JP5066914B2 - Heavy duty pneumatic radial tire - Google Patents

Description

  The present invention relates to a heavy-duty pneumatic radial tire provided with a circumferential reinforcing layer in a crown portion, and more particularly, to a heavy-duty pneumatic radial tire capable of achieving both uniformity and vulcanization failure performance. .

  In recent years, in the wide-base heavy-duty pneumatic radial tires used for trucks and buses, for the purpose of reducing the strain applied to the cross belt layer (belt layer where the reinforcing cords cross each other) embedded in the crown portion, A zigzag steel cord having a circular cross-sectional shape and having an amplitude direction in the width direction of the belt layer is wound around the belt portion at substantially 0 ° with respect to the tire circumferential direction. Providing a circumferential reinforcing layer has been proposed (see, for example, Patent Documents 1 to 3).

  The steel cord constituting such a circumferential reinforcing layer has a relatively low initial elastic modulus based on the zigzag shape before vulcanization, but is stretched by the lift deformation of the tire in the vulcanization process, Since the initial elastic modulus increases when rubber penetrates into the cord, it functions to suppress the strain applied to the cross belt layer by suppressing the expansion of the crown after vulcanization.

However, when a zigzag brazing is applied to the steel cord constituting the circumferential reinforcing layer, the winding accuracy of the steel cord is deteriorated, so that there is a problem that a vulcanization failure due to an air pool is likely to occur. On the other hand, if the zigzag amplitude applied to the steel cord is reduced in order to improve the winding accuracy, the initial elastic modulus of the cord before vulcanization increases. Cannot follow, and the tire uniformity deteriorates.
JP-A-5-338406 JP-A-6-32108 JP-A-6-183207

  An object of the present invention is to provide a heavy-duty pneumatic radial tire capable of achieving both uniformity and vulcanization failure performance even when a circumferential reinforcing layer is provided in the crown portion. is there.

In order to achieve the above object, a heavy-duty pneumatic radial tire according to the present invention is a heavy-duty pneumatic radial tire provided with a plurality of belt layers on the outer peripheral side of the carcass layer in the crown portion. 8) a 1 × N twisted structure in which strands are twisted together, a flat cross-sectional shape having a major axis in the width direction of the belt layer, and a ratio of amplitude to the major axis of 1.5 to 3.0. And winding a steel cord with a zigzag brazing that undulates in the direction of the major axis so that the wavelength is 20 mm to 50 mm along the belt layer at substantially 0 ° with respect to the tire circumferential direction. The crown portion is provided with a circumferential reinforcing layer.

  According to the present invention, since the amplitude and wavelength of the zigzag steel cord constituting the circumferential reinforcing layer are reduced, the winding accuracy of the steel cord is improved, and vulcanization failure due to air accumulation is less likely to occur. On the other hand, the steel cord constituting the circumferential reinforcing layer has a 1 × N twisted structure and a flat cross-sectional shape having a major axis in the width direction of the belt layer, so that the zigzag degree is reduced. Even in such a case, the initial elastic modulus before vulcanization can be kept small based on the twisted structure, and as a result, the deformation of the steel cord can follow the lift deformation of the tire in the vulcanization process. Therefore, even when the circumferential reinforcing layer is provided in the crown portion, it is possible to achieve both uniformity and vulcanization failure resistance.

  The circumferential reinforcing layer is preferably disposed between the belt layer and the carcass layer or disposed on the outer peripheral side of the belt layer. When such a structure is adopted, it is easier to mold the tire than when a circumferential reinforcing layer is disposed between the cross belt layers.

  The ratio of the minor axis to the major axis of the steel cord used for the circumferential reinforcing layer is preferably 0.60 to less than 1.00. Thereby, the initial elastic modulus of the steel cord before vulcanization can be reduced while maintaining good workability when the zigzag brazing is applied to the steel cord.

  The number N of strands of the steel cord used for the circumferential reinforcing layer is preferably 5-6. Furthermore, it is preferable that the twist pitch of the steel cord used for the circumferential reinforcing layer is 5 mm to 15 mm. When such a number of strands and a twist pitch are selected, the steel cord which has the said structure can be manufactured efficiently.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows a heavy-duty pneumatic radial tire according to an embodiment of the present invention, where 1 is a crown portion, 2 is a sidewall portion, and 3 is a bead portion. A carcass layer 4 is mounted between the pair of left and right bead portions 3, 3, and an end portion of the carcass layer 4 is folded around the bead core 5 from the inside of the tire to the outside. A reinforcement layer 6 is embedded in the bead portion 3 so as to wrap the bead core 5.

  A plurality of belt layers 7 a and 7 b including a plurality of reinforcing cords inclined with respect to the tire circumferential direction are embedded in the outer peripheral side of the carcass layer 2 in the crown portion 1. These belt layers 7a and 7b have a cord angle of 15 ° to 60 ° with respect to the tire circumferential direction, and are arranged so that the reinforcing cords cross each other. The number of belt layers is not particularly limited, and can be increased as necessary. A circumferential reinforcing layer 8 is disposed between the belt layers 7 a and 7 b and the carcass layer 4.

