JP2009208725A - Pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic radial tire with superior durability using a steel cord with superior fatigue resistance improved in anti-fretting property and prevented in preceding breakage of partial wires, while securing rubber intrusion property into rubber, for a carcass. <P>SOLUTION: A wire diameter dc for which spiral molding is performed has a 1+6+n structure provided with a core constituted of a wire of 0.175-0.22 mm. Spiral amplitude H and the core wire diameter dc are 1.05≤H/dc≤1.2. Spiral pitch Pc and twisting pitch Pi of an inner sheath are Pi>Pc. The core wire diameter dc and a wire diameter ds constituting the inner sheath and outer sheath are 1.05≤dc/ds≤1.2. The steel cord having an angle θ of ≤10° formed by a twisted angle θ1 of the inner sheath wire and a twisted angle θ2 of the outer sheath wire is applied to the carcass. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a pneumatic radial tire, and more particularly to a pneumatic radial tire suitable for a large vehicle that has improved fatigue resistance of a steel cord used in a carcass and improved durability of the tire.

  Multi-layer steel cords such as two-layer twist and three-layer twist are widely used in the carcass of large pneumatic radial tires for trucks, buses, etc. As shown in the 3 + 9 + 15 × 0.175 + 1 structure, a three-layer steel cord 50 having a thin wire diameter and a large number of constituent wires is generally used.

  However, in the three-layer structure steel cord 50, the cross-sectional area of the strands decreases due to fretting wear caused by friction between the strands and between the wrapping wire W and the outer sheath strand during use of the tire, and the cord strength gradually decreases. There is a problem that the cord is damaged due to an impact during running of the tire and a stress strain repeatedly applied to the buttress portion, and a problem that the corrosion fatigue resistance is insufficient due to poor rubber penetration into the inside of the cord.

  Further, the twisted structure requires three or more twisting steps when manufacturing the cord, resulting in low cord productivity and an increase in the manufacturing cost, which also affects the tire cost.

  Therefore, in order to improve the deterioration of fatigue resistance and cost due to such fretting wear, two sheath layers are arranged around one core wire, and the sheath layers are arranged in the same direction and at the same pitch. Steel cord (patent document 1) with a compact twist 1 + 18 structure (see Fig. 6) that twists together to make line contact between the strands, and the permeability of rubber by thinning the diameter and number of sheath strands Steel cord (Patent Document 2) with a 1 + 6 + (10-11) structure (see FIG. 7) with improved wrapping wire and improved durability with low fretting wear and stranded wire man-hours is disclosed. Steel cords have been proposed to reduce costs.

  In addition, there is a problem that the buttress part, which is susceptible to repeated stress strain due to bending during tire rotation, leads to cord damage due to strand breakage due to the material fatigue factor of the steel cord, resulting in a decrease in tire strength. It is done. In particular, during low-pressure running due to puncture or the like, an extremely large strain is applied to the side wall to the buttress portion, so that it is considered that the breakage of the wire progresses to the damage of the carcass cord within a short time and causes a tire failure.

  The compact stranded steel cords such as the 1 + 18 structure disclosed in the above-mentioned document 1 are advantageous in terms of fretting wear reduction and improvement in fatigue resistance and cord cost due to the line contact of the strands. Since the cord is filled and arranged inside the cord, the cord cross-sectional contour has a non-circular polygonal shape, and there is a problem that stress is easily applied to the strands at specific positions of the polygonal cord and material fatigue is likely to occur.

Therefore, in view of the idea that the strand located at the apex of the 1 + 18-structure cross-sectional polygon is susceptible to distortion and that the bending rigidity of the cord has anisotropy, the fatigue resistance is lowered. It has been proposed to improve the durability by placing the cord cross-sectional shape close to a circle by placing it at the apex of a polygonal shape (Patent Document 3).
Japanese Utility Model Publication No. 3-29355 JP-A-8-232179 Japanese Patent Laid-Open No. 2004-9879

  A compact cord with the same direction and the same pitch twist as in the above 1 + 18 structure is improved in fretting resistance due to the line contact of the wire, but due to insufficient rubber penetration, the cord is separated due to stress strain on the tire. In some cases, some of the strands may be pre-ruptured. In addition, moisture penetration may cause deterioration of durability due to corrosion fatigue and adhesion to rubber, and stress distortion due to the straightness of the core strand. Has a problem that it tends to be concentrated and is disadvantageous for fatigue resistance and easily breaks. In addition, it has been proposed to make the sheath wire thinner than the core wire, but the rubber penetration property has not been sufficiently satisfied.

