JP4523823B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire that can improve the durability of a bead portion without impairing steering stability and riding comfort.

  FIG. 3 shows a cross section of a general bead portion a of a conventional pneumatic tire. A large load acts on the bead portion a during load running, and a large strain mainly due to bending tends to occur. Such large distortion during traveling occurs periodically and gradually raises the internal temperature of the bead part a. When the temperature of the rubber further rises, damage such as a cord loose where the rubber and the cord are separated easily occurs at the interface between the main body portion b of the carcass ply and the bead apex c, particularly in the vicinity of the position indicated by the cross. Such a tendency is remarkable particularly in a small truck tire having a large internal pressure and load. Therefore, in order to improve the durability performance of the bead portion, it is essential to prevent the cord loose at the interface between the carcass ply main body portion b and the bead apex c as described above.

  Conventionally, in order to increase the bending rigidity of the bead portion a and reduce the strain, it has been considered to make the bead apex c harder and larger. However, this method has a drawback that the ride comfort is remarkably deteriorated. As prior arts for improving the durability and the like of the bead portion, there are the following.

JP-A-4-66309 Japanese Patent Laid-Open No. 11-20424

  The present invention has been devised in view of the above circumstances, and the bead apex is arranged between the apex base portion having a substantially triangular cross section, the apex main body and the carcass ply main portion, and from the apex base portion. It is composed of a sheet-shaped apex sub-part made of rubber with a small hardness, and the apex sub-part is composed of an outer sub-part arranged on the apex base side and a carcass ply main body made of softer rubber. Consists of sub-parts arranged on the part side, based on limiting their height, etc., alleviating distortion of the bead part during load running without impairing steering stability or riding comfort, It aims at providing the pneumatic tire which can improve the durability of a bead part.

The invention according to claim 1 of the present invention includes a main body portion that extends from the tread portion through the sidewall portion to the bead core of the bead portion, and the periphery of the bead core that is connected to the main body portion is folded back from the inner side in the tire axial direction. A pneumatic tire having a carcass including at least one carcass ply having a turn-up portion, and tapered from the outer surface in the tire radial direction of the bead core to the outer side in the tire radial direction between the main body portion and the turn-up portion. A bead apex comprising an apex base portion having a substantially triangular cross section extending in the form of a sheet-like apex sub-portion made of rubber and disposed between the apex base portion and the main body portion and having a hardness lower than that of the apex base portion. The apex sub-portion is attached to the outer sub-portion and the outer sub-portion disposed on the apex base side. The outer sub-portion is made of rubber whose hardness is smaller than that of the outer sub-portion, and the outer end of the outer sub-portion in the tire radial direction is more radially outer than the outer end of the apex base portion. The height of the inner sub-portion in the tire radial direction is 5 to 20 mm larger than the height of the outer end of the outer sub-portion, and the inner end of the inner sub-portion in the tire radial direction Is characterized in that it is located on the inner side in the tire radial direction than the inner end of the outer sub-portion.

In the invention according to claim 2, the difference in hardness (Hd2-Hd3) between the JIS durometer A hardness Hd2 of the outer sub-portion and the JIS durometer A hardness Hd3 of the inner sub-portion is 10-20. The pneumatic tire according to claim 1, which is a degree .

  According to a third aspect of the present invention, the height of the inner end of the inner sub-portion is 5 to 20 mm smaller than the height of the inner end of the outer sub-portion. This is a pneumatic tire.

  In the invention according to claim 4, the maximum rubber thickness of the inner sub-portion is 0.5 to 2.5 mm, and the maximum rubber thickness of the outer sub-portion is 0.5 to 3.0 mm. The pneumatic tire according to any one of claims 1 to 3, wherein the pneumatic tire is provided.

  In the invention according to claim 5, the JIS durometer A hardness Hd1 of the apex base is 70 to 100 degrees, the JIS durometer A hardness Hd2 of the outer sub part is 40 to 80 degrees, and the inner sub part is The pneumatic tire according to any one of claims 1 to 4, wherein a JIS durometer A hardness Hd3 is 40 degrees or more and less than 80 degrees.

