JPH08192608A - Bead structure for pneumatic tire - Google Patents

Abstract

PURPOSE: To strongly restrain the separation of a carcass layer at the bent end thereof. CONSTITUTION: The radial inner end of a stiffener 20 is provided with a hard stiffener section 22, and a boundary surface X is substantially inclined. As a result, rubber of high hardness extends to the vicinity of the boundary of a bead section B and a side wall section D, thereby increasing the bending rigidity of the bead section B. Also, the radial outer end of the stiffener 20 is provided with a soft stiffener section 23, and a boundary surface Y is substantially inclined. Thus, rubber of low hardness comes to be positioned at a deflection transmission route, thereby strongly absorbing deflection under transmission.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bead structure for a pneumatic tire having improved bead durability.

[0002]

2. Description of the Related Art As a conventional bead structure of a pneumatic tire, for example, a carcass layer body portion extending in a substantially radial direction and a radially outer end of the carcass layer surrounding the bead core are provided toward the outer side in the radial direction. The carcass layer folded-back portion extending substantially parallel to the body portion and the radially inner portion are arranged between the body portion and the folded portion, the radially inner end of the carcass layer is in contact with the bead core, and the radially outer portion is the body. A stiffener disposed on the outer side in the axial direction of the section is known.

When a pneumatic tire having such a bead structure is run under a load, the sidewall part directly under the load (on the ground contact side) bends and falls axially outward, and this bending causes the bead part to bend. However, at this time, since the steel cord is embedded in the folded portion of the carcass layer and the rigidity is high so that it can hardly be deformed, the bending causes the rubber surrounding the outer edge in the radial direction of the folded portion. Therefore, a large compression strain occurs. Since such a compressive strain is repeatedly generated just below the load due to running, a crack may occur in the rubber near the outer end in the radial direction of the folded portion and eventually progress to separation.

Therefore, in order to prevent such a folded end separation, the applicant of the present invention has previously proposed a bead structure of a pneumatic tire as described in Kaihei 5-16618. In this structure, a stiffener portion made of rubber having high hardness is provided at an inner end portion in the radial direction of the stiffener to improve the rigidity of the bead portion and suppress the collapse of the sidewall portion immediately below the load as described above. By providing a soft stiffener portion made of rubber having low hardness at the radial outer end portion of the stiffener, the flexure transmitted to the bead portion (radial outer end of the folded portion of the carcass layer) is absorbed. Is.

[0005]

However, even in such a conventional bead structure of a pneumatic tire,
The effect of suppressing the fold-back separation was not sufficient.

It is an object of the present invention to provide a bead structure for a pneumatic tire, which can strongly suppress the folded end separation.

[0007]

The object of the present invention is to provide a body portion of a carcass layer that extends in a substantially radial direction, and a body portion that extends from a radially inner end of the body portion toward a radially outer side while surrounding a bead core. The folded portion of the carcass layer extending in parallel and the radially inner portion are arranged between the main body portion and the folded portion, the radially inner end is in contact with the bead core, and the radially outer portion is the axial direction of the main body portion. A stiffener disposed on the outer side, the stiffener is located at the central portion in the radial direction and is in contact with the radially outer end of the folded portion, and the stiffener portion is located at the inner end portion in the radial direction and has a hardness higher than that of the central stiffener portion. A pneumatic stiffener composed of a hard stiffener part made of high rubber and a soft stiffener part made of rubber having a hardness lower than that of the middle stiffener part located at the outer end in the radial direction. In the bead structure of the ya, the boundary surface between the hard and medium stiffener portions and the boundary surface between the medium and soft stiffener portions both extend substantially radially toward the outer side as they approach the main body portion and extend substantially parallel to each other. Can be achieved.

[0008]

