JP2009248751A - Pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic radial tire suitable for use for a heavy load with improved uneven wear of a tread part and improved belt durability. <P>SOLUTION: This pneumatic radial tire comprises main belts 11, 13 composed of steel cords extending to cross with each other, and a belt 12 having a steel cord C extended at an angle of 0° relative to a tire peripheral direction. The 0° belt 12 is composed of the steel cord C having a 4×4 multiple twisting structure composed by twisting strands S so that the strands S and element wires F constituting the strands S have prescribed continuous waves formed thereon (element wire corrugated height h and strand diameter d satisfy 0.90≤h/d≤1.00, and strand corrugated height H and cord diameter D satisfy 0.90≤H/D≤1.00), and further, a cord twisting pitch Pc and the cord diameter D satisfy the relation of 5.5≤Pc/D≤6.5, and the strand twisting pitch Ps and the cord diameter D satisfy the relation of 2.5≤Ps/D≤3.5. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a pneumatic radial tire.

  In recent years, the development of trucks for the purpose of improving the efficiency of truck transportation has been actively promoted, and accordingly, the development of heavy-duty pneumatic radial tires with excellent durability and flatness of 70% or less has been requested. Yes.

  In pneumatic radial tires with a small flatness ratio called super single tires, in order to reduce tire durability due to insufficient rigidity of the belt and to improve uneven wear resistance of the tread, together with the working belt (main belt) It has been proposed to provide a layer (0 ° belt) in which steel cords are arranged at an angle of substantially 0 ° with respect to the tire circumferential direction. 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.

  However, when a rigid cord such as a normal steel cord is disposed at a substantially 0 ° angle in the tire circumferential direction, it is difficult to expand at the time of tire vulcanization. Therefore, as these steel cords, so-called high elongation cords are used in which the slope of the SS curve of the cord is gentle up to 1 to 2% and suddenly increases beyond that. Easy expansion.

  As such a high elongation cord, a cord with a double twist structure is generally used. However, in a conventional cord with a double twist structure, a large number of filaments are formed inside the cord by rubber entering the cord during vulcanization. It will be restrained by. As a result, there is a problem that the cord cannot be sufficiently stretched in the low load region when the rubber is attached, the cord during tire running is excessively strained, and the durability decreases due to stress concentration (the following patents) Reference 1).

Patent Document 2 below discloses that a steel cord having a 3 × 4 double-twist structure is twisted using strands that are corrugated. However, this document only discloses that the steel cord is used for a working belt provided so as to intersect with the tire circumferential direction at a predetermined angle, and does not disclose application to a 0 ° belt. Further, by attaching the strands, a gap is provided between the strands to allow rubber to enter the cord, and does not suggest any features of the present invention.
JP 2007-055389 A Japanese Patent Laid-Open No. 05-186976

  The present invention has been made in view of the above problems, and can ensure elongation in a low load region even in a state with rubber after vulcanization, and by using this as a cord of a 0 ° belt, An object of the present invention is to provide a pneumatic radial tire capable of improving the belt rigidity and restraint property in the direction and improving the durability and uneven wear resistance of the tire.

  A pneumatic radial tire according to the present invention includes a carcass whose both ends are locked by a pair of left and right bead cores, and at least two layers of steel cords that intersect with each other and extend on the outer peripheral side of the carcass in a tread portion. In the pneumatic radial tire including the main belt and the 0 ° belt in which the steel cord is extended at an angle of substantially 0 ° with respect to the tire circumferential direction, the steel cord constituting the 0 ° belt is: A cord of a 4 × 4 double twisted structure in which four strands are formed by twisting four strands so that each strand constituting the strand has a continuous wave in the longitudinal direction. The strands of corrugated height h and strand diameter d satisfy the relationship of 0.90 ≦ h / d ≦ 1.00, and each strand constituting the cord And the cord undulation height H and cord diameter D of the strand satisfy the relationship of 0.90 ≦ H / D ≦ 1.00, and the cord twist pitch Pc and cord diameter D satisfy the relationship of 5.5 ≦ Pc / D ≦ 6.5, and strand twist pitch Ps and cord diameter D satisfy the relationship of 2.5 ≦ Ps / D ≦ 3.5. is there.

