JP2005112134A - Tire for heavy load - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain the occurrence of deficient moldings and to improve bead durability without impairing the advantage of a bead wind structure. <P>SOLUTION: A ply turn-up part 6b of a carcass 6 is connected to a main part 10 bent along a bead core 5, spaced from the bead core 5, inclined at an angle θof 75°or less and extended, and provided with a winding part 11 having a height La ranging from 3 to 15 mm from the top face SU of the bead core. Filling rubber 12 having sulfur mixing quantity of 7 phr or more and a complex elastic modulus Ea* of 8 to 25Mpa and enclosing the periphery of the bead core 5 is disposed among the bead core 5, the ply turn-up part 6b and the ply body part 6a. <P>COPYRIGHT: (C)2005,JPO&NCIPI

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. 5A, the ply turn-up portion a of the carcass 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 formed. A tire having a bead structure (hereinafter sometimes referred to as a bead wind structure) sandwiched between the bead core b and the bead apex rubber c has been proposed.

  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 the structure described above, the end portion a1 has a small length and a large degree of bending. Therefore, the bending of the end portion a1 tends to return strongly, for example, in a green tire molding process. As a result, it becomes easy to generate molding defects such as air remaining, such as a cavity formed between the bead core b. There is also a problem that the carcass cord rubs against the bead core at the end portion a1 and breakage damage such as fretting occurs at an early stage.

  Therefore, for example, in Patent Document 1, as shown in FIG. 5 (B), a thickness of 0.5 to 8.0 mm and a 50% modulus of 1.0 to 8.mm are provided between the bead core b and the end portion a1. It has been proposed to interpose 5 Mpa of soft rubber g.

JP 2002-32124 A

  However, when such a soft rubber g is interposed, a new problem to be solved such as a new carcass cord loose is likely to occur at the inner end position Q of the bead core b in the tire axial direction. .

  The reason for the occurrence of this cord loose is that, in the bead wind structure, the carcass ply falls relatively large due to the load during running, and the rubber in the bead may cause heat such as brake pads on the vehicle side depending on driving conditions. The temperature rises excessively by picking up and heat softens. That is, when a load is applied, the rubber in the bead tends to move to the bead toe side due to the thermal softening and the large fall of the carcass ply. At this time, the ply turn-up portion a moves while being dragged by the movement, so the position Q , A large shear stress is generated between the carcass ply and the bead core b. As described above, when the soft rubber g is interposed between the bead core b and the end portion a1, it is presumed that the movement of the ply turn-back portion a is promoted to induce the cord loose.

  Therefore, the present invention is basically arranged such that a filled rubber surrounding the bead core is disposed between the bead core and the carcass ply, the sulfur content of the filled rubber is 7 phr or more, and the complex elastic modulus Ea * is 8 to 25 Mpa. As a result, it is possible to suppress the carcass cord fretting and the cord looseness at the inner end in the tire axial direction of the bead core without impairing the advantages of the bead wind structure and suppressing the occurrence of molding defects such as air residues. An object of the present invention is to provide a heavy duty tire capable of improving bead durability.

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 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.
And the winding part has an angle θ of 75 ° or less with respect to the upper surface in the radial direction of the bead core and is inclined toward the ply main body part, and at the tip of the winding part, the radial direction of the bead core While the height La from the upper surface is 3 to 15 mm,
Between the bead core, the ply folded portion, and the ply main body portion, a sulfur content is 7 phr or more, a complex elastic modulus Ea * is 8 to 25 Mpa, and a filling rubber surrounding the bead core is disposed. Yes.

  In the invention of claim 2, the winding portion is characterized in that a gap Lb between its tip and the ply main body portion is set to 1 to 10 mm.

  According to a third aspect of the invention, the complex elastic modulus Ea * of the filled rubber is greater than 13 Mpa and not greater than 20 Mpa.

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. Comprising a bead reinforcement layer having at least an outer piece inclined outward in the axial direction of the tire radially outward,
A radial height Hc from the bead base line of the outer piece is 5 to 20 mm.

  According to a fifth aspect of the invention, the bead reinforcing layer includes an inner piece extending along a tire axial direction inner side surface of the ply main body portion on an inner side in the tire axial direction of the curved portion. The radial height Hb from the bead base line is 70 mm or less.

  Here, unless otherwise specified, dimensions and the like of each part of the tire are values specified in a 5% internal pressure state in which the tire is assembled on a normal rim and filled with an internal pressure of 5% of the normal internal pressure. The tire shape in the 5% normal internal pressure state generally coincides with the tire shape in the vulcanization mold.

  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". The “regular internal pressure” is the air pressure specified by the tire for each tire. The maximum air pressure in the case of JATMA, the maximum value described in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the case of TRA, If it is ETRTO, it means "INFLATION PRESSURE".

