JP2018079931A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of improving durability of a carcass layer in a bead part.SOLUTION: A bead core 5 includes: at least two layers of central layers 10A having six or seven layers in a tire radial direction and located in a central part in the tire radial direction; at least two layers of upper layers 10B located outside the tire radial direction than the central layer 10A; and at least two layers of lower layers 10C located inside the tire radial direction than the central layer 10A. The number of metal wires at a circulating portion in the central layers 10A is the same as each other and a maximum value and is in a range of 6 to 7 wires, and the number of the metallic wires at the circulating portion in the upper layer 10B and the lower layers 10C decreases one by one from the maximum value as becoming far from the central layer 10A. A total fineness of carcass cords constituting an inner carcass layer 4A is in a range of 4000 to 5500 dtex.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a pneumatic tire that can improve the durability of a carcass layer in a bead portion.

  Conventionally, a pneumatic tire is provided with a bead core formed by bundling a plurality of metal wires in a pair of bead portions, and both ends of the carcass layer are wound up from the inside to the outside of the bead core. have. A bead core having a square cross-sectional shape (for example, see Patent Documents 1 and 2) is adopted in a passenger car tire, and a bead core having a hexagonal cross-sectional shape in a heavy-load tire including a small truck (see, for example, Patent Documents 3 to 5). ) Is generally adopted.

  By the way, in light truck tires, from the viewpoint of cost reduction, an attempt is made to change the carcass structure from 3 plies to 2 plies by adopting a carcass cord having a higher fineness and higher strength than the existing carcass cord. Yes. Thus, when the carcass structure has two plies, if a conventional bead core having a cross-sectional shape such as a quadrangle or a hexagon is used, the carcass layer is formed at the bead portion, particularly at the corner portion of the bead core where stress is likely to concentrate during load rolling. As a result, the carcass cord may be broken, and as a result, the durability of the carcass layer in the bead portion is lowered.

JP 2014-117978 A Japanese Patent Laid-Open No. 7-223412 JP 2014-198565 A JP 2012-218552 A JP 2012-188016 A

  An object of the present invention is to provide a pneumatic tire that can improve the durability of a carcass layer in a bead portion.

  In order to achieve the above object, a pneumatic tire according to the present invention includes a bead core formed by bundling a plurality of circumferential portions of metal wires in a pair of bead portions, and extends in the tire radial direction between the bead portions. Two carcass layers including a plurality of carcass cords are mounted, and the carcass layer is wound around the bead core from the inner side of the tire to the outer side, and the tire shaft at the winding portion of the inner carcass layer In a pneumatic tire constituted by an outer carcass layer having an end portion arranged on the outer side in the direction, the bead core has 6 to 7 layers in the tire radial direction and at least two layers located in a central portion in the tire radial direction A central layer, at least two upper layers positioned on the outer side in the tire radial direction from the central layer, and at least positioned on the inner side in the tire radial direction from the central layer The number of the surrounding portions of the metal wires in the central layer is the same and the maximum value in the range of 6 to 7, and the number of the surrounding portions of the upper layer and the lower layer metal wires is As the distance from the center layer increases, the maximum value decreases one by one, and the total fineness of the carcass cords constituting the inner carcass layer is in the range of 4000 to 5500 dtex.

  In the present invention, the bead core has 6 to 7 layers in the tire radial direction, at least two central layers located in the central portion in the tire radial direction, and at least 2 located outside the central layer in the tire radial direction. The upper layer of the layer and at least two lower layers positioned on the inner side in the tire radial direction from the central layer, and the number of the circumferential portions of the metal wires in the central layer is the same and the maximum value, and ranges from 6 to 7 The number of the surrounding portions of the upper and lower metal wires decreases by one from the maximum value as the distance from the center layer increases, so that the stress on the carcass layer at the corner of the bead core during load rolling is reduced. It is possible to relax the concentration and disperse the stress. As a result, it is possible to improve the durability of the carcass layer in the bead portion.

