JPH1111111A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the durability of a belt by enhancing the circumferential rigidity in the belt end part. SOLUTION: An inclination A of cords 27 (27a-27d) situated on both lateral end parts of each belt ply 26 to a tire equatorial plane E is set less than the inclination of the cord 27 situated in the lateral central part within the same belt ply 26. Thus, the circumferential rigidity in both the lateral end parts is set higher than the circumferential rigidity in the lateral central part increased by being largely extended in vulcanization.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire capable of improving belt durability.

[0002]

2. Description of the Related Art Conventionally, a pneumatic tire is formed, for example, by winding at least one carcass ply around the outer periphery of a cylindrical forming drum, setting a bead, and turning the bead to form a cylindrical green case. After winding a plurality of belt plies around the outer periphery of a cylindrical band forming drum, a tread is wound around the belt ply in the radial direction to form a BT (belt tread) band, and then the green case is formed. The green tire is formed by fitting and attaching the BT band to the radial outside of the green case while bulging the green tire into a substantially semicircular cross section, and then vulcanizing the green tire with a vulcanizing device. It is molded by that. Here, a number of mutually parallel cords inclined with respect to the tire equatorial plane are embedded in each of the belt plies described above, and the inclination of the cords in some belt plies with respect to the tire equatorial plane. The direction is opposite to the direction of inclination of the cords in the remaining belt plies.

[0003]

The belt layer as described above has a cylindrical shape when the BT band is formed at the stage of the green tire. Under the influence of the molding surface, the center portion in the width direction is deformed so as to protrude radially outward from both end portions in the width direction, and is usually deformed so as to be curved with a substantially constant radius of curvature. As a result, each belt ply has its center in the width direction stretched in the circumferential direction to a greater extent than both ends in the width direction, whereby, in the pneumatic tire after vulcanization,
The angle of inclination of the cord embedded in each belt ply with respect to the tire equatorial plane gradually decreases from both ends in the width direction toward the center in the width direction. In addition, in the conventional application specification and drawings, description and illustration are complicated,
Although the inclination angle is described as being the same in the same belt ply irrespective of the position in the width direction, it is actually gradually reduced from both ends in the width direction toward the center in the width direction as described above. is there. Here, when the inclination angle of the cord with respect to the equatorial plane of the tire becomes small, such as the central part in the width direction of the belt ply, a polygon of a triangle or more formed by superposing the cords in a plurality of belt plies in the radial direction is formed. As a result, the rigidity in the circumferential direction at the portion, that is, the crimping effect is increased. On the other hand, since both ends in the width direction of the belt ply are not stretched much in the circumferential direction even if vulcanization is performed, the above-mentioned polygon is almost the same as the shape at the time of the green tire, and as a result, the belt layer The circumferential rigidity at both ends in the width direction becomes insufficient. Therefore, when such a pneumatic tire is filled with internal pressure, or when a pneumatic tire filled with internal pressure is run, both widthwise ends of each belt ply greatly extend in the circumferential direction, that is, in the radial direction. Therefore, there is a problem in that the belt edge grows to a large diameter, and a large distortion is generated at the belt end, thereby easily causing the belt end separation.

An object of the present invention is to provide a pneumatic tire with improved belt durability by increasing circumferential rigidity at both ends in the width direction of a belt layer.

[0005]

An object of the present invention is to form a toroidal carcass layer composed of at least one carcass ply and a plurality of belt plies disposed radially outside of the carcass layer. With the configured belt layer and a tread arranged radially outside of the belt layer, while embedding a number of mutually parallel cords inclined with respect to the tire equatorial plane in each belt ply, partially In the pneumatic tire in which the inclination direction of the cords in the belt ply with respect to the tire equatorial plane and the inclination direction of the cords in the remaining belt ply are opposite, the tire equator of the cords located at both ends in the width direction of the belt ply The angle of inclination of the cord located at the center in the width direction of the same belt ply is set to be equal to or less than the angle of inclination with respect to the tire equatorial plane. It can be.

