JP2005313735A - Pneumatic radial tire for heavy load - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic radial tire having high durability which prevents separation of ply end from being generated by moving a ply tension inflection point to a bead toe side. <P>SOLUTION: The pneumatic radial tire is locked by winding a carcass ply 1 from an inside to an outside around a bead core 3 composing of a bead wire and a lamination layer of coated rubber and a rubber filler disposed on the bead core 3. An approximately circular or an approximately elliptic core cover 3a which is composed of a hard rubber of rubber hardness 85 or more at 23°C and encloses circumference is provided on the bead core 3, the rubber filler 4 of rubber hardness 60 to 75 at 23°C is provided on the core cover 3a, and a pad 6 of rubber hardness 60 to 75 at 23°C is provided so as to hold the turnup end of the carcass ply 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heavy-duty pneumatic radial tire having high durability and having a feature in the structure of a bead portion.

  In general, as shown in FIGS. 6 and 7, the pneumatic radial tire has at least one layer of carcass ply 1 having a cord arrangement in the radial direction, and both ends of the carcass ply 1 have bead portions 2 on both sides. In FIG. 2, the bead core 3 and the rubber filler 4 disposed thereon are wound up and locked from the inside to the outside. A plurality of belt layers 8 are formed on the outer side of the carcass ply 1 of the tread portion 7 having the grooves 9.

  In the bead structure at both ends of the carcass ply 1, a bead cover 3a is formed by covering a bead core 3 made of a laminate of a bead wire and a covering rubber with a cover rubber, and a rubber filler 4 is disposed thereon. Further, a pad 6 and a reinforcing chafer 5 are generally provided outside the ply winding.

  In heavy duty pneumatic tires used at high internal pressure and high load, the bead core 3 receives a rotational moment in the process of use and is pulled by a portion where the tension of the carcass ply 1 around the bead is particularly high, and the bead toe Since the part 2a causes a deformation called lifting in the radial direction, the bead part on the rim flange causes a large overhanging deformation to the outside. As a result, the shear strain at the winding end of the carcass ply 1 is increased, which causes separation and cracks, and is a major factor that deteriorates the bead durability.

  In order to improve this, Patent Document 1 discloses that the rubber filler 4 is divided into two layers (4a and 4b) as shown in FIG. 8, and the high hardness rubber 4a is disposed on the bead core side, so that the bead portion 2 is suspended. A heavy-duty pneumatic tire that suppresses upward deformation has been proposed. However, simply applying a high-hardness rubber filler only on the bead core 3 has reduced the effect improvement margin because the ply tension inflection point cannot be moved to a position close to the bead toe side.

Further, Patent Document 2 discloses a pneumatic tire having a structure in which a bead core is covered with a high modulus circular rubber layer and a carcass ply is wound while a lower modulus rubber layer is interposed. . However, this structure eliminates the deformation of the bead core and facilitates the rotational deformation around the bead core, and does not improve the durability of the tire by suppressing the torsional deformation of the bead core. On the other hand, in heavy-duty pneumatic tires, rotational deformation around the bead core should be suppressed as much as possible, and the bead portion fits with the rim, so the positional relationship with the rim, especially the rim flange and the ply end. However, although it becomes very important for the durability improvement of a bead part, said structure does not disclose them.
JP 10-147116 A JP-A-6-239114

  Accordingly, an object of the present invention is to provide a heavy-duty pneumatic radial tire with high durability in which the ply tension inflection point is moved to the bead toe side and separation of the ply end is less likely to occur.

  The above object can be achieved by the present invention as described below.

  That is, the heavy-duty pneumatic radial tire of the present invention is formed by winding and locking a carcass ply from the inside to the outside around a bead core composed of a laminate of a bead wire and a covering rubber and a rubber filler disposed on the bead core. In the heavy-duty pneumatic radial tire, the bead core is made of a hard rubber having a rubber hardness of 85 or more at 23 ° C., and provided with a substantially circular or substantially elliptical core cover that wraps the entire circumference, on the core cover. A rubber filler having a rubber hardness of 60 to 75 at 23 ° C. is provided, and a pad having a rubber hardness of 60 to 75 at 23 ° C. is provided so as to sandwich the winding end of the carcass ply. The physical property values such as rubber hardness in the present invention are specifically values measured by the measuring methods described in the examples.

