JP4410552B2 - Heavy duty radial tire - Google Patents

Description

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

  In recent years, as shown in FIG. 8, 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 connected to the bead core 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.

  However, in this structure, since the length of the end portion a1 is small, it is difficult to sufficiently lock the carcass ply, and there is a tendency that the carcass ply is easily displaced in the blow-through direction. As a result, when the tire is deformed, there is a problem that a large shear strain is generated between the carcass ply and the bead core b at the inner end position A of the bead core b in the tire axial direction, thereby inducing cord looseness in the carcass cord. This problem is caused when the end portion a1 is separated from the bead core b to reduce the strong bending back (so-called springback) of the end portion a1 that occurs in, for example, a green tire molding process, and when the bead portion is heated by a brake pad or the like. This occurs more markedly when the temperature rises excessively and the rubber softens.

  Therefore, the present invention is based on the fact that the ply turn-up portion is provided with a one-side inclined region in which the carcass cord is inclined to one side in the tire circumferential direction and a second-side inclined region in which the other side is inclined in the tire circumferential direction. It is an object of the present invention to provide a heavy duty radial tire that can increase the locking force, effectively suppress the displacement of the carcass ply in the blow-through direction, and suppress the bead damage at the position A.

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 body part extending from the tread part through the sidewall part to the bead core of the bead part. A heavy duty radial tire comprising a carcass ply provided with a series of ply turn-up parts,
The ply turn-up portion includes a main portion that bends along the inner surface in the tire axial direction, the lower surface in the radial direction and the outer outer surface in the tire axial direction of the bead core, and is in contact with or in contact with the upper surface in the radial direction of the bead core. A winding portion that extends away from the upper surface at an angle smaller than 90 ° and extends toward the ply main body, and
The ply turnup portion, the carcass cord ply body portion end R1 tire one circumferential direction f1 to the inflection point R0 located in the core lower surface-to-direction region N facing radially lower surface of the bead cores from the ply turnup portion A one-side inclined area Z1 extending in an inclined manner and an other-side inclined area Z2 in which the carcass cord extends from the inflection point R0 to the tip end Pa of the ply turn-up portion on the other side in the tire circumferential direction f2 .
And the one side inclined zone Z1 is the core lower surface versus countercurrent region N, it has a minimum angular position Q1 where the cord angle α with respect to the tire circumferential direction of the carcass cord becomes minimum Arufa1min, yet from said minimum angular position Q1 While increasing the cord angle α toward the ply body side end R1 and the inflection point R0,
The other-side inclined area Z2 has a minimum angle position Q2 at which the cord angle α is a minimum value α2min between the inflection point R0 and the tip Pa of the ply folding portion, and from the minimum angle position Q2. The cord angle α is increased toward the inflection point R0 and the tip Pa of the ply folding portion.

  In the invention of claim 2, the minimum values α1min and α2min are in the range of 60 to 80 °.

  The invention of claim 3 is characterized in that the minimum angle position Q2 is located in the main portion of the ply turn-up portion.

  According to a fourth aspect of the present invention, the bead portion is separated from the main portion along the main portion of the ply turn-up portion and passing radially inward of the ply turn-up portion, and on the outer side in the tire axial direction of the curved portion. A bead reinforcement layer including an outer piece inclined outward in the tire axial direction toward the outer side in the radial direction, and a radial height Ho from the bead base line of the outer piece to be 10 to 35 mm. It is a feature.

  According to a fifth aspect of the present invention, a distance La from the radial upper surface of the bead core is 5 to 12 mm and a distance Lb from the ply main body is 1 to 5 mm. It is said.

  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, the locking force to the carcass ply can be increased, the movement of the carcass ply in the blow-off direction can be effectively suppressed, and damage at the position A can be suppressed. Durability can be improved.

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

  In FIG. 1, a heavy-duty radial tire 1 is disposed on a carcass 6 that extends from a tread portion 2 through a sidewall portion 3 to a bead core 5 of a bead portion 4, radially outward of the carcass 6 and inward of the tread portion 2. Belt layer 7 to be formed.