As described above, when the green tire is vulcanized, each belt ply is greatly extended in the circumferential direction at a central portion in the width direction, so that when a vulcanized pneumatic tire is formed, the width of the belt ply is reduced. The inclination angle of the cord embedded in the center with respect to the tire equatorial plane is smaller than the value at the time of the green tire. As a result, the polygons, which are formed by superimposing the cords located at the central portions in the width direction of the plurality of belt plies in the radial direction, have a shape that is stretched in the circumferential direction.
The circumferential rigidity at the portion, that is, the crimping effect is increased. For this reason, in the present invention, the inclination angles of the cords located at both ends in the width direction of the belt ply with respect to the tire equatorial plane are equal to or less than the inclination angles of the cords located at the center part in the width direction of the same belt ply with respect to the tire equatorial plane. The inclination angle of the cord located at the center in the width direction with respect to the tire equatorial plane is equal to or less than the inclination angle. As a result, the polygons at the both ends in the width direction of the belt ply look more elongated in the circumferential direction than the polygons at the center portion in the width direction, and thereby, the circumferential rigidity at the both ends in the width direction of the belt ply is vulcanized. The rigidity in the circumferential direction at the central portion in the width direction, which has been increased by the large stretching at the time, can be increased up to, or equal to or greater than, the circumferential rigidity. Thereby, such a pneumatic tire is filled with internal pressure, or, even when running the pneumatic tire filled with the internal pressure, the circumferential extension of the width direction both ends of each belt ply, that is, radially outward Is small, and as a result, the distortion at the belt end is reduced, and the belt end separation is effectively suppressed.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. 1, 2 and 3, reference numeral 11 denotes a pneumatic radial tire as a product which has already been vulcanized. The tire 11 has a pair of bead portions 13 in which bead cores 12 are respectively buried, and Sidewall portion 14 extending almost radially outward from
And a substantially cylindrical tread portion 15 connecting the radially outer ends of the sidewall portions 14 to each other. The tire 11 is reinforced by a toroidal carcass layer 21 extending from one bead portion 13 to the other bead portion 13. Both end portions in the width direction of the carcass layer 21 surround the bead core 12. It is folded back from the inside in the axial direction to the outside in the axial direction. This carcass layer 21 has at least one
In this embodiment, the carcass ply 22 is composed of a single carcass ply 22. In the carcass ply 22, a non-extensible cord 23 made of steel or the like perpendicular to the equatorial plane E of the tire (extending in the radial direction) is embedded. Have been. The carcass layer
A belt layer 25 is disposed radially outward of the belt 21. The belt layer 25 includes a plurality of belt layers 25, in this embodiment, four belt plies 2.
6, that is, the first, second, third, and fourth belt plies 26a, 26b, 26
c and 26d are sequentially superposed from the radially inner side to the radially outer side. Each belt ply 26
A number of cords 27 which are inclined in the circumferential direction, that is, at a predetermined angle A with respect to the tire equatorial plane E, are buried inside the cords. These cords 27 are made of steel, Kevlar (aromatic polyamide fiber) or the like. Of non-extensible materials.
Here, the cord 27a in the first belt ply 26a is inclined upward to the right with respect to the tire equatorial plane E, and the inclination angle Aa is in a range of 45 to 70 degrees, and is approximately 50 degrees in this embodiment. The cord 27b in the second belt ply 26b is inclined upward to the right, and the inclination angle Ab is 15 degrees to 25 degrees.
Degree range, which in this embodiment is approximately 20 degrees, and
The cord 27c in the third belt ply 26c is inclined upward and to the left, and the inclination angle Ac is in the range of 15 to 25 degrees, in this embodiment, approximately 20 degrees.
The cord 27d in 26d is inclined upward and to the left, and its inclination angle Ad is in the range of 15 to 25 degrees.
20 degrees. When the belt layer 25 is composed of a plurality of belt plies 26 as described above, the tire equatorial plane E of the cords 27a and 27b in some of the belt plies 26, here, the first and second belt plies 26a and 26b. And the cords 27c and 27d in the remaining belt plies 26, here the third and fourth belt plies 26c and 26d.
Of the tire with respect to the equatorial plane E (upward to the left). The above-mentioned cords 23 and 27 may be formed by twisting a plurality of filaments, or may be constituted by a single filament. A tread 31 having a groove 30 such as a main groove and a lateral groove formed on the outer periphery is arranged radially outside the belt layer 25. Then, the outer periphery of the tread portion 15 of the tire 11 swells by vulcanization so that the center portion protrudes radially outward from both end portions,
Usually, it is curved with a constant radius of curvature. Here, the inclination angle A of the cord 27 with respect to the tire equatorial plane E is obtained by cutting a cut sample from the vulcanized tire 11 and using the cut sample.

[0008] The tire 11 as described above is formed by molding a green tire and then vulcanizing the green tire with a vulcanizing device. The green tire is illustrated in a cylindrical shape. After forming the carcass layer 21 by winding the carcass ply 22 around the outer periphery of the non-forming drum, the bead core 12 is set outside the carcass layer 21 and folded to form a cylindrical green case, and is also illustrated. A plurality of (four) belt plies 26, i.e., first, second,
After winding the belt plies 26a, 26b, 26c and 26d one after another to form the belt layer 25, a tread 31 is wound around the belt layer 25 in the radial direction to form a BT (belt tread) band. The BT is bulged radially outward while the green case bulges in a substantially semicircular cross section.
It is molded by fitting and attaching a band.