  Moreover, in order to improve this rubber penetration | invasion property and material fatigue | exhaustion, what is twisted combining a different diameter strand and a thin strand like a patent document 2 and 3 is the drawability fall of a strand, or a strand member. There is a problem that the increase and the complexity of the stranded wire process rebound to the cord cost.

  In view of the above problems, the present invention eliminates the above-mentioned drawbacks of the compact twisted 1 + 18 structure steel cord without impairing the cord productivity, and improves the fretting resistance while securing rubber penetration into the inside of the cord. An object of the present invention is to provide a pneumatic radial tire excellent in durability performance using a steel cord excellent in fatigue resistance in which a preceding wire breakage is prevented and used in a carcass.

  As a result of intensive research in order to solve the above problems, the present inventor applied a specific spiral type to the core wire of the 1 + 6 + n structure in the steel cord that reinforces the carcass, and the inner sheath and the outer sheath. It has been found that by specifying the twisted structure, the rubber penetration and the fretting resistance of the steel cord can be improved in a well-balanced manner and the fatigue resistance can be improved.

  That is, according to the present invention, in a pneumatic radial tire in which a carcass is reinforced with a steel cord, the steel cord has a single wire diameter (dc) of 0.175 to 0.22 mm subjected to helical shaping. A core composed of a strand, an inner sheath composed of six inner sheath strands disposed around the core, and n (n is 10 or 11) outer sheath strands disposed around the inner sheath The inner sheath and the outer sheath are twisted in the same direction, and the spiral type is formed by the spiral amplitude (H) and the core wire diameter (dc). 1.05 ≦ H / dc ≦ 1.2, the helical pitch (Pc) and the inner sheath twist pitch (Pi) are Pi> Pc, and the core wire diameter (dc) The strand diameter (ds) constituting the inner sheath and the outer sheath is 1.05 ≦ dc / ds ≦ 1.2, and the twist angle θ1 of the inner sheath strand with respect to the steel cord shaft, The pneumatic radial tire is characterized in that an angle θ formed by a twist angle θ2 of the outer sheath wire with respect to the steel cord shaft is 10 ° or less.

  The inner sheath wire and the outer sheath wire preferably have the same diameter (ds).

  Further, the present invention is suitable for a large-sized heavy-duty pneumatic radial tire for trucks and buses, in which the flatness of the tire cross-section where the stress distortion tends to be large between the tire side and the buttress portion is 80% or less. The durability of the carcass cord against the applied stress strain is improved and the tire life is extended.

  According to the pneumatic radial tire of the present invention, the rubber penetration of the 1 + 6 + n structure steel cord and the anti-fretting resistance can be improved in a well-balanced manner. Prevents cracking phenomenon, improves corrosion fatigue resistance, improves fretting resistance and maintains cord strength over a long period of time, improving carcass durability and greatly extending the service life of pneumatic radial tires be able to.

  Hereinafter, a pneumatic cord tire according to an embodiment of the present invention and a steel cord used for the carcass thereof will be described with reference to the drawings.

  FIG. 1 is a half sectional view of a tire T showing an example of a pneumatic radial tire for trucks and buses according to an embodiment of the present invention. Reference numeral 3 denotes a tread portion, 5 denotes a sidewall portion, and 4 denotes a bead portion. , CL is a tire center.

  The tire T is positioned on the outer side in the radial direction of the carcass ply 2 and a carcass ply 2 made of a steel cord that is folded and locked from the inner side to the outer side of the tire around the bead cores 6 embedded in the pair of bead parts 4 A tread portion 3, side wall portions 5 positioned on both sides of the carcass ply 2, and a belt ply 1 made of four steel cords on the outer peripheral side of the carcass ply 2 of the tread portion 3 are provided.