  The circumferential reinforcing layer 8 is disposed between the belt layers 7a and 7b and the carcass layer 4 in FIG. 1, but may be disposed on the outer circumferential side of the belt layers 7a and 7b as shown in FIG. The belt layers 7a and 7b may be disposed between the layers. However, if the circumferential reinforcing layer 8 is disposed between the cross belt layers 7a and 7b, it is difficult to apply the cross belt layers 7a and 7b accurately at the time of molding, and it becomes difficult to mold the tire. Therefore, the circumferential reinforcing layer 8 is formed of the belt layer 7a. 7b and the carcass layer 4 or on the outer peripheral side of the belt layers 7a and 7b.

  FIG. 3 is a plan view showing the circumferential reinforcing layer. As shown in FIG. 3, the circumferential reinforcing layer 8 is formed by continuously winding one or a plurality of steel cords C covered with rubber at substantially 0 ° with respect to the tire circumferential direction as necessary. It is formed with. The cord winding angle of the circumferential reinforcing layer 8 may be, for example, 5 ° or less with respect to the tire circumferential direction. Further, the circumferential reinforcing layer 8 may be wound in multiple layers. Such a circumferential reinforcing layer 8 is installed for the purpose of suppressing swelling of the crown portion 1 due to high internal pressure, particularly in a heavy duty radial tire having a flatness ratio of 60% or less.

  FIG. 4 is a plan view of a steel cord constituting the circumferential reinforcing layer, and FIG. 5 is a cross-sectional view thereof. As shown in FIGS. 4 and 5, the steel cord C has a 1 × N twist structure in which N (N = 3 to 8) strands f are twisted together, and the belt layer has a major axis in the width direction. It has a flat cross-sectional shape. This steel cord C is provided with a zigzag brazing. In the steel cord C, the ratio of the amplitude W to the long diameter Dl satisfies the relationship 1.5 ≦ W / Dl ≦ 3.0, and the wavelength L satisfies the relationship 20 mm ≦ L ≦ 50 mm.

  According to the pneumatic radial tire described above, since the amplitude W and the wavelength L of the zigzag steel cord C constituting the circumferential reinforcing layer 8 are reduced, the winding accuracy of the steel cord C is improved, and the pressure caused by air accumulation is increased. Sulfur failure is less likely to occur. On the other hand, the steel cord C constituting the circumferential reinforcing layer 8 has a 1 × N twisted structure and a flat cross-sectional shape having a long diameter in the width direction of the belt layer, so that the zigzag degree is reduced. Even in such a case, the initial elastic modulus before vulcanization can be kept small based on the twisted structure, and as a result, the deformation of the steel cord C can follow the lift deformation of the tire in the vulcanization process. That is, since the steel cord C has a gap between the strands, it is possible to cope with a change in the circumferential length of the crown portion 1 due to the lift deformation of the tire by reducing the gap between the strands. Therefore, even when the circumferential reinforcing layer 8 is provided on the crown 1, it is possible to achieve both uniformity and vulcanization failure resistance.

  Here, if the ratio of the amplitude W to the long diameter Dl of the steel cord C is less than 1.5, the initial elastic modulus of the steel cord C before vulcanization increases and the uniformity decreases, and conversely exceeds 3.0. As a result, the amount of air entrained in the circumferential reinforcing layer 8 increases and vulcanization failure is likely to occur. Also, if the wavelength L of the steel cord C is less than 20 mm, the amount of air entrained in the circumferential reinforcing layer 8 increases and vulcanization failure is likely to occur. Conversely, if it exceeds 50 mm, the steel cord C before vulcanization The initial elastic modulus increases and the uniformity decreases.

  The ratio of the short diameter Ds to the long diameter Dl of the steel cord C used for the circumferential reinforcing layer 8 satisfies the relationship of 0.60 ≦ Ds / Dl <1.00. Thereby, the initial elastic modulus of the steel cord C before vulcanization can be reduced while maintaining good workability when the zigzag brazing is applied to the steel cord C. If the ratio of the short diameter Ds to the long diameter Dl is less than 0.60, it becomes difficult to perform the zigzag processing on the steel cord C, and the manufacturing efficiency thereof decreases.

  The number N of strands of the steel cord C used for the circumferential reinforcing layer 8 can be selected in the range of 3 to 8, more preferably 5 to 6. When the number of the strands of the steel cord C is 4 or less, the cord shape becomes unstable, and the manufacturing efficiency is lowered. When the number of strands of the steel cord C is 7 or more, it becomes difficult to control each strand, and the manufacturing efficiency is lowered.