  Since the present invention is configured as described above, the occurrence of molding defects such as air residue can be suppressed without impairing the advantages of the bead wind structure, and the fretting of the carcass cord and the tire shaft of the bead core. The cord looseness at the inner end position in the direction can be suppressed and the bead durability can be improved.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing a 5% normal internal pressure state when the heavy load tire of the present invention is a tubeless tire for trucks and buses, and FIG. 2 is an enlarged cross-sectional view of the bead portion.

  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 formed of two or more belt plies (three or more in the case of heavy load tires) using a belt cord. In this example, the belt layer 7 includes a first belt ply 7A on the innermost side in the radial direction in which steel cords are arranged at an angle of 60 ± 15 ° with respect to the tire circumferential direction, and 10 to 10 with respect to the tire circumferential direction. A case of a four-sheet structure with second to fourth belt plies 7B to 7D arranged at a small angle of 35 ° is illustrated. 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 carcass cords are arranged at an angle of 70 to 90 ° with respect to the tire circumferential direction. A steel cord is suitable as the carcass cord, but an organic fiber cord such as nylon, rayon, polyester, aromatic polyamide or the like is also used if necessary. The carcass ply 6A includes a series of ply turn-up portions 6b that are turned back from the inner side in the tire axial direction around the bead core 5 on both sides of the ply body portion 6a straddling the bead cores 5 and 5.

  As shown in FIG. 2, the bead core 5 is a ring-shaped body formed by winding steel bead wires in multiple stages and multiple rows. In this example, the bead core 5 has a flat hexagonal shape with a horizontally long cross section. A preferable example in which the SL is substantially parallel to the rim sheet J1 of the regular rim J and the fitting force with the rim is increased over a wide range is illustrated. In this example, the regular rim J is a tubeless 15 ° taper rim, so that the radially lower surface SL and the upper surface SU of the bead core 5 are inclined at an angle of approximately 15 ° with respect to the tire axial line. . In addition, as a cross-sectional shape of the bead core 5, a regular hexagonal shape or a rectangular shape can be adopted as necessary.

  Next, in the present invention, the ply folded portion 6b of the carcass 6 is wound around the peripheral surface of the bead core 5 and the end portion of the ply folded portion 6b is held between the bead apex rubber 8 and engaged. Stopped.

  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 5.

  At this time, the winding part 11 has an angle θ of 75 ° or less with respect to the radial upper surface SU of the bead core 5 and inclines toward the ply body part 6a. This winding part 11 means the site | part of the radial direction outer side than the extension line | wire of the said radial direction upper surface SU, and has illustrated the preferable case which makes a substantially linear form in this example. Note that “substantially linear” allows deformation in vulcanization molding or the like, and can include arcs having a curvature radius of 100 mm or more in addition to straight lines. In addition, when the winding part 11 is an arc, the angle θ is the straight line X connecting the intersection point P1 where the extension line of the radial upper surface SU intersects the winding part 11 and the tip P2 of the winding part 11. An angle with respect to the upper surface SU in the radial direction. The radius of curvature when the winding portion 11 is an arc means the radius of curvature of a three-point arc passing through the intersection P1, the tip P2, and the midpoint.

  If necessary, the winding portion 11 can be bent in a bent line shape. In such a case, the angle of each bent portion with respect to the upper surface SU in the radial direction is set to 75 ° or less.

  And in the said winding part 11, while making the height La from the said radial direction upper surface SU of the front-end | tip P2 into 3-15 mm, bead core 5 between the said bead core 5, the ply folding | turning part 6b, and the ply main-body part 6a. The filling rubber 12 surrounding the periphery of is disposed.

  The filling rubber 12 is a relatively thin base portion disposed between the tire axial direction inner side surface Si, the radial lower surface SL, the tire axial direction outer side surface So of the bead core 5 and the main portion 10 of the ply folded portion 6b. 12A, and the radial upper surface SU of the bead core 5, the secondary portion 12B having a substantially triangular cross section disposed between the winding portion 11 and the ply main body portion 6a.

  Thus, since the filling rubber 12 having the sub-part 12B having a substantially triangular cross section is provided and the height La is secured to 3 mm or more, the degree of bending of the winding part 11 can be reduced. As a result, bending back of the winding part 11 is suppressed, and it is possible to suppress the occurrence of molding defects such as air residue. Further, rubbing between the carcass cord and the bead core 5 on the upper surface SU in the radial direction can be prevented, and fretting can be suppressed.

  At this time, if the height La exceeds 15 mm, stress at the time of tire deformation tends to act strongly on the tip P2 of the winding part 11, and damage such as cord loose starting from the tip P2 is likely to occur. . Therefore, the height La is preferably 5 to 15 mm, more preferably 7 to 15 mm.

