JP2947869B2 - Pneumatic radial tire - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a pneumatic radial tire.

2. Description of the Related Art Conventionally, as a pneumatic radial tire, for example, a tire as described in Japanese Patent Application Laid-Open No. 52-84610 is known. This is a toroidal carcass layer in which a number of cords extending in a direction substantially perpendicular to the tire equatorial plane are embedded, and the carcass layer is arranged radially outside of the carcass layer from 10 degrees to the tire equatorial plane. A belt layer in which a number of reinforcing elements inclined at an angle of 40 degrees are embedded, and a reinforcing layer in which a cord substantially parallel to the tire equatorial plane is embedded radially outside the belt layer over substantially the entire width. And a tread rubber disposed radially outward of the belt layer and the reinforcing layer, wherein the cord of the reinforcing layer has a high elongation of 4 to 8% in final elongation and an elastic modulus of 5000 to 8000 kg / mm ² . It consists of a metal cord. Here, the high-extensibility metal cord is formed by strands formed by a plurality of wires twisted together, and the individual strands or cords are all wound in the same direction. Conventionally, the cord of the reinforcing layer is formed of a highly extensible metal cord for the following manufacturing reasons. That is, in order to form appropriately shaped irregularities (tread pattern) on the outer surface of the tread portion during vulcanization of the green tire, the green tire must expand radially by a predetermined amount. When the cord substantially parallel to the buried tire equatorial plane is a non-stretchable metal cord, for example, a general steel cord, the amount of radial expansion as described above is insufficient, and the belt layer and the reinforcement This causes the layer to undulate in the width direction. It is conceivable to reduce the amount of inflation of the green tire so that such waving does not occur, but this increases the diameter of the green tire, and as a result, when closing the mold prior to vulcanization, the mold Rubber is caught between the segments or between the segments, resulting in molding failure. Therefore, in order to avoid the above-described molding failure, the cord substantially parallel to the tire equatorial plane must be slightly stretched at the time of vulcanization, and the amount of the stretch is also larger as the depth of the groove on the outer surface of the tread portion is larger. It must be a large value.

However, although the pneumatic radial tire as described above can be easily vulcanized and molded, the metal cord in the reinforcing layer has a low elastic modulus as described above even after the product tire is formed. Because of this, it is further expanded by the centrifugal force during the filling and running of the internal pressure, whereby it is not possible to sufficiently suppress the radial growth in the shoulder portion of the tire, and as a result, belt separation and uneven wear, For example, there has been a problem that shoulder drop wear may occur.

SUMMARY OF THE INVENTION An object of the present invention is to provide a pneumatic radial tire that can be easily vulcanized and that can sufficiently suppress the diameter growth when the tire is used.

Means for Solving the Problems Such an object is to provide a toroidal carcass layer in which a number of cords extending in a direction substantially perpendicular to the tire equatorial plane are embedded, and to be disposed radially outside the carcass layer. A belt layer in which a large number of reinforcing elements inclined at an angle of 10 to 40 degrees with respect to the tire equatorial plane are buried, and a plurality of cords that overlap at least partially with the belt layer and are substantially parallel to the tire equatorial plane. A buried reinforcing layer, a tread rubber disposed radially outside of the belt layer and the reinforcing layer and having a groove formed on the outer surface thereof, wherein a maximum depth of the groove is d, and an outer diameter of the tire is D. And m = 2d / D × 100
In the pneumatic radial tire in which the value of m is 2.55 or more, the cord of the reinforcing layer has an initial elongation in the range of (0.6 × m−1.2)% to 1.5% and an elastic modulus of 1%.
This can be achieved by using a metal cord of 0000 kg / mm ² or more.