  The belt layer 7 is composed of two or more belt plies using steel belt cords (usually three or more in the case of radial tires for heavy loads). In this example, the belt cords are connected to the tire circumferential direction. For example, the radially innermost first belt ply 7A 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. And having 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 85 to 90 ° at least in the tread portion 2 and the sidewall portion 3 with respect to the tire circumferential direction. The carcass ply 6A includes a series of ply turn-up portions 6b that are turned back from the inside in the tire axial direction around the bead core 5 on both sides of the ply main body portion 6a straddling 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 is formed of a small-length winding portion 11 that extends in contact with or away from the radial upper surface SU.

  In this example, the case where the said winding part 11 spaces apart is illustrated, and the winding part 11 has an angle (theta) below 90 degrees with respect to the said radial direction upper surface SU, Preferably it is 75 degrees or less. It inclines 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). .

  And in the said winding part 11, while making distance La from the said radial direction upper surface SU (the said tangent line K when the radial direction upper surface SU is non-planar) of the front-end | tip Pa to 5-12 mm, the said bead core 5 and ply folding | turning part A soft filler rubber 12 is disposed between 6b and 6b.

  Further, 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 main 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, since the filling rubber 12 having the base portion 12A having a substantially triangular cross section is provided and the distance La is secured to 5 mm or more, the degree of bending of the winding portion 11 can be reduced. Strong bending back (so-called spring back) occurring in the process or the like can be suppressed, and the occurrence of molding defects such as air residue due to this can be suppressed. If the distance La is less than 5 mm, the springback cannot be sufficiently suppressed, and the impact applied to the tip Pa during contact with the ground increases, so that the tip Pa is likely to be damaged. Conversely, even if the distance La exceeds 12 mm, stress at the time of tire deformation tends to act strongly on the tip Pa, so that the tip Pa is likely to be damaged.

  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 elasticity rubber having a complex elastic modulus Ea * of 2 to 25 Mpa and excellent in impact mitigating effect. Yes. 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.

  In addition, at the tip Pa, it is preferable to secure a distance Lb of 1-5 mm with the ply main body 6a. If it 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. Cord damage such as fretting is likely to occur, such as contact and rubbing with the carcass cord of the main body 6a. When the distance Lb exceeds 5 mm, it is disadvantageous for the blow-through, for example, the locking force to the winding part 11 is reduced.

  And in this invention, in order to raise the latching force in the ply folding | turning part 6b of such a bead wind structure, and to suppress the damage resulting from the blow-off or the shift | offset | difference of a blow-off direction, the said ply folding | turning part 6b is shown to FIG. The code arrangement state is as follows.

Here, FIG. 5 is a development view showing the arrangement of the carcass cord 30 to expand the ply turnup portion 6b in the plane, FIG. 6, from the center position No in the core lower surface versus countercurrent region N of the ply turnup portion 6b The radial distance X along the ply of the carcass cord 30 with respect to the tire circumferential direction of the carcass cord 30 at the position of the distance X is indicated on the horizontal axis. A code angle curve is shown with the code angle α taken on the vertical axis Y. Note The "core lower surface versus countercurrent region N", as shown in FIG. 2, the ply turnup portion 6b is meant a region facing the radially lower surface SL of the bead core 5.

Specifically, the ply turnup portion 6b, as shown in FIGS. 5 and 6, with one side inclined zone Z1 of the carcass cord 30 is extending obliquely to the tip Pa tire one circumferential direction toward the side f1 , And the other side inclined area Z2 extending incline toward the tire circumferential direction other side f2. That is, the carcass cord 30 has an inflection point R0 where the inclination direction of the carcass cord 30 changes from the one side f1 to the other side f2 in the tire circumferential direction at the boundary point between the one side inclination region Z1 and the other side inclination region Z2. Curved in a letter shape.

