JP2002274127A - Pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To certainly realize more excellent bead part durability. SOLUTION: This pneumatic radial tire is constituted by constituting a body part 6 toroidally extending between bead cores and a carcass ply 5 having a folded-back part 7 wound up toward the outside from the inside in the tire cross direction around each of the bead cores 4 of a steel cord an elastic modulus of which is more than 100 GPa and arranging a stiffener 10 on the outer peripheral side of the bead cores 4, an outer end part in the radial direction of the folded-back part 7 of the carcass ply is bent inside in the tire cross direction by a reforming work part 13, and height L2 in the radial direction of the reforming work part 13 is made L2 >L1 ×0.5 against height L1 of a folded- back part outer edge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In a pneumatic radial tire rolling under the action of a load, a large flexural deformation occurs in a pair of sidewall portions at a portion corresponding to a tread contact surface, thereby causing a radially outward deformation from a rim flange. The bead portion falls outward in the width direction and is deformed.

[0003] It is known that when the tire bead portion is deformed in this way, a large shear strain is generated at the end of the folded portion of the carcass ply around the bead core. JP-A-10-6719 and JP-A-10-309909 propose improvements in carcass lines, and JP-A-5-16618 and JP-A-8-324214 disclose a hard portion and a soft portion, respectively. There has been proposed a stiffener structure and a configuration in which a tip portion of a folded portion of the carcass ply is covered with a thin sheath rubber. Further, JP-A-63-2
No. 27406 and JP-A-2-267012 propose to improve the end shape of the folded portion of the carcass ply to improve the durability.

[0004]

However, in recent years, flat tires for heavy loads have been flattened,
Since the rate of tire rehabilitation use and the number of times of rehabilitation are also increasing, and the total input to the tire bead part is increasing, the improvement of the bead part durability according to the prior art as described above still lacks the durability. There is a problem,
Also, JP-A-63-227406,
The folded end portion shape of the carcass ply disclosed in Japanese Patent No. 67012 or the like has a problem that it is extremely difficult to realize when a steel cord having a high elastic modulus is used as a ply cord like a carcass ply of a heavy duty radial tire. Was.

Accordingly, the present invention provides a pneumatic radial tire having a carcass ply made of a steel cord and capable of reliably realizing more excellent bead portion durability, and in particular, provides a bead portion structure thereof.

[0006]

In the pneumatic radial tire according to the present invention, a carcass ply main body extending in a toroidal manner between a pair of bead cores and around each bead core are wound from the inside to the outside in the tire width direction. All the carcass plies having the carcass ply folded back portion are made of a steel cord, and a stiffener is disposed between the carcass ply main body portion and the folded back portion on the outer peripheral side of the bead core. The radially outer end portion of the folded portion is bent inward or outward in the tire width direction by the hammering portion, and a radial height L ₂ of the waisting portion measured from the minimum radial position of the carcass ply. Is set to L ₂ > L ₁ × 0.5 with respect to the folded portion outer edge height L ₁ .

Here, the minimum radius position of the carcass ply means that the tire is mounted on an applicable rim specified in JATMA YEAR BOOK and the YEAR BOOK
The point at which the radius of the carcass ply becomes the smallest under the tire posture filled with the maximum air pressure specified in OK is assumed.

In the pneumatic radial tire under load rolling, as described above, shear strain occurs at the end of the folded portion of the carcass ply due to large bending deformation of the pair of sidewalls. However, according to the results of the analysis, this distortion is due to the extension line of the folded portion of the carcass ply,
It was clarified that the angle between the carcass ply and the carcass ply body greatly affected the carcass ply.