  Next, the effect of this invention is demonstrated based on Fig.2 (a)-(c). (A) of FIG. 2 has shown position AC of each part around the bead part of a tire. FIG. 2 (b) shows the distribution of the ply tension when air is introduced (during inflation) and when a load is further applied to a portion where the tire is not in contact with the ground. FIG. 2 (c) shows the ply tension distribution of the tire ground contact portion corresponding to this. In this graph, “ply periphery” indicates a distance along the ply from the equator plane, and the ply tension is indicated by a relative value (the same applies to FIG. 3).

  Generally, as shown in FIGS. 2A to 2C, the ply tension distribution has a maximum value at a point A diagonally upward from the bead core to the inner surface side, and a minimum value at a B portion below the bead core. The maximum value is again shown at point C next to the bead core on the ply winding side. There is a clear difference between the total ply tension between AB and the total ply tension between BC, and the former is larger. For this reason, the bead core receives a rotational moment toward the inner surface side, the bead toe portion is lifted in the radial direction of the inner surface, and the bead portion on the rim flange projects outward and causes deformation. When used under high internal pressure and high load, these actions cause permanent deformation.

  According to the bead structure of the present invention, the bead core is provided with the substantially circular or substantially elliptical core cover that is made of hard rubber and wraps the entire circumference, so that the effect of suppressing the twist of the bead core is enhanced, as shown in FIG. FEM analysis results comparing the example and the comparative example), the ply tension maximum value of the A part is reduced, the point moves to the B part side, and the ply tension of the B part and the C part increases. For this reason, the difference between the total ply tension between AB and the total ply tension between BC is reduced, the rotational moment applied to the inner surface of the bead core is reduced, and the bead toe is lifted and the outer bulge deformation on the rim flange is suppressed. As a result, the shear strain at the ply-winding end can be reduced and the bead durability can be improved. The analysis data (FEM analysis result) that supports this is shown in FIG. 4, and the rubber filler made of soft rubber and the pad greatly contribute to the above-described effects.

  In the present invention, in the standard state after assembling the rim, the positional relationship between the core cover and the rim with respect to the height of the upper end of the rim flange is such that the height of the winding end is H1, and the height of the upper end of the core cover is When H2 is the height of the contact upper end with the ply inside the core cover and H3 and the height of the contact upper end with the ply outside the core cover is H4, H2 ≦ 1 / 2H1 and H2> H3 ≧ H4. It is preferable that it is satisfied. By satisfying such a condition, the lifting of the bead toe can be more reliably suppressed, and the shear strain at the ply winding-up end can be further reduced.

  In the above, the rubber hardness of the core cover is 85 or more at 23 ° C., and the dynamic elastic modulus E ′ is 20 Mpa or more at 23 ° C., and the rubber hardness and dynamic elastic modulus E at 80 ° C. It is preferable that “and” be within a reduction rate of 25%, and the dynamic elastic modulus E ′ of the rubber filler and the pad is 3 to 10 MPa at 23 ° C.

  According to this configuration, the rubber hardness and the dynamic elastic modulus E ′ of the core cover are sufficiently maintained even at high temperatures even in an actual running state, so that the separation of the ply end can be made less likely to occur due to the above-described action. . At that time, it is also important that the physical properties of each part are defined not only by the rubber hardness but also by the dynamic elastic modulus E ′.

  When the horizontal width from the specified position of the height H2 to the specified position of the height H3 is W1, and the horizontal width from the specified position of the height H2 to the specified position of the height H4 is W2, W1 <W2 It is preferable to satisfy. Thereby, the ply tension inflection point can be effectively moved to the bead toe side.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of an essential part showing an example of a heavy duty pneumatic radial tire of the present invention.

  As shown in FIG. 1, the heavy-duty pneumatic radial tire of the present invention includes a carcass 1 made of one or more plies in which steel cords, high-strength organic fiber cords, and the like are arranged in the tire radial direction. A carcass ply 1 is wound up from the inside to the outside and locked around a bead core 3 made of a laminate of a bead wire and a covering rubber and a rubber filler 4 disposed on the bead core 3. For example, the bead core 3 is formed by sequentially laminating and winding bead wires having coated rubber.

  The bead core 3 is provided with a substantially circular or elliptical core cover 3a that wraps around the entire circumference. The core cover 3a is made of a hard rubber having a rubber hardness at 23 ° C. (hardness according to JIS K6301; the same shall apply hereinafter) of 85 or more, and this hard rubber preferably has a hardness of 90 or more. If the hardness of the hard rubber is less than 85, the twist suppressing effect of the bead core 3 is insufficient.

