JP2005178521A - Tire for heavy load - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tire for heavy loads capable of reducing the weight and enhancing the durability of a bead part. <P>SOLUTION: A return part 6b of a carcass ply 6A comprises a return main part 10 to be folded along an inner surface in the tire axial direction of a bead core 5, an inner surface SL in the tire radial direction, and an outer surface So in the tire axial direction, and a return sub part 11 which is continuous to the return main part 10 and extends separate from the bead core 5. The return sub part 11 extends in an inclined manner toward a body part 6a at the angle θ below 90° with respect to an outer surface SU in the tire radial direction of the bead core 5. The minimum distance La from an outer end E1 of the return sub part 11 to the outer surface of the bead core 5 is 5-12 mm. A bead reinforcing layer 8 includes an inner piece part 8a, a middle piece part 8b continuous to the inner piece part 8a and extending along the return main part 10, and an outer piece part 8c continuous to the middle piece part 8b and extending along the return sub part 11. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a heavy duty tire capable of improving the durability of a bead portion while reducing the weight.

  Heavy duty tires are used under harsh conditions such that the filled air pressure is high and the load is large. For this reason, the bead part which bears a big load is reinforced strongly, the thickness is large and the weight is also very large. In recent years, in order to reduce the weight of such a heavy-duty tire, for example, as shown in FIG. 4, the toroid-shaped main body b1 and the both ends of the main body b1 are continuously wound around the bead core c. Patent Document 1 below proposes a heavy duty tire including a carcass ply b including a folded portion b2.

Japanese Patent Laid-Open No. 2000-21916

  In the bead structure, the outer end of the folded portion b2 is provided in the vicinity of the periphery of the bead core c with a small distortion during tire loading, and thus is hardly affected by the distortion during the traveling. Therefore, damage such as cord loose starting from the outer end of the folded portion b2 is unlikely to occur. Further, since the length of the folded portion b2 of the carcass ply b can be reduced, it is useful for reducing the weight of the tire.

  In the heavy-duty tire, damage starting from the outer end of the folded portion b2 can be suppressed, but the outer end e1 of the bead reinforcing layer e arranged in a substantially U-shaped cross-section from the viewpoint of securing the rigidity of the bead portion is It is still provided in an area where the tire has a large strain when loaded. Therefore, it can be inferred that a large strain is likely to act on the outer end e1 of the bead reinforcement layer e due to load running, and that it becomes a starting point for damage such as looseness generated from the outer end e1.

  The present invention has been devised in view of the above-described problems. Basically, not only the folded portion of the carcass ply but also the outer end position of the bead reinforcing layer is provided in an area where the strain during load running is small. Thus, an object of the present invention is to provide a heavy duty tire capable of improving the durability of the bead portion while reducing the weight of the tire.

  The invention according to claim 1 of the present invention is such that at least one folded portion that is folded from the inner side to the outer side in the tire axial direction around the bead core is connected to the toroidal body portion straddling the pair of bead cores. A heavy-duty tire comprising a carcass including a carcass ply and a bead reinforcing layer disposed in a bead portion, wherein the turned-up portion includes a tire core inner side surface, a tire radial inner surface and a tire axial outer side of the bead core. A folded main portion that bends along a side surface, and a folded sub portion that extends from the bead core and extends to the folded main portion, and the folded sub portion is 90 ° with respect to the outer surface in the tire radial direction of the bead core. And the minimum distance from the outer end of the folded sub-portion to the outer surface of the bead core is 5 to 12 mm. , Moreover, the bead reinforcing layer is characterized by comprising a Chuhen portion extending along at least the folded main part and an outer piece portion extending along said folding auxiliary portion contiguous to the middle piece.

  According to a second aspect of the present invention, the outer end of the outer piece portion terminates at a distance of 1 mm or more and 12 mm or less from the outer end of the folded subportion along the folded subportion. Item 14. The heavy duty tire according to Item 1.