  It is also important to secure a gap Lb between the tip P2 and the ply main body 6a in the range of 1 to 10 mm. If it is less than 1 mm, the carcass cord may be caused by variations in tire formation or tire deformation during running. The tip of the wire and the carcass cord of the ply main body 6a come into contact with each other and rub against each other. On the other hand, when the gap Lb exceeds 10 mm, the locking force of the winding part 11 becomes insufficient, and there is a possibility that a blow-through phenomenon may occur during traveling. Accordingly, the gap Lb is preferably 1 to 5 mm, more preferably 2 to 4 mm.

  Here, in the said winding part 11, since it is La <= 3mm, there exists a tendency for the stress at the time of a tire deformation to act on the front-end | tip P2. In particular, since the highly elastic bead apex rubber 8 having a complex elastic modulus Eb * of about 35 to 60 Mpa is adjacent to the winding portion 11 on the radially outer side, the stress tends to concentrate. Therefore, it is necessary for the filled rubber 12 to disperse and relax the stress to prevent cord looseness and the like. Therefore, in the present invention, the filled rubber 12 is made to have an impact having a complex elastic modulus Ea * of 25 Mpa or less. It is made of low-elasticity rubber with excellent relaxation effect. The value of the complex elastic modulus is a value measured using a viscoelastic spectrometer under conditions of a temperature of 70 ° C., a frequency of 10 Hz, and a dynamic strain rate of 2%.

  If the complex elastic modulus Ea * exceeds 25 Mpa, the flexibility and the stress concentration cannot be sufficiently suppressed, and the cord looseness at the tip P2 may not be prevented.

  On the other hand, if the filling rubber 12 is too soft, the ply turn-up portion 6b is promoted to move toward the bead toe, and new damage occurs, such as causing carcass cord looseness at the tire axial direction inner end position Q of the bead core b.

  As described above, this damage is caused by the fact that in the bead wind structure, the carcass ply 6 </ b> A falls relatively large when a load is applied, and the rubber in the bead easily picks up the heat of the brake pads on the vehicle and softens. To do. 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. A large shear stress is generated between the carcass ply and the bead core b at the position Q. When the complex elastic modulus Ea * of the filling rubber 12 is soft, less than 8 Mpa, the ply folding portion 6b is facilitated to move toward the bead toe, and as a result of increasing the shear stress, the cord looseness is induced at the position Q. It is.

  Therefore, in the present invention, the complex elastic modulus Ea * of the filled rubber 12 is restricted to 8 Mpa or more, and the cord looseness at the position Q is suppressed. From this point of view, the lower limit of the complex elastic modulus Ea * is preferably greater than 13 Mpa, more preferably greater than 14 Mpa, and the upper limit is preferably 23 Mpa or less, and more preferably 20 Mpa or less.

  Further, in the present invention, in order to further enhance the effect of suppressing the cord loose at the position Q, the amount of sulfur as a vulcanizing agent to be blended with the filler rubber 12 is blended by 7.0 phr or more. This is because, when the complex elastic modulus Ea within the above range is obtained by blending sulfur in an amount of 7.0 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, the movement of the ply turn-up portion 6b is not further promoted by thermal softening of the filling rubber 12, and the effect of suppressing cord looseness can be 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 7.0 to 12 phr, and more preferably in the range of 7.5 to 10 phr. In addition, in the rubber composition for normal tires, sulfur is compounded at 1.0 to 5.0 phr.

  Further, in the filling rubber 12, in order to maintain handle responsiveness and the like, the cross-sectional shape of the sub-portion 12 </ b> B is a substantially isosceles triangular shape with the side contacting the radial upper surface SU of the bead core 5 as the base. preferable.

  In this example, a bead reinforcing layer 15 is provided on the bead portion 4. As shown in FIG. 3, the bead reinforcement layer 15 includes a curved portion 15A passing through the inner portion in the radial direction along the main portion 10 of the ply folded portion 6b, and the curved portion 15A on the outer side in the tire axial direction. It is configured to include at least an outer piece 15o that is separated from the main portion 10 and that is inclined outward in the radial direction of the tire in the radial direction. In this example, a U-shaped cross section in which an inner piece 15i extending along the tire axial direction inner side surface of the ply main body portion is further provided on the inner side in the tire axial direction of the curved portion 15A.

  The bead reinforcement layer 15 is composed of one cord reinforcement 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 increases the bending rigidity of the bead portion 4 and reduces bead deformation. As a result, the bead durability can be improved. For this purpose, the radial height Hc of the outer piece 15o from the bead base line BL is in the range of 5 to 20 mm, and the radial height Hb of the inner piece 15i from the bead base line BL is 70 mm or less. Is preferred.

