JP2005112136A - Tire for heavy load - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the bead durability without impairing the advantage of a bead wind structure. <P>SOLUTION: This tire for head load is constructed so that a ply turn-up part 6b of a carcass 6 is provided with a winding part 11 connected to a main part 10 bent along a bead core 5 and coming into contact with the bead core top face Su or spaced at a small distance La 15mm or less, and the rubber thickness t between a bead wire 20 and a carcass cord 21 at the innermost point in the tire axial direction of the bead core 5 is set 0.5 to 3.0 mm. A bead part 4 is provided with a bead reinforcement layer 15 covering the ply turn-up part 6b, and the radial heights Hb and Hc of an inner piece 15i and an outer piece 15o range from 20 mm to 40 mm, and satisfy the expression: Hc ≥ Hb. <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. 7A, the carcass ply turn-up portion a is wound around the bead core b substantially once, 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. The bead structure sandwiched between the bead core b and the bead apex rubber c, and further, as shown in FIG. 7B, between the bead core b and the end portion a1, for example, a thickness of 0.5 to A bead structure (for example, Patent Document 1) in which a soft rubber g of 8.0 mm and 50% modulus of 1.0 to 8.5 Mpa is interposed and the end portion a1 is separated from the upper surface of the bead core b has been proposed.

JP 2002-32124 A

  In these bead structures (hereinafter, sometimes referred to as bead wind structures), the ply turn-up portion a is interrupted around the bead core b, so that the stress at the time of tire deformation acting on the end portion a1 is small. It is possible to effectively suppress damage such as cord loose starting from the portion a1. In addition, since the length of the ply turn-back portion a is short, there is an advantage that the tire can be reduced in weight. 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 such a bead wind structure, 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, and it is difficult to sufficiently improve bead durability. There's a problem.

  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, since the ply folding portion a moves while being dragged by the movement, it is presumed that a large shear strain is generated between the carcass ply and the bead core b at the position Q to induce the cord loose. In particular, when the soft rubber g is interposed between the bead core b and the end portion a1, the movement of the ply turn-back portion a is promoted, so that the cord looseness is more likely to occur.

  Accordingly, the present invention provides a bead portion provided with a substantially U-shaped bead reinforcement layer covering the ply turn-up portion, and the inner and outer pieces of the tire axial direction are raised to a predetermined height, and the bead core is positioned at the maximum in the tire axial direction. Based on the regulation of the rubber thickness between the bead wire and the carcass cord at the inner point within a predetermined range, the cord looseness at the inner end in the tire axial direction of the bead core is suppressed without impairing the advantages of the bead wind structure. Therefore, an object of the present invention is to provide a heavy duty tire capable of improving the 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 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 part extending toward the ply body part at a distance La of 15 mm or less from the upper surface;
And while setting the rubber thickness t between the bead wire and the carcass cord at the tire axial direction innermost point of the bead core to 0.5 to 3.0 mm,
A curved portion passing through the inner portion in the radial direction along the main portion of the ply turn-up portion in the bead portion, and a tire facing away from the main portion on the outer side in the tire axial direction of the curved portion toward the outer side in the radial direction. A bead reinforcement layer is provided that includes an outer piece that is inclined outward in the axial direction, and an inner piece that extends 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,
Moreover, the radial height Hb of the inner piece from the bead base line is greater than 20 mm and not more than 40 mm, and the radial height Hc of the outer piece from the bead base line is greater than 20 mm and not more than 40 mm and the radial height. It is characterized by being not less than Hb.

  According to a second aspect of the present invention, the winding portion is separated from the upper surface in the radial direction of the bead core, and a complex elastic modulus Ea * is 2 to 25 Mpa between the bead core, the ply folded portion, and the ply body portion. In addition, it is characterized by a filling rubber surrounding the bead core.

  According to a third aspect of the present invention, the filled rubber is characterized in that the complex elastic modulus Ea * is greater than 13 Mpa and not greater than 25 Mpa, and the sulfur content is not less than 5 phr.

  According to a fourth aspect of the present invention, 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.

  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 cord looseness at the inner end position in the tire axial direction of the bead core can be suppressed without impairing the advantages of the bead wind structure, 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 20 in multiple stages and multiple rows. In this example, the bead core 5 has a flat hexagonal shape with a horizontally long cross section, and its radial direction. A preferable example is shown in which the lower surface SL is substantially parallel to the rim sheet J1 of the regular rim J so that the fitting force with the rim is increased over a wide range. 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 sandwiched between the bead apex rubber 8 and locked. The so-called bead wind structure is used.

  Specifically, the ply turn-up portion 6b includes a main portion 10 that is bent along the tire axial direction inner surface Si, the radial direction lower surface SL, and the tire axial direction outer surface So of the bead core 5, and a small length that is continuous with the main portion 10. It is formed from the winding part 11 of a length. In addition, the winding-up part 11 means the site | part outside a radial direction rather than the extension line | wire of the radial direction upper surface SU of the said bead core.