  The invention according to claim 3 is the heavy duty tire according to claim 1 or 2, wherein the carcass ply and the bead reinforcing layer are made of a steel cord ply.

  In the heavy duty tire of the present invention, the outer end of the folded portion of the carcass ply and the outer end of the bead reinforcing layer are both provided in the peripheral region of the bead core with a small distortion during tire running. Therefore, these outer ends are not easily affected by a large strain, and thus can be prevented from becoming a starting point of damage. Thereby, durability of a bead part improves. In addition, the tire weight can be reduced as a result of the lengths of the folded portion and the inner piece being small.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing the natural state of the heavy duty tire of the present invention, and FIG. Here, the natural state is an unloaded state in which a tire is assembled on a regular rim and filled with an internal pressure of 50 kPa. In the present specification, the “regular rim” is a rim determined by the standard for each tire in a standard system including a standard on which the tire is based. For example, a standard rim for JATMA and a “Design” for TRA. “Rim” or “Measuring Rim” for ETRTO. The regular rim of this embodiment is a 15 ° deep bottom rim (so-called 15 ° taper rim) referred to as JATMA.

  The reason why the internal pressure is set to 50 kPa is to specify the natural posture of the heavy duty tire 1. The heavy duty tire is exemplified by a tubeless type pneumatic tire in this example.

  The heavy-duty tire 1 includes a carcass 6 that extends from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and a belt layer 7 that is disposed radially outside the carcass 6 and inside the tread portion 2. And the bead reinforcement layer 8 distribute | arranged to the bead part 4 is provided.

  In the present embodiment, the carcass 6 is constituted by a single carcass ply 6A in which carcass cords are arranged at an angle of 80 to 90 ° with respect to the tire equator. The carcass ply 6A of the present embodiment is configured by a steel cord ply using a steel cord as a carcass cord, but an organic fiber cord ply such as nylon, rayon, polyester, aromatic polyamide or the like can be used as necessary. . The number of carcass plies is not particularly limited to one. Details of the carcass ply 6A will be described later.

  As shown in an enlarged view in FIGS. 2 to 3, in this embodiment, the bead core 5 is formed by winding steel bead wires 16 (in this example, strands) in a multi-stage multi-row spirally. It is a ring-shaped body. The cross-sectional shape of the bead core 5 is not particularly limited, but in this example, a flat hexagonal shape having a horizontally long cross section is exemplified. With respect to the bead core 5 having a substantially hexagonal cross section, in the cross section, the surface forming the long piece on the inner side in the tire radial direction is the tire radial direction inner surface SL of the bead core 5, and the surface forming the other long side is the bead core 5. The outer surface SU in the tire radial direction is assumed. Further, the surface forming the bent line-shaped bent side that connects the inner surface SL and the outer surface SU of the bead core 5 on the inner side in the tire axial direction is the inner side surface Si of the bead core in the tire axial direction, and the opposite bent side is the tire axis. Let it be the direction outer side surface So.

  In the cross section of the bead core 5, the inner surface SL extends substantially parallel to the rim sheet J 1 of the regular rim J. This is useful for increasing the fitting force between the bead portion 4 and the rim seat J1 over a wide range. As mentioned above, the regular rim J is a 15 ° deep bottom rim for tubeless tires. Accordingly, the inner surface SL and the outer surface SU of the bead core 5 are both inclined at an angle of approximately 15 ° with respect to the tire axial line. The term “substantially” takes into account errors in manufacturing, and an error of ± 2 ° from at least the above angle is allowed. As the cross-sectional shape of the bead core 5, a regular hexagonal shape, a rectangular shape, or a circular shape can be adopted as necessary. When the cross-section of the bead core 5 is circular, a side or a side surrounding the bead core 5 is virtually defined as a square or a rectangle along the tire axial direction, and the inner surface SL, the outer surface SU, the inner surface So, and the outer surface Si are defined in regions separated by diagonal lines. Can be assigned.