Action Assume that a green tire is being vulcanized and molded by a vulcanizing apparatus. At this time, in order to appropriately form irregularities, that is, a tread pattern, on the tread portion of the raw tire, the raw tire needs to be slightly expanded radially outward. And
The amount of expansion required for the green tire at the time of this vulcanization must be larger as the depth of the concave portion, that is, the groove, of the tread pattern is larger. For this reason, according to the present invention, the cord buried substantially parallel to the tire equatorial plane in the reinforcing layer is made of a metal cord having an initial elongation ratio in the range of (0.6 × m-1.2)% to 1.5%, The necessary amount of inflation of the raw tire at the time is allowed. Here, the initial elongation is a percentage of the elongation of the cord when the load acting on the cord is increased from 0.25 kg to 5.0 kg. Also, m
Is a value represented by m = 2d / D × 100, where d is the maximum depth of the groove and D is the outer diameter of the tire, and is an amount representing the degree of the groove depth. Here, when the initial elongation of the cord of the reinforcing layer is less than (0.6 × m−1.2)%, the belt layer and the reinforcing layer are corrugated in the width direction, or the segment between the molds of the vulcanizing apparatus, the segment, or the like. The rubber cannot be used because the rubber is caught in the gap, resulting in molding failure. If it exceeds 1.5%, the cord is twisted at the end of the ply at the time of cutting and the workability is reduced, so that it cannot be used. When the pneumatic tire vulcanized in this way is filled with internal pressure or run, the tire tends to grow radially outward, but in the present invention, the tire equatorial plane is formed in the reinforcing layer. the code that is substantially parallel buried since the elastic modulus consisted 10000 kg / mm ² higher than the metal cord, the diameter growth of the aforementioned is sufficiently suppressed, as a result, belt separation and uneven wear, for example, shoulder drop Wear is reliably prevented.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

1 and 2, reference numeral 1 denotes a pneumatic tire. The tire 1 has a pair of bead portions 2, a pair of sidewall portions 3 each extending substantially radially outward from the bead portions 2, and both sidewall portions. And a tread portion 4 having a cylindrical shape extending across the three treads. The tire 1 is reinforced with a toroidal carcass layer 8 extending from one bead portion 2 to the other bead portion 2. Both sides of the carcass layer 8 are formed of a bead ring 9 and a rubber filler 10. It is wound around from the inside in the axial direction to the outside in the axial direction. The carcass layer 8 is composed of at least one carcass ply, in this embodiment one carcass ply 11, and extends substantially radially into the carcass ply 11, that is, substantially perpendicular to the tire equatorial plane S. A large number of cords 12 extending in the direction of movement are embedded. A belt layer 14 is provided on the tread portion 4 on the radially outer side of the carcass layer 8.
In the case of tires for passenger cars, one or two belt plies are laminated, and in the case of tires for trucks and buses, two or four belt plies are laminated. Is constructed by laminating two belt plies 15. These belt plies
A number of non-extensible reinforcing elements 16, for example, a single wire filament or a plurality of cords formed by twisting a plurality of filaments, are embedded in the inside of 15. The reinforcing elements 16 buried in the belt plies 15 are inclined so as to intersect the tire equatorial plane S at an angle of 10 to 40 degrees. When the belt layer 14 is composed of two or more belt plies 15, the reinforcing elements 16 are inclined and cross in opposite directions to each other in at least two belt plies 15. In the case of truck and bus tires, an auxiliary layer in which a cord inclined at an angle of 40 to 70 degrees with respect to the tire equatorial plane S is embedded inside the belt layer 14 in the radial direction may be arranged. is there.

A tread rubber 18 having a cylindrical shape is disposed on the tread portion 4 on the radially outer side of the belt layer 14, and a plurality of circumferential grooves 19 intersect with the circumferential grooves 19 on the outer surface of the tread rubber 18. A plurality of lateral grooves (not shown) extending in the direction are formed. The tread rubber
In some cases, the circumferential groove 19 is not formed on the outer surface of the 18, but only the lateral groove is formed. Here, when the maximum depth of the circumferential groove and the lateral groove described above is d (mm) and the outer diameter of the tire 1 is D (mm), the maximum depth d of the groove is expressed by the following formula ( 1) 2d / D × 100 = m ≧ 2.55 (1) is satisfied. The groove depth of the tire 1 that satisfies the above expression is equal to or deeper than a commonly used depth.