[Function] When a pneumatic tire is run under a load, the sidewall portion directly below the load (ground contact side) bends and falls axially outward, and this deflection causes the sidewall portion and the bead portion to move in the axial direction. A large compressive strain is generated in the rubber that is transmitted to the folded portion through the outer side portion and surrounds the periphery of the radially outer end of the folded portion. However, in the present invention, as described above, the boundary surface between the hard stiffener portion located at the radially inner end portion of the stiffener and the middle stiffener portion located at the central portion in the radial direction has a radius as the body portion of the carcass layer approaches. Since it is largely inclined toward the outer side in the direction, the hard stiffener part made of high hardness rubber extends to the vicinity of the boundary between the bead part and the sidewall part, and the bending rigidity of the bead part, especially the bead part radially outside the rim flange. As a result, the collapse of the sidewall portion immediately below the load is strongly suppressed, and as a result, the compressive strain generated in the rubber surrounding the radially outer end of the folded portion is reduced. Moreover, in the present invention, as described above, the boundary surface between the soft stiffener portion located at the radially outer end portion of the stiffener and the middle stiffener portion is largely inclined toward the outer side in the radial direction as it approaches the main body portion of the carcass layer. As a result, the soft stiffener part made of low hardness rubber extends to the vicinity of the folded part in a state of being biased outward in the axial direction of the stiffener, but the position of such soft stiffener part is large in the flexure transmission path. Since the portions overlap each other, the flexure is strongly absorbed by the soft stiffener portion during the transmission, and the compressive strain generated in the rubber surrounding the radially outer end of the folded portion is reduced. Further, in the present invention, since the boundary surface between the hard and medium stiffener portions and the boundary surface between the medium and soft stiffener portions described above are extended substantially in parallel,
Both hard and soft stiffeners can be maximally extended radially outward and inward, respectively,
As described above, the compression strain is sufficiently reduced, and the folding end separation can be strongly suppressed.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 and 2, reference numeral 11 denotes a pneumatic radial tire, which has a pair of bead cores 12 and a toroidal carcass layer 13, and at least one carcass layer 13 is used here. Carcass ply
It consists of 14. This carcass layer 13 is folded back while surrounding the bead core 12 from a main body portion 15 that extends toward the outer side in the radial direction on the inner side in the axial direction of both bead cores 12, while surrounding the bead core 12 from the inner end in the radial direction of the main body portion 15. The bent portion 16 is arranged on the outer side in the axial direction and extends outward in the radial direction so as to extend substantially parallel to the main body portion 15. Inside the carcass ply 14, a large number of cords made of steel, aramid fiber or the like and extending orthogonally to the tire equatorial plane S (in the radial direction) are embedded.

Reference numeral 20 denotes a pair of stiffeners. These stiffeners 20 are arranged such that the radially inner part is in close contact with the body part 15 and the folded part 16, and the radially outer part is the body part. It is arranged on the outer side in the axial direction of 15 so as to be in close contact therewith, and extends to the vicinity of the maximum tire width.
Further, these stiffeners 20 have their radial inner ends in contact with the bead core 12, and have a middle stiffener portion 21 located in the radial center portion, a hard stiffener portion 22 located in the radial inner end portion, and a radial outer end portion. And a soft stiffener portion 23 located at. Here, the middle stiffener portion 21 is made of rubber having a Shore A hardness of 58 to 68 degrees (61 degrees in this embodiment), and the volume ratio to the entire stiffener 20 is in the range of 20% to 70% (in this embodiment, 50
%). This is because if the volume ratio is less than 20%, the rigidity of the bead portion B is lowered and the collapse under the load becomes too large, while if it exceeds 70%, the volume ratio of the soft stiffener portion 23 is small. This is because it becomes impossible to sufficiently suppress the folding edge separation. The hard stiffener portion 22 is made of rubber having a Shore A hardness of 75 degrees or higher (83 degrees in this embodiment), which is higher than the middle stiffener portion 21, and the volume ratio to the entire stiffener 20 is 20% to 70%. (30% in this embodiment). The reason is the same as that of the middle stiffener section 21 described above. And the middle stiffener part
The boundary surface X that separates the hard stiffener portion 22 from the radial outer end 26 of the folding portion 16 is positioned to the inner side to some extent in the radial direction, that is, near the bead core 12, and approaches the main body portion 15. Accordingly, it is largely inclined with respect to the tire axis so as to extend radially outward. As a result, the axially inner end of the hard stiffener portion 22 extends to the vicinity of the boundary between the bead portion B and the sidewall portion D. Further, the soft stiffener portion 23 is the middle stiffener portion 21.
It is made of rubber having a Shore A hardness of 55 degrees or less (53 degrees in this embodiment), which is a lower hardness, and the volume ratio to the entire stiffener 20 is in the range of 10% to 60% (in this embodiment,
20%). This is because when the volume ratio is less than 10%, the volume ratio of the soft stiffener portion 23 becomes too small to sufficiently suppress the folding end separation, while when it exceeds 60%, the bead portion is too large. This is because the rigidity of B is lowered and the collapse just under the load becomes too large. The boundary surface Y that divides the middle stiffener portion 21 and the soft stiffener portion 23 has an axially outer end located slightly radially outward of the radially outer end 26 of the folded portion 16 and approaches the main body portion 15. Accordingly, it is largely inclined with respect to the tire axis so as to extend radially outward. As a result, the middle stiffener portion 21 contacts the radially outer end 26 of the folded portion 16. Here, the above-mentioned boundary surface X
And the boundary surface Y are substantially parallel to each other, and as a result, the middle stiffener portion 21 sandwiched between the boundary surfaces X and Y has a substantially parallelogram-shaped cross section. A chafer 27 having a textile cord embedded therein is arranged outside the carcass layer 13 in the bead portion B.