  Moreover, the carcass layer wound up around the bead core is one layer, and the total fineness of the carcass cords constituting the carcass layer is in the range of 4000 to 5500 dtex. In particular, the pneumatic tire is preferably for heavy loads. Conventionally, in a heavy load tire, in order to increase the durability of the carcass layer in the bead portion, the number of rolled up carcass layers in the bead portion is generally two. However, by adopting a carcass cord having a high total fineness and the above-described bead core structure of the present invention, the number of rolled up carcass layers can be reduced while maintaining the durability of the carcass layer in the bead portion. Can be improved.

It is meridian sectional drawing which shows the pneumatic tire which consists of embodiment of this invention. It is sectional drawing which shows an example of the bead core in the pneumatic tire of this invention. It is sectional drawing which shows an example of the bead core in the pneumatic tire of a prior art example. It is sectional drawing which shows another example of the bead core in the pneumatic tire of a prior art example.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings. 1 and 2 show a pneumatic tire according to an embodiment of the present invention. In FIG. 1, CL is a tire center line.

  As shown in FIG. 1, the pneumatic tire of the present embodiment includes a tread portion 1 that extends in the tire circumferential direction and has an annular shape, and a pair of sidewall portions 2, 2 disposed on both sides of the tread portion 1. And a pair of bead portions 3 and 3 disposed inside the sidewall portion 2 in the tire radial direction.

  A carcass layer 4 including a plurality of carcass cords extending in the tire radial direction is mounted between the pair of bead portions 3 and 3. The carcass layer 4 includes an inner carcass layer 4A located on the inner side in the tire radial direction in the tread portion 1 and an outer carcass layer 4B located on the outer side in the tire radial direction in the tread portion 1. An annular bead core 5 is embedded in each bead portion 3, and a bead filler 6 made of a rubber composition is disposed on the outer periphery of the bead core 5. The inner carcass layer 4 </ b> A is wound around the bead core 5 from the tire inner side to the outer side, and is configured to wrap the bead core 5 and the bead filler 6. The outer carcass layer 4 </ b> B has an end portion disposed on the outer side in the tire axial direction of the rolled-up portion of the inner carcass layer 4 </ b> A and extends to the side position of the bead core 5. As the carcass cords constituting these carcass layers 4A and 4B, organic fiber cords such as nylon and polyester are preferably used. A chafer 9 is disposed in each bead portion 3, and an end portion of the chafer 9 on the outer side in the tire axial direction is disposed between the inner carcass layer 4 </ b> A and the outer carcass layer 4 </ b> B. Extends to position.

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

  For the purpose of improving high-speed durability, at least one belt cover layer 8 in which reinforcing cords are arranged at an angle of, for example, 5 ° or less with respect to the tire circumferential direction is disposed on the outer peripheral side of the belt layer 7. Yes. It is desirable that the belt cover layer 8 has a jointless structure in which a strip material formed by aligning at least one reinforcing cord and covering with rubber is continuously wound in the tire circumferential direction. Further, the belt cover layer 8 may be disposed so as to cover the entire width direction of the belt layer 7, or may be disposed so as to cover only the outer edge portion of the belt layer 7 in the width direction. As the reinforcing cord of the belt cover layer 8, an organic fiber cord such as nylon or aramid is preferably used.

  In addition, although the tire internal structure mentioned above shows the typical example in a pneumatic tire, it is not limited to this.

  FIG. 2 shows an example of a bead core in the pneumatic tire of the present invention. As shown in FIG. 2, in the pneumatic tire, each bead core 5 is composed of a metal wire 50 wound in the tire circumferential direction, and a plurality of circumferential portions 50A of the metal wire 50 are arranged in the tire axial direction Tw. A plurality of layers 10 are formed to overlap the row and the tire radial direction Tr.

  Each bead core 5 includes six layers in the tire radial direction, two central layers 10A located at the center in the tire radial direction, and 2 located on the outer side in the tire radial direction from the central layer 10A. The upper layer 10B includes two lower layers 10C positioned on the inner side in the tire radial direction than the central layer 10A.