  The belt ply 1 uses a steel cord having a two-layer structure or a three-layer structure such as 3 × 0.20 + 6 × 0.35, 3 + 9 × 0.23, 3 + 9 + 15 × 0.23, and 4 for the outermost belt. A high elongation cord such as × 2 × 0.23 or 1 × 5 × 0.38 may be used instead of the steel cord.

  In the present invention, the steel cord used for the carcass ply 2 is composed of a core made of one strand having a strand diameter dc of 0.175 to 0.22 mm arranged at the center, and 6 cores arranged around the core. Steel cord of 1 + 6 + n structure composed of an inner sheath composed of two inner sheath strands and an outer sheath composed of n (n is 10 or 11) outer sheath strands arranged around the inner sheath It is.

  FIG. 2 is a cross-sectional view of a cord showing an example of a 1 + 6 + n structure steel cord according to the present invention. One core strand 12 having a strand diameter dc constituting the core 11 disposed in the center, and the core 11 Six inner sheath wires 14 having a wire diameter d1 constituting the inner sheath 13 disposed around, and eleven outer sheaths having a wire diameter d2 constituting the outer sheath 15 disposed around the inner sheath 13 This is a steel cord 10 having a 1 + 6 + 11 structure which is made of a strand 16 and in which an inner sheath 13 and an outer sheath 15 are twisted in the same direction.

  FIG. 3 is a cross-sectional view of the 1 + 6 + 10 structural steel cord 20 according to the present invention. One core strand 22 having a strand diameter dc constituting the core 21 disposed in the center, and around the core 21 Six inner sheath strands 24 having a strand diameter d1 constituting the arranged inner sheath 23 and ten outer sheath strands having a strand diameter d2 constituting the outer sheath 25 arranged around the inner sheath 23 16.

  In the present invention, the core 11 is formed as one strand 12 because the cord cross-sectional shape is flattened when the core 11 is twisted so that the stress strain is biased in the vertical and horizontal directions of the cord cross-section and fatigue resistance. When three or more strands are twisted, a continuous void is formed in the core, so that the corrosion resistance performance due to moisture intrusion from external damage or the like is deteriorated. Although it is necessary, it is because it can be twisted simultaneously with the inner sheath 13 by making it one, and a strand wire process can be simplified. In addition, when the sheath has three or more layers, the twisted structure becomes complicated. In particular, the straightness of the cord and the residual torsion are difficult to adjust in the case of twisting in the same direction, which makes manufacturing difficult.

  The number of strands of the inner sheath 13 is limited to six. If the number of strands is five or less, the interval between the inner sheath strands 14 becomes large, and it becomes difficult to obtain a stable twisted shape, thereby improving fatigue resistance and rubber penetration. If the number of strands of the inner sheath is 4 or less, the gap S1 between the inner sheath strands spreads around the core and the strands tend to be biased and the rubber penetration is deteriorated, and 7 or more strands are arranged. Therefore, it is necessary to increase the diameter difference between the core and the inner sheath wire, the strain applied to the core is increased, the fatigue resistance is lowered, and the expansion effect of the inner sheath wire 14 cannot be obtained, so that the rubber penetration property is reduced. Getting worse.

  The number of strands of the outer sheath 15 is limited to 10 or 11 when the diameters of the inner sheath strand 14 and the outer sheath strand 16 are similar, and 12 strands are arranged between the outer sheath strands 16. There is no gap S2 for allowing rubber to enter, and if the number of strands is 9 or less, the gap S2 becomes too large. , Rubber penetration will deteriorate.

  Hereinafter, a steel cord according to the present invention will be described mainly based on a steel cord 10 having a 1 + 6 + 11 structure shown in FIG.

  In the present invention, the strand diameter dc of the core strand 12 is 0.175 to 0.22 mm. If the dc is less than 0.175 mm, the cord strength becomes low. Therefore, it is necessary to increase the amount of cord used to secure the carcass strength, and the cord cost increases. If the dc exceeds 0.22 mm, the cord is used for the carcass ply. In such a case, when the tire is subjected to extreme compressive or bending stress, the wire surface distortion becomes large and fatigue resistance becomes disadvantageous. For this reason, as a carcass cord for heavy duty heavy-duty tires with severe use conditions, particularly flat radial tires with a flatness ratio of 80% or less, the wire diameter is 0.22 mm or less, preferably 0.21 mm or less, It is preferable that it is 0.20 mm or less.

