JPH03262704A - Pneumatic radial tire for heavy load - Google Patents

Abstract

PURPOSE:To prevent the end of the third ply from generating rubber cracks by specifying the extension when the cord of the fourth ply from the carcass side is broken and width of the fourth ply out of the four belt ply arranged between the carcass and a tread. CONSTITUTION:A tire is provided with four belt plies 21 to 24 between a carcass 10 and a tread 30, and each of the plies 21 to 24 is arranged with steel cords in parallel with each other. The cords of the first ply 21 and the second ply 22 are inclined in the same direction in relation to the center line 40 in the circumference of the tire, and the cords of the second ply 22 and the third ply 23 in the directions opposite to each other, and the cords of the third ply 23 and the fourth ply 24 in the same direction respectively. In the constitution mentioned above, the extension of the fourth ply 24 when the cord is broken is set to 5% or more, and the width of the fourth ply 24 is also formed larger than that of the third ply 23. The end of the third ply 23 is coated with the fourth ply 24 for preventing the end from generating rubber cracks.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a heavy-duty radial tire in which the cord tension of belt plies is made uniform to improve belt durability.

[Prior art] Even heavy-duty radial tires for trucks, buses, etc. have become flatter in recent years due to demands for increased loading capacity and lower fuel consumption, and the ratio of tire height to tire width, that is, the flattening ratio, has increased. 55% to 75% have been used.

Figure 5 shows an aspect ratio of 65% and a size of 385/65R22.5.
FIG. 2 is a partial cross-sectional view showing the vicinity of the tread of a conventional heavy-duty radial tire. FIG. 6 is a developed plan view of the carcass and each belt ply of this tire.

This tire has four belt plies 21, 22, 23, 24 between the carcass sue 0 and the tread 30, and steel cords are driven into each ply in parallel.

These plies 21.22, 23.24 are made into a carcass 10
When referring to the first to fourth plies from the side, the cords of the first ply 21 and the second ply 22 are inclined in the same direction with respect to the tire circumferential center line 40, and the cords of the second ply 22 and the third ply 23 are inclined in the same direction. The cords of the third ply 23 and the fourth ply 24 are inclined in the same direction.

In the first ply 21 adjacent to the carcass 10, the cord angle αl with respect to the tire circumferential center line 40 is 45° to 65°. In other plies 22, 23, 24, concentric line 4
Code angle α2 with respect to 0. α3. α4 is 15-25°
All are the same within the range. Moreover, the second ply 22
Although it is wider than the ply 21, the third ply 23 is narrower than the second ply 22, and the fourth ply 24 is wider than the third ply 23.
The width is even narrower. The number of ends, that is, the cord implantation density, was almost the same for all plies.

[Problems to be Solved by the Invention] In the conventional heavy-duty radial tire described above, the cord tension is reduced between the second ply 22 and the third ply 23, the cords of which are inclined in opposite directions with respect to the tire circumferential center line 40. Due to the large difference in size, the shear strain between both plies is large, and rubber cracks may occur particularly at the end of the third ply 23. Compared to cases where the aspect ratio is 80% or more, when the aspect ratio is 75% or less, shortening of life due to the occurrence of rubber cracks has become a problem.

The present invention has been made in view of the above circumstances, and has an oblateness ratio of 75% or less, has four belt plies between the carcass and the tread, and has cords drawn in parallel to each ply. The cords of the first ply and the second ply are tilted in the same direction with respect to the tire circumferential center line, and the cords of the second ply and the third ply are tilted in opposite directions. The purpose of the third ply and the fourth ply is to improve belt durability by preventing rubber cracks from occurring at the ends of the belt ply in a heavy-load radial tire in which the cords are inclined in the same direction.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the heavy-duty radial tire according to the present invention has an elongation of the cord in the fourth ply at break of 5% or more, and The width of the ply is made wider than that of the third ply.

If the cord angles of the second ply and the third ply with respect to the tire circumferential direction are almost the same, the cord driving density of the third ply should be set to 60 or more and 90 or less when the cord driving density of the second ply is 100. do.

When the cord driving density of the second ply and the third ply is almost the same, the cord angle of the third ply with respect to the tire circumferential direction is made smaller than that of the second ply, and the difference in the cord angle between both plies is reduced. Must be 4@ or more and 8@ or less.