  In the pneumatic tire of the present invention, a bead apex is disposed between the main body portion and the folded portion of the carcass ply. The bead apex is disposed between the apex base portion having a substantially triangular shape and extending from the outer surface of the bead core in the tire radial direction to the outer side in the tire radial direction, and between the apex base portion and the main body portion, and is softer than the apex base portion. Includes a sheet apex sub-part made of rubber.

  In such a pneumatic tire, a large bending distortion of the bead portion is suppressed at the apex base portion having a relatively large rubber hardness when running under load. Further, shear strain or the like generated in the vicinity of the interface between the main body portion of the carcass ply and the bead apex is alleviated by the apex sub-portion made of soft rubber. In particular, the apex sub-portion has an interface with the main portion of the carcass ply by making the sub-portion on the main portion side of the carcass ply larger in height and smaller in rubber hardness than the outer sub-portion. The change in rigidity in the vicinity can be made smooth, and the shear strain can be alleviated more effectively. Further, by forming the apex sub-part in a sheet shape, it is possible to reduce the distortion of the bead part while minimizing the increase in the volume of the bead apex. Therefore, the pneumatic tire of the present invention can improve the durability of the bead part without impairing the handling stability and the riding comfort.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a right half cross-sectional view including a tire shaft in a normal state in which the pneumatic tire 1 of the present embodiment is assembled with a normal rim J and filled with a normal internal pressure and is filled with a normal internal pressure. FIG. 2 is an enlarged view of the bead portion. The partially enlarged views are shown respectively. Unless otherwise specified, the dimensions and the like of each part of the tire are values measured in this normal state.

  In the present specification, the “regular rim” is a rim determined for each tire in a standard system including a standard on which the tire is based. For example, a standard rim for JATMA and a “Design Rim” for TRA. "Or, if ETRTO," Measuring Rim ". In addition, “regular internal pressure” is the air pressure that each standard defines for each tire in the standard system including the standard on which the tire is based. It is the maximum air pressure for JATMA and the table “TIRE LOAD LIMITS” for TRA. The maximum value described in “AT VARIOUS COLD INFLATION PRESSURES”, “INFLATION PRESSURE” for ETRTO, and 180 (kPa) for tires for passenger cars.

  The pneumatic tire 1 is disposed on the toroidal carcass 6 extending from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and on the outer side in the tire radial direction of the carcass 6 and inside the tread portion 2. A radial tire for a light truck is exemplified in this embodiment.

  The carcass 6 of the present embodiment is composed of two carcass plies 6A and 6B that overlap in the tire radial direction and outside. The inner carcass ply 6A has a main body 6A1 that extends from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and is connected to the main body portion 6A1 and is folded around the bead core 5 from the inner side in the tire axial direction to the outer side. It comprises a so-called folded ply having a folded portion 6A2. The folding height hp of the folded portion 6A2 is not particularly limited, but if it is too small, the bending rigidity of the bead portion 4 tends to be lowered, and if it is too large, the vibration absorbing action by the sidewall portion 3 is likely to be impaired. Although not particularly limited, the height hp of the folded portion 6A2 is desirably 50 to 80%, more preferably 60 to 70% of the tire cross-section height H.

  The outer carcass ply 6B is a so-called main body 6B1 that extends from the tread portion 2 through the sidewall portion 3 to the bead core 5 through the outer side in the tire axial direction of the folded portion 6A2 of the inner carcass ply 6A. Consists of a lowering ply.

  For each of the carcass plies 6A and 6B, a cord ply in which an array of a plurality of carcass cords is rubberized with a topping rubber is used. In each of the carcass plies 6A and 6B, in the finished tire, the carcass cord is inclined at an angle of, for example, 75 to 90 ° with respect to the tire equator C. For the carcass cord, for example, an organic fiber cord such as polyester, nylon, rayon, or aramid is preferably employed, but a steel cord can be employed if necessary. The carcass 6 of the present embodiment has a so-called 1-1 structure composed of two carcass plies, but it goes without saying that it can be changed to another structure as long as it includes at least one folded ply.

