JP5018955B2 - Pneumatic radial tire - Google Patents

Description

  The present invention relates to a pneumatic radial tire including a reinforcing layer formed by embedding a steel cord having a twisted layer structure composed of a plurality of strands in rubber, and more specifically, an air that can improve tire durability. Related to radial tires.

  In general, as a reinforcing material for a belt portion and a carcass portion of a pneumatic radial tire, a steel cord having a layer twist structure including a core made of at least one strand and a sheath made of a plurality of strands is used. . As such a layer twist structure, for example, an M + N + L structure in which a sheath made of N strands around a core made of M strands and a sheath made of L strands around the core is arranged. (For example, refer to Patent Document 1).

  However, in this type of steel cord, the cord is repeatedly deformed while the tire is running, so that the strands rub against each other at the point contact portion and wear, resulting in so-called fretting wear. There is a problem of losing.

  In order to suppress this fretting wear, it is known that it is effective to reduce the twist angle of the outermost strand of the steel cord. That is, the contact pressure between the strands can be reduced by reducing the twist angle of the strands of the outermost layer.

  However, when the twist angle of the outermost strand becomes small, the straightness of the cord deteriorates due to the influence of the straightness of the strand, resulting in a problem that the tire durability deteriorates. In other words, when processing a reinforcing material such as a belt part or a carcass part, a member coated with rubber by aligning a plurality of steel cords is cut, and the cut pieces are spliced along side parts. However, if the straightness of the cord deteriorates, the splicing accuracy deteriorates, so that the cord interval may be too wide or the cords may come into contact with each other. As a result, for example, in the carcass portion, a blowout failure or the like is likely to occur in the tire shoulder.

JP 2007-023400 A

  An object of the present invention is to solve the above-described problems, and in a pneumatic radial tire including a reinforcing layer formed by embedding a steel cord having a twisted layer structure composed of a plurality of strands in rubber, tire durability It is an object of the present invention to provide a pneumatic radial tire that can improve performance.

  In order to achieve the above object, a pneumatic radial tire according to the present invention is a pneumatic radial tire provided with a reinforcing layer formed by embedding a steel cord having a layer twist structure composed of a plurality of strands in rubber. A strand pre-twisted around its axis is used as the outermost strand of the cord, the wire surface twist angle of the outermost strand is set to 1 ° or more, and the twist angle of the outermost strand is set to 4 to It is characterized by being 7 °.

  In the present invention, the strand that has been twisted in advance is used as the outermost strand of the steel cord constituting the reinforcing layer, and the twist angle of the outermost strand is smaller than the conventional one by defining the wire surface twist angle. Even if the fretting wear is suppressed by 4 to 7 °, the straightness of the cord is improved, so that the splicing accuracy can be improved and the tire durability can be improved.

  In the present invention, it is preferable that the twisting direction and the twisting direction of the outermost strand are the same direction. By doing so, the effect of improving the straightness of the cord is great, and the tire durability can be further improved.

  In the present invention, the wire surface twist angle of the outermost strand is preferably set to 15 ° or less. In order to improve the straightness of the cord, it is desirable to increase the wire surface twist angle. By defining the upper limit value of the wire surface twist angle as described above, it is possible to avoid the difficulty in manufacturing the cord.

  The reinforcing layer to which the steel cord is applied is not particularly limited, but the steel cord is preferably applied to the carcass layer.

In the present invention, the twist angle θ1 and the wire surface twist angle θ2 of the outermost strand are measured as follows. First, the steel cord is taken out from the pneumatic tire, the cord is immersed in an organic solvent to swell the rubber adhering to the surface, and then the rubber is removed. Then, the cord diameter d1 (mm) of the steel cord, the outermost layer strand diameter d2 (mm), and the twist length P1 (mm) of the outermost layer strand are measured. Each dimension is an average value of measured values at at least 10 locations. Based on the cord diameter d1, the outermost layer strand diameter d2, and the twist length P1, the twist angle θ1 of the outermost layer strand is calculated from the following equation (1).
θ1 = ATAN (π × (d1−d2) / P1) × 180 / π (1)

Further, the steel cord is disassembled, the outermost layer strand is taken out, the strand is immersed in an organic solvent to swell the rubber adhering to the surface, and then the rubber is removed. Then, the strand is observed with an optical microscope in a state where the outermost strand is fixed in a straight line, and a value of ½ of the twist pitch P2 (mm) is measured from the wire trace formed on the wire surface, The twist pitch P2 is obtained by doubling it. The twist pitch P2 is an average value of measured values at at least 10 locations. The wire surface twist angle θ2 is calculated from the following equation (2) based on the twist pitch P2 and the outermost strand diameter d2.
θ2 = ATAN (π × d2 / P2) × 180 / π (2)

1 is a meridian half cross-sectional view showing a pneumatic radial tire according to an embodiment of the present invention. It is sectional drawing which shows an example of the steel cord which comprises a reinforcement layer by this invention. It is a side view which shows an example of the steel cord which comprises a reinforcement layer by this invention. It is a side view which shows the outermost layer strand of the steel cord which comprises a reinforcement layer by this invention. It is a side view which expands and shows a part of FIG.

  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 steel cord constituting a reinforcing layer in the present invention, and FIGS. 4 and 5 show steel constituting a reinforcing layer in the present invention. This shows the outermost strand of the cord.

  In FIG. 1, 1 is a tread portion, 2 is a sidewall portion, and 3 is a bead portion. A carcass 4 is mounted between the pair of left and right bead portions 3 and 3. The carcass layer includes a plurality of reinforcing cords extending in the tire radial direction, and is folded from the tire inner side to the outer side around the bead core 5 disposed in each bead portion 3. A bead filler 6 is disposed on the outer periphery of the bead core 5, and the bead filler 6 is wrapped by the main body portion and the folded portion of the carcass layer 4.