  According to the present invention, a steel cord having a double twist structure having a 4 × 4 structure, in which a strand constituting the cord and the strands constituting the strand are respectively subjected to predetermined molding, can be used. Can be prevented, so that elongation in a low load region can be secured even in a state with rubber after vulcanization. Therefore, by using this as a 0 ° belt cord, the expansion behavior at the time of tire vulcanization can be facilitated, and even in the tire, the cord elongation in the low load region is maintained and the stress concentration during traveling is dispersed. be able to. In addition, while ensuring elongation in such a low load region, the belt rigidity and restraint in the tire circumferential direction can be improved when filling the tire with internal pressure or when rolling the tire, and the durability of the tire can be improved. And the occurrence of uneven wear can be suppressed.

  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 denotes a belt composed of four belt layers, reference numeral 2 denotes a carcass, reference numeral 3 denotes a tread portion, reference numeral 4 Indicates a bead portion, and reference numeral 5 indicates a sidewall portion.

  The tire T has a single carcass 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. The carcass 2 is folded and locked from the inside to the outside of the tire so that the bead filler 7 is sandwiched around the bead core 6 embedded in the bead portion 3 at both ends. A belt 1 composed of four belt layers is disposed on the outer peripheral side of the carcass 2 in the tread portion 3.

  FIG. 2 schematically illustrates a cross-section of the tread portion 3 of the tire T according to the embodiment, and illustrates a belt configuration. In FIG. 2, the belt 1 includes four layers of a first belt 11, a second belt 12, a third belt 13, and a fourth belt 14 in order from the inner side in the tire radial direction (all belts are broken lines). Show).

  The first belt 11 and the third belt 13 are belt layers forming a main belt (working belt) of a tire, and conventional steel cords for belts are arranged at a predetermined angle with respect to the tire circumferential direction at predetermined intervals. The cords are arranged to cross each other.

  The fourth belt 14 is a so-called top belt, which 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, and improves the resistance to damage and renewability. .

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

  As shown in FIG. 3, the steel cord C constituting the 0 ° belt 12 is a composite of 4 × 4 structure in which four strands S obtained by twisting four strands (filaments) F are further twisted. A cord with a twisted structure.

  The reason why the steel cord C has a “4 × 4” double twist structure as described above is as follows. That is, if the number of strands is set to 3 to form a “3 × 4” structure, or the number of strands is set to 3 and the structure is set to “4 × 3”, the cord strength is reduced with the wire diameter unchanged. Therefore, in order to maintain the reinforcing strength, it is necessary to increase the number of cords, which is disadvantageous because the man-hour for cord reel before rubber drawing by the calendar increases. If the same cord strength as that of the “4 × 4” structure is maintained in the “3 × 4” or “4 × 3” structure, it is necessary to increase the wire diameter and increase the bending rigidity of the cord. This is because the change in the ground contact shape becomes large, and the high-speed steering stability and the ride comfort are lowered. If the number of strands is 5 or more as in the “5 × 4” structure, or the number of strands is 5 or more as in the “4 × 5” structure, the density of the number of cords can be reduced. However, this is because the tire thickness increases and the tire weight increases. Even when the number of strands is 5 or more or when the number of strands is 5 or more, the same strength as the “4 × 4” structure can be maintained by reducing the strand diameter. The wire drawing process increases and the manufacturing cost increases.

  As shown in FIG. 4, each strand F constituting the strand S is corrugated (shaped) so as to have a continuous wave in its longitudinal direction. This typing can be a spiral continuous wave, but is preferably a planar sine wave. In addition, assuming that the corrugated height of the strand F is h and the outer diameter (strand diameter) of the strand S is d, the four strands are satisfied so as to satisfy the relationship of 0.90 ≦ h / d ≦ 1.00. F is twisted together. Thus, as shown in FIG. 5, the strand S is formed so that the strands F are in close contact with each other and the rubber does not enter the internal space Ks surrounded by the four strands F in the strand S. Can do. If h / d is greater than 1.00, rubber penetrates into the tire during vulcanization of the tire, and the elongation in the low load region becomes insufficient. Conversely, if h / d is smaller than 0.90, the terminal length at the time of code cutting becomes large, and the flare property deteriorates. In addition, df in FIG. 4 shows a strand diameter.

