JPH07164837A - Pneumatic radial tire for heavy load - Google Patents

Abstract

PURPOSE:To reconcile an improvement in the durability of a bead part and the promotion of lightweightiness in a tire, in this pneumatic radial tire for heavy load. CONSTITUTION:A wire chafer 24 is subjected to a center drawing at the tire radial inner part of a bead core 14. Since this wire chafer 24 is being drawn, a tire is made lighter in weight. In addition, as the wire chafer 24 comes to be somewhat easy to move in the tire circumferential direction as a whole, if force along the circumferential direction acts on rubber of a tire side part by starting, stopping or the like, the whole wire chafer 24 and a turnover ply 12B faced to this wire chafer 24 slightly come to move in the action direction of force in consequence, and with this action, a circumferential shearing strain acting in space between a turnover ply end and circumjacent rubber is reduced to some extent, so that any ply-end separation is hard to occur and thus durability in a bead part is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy-duty pneumatic radial tire, and more particularly to a heavy-duty pneumatic radial tire having a wire chafer on a bead portion.

[0002]

2. Description of the Related Art A heavy duty pneumatic radial tire generally has a linear proportional relationship between durability and weight, and conventionally, it has been considered that weight increase for ensuring durability is unavoidable. It was

The heavy-duty pneumatic radial tire has a problem that separation easily occurs from the ply end of the carcass. Conventionally, the shear strain in the cross section due to internal pressure filling and repeated loading dominates the durability of the bead portion. Considered to be a major factor, as shown in FIG. 2, a wire chafer 116 made of steel cord is wound up on the side opposite to the bead core 114 side of the carcass ply 112, and the inclination angle of the steel cord is improved to improve durability. Etc. have been considered.

[0004]

Although it was possible to reduce the shear strain in the cross section due to internal pressure filling and repeated loading by applying the wire chafer winding structure, the durability of the bead portion under severe usage conditions At present, the power is still insufficient. It is possible to increase the number of wire chafers in order to further improve the durability of the bead portion, but there is a problem that the tire weight further increases. Durability is also important, but from the viewpoint of the environment and resources, it is also important to improve fuel efficiency by reducing the weight of tires and reduce the amount of materials used, and it has been desired to achieve both durability and weight reduction.

In view of the above facts, it is an object of the present invention to provide a heavy-duty pneumatic radial tire capable of both improving the durability of the bead portion and reducing the weight of the tire.

[0006]

Various investigations by the inventors,
As a result of examination, factors that govern the durability of the bead part of a pneumatic radial tire for heavy loads are not only internal pressure filling and shear strain in the cross section due to repeated loading, but also the circumference that occurs during start, stop, torque, stepping, and kicking. It was also found that the effect of directional shear strain was large.

The invention as set forth in claim 1 is made in view of such a fact, and a carcass ply composed of a radial array cord whose end portion is locked around a bead core and extends in a toroidal shape, and a bead. In a heavy load pneumatic radial tire provided with a wire chafer disposed on the side opposite to the bead core side of the carcass ply along the carcass ply in a portion, the wire chafer is in a tire radial direction of the bead core. It is characterized by being hollowed out inside.

Further, various investigations and examinations by the inventors have revealed that the carcass ply pulled out from around the bead core is a factor that governs the durability of the bead portion of the heavy duty pneumatic radial tire. did.

The heavy-duty pneumatic radial tire according to claim 2 is made in view of the above-mentioned fact, and in the heavy-load pneumatic radial tire according to claim 1, the radial inside of the bead core is in the tire radial direction. The feature is that the rubber gauge is 2 to 5 mm.

Further, the pneumatic radial tire for heavy load according to claim 3 is the pneumatic radial tire for heavy load according to claim 1 or 2, wherein the cord direction of the wire chafer is on the inner side in the axial direction of the tire. The cord angle of the wire chafer outside the tire axial direction is opposite to the tire radial direction, and the inclination angle of the steel cord of the wire chafer inside the tire with respect to the tire radial direction is the wire outside the tire. The feature is that it is set smaller than the inclination angle of the chafer steel cord with respect to the tire radial direction.

[0011]

In the heavy-duty pneumatic radial tire according to the present invention, since the wire chafer is provided along the carcass ply at the bead portion on the side opposite to the bead core side of the carcass ply, the bead under load The collapse of the part is reduced, and the shear strain in the section acting on the folded end can be reduced. Further, since the wire chafer is hollowed out inside the bead core in the tire radial direction, the weight of the tire is reduced.