  The belt layer 7 is composed of at least two belt plies 7A, 7B, 7C and 7D in the present embodiment, preferably three or more, and in this embodiment. Each of the belt plies 7A to 7D employs a steel cord as a belt cord. The first belt ply 7A arranged at the innermost side in the tire radial direction has a belt cord arranged at an angle of 60 ± 15 ° with respect to the tire equator C, for example. The belt cords of the second to fourth belt plies 7B7C and 7D sequentially arranged on the outer side thereof are arranged at an angle of 10 to 35 ° with respect to the tire equator C, for example. The first to fourth belt plies 7A, 7B, 7C and 7D are overlapped by providing one or more places where the belt cords cross each other between the plies.

  The carcass ply 6A includes a toroid-shaped main body portion 6a straddling between a pair of bead cores 5 and 5 (only one bead core is shown in the figure), and is connected to both sides of the carcass ply 6A and a tire around the bead core 5. It is comprised with the folding | returning part 6b turned back from the axial direction inner side to the outer side.

  Further, the folded portion 6b includes a folded main portion 10 that bends along the inner surface Si of the bead core 5 in the tire axial direction, the inner surface SL in the tire radial direction, and the outer surface So in the tire axial direction, and is separated from the bead core 5 connected to the folded main portion 10. It is composed of a folded back sub-portion 11.

  The folded sub-portion 11 is inclined at an angle θ of less than 90 ° with respect to the outer surface SU in the tire radial direction of the bead core 5 and extends toward the main body 6a. As shown in an enlarged view in FIG. 3, the folded sub-portion 11 means a portion radially outward from the tire radial outer surface SU (or an extension thereof) of the bead core 5. When the angle θ is 90 ° or more, the locking force of the folded portion 6b with respect to the bead core 5 is reduced, and the so-called blow-through phenomenon of the carcass ply 6A is likely to occur. The angle θ is particularly preferably 75 ° or less. The lower limit of the angle θ is not particularly limited, but is limited by a distance La described later.

  The folded sub part 11 of the present embodiment is exemplified by a bent line shape that is bent in an inverted V shape, but may be formed in a straight line shape or a smooth curved line shape. When the folded subsection 11 has a bent line shape (or a curved line or the like) as in the present embodiment, the angle θ intersects the extension line of the radially outer surface SU in the steel cord SC of the carcass ply 6A. An angle between a straight line F connecting the lower end P of the folded sub-part 11 and the outer end E1 of the folded sub-part 11 and the outer surface SU in the tire radial direction of the bead core 5 is set.

  Further, as shown in an enlarged view in FIG. 3, the bead core 5 is formed by winding a bead wire 16 having a circular cross section, so that the cross-sectional shape of the outer surface SU in the tire radial direction is a semicircular arc connected in the tire axial direction. It becomes a rough outline. Accordingly, when measuring a relative distance from the outer surface SU, an angle with respect to the outer surface, and the like, the tangent line K drawn on the outer surface SU is used as a reference. Further, as shown exaggeratedly in FIG. 3, when the bead wires 16 are not aligned in a straight line but vary inward and outward in the tire radial direction, one tangent cannot be drawn on the tire radial outer surface SU of the bead core 5. . In this case, the tangent line K is in contact with the bead wire 16o located on the outermost side in the tire axial direction and the bead wire 16i located on the innermost side in the tire axial direction in the bead wire row forming the outer surface SU in the tire radial direction of the bead core 5. Approximate with tangent.

  Moreover, the shortest distance La from the outer end E1 to the tire radial direction outer surface SU of the bead core 5 is set to 5-12 mm. When the shortest distance La is less than 5 mm, the folded back sub-section 11 is likely to spring back with respect to the folded back main section 10, so that the formability of the green cover is deteriorated and the folded back sub-section 11 and the bead core during vulcanization. An air pocket is easily formed between the outer surface SU and the outer surface SU. On the contrary, when the shortest distance La exceeds 12 mm, the stress at the time of tire deformation tends to act strongly on the outer end E1 of the turn-up sub-part 11, and damage such as cord loose starting from the outer end tends to occur. . The shortest distance La is particularly preferably 7 to 12 mm.