That is, in a heavy-duty tire filled with a high air pressure, when the tire is mounted on the rim and filled with the air pressure, the tire is bonded to the rubber sandwiched between the folded portion of the carcass ply and the rim flange of the bead portion. Although a compressive force is generated, since the rubber is an incompressible material, the rubber is elastically deformed toward the distal end of the rim flange RF by an amount corresponding to the compressive force as shown by an arrow A in FIG. become. On the other hand, the folded portion T of the carcass ply P made of a steel cord is difficult to be deformed by the rubber.
A large shear strain occurs in the rubber portion adjacent to the outer side in the tire width direction. In addition, when a load is applied to the tire, the compressive force of the rubber by the rim flange RF further increases due to the bending deformation of the bead portion B as shown by the phantom line in the figure, and the shear strain also increases. However, according to the analysis result, such a shear strain is effectively reduced by a canceling action based on a compressive force from the main body M side of the carcass ply P as shown by an arrow C in the figure. it can, in this case, the extension line of the folded portion T of the carcass ply P, the angle theta _B of the main body portion M has been found to affect the shear strain greater.

Therefore, in this tire, the radially outer end portion of the folded portion of the carcass ply is bent inward, for example, in the width direction of the tire by a hammering processing portion.
By securing a large tip of the angle theta _B realizing the increase in compressive force applied from the main body portion side of the carcass ply.

When the outer end portion of the folded portion of the carcass ply is bent toward the carcass ply main body side without a plastic working process, as shown by a solid line in FIG. It is necessary to increase the thickness or, as shown by the solid line in FIG. 15, it is necessary to reduce the thickness of the stiffener in the vicinity of the outer end portion of the folded portion of the carcass ply. According to the latter, there is a problem that the amount of shear deformation of the stiffener itself is increased and the durability of the bead portion is reduced. The same applies to the case where the outer end portion of the folded portion is bent to the outside in the width direction without any curling, and an increase in the amount of heat generated or the amount of shear deformation of the stiffener becomes a problem.

[0012] For these points, in this tire, the imprint processing unit, L 2 a radial height L ₂ measured from the minimum radial position of the carcass ply, the folded outer edge relative to the height L _1> L _By setting the range of ₁ × 0.5, the calorific value and the shear strain of the stiffener are effectively reduced. That is, when the height L ₂ of the imprint processing unit is too low, it has been experimentally confirmed that shear strain of stiffener durability is lowered increases.

This is because, in addition to the above, the distance d between the outer edge and the main body on a straight line passing through the outer edge of the folded portion of the carcass ply and orthogonal to the main body.
_1, and the ratio of the distance d ₂ from the outer edge to the bead outer surface turned out to be particularly remarkable when the range of 0.5 to 2.0.

[0014] In such a tire, both the bent portion radially outward from the hammered portion and the portion near the hammered portion radially inward from the bent portion are both included in the cross section in the tire width direction. In the case of extending substantially linearly, there is an advantage that the shear strain in the cross-section can be reduced without increasing the rigidity step of the circumferential rigidity, particularly for a radial tire having an aspect ratio of 70 or less.

[0015] wherein preferably, the bent portion, the bending angle theta _A in imprint processing unit in the range of 10 to 60 degrees.
Bending angle theta _A, it increases, the shear strain of the rubber at the outer end outside the folded portion is reduced have been identified, in the other hand, the larger the the angle theta _A, previously described Since the concentration of the shear strain of the stiffener becomes a problem, the upper limit is set to 60 degrees. Incidentally, the angle theta _A is not practical too large cost against the effect of distortion reduction is less than 10 degrees. FIG.
As shown the relationship between the bending angle theta _A and cord strength in 6,
When plastic working is applied to a steel cord, the cord strength of the plastic working part generally decreases according to the degree of plastic working,
Decrease in strength code 60 degrees or higher bending angle theta _A becomes remarkable.

However, the same applies to the case where the outer end portion of the folded portion is bent outward in the width direction, and there is a problem that the strength of the cord is reduced particularly at a limit of 60 degrees.