In the conventional structure, since the wire chafer is arranged around the bead core, the wire chafer is sandwiched between the bead core and the rim, and movement of the entire wire chafer in the circumferential direction is strongly restricted. Therefore, when a force along the circumferential direction acts on the rubber on the tire side by starting, stopping, torque, stepping in, and kicking out, a large circumferential shear occurs between the folded ply end facing the wire chafer and the surrounding rubber. Distortion has occurred. However, in the present invention, since the wire chafer is hollowed out inside the bead core in the tire radial direction, the entire wire chafer is slightly movable in the tire circumferential direction. Therefore, when a force along the circumferential direction acts on the rubber of the tire side portion due to starting, stopping, torque, stepping, and kicking, the entire wire chafer and the folded ply facing this wire chafer will move in the direction of force. The movement of the ply end is reduced, the shearing strain in the circumferential direction acting between the end of the folded ply and the surrounding rubber is reduced, the ply end separation hardly occurs, and the durability of the bead portion is improved.

In the heavy-duty pneumatic radial tire according to the present invention, the rubber gauge on the inner side in the tire radial direction of the bead core is set to 2 to 5 mm, which is thinner than that of the conventional tire of the same size. The inner side of the tire in the radial direction is increased, the restraint force of the carcass ply is increased, and the carcass ply becomes stronger against pulling out of the folded portion due to internal pressure filling, and the shear strain in the section acting on the folded end can be reduced. The carcass ply ply may be exposed when the rubber gauge on the inner side in the tire radial direction of the bead core is 2 mm or less, and the carcass ply restraining effect is small when the rubber gauge is 5 mm or more.

In the pneumatic radial tire for heavy load according to the third aspect of the invention, the steel cord of the wire chafer on the inner side in the tire axial direction and the steel cord of the wire chafer on the outer side in the tire axial direction intersect with each other to form a bead portion. Increases rigidity.

Further, since the cord angle of the wire chafer outside the tire radial direction with respect to the tire radial direction is set large, the crossing angle formed by the steel cord of the wire chafer outside the tire and the ply cord of the folded portion is large. Therefore, the rigidity of the bead portion can be further enhanced by compensating for the decrease in the rigidity of the bead portion due to the hollowing of the wire chafer.

On the other hand, since the cord angle of the steel cord of the wire chafer inside the tire radial direction with respect to the tire radial direction is set to be small, the steel cord of the wire chafer inside the tire and the ply cord on the carcass body side are formed. The crossing angle becomes small, the flexibility in the tire circumferential direction increases, and the circumferential shear strain can be reduced more effectively.

[0017]

EXAMPLE A heavy duty pneumatic radial tire 10 (tire size 11R22.5) according to an example of the present invention will be described with reference to FIG.

As shown in cross section in FIG. 1, both ends of the carcass ply 12 in the tire width direction (only one is shown in FIG. 1).
Is folded back from the inside of the tire to the outside of the bead core 14 around the bead core 14 having a substantially hexagonal cross section along the tire axial direction.

Body ply 12 of carcass ply 12
In the area surrounded by A and the folded ply 12B, a stiffener 20 for maintaining high rigidity of the bead portion 18 and smoothly transmitting the repeated stress received by the side portion 16 to the bead portion 18 is arranged. . The thickness of the stiffener 20 is gradually reduced outward in the tire radial direction (direction of arrow A).

In the vicinity of the bead core 14, a wire chafer 24 is arranged on the body ply 12A of the carcass ply 12 and the folded ply 12B on the side opposite to the bead core 14 side. The wire chafer 24 is a rubber coating of a plurality of steel cords arranged in parallel, and the steel cords are inclined at a predetermined angle with respect to the tire radial direction.

The wire chafer 24 is hollowed out inside the bead core 14 in the tire radial direction and divided into two inside and outside in the tire axial direction. Start, stop, torque, stepping,
A circumferential shear strain is generated in the bead portion 18 due to kicking or the like, but by dividing into two, flexibility in the tire radial direction is exerted, and the wire chafer 24 facing the folding ply 12B is located outside in the tire radial direction. This is for suppressing the circumferential shear strain generated between the edge and the surrounding rubber.

Here, the cord direction of the wire chafer 24 facing the body ply 12A and the folded back ply 1
It is preferable that the cord direction of the wire chafer 24 facing 2B is inclined in the opposite direction to the tire radial direction so as to intersect. This is because crossing the cords increases the rigidity of the bead portion 18 and reduces the collapse of the bead portion 18 during load rolling.

Further, the angle of inclination of the steel cord of the wire chafer 24 facing the body ply 12A is changed to the wire chafer 2 facing the folding ply 12B.
4 is smaller than the inclination angle of the steel cord, and the inclination angle of the steel cord on the body ply 12A side with respect to the tire radial direction is 30 ° to 60 °.
The inclination angle of the steel cord on the 2B side with respect to the tire radial direction is preferably 70 ° to 80 °. This is because the crossing angle between the steel cord of the wire chafer 24 on the outside of the tire and the cord of the folding ply 12B is increased to enhance the rigidity reduction due to the hollowing of the wire chafer 24 and enhance the effect of suppressing the collapse of the bead portion 18. In addition, the steel cord of the wire chafer 24 inside the tire and the body ply 12
By reducing the intersecting angle with the cord A, the effect of reducing the circumferential shear strain is enhanced.