  Further, it is desirable that the outer end E1 of the folded sub-part 11 is separated from the main body part 6a of the carcass ply 6A by a distance (between cords) Lb of 1 to 5 mm. When the distance Lb is less than 1 mm, the outer end (carcass cord) E1 of the folded sub-part 11 comes into contact with and rubs against the main body 6a (carcass cord) due to variations during tire molding, bead deformation during running, and the like. It tends to cause cord damage such as fretting. On the other hand, when the distance Lb exceeds 5 mm, the locking force to the bead core 5 by the folded sub-part 11 is insufficient, and the blow-through phenomenon is likely to occur.

  The folded portion 6b as described above is a peripheral region of the bead core having a small distortion even when the outer end E1 is running with a tire loaded (the state in which the inner end E1 is loaded with a normal internal pressure and is loaded). Therefore, durability is improved. Further, since the turn-up height of the carcass ply 6A is smaller than that of a conventional heavy load tire, the weight of the tire can be reduced.

  Examples of the bead reinforcing layer 8 include a steel cord ply in which steel cords are arranged at an angle of 10 to 40 ° with respect to a tire circumferential line. The bead reinforcing layer 8 of the present embodiment includes an inner piece portion 8a extending inward in the tire axial direction of the main body portion 6a of the carcass ply 6A, and a middle piece portion 8b extending along the folded main portion 10 connected to the inner piece portion 8a. And an outer piece portion 8c extending along the folded sub portion 11 and continuing to the middle piece portion 8b is exemplified.

  The inner piece portion 8a serves to suppress the collapse of the main body portion 6a of the carcass ply 6A when a load is applied, and thus to reduce the strain acting on the tip Pa of the folded sub portion 11. In order to obtain such an action, the height Hi of the outer end E3 of the inner piece 8a from the bead base line BL is equal to the maximum height Hc of the bead core 5 (the maximum radial distance from the bead base line BL to the bead core in the tire radial direction). 100% or more of the height to the outer position), more preferably 120% or more is desirable. On the other hand, when the height Hi increases, stress tends to concentrate on the outer end E3 of the inner piece 8a, so that the maximum height Hc of the bead core 5 is 400% or less, more preferably 300% or less. desirable.

  In this embodiment, the inner piece portion 8a and the main body portion 6a are bonded via respective topping rubbers. For example, at least an outer end region having a length of about 10 mm including the outer end E3 of the inner piece portion 8a. In this case, it is desirable to interpose an insulation rubber of about 0.5 to 1.5 mm between the main body 6a. In this case, the shearing force generated between the cords of the inner piece portion 8a and the main body portion 6a can be relaxed and the strain at the outer end E3 can be eased to further improve the durability of the bead portion 4.

  The middle piece portion 8 b is arranged in contact with the folded main portion 10. This portion is also because the influence of distortion during traveling is small because the portion is strongly compressed between the bead core 5 and the rim seat J1.

  Further, the outer piece 8 c extends along the folded sub-part 11. In the example of FIG. 2, the outer piece 8 c extends in parallel with the folded sub-part 11 by bonding the topping rubbers to each other. Such a bead reinforcement layer 8 can position the outer end E2 of the outer piece portion 8c in the peripheral region of the bead core 5 with less distortion during tire load running. Therefore, not only the outer end E1 of the turn-up sub-part 11 of the carcass ply 6A but also damage such as cord loose starting from the outer end E2 can be suppressed over a long period of time, and the durability of the bead part 4 can be further increased. The improvement of sex can be expected.

  As a preferred embodiment, the outer end E2 of the outer piece portion 8c is terminated on the outer side in the tire axial direction with respect to the outer end E1 of the folded sub portion 11 (the outer end E2 of the outer piece portion 8c is the outer end E1 of the folded sub portion 11). It is desirable to terminate before this. When the outer end E2 of the outer piece 8c extends further beyond the outer end E1 of the folded sub-part 11, the outer end E2 contacts and separates from the carcass cord of the main body 6a of the carcass ply 6A during tire loading. It is not preferable because it is easy to repeat and may damage the carcass cord.