  In the present invention, the rubber hardness of the core cover 3a is 85 or more at 23 ° C., and the dynamic elastic modulus E ′ is 20 Mpa or more at 23 ° C., whereas the rubber hardness and dynamic elastic modulus at 80 ° C. E ′ is preferably within 25% of each reduction rate. If each reduction rate exceeds 25%, the rubber hardness and dynamic elastic modulus E ′ of the core cover 3a will decrease at high temperatures in the actual running state, so that bead toe lifting and tension deformation on the rim flange are suppressed. There is a tendency that the shearing force of the ply-winding end 1a cannot be reduced because it cannot be exhausted.

  A rubber filler 4 having a rubber hardness of 60 to 75 at 23 ° C. is provided on the core cover 3a, and the rubber filler 4 preferably has a hardness of 60 to 70. When the hardness of the rubber filler 4 is less than 60, the rigidity of the entire bead portion 2 is lowered and the original function is hardly exhibited. When the hardness of the rubber filler 4 exceeds 75, the stress concentration on the ply-winding end 1a Tend to be larger. For the same reason, the dynamic elastic modulus E ′ of the rubber filler 4 is preferably 3 to 10 MPa at 23 ° C.

  The rubber filler 4 has a substantially deformed triangular cross section extending in the tire radial direction (however, the base is arcuate). The winding end 1 a of the carcass ply 1 is preferably located in the middle of the oblique side of the rubber filler 4.

  Further, a pad 6 having a rubber hardness of 60 to 75 at 23 ° C. is provided so as to sandwich the winding end 1 a of the carcass ply 1 together with the rubber filler 4. The pad 6 is preferably made of the same rubber material as the rubber filler 4. This is because if a rubber material having a difference in hardness is used at the rolled-up end 1a of the carcass ply 1, there is a possibility that it becomes a starting point of separation. Therefore, the dynamic elastic modulus E ′ of the pad 6 is also preferably 3 to 10 MPa at 23 ° C.

  The bead wire covering rubber forming the bead core 3 preferably has a minimum volume that can be laminated. Thus, the effect of the combination with the core cover 3a is further increased by forming a compact bead core and increasing its rigidity.

  The bead core 3 is normally filled with a bead wire having a circular cross section in a close-packed manner, and the cross-sectional shape of the aggregate is a hexagon. This prevents the cross-sectional shape from being deformed by an external force. Further, the bead core 3 is arranged so that the bottom side of the hexagonal bead core 3 is substantially parallel to the rim 10.

  A bead portion reinforcing layer 5 called a chafer having a steel cord or an organic fiber cord is provided on the outer surface of the rolled-up bottom portion of the carcass ply 1. In the illustrated example, the case where the bead portion reinforcing layer 5 is composed of two reinforcing layers having organic fiber cords is shown. Further, the lower side of the pad 6 has a structure in which it enters between the rolled-up portion of the carcass ply 1 and the bead portion reinforcing layer 5.

  In the present invention, in the standard state after assembling the rim, the positional relationship between the core cover 3a and the rim 10 with respect to the height of the upper end of the rim flange 10a is as follows. Is H2, the height of the contact upper end with the ply 1 inside the core cover 3a is H3, and the height of the contact upper end with the ply 1 outside the core cover 3a is H4, H2 ≦ 1 / 2H1 and H2 It is preferable that> H3 ≧ H4 is satisfied. The bead structure shown in FIG. 1 shows an example in which the height H2 is about half of the height H1, and the core cover 3a has a cross-sectional shape close to a substantially circular shape.

  If H2 ≦ 1 / 2H1 is not satisfied, the shear strain of the ply-winding end 1a increases and the possibility of causing separation tends to increase. If H2> H3 ≧ H4 is not satisfied, the ply tension inflection point is increased. Since it cannot move to the bead core side, there is a tendency that bead lifting cannot be suppressed.

  Further, when the horizontal width from the specified position of the height H2 to the specified position of the height H3 is W1, and the horizontal width from the specified position of the height H2 to the specified position of the height H4 is W2, W1 <W2 is satisfied. preferable. If W1 <W2 is not satisfied, the ply tension inflection point cannot be moved to the bead core side, so that there is a tendency that bead lifting cannot be suppressed.

  The heavy-duty pneumatic radial tire of the present invention is the same as the conventionally known tire except for the structure around the bead portion, and is the same as that shown in FIG. One or more belt layers 8 are arranged on the outer side of the carcass ply 1 of the tire tread portion 7 as in the prior art, and further a belt reinforcing layer is arranged if necessary. A tread pattern having a plurality of main grooves 9 in the tire circumferential direction is formed on the surface. An inner liner is usually provided on the inner side of the carcass ply 1, and sidewall rubber is provided on the outer side.

