JP4865274B2 - Pneumatic radial tire - Google Patents

Description

  The present invention relates to a pneumatic radial tire, and more particularly to a heavy-duty pneumatic radial tire with improved durability.

  In recent years, with the aim of improving truck transportation efficiency, European truck manufacturers have been aggressively pushing ahead with the development of trucks, and as a result, developing heavy duty pneumatic radial tires with superior flatness ratios of 70% or less. Is desired.

  In a pneumatic radial tire with a small aspect ratio called a super single tire, in order to improve belt durability deterioration and uneven wear resistance due to insufficient rigidity of the belt part, it is between the working belt (main belt) or between the working belt and the carcass. There has been proposed a radial tire in which an additional ply made of a steel cord is disposed between the plies at an angle of substantially 0 ° with respect to the tire circumferential direction (for example, Patent Documents 1 to 3).

According to such a tire, it is possible to effectively prevent the tread from bulging outward in the radial direction when the tire is filled with internal pressure and when the tire is rolling with a load, compared to a tire provided with only a working belt. Thus, it is considered that the durability of the belt can be improved.
Special Table 2000-504655 JP 2001-512390 A JP-T-2001-522749

  However, if a rigid cord such as a normal steel cord is disposed at a substantially 0 ° angle in the tire circumferential direction, it becomes difficult to expand during tire vulcanization. A so-called high elongation cord is used in which the slope of the SS curve is gentle up to 1 to 2% and suddenly increases beyond that, thereby facilitating expansion during vulcanization.

  However, as the above-mentioned high elongation cords, cords having a double twist structure such as a 3 × 7, 4 × 4 structure are generally used. However, these double twist cords have a drawback that the manufacturing cost is high and the tire cost is affected. is there.

  In addition, rubber penetrates the inside of the cord during vulcanization, and a large number of filaments are restrained inside the cord, making it impossible to secure sufficient low-load elongation. There is a problem that the performance is lowered.

  The present invention has been made in view of the above problems, and by reducing the price of the cord having the characteristics of the above-mentioned high elongation cord, the uneven wear of the tread portion is improved and the belt durability is improved. An object of the present invention is to provide a pneumatic radial tire suitable for the above.

  The present invention has been made as a result of intensive studies to solve the above-described problems of the prior art. That is, the ends of the steel cords arranged in the tire circumferential direction around the pair of left and right bead cores are folded and locked. And at least two layers of main belts made of steel cords that intersect and extend on the outer periphery side of the tread portion of the carcass, and steel cords at an angle of substantially 0 ° with respect to the tire circumferential direction. In a pneumatic radial tire provided with an extended 0 ° belt, a steel cord constituting the 0 ° belt has a 1 × N (N = 3 to 3) wire diameter D of 0.3 to 0.4 mm. 5) It is a structure, and each strand which comprises this steel cord has a spiral continuous wave in a longitudinal direction, and the undulation height H and strand diameter D of this continuous wave are 1.1 <= H / Satisfies the relationship of D ≦ 1.5, One said steel cord twisting pitch P (mm) is a pneumatic radial tire, which is a 5.0 ≦ P ≦ 10.0.

  Moreover, it is preferable that the cord diameter of the 1 × N steel cord is smaller than the diameter of the steel cord constituting the main belt.

  The 0 ° belt can be provided by continuously winding the 1 × N steel cord in the circumferential direction of the tire in a spiral shape.

  Furthermore, the 0 ° belt is disposed adjacent to at least one layer of the main belt, and the width of the 0 ° belt is preferably 90% or less of the width of the adjacent main belt.

  The pneumatic radial tire of the present invention is suitable for a tire having an aspect ratio of 60% or less.

  According to the pneumatic radial tire of the present invention, by applying a continuous wave to the strand, a low load elongation property sufficient even in a state with rubber after vulcanization while being an inexpensive single twist structure 1 × N steel cord This can be used as a 0 ° belt cord to facilitate expansion behavior during tire vulcanization, while improving belt rigidity and restraint in the tire circumferential direction, and even in the low load region of the tire. It is possible to maintain the elongation and disperse the stress concentration during traveling, thereby improving the durability of the tire and suppressing the occurrence of uneven wear.