  As shown in FIG. 2, the core wire 12 is spiral-shaped. Here, the spiral shape means a helical shape that is a three-dimensional waveform patterning, that is, a so-called morning glory spiral shape.

  By making the core strand 12 into a spiral R, the strand 14 of the inner sheath 13 can be expanded more in the cord radial direction than the linear core, making it easier to create a gap between the strands 14, Rubber can be penetrated to the strand 12, and by giving the core strand 12 an angle with respect to the cord axis direction, stress concentration on the core strand 12 can be alleviated and fatigue resistance can be improved. .

  As shown in FIG. 4, the spiral R is shaped such that the spiral amplitude H and the core wire diameter dc have a relationship of 1.05 ≦ H / dc ≦ 1.2, and the spiral pitch Pc and the inner sheath The twist pitch Pi satisfies the relationship Pi> Pc.

  When H / dc exceeds 1.2, the amplitude shape of the spiral becomes unstable, and it becomes difficult to evenly arrange the inner sheath wire 14 around the core wire 12. Part where rubber does not penetrate up to 11 occurs, and fatigue resistance also deteriorates. When H / dc is less than 1.05, the expansion effect of the inner sheath wire 14 cannot be obtained due to the spiral shape, and the rubber does not enter the core 11.

  Further, when Pc is longer than Pi, the inner sheath wire 14 is buried in the spiral molding of the core strand 12, and the expansion effect of the inner sheath wire 14 due to the spiral shape is not fully utilized. Furthermore, the core wire 12 tends to be close to a straight line and fatigue resistance tends to decrease.

  As for the cross-sectional shape of the spiral, the circumscribed circle drawn by the spiral is usually circular, but the circumscribed circle may be elliptical or track-shaped.

  The relationship between the core wire diameter dc and the wire diameter ds constituting the inner sheath wire 14 and the outer sheath wire 16 is 1.05 ≦ dc / ds ≦ 1.2.

  By making the core wire diameter dc slightly larger than the inner sheath and outer sheath wire diameter ds, the straightness of the cord is improved, and the inner sheath wire 14 and the outer sheath wire 16 are adjacent to each other. The gaps S1 and S2 into which the rubber enters the cord 10 can be formed. If the dc / ds is less than 1.05, the expansion effect of the inner sheath wire 14 cannot be sufficiently obtained even if the H / dc is 1.2.

  Further, by making the core strand diameter dc slightly larger than ds, the contact pressure between the core strand 12 and the inner sheath strand 14 can be lowered to prevent deterioration of fatigue. However, if the difference between the core wire diameter dc and the inner sheath wire diameter d1 is made larger than 1.2 times, the difference in fatigue between them will increase, and the inner sheath wire 14 will It is not preferable because it tends to move around, and the strands 14 are biased to deteriorate the rubber penetration and the fretting wear of the core strands 12 to deteriorate the fatigue resistance.

  At this time, the diameter di of the inner sheath strand 14 and the diameter do of the outer sheath strand 16 may all be the same strand diameter ds, and di and do may be different. All having the same diameter are preferable in terms of cord productivity and cost.

  Although it is conceivable to combine different-diameter strands in the same sheaths 13 and 15, it affects the cord productivity such as an increase in the number of strand members and the stranded wire process becoming complicated, so the viewpoint of suppressing the cord manufacturing cost. Therefore, it is preferable to use the same wire diameter in at least the same sheath.

  In the steel cord 10 according to the present invention, the inner sheath 13 and the outer sheath 15 are twisted in the same direction. As a result, the problem of fretting wear caused by point contact between the strands 14 and 16 of the inner sheath 13 and the outer sheath 15 due to different direction twisting, which is the main cause of the decrease in cord strength of the layer twist cord, is reduced, and the contact area between the strands By increasing, the contact pressure per unit area can be reduced and the fretting resistance can be improved.

  As shown in FIG. 5, the steel cord 10 has an angle θ formed by the twist angle θ1 of the inner sheath wire 14 with respect to the cord axis O and the twist angle θ2 of the outer sheath wire 16 with respect to the cord axis O. It is 10 ° or less.

