JP2009161051A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of improving operational stability by effectively reinforcing bead parts while restraining a weight increase. <P>SOLUTION: In this pneumatic tire, the aspect ratio is set to 55% or less, and a rim diameter is set to 18 inches or more, and a carcass layer 4 of at least pone layer is installed between a pair of bead parts 3 and 3. A bead core 5 embedded in the respective bead parts 3 is composed of an annular core 5a forming an annular shape in the tire peripheral direction, and a sheath of at least one layer formed of a sheath wire 5b spirally wound on the periphery of the annular core 5a. The bead core 5 is covered with a rubber cover 6, and a bead filler 7 is arranged on the bead core 5 covered with the rubber cover 6. JIS hardness of the rubber cover 6 is set higher than JIS hardness of the bead filler 7, and an organic fiber cover 8 including an organic fiber cord 8a is arranged so as to wrap in the bead core 5 and the bead filler 7 covered with the rubber cover 6. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a pneumatic tire using a so-called cable bead as a bead core. More specifically, the present invention relates to a pneumatic tire capable of effectively reinforcing a bead portion while suppressing an increase in weight and improving steering stability. .

  As a bead core for a pneumatic tire, a so-called cable bead is proposed in which a sheath wire is spirally wound around an annular core to form a sheath of at least one layer (see, for example, Patent Documents 1 to 3). Such a cable bead has an advantage of higher strength than a normal bead core formed by winding one or a plurality of wires in layers.

  However, since the cable bead has a generally circular cross-sectional shape, it tends to be twisted and deformed when the tire is greatly bent. Particularly, when the tire inner diameter is increased, the twisted deformation becomes large, and as a result, steering stability is lowered. Tend to. On the other hand, for pneumatic tires having a flatness ratio of 55% or less and a rim diameter of 18 inches or more, for example, pneumatic tires for SUVs (Sports Utility Vehicles), the use of cable beads is desired. However, at the same time, excellent handling stability is also required.

Conventionally, a structure in which a cable bead is covered with a cover containing an organic fiber cord (for example, see Patent Document 1) or a structure in which a cable bead and a bead filler are integrally wrapped with a rubber cover (for example, see Patent Document 2) has been proposed. However, these structures do not provide sufficient steering stability.
JP 2006-137348 A JP 2002-254910 A JP 11-314507 A

  An object of the present invention is to provide a pneumatic tire capable of effectively reinforcing a bead portion while suppressing an increase in weight and improving steering stability.

  In order to achieve the above object, a pneumatic tire according to the present invention is a pneumatic tire having a flatness of 55% or less, a rim diameter of 18 inches or more, and at least one carcass layer mounted between a pair of bead portions. The bead core embedded in each bead portion is composed of an annular core having an annular shape along the tire circumferential direction and at least one layer of sheath formed by a sheath wire spirally wound around the annular core. The bead core is covered with a rubber cover, a bead filler is disposed on the bead core covered with the rubber cover, the JIS hardness of the rubber cover is higher than the JIS hardness of the bead filler, and the rubber cover An organic fiber cover including an organic fiber cord is disposed so as to enclose the bead core coated with the bead filler and the bead filler. Is shall.

  In the present invention, as a bead core of a pneumatic tire having a flatness ratio of 55% or less and a rim diameter of 18 inches or more, a so-called cable formed by spirally winding a sheath wire around an annular core to form a sheath of at least one layer. In adopting the bead, the bead core is covered with a rubber cover harder than the bead filler, and the bead core and the bead filler covered with the rubber cover are wrapped with the organic fiber cover, so that the bead portion can be formed while minimizing the weight increase. It becomes possible to effectively reinforce and improve steering stability.

  In the present invention, the bead core sheath preferably has two layers. Thereby, the improvement effect of steering stability can fully be exhibited, suppressing a weight increase. The thickness of the rubber interposed between the outermost sheath wire of the bead core and the organic fiber cord of the organic fiber cover is preferably 0.2 mm to 0.5 mm at the thinnest portion. As a result, it is possible to more reliably prevent a failure caused by rubbing between the sheath wire and the organic fiber cord while suppressing an increase in weight.

  The rubber cover preferably has a JIS hardness of 80 to 95, and the bead filler preferably has a JIS hardness of 60 to 75. Thereby, favorable steering stability can be ensured. The carcass layer is preferably a single layer. That is, when the carcass layer is made into a single layer for weight reduction, steering stability is lowered. In such a case, a remarkable effect can be obtained by applying the above structure.

  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. The pneumatic tire of this embodiment has a flatness ratio of 55% or less, preferably 30% to 55%, a rim diameter of 18 inches or more, preferably 18 inches to 22 inches, and a pneumatic tire for SUV. It is. In such a tire with a low flatness ratio, a large force acts on the sidewall part and the bead part during traveling, and the rim diameter is large, so when the cable bead conventionally used as the bead core is adopted as it is, the cable bead The amount of deformation tends to increase.