In this case, the inflection point R0 is located in the core lower surface versus countercurrent region N. Moreover the the one side inclined zone Z1, has a minimum angular position Q1 where the cord angle α to the core lower surface versus countercurrent region N becomes the minimum value Arufa1min, carcass cords 30, the inflection point from the minimum angular position Q1 The cord angle α is increased toward R0 and toward the ply body side end R1 of the ply turn-up portion 6b from the minimum angle position Q1. Further, in the other-side inclined area Z2, the cord angle α has a minimum angle position Q2 at which the cord angle α becomes a minimum value α2min between the inflection point R0 and the tip Pa, and the carcass cord 30 has the minimum angle position. The cord angle α is increased from Q2 toward the inflection point R0 and from the minimum angle position Q2 toward the tip Pa. The carcass cord 30 has a cord angle α of 5 ° or less, preferably 3 ° or less Δα (between Q1 → R1, Q1 → R0, Q2 → R0, and Q2 → Pa. 6), it is preferable to gradually increase the cord angle α between the respective parts without the reduction part R2.

  Since the carcass cord 30 is curved in an S shape, the ply turn-up portion 6b can increase the length of the cord wound around the bead core 5 as compared with the linear shape. In addition, since the drag force in the direction of pulling out the cord can be increased by the S-shaped curve, in combination with the increase in the cord length, the locking force to the ply turn-up portion 6b can be further improved. Damage at the position A due to the shift can be effectively suppressed.

  For this purpose, the minimum values α1min and α2min are preferably set in the range of 60 to 80 °, and it is difficult to ensure the effect of improving the locking force at 80 ° or more. If the minimum values α1min and α2min are smaller than 60 °, the cord interval becomes too small and the carcass cord 30 tends to be fretting. Further, the minimum angle position Q2 may be positioned in the main portion 10 of the ply turn-up portion 6b, in particular, on the ply body portion 6a side with respect to the outer end position B in the tire axial direction of the bead core 5 (shown in FIG. 2). This is preferable in terms of the effect of improving the stopping force. The difference between the cord angle α0 on the tire equator Co and the minimum values α1min and α2min is preferably 10 ° or more.

  Next, in this example, in order to further suppress damage at the position A, a bead reinforcing layer 15 is provided in the bead portion 4. The bead reinforcing layer 15 is formed of a cord ply in which steel cords are arranged at an angle of, for example, 10 to 40 ° with respect to a tire circumferential direction line, and as shown in FIG. 3, along the main portion 10 of the ply turn-up portion 6b. A curved portion 15A that passes inward in the radial direction, and an outer piece 15o that is inclined outwardly in the tire axial direction and away from the main portion 10 on the outer side in the tire axial direction of the curved portion 15A. At least comprise. In this example, a preferable case is illustrated in which an inner piece 15i extending along the inner side surface in the tire axial direction of the ply main body portion 6a is connected to the curved portion 15A on the inner side in the tire axial direction.

  Here, as described above, the damage at the position A is mainly caused by the displacement of the ply turn-up portion 6b in the blow-through direction, and the bead portion 4 picks up the heat on the vehicle side such as a brake pad and is excessive. This occurs more markedly when the temperature rises and the rubber is heat softened. That is, the rubber in the heat-softened bead tends to move to the bead toe side when pressed against the flange when a load is applied. At this time, the ply turn-up portion 6b is dragged by the movement and the deviation in the blow-through direction is shifted. Encourage.

  The outer piece 15o exhibits a function as a shielding plate when the radial height Ho becomes 10 mm or more, preferably 20 mm or more, and the rubber movement F toward the bead toe side (indicated by a one-dot chain line in FIG. 3). Can be reduced by the shielding effect. However, if the radial height Ho exceeds 35 mm, damage due to stress concentration tends to occur at the tip of the outer piece 15o. Further, the inner piece 15i has a reinforcing effect such as suppressing the fall of the carcass ply 6A when a load is applied and reducing the distortion at the tip Pa to a smaller extent. Therefore, the inner piece 15i has a reinforcing effect from the bead base line BL. The radial height Hi is preferably 10 mm or more, more preferably 20 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.