  The winding portion 11 is in contact with the radial upper surface SU and extends toward the ply main body 6a, or is separated from the radial upper surface SU by a small distance La of 15 mm or less toward the ply main body. As a result, the weight is reduced and the stress acting on the tip P2 of the winding part 11 is reduced, and damage starting from the tip P2 is suppressed.

  In particular, in the present example, the winding portion 11 has an angle θ of 75 ° or less with respect to the radial upper surface SU, and inclines in a straight line or a bent line, thereby gradually increasing from the radial upper surface SU. The case where it leaves | separates is illustrated. At this time, the distance La from the upper surface SU in the radial direction of the tip P2 is set to 15 mm or less, and the filled rubber 12 surrounding the bead core 5 is interposed between the bead core 5, the ply turn-up portion 6b, and the ply body portion 6a. It is arranged.

  The “straight line shape” allows deformation in vulcanization molding or the like, and can include an arc having a radius of curvature of 100 mm or more in addition to a straight line. Further, when the hoisting part 11 is an arc, the angle θ is such that a straight line connecting the intersection P1 where the extension line of the radial upper surface SU intersects the hoisting part 11 and the tip P2 is relative to the radial upper face SU. An angle. 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. When the winding portion 11 is bent, the angle θ of each bent portion with respect to the upper surface SU in the radial direction is set to 75 ° or less.

  Further, the filling rubber 12 is relatively thin 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 turn-up portion 6b. The base portion 12A is formed from 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, when the sub-part 12B has a substantially triangular cross-section, the degree of bending of the winding part 11 can be reduced. As a result, for example, in the green tire molding process, it is possible to suppress the occurrence of molding defects such as the air remaining between the bead core 5 and the bent portion of the winding part 11 returning strongly. In addition, it is useful for suppressing fretting such as rubbing between the carcass cord and the bead wire on the radially upper surface SU.

  For this purpose, the distance La is preferably 3 mm or more. However, if the distance La exceeds 15 mm, the advantage of the bead wind structure is impaired, and the stress acting on the tip P2 of the winding part 11 tends to increase. Therefore, the distance La is more preferably in the range of 5 to 10 mm, more preferably 6 to 8 mm.

  It is also important to ensure the gap Lb between the tip P2 and the ply main body 6a within a range of 1 to 10 mm. If it is less than 1 mm, the carcass may be deformed due to variations in tire formation or tire deformation during travel. Fretting is likely to occur, for example, the tip of the cord and the carcass cord of the ply main body portion 6a come into contact 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.

  In addition, the filling rubber 12 is formed of a low elastic rubber having an excellent impact relaxation effect with a complex elastic modulus Ea * of 2 to 25 Mpa in order to further relax vibrations and stress acting on the tip P2 of the winding part 11. Preferably, if it exceeds 25 MPa, the flexibility is impaired, and therefore cord looseness is likely to occur at the tip P2. 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%.

  Further, in the bead wind structure tire, the carcass cord is likely to have a cord loose at the inner end position Q of the bead core 5 in the tire axial direction, and damage specific to the bead wind structure tire occurs.

  As described above, in the bead wind structure, this damage is caused by the fact that the carcass ply 6A falls relatively large when a load is applied, and the rubber in the bead picks up heat from the brake pads on the vehicle side depending on the driving conditions. Caused by excessive temperature rise and thermal 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 occurs between the carcass ply 6A and the bead core 5 at the position Q to induce the cord loose.

  Therefore, in the present invention, in order to suppress such damage, a predetermined U-shaped bead reinforcement layer 15 is provided on the bead portion 4 and the rubber thickness between the bead wire 20 and the carcass cord 21 at the position Q is set. The length t (shown in FIG. 4) is restricted to a predetermined range.

  Specifically, 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 the tire circumferential direction line, and as shown in FIG. 3, the main portion of the ply folded portion 6b. 15A and a curved portion 15A passing inward in the radial direction along the tire 10, and an outer piece inclined outward in the tire axial direction toward the radially outer side away from the main portion 10 outside the curved axial portion 15A in the tire axial direction. 15o 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 radial height Hb of the inner piece 15i from the bead base line BL is set to be greater than 20 mm and not more than 40 mm, and the radial height Hc of the outer piece 15o from the bead base line BL is greater than 20 mm. Further, it is set to 40 mm or less and the radial height Hb or more. The “bead base line BL” means a tire axial line passing through a rim diameter position determined by a standard based on the tire.

  Thus, in the bead reinforcing layer 15, when the radial height Hc of the outer piece 15o is set higher than 20 mm, the outer piece 15o functions as a shielding plate and moves toward the bead toe side. It is possible to reduce the rubber movement F (shown by a one-dot chain line in FIG. 3) by the shielding effect. Further, in the inner piece 15i, the ply main body portion 6a is coupled to reinforce the ply main body portion 6a. Therefore, by setting the radial height Hb to be higher than 20 mm, the carcass ply 6A is allowed to fall when a load is applied. It can be reduced. And by these interactions, the rubber movement F is effectively suppressed, and the accompanying dragging of the ply turn-up portion 6b is suppressed, thereby reducing the shear strain between the carcass ply 6A and the bead core 5 at the position Q. It is possible.