  In the two central layers 10A, the number of the surrounding portions 50A of the respective metal wires is the same, and the number of the surrounding portions 50A of the metal wires is the maximum value (N) of all the layers 10 constituting the bead core 5. ) On the other hand, in the upper layer 10B and the lower layer 10C, the number of the surrounding portions 50A of the respective metal wires is arranged so as to decrease one by one from the maximum value (N) as the distance from the central layer 10A increases.

  That is, in each of the above layers, the number of the metal wire loop portions 50A is 6 in the central layer 10A having the maximum value (N), 5 in the upper layer 10B and the lower layer 10C adjacent to the central layer 10A, and further in the layer 10 Among them, the upper layer 10B and the lower layer 10C located at both ends in the tire radial direction are composed of four pieces. Thereby, the cross-sectional shape of the bead core 5 is substantially octagonal.

  Here, when the cross-sectional shape of the bead core 5 is a quadrangle as in the prior art (see FIG. 3) or when the cross-sectional shape of the bead core 5 is a hexagon (see FIG. 4), the corners of the bead core 5 (see FIG. 3 or FIG. 3). 4), the carcass cord and the bead core 5 are in contact with each other, and stress on the carcass layer 4 tends to concentrate at the corners of the bead core 5, leading to breakage of the carcass layer 4.

  On the other hand, in the bead core 5 in the pneumatic tire of the present invention, the two central layers 10A are adjacent to each other, and the surrounding portions 50A of the respective metal wires are arranged at the same position with respect to the tire axial direction. Yes. That is, in the two central layers 10A, the outer edges of the metal wire circumferential portions 50A located at both ends in the tire axial direction are aligned with respect to the tire radial direction so that the region where the carcass cord and the bead core 5 are in contact with each other has a flat shape. It becomes possible to do. Thereby, the concentration of stress on the carcass layer 4 in the region where the carcass cord and the bead core 5 are in contact can be relaxed, and the stress can be dispersed. As a result, the durability of the carcass layer 4 in the bead portion 3 can be improved.

  In the pneumatic tire, the carcass layer 4 wound up around the bead core 5 is one layer, and the total fineness of the carcass cords constituting the carcass layer 4 is set in a range of 4000 to 5500 dtex. Such a pneumatic tire is suitable as a heavy duty tire including a small truck. As a result, in heavy duty tires used under conditions of high internal pressure and high load, it is possible to reduce the number of rolled up carcass layers 4 and improve cost while maintaining the durability of the carcass layers 4. Become.

  In the pneumatic tire described above, the number of metal wire circumferential portions 50A in the central layer 10A is preferably in the range of 4 to 7, and the number of layers in the tire radial direction of the bead core 5 is preferably in the range of 4 to 7 layers. More preferably, the number of the surrounding portions 50A of the metal wire is in the range of 6 to 7, and the number of layers of the bead core 5 in the tire radial direction is in the range of 6 to 7 layers. Thereby, both durability and cost performance of the carcass layer 4 in the bead part 3 can be achieved. Here, when the number of the surrounding portions 50A of the metal wire and the number of layers in the tire radial direction of the bead core 5 are larger than the above range, the cost is deteriorated, and when the number is smaller on the other hand, the bead core 5 is formed on the bottom and side surfaces. The flat area becomes narrow, the effect of dispersing stress on the carcass layer 4 in the bead portion 3 becomes small, and further, it becomes difficult to ensure the safety factor of the bead itself.

  In the embodiment of the present invention described above, in the structure of the bead core 5, the structure that is symmetric with respect to the tire axial line passing through the center of the bead core 5 has been described. There is no need for a structure. That is, the upper layer 10B and the lower layer 10C may have different numbers of layers.

  With tire size 235 / 85R16, a pair of bead portions each have a bead core formed by bundling a plurality of metal wire portions in a row, and both ends of the carcass layer are wound from the inside to the outside of the tire around the bead core. In the pneumatic tires, tires of Examples 1 and 2 having different bead core configurations were manufactured.

