JPH082219A - Pneumatic radial tire for heavy load excellent in durability at bead part - Google Patents

Abstract

PURPOSE:To provide a plan pertaining to the structure of a bead part to check any separation to be produced in an interval between a carcass body side and a stiffener. CONSTITUTION:This is a pneumatic radial tire that structures a carcass, as a skeleton, having a carcass body 3 consisting of a radial arranged ply of a rubber coated cord toroidally lying astride an interval between a pair of bead cores 1 and 1 and a ply turnover part 4 extending as folding from the inside to outside of a tire respectively around these bead cores 1 and a stiffener 5 installed on these bead cores 1 from the carcass body 3. Accordingly, in at least a partial area of the carcass body 3 adjacent to the stiffener 5, coated rubber 3a of the carcass body is thickened to some extent as compared with the rest area.

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 used for buses, trucks and the like, and particularly to improve the durability of a bead portion.

[0002]

2. Description of the Related Art In pneumatic radial tires for heavy loads,
In order to receive a heavy load, it is indispensable that the bead portion be strong. Therefore, a stiffener made of rubber having high modulus and hardness is arranged on the bead core to secure the rigidity of the bead portion.

[0003]

However, when a tire in which rubber having a high modulus and hardness is arranged on a bead core is used under a condition of high internal pressure and heavy load, the bead portion is formed on the bead during rolling of the tire. When the displacement occurs, a gap occurs between the stiffener and the cord of the carcass, which causes a large strain in the rubber cover of the carcass, and the stiffener and the carcass body side extending from the crown portion of the tire to the bead core. In the meantime, separation occurs,
The problem is that it impairs the durability of the tire.
Therefore, an object of the present invention is to propose a bead structure for suppressing the separation between the carcass body side and the stiffener.

[0004]

According to the present invention, there is provided a carcass body composed of a radial array ply of rubber-coated cords straddling in a toroidal shape between a pair of bead cores, a bead core from the carcass body, and a bead core on the bead core. A pneumatic radial tire with a carcass having a folded portion of the ply that rewinds from the inside of the tire to the outside around the stiffener installed in, and is at least one of the carcass bodies adjacent to the stiffener. A heavy load pneumatic radial tire excellent in durability of a bead portion, characterized in that a rubber portion of the carcass body is thicker in a region of a portion than in a remaining region.

The thickened coating rubber of the carcass body has a thickness 0.5 to 1.7 times the cord diameter of the carcass, and the region where the thickness of the coating rubber of the carcass body is increased is
It is particularly advantageous to center the position corresponding to the upper end of the rim flange when the tire is mounted on the specified rim and filled with the specified internal pressure. Further, as the carcass, an organic fiber cord covered with rubber can be used. The present invention is particularly effective for tires used at an internal pressure of 3.5 kgf / cm ² or more.

Now, FIG. 1 shows a cross section of a heavy duty pneumatic radial tire according to the present invention for the left half. In the drawing, 1 is a bead core whose only one side is shown, 2 is a carcass consisting of one ply, and from a carcass body 3 extending to the bead core along the inner wall of the tire and a carcass folding part 4 in series with this carcass body 3. Become.
Further, 5 is a stiffener mounted on the bead core 1, 6 is a belt layer, 7 is a tread portion, 8 is a specified rim, and 9 is a flange thereof.

The carcass body 3 is formed by arranging radially arranged plies of organic fiber cords or steel cords in a toroidal shape across a pair of bead cores 1, and is wound around the bead cores 1 from inside to outside of the tire. Further, it has a folded portion 4 extending to the sidewall portion.

The belt layer 6 is composed of a plurality of layers of rubber-coated steel cords laminated around the outer periphery of the crown portion of the carcass body 3, and is embedded in tread rubber to serve to reinforce the tread portion 7. In accordance with the conventions for tires of this type that are conventional in.

In the present invention, in at least a part of the carcass body 3 adjacent to the stiffener 5, in all the adjacent regions R in the illustrated example, the covering rubber 3a of the carcass body is made thicker than the remaining region, It is characterized in that the shear strain generated between the cover rubber of the carcass body 3 and the stiffener 5 is relaxed.

[0010]

In the tire of this type, the displacement of the tire bead portion, which occurs under actual use conditions, occurs in the area corresponding to the vicinity of the upper portion of the flange of the specified rim. At this time, if the stiffener has a high modulus and hardness, shear strain occurs in the rubber covering the carcass cord that exists between this stiffener and the carcass cord with a larger modulus, resulting in the boundary between the carcass body and the stiffener. Separation may occur on the surface.