[0017] Preferably, the steel cords in the radial direction outside the imprint processing unit, with respect to the circumferential line therethrough, and less than 30 degrees 90 degrees circumferentially angle theta _C. When a twisting steel cord is subjected to a twisting process, the outer side of the twisted portion is set to 90% with respect to the circumferential line segment in accordance with the twist tension, twisting direction, and amount of plastic deformation of the cord. It is possible to make the angle less than degrees, according to this, it is possible to reduce the rigidity step in the radial direction near the outer end of the folded portion of the carcass ply, to achieve further reduction of distortion, This is more effective as the angle θ _C is smaller. On the other hand, when the angle is less than 30 degrees, the rigidity step in the circumferential direction is rather large, and conversely, the durability is reduced.

The bending direction of the outer end portion of the folded portion of the carcass ply by the hammered portion is set to the outside in the tire width direction when the aspect ratio is 75 or more, and the aspect ratio is 70 or less. In the case of, it is set to the inside in the width direction. For tires with an aspect ratio of 70 or less, since the tire is generally used at a higher pressure and the compression force of the bead portion due to the rim flange becomes larger, the shear strain generated on the outer end portion of the folded portion on the outer side in the tire width direction. However, in such a tire, by forming a bent portion inward in the width direction, distortion of the tire is reduced by using the compressive force from the carcass ply body as described above. Realize reduction.

On the other hand, in a tire having a nominal aspect ratio of 75 or more, since the end of the folded ply is generally disposed radially outward with respect to the rim flange, elastic deformation of the rubber due to compression deformation of the bead portion and the flange is performed. Is less affected by
Conversely, the effect of the compressive force from the main body of the carcass ply increases, and the compressive force normally causes separation inside the widthwise end of the folded ply end. In such a case, a thicker stiffener at the outer end portion of the folded portion is more effective in alleviating the compressive force from the folded body portion and is more effective in reducing the above-described compressive strain. Then, the outer end portion of the folded portion is bent outward in the width direction.

That is, when the end position of the folded ply is low, the folded ply is bent in the width direction in order to effectively use the compressive force to cancel the rubber extrusion deformation accompanying the compressive deformation with the rim flange. When the end position is high, the compressive force from the ply body becomes a problem, so that the ply end is bent outward in the width direction to reduce the compressive strain.

Preferably, a cushioning rubber, for example, having a Shore A hardness of 75 is provided in a region sandwiched between the bent portion of the bent portion and an extension of a portion radially inward of the bent portion. The following cushion rubber is provided.

According to this, since both the shear strain and the compressive strain are effectively absorbed by the cushioning rubber, the concentration of the strain on the outer end or the inner end portion of the folded portion is effectively prevented. The same applies to the case where the cushion rubber is provided from the folded portion located on the radially inner side of the bent portion and the outer side in the tire width direction from the extension of the folded portion. In this case, when the cushion rubber is the same as the side rubber or the stiffener rubber, it is possible to effectively prevent an increase in rubber type.

Further, the stiffener is composed of a hard portion located on the radially inner side and a soft portion located on the radially outer side, and the stiffener passes through the outer edge of the folded portion of the hard portion and the main body portion. When the thickness on the straight line perpendicular to the stiffener is less than half of the thickness of the stiffener at the outer edge of the folded part, both the soft and hard parts are used to reduce the calorific value of the stiffener rubber and achieve both high rigidity of the stiffener. In this case, it is possible to effectively prevent the concentration of shear strain on the stiffener near the outer edge of the folded portion. Here, the hard part has a Shore A hardness of 70 or more, and the soft part has a Shore A hardness of 6 or more.
It is preferably set to 5 or less.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view in the width direction of a tire half, showing an embodiment of the present invention in a posture in which a rim-assembled tire is filled with the highest air pressure. here,
Rim R means the applicable rim specified in JATMA YEAR BOOK, and the maximum air pressure is also Y
This refers to the maximum air pressure specified in EAR BOOK.

