JP4908809B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a heavy duty pneumatic tire having a wind bead in which a carcass ply is wound around a bead core.

  In the bead portion of a conventional pneumatic tire, the carcass ply is generally wound back by a bead core, and the folded portion extends in the direction of the sidewall portion.

  On the other hand, a so-called WIND bead structure is disclosed in which the carcass ply is not wound around the bead core but is wound around the bead core (see, for example, Patent Document 1 and Patent Document 2).

In any bead portion structure, a reinforcing rubber called a stiffener (for example, a combination of hard rubber and soft rubber) may be disposed outside the bead core in the tire radial direction.
JP 2001-191755 A JP 2001-191756 A

  In the configuration of a general bead portion that does not have a WIND bead structure, when a load is applied to the tire, the entire bead portion may fall down and a failure may occur with the ply end of the carcass ply as a failure nucleus. For this reason, conventionally, by increasing the height of the hard rubber of the stiffener (the height of the hard rubber is approximately half of the overall height of the stiffener), the fall of the bead portion during the load action is suppressed, An attempt was made to reduce the distortion generated at the end of the ply as much as possible.

  However, in the case of the WIND bead structure, since the carcass ply is wound around the bead core, there is no failure at the end of the ply at the time of loading, but if the stiffener has a high hard rubber height as described above, The distortion between the hard rubber and the carcass ply (the carcass main body located between the pair of bead portions) increases, and a failure may occur from here.

  In consideration of the above fact, the present invention prevents the occurrence of a failure between the hard rubber portion of the stiffener and the carcass main body portion during a load operation in a pneumatic tire having a WIND bead structure. The purpose is to improve durability.

According to the first aspect of the present invention, a carcass main body portion disposed between the bead portions between the pair of bead portions and a bead core of the bead portion wound around the bead core and wound around the bead core. And at least one layer of a carcass ply wound around the outermost end in the tire axial direction of the bead core along the tire axial direction, and a chafer disposed outside the carcass ply in the bead portion a layer, extend axially outward and the carcass main body portion having a plurality of rubber portions of different hardness from the bead core and / or the winding portion in the tire radial direction outer side of the bead portion, the hardest A hard rubber portion is disposed adjacent to the bead core and / or the winding portion, and in the cross section in the tire axial direction, the bead core and / or of the hard rubber portion The width of the bottom surface in contact with the winding unit includes a stiffener 50 to 100% of the maximum width of the bead core, of the bead portion, said stiffener, and said winding portion, said chafer layer, the side And a rubber different from the stiffener disposed in a region surrounded by a sidewall rubber disposed on the tire outer surface of the wall portion.

  Here, the lower limit of the width of the bottom surface of the hard rubber part is set to 50% of the maximum width of the bead core. Below this, the bending rigidity of the bead part is too low, and the amount of deformation of the bead part collapsed when a load is applied This is because the durability of the bead portion decreases and the upper limit is set to 100%. If the upper limit is exceeded, the carcass line of the bead portion enters the tire axial direction inside from the design target, and the load action This is because the deformation amount of the bead portion collapses at the time, and the durability of the bead portion cannot be secured.

  In the pneumatic tire according to claim 1, since the bottom width of the hard rubber portion in the stiffener is appropriately set, the bending rigidity of the bead portion is optimized. For this reason, the fall deformation amount of the bead part at the time of a load action decreases, and durability of a bead part improves.

  A second aspect of the present invention is the pneumatic tire according to the first aspect, wherein the bead core is formed in a hexagonal cross section in the tire axial direction cross section, and the tire shaft on the bottom surface of the bead core which is the inner side in the tire radial direction of the bead core. The height of the hard rubber portion in the direction perpendicular to the straight line is defined as a straight line connecting the outermost point in the direction and the innermost point in the tire axial direction on the upper surface of the bead core that is the outer side in the tire radial direction of the bead core. The cross-sectional height is 7.5 to 20%.

  Here, the reason why the lower limit of the height of the hard rubber portion is set to 7.5% of the tire cross-sectional height is that if it falls below this, the fall deformation amount of the bead portion increases and the durability of the bead portion decreases. The upper limit is set to 20% of the tire cross-section height. If the upper limit is exceeded, the end of the hard rubber part approaches the region where the strain is greatest when the load is applied, and a failure occurs between the hard rubber part and the carcass ply. This is because it tends to occur.

  In the pneumatic tire according to claim 2, since the height of the hard rubber portion is appropriately set, a large distortion does not occur between the hard rubber portion and the carcass ply when a load is applied. The occurrence of failure can be suppressed.