Therefore, in the present invention, in at least a partial region of the carcass body adjacent to the stiffener,
The covering rubber of the carcass body is made thicker than the remaining region, and the thickened rubber layer alleviates the shear strain generated at the boundary surface between the carcass body and the stiffener and suppresses the separation here.

Here, it is desirable that the thickened rubber cover of the carcass body has a thickness 0.5 to 1.7 times the cord diameter of the carcass. This is because when the thickness of the coated rubber is less than 0.5 times the carcass cord diameter, the shear strain relaxation effect is poor, while when it exceeds 1.7 times, the thickness difference with the coated rubber in other areas becomes large, and Product defects such as the formation of an air layer at the boundary between the two regions will occur.

Further, the region of the carcass body where the thickness of the covering rubber is increased is centered around the position corresponding to the upper end of the rim flange in the state where the tire is mounted on the specified rim and filled with the specified internal pressure, and more preferably, this position is set. It is particularly advantageous to provide the stiffener in the center in the range of 40 to 100% of the contact surface with the carcass body. That is, when the thickened region of the coated rubber is less than 40% of the contact surface of the stiffener with the carcass body, the effect of relaxing the shear strain generated at the boundary between the two becomes small.

[0014]

EXAMPLES Tire size 195 according to the structure shown in FIG.
R14LT 8PR pneumatic radial tires for light trucks
Various prototypes were made under the specifications shown in Table 1. In addition, as a comparison, a tire having a similar structure and in which the carcass-covered rubber was not partially thickened was also prototyped. In all of the tested tires, the stiffener 5 has a modulus at 50% elongation of 80.
kgf / cm ² and Shore hardness: 70 ° of rubber is used, and carcass 2 has two plies of radial arrangement structure composed of 0.7 mm diameter polyester cord of 1500d / 2 structure (number of punching: 50 pieces / 5 cm), and the belt layer 7 is a ply made of steel cord with a structure of 1 × 3 + 6 (24 hammers / 5 cm)
Was used as a crossing layer.

The tires thus obtained were filled with an internal pressure of 6.0 kgf / cm ² and then mounted on a drum durability tester, respectively, at a speed of 60 km / h under a load of 1500 kg.
After running 000 km, each tire was disassembled and the total length of the separation generated at the boundary between the carcass body and the stiffener was measured. This measurement result is also shown in Table 1 as an index when the result of the comparative tire is 100.

[0016]

[Table 1]

[0017]

According to the present invention, in a tire in which a stiffener made of hard rubber is placed on a bead core to reinforce the bead portion, it is possible to suppress the separation that tends to occur at the boundary between the carcass and the stiffener, and thus this type of tire It is possible to improve the durability of the bead part.

[Brief description of drawings]

FIG. 1 is a schematic view showing a tire structure according to the present invention.

FIG. 2 is an enlarged view of a bead portion.

[Explanation of symbols]

 1 Bead core 2 Carcass 3 Carcass body 3a Covering rubber 4 Folding part 5 Stiffener 6 Belt layer 7 Tread part 8 Regular rim 9 Flange

Claims (4)

[Claims] 1. A carcass body composed of a radial array ply of rubber-coated cords straddling in a toroidal shape across a pair of bead cores, and each bead core from the carcass body and around a stiffener installed on the bead core. A skeleton of a carcass having a folded portion of the ply that extends from the inside of the tire to the outside and is a pneumatic radial tire, in at least a part of the region of the carcass body adjacent to the stiffener,
A heavy-duty pneumatic radial tire having excellent bead portion durability, characterized in that the coating rubber of the carcass body is made thicker than the remaining region. 2. The heavy-duty pneumatic radial tire according to claim 1, wherein the thickened rubber cover of the carcass body has a thickness of 0.5 to 1.7 times the cord diameter of the carcass. 3. The region of the carcass body in which the thickness of the covering rubber is increased is provided around a position corresponding to the upper end of the rim flange in a state where the tire is mounted on a specified rim and the specified internal pressure is filled. Pneumatic radial tires for heavy loads. 4. The heavy-duty pneumatic radial tire according to claim 1, wherein the carcass is formed by coating an organic fiber cord with rubber.