  Accordingly, the outer sheath wire 16 is prevented from falling between the inner sheath wires 14, and the formation of the gaps S1 and S2 is stably ensured by bringing the cross-sectional shape of the steel cord 10 close to a circle, and the rubber. In addition to ensuring penetration, the problem of stress concentration on the specific strand of the cross-sectional polygonal code can be solved.

  When the angle θ (| θ1−θ2 |) formed between θ1 and θ2 exceeds 10 °, the inner sheath wire 14 and the outer sheath wire 16 are brought into point contact, and the contact pressure between the two increases, resulting in fretting wear. It becomes large and the code strength tends to decrease. In addition, the fretting portion has the surface of the wire stripped, and the wire is easily corroded, which also adversely affects the corrosion fatigue property of the cord. In general, θ1 and θ2 are in a relationship of θ1 ≧ θ2, that is, the outer sheath 15 is twisted at a pitch P2> P1 longer than the inner sheath 13 to suppress a decrease in cord productivity and an increase in cord unit mass. ing.

  In the present invention, the twist angle θ1 of the inner sheath wire 14 is preferably 12 to 20 °.

  If the twist angle θ1 of the inner sheath strand is less than 12 °, the strand axis approaches the cord axis O in parallel, that is, the twist pitch P1 becomes longer and fatigue resistance decreases, and 20 ° is reduced. If it exceeds, the twisting pitch P1 becomes too short, and the twisting efficiency is lowered.

Moreover, each strand which comprises said steel cord 10 consists of high carbon steel (For example, the piano wire prescribed | regulated to JISG3502) whose carbon content is about 0.70 to 0.95 weight%, 2500 has a 3500 N / mm ² approximately tensile strength, further strength from the viewpoint of weight reduction is preferably 2700N / mm ² or more, and more preferably high tensile strength wires in addition 2900N / mm ² or more. However, if the tensile strength exceeds 3500 N / mm ² , it is not preferable because a defect that fatigue resistance deteriorates due to deterioration of wire drawing workability or embrittlement of steel appears.

  Further, the surface of the wire is coated with brass plating having a copper ratio of 63 to 67% with an adhesion amount of about 4 to 6 g / Kg in order to improve the adhesion to rubber. Further, ternary alloy plating in which a brass contains a small amount of a third metal such as cobalt or nickel may be used.

  The production of the steel cord 10 is not particularly limited. For example, the six strands 14 of the inner sheath 13 are focused around the core strand 12 that is preliminarily molded in a predetermined spiral shape. Are introduced into a buncher type twisted wire machine or a tubular type twisted wire machine and twisted at a predetermined pitch to form a 1 + 6 structure. Next, the 1 + 6 structure once wound around the bobbin is pulled out, and the 11 strands 16 of the outer sheath 15 are focused around it, and introduced into a normal buncher type twisting machine or a tubular type twisting machine, By twisting at a predetermined pitch in the same direction as the 1 + 6 structure, the steel cord 10 having the 1 + 6 + 11 structure can be manufactured by two stranded wire processes. It is preferable to use a tubular twisting machine in which the core strand 12 does not twist during twisted wire processing.

  Here, the spiral twist direction of the core strand 12 may be the same direction as the twist direction of the sheaths 13 and 15 or may be the opposite direction. In the case of the same direction, the fretting resistance is advantageous, and in the case of the reverse direction, the rubber penetration is favored.

  Also, there is no particular limitation on the method of spirally forming the core wire 12. For example, by passing the wire 12 at a predetermined speed through a mirror plate rotating at a predetermined amplitude, a predetermined spiral amplitude and pitch are provided. You can get a bare wire.

  The pneumatic radial tire of the present invention uses the steel cord as a reinforcing material for the carcass ply, thereby improving the rubber penetration and the fretting resistance in a well-balanced manner, and achieving a long life with excellent carcass durability. It can be a pneumatic radial tire, and is particularly suitable for a tire with a flatness ratio of 80% or less used for heavy-duty vehicles such as trucks, buses, and light trucks. Moreover, the cord productivity can be increased over the conventional 3 + 9 + 15 structure steel cord, which can contribute to cost reduction.