22 is at least partially overlapped with the belt layer 14, in this embodiment, disposed radially outside the carcass layer 8 and radially inside the belt layer 14;
14 is a reinforcing layer that overlaps the widthwise central portion of the reinforcing layer 14. The reinforcing layer 22 is composed of at least one reinforcing ply having a cord 23 embedded therein, in this embodiment, two reinforcing plies 24 superimposed on each other. The cords 23 are arranged substantially parallel to the tire equatorial plane S. here,
The above-mentioned reinforcing layer 22 includes, for example, at least one cord 23.
A plurality of rubber-coated strips are spirally wound from one axial direction to the other axially to form a reinforcing ply 24 on the radially inner side.
The reinforcing ply 24 may be formed by spirally winding the reinforcing ply 24 on the outer side in the axial direction or the other in the axial direction to form a reinforcing ply 24 on the outer side in the radial direction. A radially inner reinforcing ply 24 is formed by joining both ends in the winding direction in the longitudinal direction, and another belt-shaped member is similarly wound around the outer side of the reinforcing ply 24 and both ends are joined together to form a radial direction. The outer reinforcing ply 24 may be formed by molding, and is not limited to these forming methods.

The cord 23 has an initial expansion rate of (0.6 × m−1.2)%
Consists of metal cords in the 1.5% range. Here, m is a value obtained by the above equation (1). In this way, the initial expansion rate of the cord 23 is (0.6 × m−1.2)%
With the above metal cord, when the green tire is vulcanized and molded by the vulcanizing apparatus, the green tire is allowed to expand, and the appropriately shaped irregularities in the tread portion of the green tire, that is, the tread pattern is reliably formed. Is possible, but (0.6 × m
If the ratio is less than -1.2)%, the belt layer 14 and the reinforcing layer 22 may be wavy in the width direction, or rubber may be caught between the molds or between the mold segments, resulting in poor molding. Further, by using the equation (0.6 × m−1.2), the initial extension rate of the cord 23 according to the groove depth can be easily obtained without repeating trial and error. Also,
If the initial elongation exceeds 1.5%, twisting of the cord 23 will occur at the end of the ply at the time of cutting, and workability will be reduced. Therefore, the initial elongation must be 1.5% or less. Here, the initial elongation is a load applied to the cord 23 of 0.25 kg.
It shows the elongation of the cord 23 when it is increased from 5.0 to 5.0 kg in percentage. When the cord 23 having an initial elongation of a certain value between (0.6 × m-1.2)% and 1.5% is used, the reinforcing layer at the time of vulcanization is used.
In order to determine the circumferential elongation of the reinforcing layer 22, the circumferential elongation of the reinforcing layer 22 is set gradually smaller than a value at which it is confirmed that the reinforcing layer 22 and the belt layer 14 generate wavy waves in the width direction after vulcanization. And vulcanizing the reinforcing layer 22 and the belt layer 14 in a circumferential direction at which no waving occurs in the width direction. At this time, the initial elongation is from (0.6 × m−1.2)% to 1.
As long as a code having a value of 5% is selected, a tire that does not cause a bad appearance on the tread surface can be found by using the above-described method. Note that the determined elongation percentage of the reinforcing layer 22 is a value that is close to the initial elongation percentage of the cord 23, but is not the same value. The code 23
As a rubber, a cord can be used in which rubber enters between the filaments or the strands constituting the cord 23 by vulcanization, and the filament and the strand are hardly moved. In this case, the initial elongation of the cord 23 is reduced. Alternatively, it may be set to a value larger than the initial elongation rate of the cord into which rubber does not enter. However, at this time, the circumferential elongation rates of both reinforcing layers 22 are the same. In this case, compared to the cord in which rubber does not enter, a large amount of the initial elongation is not used for elongation at the time of vulcanization, and remains when the internal pressure is filled in the vulcanized tire. As a result, it is considered that the tire 1 grows in a large diameter, but such a situation is prevented by restricting the movement of the filaments and strands constituting the cord 23 as described above. Also, as described above, when the reinforcing layer 22 is disposed radially inward of the belt layer 14 instead of radially outward, when the outer diameter of the raw tire is the same, when the reinforcing layer 22 is disposed radially outside of the belt layer 14. The expansion amount at the time of vulcanization is larger than that of The reason is that the belt layer 14 before vulcanization does not have a smooth surface due to the reinforcing elements 16 buried in the belt layer 14, and protrudes where the reinforcing elements 16 are present. Although the maximum gauge is thick because it is concave where it does not exist, the unevenness existing on the surface of the belt layer 14 is averaged when vulcanization is performed. This is because the thickness of the reinforcing layer 22 becomes thinner, and as a result, the reinforcing layer 22 needs to expand more by the thinner. In other words, the initial elongation of the cord 23 of the reinforcing layer 22 is
When the reinforcing layer 22 is disposed radially outside the belt layer 14 and when the reinforcing layer 22 is disposed radially inward, a larger value is required when the reinforcing layer 22 is disposed radially inward, and vulcanization molding is difficult. That is. However, if the cord 23 embedded in the reinforcing layer 22 is a metal cord having a large initial elongation as described above, the reinforcing layer 22 is surely expanded in the vulcanizing kettle. It can be vulcanized without any problems.

