JPH0659766B2 - Radial tires for heavy loads - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heavy load radial tire capable of improving the durability of a bead portion.

[Conventional technology]

Regarding heavy-duty radial tires used for trucks, buses, etc. defined by JIS D4202, the operation under severe conditions for tires of high speed and high load is increasing with the development of a highway network in recent years.

Due to this increase in load, the amount of flexure of the tire increases, and the number of cycles that undergo flexure increases due to the increase in speed, so that the internal temperature rises and the bead portion is easily damaged.

As shown in FIG. 1, the bead portion of the conventional tire is usually for the purpose of reinforcing the vicinity of the end of the folded portion of the carcass ply 2 folded back to the bead core 3 by low turn-up,
The reinforcing layer 4 made of a metal cord is wound toward the inside of the tire along the folded-back portion with the terminal 4a positioned higher than the terminal 2a of the folded-back portion of the carcass ply 2. Also, as shown in FIG. 2, the bead apex is sometimes composed of a stiffener 11 made of hard rubber and a buffer 12 made of soft rubber.

On the other hand, since the cords of the carcass ply are arranged in the radial direction, the sidewalls are flexible, and the carcass ply is largely bent outward in the axial direction of the tire due to load rolling of the tire, especially at the upper part of the flange, and the carcass ply has a convex shape. Transformed,
This deformation amount is much larger than that of the bias tire.

As a result, the bead portion connected to the sidewall is also subjected to large repeated strain.

Moreover, in addition to internal heat generation due to repeated strain, the temperature generated in the brake drum of the car is transmitted from the rim flange to the tire, so the temperature of the bead is 120 to 170 ° C.
It is also known to reach.

As described above, the bead portion is exposed to thermal / dynamic fatigue. Moreover, the adhesion between rubber and cord, which affects the tire durability, and the adhesion between rubber and rubber depends on these thermal and dynamic fatigue factors. Especially, when the internal temperature of the tire exceeds a certain temperature, the adhesion becomes sharp. It is known to decline.

Therefore, it is important to suppress the temperature generated inside the tire to a low level in order to improve the durability of the tire as well as the technology that secures the adhesion between the rubber and the cord and between the rubber and the rubber that have little temperature dependence. .

On the other hand, as one of the conventional proposals for improving the durability of the bead portion, there is Japanese Patent Publication No. 52-11148 of the present applicant. As shown in FIG. 2, this is the end 4a of the reinforcing layer 4 of the metal cord and the folded portion 2'of the carcass ply 2.
In order to reduce the concentration of strain and stress at the terminal 2a of
A fiber reinforced layer with rubber coating on the organic fiber cord,
It is intended to be arranged on the outer side of the reinforcing layer in the axial direction of the tire to reduce the difference in rigidity in the radial direction, the circumferential direction and the lateral direction, and suppress the local movement of the bead portion.

[Problems to be Solved by the Invention]

However, in the above-mentioned proposal, although the durability of the tire is improved to some extent by reinforcing the bead portion with the fiber cord, the occurrence behavior of the strain in the bead portion when high internal pressure is filled in the tire, As shown in FIG. 3, as the main body portion 2 of the carcass ply is pulled upward in the radial direction of the tire, the terminal 2a of the folded portion is pulled downward in the radial direction, and the adjacent metal cords are reinforced in association with this movement. The layer 4 and the fiber reinforced layer 6 are also pulled downward, and similarly, the bead core 3 also rotates in the direction of the arrow, and a radial shear strain is generated between these layers. Then, the so-called "blowing through" phenomenon in which the carcass ply 2 slips out of the bead core 3 that occurs when the adhesion force between these layers cannot withstand this shearing force,
It was seen to happen.

This is because the proposed tire has two or more fiber-reinforced layers laminated on the outside of the folded portion of the carcass ply, as described above, in addition to the reinforcement layer, so that the bead portion has a large thickness. It was assumed that the internal temperature was likely to rise and that the cord end of the organic fiber also became the core of crack generation due to stress concentration.

An object of the present invention is to provide a heavy load radial tire capable of effectively eliminating such drawbacks of the prior art and improving the durability of the bead portion.

