JPH05238203A - Pneumatic tire - Google Patents

Abstract

PURPOSE:To provide a pneumatic tire of which uniformity can be improved and unevenness of the surface of a side wall part can be reduced so as to improve appearance. CONSTITUTION:A carcass material 1 is constituted by covering carcass cords 5 orientedly arranged in the width direction of a tire by coat rubber, the driving density of the carcass cords on at least one-side of the end parts 2, 4 extended in the circumferential direction of a tire is reduced than that of the center part 3. A carcass layer is formed by arranging the carcass material 1 along the circumferential direction of the tire, overlapping its both end parts, and lap-slicing them.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a pneumatic tire,
In particular, the present invention relates to a pneumatic tire having reduced steps formed in the lap splice portion of the carcass layer.

[0002]

2. Description of the Related Art In a pneumatic tire, the carcass layer is formed by arranging a belt-shaped carcass material corresponding to one tire circumference in the tire circumferential direction and lapping and splicing both end portions of the carcass material. There is. In this case, as the carcass material, a material in which the driving density of the carcass cord, that is, the number of ends per unit width is uniform is used.

[0003]

However, the splice portion of the carcass layer formed by using the carcass material having the uniform driving density of the carcass cord as described above is
Since the density of the carcass cord is partially increased by overlapping, the carcass cord is thickened in a step shape. Therefore, this increases the radial force variation (RFV) and the width force variation (LFV) of the tire, thus reducing the uniformity and the performance such as riding comfort. Further, stress is concentrated on the lap splice portion, which is a cause of tire failure. Further, since the step of the lap splice portion appears as streaky irregularities on the surface of the sidewall portion, there is a problem that the tire appearance is impaired. In particular,
As the thickness of the rubber of the sidewall portion is gradually reduced in order to reduce the weight of the tire as in recent years, streaky irregularities are becoming more and more prominent.

An object of the present invention is to provide a pneumatic tire which can improve uniformity and can reduce irregularities on the surface of the sidewall portion to improve the appearance.

[0005]

In the pneumatic tire according to the present invention, a carcass material formed by coating carcass cords with carcass cords oriented in parallel is formed so that the carcass cords intersect the tire circumferential direction. While orienting and winding in the tire circumferential direction, the end portion is lap-spliced to form a carcass layer, and the driving density of the carcass cord of at least one end portion of the lap splice portion is set to a value other than the lap splice portion. It is characterized in that it is made smaller than the driving density of the carcass cord of the part.

By reducing the driving density of the carcass cord at one end or both ends of the carcass material as compared with the other portion, it is possible to reduce the step formed in the lap splice portion of the carcass layer. . Therefore, the uniformity of the tire can be improved. Further, since stress concentration on the lap splice portion is reduced, tire failure is reduced. Furthermore, by reducing the step difference of the lap splice portion of the carcass layer, the unevenness of the sidewall portion surface is inevitably reduced, so that the tire appearance can be improved.

The present invention reduces the driving density (the number of ends per unit width) of the carcass cord at least at one end of the portion where the end of the carcass material wraps,
In other words, the gist is to reduce the number of sparse ends. It is preferable that the wrap width for reducing the number of sparse ends is 3 to 12 mm. If the lap width is less than 3 mm, the splice strength becomes insufficient, and conversely, if it exceeds 12 mm, it becomes difficult to reduce the step difference of the lap splice portion due to the influence of the coat rubber that coats the carcass cord.

Further, it is preferable that the driving density of the carcass cord at the end portion where the number of sparse ends is reduced is reduced by 5 to 30% as compared with the other portion where the lapping is not performed. If the sparse end number conversion ratio is less than 5%, the effect due to the sparse end number conversion is insufficient and it becomes difficult to reduce the step difference of the lap splice portion, and if it exceeds 30%, the splice strength becomes insufficient.

The structure of the present invention will be described below with reference to the accompanying drawings. In addition, although the case of a radial tire will be described below, the present invention can be applied to both a radial tire and a bias tire. In FIG. 1, a carcass material 1 is composed of a carcass cord 5 in which a plurality of carcass cords 5 oriented in parallel in the tire width direction (tire rotation axis direction) are covered with a coat rubber. The driving density of the carcass cords in at least one of 4 is smaller than that in the central portion 3. For example, when the number of ends of the carcass cord 5 in the central part 3 per 50 mm width is 54, the number of ends in the ends 2 and 4 is 51 (5% decrease), 49.
Books (10% reduction), 46 (15% reduction), 43 (2
0% decrease), 41 lines (25% decrease), 38 lines (30% decrease), etc. Such a carcass material 1 can be easily manufactured by selectively reducing the number of the carcass cords 5 supplied to the end portions 2 and 4 when rubber is attached to the carcass cords 5 by a calendar.

In the pneumatic tire according to the present invention, the carcass material 1 corresponding to one tire circumference prepared as described above is wound around a forming drum, and both ends thereof are lap-spliced as shown in FIG. After molding the green tire, internal pressure is applied in the mold to vulcanize it while pressing the inner surface of the mold. In this vulcanization process, the coat rubber in the lap portion flows, so that the thickness changes as shown in FIG. 3 to FIG.

As described above, the end portions 2, 4 of the carcass material 1 are
Since the carcass cords 5 of the lap splice portion are arranged so as to cut into each other by reducing the driving density of the carcass cord 5 in comparison with the central portion 3, the step difference in the lap splice portion of the carcass layer 11 is as shown in FIG. Can be reduced to Therefore, the uniformity of the tire can be improved, and the unevenness of the sidewall portion surface of the lap splice portion of the carcass layer 11 can be reduced to improve the tire appearance. Further, stress concentration is not caused in the lap portion.

[0012]

As described above, according to the present invention, the carcass layer is formed by reducing the driving density of the carcass cord at at least one end of the lap splice portion of the carcass material as compared with the portion other than the lap splice portion. Therefore, the uniformity of the tire can be improved, and the unevenness of the sidewall surface can be reduced to improve the tire appearance. Further, it is possible to reduce stress concentration on the lap splice portion and reduce tire failures. As a result, the commercial value of the tire can be further increased.

[Brief description of drawings]

FIG. 1 is a plan view showing a carcass material used in a pneumatic tire according to the present invention.

FIG. 2 is a sectional view showing a lap-spliced state of a carcass material in the present invention.

FIG. 3 is a cross-sectional view showing a lap splice portion during vulcanization in the present invention.

FIG. 4 is a cross-sectional view showing a lap splice portion of a carcass layer of a pneumatic tire according to the present invention.

[Explanation of sign]

 1 Carcass material 2,4 Edge of carcass material 3 Central part of carcass material 5 Carcass cord 11 Carcass layer

Claims (1)

[Claims] 1. A carcass material in which carcass cords oriented in parallel are coated with a coat rubber is oriented in such a manner that the carcass cords intersect the tire circumferential direction, and the carcass cord is wound in the tire circumferential direction. A carcass layer is formed by lap-splicing the ends, and the driving density of the carcass cords of at least one end of the lap splicing portion is made smaller than the driving density of the carcass cords of the portion other than the lap splicing portion. tire.