The cord 23 is made of a metal cord having an elastic modulus of 10,000 kg / mm ² or more. The reason is that if the elastic modulus is less than 10,000 kg / mm ² , when the vulcanized tire 1 is filled with internal pressure or run, the tire 1
This is because the shoulder portion grows largely radially outward. Therefore, the elastic modulus of the cord 23 is 10,000 kg / mm ²
With the above-described metal cord, the diameter growth is reliably suppressed, thereby reliably preventing belt separation and uneven wear, for example, shoulder drop wear. here,
The elastic modulus refers to the elastic modulus at the time of a load of 30% of the breaking load, and is preferably 12000 kg / mm ² or more. It is well known that the maximum value of the elastic modulus is about 20,000 kg / mm ² .

When the cord 23 is taken out from the vulcanized tire 1 to measure the initial elongation and elasticity as described above, the measurement is performed after removing the covering rubber using, for example, 5N hydrochloric acid. Prior to removing the rubber, it is preferable that both ends of the taken out measurement piece be bent at least 90 degrees in a state of being covered with the rubber so that the twist of the cord 23 is not returned and broken.

Here, as the code 23 in the above-mentioned numerical range, for example, there is a code described in Japanese Patent Application Laid-Open No. 60-116504. That is, before twisting the filaments constituting the cord into the cord, the cord is shaped by applying a stress exceeding the elastic limit in advance to a shape similar to the filament shape in the twisted cord, and then twisting these filaments. It is molded into a cord. By doing so, a cord having a high initial elongation and a high elastic modulus as described above can be formed. In such a cord, when vulcanizing, the rubber easily penetrates into the area surrounded by the filament of the cord, and therefore, when determining the initial elongation and the circumferential elongation during vulcanization, the degree of freedom is determined as described above. Although there is a merit that the size becomes large, the object of the present invention can be sufficiently achieved even if rubber does not enter. Here, the amount of shaping (amplitude) given to the filament in advance is preferably 98% or more of the maximum diameter of the filament in the cord state. The twist structure of this cord is 1 × 3, 1 × 4, 1
A single layer twist structure of × 5, 1 × 6 or a double layer twist structure of 2 + 7, 2 + 8 is used. It should be noted that in such a cord, when the pitch is shortened, the initial elongation increases, but when the pitch is shortened until the initial elongation exceeds 1.5%, the elastic modulus decreases. For these reasons, the initial elongation must be 1.5% or less.