  In this example, the belt layer 7 includes at least two belt plies 7A, 7B, and 7C in which the belt cord is inclined with respect to the tire equator at a small angle of about 15 to 45 °, for example, three in this example. The belt cords are overlapped in a direction that intersects each other. By tightening the carcass 6 in the tread portion 2, the belt layer 7 can increase its rigidity and improve steering stability and wear resistance.

  As shown in FIG. 2 in an enlarged manner, the bead apex 8 is disposed in the bead portion 4 between the main body portion 6A1 and the folded portion 6A2 of the inner carcass ply 6A. The bead apex 8 is disposed between the apex base portion 9 having a substantially triangular cross section that tapers outwardly from the outer surface 5t in the tire radial direction of the bead core 5 and between the apex base portion 9 and the main body portion 6A1. And it is comprised from the sheet-like apex subpart 10 which consists of rubber | gum whose hardness is smaller than the said apex base part. An inner liner 12 made of rubber having excellent air impermeability is provided on the inner side in the tire axial direction of the main body 6A1. Further, a clinch apex 13 made of rubber that is hard and has excellent wear resistance is provided at a portion of the bead portion that contacts the rim J. Reference numeral 14 denotes a sidewall rubber.

  The apex base 9 of the present embodiment has an inner end located on the outer surface 5t of the bead core 5, and the inner end is configured with a width Wa substantially equal to the outer surface 5t of the bead core 5. Although not particularly limited, it is desirable that the outer end 9t of the apex base 9 in the tire radial direction has a height ha of 10% or more, more preferably 25% or more of the tire cross-section height H from the bead base line BL. When the height ha is less than 10% of the tire cross-section height H, the bending rigidity of the bead portion 4 tends to be insufficient. On the other hand, if the height ha is too large, the vibration absorbing ability of the sidewall portion 3 is lowered and the ride comfort tends to be impaired. From such a viewpoint, the height ha of the apex base 9 is preferably 50% or less, more preferably 35% or less of the tire cross-section height H. Particularly preferably, the ratio (ha / Wa) between the width Wa and the height ha at the inner end of the apex base 9 is preferably 1.0 to 5.0, more preferably 3.0 to 4.5. Is desirable.

  Further, since the apex base 9 occupies a relatively large volume in the bead apex 8, the basic bending rigidity of the bead portion 4 is determined. In other words, if the JIS durometer A hardness of the rubber constituting the apex base 9 is too small, the distortion of the bead portion 4 during load running increases, and the durability tends to deteriorate due to excessive heat generation. However, there is a tendency that the impact relaxation ability is remarkably lowered and the ride comfort is deteriorated. From such a viewpoint, the apex base 9 is preferably made of rubber having a JIS durometer A hardness Hd1 of 70 to 100 degrees, more preferably 85 to 95 degrees.

  The apex sub-portion 10 is made of rubber having a smaller hardness than the apex base 9 and is in the form of a sheet having a small thickness, so that a rigid step between the cord of the carcass ply main body 6A1 and the apex base 9 is formed. Can be relaxed and the shear strain between them can be relaxed and absorbed. As a result, the carousel cord can be prevented from being damaged such as the cord looseness that peels off from the surrounding rubber.

  Moreover, in the pneumatic tire 1 of the present invention, the apex sub-portion 10 is attached to the outer sub-portion 10o disposed on the apex base 9 side, the outer sub-portion 10o, and the outer sub-portion 10o. Also, it is composed of two layers with the sub part 10i made of rubber having a small hardness.

  The outer sub-portion 10 o is formed in a sheet shape with a small thickness, and the outer end 10 ot in the tire radial direction is located on the outer side in the tire radial direction with respect to the outer end 9 t of the apex base 9. That is, the height h3 of the outer sub part 10o from the bead base line BL is larger than the height ha of the outer end of the apex base part 9. By attaching a relatively soft outer sub-portion 10o to the outer end 9t of the apex base 9 made of hard rubber, stress concentration that tends to occur at the outer end 9t can be alleviated, and the outer end 9t is the starting point. Helps to suppress rubber peeling over a long period of time.