A belt layer 29 is provided on the outer side of the carcass layer 13 in the radial direction, and the belt layer 29 is formed by laminating at least two belt plies 30 each having a non-stretchable cord embedded therein. . The cords respectively embedded in the belt plies 30 are tire equatorial planes S.
The belt plies 30 intersect with each other at a predetermined angle, and the belt plies 30 intersect and incline in mutually opposite directions. A tread rubber 31 is provided on the outer side in the radial direction of the belt layer 29.
Are arranged, and a plurality of main grooves 32 extending in the circumferential direction and lateral grooves (not shown) intersecting with the main grooves 32 are formed on the outer surface of the tread rubber 31.

Next, when such a tire 11 is run while applying a load, the sidewall portion D immediately below the load (ground contact side) bends and falls axially outward, and this deflection causes the sidewall portion D and the bead to fall. The rubber is transmitted to the folded-back portion 16 through the axially outer side portion of the portion B and causes a large compressive strain in the rubber surrounding the radially outer end 26 of the folded-back portion 16.
However, in this embodiment, as described above, since the boundary surface X between the hard stiffener portion 22 and the middle stiffener portion 21 is largely inclined, the hard stiffener portion 22 made of high hardness rubber has the bead portion B and the sidewall portion. It extends to the vicinity of the boundary with D to increase the bending rigidity of the bead portion B, particularly the bead portion B radially outside the rim flange, whereby the collapse of the sidewall portion D immediately below the load is strongly suppressed, and as a result, In addition, the compressive strain generated in the rubber surrounding the radially outer end 26 of the folded portion 16 is reduced.
Moreover, in this embodiment, since the boundary surface Y between the soft stiffener portion 23 and the middle stiffener portion 21 is largely inclined as described above, the soft stiffener portion 23 made of low hardness rubber is located outside the stiffener 20 in the axial direction. Folded part 16 in a biased state
Came to extend to the vicinity of. As a result, the arrangement position of the soft stiffener portion 23 and the flexure transmission path are overlapped with each other at most, whereby the flexure is strongly absorbed by the soft stiffener portion 23 during the transmission,
This reduces the compressive strain generated in the rubber surrounding the radially outer end 26 of the folded portion 16. Furthermore, in this embodiment, since the boundary surface X between the hard and middle stiffener portions 22 and 21 and the boundary surface Y between the middle and soft stiffener portions 21 and 23 described above are extended substantially in parallel, Stiffener section 22,
Both of 23 can be extended to the outside and the inside in the radial direction to the maximum extent, whereby the compression strain can be sufficiently reduced as described above, and the separation at the folded end can be strongly suppressed. Of.

Next, a test example will be described. In this test, a comparative tire in which the boundary surface X of the stiffener is slightly inclined toward the outer side in the radial direction as it approaches the main body portion, while the boundary surface Y is slightly inclined toward the inner side in the radial direction as it approaches the main body portion. Then, a test tire was prepared in which both the stiffener boundary surfaces X and Y were greatly inclined toward the outer side in the radial direction as they approached the main body as shown in FIGS. Here, the size of each tire is 11 /
70R22.5, and the Shore A hardness and area ratio of the rubber constituting the medium, hard and soft stiffener parts are as described in the above-mentioned examples. Next, each of these tires was filled with JATMA standard internal pressure (8 kg / cm ² ) and a load of 250% of the standard standard load was applied on the drum at a speed of 60 km per hour due to separation due to separation at the bead. It was run until it occurred. As a result, if the mileage of the comparative tire is 100,
It was 120 for the test tire, and the durability of the bead portion was definitely improved.

[0014]

As described above, according to the present invention, the folding end separation can be strongly suppressed.

[Brief description of drawings]

FIG. 1 is a meridional sectional view of a pneumatic tire showing an embodiment of the present invention.

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

[Explanation of symbols]

 11 ... Tire 12 ... Bead core 13 ... Carcass layer 15 ... Body part 16 ... Folding part 20 ... Stiffener 21 ... Medium stiffener part 22 ... Hard stiffener part 23 ... Soft stiffener part X ... Boundary surface Y ... Boundary surface

Claims (1)

[Claims] 1. A body portion of a carcass layer extending in a substantially radial direction, and a folded portion of a carcass layer extending outward in the radial direction while enclosing a bead core from a radially inner end of the body portion, and a folded portion of the carcass layer. A radially inner portion is arranged between the main body portion and the folded portion, the radial inner end is in contact with the bead core, and a radially outer portion comprises a stiffener arranged axially outside the main body portion, A middle stiffener portion located at the center of the stiffener in the radial direction and in contact with the radially outer end of the folded portion, a hard stiffener portion made of rubber having a hardness higher than that of the middle stiffener portion at the inner end of the radial direction, and a radius. In the bead structure of the pneumatic tire, which is composed of a soft stiffener part made of rubber having a hardness lower than that of the middle stiffener part at the outer end in the direction, Air characterized in that the boundary surface between the middle stiffener portions and the boundary surface between the middle and the soft stiffener portions are both largely inclined toward the outside in the radial direction as they approach the main body portion and extend substantially in parallel. The bead structure of the filled tire.