Next, a first test example will be described. For this test,
Comparative tires 1, 2, 3, 4 and test tires 1, 2, 3,
4 was prepared. Here, comparative tire 1, test tire 1
Are tires each having a size of 11R22.5 (the tire outer diameter D is 1050 mm), which has a belt layer having a width of 160 mm and a reinforcing layer disposed radially inward of the belt layer and including two reinforcing plies having a width of 110 mm. , The maximum depth d is 1 on the outer surface of the tread rubber
A 3.5 mm groove is formed. On the other hand, both the comparative tire 2 and the test tire 2 have a size of 255 / 70R22.5 (tire outer diameter D
Has a reinforcing layer consisting of a belt layer having a width of 170 mm and two reinforcing plies having a width of 115 mm disposed radially inward of the belt layer. The outer surface of the tread rubber has a maximum depth d. Has a groove of 12.0 mm. Furthermore, the size of both the comparative tire 3 and the test tire 3 is 385 / 65R22.5
(Tire outer diameter D is 1075 mm), a belt layer having a width of 260 mm and 180 m disposed radially inside the belt layer.
It has a reinforcing layer consisting of two reinforcing plies with a width of m, and a groove having a maximum depth d of 13.8 mm is formed on the outer surface of the tread rubber. The comparative tire 4 and the test tire 4 are both 185 / 70R14 tires (tire outer diameter D is 623 mm) and have a length of 130 m.
It has a reinforcing layer consisting of a belt layer having a width of m and a reinforcing ply having a width of 90 mm disposed radially inward of the belt layer, and a groove having a maximum depth d of 8.0 mm is formed on the outer surface of the tread rubber. Have been. Here, the value of the above formula (0.6 × m−1.2) is 0.34 for both the comparative and test tires 1 and 0.35 for both the comparative and test tires 2 and 0.35 for the comparative and test tires 3. 0.34 for both, comparison and test tire 4
0.34. Further, the belt layers of the comparative and test tires 1, 2, and 3 are composed of three belt plies, and these belt plies intersect the tire equatorial plane at 18 degrees (1 × 3) × 0.20 + 6. × 0.35 crossed code
There are 27 shots per 50mm. On the other hand, the belt layer of the comparative and test tire 4 is composed of two belt plies, and these belt plies intersect each other at (1 × 2) × 0.23 + 6 × 0.23 with the tire equatorial plane at 20 degrees. 22 cords are inserted per 50mm. A cord having an initial elongation of 0.28% is embedded in the reinforcing layers of the comparative tires 1, 2, 3, and 4, and the circumferential elongation of the reinforcing layers of these tires at the time of vulcanization is reinforced as described above. Mold-type vulcanizing device (the tread pattern is applied to a plurality of mold segments in the circumferential direction, while gradually decreasing from the circumferential elongation rate at which the layer and the belt layer cause widthwise waving until the waving does not occur. The outer surface of the tread rubber of the tire, which was vulcanized many times by a divided type vulcanizing device) and no waviness was observed, was observed. As a result, in each of the comparative tires, the rubber was bitten between the mold segments of the split mold, and a film-like rubber was formed on the outer surface of the tread portion of the vulcanized tire. On the other hand, in the test tires 1, 2, 3, and 4, a cord having an initial elongation of 0.35% was embedded in the reinforcing layer, and the circumferential elongation during the vulcanization of the reinforcing layer was gradually reduced in the same manner as described above. Then, the vulcanization was repeated while lowering the value to find a value at which no waving occurs in the width direction in the reinforcing layer and the belt layer, and the outer surface of the tread rubber of the tire at the circumferential elongation was observed. As a result, none of the test tires had any rubber biting, and the condition of the outer surface of the tread portion was good. Thus, the initial expansion rate of the code is (0.6 × m−1.
2) When it is not less than%, favorable vulcanization molding can be performed even if the outer diameter D of the tire is different.