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

  Each steel cord of 1 + m + n structure (m is 5 to 7, n is 9 to 12) in which the core wire of the example and the comparative example is preliminarily spiral-shaped according to the cord specifications described in Tables 1 and 2 Was manufactured by two stranded wire processes using an ordinary tubular stranded wire machine.

  Each wire used in these steel cords is dry-drawn from a 5.5 mm rod of piano wire material SWRS82A specified in JIS G3502 to an intermediate wire of a predetermined diameter by repeating patenting and wire drawing. This was obtained by subjecting the surface to brass plating (copper ratio: 64%, plating adhesion amount: 4.5 g / Kg), followed by final wire drawing using an ordinary wet wire drawing machine.

  The steel cords of the conventional examples 1 and 2 were manufactured by a conventional method using a tubular twisting machine using a strand having a predetermined diameter obtained in the same manner as described above, and the conventional example 1 was 3 + 9 + 15 × 0. .175, Conventional Example 2 is a 0.20 + 18 × 0.18 compact twisted cord manufactured in a single twisting process.

  These steel cords were evaluated for fatigue resistance and fretting resistance, rubber penetration, and tire durability by a belt fatigue test by the following test methods. The results are shown in Tables 1 and 2.

[Belt fatigue]
A belt strip vulcanized sample (width 3 x length 45 cm) embedded in rubber with the number of cords to be driven 17 / 25.4 mm was prepared, and a 2-inch pulley (load load) using a firestone belt fatigue tester 40 kg), the cord was taken out of the sample, the cord strength was measured, and the retention rate with respect to the cord strength before the fatigue test was determined. The average value of 10 cords is shown as an index with the conventional example 2 as 100. The greater the index, the better the fatigue resistance.

[Fretting resistance]
The cord was taken out from the sample after the belt fatigue test, and the fretting wear level of the inner sheath and the outer sheath was observed with a microscope by magnifying the strand 20 times. “◎” indicates that fretting is hardly observed, “○” indicates that the wire diameter reduction rate reaches 1/8 of the maximum diameter, and the wire diameter reduction rate reaches 1/6 of the maximum diameter. "△" for the wire, "x" for the wire diameter reduction rate up to 1/4 of the diameter, and "XX" for the wire wire diameter reduction rate up to 1/2 of the diameter , And are shown in the table.

[Rubber penetration]
The cord taken out from the belt fatigue test sample was carefully removed over 25 cm of the outer sheath and inner sheath, and the rubber adhesion length around the core wire was measured. The case where the outer periphery of the core wire adhered to the rubber over the entire length of 25 cm was evaluated as a rubber adhesion rate of 100%. The average value of five cords is shown in the table. The larger the value, the better the rubber penetration.

[Tire durability]
A radial tire having a size of 265 / 60R22.5 was manufactured by making the topping of each cord covered with rubber on both sides with the number of cords to be driven 17 / 25.4 mm and applying it to the carcass ply. Tire durability was evaluated by a drum test under the following conditions. The belt ply is 3 × 0.20 + 6 × 0.35 for the No. 1 belt (8 shots / 25.4 mm), 3 + 9 + 15 × 0.23 for the No. 3 belt (12 shots / 25.4 mm) The No. 4 belt was a steel cord of 1 × 5 × 0.38 (number of driven 12 wires / 25.4 mm), and a common member was used for each part other than the carcass.

<Drum test conditions>
Using a drum tester having 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, and the speed is 56 km / h, and the load is 66% of JATMA maximum load for 4 hours. Next, after running at 84% of the maximum load for 16 hours, at 101% of the maximum load for 24 hours, and further at 110% of the maximum load for 24 hours, until the failure occurs while increasing the load by 10% every 12 hours I drove it. The travel distance until the occurrence of the failure is shown in the table as an index with the conventional example 2 as 100. The larger the index, the better the durability.

  As shown in the table, Conventional Example 1 is inferior in fretting resistance, belt fatigue, and tire durability, and Conventional Example 2 has good fretting resistance, but has poor rubber penetration and a high risk of corrosion fatigue resistance. On the other hand, Examples 1-2 according to the present invention can improve rubber penetration and fatigue resistance in a well-balanced manner and improve tire durability.