  According to a third aspect of the present invention, in the pneumatic tire according to the first or second aspect, the bead core has a hexagonal cross section in a cross section in the tire axial direction, and the bead core is the inner side in the tire radial direction of the bead core. The height of the stiffener in the direction perpendicular to the straight line is based on a straight line connecting the outermost point in the tire axial direction on the bottom surface and the innermost point in the tire axial direction on the upper surface of the bead core that is the outer side in the tire radial direction of the bead core. The tire cross-sectional height is 25 to 45%.

  Here, the lower limit of the height of the stiffener is set to 25% of the tire cross-sectional height. Below this, the boundary surface between the hard rubber portion of the stiffener and the rubber portion other than the hard rubber portion is easily peeled off. In addition, the upper limit is set to 45% of the tire cross-section height. If the upper limit is exceeded, the carcass line of the bead portion enters the inside of the tire axial direction from the design target, and the bead portion of the bead portion during load action This is because the fall deformation amount becomes large and the durability of the bead portion cannot be secured.

  In the pneumatic tire according to claim 3, since the height of the stiffener is appropriately set, peeling does not occur at the boundary surface between the hard rubber portion and the other rubber portion in the stiffener at the time of loading, and The durability of the bead portion can also be secured.

  According to a fourth aspect of the present invention, in the pneumatic tire according to any one of the first to third aspects, a 50% elongation modulus of the hard rubber portion is 5.5 to 7.0 MPa, and the stiffener The 50% elongation modulus of the rubber part other than the hard rubber part in is 0.5 to 2.5 MPa.

  Here, the lower limit is set for the 50% elongation modulus of the hard rubber part and the rubber part other than the hard rubber part in the stiffener. This is because the durability of the portion cannot be ensured. Moreover, the upper limit is set because if the value exceeds the upper limit, the stiffener becomes too hard and the stiffener itself is easily broken.

  In the pneumatic tire according to claim 4, since the 50% elongation modulus of each rubber part of the stiffener is appropriately set, the stiffener is hardly broken and the durability of the bead part is secured.

  According to a fifth aspect of the present invention, in the pneumatic tire according to any one of the first to fourth aspects, a 50% elongation modulus is 0.5 to 2 between the hard rubber portion and the carcass main body portion. A buffer rubber layer of .5 MPa is disposed, and the thickness of the buffer rubber layer at the outermost end in the tire radial direction of the hard rubber portion is 0.5 to 10 mm.

  Here, the reason why the lower limit of the 50% elongation modulus of the buffer rubber layer is 0.5 MPa is that if it is less than this, the rigidity of the bead portion is low, the collapse deformation becomes large, and the durability cannot be secured. If the pressure exceeds 2.5 MPa, peeling tends to occur at the boundary between the hard rubber portion and the carcass ply when loaded.

  Moreover, the reason why the lower limit of the thickness of the buffer rubber layer is set to 0.5 mm is that if the thickness is less than this, the shear strain between the hard rubber portion and the carcass main body portion increases, and the upper limit is set to 10 mm. If this is exceeded, the heat generated in the bead portion becomes large and the failure tends to occur.

  In the pneumatic tire according to claim 5, since the shock absorbing rubber layer is appropriately disposed between the hard rubber portion and the carcass main body portion, the shear between the hard rubber portion and the carcass main body portion under load action An increase in strain can be suppressed and cracking can be prevented.

  As described above, according to the pneumatic tire of the present invention, in a pneumatic tire having a WIND bead structure, it is possible to prevent a failure from occurring between the hard rubber portion of the stiffener and the carcass main body portion when a load is applied. And, it has an excellent effect that the durability of the bead portion can be improved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[First Embodiment]
In FIG. 1, the pneumatic tire 100 according to the present embodiment has a WIND bead structure. Specifically, the pneumatic tire 100 is disposed between a pair of bead portions 12 in a toroidal shape, and between the bead portions 12. Winding wound around the bead core 16 of the carcass main body portion 14A and the bead portion 12 positioned from the inside to the outside and wound along the bead core 16 inward in the tire axial direction from the outermost end in the tire axial direction of the bead core 16. The carcass ply 14 having at least one layer including the recessed portion 14B, a plurality of rubber portions (hard rubber portion 28 and soft rubber portion 30) having different hardnesses, the outer side in the tire axial direction of the carcass main body portion 14A, the bead core 16, and And / or a stiffener 18 extending outwardly in the tire radial direction of the bead portion 12 from the winding portion 14B.

  A chafer layer 20 having a first chafer 20A made of, for example, a wire and a second chafer 20B made of, for example, an organic fiber is disposed outside the carcass ply 14 in the bead portion 12, and the chafer layer 20 is made of a rubber chafer. Covered by fur 22. Further, an inner liner 24 is disposed on the inner surface of the tire, and a sidewall rubber 26 is disposed on the outer surface of the tire in the sidewall portion 10.