In the figure, 1 is a tread portion, 2 is a tread portion 1
Side wall part that extends inward in the radial direction
Reference numeral 3 denotes a bead portion continuous to the radially inner end of the sidewall portion 2, and reference numeral 4 denotes a bead core disposed on the bead portion 3. Here, the elastic modulus is 100
All the carcass plies 5 formed of a steel cord of GPa or more and forming a skeleton structure of the tire are disposed so as to extend in a toroidal manner.
Is formed of a main body 6 extending between the bead cores 4 and a folded portion 7 wound around each bead core 4 from the inside to the outside in the tire width direction.

Here, on the outer peripheral side of the bead core 4,
A stiffener 10 composed of two types of hard and soft parts 8 and 9 is disposed to extend radially outward from a position sandwiched between the main body 6 and the folded portion 7, and a plurality of stiffeners are provided around the bead core 4. , A reinforcing layer 11 made of steel or organic fiber cord, and a plurality of reinforcing layers 12 made of steel or organic fiber cord are arranged on the outside of the folded portion 7 in the tire width direction.

Here, in this tire, the radially outer end portion of the folded portion 7 is formed into a bent portion 7a which is bent inward in the tire width direction by plastic deformation in the bending portion 13, and the bending process is performed. Radial height L of the portion 13 measured from the minimum radial position MIN of the carcass ply 5
_2, to the same height _{L 1} of the outer edge of the folded portion 7, and _L 2> _{L 1} × 0.5.

Further, in this tire, both the bent portion 7a of the folded portion 7 and the portion in the radially inner side portion 7b of the bent portion 13 near the bent portion extend substantially linearly. is, together, on a straight line l that is perpendicular to the body portion 6 through the outer edge of the bent portion 7a, the distance d ₁ between the outer edge and the body portion 6, from the outer edge to the bead outer surface The ratio d ₁ / d ₂ to the distance d ₂ is 0.5
In addition, the bending angle? _A of the bent portion 7a in the bending portion 13 is set in the range of 10 to 60 degrees. Note that, in the method shown in this figure, the folded portion 7, thus, the extension of the bent portion 7a, the angle theta _B of the body portion 6 may be, for example, in the range of 30 to 90 degrees.

In the tire configured as described above, more preferably, the steel cord of the bent portion 7a of the carcass ply turn-up portion 7 on the radially outward side of the hammering portion 13 is shown in FIG. as such, the circumferential segment CI through the imprint processing unit 13, to more precisely tangent drawn to the circumferential line segment CI, and the circumferential angle theta _C of less than 30 degrees 90 degrees, thereby In addition, the rigidity step between the extension area of the folded portion 7 and the area outside thereof is reduced.

In the meantime, the bending direction of the bent portion 7a may be set to the inside of the tire width direction as shown in a tire having an aspect ratio of 70 or less, as shown in FIG. In a tire having a nominal aspect ratio of 75 or more, it is preferable to use the outer side in the tire width direction as shown in FIG. 3 in order to reduce the compression force from the main body side of the carcass ply 5. This is preferable for reducing the compression strain.

Preferably, a region sandwiched between the bent portion 7a and an extension of the portion 7b on the radially inner side of the hammering portion 13 is hatched as shown in FIGS. For example, cushion rubber 14 having a Shore A hardness of 75 or less
And the folded portion 7, more directly the bent portion 7a
Alleviates the occurrence of shear strain and compressive strain on the outer end portion of the steel.

The stiffener 10 is connected as shown in FIG.
In the case where the carcass is composed of the hard portion 8 located on the radially inner side and the soft portion 9 located on the radially outer side, as shown in FIG. 3, the carcass passes through the outer edge of the bent portion 7a. Its hard part 8 on a straight line 1 perpendicular to the ply body 6
Of the thickness t, of the stiffener thickness d ₃ on the straight line l 1
When it is less than / 2, the concentration of shear strain on the stiffener 10 near the outer edge of the bent portion 7a can be effectively prevented. Incidentally, stiffener thickness referred to herein is equivalent to the distance d ₁ in the method shown in FIG.