[Means for Solving the Problems]

The present invention is a heavy-load radial tire in which a carcass ply made of metal cords in a radial arrangement is folded around a bead core from the inner side to the outer side in the tire axial direction, and the bead portion of the tire is reinforced by a reinforcing layer using a metal cord. The reinforcing layer extends from the outer side in the tire axial direction of the folded portion of the carcass ply to the inner side in the tire axial direction through the bead base.
A reinforcing layer and a second reinforcing layer extending radially upward and downward along the inner side of the main body of the carcass ply in the axial direction of the tire, and the cord obliquely intersects the cord of the carcass ply. Vertical height h ₂ from the bead base of the carcass ply is made slightly lower than the vertical height h ₁ of the end of the carcass ply, and the vertical height h ₃ of the upper end of the second reinforcing layer from the bead base. Is greater than the vertical height h ₄ of the end of the inner portion where the first reinforcing layer is wound inward and substantially equal to the vertical height h _{1 of the} folded portion, and moreover, the vertical height of the lower end of the second reinforcing layer is the h ₅ is, as well as smaller than the vertical height h ₄ of the terminal of the inner portion of the first reinforcing layer, the lower portion of the second reinforcing layer, the main body and the first reinforcing layer of carcass ply Between the inner part of the carcass and Vertical height h ₁ of the folded portion of the terminal, as well as 0.3 to 0.5 times the vertical height h ₆ of the tire maximum width position, yet a body portion of said carcass ply, between the folded portion, A heavy-duty radial tire having a bead apex made of a soft rubber having a JIS hardness of 45 ° to 65 °.

[Action]

A carcass ply made of a metal cord, a first reinforcing layer made of a metal cord wound along the folded portion of the carcass and wound inward in the tire axial direction, and a second reinforcing layer made of a metal cord extending inside the main body of the carcass. And the height of each terminal is specified. As a result, the layer made of, for example, an organic fiber cord, which is arranged outside the folded portion, can be removed or reduced, the bead portion can be thinned, and the internal temperature rise in the bead portion can be suppressed.

In addition, the lower part of the second reinforcing layer is sandwiched between the inner part of the first reinforcing layer wound inward in the tire axial direction and the carcass body, and as a result of joining the second reinforcing layer, The lower part is firmly held, and the dynamic shear strain generated at each load rolling of the tire is effectively suppressed in cooperation with the first reinforcing layer,
It also reduces the tensile stress and contributes to the suppression of the "blowing through" phenomenon. When the reinforcing layer is, for example, one layer, it cannot follow the deformation of the carcass during traveling, and peeling easily occurs at the upper end 6a of the second reinforcing layer. Therefore, by forming the reinforcing layer into two layers, Reduces peeling.

A bead apex made of soft rubber is arranged to disperse strain caused by deformation of the bead portion and prevent concentration of stress.

〔Example〕

 An embodiment of the embodiment will be described below with reference to the drawings.

Heavy-duty radial tire of the present invention (hereinafter referred to as tire)
Is a carcass ply consisting of a metal cord of a radial or semi-radial so-called radial arrangement that extends at an angle of approximately 90 degrees with respect to the circumferential center plane of the tire. , Is reinforced by a reinforcing layer using a metal cord.

Folded portion 2 'of the carcass ply, the vertical height h ₁ of the terminal 2a, to the vertical height h ₆ from the bead base in the tire maximum width position when filled with prescribed air pressure in the tire, 0.3 The range is about 0.5 times. 0.3
If it is equal to or less than twice, the rigidity of the bead portion is lowered and the rim-chiefing phenomenon is likely to occur. On the other hand, since the ply turn-back portion 2 ′ is short, the ply blow-through phenomenon is likely to occur due to the insufficient attachment area. On the other hand, if it is 0.5 times or more, the terminal 2a is arranged in the side wall portion where the bending is severe.
It may cause cracks.

In this way, by setting the vertical height h ₁ of the folded-back portion 2 ′ of the carcass ply within the range of (0.3 to 0.5) h ₆ , it is possible to reduce “distortion of the end portion” and prevent “blown-out” of the ply. It has been confirmed from an experiment that it is effective.

