JP3964861B2 - Heavy duty tire - Google Patents

Description

  The present invention relates to a heavy-duty tire with improved bead durability while reducing weight by improving the structure of a ply turn-up portion of a carcass.

  In recent years, as shown in FIG. 6, the carcass ply turn-up portion a is wound substantially once around the bead core b, and the end portion a1 of the ply turn-up portion a along the radial upper surface bs of the bead core b is Tires having a bead structure (hereinafter sometimes referred to as a bead wind structure) sandwiched between b and bead apex rubber c have been proposed (see, for example, Patent Documents 1 and 2).

Japanese Patent Laid-Open No. 11-32244 Japanese Patent Laid-Open No. 2000-21916

  In this structure, the ply turn-up portion a is interrupted around the bead core b, so that stress at the time of tire deformation does not act on the end portion a1, and therefore damage such as cord loose starting from the end portion a1 is caused. It can be effectively suppressed. Moreover, since the length of the ply turn-up portion a is small, there is an advantage that the weight of the tire can be reduced. The blow-through phenomenon of the carcass ply is prevented by the end portion a1 being sandwiched and locked between the bead core b and the bead apex rubber c.

  However, in this structure, since the length of the end portion a1 is small and the degree of bending is large, a strong bending back (so-called spring back) occurs in the end portion a1 in, for example, a raw tire molding process. Further, molding defects such as air residue are likely to occur, such as a cavity formed between the bead core b.

  Therefore, the present inventor previously inserted a small-height filling rubber between the end portion a1 and the bead core b and dared to separate the end portion a1 from the bead core b to reduce the degree of bending. Proposed to suppress. However, at this time, there is a problem that it is difficult to maintain the excellent bead durability of the bead wind structure, for example, the tip of the end portion a1 is easily damaged.

  Therefore, in the present invention, when the height of the end portion of the end portion of the carcass ply is regulated, or the end portion is separated from the bead core on the basis of regulating the tensile strength of the carcass cord and the number of driving in the ply turn-up portion. Another object of the present invention is to provide a heavy duty tire that can maintain the excellent bead durability of the bead wind structure.

In order to achieve the above object, the invention of claim 1 of the present application is folded back from the inner side in the tire axial direction around the bead core to the ply main body part extending from the tread part through the sidewall part to the bead core of the bead part. A heavy-duty tire having a carcass ply provided with a series of ply turn-up parts,
The ply turn-up part comprises a main part that bends along the inner surface in the tire axial direction of the bead core, a lower surface in the radial direction, and an outer side surface in the tire axial direction, and a winding part that continues to the main part and extends away from the bead core.
The winding portion has an angle θ smaller than 90 ° with respect to the upper surface in the radial direction of the bead core and is inclined toward the ply main body portion, and extends.
The radial height L1 from the bead base line at the tip of the winding part is 0.07 to 0 in a ratio L1 / L0 to the radial height L0 from the bead base line of the inner surface of the ply body at the tire equator. .12 ,
Furthermore, between the bead core, the ply folded portion, and the ply main body portion, a sulfur blending amount of 7 to 12 phr, a complex elastic modulus Ea * of 2 to 25 Mpa, and a filled rubber surrounding the bead core is disposed. It is characterized by.

In the invention of claim 2, a series of ply turn-up portions that are turned from the inner side to the outer side in the tire axial direction around the bead core are provided in the ply main body portion that extends from the tread portion to the side wall portion and reaches the bead core of the bead portion. A heavy duty tire with a carcass ply,
The ply turn-up part comprises a main part that bends along the inner surface in the tire axial direction of the bead core, a lower surface in the radial direction, and an outer side surface in the tire axial direction, and a winding part that continues to the main part and extends away from the bead core.
The winding portion has an angle θ smaller than 90 ° with respect to the upper surface in the radial direction of the bead core and is inclined toward the ply main body portion, and extends.
The bead core has a tensile strength T0 of 150 to 270 kN,
Moreover, in the ply turn-up portion, the tensile strength T1 per one carcass cord is 0.0045 to 0.0086 times the tensile strength T0 of the bead core, and the number of driven carcass cords is 30 to 45/5 cm. ,
Furthermore, between the bead core, the ply folded portion, and the ply main body portion, a sulfur blending amount of 7 to 12 phr, a complex elastic modulus Ea * of 2 to 25 Mpa, and a filled rubber surrounding the bead core is disposed. It is characterized by.