  Heavy duty pneumatic tires are used for vehicles with relatively heavy gross vehicle weight such as trucks and buses.

[Other Embodiments]
(1) In the above-described embodiment, the example in which the height H2 is about half of the height H1 (FIG. 5B) is shown. However, as shown in FIG. 5A and FIG. Then, it is possible to change the relationship between the height H2 and the height H1. Along with this, the core cover 3a becomes nearly elliptical, and H2> H3 ≧ H4 in FIG. 5B satisfies H2> H4 ≧ H3 as shown in FIG. 5C. There is a case.

  (2) In the above-described embodiment, an example in which the cross-sectional shape of the core cover is an arc or a curve has been shown. However, in the present invention, the cross-sectional shape of the core cover may include a single or a plurality of straight lines. These are also included in the substantially circular or elliptical core cover according to the present invention.

  (3) In the above-described embodiment, an example in which a bead core having a circular cross section is closely packed and a hexagonal bead core is used has been described. However, in the present invention, the bead core has a polygonal shape having various cross sections. It may be. In that case, it is possible to use polygonal bead wires having various cross sections.

  Examples and the like specifically showing the configuration and effects of the present invention will be described below. In addition, the evaluation item in an Example etc. measured as follows.

(hardness)
Measured according to JIS K6253 type A durometer hardness test.

(Dynamic elastic modulus)
After vulcanization at 150 ° C. for 30 minutes, a sample having a width of 5 mm, a thickness of 1 mm, and a length of 20 mm was prepared, and using a spectrometer, an initial strain of 5%, a dynamic strain of ± 1%, a frequency of 50 Hz, and a temperature of 23 ° C. And 80 ° C.

(1) Bead endurance test As a heavy load endurance test, the vehicle traveled to a failure at a tire internal pressure of 900 kPa, a load of 210% (heavy load condition) and 25 km / h, and the travel distance and failure mode were evaluated.

(2) Bead part exothermic temperature The bead part temperature was measured after driving | running | working for 5 hours on the same test conditions as said (1). The measurement location was the back surface of the carcass ply on a line perpendicular to the carcass line from the winding end of the carcass ply.

(3) Bead toe lifting amount The cross-sectional state at the time of a new article and the sectional state after completion of the bead durability test were compared, and the parallel distance from the bead base to the bead toe was defined as the lifting amount.

Comparative Example 1 (conventional bead structure)
In the bead structure shown in FIG. 7, a heavy-duty pneumatic radial tire (size 11R22.5 14PR) having a conventional bead structure made of a single rubber having a hardness of 70 is prepared as a bead portion reinforcement layer of nylon cord, The above evaluation was performed. The tires of the examples and comparative examples all have the same conditions for the structures other than the bead part such as a belt structure.

Comparative Example 2 (two-layer bead filler structure)
In the bead structure shown in FIG. 7, the bead portion reinforcing layer of the nylon cord, the hardness of the rubber filler is soft 70 and hard 90, the ratio of the hard rubber filler is 31%, and the inner interface point between the hard rubber filler and the soft rubber filler Is a heavy-duty pneumatic radial tire (size 11R22.) Having a height of 7.5 mm from the upper end of contact with the ply inside the core cover and an outer interface point between the hard rubber filler and the soft rubber filler being 5 mm from the upper end of the rim flange. 5 14PR) was prepared and evaluated as described above.

Example 1
In the bead structure shown in FIG. 1, a nylon cord bead portion reinforcing layer is used, the core cover has a hardness (23 ° C.) of 90, a hardness (80 ° C.) of 85, a dynamic elastic modulus E ′ (23 ° C.) of 25 MPa. The elastic modulus E ′ (80 ° C.) is 22 Mpa, the rubber filler hardness (23 ° C.) is 65, the dynamic elastic modulus E ′ (23 ° C.) is 7 Mpa, the pad hardness (23 ° C.) is 65, dynamic. The elastic modulus E ′ (23 ° C.) was 7 Mpa, the height H1 was 22 mm, the height H2 was 11 mm, the height H3 was 6 mm, the height H4 was 4 mm, the horizontal width W1 was 8 mm, and the horizontal width W2 was 10 mm. A heavy-duty pneumatic radial tire (size 11R22.5 14PR) was produced and evaluated as described above.

  The results are shown in Table 1.