In this embodiment, the inclination angle of the steel cord on the body ply 12A side with respect to the tire radial direction is 40.
The angle of inclination of the steel cord on the side of the folded back ply 12B with respect to the tire radial direction is 75 °.

The width L _A of the wire chafer 24 facing the body ply 12A along the body ply 12A is 50 mm in this embodiment, and is equal to that of the folded ply 12B of the wire chafer 24 facing the folded ply 12B. Along the width L _B is 25 mm in this embodiment.

The rubber gauge T on the inner side in the tire radial direction of the bead core 14 is preferably smaller than the rubber gauges (generally 6 to 8 mm) of other tires of the same size and set to 2 to 5 mm. This is to increase the compressive force with the rim 26 that acts on the inner side of the bead core 14 in the tire radial direction more than before, whereby the carcass ply 12 on the inner side of the bead core 14 in the tire radial direction becomes the bead core 1.
This is for securing the drag force against pulling out by strongly pressing and restraining between 4 and the bead seat portion of the wheel.
If it is 2 mm or less, the carcass ply 12 may be exposed, and if it is 5 mm or more, the effect of restraining the carcass ply 12 is reduced. In this embodiment, the rubber gauge T inside the bead core 14 in the tire radial direction is set to 4 mm. (Test Example) Pneumatic radial tire for heavy load of the present example and pneumatic radial tire for heavy load of the conventional example (as shown in FIG. 2, the wire chafer 116 is not divided into two, Width L is 9
The angle of inclination of the cord is 0 mm and 60 °. Table 1 below shows the results of examining the tire circumferential strain in the vicinity of the folded end of the carcass ply of FIG.

Regarding the strain in the tire circumferential direction, a lattice pattern serving as a measurement reference was attached to the tire side portion, and the amount of strain was expressed by the deformation amount of the lattice. The result is expressed as an index with the conventional pneumatic radial tire for heavy load being 100, and the smaller the value, the smaller the tire circumferential strain.

Each test tire had a tire size of 1
1R22.5, the internal pressure is 11.7kg / cm ² . Table 1 also shows the results of the bead endurance tests of the heavy duty pneumatic radial tires of the present example and the conventional heavy duty pneumatic radial tires. The results are shown as an index with the conventional heavy-duty pneumatic radial tire set to 100, and the larger the value, the better the durability of the bead portion.

The bead endurance test method was as follows. The vehicle was run on the indoor drum at a speed of 60 km / h and a load of 6270 kg for the first 144 hours, then the load was applied for the next 72 hours, and then continued for 72 hours.
For the time, the step of applying a further load was continued until the bead portion failed.

Further, Table 1 also shows the results of weighing the pneumatic radial tires for heavy load of the present embodiment and the pneumatic radial tires for heavy load of the conventional example. The result is expressed as an index with the conventional pneumatic radial tire for heavy load being 100, and the smaller the value, the lighter the weight.

[0031]

[Table 1]

From the test results shown in Table 1 above, it can be seen that the pneumatic radial tire for heavy load of this embodiment has a small circumferential strain at the bead portion, is excellent in bead portion durability, and achieves weight reduction. it is obvious.

[0033]

Since the pneumatic radial tire for heavy loads of the present invention has the above-mentioned constitution, it has an excellent effect that both the durability of the bead portion and the weight reduction of the tire can be achieved at the same time.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a bead portion of a heavy duty pneumatic radial tire according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a bead portion of a conventional heavy-duty pneumatic radial tire.

[Explanation of symbols]

 10 Pneumatic radial tire for heavy load 12 Carcass ply 14 Bead core 18 Bead part 24 Wire chafer

Claims (3)

[Claims] 1. A carcass ply having radial arrangement cords whose ends are locked around a bead core and extends in a toroidal shape, and a carcass ply arranged at a bead portion along the carcass ply on a side opposite to the bead core side of the carcass ply. A heavy-duty pneumatic radial tire including an installed wire chafer, wherein the wire chafer is hollowed out inside the bead core in the tire radial direction. 2. The heavy-duty pneumatic radial tire according to claim 1, wherein a rubber gauge inside the bead core in the tire radial direction is 2 to 5 mm. 3. The cord direction of the wire chafer inside the tire axial direction and the cord direction of the wire chafer outside the tire axial direction are opposite to the tire radial direction, and the wire inside the tire. The tilt angle of the chafer steel cord with respect to the tire radial direction is set to be smaller than the tilt angle of the steel cord of the wire chafer outside the tire with respect to the tire radial direction. Pneumatic radial tire for heavy loads.