  In this specification, unless otherwise specified, the dimensions and the like of each part of the tire are values specified in a 50 kPa filling state in which the tire is assembled on a regular rim and filled with an internal pressure of 50 kPa. The “regular rim” is a rim determined for each tire in the standard system including the standard on which the tire is based, for example, a standard rim for JATMA, “Design Rim” for TRA, or ETRTO means "Measuring Rim".

  Since the present invention is configured as described above, even when the ply folded portion of the carcass is separated from the top surface of the bead core, damage at the tip can be suppressed, and the bead wind structure has excellent properties while suppressing molding defects. The bead durability can be maintained.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing a 50 kPa filling state of the heavy duty tire of the first invention of the present application, and FIGS. 2 and 3 are cross-sectional views showing an enlarged bead portion thereof.

  In FIG. 1, a heavy load tire 1 is disposed on a carcass 6 that extends from a tread portion 2 to a bead core 5 of a bead portion 4 through a sidewall portion 3, and on the radially outer side of the carcass 6 and on the inner side of the tread portion 2. Belt layer 7.

  The belt layer 7 is composed of two or more belt plies using steel belt cords (usually three or more in the case of heavy duty tires). The first innermost belt ply 7A in the radial direction arranged at an angle of 60 ± 15 °, and the second to fourth belt plies 7B to 7D arranged at a small angle of 10 to 35 ° with respect to the tire circumferential direction, for example. This is an example of a four-sheet structure. The belt plies 7 </ b> A to 7 </ b> D are provided with one or more places where the belt cords cross each other between the plies, and are superposed to enhance belt rigidity and reinforce the tread portion 2 with a tagging effect.

  The carcass 6 is formed of a single carcass ply 6A in which steel carcass cords are arranged at an angle of 70 to 90 ° with respect to the tire circumferential direction. The carcass ply 6 </ b> A includes a series of ply folding portions 6 b that are folded from the inner side to the outer side in the tire axial direction around the bead core 5 on both sides of the ply main body portion 6 a that extends between the bead cores 5 and 5.

  As shown in FIG. 2, the bead core 5 is, for example, a ring-shaped body formed by winding steel bead wires in multiple stages and multi-rows. In this example, a flat hexagonal shape having a horizontally long cross section is illustrated. The bead core 5 has a radially lower surface SL substantially parallel to the rim sheet J1 of the regular rim J, thereby increasing the fitting force with the rim over a wide range. In this example, the case where the regular rim J is a 15 ° tapered rim for tubeless is illustrated, and therefore, the radially lower surface SL and the upper surface SU of the bead core 5 are approximately 15 ° with respect to the tire axial line. It is inclined at an angle. As a cross-sectional shape of the bead core 5, a regular hexagonal shape and a rectangular shape can be adopted as necessary.

  Next, in the tire of the present application, the ply turn-up portion 6b of the carcass 6 is wound around the peripheral surface of the bead core 5 and the end portion is sandwiched between the bead apex rubber 8 and locked so-called bead wind. Composed of structure.

  Specifically, the ply turn-up portion 6b includes a main portion 10 that bends along a tire axial direction inner side surface Si, a radial direction lower surface SL, and a tire axial direction outer surface So of the bead core 5, and the bead core connected to the main portion 10. 5 and a winding part 11 extending away from the upper surface SU in the radial direction.