  Here, when the outer end 10ot of the outer sub-portion 10o is close to the outer end 9t of the apex base 9, there is a tendency that the effect of preventing stress concentration at the outer end 9t of the apex base 9 is not sufficiently obtained. is there. From such a viewpoint, the difference (h3−ha) between the respective outer end heights h3 and ha is preferably 5 mm or more, more preferably 15 mm or more. The upper limit of the difference (h3-ha) is not particularly limited, but if it is too large, not only will the tire weight be increased, but the effect of improving the durability of the bead portion will also peak. From such a viewpoint, the difference (h3−ha) is desirably 60 mm or less.

  Further, it is desirable that the inner end 10ob of the outer sub-portion 10o in the tire radial direction extends at least to the outer surface 5t of the bead core 5. Thereby, over the entire length of the apex base 9, the shear strain between the main part 6A1 of the carcass ply and the like can be effectively reduced. In this embodiment, the inner end 10ob of the outer sub-portion 10o extends inward in the tire radial direction along the inner surface of the bead core 5 in the tire axial direction, and ends at a position approximately in the middle of the cross-sectional height of the bead core 5. What to do is illustrated. This position is useful for preventing the occurrence of damage starting from the inner end 10ob of the outer sub-portion 10o because the distortion generated during load running is small.

  The outer sub-portion 10o is made of rubber having a smaller hardness than the apex base 9, and the JIS durometer A hardness Hd2 is preferably 40 to 80 degrees, more preferably 50 to 70 degrees. If the JIS durometer A hardness Hd2 of the rubber constituting the outer sub-portion 10o is less than 40 degrees, not only the rigidity with the apex base 9 is excessively increased, but also the bending rigidity of the bead portion 4 is lowered to stabilize the operation. On the contrary, if it exceeds 80 degrees, the effect of relaxing and absorbing the shear strain between the apex base portion 9 and the main body portion 6A1 tends to decrease. From such a viewpoint, particularly preferably, the difference in hardness (Hd1−Hd2) between the JIS durometer A hardness Hd1 of the apex base 9 and the JIS durometer A hardness Hd2 of the outer sub-portion 10o is 10-20. It is desirable that the degree.

  Further, the maximum thickness to of the outer sub part 10o is not particularly limited, but is preferably 0.5 mm or more, more preferably 1.0 mm or more. If the maximum thickness to of the outer sub-portion 10o is less than 0.5 mm, the ability to absorb relaxation such as shear strain between the apex base 9 and the main body 6A1 tends to be lowered. On the other hand, if the maximum thickness to of the outer sub-portion 10o is too large, the rubber volume of the bead apex 8 is increased, and the ride comfort may be significantly deteriorated. From such a viewpoint, the maximum thickness to of the outer sub-portion 10o is preferably 3.0 mm or less, more preferably 2.5 mm or less. The outer sub-portion 10o of the present embodiment prevents stress concentration at each end by tapering the vicinity of the outer end 10ot and the inner end 10ob toward each end. The other part is exemplified as being formed with a substantially constant thickness.

  The inner sub-portion 10i is made of rubber attached to the outer sub-portion 10o and having a lower hardness than the outer sub-portion 10o. At the time of bending deformation of the bead portion as shown in FIG. 3, a larger tensile strain and shear strain act as the body portion 6A1 of the carcass ply 6A approaches. In the bead apex 8 of the present embodiment, the rubber closer to the main body portion 6A1 of the carcass ply 6A is configured to have a smaller hardness, so that a large strain near the main body portion 6A1 of the carcass ply can be effectively relaxed and absorbed. Thereby, damage such as the above-mentioned cord looseness of the carcass ply can be suppressed over a long period of time.