The reinforcing layer is disposed on the tire axial direction inner side of the carcass ply main body portion 2 and the first reinforcing layer 4 which is wound from the tire axial direction outer side of the folded-back portion 2'to the tire axial direction inner side through the bead base. The second reinforcing layer 6 is included.

In this way, the first reinforcing layer 4 is continuous with the inner portion 4 ′ wound along the main body portion 2 of the tire by being wound inward through the bead base and on the outer portion along the outer side of the folded portion 2 ′ of the carcass ply. Will be formed.

Further, the vertical height h of the terminal 4a on the outer side of the first reinforcing layer 4
₂ , that is, the radial distance of the end 4a from the bead base is in the range of 0.7 to 0.9 times the vertical height h ₁ of the end 2a of the folded portion 2'of the carcass ply, whereby the first reinforcing layer is formed. The end 4a of the outer portion of 4 is located below the end 2a of the folded portion 2 '.

In the conventional tire, as shown in FIG. 2, the vertical height of the end 4a of the reinforcing layer 4 is set to be larger than the vertical height of the end 2a of the folded portion 2'of the carcass ply.
As a starting point of structural damage in the bead part, it was found that this part occurred most often.

According to the research conducted by the inventor of the present invention, the reason for this is that when the tire rolls under load, the end 4a of the reinforcing layer has a high rigidity as if it is a "protruding rod" because of the transmission of the flexible bending from the sidewall portion to the bead portion. It was found that this peripheral rubber is destroyed because it makes a resistance movement like "and it is repeated every time the tire touches the ground. Moreover, the speed at which the rubber breaks becomes faster as the height of the end 4a of the reinforcing layer 4 increases.

Therefore, in the tire of the present invention, the vertical height h ₂ of the terminal 4a of the first reinforcing layer 4 is smaller than the vertical height h ₁ of the terminal 2a of the folded portion 2'of the carcass ply as shown in FIG. The above range is set. If it is 0.7 times or less, the rigidity of the bead portion is excessively lowered, so that the case is damaged and the rim chafing is promoted when used under a heavy load. On the contrary, in the range of more than 0.9 and close to 1.0 times, the terminal 2a of the folded portion 2'of the carcass ply and both terminals 4a of the first reinforcing layer 4 overlap,
The step of rigidity increases and damage occurs early.

In addition, the end 4 of the inner portion 4'where the first reinforcing layer 4 is wound inside
The vertical height h ₄ of b is smaller than the vertical height h _{2 of the} outer portion.

Further, the lower portion of the second reinforcing layer 6 is sandwiched between the inner portion 4'of the first reinforcing layer 4 and the main body portion 2 of the carcass ply.

Further, the vertical height h ₃ of the upper end 6a of the second reinforcing layer 6 is to prevent stress concentration at the end 2a of the carcass ply turnback portion 2'and to reinforce the bead portion as the height h ₃ is larger. However, above 1.3 times the vertical height h ₁ of the folded portion 2 ′, the effect becomes constant, the tire weight increases, and the tire cost increases. On the other hand, when it is 0.7 times or less, the effect of preventing stress concentration decreases.

Furthermore, the second reinforcing layer 6 also has an effect of combining stress concentration at the end 4b of the inner portion 4'of the first reinforcing layer 4 and separation at the boundary surface between the inner portion 4'and the main body portion 2 of the carcass ply. To help prevent it. Therefore, the vertical height h ₅ of the lower end 6b of the second reinforcing layer 6 is smaller than the height h ₄ of the end of the inner portion 4'of the first reinforcing layer 4, and the intermediate height position of the bead core 3 is It is in the vicinity. As a result, the lower part of the second reinforcing layer 6 and the inner part 4 ′ of the first reinforcing layer 4 and the carcass ply body 2 are
, It is sandwiched over a certain width.

In this way, the inner portion 4 ′ of the first reinforcing layer 4 sandwiches the lower portion of the second reinforcing layer 6 with the main body portion of the carcass ply. Therefore, the vertical height h ₄ of the terminal 4b of the inner portion 4'of the first reinforcing layer 4 is set to a height for maintaining the overlap zone () with the second reinforcing layer 6 at an appropriate width to disperse the strain. Is desirable.