  As a particularly preferable aspect, it is desirable that the outer end E2 of the outer piece portion 8c terminates with a distance Lc of 1 mm or more and 12 mm or less from the outer end E1 of the folding subsection 11 along the folding subsection 11. When the distance Lc is less than 1 mm, the folded sub-part 11 and the outer ends E1 and E2 of the outer piece part 8c come close to each other, so that a large rigidity step is formed in this part, and concentration of distortion is caused in this part. It becomes easy. On the other hand, when the distance Lc exceeds 12 mm, the locking effect on the folded sub-part 11 is reduced, and there is a risk that the folded sub-part 11 may be blown out during severe load traveling. From such a viewpoint, the distance Lc is preferably 2 mm or more and 10 mm or less.

  Further, the outer piece portion 8c and the folded sub-portion 11 are arranged such that the topping rubber is overlapped and bonded together, and as shown in FIG. The shortest distance Ld between the carcass cord 11 and the carcass cord is 0.2 mm or more, more preferably 0.5 mm or more. May be included. As a result, the shearing force between the steel cords can be relaxed, and loosening and the like at the outer end E2 of the outer piece 8c can be more reliably prevented. However, if the shortest distance Ld is too large, the outer end E2 of the outer piece 8c tends to approach a region having a large strain when the tire is loaded, so that it is 20 mm or less, more preferably 15 mm or less, and further 10 mm or less. In particular, it is desirable that the thickness is 5 mm or less.

  Further, in the heavy load tire 1 of the present embodiment, the filling rubber 12 is disposed in a region surrounded by the main body portion 6a and the folded portion 6b of the carcass ply 6A. The filling rubber 12 includes, for example, a base portion 12A having a substantially triangular cross section disposed between the outer surface SU in the tire radial direction of the bead core 5, the folded sub portion 11, and the main body portion 6a. Such a base portion 12A suppresses the springback of the folding sub-portion 11 by reducing the folding sub-portion 11 from excessively approaching the bead core 5, and also suppresses the occurrence of molding defects such as air residue during molding. Useful. Further, the filling rubber 12 includes a sub-part 12B having a relatively thin cross section and a substantially U-shape disposed between the bead core 5 and the folded main part 10.

  The filled rubber 12 is preferably made of a low elastic rubber composition having a complex elastic modulus Ea * of 2 to 25 MPa and an excellent impact or stress relaxation effect. Thereby, although it is small, the distortion which acts on the outer end E1 of the folding | turning subpart 11 is absorbed effectively, and it helps to prevent generation | occurrence | production of a cord loose. If the complex elastic modulus Ea * exceeds 25 MPa, the flexibility tends to be impaired and the stress relaxation effect tends not to be sufficiently obtained. Conversely, if the complex elastic modulus Ea * is less than 2 MPa, it becomes excessively soft and the folded portion 6b becomes rubber. It is easy to be dragged along with the deformation of the above, and there is a risk of causing the above-mentioned blow-out or the like when the temperature rises due to heat of the brake pad or the like transmitted through the rim J. From such a viewpoint, it is desirable that the complex elastic modulus Ea * of the filled rubber 12 is larger than 3 MPa, further larger than 8 MPa, and further larger than 13 MPa. 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%.

  The filled rubber 12 is preferably made of a high sulfur compounded rubber having a sulfur compounding amount of 5.0 phr or more as a vulcanizing agent. When sulfur is blended in an amount of 5.0 phr or more, the rubber is given a characteristic that is not easily softened by heat. On the other hand, when the compounding amount of sulfur exceeds 12 phr, vulcanization is excessively promoted, and rubber burns easily occur. Therefore, the amount of sulfur is preferably in the range of 5.0 to 12 phr, the lower limit is more preferably 7.0 phr or more, and the upper limit is more preferably 10 phr or less. In addition, the compounding quantity of sulfur of the rubber composition for general tires is 1.0-4.5 phr at most.