  If the complex elastic modulus Ea * of the filling rubber 12 is too soft, less than 2 Mpa, the ply folding portion 6b is easily dragged by the rubber movement F, which is disadvantageous for damage at the position A. Therefore, the lower limit value of the complex elastic modulus Ea * is preferably set to be greater than 3 Mpa, more preferably greater than 8 Mpa, and even greater than 13 Mpa. At this time, it is preferable to use a high-sulfur compounded rubber having a sulfur compounding amount of 5.0 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 5.0 phr or more, the rubber is difficult to heat soften. Therefore, even when the bead temperature rises excessively due to heat from the brake pad or the like, it is possible to suppress the displacement of the ply turn-up portion 6b from being promoted. If the amount of sulfur exceeds 12 phr, the vulcanization becomes too fast and the rubber burns easily, so that the adhesion with the adjacent member may be reduced. Accordingly, the blending amount of sulfur is preferably in the range of 5.0 to 12 phr, the lower limit value is 7.0 phr or more, and the upper limit value is more preferably 10 phr or less. In addition, in the rubber composition for normal tires, sulfur is compounded at 1.0 to 4.5 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 portion 8A is set in the range of 40 to 60% of the total height h0 of the bead apex rubber 8, so that both ride comfort and steering stability are achieved. I am trying.

  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-duty radial tire (11R22.5) having the structure of FIG. 1 and based on the specifications shown in Table 1 was prototyped, and 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. 7, 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 radial 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. FIG. 5 is a development view showing an arrangement state of carcass cords with a ply folding portion developed on a plane. The radial distance X along the ply from the center position in the core lower surface facing region of the ply turn-up portion is taken as the horizontal axis, and the cord angle α with respect to the tire circumferential direction of the carcass cord at the distance X is taken as the vertical axis Y. It is a diagram which shows a code | cord angle curve. 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 folding part 10 Main part 11 Winding part 15 Bead reinforcement layer 15A Curved part 15o Outer piece 30 Carcass cord P1 Ply body part side end Pa tip
N core lower surface versus countercurrent region Z1 on one side inclined zone Z2 other inclined region

Claims (5)

A heavy duty radial with a carcass ply provided with 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 on the ply body portion extending from the tread portion to the bead core through the sidewall portion. Tire,
The ply turn-up portion includes a main portion that bends along the inner surface in the tire axial direction, the lower surface in the radial direction, and the outer outer surface in the tire axial direction of the bead core, and the radial direction upper surface of the bead core that is connected to the main portion. A winding portion that extends away from the upper surface at an angle smaller than 90 ° and extends toward the ply main body, and
The ply turnup portion, the carcass cord ply body portion end R1 tire one circumferential direction f1 to the inflection point R0 located in the core lower surface-to-direction region N facing radially lower surface of the bead cores from the ply turnup portion A one-side inclined area Z1 extending in an inclined manner and an other-side inclined area Z2 in which the carcass cord extends from the inflection point R0 to the tip end Pa of the ply turn-up portion on the other side in the tire circumferential direction f2 .
And the one side inclined zone Z1 is the core lower surface versus countercurrent region N, it has a minimum angular position Q1 where the cord angle α with respect to the tire circumferential direction of the carcass cord becomes minimum Arufa1min, yet from said minimum angular position Q1 While increasing the cord angle α toward the ply body side end R1 and the inflection point R0,
The other-side inclined area Z2 has a minimum angle position Q2 at which the cord angle α is a minimum value α2min between the inflection point R0 and the tip Pa of the ply folding portion, and from the minimum angle position Q2. The radial tire for heavy loads, wherein the cord angle α is increased toward the inflection point R0 and the tip Pa of the ply turn-up portion.   The radial tire for heavy loads according to claim 1, wherein the minimum values α1min and α2min are in a range of 60 to 80 °.   3. The heavy duty radial tire according to claim 1, wherein the minimum angular position Q <b> 2 is located in the main portion of the ply turn-up portion.   The bead portion includes a curved portion that passes along a radial inner side along the main portion of the ply turn-up portion, and a tire that is radially outward and away from the main portion on the outer side in the tire axial direction of the curved portion. 4. A bead reinforcement layer including an outer piece inclined outward in the axial direction is provided, and a radial height Ho from the bead base line of the outer piece is set to 10 to 35 mm. A heavy-duty radial tire according to any one of the above.   The tip Pa of the winding portion has a distance La from the radial upper surface of the bead core of 5 to 12 mm and a distance Lb from the ply main body of 1 to 5 mm. A heavy-duty radial tire according to any one of the above.

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