  Hereinafter, a pneumatic radial tire according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a half sectional view of a tire T showing an example of a heavy-duty pneumatic radial tire. Reference numeral 1 is a belt composed of four layers of belt plies, 2 is a carcass, 3 is a tread portion, and 4 is a bead portion. Reference numeral 5 denotes a sidewall portion.

  The tire T has a single carcass ply 2 in which steel cords extending in the tire width direction are arranged at predetermined intervals in the tire circumferential direction between a pair of left and right bead portions 4, and both end portions thereof are connected to the bead portions 3. The bead filler 7 is sandwiched around the embedded bead core 6 and folded and locked from the inside to the outside of the tire. On the outer peripheral side of the carcass ply 2 of the tread portion 3, a belt 1 composed of four layers of belt plies is disposed.

  FIG. 2 schematically shows a cross section of the tread portion 3 of the tire according to the embodiment, and illustrates the configuration of the belt ply.

  In FIG. 2, the belt 1 is composed of four layers of belt plies 11, 12, 13, and 14 (shown by broken lines). Belt plies 11 and 13 are belt layers forming the main belt of the tire, and steel cords for belts such as 3 × 0.20 + 6 × 0.35, 3 + 9 + 15 × 0.23, etc., are at a predetermined angle with respect to the tire circumferential direction. Are arranged so as to cross each other.

  In addition, the belt ply 14 is a protective belt arranged at a constant angle in the tire circumferential direction made of a steel cord excellent in cut resistance and rubber penetration, so-called top belt, and improves the resistance to damage and renewability. Yes.

  The belt ply 12 shown in the drawing constitutes a 0 ° belt according to the present invention in which steel cords are arranged and extended at predetermined intervals at an angle of substantially 0 ° with respect to the tire circumferential direction.

  On the other hand, the belt 100 of the conventional tire T1 is composed of four layers of belt plies of angled main belts 111, 112, 113 and a top belt 114 as shown in the schematic diagram of FIG.

  In the tire T of the embodiment, the steel cord 10 used for the 0 ° belt 12 has a 1 × N (N = 3 to 5) structure in which the wire diameter D is 0.3 to 0.4 mm.

  With a steel cord 10 of 1 × N structure, if the number N of wires is less than 3, the cord rigidity is insufficient. If it exceeds 5, the arrangement of the wires becomes unstable when twisted, and the cord shape becomes unstable. If the diameter D is less than 0.3 mm, the rigidity is insufficient, and if it exceeds 0.4 mm, the fatigue resistance decreases.

  Each strand constituting the steel cord 10 is provided with a spiral continuous wave processed in the longitudinal direction of the strand F as shown in FIG. The continuous wave undulation height H and the wire diameter D preferably satisfy the relationship 1.1 ≦ H / D ≦ 1.5, ensuring mechanical properties such as cord elongation and rubber penetration. Further, by being twisted at a twist pitch described later, even when the rubber after vulcanization is attached, it is possible to have a predetermined range of elongation characteristics when stretched in a low load region.

  If the above H / D is less than 1.1, sufficient elongation in the low load region cannot be obtained with rubber after vulcanization, and if it exceeds 1.5, the shape of the cord becomes unstable and the processability is reduced. There is a risk of damage. The pitch Pf of the continuous wave is not particularly limited, but is preferably in the range of about 0.25 ≦ Pf / P ≦ 1.50 with respect to the twisting pitch P of the cord.

  Such a spiral continuous wave can be corrugated by a known mold forming device in which mold pins and rollers are arranged in a staggered manner. For example, the wire focusing voice and the wire supply bobbin of a buncher type twisting machine The steel cord 10 having a 1 × N structure can be manufactured in one process by disposing the molding apparatus between them.

  The twist pitch P (mm) of the steel cord 10 is 5.0 ≦ P ≦ 10.0 mm. If P is less than 5 mm, the twisted wire processing becomes difficult due to the wavy wire, and the shape tends to collapse. If it exceeds 1, the elongation of the bare cord cannot be sufficiently obtained, and expansion during vulcanization becomes difficult.

  As shown in FIG. 5 (in the case of N = 5), the steel cord 10 has gaps S randomly formed between the strands F in the longitudinal direction of the cord so that rubber can penetrate into the cord. Can be improved.