  As shown in FIG. 6, each strand S constituting the cord C is corrugated (shaped) so as to have a continuous wave in its longitudinal direction. This typing can be a spiral continuous wave, but is preferably a planar sine wave. In addition, assuming that the corrugated height of the strand S is H and the outer diameter (cord diameter) of the cord C is D, the four strands S satisfy the relationship of 0.90 ≦ H / D ≦ 1.00. Twisted. Accordingly, as shown in FIG. 3, the cord C can be formed such that the strands S are in close contact with each other and the rubber does not enter the internal space Kc surrounded by the four strands S in the cord C. . If the above H / D is larger than 1.00, rubber penetrates into the inside during tire vulcanization, and the elongation in the low load region becomes insufficient. On the other hand, if the H / D is smaller than 0.90, the length of the terminal breakage at the time of code cutting becomes large, and the flare property deteriorates.

  In this steel cord C, the cord twist pitch Pc and the cord diameter D satisfy the relationship of 5.5 ≦ Pc / D ≦ 6.5, and the strand twist pitch Ps and the cord diameter D are 2.5 ≦ Ps / It is configured to satisfy the relationship of D ≦ 3.5. If the Pc / D is larger than 6.5, it is not possible to obtain an elongation in a sufficiently low load region. Conversely, if the Pc / D is smaller than 5.5, it is effective for improving the elongation. , The shape becomes non-uniform. When Ps / D is larger than 3.5, elongation in a sufficiently low load region cannot be obtained. Conversely, when Ps / D is smaller than 2.5, it is effective for improving elongation. , The shape becomes non-uniform.

  In the steel cord C having such a twisted structure, the strand F is formed by twisting the four strands F so that the corrugated height h and the strand d satisfy the above relationship after the strand F is molded. And then twisting the four strands S so that the corrugation height H and the cord diameter D satisfy the above relationship. At that time, since the strands F and the strands S are given a predetermined type, the strands F and the strands S can be tightly twisted together without gaps, preventing rubber from entering the interior. be able to. The wire F and the strand S can be molded using a known molding apparatus in which molding pins and rollers are arranged in a staggered manner. The direction in which the strands S are twisted is preferably the same direction as the direction in which the strands F are twisted. In addition, the above-described molding of the strands F and strands S is substantially the same as the original state after the steel cord C is taken out of the tire and disassembled into the strands S and strands F. It is possible to specify the typed configuration.

Since the steel cord C obtained in this way has the above-mentioned 4 × 4 double twist structure, the ordinate indicates the load (N) and the abscissa indicates the elongation (%) with the vulcanized rubber attached. As shown in FIG. 7, the SS curve shows a behavior as a semi-elastic cord having an inflection point Z that has a gentle slope in a low load region and a slope that 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 .

  In the present embodiment, the elongation A (%) (see FIG. 7) of the intersection between 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 <2. 0.0 is preferred. If the elongation A at this intersection is less than 0.5%, the stress distribution during running tends to be insufficient, and if it is 2.0% or more, a sufficient restraint force of the 0 ° belt cannot be obtained. It is in.

  In particular, in the present embodiment, the rubber does not enter the steel cord C at the time of vulcanization molding of the tire, so that the strands are not restrained by the rubber inside the cord. However, it is possible to make the inclination in the low load region gentle and ensure the elongation in the sufficiently low load region. Accordingly, the elongation (%) at the intersection A is more preferably 1.0 ≦ A <2.0.

  The positional relationship of the 0 ° belt 12 within the belt 1 is not particularly limited, but it is preferable that at least one main belt is disposed outside the 0 ° belt in the tire radial direction. More specifically, the 0 ° belt 12 is preferably disposed between the main belts 11 and 13 or between the main belt 11 and the carcass 2 on the inner side in the tire radial direction. The width of the 0 ° belt 12 is preferably 90% or less of the width of the belt layer 13 on the outer side in the tire radial direction, whereby the stress concentration on the 0 ° belt edge portion can be reduced, and the stress concentration It is possible to prevent the edge portion from being deteriorated in durability due to distortion.

  The 0 ° belt 12 may be disposed between the main belt 13 and the top belt 14, but generally, the top belt 14 has a width of 90% or less of the main belts 11 and 13; If the 0 ° belt 12 is disposed in this portion with a width of 90% or less with respect to the outer belt layer, the width of the 0 ° belt 12 becomes too narrow and it is difficult to obtain a sufficient restraining force at the shoulder portion. Therefore, the 0 ° belt 12 is preferably disposed between the main belts 11 and 13 or between the main belt 11 and the carcass 2 as described above. Further, the cord C of the 0 ° belt 12 is not easily filled with rubber as described above, and thus generally has a problem of being easily rusted. However, the cord C between the main belts 11 and 13 and the main belt 11 By arrange | positioning between the carcass 2, it is hard to be damaged from the tread surface, and the problem of rust can be avoided.