  The hardest hard rubber portion 28 in the stiffener 18 is disposed adjacent to the bead core 16 and / or the winding portion 14B, and contacts the bead core 16 and / or the winding portion 14B of the hard rubber portion 28 in the cross section in the tire axial direction. The width w of the bottom surface 28 </ b> A is 50 to 100% of the maximum width W of the bead core 16.

  The width w of the bottom surface 28A is, for example, a width in a direction parallel to the bead base surface 12A of the bead portion 12. In the present embodiment, as shown in FIG. 1, the direction of the maximum width W of the bead core 16 is also substantially parallel to the bead base surface 12A.

  Here, the lower limit of the width of the bottom surface 28A in the hard rubber portion 28 is set to 50% of the maximum width of the bead core 16. Below this, the bending rigidity of the bead portion 12 is too low, and the bead portion during the load action This is because the deformation amount of 12 falls and the durability of the bead portion 12 decreases, and the upper limit is set to 100%. If the upper limit is exceeded, the carcass line of the bead portion 12 (the contour formed by the carcass main body portion 14A). This is because the shape) enters the inner side in the tire axial direction from the design target, and the amount of collapse of the bead portion 12 when the load is applied increases, so that the durability of the bead portion 12 cannot be secured.

  The bottom surface 28 </ b> A of the hard rubber portion 28 also serves as the bottom surface of the stiffener 18. In the bead portion 12, for example, in a region surrounded by the stiffener 18, the winding portion 14 </ b> B, the chafer layer 20, and the sidewall rubber 26. A rubber 34 different from that of the stiffener 18 is disposed. The reason why the rubber 34 is disposed is to improve the adhesion between the wire cord of the first chafer 20A and the organic fiber cord of the second chafer 20B. The height h3 of the rubber 34 is set to be higher than the height h1 of the hard rubber portion 28 and lower than the height h2 of the soft rubber portion 30. This is because, when the height h3 of the rubber 34 is lower than the hard rubber portion 28, the adhesion to the cord of the second chafer 20B is deteriorated, and the second chafer 20B and the soft rubber portion 30 are in direct contact with each other. This is because separation may occur. If the height h3 of the rubber 34 is higher than the height h2 of the soft rubber portion 30, the carcass 14 enters the inside of the tire as much as the rubber 34 has entered, and this causes the bead portion 12 to fall and deform under load. The reason for this is that the durability becomes large and durability cannot be ensured.

  In the cross section in the tire axial direction, the bead core 16 has a hexagonal cross section. A straight line BL connecting a point A on the outermost side in the tire axial direction of the bead core bottom surface 16A that is the inner side in the tire radial direction of the bead core 16 and a point B on the innermost side in the tire axial direction of the bead core upper surface 16B that is on the outer side in the tire radial direction of the bead core 16. , The height h1 of the hard rubber portion 28 in the direction perpendicular to the straight line BL is 7.5 to 20% of the tire cross-sectional height (not shown).

  Here, the lower limit of the height h1 of the hard rubber portion 28 is set to 7.5% of the tire cross-section height. The reason why the upper limit is set to 20% of the tire cross-sectional height is that if the upper limit is exceeded, the region where the strain becomes the largest when the load is applied (out of the boundary surface 38 between the stiffener 18 and the carcass main body portion 14A). This is because the end of the hard rubber portion 28 comes close to the outer region in the tire radial direction and a failure between the hard rubber portion 28 and the carcass ply 14 is likely to occur.

  Further, in the tire axial section, the height of the stiffener 18 (height of the soft rubber portion 30) h2 in the direction perpendicular to the straight line BL is 25 to 45% of the tire sectional height.

  Here, the lower limit of the height h2 of the stiffener 18 is set to 25% of the tire cross-sectional height. Below this, the hard rubber portion 28 and the soft rubber portion 30 in the stiffener 18 (rubbers other than the hard rubber portion 28). The upper limit is set to 45% of the tire cross-sectional height, and if this is exceeded, the carcass line of the bead portion 12 is in the tire axial direction from the design target. This is because it enters the inside and the amount of deformation of the bead portion 12 when the load is applied increases, and the durability of the bead portion 12 cannot be ensured.

  The 50% elongation modulus of the hard rubber portion 28 is 5.5 to 7.0 MPa, and the 50% elongation modulus of the soft rubber portion 30 is 0.5 to 2.5 MPa.