  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 10 to 40 °, for example.

  In the pneumatic radial tire described above, a steel cord having a twisted layer structure composed of a plurality of strands as a reinforcing cord constituting at least one reinforcing layer (preferably, the carcass layer 4) selected from the carcass layer 4 and the belt layer 7 8 is used (see FIG. 2). In FIG. 2, the steel cord 8 is formed in a 3 + 8 structure in which a sheath 12 composed of eight strands 11 is arranged around a core 10 composed of three strands 9. In the present invention, the layer twist structure is not limited to the 3 + 8 structure shown in the figure, and an M + N structure in which a sheath made of N strands is arranged around a core made of M strands, and an L around the core. An M + N + L structure in which a sheath made of strands of wires is added can be used. Here, it is preferable that 1 ≦ M ≦ 3, 6 ≦ N ≦ 9, and 12 ≦ L ≦ 15.

  In the present invention, the fretting wear is suppressed by setting the twist angle θ1 of the outermost strand of the steel cord 8 to 4 to 7 ° which is smaller than the conventional one (see FIG. 3). In FIG. 3, for easy understanding, the twist angle θ <b> 1 is depicted to be larger than actual. However, since there is a problem that the straightness of the cord is reduced simply by reducing the twist angle θ1, in the present invention, the outermost layer strand of the steel cord 8, that is, the strand 11 constituting the sheath 12, A strand (see FIGS. 4 and 5) pre-twisted around the shaft is used. In FIG. 5, a wire trace 13 resulting from the wire drawing is formed on the surface of the wire 11. The twist pitch P <b> 2 (mm) determined based on the wire draw 13 and the wire 11. The wire surface twist angle θ2 with respect to the axial direction of the strand 11 calculated from the strand diameter d2 (mm) is set to 1 ° or more, preferably 1 ° to 15 °.

  As described above, the strand 11 twisted around the axis is used as the outermost strand 11 and the straightness of the strand 11 is improved by defining the wire surface twist angle θ2 with respect to the axial direction of the strand 11. The straightness of the entire steel cord 8 can be improved. Therefore, the tire endurance performance can be improved by setting the twist angle θ1 of the outermost strand to a range smaller than the conventional one without reducing the straightness of the cord.

  Here, if the twist angle θ1 of the outermost layer strand is less than 4 °, the strand is likely to move, so that fretting wear is likely to be induced. Conversely, if it exceeds 7 °, a sufficient fretting wear prevention effect cannot be obtained.

  Further, if the wire surface twist angle θ2 is less than 1 °, the effect of improving the straightness of the outermost strand 11 becomes insufficient. On the other hand, if it exceeds 15 °, straightness is improved, but it becomes difficult to manufacture the cord due to excessive twisting.

  In the pneumatic radial tire, it is preferable that the twisting direction and the twisting direction of the outermost strand 11 are the same direction. This can improve the straightness of the code. That is, when the twist direction and the twist direction of the strand 11 of the outermost layer are made the same, the twist of the strand 11 increases with the twist, so that the straightness is obtained even if the twist angle of the outermost layer is small. It becomes easy to improve.

  In the pneumatic tire, a reinforcing cord usually used in the tire industry can be used for a portion where the steel cord 8 is not applied as the reinforcing cord of the carcass layer 4 and the belt layer 7. Examples of such a reinforcing cord include a steel cord formed by twisting a plurality of filaments, and an organic fiber cord represented by nylon and polyester.

  In a pneumatic radial tire having a carcass layer in which a tire cord is made common to 295 / 80R22.5, and a steel cord having a twisted layer structure composed of a plurality of strands is embedded in rubber, a twisted structure of the steel cord, The wire diameter, the outermost strand twist length, the outermost strand twist angle θ1, the outermost strand twist direction, the outermost strand wire surface twist angle θ2, and the outermost strand twist direction The tires of Conventional Example 1, Comparative Example 1, and Examples 1 to 5 set as 1 were manufactured.

  About these test tires, the tire durability performance was evaluated by the following evaluation method, and the results are also shown in Table 1.

Tire durability performance The test tire is mounted on a wheel with a rim size of 22.5 × 8.25, and is run on a rotating drum with a diameter of 1707 mm at an air pressure of 850 kPa, a load of 45 kN, and a speed of 45 km / h until the tire breaks down. Was measured. The conventional example is indicated by an index of 100. A larger index value means a longer mileage and better tire durability.

  As can be seen from Table 1, in each of Examples 1 to 5, the straightness of the steel cord was improved and the tire durability performance was improved in comparison with the conventional example. On the other hand, since the straightness of the cord deteriorated in Comparative Example 1, the effect of improving the tire durability performance was insufficient.

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass 5 Bead core 6 Bead filler 7 Belt layer 8 Steel cord 9 Strand 10 Core 11 Strand 12 Sheath 13 Wire trace

Claims (4)

In a pneumatic radial tire having a reinforcing layer formed by embedding a steel cord having a twisted layer structure composed of a plurality of strands in rubber,
As the outermost strand of the steel cord, a strand pre-twisted around its axis is used, the wire surface twist angle of the outermost strand is set to 1 ° or more, and the twist angle of the outermost strand is set. A pneumatic radial tire characterized by being set to 4 to 7 °.   The pneumatic radial tire according to claim 1, wherein the twisting direction and the twisting direction of the outermost strand are the same direction.   The pneumatic radial tire according to claim 1 or 2, wherein a wire surface twist angle of the outermost strand is set to 15 ° or less. The pneumatic radial tire according to claim 1, wherein the reinforcing layer is a carcass layer.

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