  On the other hand, when the 0 ° belt is disposed between the main belt or between the main belt and the carcass as described above, if the 0 ° belt layer 12 is thicker than the main belt layers 11 and 13, the distortion inside the belt is zero. ° Concentration on the belt 12 may cause deterioration of separation resistance. For this reason, the cord diameter D of the steel cord C of the 0 ° belt 12 is preferably smaller than the cord diameter of the steel cords constituting the main belts 11 and 13, thereby allowing the separation at the belt edge portion to proceed. The tire durability can be improved by delaying.

  The 0 ° belt 12 can be provided by winding the steel cord C in a spiral shape continuously in the circumferential direction of the tire T. The cord angle of the steel cord C is substantially 0 ° with respect to the tire circumferential direction. For example, one cord C 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 C are aligned and covered with rubber is wound by spirally winding the ribbon-like side ends for each circumference of the molding drum during tire molding. Is called. Thus, by winding the steel cord C continuously in a spiral shape, sufficient belt rigidity can be obtained without being affected by the joint or the like.

  With the pneumatic radial tire of the present embodiment configured as described above, the durability and uneven wear resistance of the tire can be improved by providing the 0 ° belt having the above-described configuration, and particularly heavy-duty vehicles for trucks. It is suitable for a tire having a flatness ratio (ratio of tire height / total tire width) of 60% or less.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to these Examples.

  A radial tire having a tire size of 315 / 60R22.5 having the belt configuration shown in FIG. 2 was prototyped. The 0 ° belt was placed on the second belt 12 and each steel cord shown in Tables 1 and 2 was used. The configurations of the first to fourth belts are shown in Table 3 for the examples and comparative examples, and Table 4 for the conventional examples. A common member was used for each part other than the belt. In the angle column in the table, the right and left indicate the belt cord inclination direction.

  The conventional example is an example in which the 0 ° belt shown in FIG. 8 is not used. The tire T1 according to the conventional example includes an air having a belt 100 including four belt layers of first to third belts (main belts) 111, 112, 113 having an angle and a fourth belt (top belt) 114. This is a radial tire.

  The following evaluation was performed on each of the tires. The results are shown in Tables 1 and 2.

[Tensile test]
Each steel cord is subjected to a tensile test with vulcanized rubber (based on JIS G3510). From the SS curve shown in FIG. 7, the tangent line X of the slope in the low load region and the tangent line of the slope after the inflection point are shown. The elongation A (%) at the intersection with Y was determined. The tensile elastic modulus in the low load region was calculated as the strength when it was assumed that the elongation was 100% obtained from the tangent line of the maximum gradient portion near the origin of the SS curve.

[Rubber penetration]
The steel cord is embedded in rubber and vulcanized, then the cord is taken out from the rubber, the cord is divided into two, the surface of the strand S facing the internal space Kc is visually observed, and the area covered with rubber Was expressed as a percentage. Moreover, the strand S was divided into two, the surface of the strand F facing the internal space Ks was visually observed, and the area covered with rubber was expressed as a percentage. And it was displayed as “percentage of the former Kc / percentage of the latter Ks”.

[Cord 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.

[Flare]
Using a cord of 300 mm or more, a part of the cord was fixed, and a portion away from the fixed location by 50 mm or more was cut by applying a cutter perpendicular to the cord axis, and the length of the terminal was measured. Using Comparative Example 2 as a control, the lengths of the roses were compared and evaluated as x: inferior (the length of the rose was long), ○: good (the length of the rose was equal or greater).

[Tire durability]
Increased by 8 km / h every 12 hours from a speed of 56 km / h using a drum testing machine with a steel rotating drum with a smooth surface and a diameter of 1700 mm. The car was run until a 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 with 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, in Examples 1 to 3, there was no penetration of rubber into the cord, and sufficient low load elongation characteristics were ensured in a state with rubber after vulcanization. Therefore, the durability and uneven wear resistance of the tire were excellent.

  On the other hand, in Comparative Example 1, since h / d is less than 0.90, the flare is very poor, and the cord has a large variation when cutting the topping with the cord covered with rubber. It was not suitable. In Comparative Example 2, since h / d exceeds 1.00, rubber penetrates into the cord (specifically, the internal space Ks of the strand) in a state with rubber after vulcanization. In addition, the elongation in the low load region is insufficient, the stress concentration due to strain during running cannot be dispersed, and the durability of the tire is reduced.