  Here, the lower limit is set for the 50% elongation modulus of the hard rubber portion 28 and the soft rubber portion 30 in the stiffener 18. If the lower limit is not reached, the amount of deformation of the bead portion 12 when the load is applied increases and the bead portion becomes larger. This is because the durability of 12 cannot be ensured. Also, the upper limit is set because if the value exceeds the upper limit, the stiffener 18 becomes too hard and the stiffener 18 itself is easily destroyed.

  The tire inner end portion of the first chafer 20A is at a position higher than the height h1 of the hard rubber portion 28, and the tire outer end portion is at a position lower than the height h1. This is to reinforce the bead portion 12 more firmly inside the tire and to prevent separation at the chafer end inside the tire.

Also, the tire inner end portion of the second chafer 20B is at a position lower than the height h1 of the hard rubber portion 28 and lower than the straight line BL, contrary to the first chafer 20A, and the tire outer end portion is The first chafer 20A is covered at a position equivalent to or slightly higher than the height h1 of the hard rubber portion 28. This is because separation is likely to occur at the end portion of the first chafer 20A on the outer side of the tire, and this is pressed down.
(Function)
In the pneumatic tire 100 according to the present embodiment, the width of the bottom surface 28A of the hard rubber portion 28 in the stiffener 18 is appropriately set, so that the bending rigidity of the bead portion 12 is not too strong and not too weak. It becomes. For this reason, the fall deformation amount of the bead part 12 at the time of a load action decreases, and durability of the bead part 12 improves.

  Further, in the stiffener 18, the height h1 of the hard rubber portion 28 is set appropriately, so that a large distortion does not occur between the hard rubber portion 28 and the carcass ply 14 when a load is applied, and a failure occurs from this portion. Can be suppressed.

  In addition, since the height h2 of the stiffener 18 is also set appropriately, no peeling occurs at the boundary surface 36 between the hard rubber portion 28 and the soft rubber portion 30 in the stiffener 18 when a load is applied, and the durability of the bead portion 12 is maintained. Can also be secured.

Since the 50% elongation modulus of each rubber portion of the stiffener 18 is set appropriately, the stiffener 18 is hardly broken and the durability of the bead portion 12 is ensured.
[Second Embodiment]
In FIG. 2, a buffer rubber layer 32 having a 50% elongation modulus of 0.5 to 2.5 MPa is disposed between the hard rubber portion 28 of the pneumatic tire 200 and the carcass main body portion 14A. The thickness of the buffer rubber layer 32 at the outermost end 28B in the tire radial direction is 0.5 to 10 mm.

  Here, the reason why the lower limit of the 50% elongation modulus of the buffer rubber layer 32 is set to 0.5 MPa is that if it is less than this, the rigidity of the bead portion 12 is low, the falling deformation becomes large, and the durability cannot be secured. The reason why the upper limit is set to 2.5 MPa is that if the upper limit is exceeded, peeling tends to occur at the boundary surface between the hard rubber portion 28 and the carcass ply 14 at the time of load.

  Moreover, the reason why the lower limit of the thickness of the buffer rubber layer 32 is set to 0.5 mm is that if the thickness is less than this, the shear strain between the hard rubber portion 28 and the carcass main body portion 14A increases, and the upper limit is 10 mm. The reason for this is that if it exceeds this, the heat generation of the bead portion 12 becomes large, and the failure tends to occur.

  The buffer rubber layer 32 is not only between the hard rubber portion 28 and the carcass main body portion 14A, but also between the soft rubber portion 30 and the carcass main body portion 14A, for example, approximately 2 with respect to the height h1 of the hard rubber portion 28. It extends to about twice as high.

  When the buffer rubber layer 32 is thick, the position of the hard rubber portion 28 is shifted to the outside in the tire axial direction, and the soft rubber portion 30 is partially thinned by the amount of the hard rubber portion 28 being shifted. Become. As a result, the soft rubber portion 30 and the buffer rubber layer 32 that are softer than the hard rubber portion 28 are in a state where the hard rubber portion 28 is sandwiched from both sides in the substantially tire axial direction, and the durability of the bead portion 12 is improved. Increase.

Since other parts are the same as those in the first embodiment, the same parts are denoted by the same reference numerals in the drawings, and description thereof is omitted.
(Function)
In the pneumatic tire 200 according to the present embodiment, since the shock-absorbing rubber layer 32 is appropriately disposed between the hard rubber portion 28 and the carcass main body portion 14A, the hard rubber portion 28 and the carcass main body portion 14A at the time of load action. Increase in shear strain between the two can be suppressed, and cracking can be prevented.
(Test example)
Under the conditions shown in Table 1, tires according to Examples, Conventional Example 1 and Conventional Example 2 were prototyped and subjected to a bead portion durability test. The tire sizes are all 435 / 45R22.5.