表１の結果が示すように、実施例１では比較例１（従来品）と比較して、ビードトウ吊り上り量が小さく、ビード部の発熱も改善され、耐久性も大幅に改善された。これに対して、２層ビードフィラー構造を有する比較例２では、ビード部の発熱は改善されるものの、ビードトウ吊り上り量が大きく、耐久性は不十分となった。

As shown in the results of Table 1, in Example 1, the amount of bead toe lifted was small, the heat generation at the bead portion was improved, and the durability was greatly improved as compared with Comparative Example 1 (conventional product). On the other hand, in Comparative Example 2 having a two-layer bead filler structure, although heat generation in the bead portion was improved, the amount of bead toe lifted was large, and durability was insufficient.

Reference example 1
In Example 1, as shown in FIG. 5A, the upper end height H2 of the core cover is made smaller, the height H2 is 5.5 mm, the height H3 is 3 mm, the height H4 is 2 mm, and the horizontal width. Except that W1 was set to 8 mm and the horizontal width W2 was set to 10 mm, a heavy-duty pneumatic radial tire was produced in the same manner as in Example 1, and the above evaluation was performed. As a result, the lifting amount of the bead toe is 2.0 mm, and compared with the result of Example 1, the shear strain at the ply winding end is reduced by 5%, the heat generation at the bead part is increased by about 5 ° C., and the durability is It was in the direction of getting worse.

Reference example 2
In the first embodiment, as shown in FIG. 5C, the upper end height H2 of the core cover is increased, the height H2 is 22 mm, the height H3 is 18 mm, the height H4 is 16 mm, and the horizontal width W1 is set. A heavy-duty pneumatic radial tire was produced in the same manner as in Example 1 except that the horizontal width W2 was 6 mm, and the above evaluation was performed. As a result, the lifting amount of the bead toe is 0.9 mm, and compared with the result of Example 1, the shear strain at the ply winding end is increased by 35%, and the heat generation at the bead part is equivalent, but the durability is deteriorated. It was a direction to do.

Cross-sectional view of relevant parts showing an example of a heavy-duty pneumatic radial tire of the present invention The graph which shows the ply tension | tensile_strength of each part for demonstrating the subject of this invention The graph which shows the ply tension | tensile_strength of each part for demonstrating the effect of this invention Main part explanatory drawing for demonstrating the effect of this invention Sectional drawing of the principal part which shows the other example of the pneumatic radial tire for heavy loads of this invention A meridian cross-sectional view showing an example of a heavy-duty pneumatic radial tire of the present invention Cross-sectional view of relevant parts showing an example of a conventional heavy-duty pneumatic radial tire Cross-sectional view of relevant parts showing another example of a conventional heavy-duty pneumatic radial tire

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Carcass ply 2 Bead part 3 Bead core 3a Core cover 4 Rubber filler 6 Pad 10 Rim 11 Rim flange

Claims (4)

In a heavy-duty pneumatic radial tire in which a carcass ply is wound from the inside to the outside and locked around a bead core made of a laminate of a bead wire and a covering rubber and a rubber filler disposed on the bead core.
The bead core is made of a hard rubber having a rubber hardness of 85 or more at 23 ° C., and is provided with a substantially circular or substantially elliptical core cover that wraps the entire circumference, and has a rubber hardness of 60 to 23 at 23 ° C. on the core cover. A heavy-duty pneumatic radial tire characterized in that 75 rubber fillers are provided and pads with rubber hardness of 60 to 75 at 23 ° C. are provided so as to sandwich the rolled-up end of the carcass ply.   In the standard state after assembling the rim, the positional relationship between the core cover and the rim with respect to the height of the upper end of the rim flange is as follows: the height of the winding end is H1, the height of the upper end of the core cover is H2, and the core cover When the height of the contact upper end with the inner ply is H3 and the height of the contact upper end with the core ply is H4, H2 ≦ 1 / 2H1 and H2> H3 ≧ H4 are satisfied. The heavy-duty pneumatic radial tire according to claim 1.   The rubber hardness of the core cover is 85 or more at 23 ° C. and the dynamic elastic modulus E ′ is 20 Mpa or more at 23 ° C., and the rubber hardness and dynamic elastic modulus E ′ at 80 ° C. 3. The heavy-duty pneumatic radial tire according to claim 1, wherein the rate of decrease is within 25%, and the dynamic elastic modulus E ′ of the rubber filler and the pad is 3 to 10 MPa at 23 ° C. 4.   When the horizontal width from the specified position of the height H2 to the specified position of the height H3 is W1, and the horizontal width from the specified position of the height H2 to the specified position of the height H4 is W2, W1 <W2 is satisfied. The heavy-duty pneumatic radial tire according to claim 2.

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