  Here, it is desirable that a rubber having a JIS durometer A hardness Hd3 of 40 degrees or more and less than 80 degrees, more preferably 50 to 70 degrees is used for the inner sub-portion 10i. If the hardness Hd3 is less than 40 degrees, the bending rigidity of the bead part 4 may be significantly reduced and the steering stability may be deteriorated. Conversely, if the hardness Hd3 is 80 degrees or more, the outer sub-part 10o and the main body part 6A1 The effect of relaxing and absorbing the shear strain between the two is likely to decrease. From this point of view, particularly preferably, the difference in hardness (Hd2−Hd3) between the JIS durometer A hardness Hd2 of the outer sub-portion 10o and the JIS durometer A hardness Hd3 of the inner subportion 10i is 0. It is desirable that the angle is greater than 30 degrees and 30 degrees or less, more preferably 10 to 20 degrees.

It is particularly preferable to use a rubber having the same composition as the topping rubber of the carcass ply 6A for the inner sub-portion 10i. Such sub-portion 10i has very high adhesion to the topping rubber of the carcass ply, and after vulcanization, the influence of the interface between the two can be substantially eliminated. Therefore, Ru can more reliably suppress the like cord loose of the carcass ply. Maximum thickness ti of the secondary portion 10i of was or is not particularly limited, but is preferably 0.5mm or more, and more preferably not less than 1.0 mm. When the maximum thickness ti of the inner sub-portion 10i is less than 0.5 mm, the ability to absorb relaxation such as shear strain between the outer sub-portion 10o and the main body portion 6A1 tends to decrease. On the other hand, even if the maximum thickness ti of the inner sub-portion 10i is too large, the rubber volume of the bead apex 8 may be increased, and the steering stability may be reduced. From such a viewpoint, the maximum thickness ti of the inner sub-portion 10i is preferably 2.5 mm or less, more preferably 2.0 mm or less. Similarly to the outer sub-portion 10o, the sub-portion 10i in the present embodiment is tapered at the ends of the outer end 10it and the inner end 10ib toward the respective end portions, thereby causing stress at each end portion. concentrated and to prevent the portion between them is, those formed with a substantially constant thickness Ru is illustrated. Radially outer end 10it the secondary portion 10i of was or is located radially outward of the tire than the outer edge 10ot outside the secondary portion 10o, the radially inner end 10ib the secondary portion 10i of the inner is It is located on the inner side in the tire radial direction than the inner end 10ob of the outer sub part 10o. Accordingly, the outer sub-portion 10o is not in direct contact with the carcass ply main body portion 6A1, and the shear strain between them is effectively relaxed and absorbed by the softest sub-portion 10i over the entire area. be able to.

  Particularly preferably, the height h1 of the outer end 10it of the inner sub-portion 10i is 5-20 mm, more preferably 10-15 mm larger than the height h3 of the outer end 10ot of the outer sub-portion 10o. When the height difference (h1-h3) is less than 5 mm, the ability to relieve strain between the outer sub-portion 10o and the carcass ply main body 6A1 tends to be lowered. In addition, since the outer ends 10 ot and 10 it of the sub-portions are close to each other, a rigid step is likely to be formed, which is not preferable because looseness starting from the position and defects in the manufacturing process are likely to occur. Conversely, when the height difference (h1-h3) exceeds 20 mm, the tire weight is unnecessarily increased although it hardly contributes to bead durability, which is not preferable.

The inner end 10ib of the inner sub-portion 10i extends inward in the tire radial direction, is wound from the inner surface of the bead core 5 to the inner surface 5i side of the bead core 5, and terminates at a position in contact with the inner surface 5i. The position where the inner end 10 ib is provided also has a very small distortion during load traveling, so that damage starting from the inner end 10 ib of the inner sub-portion 10 i can be effectively prevented. For the same reason as described above , the height h2 of the inner end 10ib of the inner sub-portion 10i is 5 to 20 mm, more preferably 10 to 15 mm smaller than the height h4 of the inner end 10ob of the outer sub-portion 10o. Is desirable.

  Although the embodiment of the present invention has been described above, it goes without saying that the pneumatic tire of the present invention can be applied to a tire for a passenger car or a tire for a motorcycle.