As shown in FIG. 6, the steel cord 10 has a vulcanized rubber attached, and an SS curve with the vertical axis representing the load (N) and the horizontal axis representing the elongation (%), as shown in FIG. It shows a behavior having an inflection point Z that behaves with a gentle inclination, and the inclination suddenly increases as the load increases. Specifically, the tensile elastic modulus in a low load region is preferably 5000 N / mm ² or less, more preferably 4000 to 5000 N / mm ² .

  This means that in the low load region of the SS curve, when a tensile force is applied in the cord axis direction, each strand gradually tightens the rubber R that has entered the inside of the cord toward the inside, thereby showing a gentle inclination due to rubber elasticity. When the allowance due to the wire is lost, the steel wire suddenly changes to a large inclination, and the inflection point Z is obtained.

  In the present invention, it is preferable that the elongation A (%) of the intersection of the tangent line X of the slope in the low load region and the tangent line Y of the slope after the inflection point is 0.5 ≦ A ≦ 1.5. It is. If the elongation at the intersection A is less than 0.5%, the cord rigidity becomes high and the stress distribution during running becomes insufficient, and if it exceeds 1.5%, the 0 ° belt restraint force is insufficient and the durability is lowered. Tend to.

  The positional relationship of the 0 ° belt 12 in the belt layer 1 is not particularly limited, but the 0 ° belt 12 is disposed adjacent to at least one layer of the main belts 11 and 13, that is, the 0 ° belt 12. Is preferably disposed between the main belt layers 11 and 13 or between the main belt 11 and the carcass ply 2 on the inner side in the tire radial direction. By setting the width of the 0 ° belt 12 to 90% or less of the width of the belt layer on the outer side in the radial direction, stress concentration on the 0 ° belt edge portion can be reduced.

  In this case, the cord diameter of the steel cord of the 0 ° belt 12 is preferably smaller than the diameter of the steel cord constituting the main belts 11 and 13, and the 0 ° belt layer 12 is thicker than the main belt layers 11 and 13. This is because the distortion inside the belt concentrates on the 0 ° belt and the separation resistance deteriorates.

  Further, the 0 ° belt 12 may be disposed between the main belt 13 and the top belt 14 on the radially outer side.

  The 0 ° belt 12 can be provided by winding the steel cord 10 continuously in the circumferential direction of the tire T in a spiral shape. The cord angle of the steel cord 10 is substantially 0 ° with respect to the tire circumferential direction. For example, one cord 10 is wound in a spiral shape while being shifted in the width direction of the tire T. Further, a ribbon-like belt-like member in which several cords 10 are aligned and covered with rubber is wound by spirally winding the ribbon-like side end portions for each circumference of the molding drum during tire molding. Is called.

  The pneumatic radial tire according to the present invention can improve the durability and uneven wear resistance of the tire by using the 1 × N steel cord for the 0 ° belt having the above-described configuration. It is suitable for a tire having a flatness ratio (ratio of tire height / total tire width) of 60% or less used in a load vehicle. Moreover, it can contribute to cost reduction by increasing code productivity.

  Next, the present invention will be specifically described with reference to examples.

  A radial tire having a tire size of 385 / 55R22.5 having the belt configuration shown in FIG. 2 was prototyped. The 0 ° belt was placed on the No. 2 belt 12 and each steel cord shown in Tables 1 and 2 was used. The configuration of Nos. 1 to 4 belts is shown in Table 3 for the examples and comparative examples, and Table 4 for the conventional examples. In the conventional example, the 0 ° belt is not used, and in the angle column in the table, the right and left indicate the inclination direction of the belt cord.

  The following evaluation was performed and the results are shown in Tables 1 and 2. A common member was used for each part other than the belt.

[Tensile test]
Each steel cord is subjected to a tensile test (based on JIS G3510) with vulcanized rubber, and the tangent of the slope in the low load region and the tangent of the slope after the inflection point from the SS curve shown in FIG. The elongation A (%) at the intersection and the tensile elastic modulus in the low load region were determined.

[Shape stability]
Regarding the shape stability of the cord, the appearance of the twisted cord was visually observed. ○: good, Δ: slightly out of shape but no problem in use, x: out of shape.