Next, a second test example will be described. For this test,
Comparative tires 5, 6, and 7 and test tires 5, 6, and 7 were prepared. Here, comparative tires 5, 6 and test tires 5, 6
Are tires each having a size of 11R22.5 (the tire outer diameter D is 1050 mm), which has a belt layer having a width of 160 mm and a reinforcing layer disposed radially inward of the belt layer and including two reinforcing plies having a width of 110 mm. A groove having a maximum depth of d17.5 mm is formed on the outer surface of the tread rubber of the comparison and test tire 5, and a groove having a maximum depth d of 22.5 mm is formed on the outer surface of the tread rubber of the comparison tire 6. Have been. On the other hand, the size of both the comparative tire 7 and the test tire 7 is 255 / 70R22.5 (tire outer diameter D is 930 mm).
The tire has a reinforcing layer consisting of a belt layer having a width of 170 mm and two reinforcing plies having a width of 115 mm disposed radially inward of the belt layer, and has a maximum depth d of 15.0 mm on the outer surface of the tread rubber. Grooves are formed. Here, the above equation (0.
The value of 6 × m−1.2) is 0.80 for both the comparative and test tires 5, 1.37 for both the comparative and test tires 6, and 0.74 for both the comparative and test tires 7. . The belt layer of each of these tires is composed of three belt plies.
Twenty-six (1 × 3) × 0.20 + 6 × 0.35 intersecting cords are inserted per 50 mm. Then, cords having an initial elongation of 0.7%, 1.3%, and 0.7% are embedded in the reinforcing layers of these comparative tires 5, 6, and 7, respectively. As described above, while gradually decreasing from the circumferential elongation at which the widthwise waving occurs in the reinforcing layer and the belt layer,
The tire was vulcanized many times by a split mold vulcanizing apparatus until no waving occurred, and the outer surface of the tread rubber in the tire where no waving occurred was observed. As a result, in each of the comparative tires, the rubber was bitten between the mold segments of the split mold, and a film-like rubber was formed on the outer surface of the tread portion of the vulcanized tire. On the other hand, for the test tires 5, 6, and 7, the initial elongation rate of the reinforcing
0.8%, 1.4%, and 0.8% of the cord are buried, and vulcanization is repeated while gradually reducing the circumferential elongation during vulcanization of the reinforcing layer in the same manner as described above. The outer surface of the tread rubber of the tire was observed at the circumferential elongation at a value at which no waving was generated. As a result, none of the test tires had any rubber biting, and the condition of the outer surface of the tread portion was good. And
As is clear from the results of the first test example and the results of the second test example, when the initial elongation of the cord is (0.6 × m-1.2)% or more, the maximum depth of the groove in the tread portion of the tire is determined. Good vulcanization molding can be performed even if d is different.