[Function] In the heavy-duty radial tire according to the present invention, the end portion of the third ply is covered and protected by the wide fourth ply reinforced with a highly elongated cord.

Furthermore, in a tire with the number of ends of the second and third plies in the above relationship, the tension per cord decreases in the second ply with a high number of ends, while the tension per cord decreases in the third ply with a low number of ends. The tension per cord is increased and the cord tension is equalized between the second and third plies. Therefore, shear strain between both plies is alleviated.

In a tire with the cord angles of the second and third plies in the above relationship, the tension per cord decreases in the second ply with a large cord angle, while the tension per cord decreases in the third ply with a small cord angle. The tension of the cord increases and the cord tension equalizes between the second and third plies. therefore,
In this case as well, the shear strain between both plies is alleviated.

[Example] Fig. 1 is a partial sectional view showing the vicinity of the tread of a heavy-duty radial tire according to an example of the present invention, which has an aspect ratio of 65% and a size of 385/65R22.5 as described above. . FIG. 2 is a developed plan view of the carcass and each belt ply of this tire.

This tire also has four belt plies 21, 22, 23, 24 between the carcass 10 and the tread 30, and steel cords are driven in parallel to each ply.

Furthermore, with respect to the tire circumferential center line 40, the first ply 21 (cord angle α1) and the second ply 22 (cord angle α2)
), the cords are inclined in the same direction, and the second ply 22 and third ply 23 (cord angle α3) have cords inclined in opposite directions, and the third ply 23 and fourth ply 24 (cord angle a
4) The cord is tilted in the same direction. however,
The second ply 22 is wider than the first ply 21, the third ply 23 is narrower than the second ply 22, and the fourth ply 22 is wider than the first ply 21.
4 is wider than the third ply 23.

Six types of tires having the above belt structure (FIGS. 1 and 2) are shown in Table 1 as Examples 1 to 6. In the same table, conventional heavy-duty radial tires having the belt structures shown in FIGS. 5 and 6 are also shown as Comparative Examples 1 and 2.

In the same table, the cord structure r3+6J is made by twisting three steel wires together and then twisting six steel wires around them, and the cord with this structure has approximately the same elongation at break. It is 3%. r3+9+15J is a three-layer code structure. The r4X2J cord structure consists of four strands twisted together, with each strand having two
Made by twisting real steel wires together.

However, the strands in the r4X2J cord used for the fourth ply 24, which is the outermost belt ply, are twisted in the same direction as the steel wires, and this cord has a large elongation at break, about 6%. be.

Table 1 shows the belt durability of each tire as an index. This durability comparison is based on the distance traveled before failure occurs near the belt.

If r4X2J is adopted as the cord structure of the fourth ply 24 as shown in Comparative Example 2, the belt durability is improved compared to the case of r3+6J in Comparative Example 1. Therefore, in all the embodiments, r4X2J steel cord is used for the fourth ply 24.

As shown in Example 1, by adopting the belt structure shown in FIGS. 1 and 2, the width of the fourth ply 24 is simply increased compared to the case of Comparative Example 2, and the end portion of the third ply 23 is Since the belt is covered with the fourth ply 24 having high cord elongation, the belt durability is improved by 7%.

As shown in Example 2, if the cord angle α1 of the first ply 21 is reduced to 45'', belt durability is slightly lower than in Example 1, but belt durability is higher than in Comparative Example 2. It will be done.

As shown in Example 3, the number of ends of the second ply 22 is
If the number of ends of the third ply 23 is increased to 1.16 times that of the first ply 21, the belt durability will be improved compared to Example 1, and as shown in Example 4, the number of ends of the third ply 23 will be increased to 0.71 times that of the first ply 21. If you lower it twice, the belt durability will be further improved. When the number of ends of the second ply 22 is set to 100, the number of ends of the third ply 23 is approximately 86 in the case of Example 3, and the number of ends of the third ply 23 is approximately 86 in the case of Example 4.
The case is about 71. FIG. 3 shows the relationship between the cord position in the second ply 22 and the third ply 23 and the tension per cord in the case of Example 4 (CL:
Tire circumferential center line position, SH: tire shoulder position,
MW: tire width). Compared to Comparative Example 2 shown by the solid line, the tension per cord decreases in the second ply 22 with an increased number of ends, while the tension per cord increases in the third ply 23 with a decreased number of ends. As a result, the cord tension becomes uniform between the second and third plies 22 and 23. Therefore, the shear strain between both plies 22 and 23 is alleviated.