  The twist pitch of the steel cord C used for the circumferential reinforcing layer 8 is preferably 5 mm to 15 mm. When the twist pitch of the steel cord C is 5 mm or less, the production efficiency per unit time is lowered. If the twist pitch of the steel cord C is 15 mm or more, zigzag processing becomes difficult, and the production efficiency is lowered.

  A heavy-duty pneumatic radial tire having a tire size of 435 / 45R22.5 (rim size: 22.5 × 14.00) and a belt layer provided on the outer peripheral side of the carcass layer in the crown portion. The steel cord is wound at substantially 0 ° with respect to the tire circumferential direction to provide a circumferential reinforcing layer, and the steel cord twist structure, twist pitch, major axis Dl, minor axis Ds, amplitude W, Pneumatic tires of Conventional Example 1, Examples 1 to 7 and Comparative Examples 1 to 4 having various wavelengths L as shown in Table 1 were manufactured.

  Note that a steel cord of 3 × 0.32 + 8 × 0.35HT was used for the belt layer, the cord driving density was 20/50 mm, and the cord angle with respect to the tire circumferential direction was 20 °. The width of the inner belt layer was 250 mm, and the width of the outer belt layer was 200 mm. On the other hand, the width of the circumferential reinforcing layer was 300 mm, and the cord driving density was adjusted so that the steel cord weights of all the test tires were the same.

  These test tires were evaluated for vulcanization failure performance and uniformity by the following methods, and the results are also shown in Table 1.

Anti-vulcanization failure performance:
The test tire was placed in a vacuum chamber (5 kPa), the entire circumference of the crown portion was radiographed, 10 test tires were evaluated based on the following three evaluation points, and the total value of the evaluation points was obtained. The evaluation results are shown as an index with Conventional Example 1 as 100. A larger index value means better vulcanization failure resistance performance.
1 point: There is a gap of 5 mm or more.
2 points: There are gaps of less than 1 to 5 mm.
3 points: The gap is less than 1 mm.

Uniformity:
Under the conditions of the test internal pressure 900 kPa, the load 50 kN, and the tire rotation speed 60 rpm, the magnitude of the force variation in the tire radial direction (N: radial force variation) is measured for each of the ten test tires, and the total value of the measured values Asked. The evaluation results are shown as an index with the conventional example 1 as 100, using the reciprocal of the total value of the measured values. A larger index value means better uniformity.

  As is apparent from Table 1, the tires of Examples 1 to 7 were able to improve the vulcanization failure resistance performance while maintaining good uniformity as compared with Conventional Example 1. However, in Examples 3 to 7, the manufacturing efficiency of the cord was lowered. On the other hand, although the tires of Comparative Examples 1 and 2 were able to improve the vulcanization failure resistance performance, the uniformity was worse than that of Conventional Example 1. Although the tires of Comparative Examples 3 and 4 had good uniformity, the vulcanization failure resistance performance was worse than that of Conventional Example 1.

1 is a meridian half sectional view showing a heavy duty pneumatic radial tire according to an embodiment of the present invention. FIG. It is a meridian half sectional view showing a heavy duty pneumatic radial tire according to another embodiment of the present invention. It is a top view which shows the circumferential direction reinforcement layer. It is a top view of the steel cord which comprises the circumferential direction reinforcement layer. It is a cross-sectional view of a steel cord constituting a circumferential reinforcing layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Crown part 2 Side wall part 3 Bead part 4 Carcass layer 5 Bead core 6 Reinforcement layer 7a, 7b Belt layer 8 Circumferential reinforcement layer C Steel cord f Wire

Claims (6)

A heavy duty pneumatic radial tire provided with a belt layer on the outer peripheral side of the carcass layer in the crown portion, and having a 1 × N twist structure in which N (N = 3 to 8) strands are twisted together, and the belt layer has a flat cross-sectional shape to the width direction and the major axis, and shaping zigzag undulating in the direction of the major axis such that the amplitude ratio of the relative said major axis is wavelength and 20mm~50mm at 1.5-3.0 A heavy-duty pneumatic radial tire provided with a circumferential reinforcing layer in the crown portion by winding a steel cord subjected to wrapping at substantially 0 ° with respect to the tire circumferential direction along the belt layer.   The heavy-duty pneumatic radial tire according to claim 1, wherein the circumferential reinforcing layer is disposed between the belt layer and the carcass layer.   The heavy-duty pneumatic radial tire according to claim 1, wherein the circumferential reinforcing layer is disposed on an outer peripheral side of the belt layer.   The heavy-duty pneumatic radial tire according to any one of claims 1 to 3, wherein a ratio between a minor axis and a major axis of the steel cord used for the circumferential reinforcing layer is 0.60 to less than 1.00.   The heavy-duty pneumatic radial tire according to any one of claims 1 to 4, wherein the number N of strands of steel cord used for the circumferential reinforcing layer is 5-6.   The heavy radial pneumatic tire according to any one of claims 1 to 5, wherein a twist pitch of a steel cord used for the circumferential reinforcing layer is 5 mm to 15 mm.

Images