  The maximum width W of the bead core was 20 mm, and the bottom width w of the hard rubber portion was 65% of 13 mm. The 50% elongation modulus of the hard rubber part and the soft rubber part is 5 MPa and 1.0 MPa, respectively. In Table 1, the soft rubber part thickness refers to the thickness of the soft rubber part at the hard rubber part height h1.

  The test was performed at a speed of 10 km / h when the tire had an internal pressure of 900 kPa and a load of 5000 kgf (49 kN) was applied on the drum tester, and after running for 60 minutes at a constant speed, there was no failure in the bead part. The maximum speed that did not break down was measured. The test results are indicated by an index with Conventional Example 1 being 100, and the larger the value, the better the result.

  According to this test example, in the example of the present invention, it was confirmed that the durability of the bead portion was improved by 33% with respect to the conventional example 1. In Conventional Example 2, since the height of the hard rubber portion is too high, the bead portion durability is lower than in Conventional Example 1.

It is sectional drawing which shows the bead part of the pneumatic tire which concerns on 1st Embodiment. It is sectional drawing which shows the bead part of the pneumatic tire which concerns on 2nd Embodiment.

Explanation of symbols

10 side wall portion 12 bead portion 14 carcass ply 14A carcass main body portion 14B winding portion 16 bead core 16A bottom surface 16B top surface 18 stiffener
20 chafers
26 side wall rubber 28 hard rubber part 28A bottom face 28B outermost end in the tire radial direction 30 soft rubber part (rubber part other than hard rubber part)
32 Buffer rubber layer
34 Rubber 36 Boundary surface 38 Boundary surface 100 Pneumatic tire 200 Pneumatic tire A A point on the outermost side in the tire axial direction on the bottom surface of the bead core B A point on the innermost side in the tire axial direction on the top surface of the bead core BL Straight line w Width of the bottom surface of the hard rubber portion W Maximum width of

Claims (5)

A carcass main body disposed between the bead portions between the pair of bead portions and wound around the bead core of the bead portion from the inside to the outside, and the tire shaft of the bead core along the bead core At least one layer of carcass ply having a winding portion wound inward in the tire axial direction from the outermost end in the direction;
A chafer layer disposed outside the carcass ply in the bead portion;
Tire axial direction outer side and the carcass main body portion having a plurality of rubber portions of different hardness and extending from the bead core and / or the winding portion in the tire radial direction outer side of the bead portion, the hardest hardness rubber portion Is disposed adjacent to the bead core and / or the winding portion, and in the tire axial cross section, the width of the bottom surface of the hard rubber portion that contacts the bead core and / or the winding portion is the maximum of the bead core. A stiffener that is a significant 50-100% ,
Of the bead portion, the stiffener disposed in a region surrounded by the stiffener, the entangled portion, the chafer layer, and a sidewall rubber disposed on the tire outer surface of the sidewall portion, With different rubber,
Pneumatic tire having In the tire axial cross section, the bead core is formed in a hexagonal cross section,
Based on a straight line connecting the outermost point in the tire axial direction on the bottom surface of the bead core, which is the inner side in the tire radial direction of the bead core, and the innermost point in the tire axial direction on the upper surface of the bead core, which is the outer side in the tire radial direction of the bead core. The pneumatic tire according to claim 1, wherein a height of the hard rubber portion in a direction perpendicular to the tire is 7.5 to 20% of a tire cross-sectional height. In the tire axial cross section, the bead core is formed in a hexagonal cross section,
Based on a straight line connecting the outermost point in the tire axial direction on the bottom surface of the bead core, which is the inner side in the tire radial direction of the bead core, and the innermost point in the tire axial direction on the upper surface of the bead core, which is the outer side in the tire radial direction of the bead core. The pneumatic tire according to claim 1 or 2, wherein a height of the stiffener in a direction perpendicular to the tire is 25 to 45% of a tire cross-sectional height. The 50% elongation modulus of the hard rubber part is 5.5 to 7.0 MPa,
The pneumatic tire according to any one of claims 1 to 3, wherein a 50% elongation modulus of a rubber portion other than the hard rubber portion in the stiffener is 0.5 to 2.5 MPa. . A buffer rubber layer having a 50% elongation modulus of 0.5 to 2.5 MPa is disposed between the hard rubber portion and the carcass main body portion,
The pneumatic according to any one of claims 1 to 4, wherein a thickness of the buffer rubber layer at an outermost end in the tire radial direction of the hard rubber portion is 0.5 to 10 mm. tire.

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