  In Comparative Example 3, since the H / D is less than 0.90, the flare is very poor, the cord has a large variation when the topping with the rubber covered is cut, and is not suitable for tire molding. It was. In Comparative Example 4, since H / D exceeds 1.00, rubber penetrates into the cord (specifically, the inner space Kc of the cord) with rubber after vulcanization. In addition, the elongation in the low load region is insufficient, the stress concentration due to strain during running cannot be dispersed, and the durability of the tire is reduced.

  Comparative Example 5 is effective in improving elongation because Pc / D is less than 5.5. However, the cord shape is not stable, resulting in a decrease in cord durability and a decrease in tire durability. It was. Further, in Comparative Example 6, since Pc / D exceeds 6.5, the elongation A in the low load region in the state with rubber after vulcanization is small, and the stress concentration due to strain during running cannot be dispersed, and the durability of the tire The sex was decreasing.

  In Comparative Example 7, since Ps / D was less than 2.5, the twist strain was increased, the cord durability was lowered, the cord shape was not stable, and the tire durability was lowered. Further, in Comparative Example 8, since Ps / D exceeds 3.5, the elongation A in the low load region with the rubber after vulcanization is small, and the stress concentration due to strain during running cannot be dispersed, resulting in durability of the tire. The sex was decreasing.

  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 of the steel cord of embodiment. It is explanatory drawing of the corrugation of a strand continuous wave. It is sectional drawing of the strand which comprises a steel cord. It is explanatory drawing of the corrugation of a strand continuous wave. It is a graph which shows an example of the SS curve of a cord with rubber. It is sectional drawing which shows the belt structure of a prior art example typically.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Belt 2 ... Carcass 6 ... Bead core 11, 13 ... Main belt 12 ... 0 degree belt C ... Steel cord S ... Strand F ... Strand

Claims (5)

A carcass whose both ends are locked by a pair of left and right bead cores, at least two main belts made of steel cords that cross each other and extend on the outer periphery side of the carcass in the tread portion, and the tire circumferential direction A pneumatic radial tire having a 0 ° belt with a steel cord extending substantially at an angle of 0 °,
The steel cord constituting the 0 ° belt is a cord of a 4 × 4 double twist structure in which four strands obtained by twisting four strands are twisted, and each of the strands constituting the strand The strand is corrugated so as to have a continuous wave in the longitudinal direction, and the continuous wave corrugation height h of the strand and the strand diameter d satisfy a relationship of 0.90 ≦ h / d ≦ 1.00, Each strand constituting the cord is corrugated so as to have a continuous wave in the longitudinal direction, and the corrugation height H and cord diameter D of the continuous wave of the strand are 0.90 ≦ H / D ≦ 1.00. The cord twist pitch Pc and the cord diameter D satisfy the relationship of 5.5 ≦ Pc / D ≦ 6.5, and the strand twist pitch Ps and the cord diameter D satisfy 2.5 ≦ Ps / D ≦ 3. .5 satisfying the relationship,
A pneumatic radial tire characterized by that. In the steel cord of the 0 ° belt, rubber does not enter the internal space surrounded by the four strands in each strand, and the internal space surrounded by the four strands in the cord Rubber has not penetrated into the
The pneumatic radial tire according to claim 1. The steel cord of the 0 ° belt has a gentle slope in the low load region in the SS curve with the load (N) on the vertical axis and the elongation (%) on the horizontal axis with rubber after vulcanization. And an inflection point where the inclination increases when the load increases, and the elongation A (%) of the intersection of the tangent of the inclination in the low load region and the tangent of the inclination after the inflection point is 0.5 ≦ A <2.0.
The pneumatic radial tire according to claim 1 or 2, characterized in that The main belt of at least one layer is arranged outside the 0 ° belt in the tire radial direction, the width of the 0 ° belt is 90% or less of the width of the main belt outside the tire radial direction, and The cord diameter of the steel cord is smaller than the cord diameter of the steel cord constituting the main belt on the outer side in the tire radial direction,
The pneumatic radial tire according to any one of claims 1 to 3, wherein: The 0 ° belt is formed by continuously winding the steel cord having the 4 × 4 structure in the circumferential direction of the tire in a spiral shape.
The pneumatic radial tire according to any one of claims 1 to 4, wherein:

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