JP2007216710A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire which reduces the amount of use of bead wires without degrading the safety factor of the tire by effectively using the bead wires as a tension material. <P>SOLUTION: In the pneumatic tire having a bead core 5 which is constituted by annularly winding and stacking a plurality of bead wires 5a-5h arrayed parallel to each other, the breaking elongation of the bead wire 5a closest to the bead toe side is increased more than that of the means breaking elongation of the other bead wires 5b-5h by the difference of ≥ 0.5%, and the breaking strength of the bead wire 5a closest to the bead toe side is set to be ≥ 80% of the mean breaking strength of the other bead wires 5b-5h. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a pneumatic tire including a bead core configured by winding a plurality of bead wires arranged in parallel in a ring shape, and more specifically, by effectively utilizing the bead wire as a tensile material, The present invention relates to a pneumatic tire that makes it possible to reduce the amount of bead wire used without lowering the safety factor.

  As a bead core of a pneumatic tire, one bead wire is continuously wound (for example, refer to Patent Document 1), or a plurality of bead wires arranged in parallel are annularly wound and configured. There is a thing (for example, refer to patent documents 2). In either case, the strength of the bead core varies depending on the amount of bead wire used.

In recent years, weight saving for the purpose of reducing fuel consumption of vehicles and resource saving by reducing materials have become important issues in the tire industry. In view of such problems, it has been studied to reduce the amount of bead wire used. However, if the use amount of the bead wire is reduced, the strength of the bead core is inevitably lowered, and the safety factor of the tire is lowered.
JP 2005-28944 A JP-A-2005-145082

  An object of the present invention is to provide a pneumatic tire that can reduce the amount of bead wire used without lowering the safety factor of the tire by effectively utilizing the bead wire as a tensile material. .

  In order to achieve the above object, a pneumatic tire of the present invention is a pneumatic tire having a bead core formed by annularly winding a plurality of bead wires arranged in parallel, and the breaking elongation of the bead wire on the most bead toe side. With a difference of 0.5% or more than the average breaking elongation of the other bead wires, and the breaking strength of the bead wire on the most bead toe side is 80% or more of the average breaking strength of the other bead wires. It is what.

  The present inventor has earnestly studied the strength of a bead core formed by winding a plurality of bead wires arranged in parallel in an annular shape, and obtained the following knowledge. That is, when a water pressure resistance test is performed on the pneumatic tire having the bead core, the innermost layer portion of the bead wire on the bead toe side is located at a position where the winding start terminal of the bead wire exists, that is, at a position where the number of stacked bead wires changes. As a starting point, it was found that the bead core breaks and that the break tends to spread to the bead heel side and the tire radial direction outside. This is because the tension applied to the innermost layer portion of the bead wire on the bead toe side is the highest, and after the innermost layer portion of the bead wire on the bead toe side is broken, the adjacent portions are successively broken. In other words, the innermost layer portion of the bead wire on the most bead toe side breaks before the other part of the bead core except the innermost layer portion of the bead wire on the most bead toe side works sufficiently as a tensile material, and as a result, the pressure resistance is reduced. It is inferior.

  Therefore, in the present invention, as the bead wire on the most bead-toe side, a bead wire having sufficient breaking strength as compared with other bead wires and more easily stretched than other bead wires is used. Therefore, when tension is applied to the bead core, the bead wire on the most bead toe side is stretched, while the other bead wires sufficiently work as a tensile material. As a result, the bead wire can be effectively used as a tensile material, and the use amount of the bead wire can be reduced without reducing the safety factor of the tire.

  In this invention, it is preferable that the cross-sectional shape of all the bead wires which comprise a bead core is made into a rectangle. Further, the breaking elongation of the bead wire on the most bead toe side is preferably 4% to 10%, and the breaking strength of the bead wire on the most bead toe side is preferably 1500 MPa to 2300 MPa. Furthermore, the breaking elongation E1 (%) of the bead wire on the most bead toe side and the breaking elongation E2 (%) of the bead wire on the most bead heel side are expressed by the inner peripheral length C1 (mm) of the bead wire on the most bead toe side and It is preferable to have a relationship of E1-E2> (C2-C1) / C2 × 100% with respect to the inner circumferential length C2 (mm). In other words, even when the bead wire on the most bead toe side is stretched to the same length as the bead wire on the most bead heel side, all the bead wires included in the bead core are satisfied by satisfying a relationship that does not cause breakage of the bead wire on the most bead toe side. It can be used to the maximum extent as a tensile material.

Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows a pneumatic tire according to an embodiment of the present invention, and FIG. 2 shows an enlarged bead portion of the pneumatic tire. FIG. 3 shows a plurality of bead wires arranged in parallel, and FIG. 4 shows a bead core formed by winding a plurality of bead wires arranged in parallel in an annular shape.

  In FIG. 1, 1 is a tread portion, 2 is a sidewall portion, and 3 is a bead portion. As shown in FIG. 1, a carcass layer 4 is mounted between one bead portion 3 and the other bead portion (not shown), and an end portion of the carcass layer 4 is around the bead core 5 from the inside of the tire to the outside. Is rolled up. A plurality of belt layers 6 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. These belt layers 6 include reinforcing cords that are inclined with respect to the tire circumferential direction, and are arranged so that the reinforcing cords cross each other between the layers.

  In the pneumatic tire, as shown in FIGS. 2 to 4, the bead core 5 is configured by winding six bead wires 5 a to 5 h arranged in parallel in an annular manner in six layers along the tire circumferential direction. It is. The cross-sectional shape of the bead wires 5a to 5h constituting the bead core 5 is not particularly limited, and may be a rectangle, a parallelogram, or a circle, but it is desirable that all of them be a rectangle. However, the rectangle mentioned here includes a rectangle whose corners are chamfered.

  The breaking elongation of the bead wire 5a closest to the bead toe (the innermost side in the tire axial direction) is higher than the average breaking elongation of the other bead wires 5b to 5h, and the difference is 0.5% or more, preferably 0.5% to 6. It is set to be 0%. The breaking strength of the bead wire 5a closest to the bead toe is set to be 80% or more, preferably 80% to 130% of the average breaking strength of the other bead wires 5b to 5h.

  When a tension acts on the carcass layer 4 wound around the bead core 5 in the pneumatic tire including the bead core 5 configured by annularly winding the plurality of bead wires 5 a to 5 h arranged in parallel in this way. The bead core 5 tends to expand outward in the tire radial direction as a whole due to the tension of the carcass layer 4, but at the same time, the bead core 5 is twisted due to the winding structure of the carcass layer 4, and the bead wire 5a closest to the bead toe side. Tension increases.

  In the pneumatic tire described above, by using a bead core 5a having a sufficient breaking strength as compared to the other bead wires 5b to 5h and being easier to extend than the other bead wires 5b to 5h as the bead wire 5a on the most bead toe side. When the tension is applied to the bead toe, the bead toe side bead wire 5a expands, while the other bead wires 5b to 5h sufficiently work as tensile materials. Therefore, the bead wires 5a to 5h can be effectively used as a tensile material. When the use amount of the bead wires 5a to 5h is the same as the conventional one, the strength of the bead core 5 can be increased as compared with the conventional case. However, when the use amount of the bead wires 5a to 5h is reduced as compared with the conventional case, the safety of the tire is increased. The rate can be maintained at the same level as before.

  Here, if the breaking elongation of the bead wire 5a on the most bead toe side is not higher than the average breaking elongation of the other bead wires 5b to 5h by 0.5% or more, the bead wire 5a on the most bead toe side is preferential. It becomes easy to break, and the pressure resistance of bead core 5 falls. Further, when the breaking strength of the bead wire 5a on the most bead toe side is less than 80% of the average breaking strength of the other bead wires 5b to 5h, the bead wire 5a on the most bead toe side is easily broken preferentially, and the pressure resistance of the bead core 5 is increased. Decreases.

  The breaking elongation of the bead wire 5a closest to the bead toe is preferably 4% to 10%, and the breaking strength of the bead wire 5a closest to the bead toe is 1500 MPa to 2300 MPa. If the breaking elongation of the bead toe side bead wire 5a is less than 4%, the bead toe side bead wire 5a is most likely to break. When the breaking strength of the bead toe side bead wire 5a is less than 1500 MPa, the bead toe side bead wire 5a is most likely to break.

  In particular, when the inner peripheral length of the bead wires 5a to 5h is gradually increased from the bead toe side to the bead heel side in accordance with the inclination of the rim bead sheet, the breaking elongation E1 (%) of the bead wire 5a on the most bead toe side and the most bead heel are obtained. The breaking elongation E2 (%) of the side bead wire 5h is defined as E1-E2 with respect to the inner peripheral length C1 (mm) of the bead wire 5a closest to the bead toe and the inner peripheral length C2 (mm) of the bead wire 5h closest to the bead heel. > (C2-C1) / C2 × 100%. However, the inner peripheral length is the length of the portion of each bead wire that is located on the innermost side in the tire radial direction. By satisfying such a relationship, even when the bead wire 5a on the most bead toe side is extended to the same length as the bead wire 5h on the most bead heel side, the bead toe side bead wire 5a can be prevented from breaking. . And all the bead wires 5a-5h contained in the bead core 5 can be utilized to the maximum as a tensile material.