Next, the above-described green tire is accommodated in a vulcanizing device and vulcanized.
As described above, the central portion in the width direction is greatly stretched in the circumferential direction, so that when the pneumatic tire 11 has been vulcanized, the cord 27 embedded in the central portion in the width direction of the belt ply 26 is the tire equator. Incline to approach surface E,
The inclination angle A with respect to the tire equatorial plane E is smaller than the value at the time of the green tire. As a result, a polygon D, which is a triangle or more, formed by superposing the cords 27 located at the central portions in the width direction of the plurality of belt plies 26 in the radial direction has a shape elongated in the circumferential direction. , Ie, the crimping effect is increased. For this reason, in this embodiment, the inclination angle A of the cords 27 located at both ends in the width direction of each belt ply 26 with respect to the tire equatorial plane E is set to the tire of the cord 27 located at the center in the width direction within the same belt ply 26. Inclination angle A or less with respect to the equatorial plane E,
That is, the inclination angle A of the cord 27 located at the center in the width direction with respect to the tire equatorial plane E is equal to or less than the inclination angle A. As a result, the polygons D at the both ends in the width direction of each belt ply 26 look more elongated in the circumferential direction than the polygon D at the center in the width direction. The circumferential stiffness can be increased up to, or equal to or greater than, the circumferential stiffness at the central portion in the width direction, which is increased by being greatly stretched during vulcanization. Thereby, even if such a pneumatic tire 11 is filled with the internal pressure, or even if the pneumatic tire 11 filled with the internal pressure is run, the circumferential elongation at the both ends in the width direction of each belt ply 26, i.e., the radius The radial growth outward in the direction is small, and as a result, the distortion at the belt end is reduced, and the belt end separation is effectively suppressed.

[0010]

Next, test results will be described. In this test, the first, second, third, and fourth belt plies 26a,
Codes 27a, b, b at both ends in the width direction of b, c, d
Tilt angles Aa, Ab, Ac, Ad of tires c and d with respect to equatorial plane E
The values obtained by dividing the inclination angles Aa, Ab, Ac, and Ad with respect to the tire equatorial plane E of the cords 27a, b, c, and d at the center in the width direction are 0.92, 0.86, 0.86, and 0.86, respectively. And test tires having values of 1.13, 1.18, 1.18, and 1.18, respectively. Where all belt plies
The elongation at the center in the width direction and the elongation at both ends in the width direction are substantially the same, but the inclination angle Aa of the cord 27a in the first belt ply 26a is larger than the other inclination angles Ab, Ac, and Ad. Since it is large, it is greatly affected by vulcanization, and the divided value is different from other belt plies as described above. Also, the belt layer 25 of each tire 11
Was the same as that described in the above embodiment, and the size of each tire 11 was 11R22.5, and the rim to which these tires were attached was 7.50. Next, each of these tires 11
After applying an internal pressure of 800 kPa to the drum, apply a vertical load of 3000 kgf and move on the drum at a speed of 60 km / h at a speed of 5 km / h every 30 minutes.
In each of the tires 11, the speed at which the belt end separation occurred was determined. When the result is shown with the conventional tires with an index of 100,
In the test tire, the belt durability was improved up to the index of 120. Here, the index 100 was 125 km / h.

After filling the tire 11 with an internal pressure of 800 kPa, the tire 11 is run on a drum at a speed of 60 km / h while applying a vertical load of 3000 kgf and a horizontal load of 300 kgf (10% of the vertical load). The running distance when the edge separation occurred was determined. When the results are shown in the conventional tires with an index of 100, the belt durability of the test tires was improved to an index of 142. Here, the index 100 was 2000 km.

Next, four tires 11 were prepared, and these tires 11 were mounted on a commercial truck and set at 800 kPa.
After the inner pressure is charged, the vehicle is driven 100,000 km on a 30% paved highway and 70% paved general road while applying an average load of 2800 kg. The crack length of 26a along the cord 27a was measured for 20 cords. The result was an average of 7.2 mm for the conventional tire, but an average of 2.6 mm for the test tire.
And the separation resistance was improved.

[0013]

As described above, according to the present invention, the circumferential rigidity at the end of the belt can be increased, so that the belt durability can be improved.

[Brief description of the drawings]

FIG. 1 is a meridian sectional view of a pneumatic tire according to an embodiment of the present invention.

FIG. 2 is a partially broken plan view thereof.

FIG. 3 is a plan view showing a state in which cords in a plurality of belt plies are superimposed.

[Explanation of symbols]

 11 ... pneumatic tire 21 ... carcass layer 22 ... carcass ply 25 ... belt layer 26 ... belt ply 27 ... cord 31 ... tread E ... tire equatorial plane A ... inclination angle

Claims (1)

[Claims] 1. A toroidal carcass layer comprising at least one carcass ply, a belt layer disposed outside the carcass layer in a radial direction and formed by stacking a plurality of belt plies, and a radius of the belt layer. And a plurality of parallel cords that are inclined with respect to the tire equatorial plane are embedded in each belt ply, and the tire equatorial plane of the cords in some belt plies is provided. In the pneumatic tire in which the inclination direction to the tire and the inclination direction of the cords in the remaining belt plies are opposite, the inclination angles of the cords located at both ends in the width direction of the belt plies with respect to the tire equatorial plane are set to the width of the same belt plies. A pneumatic tire characterized in that the cord located at the center in the direction has an inclination angle of not more than the tire equatorial plane.