  At this time, the winding part 11 has an angle θ smaller than 90 °, preferably 75 ° or less, with respect to the radial upper surface SU of the bead core 5 and extends toward the ply body 6a. The winding portion 11 means a portion radially outward from the extension line of the radial upper surface SU, and in this example, a bent line shape that is bent in a substantially square shape is illustrated, It can also be formed in a curved line shape such as an arc shape.

  In the bead core 5, as shown in an exaggerated manner in FIG. 4, the radial upper surface SU may be non-planar, for example, the bead wires 40 are not aligned in a straight line but are arranged up and down. In such a case, the radial upper surface SU has a tangent line K that contacts the bead wire 40o located on the radially outermost side and the bead wire 40i located on the radially innermost side in the bead wire row (upper row) forming the upper surface SU. Define as When the winding part 11 is a curved line or a curved line, the angle θ is an extension line of the radial upper surface SU (if the radial upper surface SU is non-planar). A straight line connecting the lower end Pb of the winding part 11 intersecting the tangent K) and the tip Pa of the winding part 11 is defined as an angle with respect to the radial upper surface SU (or the tangent K when the radial upper surface SU is non-planar). .

  In the first aspect of the invention, the radial height L1 from the bead base line BL of the tip Pa of the winding portion 11 is the radial height from the bead base line BL of the inner surface of the ply body portion 6a at the tire equator Co. The ratio L1 / L0 with respect to L0 (shown in FIG. 1) is restricted within a range of 0.07 to 0.12, and a filling rubber 12 is disposed between the bead core 5 and the winding part 11.

  In this example, the filling rubber 12 includes a base portion 12A having a substantially triangular cross section disposed between the radial upper surface SU of the bead core 5, the winding portion 11 and the ply body portion 6a, and the bead core 5. The tire axial direction inner side surface Si, the radial direction lower surface SL, the tire axial direction outer side surface So, and a relatively thin film-like sub-portion 12B disposed between the main portion 10 of the ply turn-up portion 6b. The preferred case is illustrated. The filling rubber 12 can also be formed only from the base 12A.

  Thus, the filling rubber 12 having the base portion 12A having a substantially triangular cross section is provided, and the height L1 of the winding portion 11 is secured to 0.07 times or more the height L0 of the ply body portion 6a. The degree of bending of the winding part 11 can be reduced, the spring back of the winding part 11 can be suppressed, and the occurrence of molding defects such as air residue can be suppressed. If the height L1 is less than 0.07 times, the springback cannot be sufficiently suppressed, and the impact applied to the tip Pa at the time of grounding is increased, so that the tip Pa is likely to be damaged. On the contrary, even if the height L1 exceeds 0.12 of the height L0 of the ply main body 6a, stress at the time of tire deformation tends to act on the tip Pa, so that the tip Pa is damaged. In any case, the excellent bead durability of the bead wind structure cannot be maintained.

  From such a viewpoint, it is preferable that the distance La from the radial upper surface SU of the bead core 5 at the tip Pa of the winding portion 11 is in the range of 5 to 12 mm. In addition, at the tip Pa, it is also preferable to secure a distance Lb of 1-5 mm with the ply main body portion 6a. When the tip is less than 1 mm, the tip of the carcass cord and the ply are caused by variations during tire formation or tire deformation during travel. If the carcass cord of the main body 6a comes into contact with and rubs against each other, it is easy to cause damage to the cord such as fretting. On the contrary, if it exceeds 5 mm, the locking force of the winding portion 11 is reduced, which is disadvantageous for blow-through.

  In this example, in order to further relieve the stress and impact acting on the tip Pa, the filled rubber 12 is formed of a low elastic rubber having a complex elastic modulus Ea * of 2 to 25 Mpa and excellent in impact mitigating effect, and A substantially U-shaped bead reinforcing layer 15 is provided on the bead portion 4.