  A 195 / 85R16 114 / 112L light truck having the basic shape shown in FIG. 1 was prototyped based on the specifications shown in Table 1, and the durability performance and actual vehicle performance of the bead portion were evaluated. The test method is as follows.

<Durability of bead part>
Each sample tire is mounted on a rim (16 × 5.5K), and a drum with a diameter of 1.7 m is applied while applying a large load to the bead portion with an internal pressure of 600 kPa, a longitudinal load of 1.3 times the normal load, and a speed of 50 km / h. The vehicle was run for 8000 km, and the running distance until the tire (bead part) was damaged was measured. The evaluation was expressed as an index with the traveling distance of Comparative Example 1 as 100. The larger the value, the higher the durability of the bead part and the better.

<Real vehicle performance>
Each test tire (rim: 16 x 5.5K, internal pressure 600 kPa) is mounted on 6 wheels of a 2-carriage domestic light truck, and the driver runs on a dry asphalt road tire test course with one driver on board. A comprehensive evaluation was performed based on the driver's sensuality in terms of steering wheel response, rigidity, grip, etc., ride comfort, and wandering performance. The results are displayed as an index with Comparative Example 1 as 100. The larger the value, the better.
Table 1 shows the test results.

  As a result of the test, it was confirmed that the tire of the example improved the durability of the bead portion without impairing the handling stability and the ride comfort.

It is a right half sectional view of a pneumatic tire showing an embodiment of the present invention. It is an enlarged view of the bead part. It is a cross-sectional schematic diagram which shows the bead part of the conventional pneumatic tire.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 6A, 6B Carcass ply 6A1, 6B1 Main part 6A2 Turn-up part 7 Belt layer 8 Bead apex 9 Apex base part 10 Sub part 10it in apex sub part 10i Outer end 10ib Outer subinner end 10ib Outer subpart 10ot Outer subouter end 10ob Outer subinner inner end

Claims (5)

At least one carcass ply having a main body part that extends from the tread part through the sidewall part to the bead core of the bead part, and a folded part that is connected to the main body part and folded around the bead core from the inner side to the outer side in the tire axial direction. A pneumatic tire with a carcass including
Between the main body portion and the folded portion, an apex base portion having a substantially triangular cross section extending in a tapered shape from the outer surface in the tire radial direction of the bead core to the outer side in the tire radial direction;
A bead apex is arranged between the apex base and the main body and a sheet-like apex sub-part made of rubber having a smaller hardness than the apex base,
The apex sub-portion is composed of an outer sub-portion arranged on the apex base portion side, and an inner sub-portion made of rubber attached to the outer sub-portion and having a smaller hardness than the outer sub-portion. As
An outer end in the tire radial direction of the outer sub-portion is located on the outer side in the tire radial direction with respect to an outer end of the apex base,
And the height in the tire radial direction of the inner sub-portion is 5 to 20 mm larger than the height of the outer end of the outer sub-portion ,
In addition, the inner end of the inner sub-portion in the tire radial direction is located on the inner side in the tire radial direction than the inner end of the outer sub-portion.
The air according to claim 1 , wherein a difference in hardness (Hd2-Hd3) between the JIS durometer A hardness Hd2 of the outer sub part and the JIS durometer A hardness Hd3 of the inner sub part is 10 to 20 degrees. Enter tire.
  3. The pneumatic tire according to claim 1, wherein a height of an inner end of the inner sub-portion is 5 to 20 mm smaller than a height of the inner end of the outer sub-portion.   The maximum rubber thickness of the inner sub-portion is 0.5 to 2.5 mm, and the maximum rubber thickness of the outer sub-portion is 0.5 to 3.0 mm. The pneumatic tire according to any one of 1 to 3.   JIS durometer A hardness Hd1 of the apex base is 70 to 100 degrees, JIS durometer A hardness Hd2 of the outer sub part is 40 to 80 degrees, and JIS durometer A hardness Hd3 of the inner sub part is 40 degrees. The pneumatic tire according to any one of claims 1 to 4, wherein the pneumatic tire is at least 80 degrees.

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