  On the other hand, in Comparative Example 1, since the core wire is linear, the rubber penetration is inferior, and the tire durability is not as good as that of the example. Since the comparative example 2 is Pc> Ps, the inner sheath wire is buried in the core wire and the rubber penetration is not improved. In Comparative Example 3, since the H / dc is larger than 1.2, the twisted shape of the inner sheath becomes unstable, and the belt fatigue and tire durability are inferior. In Comparative Example 4, since the core wire is thick, the strain tends to concentrate, and the belt fatigue and tire durability tend to decrease. In Comparative Example 5, the dc / ds is less than 1.05, so that the rubber penetration is insufficient. In Comparative Example 6, the number of strands of the inner sheath is 5, so that the twisted shape of both the inner sheath and the outer sheath is not stable, and the belt fatigues. Improvement of tire performance and tire durability cannot be obtained. In Comparative Example 7, the inner sheath is composed of seven strands and the rubber penetration is poor, and in Comparative Example 8, the rubber penetration is good because of the nine outer sheath strands, but the bias of the strands cannot be evenly arranged and the belt fatigue The tire durability is lowered, and Comparative Example 9 has 12 outer sheath wires, which has poor rubber penetration, and the effect of using a spiral wire for the core cannot be obtained. In Comparative Example 10, since θ was 10 ° or more, the inner sheath and the outer sheath were brought into point contact, resulting in a decrease in fretting resistance and inferior belt fatigue and tire durability.

  As described above, the pneumatic radial tire according to the present invention can be applied to a pneumatic radial tire in which a carcass is reinforced with a steel cord, and particularly a heavy-duty pneumatic radial tire for trucks and buses having a flatness ratio of 80% or less. It is suitable for.

1 is a half sectional view of a pneumatic radial tire according to an embodiment. It is sectional drawing of the 1 + 6 + 11 structure steel cord of embodiment. It is sectional drawing of the 1 + 5 + 10 structure steel cord of embodiment. It is a side view of the strand explaining the spiral type | molding of a core. It is a sheath side view explaining the twist angle of a sheath strand. It is sectional drawing of a 1 + 18 structure steel cord. It is sectional drawing of the conventional 1 + 6 + 11 structure steel cord. It is sectional drawing of a 3 + 9 + 15 structure steel cord.

Explanation of symbols

10 …… Steel cord 11 …… Core 12 …… Core strand 13 …… Inner sheath 14 …… Inner sheath strand 15 …… Outer sheath 16 …… Outer sheath strand S1, S2 …… Gap between strands dc ... Core wire diameter ds ... Sheath wire diameter H ... Spiral amplitude Pc ... Spiral pitch Pi ... Twist pitch of inner sheath

Claims (3)

In pneumatic radial tires with carcass reinforced with steel cords,
The steel cord has a core made of a single strand having a strand diameter (dc) of 0.175 to 0.22 mm, which is spirally shaped, and six inner sheath elements disposed around the core. An inner sheath comprising a wire and an outer sheath comprising n (n is 10 or 11) outer sheath wires arranged around the inner sheath, and the inner sheath and the outer sheath are twisted in the same direction. A combined 1 + 6 + n structure,
In the spiral molding, the spiral amplitude (H) and the core wire diameter (dc) are 1.05 ≦ H / dc ≦ 1.2, the spiral pitch (Pc) and the inner sheath twist pitch (Pi). And Pi> Pc,
The core wire diameter (dc) and the wire diameter (ds) constituting the inner sheath and outer sheath are 1.05 ≦ dc / ds ≦ 1.2, and
A pneumatic radial tire characterized in that an angle θ formed by a twist angle θ1 of the inner sheath wire with respect to the steel cord shaft and a twist angle θ2 of the outer sheath wire with respect to the steel cord shaft is 10 ° or less. . 2. The pneumatic radial tire according to claim 1, wherein the inner sheath wire and the outer sheath wire all have the same diameter (ds). The pneumatic radial tire according to claim 1 or 2, wherein the tire has a flat section with a flatness ratio of 80% or less.

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