  The value of the complex elastic modulus is a value measured using a viscoelastic spectrometer under the conditions of a temperature of 70 ° C., a frequency of 10 Hz, and a dynamic strain rate of 2%. If it exceeds 25 Mpa, the flexibility is inferior and stress and impact are alleviated. The effect is insufficient.

  The bead reinforcing layer 15 is made of a cord ply in which steel cords are arranged at an angle of, for example, 10 ° to 40 ° with respect to the tire circumferential direction line, and as shown in FIG. A curved portion 15A that passes radially inward along the tire portion 15A, and an outer piece 15o that is inclined outwardly in the tire axial direction and radially outwardly away from the main portion 10 outside the curved portion 15A in the tire axial direction. And an inner piece 15i extending along the inner side surface in the tire axial direction of the ply main body portion 6a on the inner side in the tire axial direction of the curved portion 15A.

  The inner piece 15i serves to reinforce the carcass ply 6A when the load is applied and reduces the distortion at the tip Pa. Therefore, the radius of the inner piece 15i from the bead base line BL is reduced. The direction height Hi is preferably 10 mm or more, more preferably 25 mm or more. However, if it exceeds 60 mm, damage due to stress concentration tends to occur at the tip of the inner piece 15i.

  Further, the outer piece 15o has a role of suppressing damage peculiar to the bead wind structure such as a cord loose in the carcass cord at the inner end position Q of the bead core 5 in the tire axial direction. The radial height Ho from the BL is preferably 20 mm or more.

  The damage unique to the bead wind structure is that the bead wind structure has a relatively large fall of the carcass ply 6A when a load is applied, and the rubber in the bead heats the brake pads on the vehicle side depending on the driving conditions. This causes excessive temperature rise and heat softening. That is, when a load is applied, the rubber in the bead softened by heat tends to move to the bead toe side by being pressed between the flange, and at this time, the ply turn-up portion 6b moves while being dragged by the movement. It is presumed that a large shear strain is generated between the carcass ply 6A and the bead core 5 at the position Q to induce cord looseness.

  The outer piece 15o exhibits a function as a shielding plate when the radial height Ho is increased to 20 mm or more, and reduces the rubber movement F (indicated by a one-dot chain line in FIG. 3) toward the bead toe side by a shielding effect. sell. As a result, it is possible to reduce the shear strain between the carcass ply 6A and the bead core 5 at the position Q and to suppress the cord looseness. However, if the radial height Ho exceeds 40 mm, damage due to stress concentration tends to occur at the tip of the outer piece 15o.

  If the complex elastic modulus Ea * of the filling rubber 12 is too soft, less than 2 Mpa, the ply turn-up portion 6b is easily dragged by the rubber movement F, which is disadvantageous for damage at the position Q. Therefore, the lower limit value of the complex elastic modulus Ea * is preferably set to be greater than 3 Mpa, and more preferably greater than 5 Mpa. At this time, it is preferable to use a high-sulfur compounded rubber having a sulfur compounding amount of 4.0 phr or more as the filling rubber 12. This is because when the complex elastic modulus Ea in the above range is obtained by blending sulfur in an amount of 4.0 phr or more, the rubber is hard to be softened. Accordingly, even when the bead temperature rises excessively due to heat from the brake pad or the like, the movement of the ply turn-up portion 6b is not promoted by the thermal softening of the filling rubber 12, and the effect of suppressing the cord looseness can be maintained. It is. In addition, the adhesive strength between rubber and cord is improved. If the amount of sulfur exceeds 12 phr, the vulcanization will be too fast and the rubber will be easily burned, so that the adhesiveness with adjacent members may be reduced. Therefore, the blending amount of sulfur is preferably in the range of 4.0 to 12 phr, the lower limit is more than 7.0 phr, and the upper limit is more preferably 10 phr or less. In a normal rubber composition for tires, sulfur is blended at 1.0 to 3.5 phr.