  In Examples 1 and 2, the number of carcass layers, the number of wound carcass layers, the total fineness (dtex) of the carcass cord, the bead core structure, and the cross-sectional shape of the bead core were set as shown in Table 1.

  Moreover, the tires of Conventional Examples 1 to 3 and Comparative Example 1 were prepared. The tire of Conventional Example 1 uses a bead core having a square cross-sectional shape with the number of rolled up carcass layers being 2, the total fineness of the carcass cord being 3340 dtex. The tire of Conventional Example 2 has the same structure as Conventional Example 1 except that the number of carcass layers is two and the number of rolled up carcass layers is one. The tire of Conventional Example 3 has the same structure as Conventional Example 2 except that a bead core having a hexagonal cross-sectional shape is used. A tire of Comparative Example 1 having the same structure as Example 2 was prepared except that a bead core having a square cross-sectional shape was used.

  For these test tires, the durability and cost of the carcass layer in the bead portion were evaluated by the following test method, and the results are also shown in Table 1.

Durability of the carcass layer at the bead:
Each test tire is assembled on a wheel with a rim size of 16 × 6.5J, and the speed is 60 km / h, 130% of the maximum air pressure of JATMA standard, 150% of the maximum load of JATMA standard, and a slip angle of 2 °. A running test was conducted. The vehicle was run until a failure occurred in the bead portion, and the travel distance was measured. The evaluation results are shown as an index with the conventional example being 100. The larger the index value, the better the durability of the carcass layer in the bead portion.

cost:
The cost of each test tire was calculated. The evaluation results are shown as an index with the conventional example being 100, using the reciprocal of the calculated value. The larger the index value, the lower the cost.

  As can be seen from Table 1, the pneumatic tires of Examples 1 and 2 were simultaneously improved in durability and cost of the carcass layer in the bead portion in comparison with Conventional Example 1.

  On the other hand, in the conventional example 2, since the number of carcass layers and the number of carcass layers wound up were reduced, the cost was improved, but the durability of the carcass layer in the bead portion was greatly deteriorated. In Conventional Example 3, since the number of carcass layers and the number of carcass layers wound up were reduced and the cross-sectional shape of the bead core was hexagonal, the cost was improved, but the durability of the carcass layer at the bead portion deteriorated. Moreover, in Comparative Example 1, since the cross-sectional shape of the bead core was a square, the durability of the carcass layer in the bead portion was deteriorated.

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass layer 4A Inner carcass layer 4B Outer carcass layer 5 Bead core 6 Bead filler 7 Belt layer 8 Belt cover layer 9 Chafer 10 layer 10A Central layer 10B Upper layer 10C Lower layer 50 Metal wire 50A Circulation portion

Claims (2)

A pair of bead portions each includes a bead core formed by bundling a plurality of metal wire winding portions in a row, and two layers of carcass layers including a plurality of carcass cords extending in the tire radial direction are mounted between the bead portions. The carcass layer is composed of an inner carcass layer wound around the bead core from the inside of the tire to the outside, and an outer carcass layer having an end disposed on the outer side in the tire axial direction of the rolled-up portion of the inner carcass layer. In pneumatic tires,
The bead core has 6 to 7 layers in the tire radial direction, and has at least two central layers positioned at the center in the tire radial direction, and at least two upper layers positioned on the outer side in the tire radial direction from the central layer. And at least two lower layers located on the inner side in the tire radial direction than the central layer, and the number of the circumferential portions of the metal wires in the central layer is the same number and the maximum value in the range of 6 to 7 The number of the surrounding portions of the upper layer and the lower layer metal wires decreases one by one from the maximum value as the distance from the central layer increases, and the total fineness of the carcass cords constituting the inner carcass layer is 4000 to 5500 dtex. A pneumatic tire characterized by being in range.   The pneumatic tire according to claim 1, wherein the pneumatic tire is for heavy loads.

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