Therefore, the vertical height h ₄ of the terminal 4b of the first inner portion 4 of the reinforcing layer 4 'is in the range of 0.5 to 0.8 times the vertical height h ₃ of the upper terminal 6b of the second reinforcing layer 6 And

If it is 0.5 times or less, the width of the overlap zone () becomes narrow, resulting in insufficient strain dispersion and lateral rigidity. On the other hand, if it is 0.8 times or more, the upper end 6a of the second reinforcing layer 6 and the end 4b of the inner portion 4'of the first reinforcing layer 4 of the metal cord are close to each other, which is not preferable.

The vertical height h ₅ of the lower end 6b of the second reinforcing layer 6 is 10
The lower end 6b is positioned inside the stable bead core having a minimum movement and a small dynamic strain as described above to reduce the concentration of strain (stress) on the cord end.

Further, the arrangement angle of the cords of the second reinforcing layer 6 is in the range of 10 to 50 degrees with respect to the cord of the body portion 2 of the carcass ply at the position of the vertical height h ₄ of the lower end thereof, particularly preferably 20 to It is set so that it crosses at an angle of 40 degrees.

Further, the cords of the second reinforcing layer 6 intersect each other at an intermediate value of the angles formed by the carcass ply and the first reinforcing layer, so that the cords are arranged in a triangle arrangement to enhance the reinforcing effect of the bead portion, It was confirmed by actual vehicle tests that the deformation could be reduced. Therefore, the cord arrangement angle of the first reinforcing layer 4 is 4 as shown in the right column of Table 1.
It is set to 0 to 80 °.

Further, since the cords of the second reinforcing layer 6 obliquely intersect with the cords of the carcass ply as described above, the gap between the cords due to the deformation of the carcass ply, that is, the increase of the cord path is reduced by
The cord of the reinforcing layer 6 is suppressed, and the deformation of the bead portion can be suppressed.

Furthermore, the tire has a triangular cross-section that extends from the top of the bead core 3 to the bottom as it is sandwiched between the carcass ply body 2 and the folded-back portion 2'and gradually decreases in thickness in the radial direction of the tire. The annular apex rubber b is arranged.

As this rubber b, JIS hardness is 45 to 65 degrees and 10
It has been found that the durability of the bead portion can be improved by using a single soft rubber composition having a 0% modulus of 10 to 45 kg / cm ³ .

In the case of a conventional tire, as a bead apex, as shown in FIGS. 1 and 2, a composite apex consisting of two layers of a stiffener 11 having a high hardness and a buffer 12 having a hardness lower than that, a single layer Has a hardness of 70 to 8
By using a rubber composition having a high hardness of 5 degrees, the lateral rigidity of the upper portion of the bead core is increased and the deformation of the bead portion is suppressed,
It prevented damage such as rim chafing.

However, as in the present invention, the inner side in the tire axial direction of the carcass ply body portion 2 is provided with the first reinforcing layer 4 and the second reinforcing layer 6
By reinforcing at least the cord of the second reinforcing layer 6 and the cord of the carcass ply at an angle, the deformation of the bead portion is greatly suppressed, and the hard rubber having a high internal heat generation as in the prior art is used. It does not need to be used for, but effectively absorbs not only the deformation (strain) in the cross-sectional direction that acts on the bead portion but also the deformation (strain) that occurs in the circumferential direction, making it easy to restore the original state immediately. Soft rubber with low heat generation,
Moreover, it is possible to use a single layer of rubber as the bead apex.

It has been confirmed that the tire of the present invention can be easily mounted on a rim for a tubeless tire having a bead base with a 15 ° taper by using a single layer of soft rubber for the bead apex.

〔Example〕

Tire size 12R22.5 14PR. And 10.0
0R20 14PR. In the tire of the above, the breaker structure etc. are the same as the conventional one, and a test tire is prepared with the reinforcing structure of the bead portion as the specifications shown in Table 1, and the bead durability test is conducted, and the conventional reinforcing structure (Japanese Patent Publication No. Sho 52-111481) is used. No.) and each of the above tire sizes. As a result of the test, as shown in FIGS. 5 (a) and 5 (b), it was confirmed that the tire of the present invention has excellent durability and bead portion reinforcing property. In addition, 12R2 mounted on a 15 ° taper rim
It was also demonstrated in these tests that the 2.5 tire was superior to the prior art tire in both ease of mounting on the rim and matching with the rim.