  In this example, the bead apex rubber 8 includes a lower apex rubber portion 8A having a complex elastic modulus Eb1 * of 35 to 60 Mpa, a radially elastic outer adjacent complex elastic modulus Eb2 *, and a filled rubber. 12 having a two-layer structure with the upper apex rubber portion 8B smaller than the complex elastic modulus Eb * of the lower apex rubber portion 8A and lower than the complex elastic modulus Ea * of 12. In the example, the height h01 in the radial direction from the bead base line BL of the lower apex rubber part 8A is set in the range of 40 to 60% of the total height h0 of the bead apex rubber 8, so that both riding comfort and steering stability are achieved. I am trying.

Next, the tire of the second invention of the present application will be described.
In the tire of the second aspect of the invention, the tire of the first aspect of the invention regulates the radial height L1 from the bead base line BL of the tip Pa of the winding portion 11, whereas the ply turn-up portion 6b The tensile strength T1 per one and the number of driving carcass cords are restricted, and the damage of the winding part 11 is suppressed.

  Specifically, in the ply turn-up portion 6b, the tensile strength T1 per carcass cord is 0.0045 to 0.0086 times the tensile strength T0 of the bead core 5, and the number of carcass cords to be driven is 30 to 45. / 5cm is regulated.

  This is because if the number of driven carcass cords in the ply turn-up portion 6b, particularly the winding-up portion 11, is less than 30 / 5cm, the rubber between the cords in the winding-up process becomes more stretched and thinned, and the cord is sufficiently covered. This is because, as a result, the resistance to stress and impact is reduced, and the wound portion 11 is likely to be damaged. Therefore, in the first invention, the stress and impact itself are reduced and the damage at the winding part 11 is suppressed, whereas in the second invention, the number of driving is increased to 30/5 cm or more, and the resistance to stress and impact is increased. By raising, the damage in the winding part 11 is suppressed. If the number of driven wires exceeds 45/5 cm, the cord end is likely to be disturbed in the winding process, which causes a similar decrease in stress and impact resistance.

  At this time, it is important that the tensile strength T1 per carcass cord is 0.0045 times or more the tensile strength T0 of the bead core 5, and if it is less than 0.0045 times, the necessary carcass strength is secured. This tends to cause damage to the carcass such as a broken cord. On the other hand, when it exceeds 0.0086 times, not only the quality becomes excessive, but also the cord becomes rigid and the spring back becomes large in the raw tire molding process, which is disadvantageous for suppressing molding defects. In addition, the tensile strength T0 of the bead core is set in the range of 150 to 270 kN from the viewpoint of the rim assembly property and the fitting force with the rim.

  The tensile strengths T1 and T0 were measured at a tensile speed of 5 cm / min in accordance with the tensile test of the cutting load and the total elongation at the time of cutting (section 6.4) in JIS G3510 “steel tire cord test method”, respectively. This is the maximum load required to cut the test piece.

  In the tire of the second invention, as in the tire of the first invention, the distance La from the radial upper surface SU of the bead core 5 of the tip Pa is 5 to 12 mm, and the distance of the tip Pa from the ply main body portion 6a. The structure described in the first invention other than the radial height L1 can be appropriately employed such that Lb is preferably 1 to 5 mm.

  For heavy duty tires, it is more preferable for the bead durability that the features of the first and second inventions are duplicated.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

  A heavy load tire (11R22.5) according to the first invention based on the specifications shown in Table 1 and the structure shown in FIG. 1 and a heavy load tire (11R22.5) according to the second invention based on the specifications shown in Table 2 are respectively prototyped. In addition, the bead durability of each sample tire was measured and compared with each other. Specifications other than those listed in the table are the same.

  As shown in FIG. 5, the conventional example has a structure in which the ply folded portion of the carcass is wound up along the outer surface of the bead apex rubber, and the height h2 of the ply folded portion from the bead base line is 65 mm.