Next, a third test example will be described. For this test,
Comparative tires 8, 9, 10, 11 and test tires 8, 9, 10 were prepared, respectively, where the size of each tire was 11R2.
2.5 (the tire outer diameter D was 1050 mm), and the maximum depth d of the groove on the outer surface of the tread rubber was 13.5 mm. Here, the values of the equation (0.6 × m−1.2) for each of these tires are all 0.34
It is. The belt layer of each tire is composed of three belt plies, and the outer belt plies have a width of 120 m.
m, the width of the middle belt ply is 160 mm, and the width of the inner belt ply is 180 mm. Each belt ply is inclined at 18 degrees with respect to the tire equatorial plane (1 × 3) × 0.20 +
27 x 6 x 0.35 crossed cords are hit per 50mm. On the other hand, the reinforcing layer is disposed between the belt layer and the carcass layer, and is composed of two reinforcing plies each having a width of 110 mm. In each reinforcing ply, a cord as shown in a separate table is embedded substantially parallel to the tire equatorial plane. Then, the raw tire in which such a cord is embedded is obtained by determining the circumferential elongation of the reinforcing layer in which the waving in the width direction of the reinforcing layer and the belt layer does not occur as described above, and vulcanizing the raw tire by a split mold type vulcanizing apparatus. It is sulfurized. Note that the comparative tire 11 was vulcanized by setting the circumferential elongation of the reinforcing layer during vulcanization to the same value as that of the test tire 8;
Since the initial elongation of the cord was insufficient with respect to the set elongation in the circumferential direction, the belt layer of the vulcanized tire was wavy in the width direction, resulting in a defective tire. Here, the used cord weight ratio in the separate table was determined based on a value obtained by actually measuring the cord weight per unit length and multiplying the actually measured value by the number of drivings. In this case, the code embedded in the comparative tire 8, that is, the value of the code of 4 × 4 × 0.23 5.9 (g / m) × 18 (lines / 50 mm) = 104.4 g / 500 cm ² is indicated as an index by 100. . In addition, the diameter growth amount in the separate table shows that the internal pressure of each vulcanized tire is 0.3 kg / cm ²
This is a value obtained by measuring the amount of radial growth radially outward at both shoulder portions when filling up to 7.5 kg / cm ^2, and averaging the maximum values of both measured values. As is clear from this separate table,
In the comparative tire 8, the cord weight used is large, and as a result, the tire becomes expensive. Also,
The comparative tires 9 and 10 have a large diameter growth amount and have poor workability during manufacturing. On the other hand, the test tire 8,
In Nos. 9 and 10, the weight of the cord used is small, the diameter growth is small, and the workability is good.

In the above-described embodiment, the reinforcing layer 22 is formed by the belt layer.
Although it is arranged radially inward of 14, that is, between the belt layer 14 and the carcass layer 8, it may be arranged radially outside of the belt layer in the present invention.
One reinforcing ply may be arranged radially outside the belt layer, and the other reinforcing ply may be arranged radially inside the belt layer.

Effect of the Invention As described above, according to the present invention, vulcanization molding is easy, and furthermore, it is possible to sufficiently suppress the diameter growth during use of the tire without increasing the weight of the cord used, or The weight of the cord can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a meridian sectional view showing an embodiment of the present invention, and FIG.
The figure is a sectional view taken along the line II of FIG. 8 ... Carcass layer, 12 ... Cord 14 ... Belt layer, 16 ... Reinforcing element 18 ... Tread rubber, 22 ... Reinforcing layer 23 ... Cord, S ... Tire equatorial plane

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-250483 (JP, A) JP-A-1-314744 (JP, A) JP-A-3-96402 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) B60C 9/00 B60C 9/18 B60C 11/00

Claims (1)

(57) [Claims] 1. A toroidal carcass layer in which a large number of cords extending in a direction substantially perpendicular to the tire equatorial plane are embedded, and a carcass layer disposed radially outside of the carcass layer at 10 degrees to the tire equatorial plane. A belt layer in which a number of reinforcing elements inclined at an angle of 40 degrees are embedded, a reinforcing layer in which at least a portion of the belt layer overlaps and a cord substantially parallel to the tire equatorial plane is embedded, and a belt layer and reinforcement A tread rubber having a groove formed on the outer surface thereof, which is arranged radially outside of the layer, wherein the maximum depth of the groove is d, the outer diameter of the tire is D, and m = 2d / D × 100. When the value of m is 2.55 or more in the pneumatic radial tire,
The cord of the reinforcing layer has an initial elongation of (0.6 × m′-1.2)
A pneumatic radial tire comprising a metal cord having a modulus of elasticity of not less than 10,000 kg / mm ^{2 in} a range of 10% to 1.5%.