[Tire durability]
Using a drum testing machine with a 1700 mm diameter rotating drum made of steel with a smooth surface, the ambient temperature is 38 ± 3 ° C., the tire internal pressure is 900 KPa, the load load is 4500 Kg, and the speed is 56 Km / h, 8 Km / h every 12 hours. Increased and allowed to run until failure occurred. The distance traveled until the failure occurred is shown in Table 1 as an index with the conventional example being 100. The larger the index, the better the durability.

[Uneven wear resistance]
Attached to the driving wheel of a large truck, the tread contact surface after traveling 50,000 km in an actual vehicle was observed, and the occurrence of uneven wear was judged as good to equivalent to bad based on the conventional example.

As shown in the table, Examples 1 and 2 are excellent in both tire durability and uneven wear resistance. On the other hand, each comparative example that departs from the present invention has the following drawbacks. That is, the comparative example 1 has a 1 × 2 cord structure, the cord rigidity is insufficient, and the durability and uneven wear resistance are inferior. In the comparative example 2 of the 1 × 6 structure, one strand is The cord partially enters the inside of the cord and the stability of the cord is poor. As a result, the fatigue resistance of the cord is lowered and the tire durability is inferior. In Comparative Example 3 with a small H / D, the low load region elongation is insufficient, the stress concentration during running cannot be dispersed, and the durability of the tire is lowered. Conversely, in Comparative Example 4 with a large H / D, the low load is low. The area elongation becomes too large, the belt binding force is insufficient, and uneven wear is not improved. In Comparative Example 5, the twisted pitch is small and the cord shape is not stable, the durability is lowered, and in Comparative Example 6 where the pitch is large, the cord cannot follow expansion during tire vulcanization, and the belt shape is not formed as designed, The stress during running cannot be dispersed and the durability is poor. In Comparative Example 7 where the width of the 0 ° belt is wide, stress concentrates on the edge portion and distortion occurs. Therefore, separation occurs in the edge portion, and in Comparative Example 8 where the cord diameter of the 0 ° belt is thicker than the cord of the main belt, The separation progresses quickly and durability is not improved.

  As described above, the pneumatic radial tire according to the present invention is excellent in belt durability and uneven wear resistance, and therefore can be used for heavy duty truck and bus tires. Particularly, the flatness is 60%. It is suitable for the following radial tires.

1 is a half sectional view of a pneumatic radial tire according to an embodiment. It is sectional drawing which shows the belt structure of embodiment typically. It is sectional drawing which shows the belt structure of a prior art example typically. It is explanatory drawing of the corrugation of a strand continuous wave. It is sectional drawing of the steel cord of embodiment. It is a graph which shows an example of the SS curve of a cord with rubber.

Explanation of symbols

11, 13 …… Main belt 12 …… 0 ° belt T …… Pneumatic radial tire

Claims (5)

A carcass in which ends of steel cords arranged in the tire circumferential direction around a pair of left and right bead cores are folded and locked, and at least an outer peripheral side of the tread portion of the carcass and made of steel cords that intersect and extend from each other In a pneumatic radial tire including a two-layer main belt and a 0 ° belt having a steel cord extended at an angle of substantially 0 ° with respect to the tire circumferential direction,
The steel cord constituting the 0 ° belt has a 1 × N (N = 3 to 5) structure in which the strand diameter D is 0.3 to 0.4 mm, and each strand constituting the steel cord is long. A spiral wave in the direction, the corrugation height H of the continuous wave and the wire diameter D satisfy the relationship 1.1 ≦ H / D ≦ 1.5, and the twist pitch of the steel cord P (mm) is 5.0 <= P <= 10.0. The pneumatic radial tire characterized by the above-mentioned. The 1 × cord diameter of N steel cord, pneumatic radial tire according to claim 1, wherein a smaller diameter than the steel cord diameter constituting the main belt. The 0 ° belt, pneumatic radial tire according to claim 1 or 2, characterized in that the 1 × N steel cord wound spirally in the circumferential direction a series of the tire. The 0 ° belt, the main belt is arranged adjacent to at least one layer of the claims 1-3, wherein the width of the 0 ° belt is not more than 90% of the width of the main belt adjacent Pneumatic radial tire described in any one. The flat radial tire according to any one of claims 1 to 4 , wherein the flatness is 60% or less.

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