In such a tire, the folded portion 7
Of, as parameters the bending angle theta _A folding portion 7a in the width direction inner side, as shown in FIG. 1, size 285/60
With respect to the radial tire for heavy load of R22.5, the shear strain of the rubber in the width direction outside near the outer end of the bent portion 7a was obtained as shown in FIG. 4, and the durability index of the bead portion was obtained. The result was as shown in FIG.

According to FIG. 4, as the bending angle theta _A increases, it is clear that the shear strain is reduced. However, if the angle theta _A is too large, in addition to the concentration of shearing strain of the stiffener 10 is forced, because it causes a decrease in the cord strength, the upper limit of the bending angle theta _A is preferably 60 ° . And according to this, as shown in FIG. 5, excellent durability can be exhibited. Further, in the tire of the same size, the circumferential shear strain (γ _rc ) and the in-section shear strain (γ _rz ) were obtained by using the circumferential angle θ _C shown in FIG. 2 as a parameter, and as shown in FIG. When the durability index of the bead portion was determined, it was as shown in FIG.

Here, according to FIG. 6, the circumferential shear strain (γ _rc ) gradually increases as the bending angle θ _c decreases, and the in-section shear strain (γ _rz ) gradually decreases, so that the bending angle θ _c Accordingly, to understand that it is possible to control each of the strain, according to FIG. 7, on the basis of the change in the bending angle theta _a, in the structure of the present study as a result, it can be seen that the bead portion durability is greatly improved.

[0036]

Example 1 A heavy-duty radial tire having a size of 285/60 R22.5 and having a basic structure of the bead portion shown in FIG. 8 was subjected to a bead portion durability test. As a result, the results shown in Table 1 were obtained. Note that Comparative Examples 1, 2, and 3 in the table correspond to FIGS.
1 having a bead portion structure shown in FIG.

In the above durability test, the maximum air pressure was 90
0 kPa, the applied rim is 9.00 × 22.5, and a load 1.5 times the maximum load capacity of 3150 kg is applied.
/ H, by rolling the tire under load until the bead breaks, and the test result of the tire of Comparative Example 1 is evaluated as an index, and the larger the index value, the better the durability. did. In addition, since the nominal of an aspect ratio is 60 for both the comparative example and the example tire,
The bent portion was bent inward in the tire width direction.

[0038]

[Table 1]

According to Table 1, all of the example tires
It is clear that superior bead portion durability can be exhibited as compared with the comparative example.

Example 2 A heavy-duty radial tire having a size of 11R22.5, which has a bead structure shown in FIG. 3 and a comparative example having a bead structure shown in FIG. When the same durability test as described above was performed, the results shown in Table 2 were obtained. In this test, the filling air pressure was set to the maximum air pressure of 700 kPa, the applied rim was set to 7.50 × 22.5, and the load was set to 1.5 times the maximum load capacity of 2725 kg.

[0041]

[Table 2]

According to Table 2, it is found that the bead portion durability is remarkably improved in the example tire.

[0043]

As is apparent from the above description, according to the present invention, the radially outer end of the folded portion of the carcass ply is bent inwardly or outwardly in the tire width direction by means of the bent portion. At the same time, by specifying the radial height of the hammered portion, the durability of the bead portion can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a widthwise cross-sectional view showing an embodiment of the present invention for a half portion of a tire.

FIG. 2 is an explanatory view showing an angle of a bent portion of a steel cord with respect to a circumferential line segment.

FIG. 3 is a sectional view of a bead portion showing another embodiment of the present invention.

FIG. 4 is a graph showing the effect of bending angle on shear strain.

FIG. 5 is a graph showing the effect of bending angle on bead portion durability.

FIG. 6 is a graph showing the effect of the circumferential angle on the circumferential shear strain and the cross-sectional shear strain at the end of the folded ply.

FIG. 7 is a graph showing the effect of circumferential angle on bead portion durability.