  This shear strain reduction effect is more exhibited when Hb ≦ Hc, but when the difference (Hc−Hb) increases beyond 10 mm, the shear strain reduction effect tends to decrease, and the outer piece 15o The stress tends to concentrate at the outer end. Therefore, the difference (Hc−Hb) is preferably 0 or more and 10 mm or less. Even when the radial heights Hb and Hc exceed 40 mm, the effect of reducing the shear strain cannot be effectively exhibited.

  In order to suppress the cord rule at the position Q, as shown in an enlarged view in FIG. 4, the thickness t of the rubber G between the bead wire 20 and the carcass cord 21 at the position Q is set to 0.5-3. It is also important to secure the thickness within a range of 0 mm and relax and absorb the shear stress by elastic deformation of the rubber G. When the rubber thickness t is less than 0.5 mm, even when the bead reinforcing layer 15 is provided, the shear stress between the carcass ply 6A and the bead core 5 cannot be sufficiently relaxed and absorbed, and the position Q Invoke chord loose. However, if the rubber thickness t exceeds 3.0 mm, the locking force to the ply turn-up portion 6b becomes insufficient, and there is a possibility that a blow-through phenomenon may occur during traveling. Accordingly, the rubber thickness t is preferably in the range of 1.2 mm to 3.0 mm, 1.5 to 3.0 mm, and more preferably 2.0 to 3.0 mm. As a means for adjusting the rubber thickness t within the above range, in this example, the thickness t1 of the base portion 12A of the filling rubber 12 is set to be thick, but there is another gap between the base portion 12A and the carcass ply 6A. Means such as interposing a rubber layer or setting the thickness t2 of the topping rubber in the carcass ply 6A to be thicker than usual can be used.

  Next, when the complex elastic modulus Ea * of the filling rubber 12 is too soft as less than 2 Mpa, the ply folding portion 6b is easily dragged by the rubber movement F, which is disadvantageous for the cord loose at the position Q. . Therefore, it is preferable to set the complex elastic modulus Ea * to be greater than 3 Mpa, and more preferably 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. 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. 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 amount of sulfur is more preferably in the range of 5.0 to 12 phr, more preferably in the range of 7.0 to 12 phr, and still 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.

  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 is not particularly limited as long as it is smaller than the height hm.

  Next, FIG. 5 shows another embodiment of the filling rubber 12. In this example, the case where the sub-portion 12B of the filling rubber 12 forms a thin sheet with a substantially constant thickness is illustrated. In addition, in the filling rubber 12, the said winding part 11 can also be extended toward the ply main-body part 6a in contact with the radial direction upper surface SU of the bead core 5 by deleting the said sub part 12B.

  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 of FIG. 1 having a tire size of 11R22.5 was prototyped based on the specifications in Table 1, and the bead strength and bead durability of each sample tire were measured and compared with each other. Specifications other than those in Table 1 are the same.

  As shown in FIG. 6, 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 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 an enlarged view which shows the rubber | gum thickness between a bead wire and a carcass cord in the tire axial direction innermost point of a bead core. It is sectional drawing which shows the other example of a filling rubber. 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 portion 3 Side wall portion 4 Bead portion 5 Bead core 6A Carcass ply 6a Ply main body portion 6b Ply folded portion 10 Main portion 11 Winding portion 12 Filled rubber 15 Bead reinforcement layer 15a Curved portion 15i Inner piece 15o Outer piece 20 Bead wire 21 Carcass Code Q Bead core innermost point in the tire axial direction

Claims (4)

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 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 part extending toward the ply body part at a distance La of 15 mm or less from the upper surface;
And while setting the rubber thickness t between the bead wire and the carcass cord at the tire axial direction innermost point of the bead core to 0.5 to 3.0 mm,
A curved portion passing through the inner portion in the radial direction along the main portion of the ply turn-up portion in the bead portion, and a tire facing away from the main portion on the outer side in the tire axial direction of the curved portion toward the outer side in the radial direction. A bead reinforcement layer is provided that includes an outer piece that is inclined outward in the axial direction, and an inner piece that extends 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,
Moreover, the radial height Hb of the inner piece from the bead base line is greater than 20 mm and not more than 40 mm, and the radial height Hc of the outer piece from the bead base line is greater than 20 mm and not more than 40 mm and the radial height. A heavy-duty tire characterized by having a height Hb or more.   The winding portion is spaced apart from the upper surface in the radial direction of the bead core, and a filled rubber surrounding the bead core with a complex elastic modulus Ea * of 2 to 25 Mpa is disposed between the bead core, the ply folded portion, and the ply body portion. The heavy duty tire according to claim 1.   3. The heavy duty tire according to claim 2, wherein the filled rubber has a complex elastic modulus Ea * of greater than 3 Mpa and less than or equal to 25 Mpa and a sulfur content of 5 phr or greater.   The heavy load tire according to any one of claims 1 to 3, wherein the winding portion has a gap Lb between a tip thereof and the ply main body portion of 1 to 10 mm.

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