  In FIG. 1, 1 is a tread portion, 2 is a sidewall portion, and 3 is a bead portion. A single carcass layer 4 is mounted between the pair of left and right bead portions 3 and 3. The carcass layer 4 is wound around the bead core 5 from the inside to the outside of the tire.

  The bead core 5 includes a two-layer sheath formed by an annular core 5a (steel wire) that is annular along the tire circumferential direction, and a sheath wire 5b (steel wire) that is spirally wound around the annular core 5a. It is composed of The bead core 5 is covered with a rubber cover 6, and a rubber bead filler 7 is disposed on the bead core 5 covered with the rubber cover 6. The JIS hardness of the rubber cover 6 is higher than the JIS hardness of the bead filler 7. Here, the JIS hardness is a hardness measured using a durometer (type A) in accordance with a durometer hardness test specified in JIS K6253. Further, an organic fiber cover 8 is disposed in the bead portion 3 so as to wrap the bead core 5 and the bead filler 7 covered with the rubber cover 6. The organic fiber cover 8 includes a plurality of aligned organic fiber cords 8a, and the organic fiber cords 8a are arranged so that an angle with respect to the tire circumferential direction is 30 ° to 60 °. As the organic fiber cord of the organic fiber cover 8, an aramid fiber cord, a nylon fiber cord, a polyester fiber cord, or the like can be used. In particular, a highly elastic one represented by an aramid fiber cord can be used. preferable.

  On the other hand, two belt layers 9 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. These belt layers 9 include reinforcing cords that are inclined with respect to the tire circumferential direction, and these reinforcing cords are arranged so as to intersect each other between the layers. In addition, the winding-up end portion of the carcass layer 4 described above extends to a position overlapping the end portion of the belt layer 9 in the tire width direction. A belt cover layer 10 is embedded on the outer peripheral side of the belt layer 9. The belt cover layer 10 includes a reinforcing cord that is substantially 0 ° with respect to the tire circumferential direction. Such a belt cover layer 10 is formed by winding a strip formed by rubber coating one or a plurality of reinforcing cords spirally in the tire axial direction while orienting the strip in the tire circumferential direction.

  As described above, as a bead core for a pneumatic tire having a flatness ratio of 55% or less and a rim diameter of 18 inches or more, a sheath wire 5b is spirally wound around the annular core 5a to form at least one sheath. In adopting the bead core 5 (cable bead), the bead core 5 is covered with a rubber cover 6 harder than the bead filler 7, and the bead core 5 and the bead filler 7 covered with the rubber cover 6 are wrapped with the organic fiber cover 8. Further, it is possible to effectively reinforce the bead portion 3 while suppressing an increase in weight, and to improve steering stability. That is, the torsional deformation of the bead core 5 is suppressed by interposing the rubber cover 6 harder than the bead filler 7 between the bead core 5 and the bead filler 7, and the bead core 5, the rubber cover 6 and the bead filler are further suppressed by the organic fiber cover 8. It is possible to exert an excellent reinforcing effect by increasing the unity with 7.

  Here, the sheath of the bead core 5 is preferably two layers as shown in the figure. By making the sheath of the bead core 5 into two layers, the effect of improving the steering stability can be sufficiently exhibited while suppressing an increase in weight. That is, if the sheath of the bead core 5 is three layers or more, the weight increases, and if it is one layer, the rubber volume around the bead core becomes excessive and the effect of improving the steering stability is lowered.

  The thickness of the rubber interposed between the outermost sheath wire 5b of the bead core 5 and the organic fiber cord 8a of the organic fiber cover 8 is 0.2 mm to 0.5 mm at the thinnest portion. Thereby, it is possible to more reliably prevent a failure caused by rubbing between the sheath wire 5b and the organic fiber cord 8a while suppressing an increase in weight. If the rubber thickness is less than 0.2 mm at the thinnest part, failure due to rubbing between the sheath wire 5b and the organic fiber cord 8a tends to occur, and conversely if it exceeds 0.5 mm, the weight increases. The thickness of the rubber interposed between the outermost sheath wire 8b of the bead core 5 and the organic fiber cord 8a of the organic fiber cover 8 is 0.2 mm to 1.5 mm including the thinnest part and the thickest part. It is desirable.

  The rubber cover 6 has a JIS hardness set in a range of 80 to 95. When the JIS hardness of the rubber cover 6 is less than 80, the response at the time of steering is lowered due to the reduction in rigidity. Conversely, when it exceeds 95, the response at the time of steering becomes too sensitive and the steering stability is hindered.

