examples 8 to 12 had an insufficient effect of improving the durability of the bead portion in comparison with Comparative Example 7.

1 Tread part 2 Side wall part 3 Bead part 4 Carcus layer 4A Main body part 4B Winding part 5 Bead core 6 Bead filler 7 Belt layer 8 Belt cover layer 9 Reinforcing layer 10 Steel cord 11 Filament

Claims (3)

In a pneumatic radial tire in which a carcass layer is mounted between a pair of bead portions and the carcass layer is wound around a bead core arranged in each bead portion.
A reinforcing layer containing a plurality of steel cords aligned with each of the bead portions is arranged so as to abut against the carcass layer, and each of the steel cords is twisted with at least two layers composed of a plurality of filaments. It has a structure, and the number of filaments in the outermost layer of the steel cord is equal to or less than the number of filaments in the inner layer.
When the reinforcing layer is viewed from the contact surface side with the carcass layer, the steel cord is arranged downward to the right, while the twist direction of the filament of the outermost layer of the steel cord is Z twist, or A pneumatic radial tire characterized in that the steel cord is arranged downward to the left, while the twist direction of the filament of the outermost layer of the steel cord is S twist. The pneumatic radial tire according to claim 1, wherein the outermost layer of the steel cord has one or two filaments. The reinforcing layer defined by A = S × E based on the cross-sectional area S (mm ² / piece) of the steel cord constituting the reinforcing layer and the driving density E (book / 50 mm) of the steel cord in the reinforcing layer. The pneumatic radial tire according to claim 1 or 2, wherein the steel cord amount A of the above is in the range of 6.0 to 10.0.

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