  If the height Hc in the radial direction is less than 5 mm, the bead deformation cannot be suppressed. Conversely, if the height Hc exceeds 20 mm, the effect of improving the bead durability cannot be expected in any case such as stress is concentrated on the outer end. On the other hand, if the height Hb in the radial direction exceeds 70 mm, stress concentrates on the outer end of the plate and the bead is liable to be damaged, and the longitudinal rigidity is excessively increased, resulting in deterioration of ride comfort. Therefore, the radial height Hb is preferably 10 mm or more, 25 mm or more, and more preferably 40 mm or more from the viewpoint of the reinforcing effect. However, the inner piece 15i can be deleted as required, and the inner end in the tire axial direction of the curved portion 15A may be terminated at the same height as the bead base line BL. The “bead base line BL” means a tire axial line passing through a rim diameter position determined by a standard based on the tire.

  In this example, in order to make the bead portion 4 slimmer, and to improve the durability by reducing the weight and the accompanying heat storage, the ply body portion 6a is arranged in the radial direction from the radially inner end position Q4. A straight line portion 6a1 extending linearly outward is provided, and a height h1 of the straight line portion 6a1 from the bead base line BL is set to a radial height h0 of the bead apex rubber 8 from the bead base line BL. Is set to 50% or more, 60% or more, and further 70% or more.

  As the bead apex rubber 8, in this example, the lower apex rubber portion 8A having a complex elastic modulus Eb1 * of 35 to 60 Mpa, the radially elastic outer side and the complex elastic modulus Eb2 * are filled with the filled rubber 12 This example illustrates a two-layer structure of the apex rubber portion 8A which is larger than the complex elastic modulus Ea * and lower than the complex elastic modulus Eb * of the lower apex rubber portion 8A. Then, 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 height h0, thereby achieving both riding comfort and steering stability. The upper limit of the height h1 should be smaller than the height hm (shown in FIG. 1) from the bead base line of the maximum ply width point Pm where the outer surface of the ply body 6a projects most outward in the tire axial direction. There is no particular restriction.

  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 having the structure shown in FIG. 1 and having a tire size of 11R22.5 was manufactured based on the specifications in Table 1, and the bead strength, bead durability, and occurrence rate of molding defects of each sample tire were measured and compared with each other. did. Specifications other than those in Table 1 are the same.

  As shown in FIG. 4, 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 strength;
The tire was mounted on a rim (7.50 × 22.5), water was filled into the tire lumen from the valve, and the breaking water pressure when the tire burst was measured. The higher the value, the better.

(2) 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 load (27.25 kN × 3). The running time until the occurrence of the problem is shown as an index with the conventional example as 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 150 ° C., and the running time until the bead portion was damaged was indicated by 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.

(3) Incidence of molding defects;
100 tires were created and the incidence of defective tires was calculated. For the defective tire, the tire was photographed with a CT scanner, and the presence or absence of air remaining was detected.

  As shown in the table, it can be confirmed that both the general bead durability and the thermal bead durability are improved in the example products without causing molding defects.

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 sectional drawing which shows the bead structure of the prior art example of Table 1. (A), (B) 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 12 Filling rubber 15 Bead reinforcement layer 15a Curved part 15i Inner piece 15o Outer piece P1 tip

Claims (5)

A heavy duty tire comprising a carcass ply in which a ply main body portion extending from a tread portion to a bead core in a bead portion and a bead core in a bead portion is provided with a series of ply turn-around portions around the bead core. 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.
And the winding part has an angle θ of 75 ° or less with respect to the upper surface in the radial direction of the bead core and is inclined toward the ply main body part, and at the tip of the winding part, the radial direction of the bead core While the height La from the upper surface is 3 to 15 mm,
Between the bead core, the ply folded portion, and the ply body portion, a sulfur content is 7 phr or more, a complex elastic modulus Ea * is 8 to 25 Mpa, and a filled rubber surrounding the bead core is disposed. Heavy duty tires.   The heavy duty tire according to claim 1, wherein the winding portion has a gap Lb between a tip thereof and the ply main body portion of 1 to 10 mm.   3. The heavy duty tire according to claim 1, wherein a complex elastic modulus Ea * of the filled rubber is greater than 13 Mpa and not greater than 25 Mpa. 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. Comprising a bead reinforcement layer having at least an outer piece inclined outward in the axial direction;
The heavy load tire according to any one of claims 1 to 3, wherein a height Hc in a radial direction from the bead base line of the outer piece is 5 to 20 mm.   The bead reinforcing layer includes an inner piece extending along an inner side surface in the tire axial direction of the ply main body portion on the inner side in the tire axial direction of the curved portion, and a radial height from the bead base line of the inner piece. The heavy load tire according to any one of claims 1 to 4, wherein the height Hb is 70 mm or less.

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