  In the above-described embodiment, a pneumatic tire including a bead core configured by winding six layers of eight bead wires arranged in parallel has been described. However, in the present invention, the number of arranged bead wires and the number of stacked layers are particularly limited. It is not a thing. For example, the number of bead wires arranged may be 4 to 10, and the number of stacked layers may be 4 to 8 layers.

  In the pneumatic tire of tire size 11R22.5, tires of conventional examples, examples 1 to 3 and comparative examples in which only the configuration of the bead core was varied were manufactured.

  In the conventional example, Examples 1 to 3, and Comparative Example, a bead core was configured by appropriately combining a normal wire having a physical property shown in Table 1 and a high elongation wire as a bead wire. In particular, in the conventional example, only the normal wire is used without using the high elongation wire, and in Examples 1 to 3 and the comparative example, the high elongation wire is arranged at a predetermined position shown in Table 1, and is placed at other positions. Usually wires were placed. The breaking elongation (%) and breaking strength (N) of the bead wire were obtained from a strain-load curve obtained from a tensile test according to JIS G3510. As a testing machine, an autograph (AGS 5 kN) manufactured by Shimadzu Corporation was used, the tensile measure was 50 mm / min, and the length of the test piece was 250 mm.

  In Table 1, the breaking elongation and breaking strength of the “toe side wire” are values of one bead wire on the most bead toe side, and the breaking elongation and breaking strength of “other wire” are other bead wires excluding the bead wire on the most bead toe side. Is the average value. The ratio of the breaking strength means the percentage (%) of the breaking strength of the bead wire on the most bead toe side relative to the average breaking strength of other bead wires excluding the bead wire on the most bead toe side. The difference in breaking elongation is a value obtained by subtracting the average breaking elongation of other bead wires from the breaking elongation of the bead wire closest to the bead toe side.

  For these test tires, the weight index and the fracture pressure index were determined by the following measurement method, and the results are also shown in Table 1.

Weight index:
For each test tire, the weight of the bead core was measured. The measurement results are shown as an index with the conventional example being 100. A smaller index value means a lighter weight.

Breaking pressure index:
About each test tire, the water pressure was raised in the cavity and the breaking pressure when the tire was broken was measured. The measurement results are shown as an index with the conventional example being 100. A larger index value means better pressure resistance.

  As shown in Table 1, in the tires of Examples 1 and 2, the weight of the bead core is equal to that of the conventional example, but the fracture pressure index is larger than that of the conventional example. Further, in the tire of Example 3, the weight of the bead core was smaller than that of the conventional example, but a fracture pressure index equivalent to that of the conventional example was ensured. In the comparative tire, a high elongation wire was used, but no improvement effect was observed.

It is a meridian half section view showing a pneumatic tire according to an embodiment of the present invention. It is sectional drawing which expands and shows the bead part of the pneumatic tire of FIG. It is a top view which shows the several bead wire arranged in parallel. It is a side view which shows the bead core comprised by winding the some bead wire arranged in parallel cyclically | annularly.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass layer 5 Bead core 5a-5h Bead wire 6 Belt layer

Claims (4)

  In a pneumatic tire having a bead core configured by annularly winding a plurality of bead wires arranged in parallel, the breaking elongation of the bead wire on the most bead toe side is 0.5% or more than the average breaking elongation of the other bead wires. A pneumatic tire in which the breaking strength of the bead wire on the most bead toe side is 80% or more of the average breaking strength of other bead wires.   The pneumatic tire according to claim 1, wherein the cross-sectional shape of all bead wires constituting the bead core is rectangular.   The pneumatic tire according to claim 1 or 2, wherein the breaking elongation of the bead wire on the most bead toe side is 4% to 10%, and the breaking strength of the bead wire on the most bead toe side is 1500 MPa to 2300 MPa.   The break elongation E1 (%) of the bead wire on the most bead toe side and the break elongation E2 (%) of the bead wire on the most bead toe side are defined as the inner circumference C1 (mm) of the bead wire on the most bead toe side and the inner circumference of the bead wire on the most bead heel side. The pneumatic tire according to any one of claims 1 to 3, which has a relationship of E1-E2> (C2-C1) / C2 × 100% with respect to the length C2 (mm).

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