(1) Bead durability;
<I> General bead durability:
Using a drum tester, the tire was run at a speed of 30 km / h under the conditions of a rim (7.50 × 22.5), internal pressure (700 kPa), and longitudinal load (27.25 kN × 3). The running time until damage occurred is shown as an index with the conventional example being 100. The greater the value, the better the durability.
<Ii> Thermal bead durability:
A bead durability test similar to that described above was carried out with the rim heated to 130 ° C., and the running time until the bead portion was damaged was shown as an index with the conventional example being 100. The greater the value, the better the durability. In the thermal bead durability, damage is generated starting from the cord loose at the inner end of the bead core in the tire axial direction.

  As shown in the table, it can be confirmed that the example products are improved in both general bead durability and thermal bead durability.

It is sectional drawing which shows one Example of the tire for heavy loads of this invention. It is sectional drawing which expands and shows the bead part. It is sectional drawing which expands and shows the bead part. It is a diagram explaining the definition of an upper surface when a radial direction upper surface makes a non-planar surface. It is sectional drawing which shows the bead structure of the prior art example of Table 1. It is sectional drawing explaining the prior art of a bead wind structure.

Explanation of symbols

2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6A Carcass ply 6a Ply body part 6b Ply turn-up part 10 Main part 11 Winding part

Claims (3)

A heavy duty tire comprising a carcass ply in which a ply folding part is provided in a series of ply folding parts that are folded from the inner side to the outer side in the tire axial direction around the bead core on the ply body part extending from the tread part to the bead core through the sidewall part. Because
The ply turn-up part comprises a main part that bends along the inner surface in the tire axial direction of the bead core, a lower surface in the radial direction, and an outer side surface in the tire axial direction, and a winding part that continues to the main part and extends away from the bead core.
The winding portion has an angle θ smaller than 90 ° with respect to the upper surface in the radial direction of the bead core and is inclined toward the ply main body portion, and extends.
The radial height L1 from the bead base line at the tip of the winding part is 0.07 to 0 in a ratio L1 / L0 to the radial height L0 from the bead base line of the inner surface of the ply body at the tire equator. .12 ,
Furthermore, between the bead core, the ply folded portion, and the ply main body portion, a sulfur blending amount of 7 to 12 phr, a complex elastic modulus Ea * of 2 to 25 Mpa, and a filled rubber surrounding the bead core is disposed. Heavy duty tire characterized by A heavy duty tire comprising a carcass ply in which a ply folding part is provided in a series of ply folding parts that are folded from the inner side to the outer side in the tire axial direction around the bead core on the ply body part extending from the tread part to the bead core through the sidewall part. Because
The ply turn-up part comprises a main part that bends along the inner surface in the tire axial direction of the bead core, a lower surface in the radial direction, and an outer side surface in the tire axial direction, and a winding part that continues to the main part and extends away from the bead core.
The winding portion has an angle θ smaller than 90 ° with respect to the upper surface in the radial direction of the bead core and is inclined toward the ply main body portion, and extends.
The bead core has a tensile strength T0 of 150 to 270 kN,
Moreover, in the ply turn-up portion, the tensile strength T1 per one carcass cord is 0.0045 to 0.0086 times the tensile strength T0 of the bead core, and the number of driven carcass cords is 30 to 45/5 cm. ,
Furthermore, between the bead core, the ply folded portion, and the ply main body portion, a sulfur blending amount of 7 to 12 phr, a complex elastic modulus Ea * of 2 to 25 Mpa, and a filled rubber surrounding the bead core is disposed. Heavy duty tire characterized by The bead core has a hexagonal cross section in which the lower surface and the upper surface in the radial direction are substantially parallel to the rim sheet of the 15 ° taper rim, and the filled rubber includes the upper surface in the radial direction of the bead core , the winding portion, and the ply body portion. The heavy duty tire according to claim 1, further comprising a base portion having a triangular cross section disposed between the two.

Images