As shown in Embodiment 5, if the cord angle α2 of the second ply 22 is made 2" larger than the cord angle α4 of the fourth ply 24, and at the same time the cord angle α of the third ply 23 is made 2" smaller than α4, the embodiment Belt durability comparable to that of 4 can be obtained. In this case, the difference in cord angle between the second and third plies 22,23 is 4''.

As shown in Embodiment 6, if α2 is made 6" larger than α4 and at the same time α3 is made 2 m smaller than α4, the difference in cord angle between the second and third plies 22.23 becomes 8°, and Embodiment 5 Although the belt durability is slightly lower than in the case of Embodiment 6, the belt durability is still higher than that of the conventional case. FIG. The relationship with the tension per book is shown by the broken line.Compared to the case of Comparative Example 2 shown by the solid line, in the second ply 22 with a larger cord angle, the cord 1
While the tension per cord decreases, the tension per cord increases in the third ply 23 with a smaller cord angle.
The cord tension becomes uniform between the second and third plies 22 and 23.

Therefore, in this case as well, the shear strain between the plies 22 and 23 is alleviated.

Note that the cord angle αl of the first ply 21 adjacent to the carcass 10 is suitably 40″ to 55°.

The elongation at break of the steel cord used for the fourth ply 24, which is the outermost belt ply, must be 5% or more, but it is appropriate that the upper limit is 7%.

C Effect of the Invention] As explained above, in the heavy-duty radial tire according to the present invention, the end of the third ply is protected by being covered with the wide fourth ply reinforced with a highly elongated cord. . Therefore, unlike the conventional method, occurrence of rubber cracks at the third fly end can be prevented. Moreover, by making the cord driving density or the cord angle different between the second and third plies, the cord tension can be increased even between the second and third plies where the cords are inclined in opposite directions with respect to the tire circumferential center line. This makes the belt more uniform and improves the durability of the belt.

[Brief explanation of drawings]

1 is a partial sectional view showing the vicinity of the tread of a radial tire for heavy loads according to an embodiment of the present invention; FIG. 2 is a developed plan view of the carcass and each belt ply of the radial tire for heavy loads shown in the previous figure; FIG. Figure 3 shows the relationship between the cord position in the belt ply and the tension per cord (Example 4), and Figure 4 shows another relationship between the cord position in the belt ply and the tension per cord. Fig. 5 is a partial sectional view showing the vicinity of the tread of a conventional heavy-duty radial tire; Fig. 6 is a developed plan view of the carcass and each belt ply of the heavy-duty radial tire shown in the previous figure. It is. Explanation of symbols 10... Carcass, 21.22, 23.24... Belt ply, 30... Tread, 40... Tire circumferential center line, α, α2, α3, α4゛゛cord angle. L 1LsH Belt Ply Co.: Apparatus Fig. 3 W Pertgelai Co. ia installation Fig. 4 Fig. 2

Claims (1)

[Claims] 1. The flatness ratio is 75% or less, and there are four belt plies between the carcass and the tread, and cords are driven in parallel to each ply, When these plies are designated as the first to fourth plies from the carcass side, the cords of the first ply and the second ply are inclined in the same direction with respect to the tire circumferential center line, and the cords of the second ply and the third ply are In a heavy-duty radial tire in which the cord is inclined in the opposite direction, and the third and fourth ply cords are inclined in the same direction, the fourth ply has an elongation of the cord at break of 5% or more, A radial tire for heavy loads that is wider than the third ply. 2. The cord angles of the second ply and the third ply with respect to the tire circumferential direction are almost the same, and when the cord implantation density of the second ply is taken as 100, the cord implantation density of the third ply is 60 or more and 90 or less. The heavy load radial tire according to claim 1. 3. The cord driving density of the second ply and the third ply is almost the same, and the cord angle with respect to the tire circumferential direction is the same as that of the third ply.
The heavy-duty radial tire according to claim 1, wherein the ply is smaller than the second ply, and the difference in cord angle between both plies is 4° or more and 8° or less.