FIG. 8 is a cross-sectional view showing a basic bead structure of the example tire.

FIG. 9 is a transverse sectional view showing a bead portion structure of the tire of Comparative Example 1.

FIG. 10 is a transverse sectional view showing a bead portion structure of the tire of Comparative Example 2.

FIG. 11 is a transverse sectional view showing a bead portion structure of the tire of Comparative Example 3.

FIG. 12 is a transverse sectional view showing a bead portion structure of a tire of Comparative Example 4.

FIG. 13 is a cross-sectional view of a bead portion showing a mode of occurrence of shear strain.

FIG. 14 is a schematic cross-sectional view of a bead portion showing an aspect of an increase in a compressive force applied from the carcass ply main body side.

FIG. 15 is a schematic cross-sectional view of a bead portion showing another mode of increasing the compressive force acting from the carcass ply main body side.

FIG. 16 is a graph showing a relationship between a bending angle and a cord strength.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 tread portion 2 side wall portion 3 bead portion 4 bead core 5 carcass ply 6 main body portion 7 folded portion 7a bent portion 7b radially inward portion 8 hard portion 9 soft portion 10 stiffener 11,12 reinforcing layer 13 combing portion 14 rubber buffer R rim L _{1, L 2} height d _{1, d 2} the distance d ₃ stiffener thickness theta _A bending angle theta _B intersection angle theta _C circumferential angle BH bead heel l linear CI circumferential segment

Claims (8)

[Claims] 1. A carcass ply having a body portion extending toroidally between a pair of bead cores and a folded portion wound up from the inside to the outside in the tire width direction around each bead core is made of a steel cord. A pneumatic radial tire having a stiffener disposed between a main body portion and a folded portion of a carcass ply on an outer peripheral side of a bead core, wherein a radially outer end portion of the folded portion of the carcass ply is formed with a curving portion. the causes are bent inside or outside in the tire width direction, of the imprint processing unit, the radial height L ₂ measured from the minimum radial position of the carcass ply, to the height L ₁ of the folded outer edge, L _A pneumatic radial tire that satisfies ₂ > L ₁ × 0.5. 2. A bent portion radially outward from the hammered portion and a portion near the hammered portion radially inward from the waisted portion are both substantially linear in a cross section in the tire width direction. The pneumatic radial tire according to claim 1, which is extended. 3. A distance d ₁ between the outer edge and the main body on a straight line passing through the outer edge of the folded portion and orthogonal to the main body.
3. The pneumatic radial tire according to claim _{1, wherein} a ratio d ₁ / d ₂ of the distance d ₂ from the outer edge to the outer surface of the bead portion is in a range of 0.5 to 2.0. 4. Wherein the bent portion, the pneumatic radial tire according to claim 1, a bending angle theta _A in imprint processing section comprising a range of 10 to 60 degrees. 5. The steel cord on the radially outer side of the hammered portion has a circumferential angle θ _C of 30 ° or more and less than 90 ° with respect to a circumferential line passing therethrough.
The pneumatic radial tire according to any one of the above. 6. When the nominal aspect ratio is 75 or more, the radially outward portion of the hammered portion is bent outward in the tire width direction. When the nominal aspect ratio is 70 or less, the radius is reduced. The pneumatic radial tire according to any one of claims 1 to 5, wherein an outer side portion in the direction is bent inward in the tire width direction. 7. A cushioning rubber is provided in a region sandwiched between a bent portion of the hammering portion and an extension of a portion radially inward of the hammering portion. 7. The pneumatic radial tire according to any one of 6. 8. The stiffener includes a hard portion located on the radially inner side and a soft portion located on the radially outer side, and the stiffener passes through the outer edge of the folded portion of the hard portion to form the main body. The thickness on a straight line perpendicular to the stiffener thickness at the outer edge of the folded portion is less than half.
7. The pneumatic radial tire according to any one of 7.