[Effects of the Invention] As described above, in the tire of the present invention, the first reinforcing layer made of the metal cord is provided along the folded portion of the carcass ply, and the second reinforcing layer made of the metal cord is provided along the main body of the carcass. Therefore, the thickness of the bead portion can be reduced and the temperature rise can be suppressed. Further, since the lower portion of the second reinforcing layer is arranged so as to be sandwiched between the main body portion and the inner portion of the first reinforcing layer which is wound inside the tire, the movement of the reinforcing layer becomes larger than that in a series. To reduce peeling of the upper end 6a of the second reinforcing layer.

Further, the decrease in the temperature rise described above can suppress the deterioration of adhesion and reduce the "blowing through" phenomenon, thereby improving the bead durability and increasing the number of tire retreading.

Also, the cord of the second reinforcing layer is arranged so as to cross the cord of the carcass ply so as to prevent expansion of the cord path and reduce bead deformation. In addition, it is transmitted from the carcass ply to the rim flange via the bead core. The force generated for each ground rolling is transmitted while being dispersed in a wide circumferential direction, so that the durability of the bead portion is further improved.

Moreover, as an apex, JIS hardness is 45 to 65
Since a single layer made of soft rubber with a 100% modulus of 10 to 45 kg / cm ³ is adopted, stress is dispersed compared to the case where hard rubber is used, and partial increase in internal temperature of the bead part is suppressed. Therefore, the durability of the bead portion can be further improved.

[Brief description of drawings]

FIG. 1 is a sectional view of a bead portion of a general radial structure tire,
FIG. 2 is a sectional view of a bead portion of a conventional tire having a reinforced bead portion, FIG. 3 is a diagram showing a direction of a force acting when a tire having a structure shown in FIG. 2 is filled with a high internal pressure, and FIG. One side sectional view of a tire showing an embodiment of the present invention, FIG. 5 is a graph showing the results of a bead durability test by a drum of a tire having a conventional reinforcing structure and a tire having a reinforcing structure according to the present invention. ) The figure shows a tire size of 10.00R20
14PR. (b) The figure shows tire size 12R22.5 14
PR. Shows the durability of. 2 ... Main part of carcass ply, 2 '... folded part, 3 ... bead core, 4 ... first reinforcing layer, 4' ... inner part, 6 ... second reinforcing layer.

Claims (1)

[Claims] 1. A heavy-load radial tire in which a carcass ply made of radial-arranged metal cords is folded back around the bead core from the inner side in the tire axial direction to the outer side, and a bead portion of the tire is reinforced by a reinforcing layer using a metal cord. And the reinforcing layer extends from the outer side in the tire axial direction of the folded portion of the carcass ply to the inner side in the tire axial direction through the bead base.
A reinforcing layer and a second reinforcing layer extending radially upward and downward along the inner side of the main body of the carcass ply in the axial direction of the tire, and the cord obliquely intersects the cord of the carcass ply. Vertical height h ₂ from the bead base of the carcass ply is made slightly lower than the vertical height h ₁ of the end of the carcass ply, and the vertical height h ₃ of the upper end of the second reinforcing layer from the bead base. Is greater than the vertical height h ₄ of the end of the inner portion where the first reinforcing layer is wound inward and substantially equal to the vertical height h _{1 of the} folded portion, and moreover, the vertical height of the lower end of the second reinforcing layer is the h ₅ is, as well as smaller than the vertical height h ₄ of the terminal of the inner portion of the first reinforcing layer, the lower portion of the second reinforcing layer, the main body and the first reinforcing layer of carcass ply Between the inner part of the carcass and With vertical height h ₁ of the folded portion of the terminal is set to 0.3 to 0.5 times the vertical height h ₆ of the tire maximum width position, and the main body portion of the carcass ply, between the folded portion, JIS hardness The radial tire for heavy loads is characterized in that a bead apex made of soft rubber having an angle of 45 ° to 65 ° is arranged.