  On the other hand, the JIS hardness of the bead filler 7 is set in a range of 60 to 75. When the JIS hardness of the bead filler 7 is less than 60, the response at the time of steering is lowered due to a decrease in rigidity. On the other hand, when it exceeds 75, the response at the time of steering becomes too sensitive and the steering stability is inhibited. In order to exhibit good steering stability, the height H of the bead filler 7 measured in the tire radial direction from the surface of the rubber cover 6 is desirably set in the range of 5% to 25% of the tire cross-sectional height. .

  It is preferable to adopt a structure in which the carcass layer 4 is formed as a single layer as shown in the figure, and the winding end portion extends to a position where it overlaps with the end portion of the belt layer 9 in the tire width direction. When the carcass layer is made into a single layer for weight reduction, the steering stability will be lower than when two or more carcass layers are provided. It is possible to achieve both improvement in performance.

  In a pneumatic tire having a tire size of 275 / 45R20 and a carcass layer mounted between a pair of bead portions, a bead core embedded in each bead portion is formed in an annular shape along the tire circumferential direction, Comparative Examples 1 and 2 and Example 1 in which the reinforcing structure of the bead core is made different as shown in Table 1 and is composed of at least one layer sheath formed by a sheath wire spirally wound around the annular core. -5 pneumatic tires were produced.

  In Comparative Example 1, a bead core is covered with an organic fiber cover (A) containing an aramid fiber cord, and a bead filler having a JIS hardness of 90 is disposed on the bead core covered with the organic fiber cover (A). In Comparative Example 2, a bead filler having a JIS hardness of 90 is disposed on a bead core, and a rubber cover (B) having a JIS hardness of 80 is disposed so as to wrap the bead core and the bead filler.

  In Examples 1 to 5, a bead core is covered with a rubber cover (C), a bead filler is placed on the bead core covered with the rubber cover (C), and the bead core and beads covered with these rubber covers (C) are used. An organic fiber cover (D) including an aramid fiber cord is disposed so as to wrap the filler. In Examples 1 to 5, the structure of the bead core, the JIS hardness of the rubber cover (C), the minimum thickness of the rubber cover (C) (the minimum thickness of the rubber interposed between the sheath wire and the organic fiber cord), the bead Various fillers had different JIS hardness.

  In Comparative Examples 1-2 and Examples 1-5, a core wire with a diameter of 1.8 mm was used for the annular core of the bead core, and a sheath wire with a diameter of 1.4 mm was used for the sheath of the bead core.

  These test tires were evaluated for steering stability and tire weight by the following methods, and the results are also shown in Table 1.

Steering stability:
The test tire was assembled on a wheel with a rim size of 20 × 9 J and mounted on a test vehicle, and sensory evaluation was performed by a test driver on a dry road surface test course under a condition of air pressure of 240 kPa. The evaluation results are shown as an index with Comparative Example 1 as 100. The larger the index value, the better the steering stability.

Tire weight:
The weight of the test tire was measured. The evaluation results are shown as an index with Comparative Example 1 being 100, using the reciprocal of the measured value. A larger index value means lighter weight.

  As is clear from Table 1, the tires of Examples 1 to 5 were able to greatly improve steering stability while minimizing the increase in weight in comparison with Comparative Examples 1 and 2.

It is meridian sectional drawing which shows the principal part of the pneumatic tire which consists of embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass layer 5 Bead core 5a Annular core 5b Sheath wire 6 Rubber cover 7 Bead filler 8 Organic fiber cover 8a Organic fiber cord 9 Belt layer 10 Belt cover layer

Claims (6)

  In a pneumatic tire having a flatness ratio of 55% or less and a rim diameter of 18 inches or more, and having at least one carcass layer mounted between a pair of bead portions, bead cores embedded in each bead portion are arranged in the tire circumferential direction. And an at least one layer sheath formed by a sheath wire spirally wound around the annular core, the bead core is covered with a rubber cover, and the rubber cover The bead filler is disposed on the coated bead core, the JIS hardness of the rubber cover is set higher than the JIS hardness of the bead filler, and the bead core covered with the rubber cover and the organic fiber are wrapped around the bead filler. A pneumatic tire comprising an organic fiber cover including a cord.   The pneumatic tire according to claim 1, wherein the bead core has two sheaths.   The rubber which is interposed between the outermost sheath wire of the bead core and the organic fiber cord of the organic fiber cover is 0.2 mm to 0.5 mm in the thinnest portion. Item 3. The pneumatic tire according to Item 2.   The pneumatic tire according to any one of claims 1 to 3, wherein the rubber cover has a JIS hardness of 80 to 95.   The pneumatic tire according to any one of claims 1 to 4, wherein the bead filler has a JIS hardness of 60 to 75.   The pneumatic tire according to claim 1, wherein the carcass layer is a single layer.

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