  Further, a bead apex 13 having a substantially tapered cross section is provided on the outer side in the tire radial direction of the folded sub-part 11 and the outer piece 8c. The bead apex 13 of the present embodiment has an inner apex portion 13a having a complex elastic modulus Eb1 * of 35 to 60 MPa, more preferably 40 to 55 MPa, and a rubber that is adjacent to the outer side in the tire radial direction and has a complex elastic modulus Eb2 *. An example is one having a two-layer structure with an outer apex portion 13b made of a rubber composition larger than 12 complex elastic modulus Ea * and smaller than the complex elastic modulus Eb1 * of the inner apex portion 13a. In this case, the radial height Ha from the bead base line BL of the inner apex portion 13a is preferably in the range of 40 to 60% of the total height Hb of the bead apex 8. Thereby, riding comfort and handling stability can be made compatible in a high dimension.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, it cannot be overemphasized that this invention can be deform | transformed and implemented in various aspects, without being limited to illustrated embodiment.

Prototype heavy-duty tires (size: 11R22.5, pattern: 5 ribs, groove depth 14 mm, tread width 230 mm, tread radius of curvature 700 mm) having the basic structure shown in FIG. The tire weight and bead durability were measured. As a comparative example, the same test was performed on the tire (comparative example) shown in FIG. 4 to compare the performance. The specifications not listed in the table are the same for each tire as follows. The test method is as follows.
(Example)
θ = 55 ° La = 7mm
Lb = 3mm
Hi / Hc = 200%
Ea * = 20 MPa
Eb1 * = 50 MPa
Eb2 * = 40 MPa
(Comparative example)
Hi / Hc = 220%
Ho / Hc = 170%
Ec * = 50 MPa

<Tire weight>
The weight per tire is measured and displayed as an index with a comparative example of 100. The smaller the value, the better.

<Bead durability>
Using a drum tester, the tire was assembled on a rim (size: 7.50 × 22.5) heated to 130 ° C., filled with an internal pressure of 700 kPa, and then subjected to a longitudinal load (3 times 27.25 kN) at a speed of 30 km. It was run at / h, and the running time until the bead portion was damaged was measured. The reason for heating the rim is to create a more severe situation. The evaluation was expressed as an index with the traveling time of the comparative example as 100. The larger the value, the better.

  As a result of the test, the heavy duty tire of the example can significantly improve the durability of the bead portion while reducing the weight of the tire.

It is a right half sectional view showing one embodiment of the heavy duty tire of the present invention. It is the elements on larger scale which expand and show the bead part. It is the cross-sectional schematic which expands and shows the bead part further. It is a fragmentary sectional view of the bead part of the conventional heavy duty tire.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heavy load tire 2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 6A Carcass ply 6a Carcass ply main part 6b Carcass ply turn part 8 Bead reinforcement layer 8a Inner piece part 8b Middle piece part 8c Outer piece part 10 Folded main part 11 Folded sub part E1 Folded sub part outer end E2 Outer piece outer end E3 Inner piece outer end

Claims (3)

A carcass including at least one carcass ply in which a toroidal main body portion straddling a pair of bead cores and a folded portion that is folded back from the inner side to the outer side in the tire axial direction around the bead core are arranged in the bead portion. A heavy duty tire with a bead reinforcement layer,
The folded portion includes a folded main portion that bends along the inner surface in the tire axial direction of the bead core, the inner surface in the tire radial direction, and the outer surface in the tire axial direction, and a folded sub portion that extends from the bead core and extends away from the bead core. Consists of
The folded sub-portion is inclined at an angle θ of less than 90 ° with respect to the outer surface in the tire radial direction of the bead core and extends toward the main body, and from the outer end of the folded sub-portion to the outer surface of the bead core. The shortest distance is 5-12mm,
Moreover, the bead reinforcing layer includes at least a middle piece portion extending along the folded main portion and an outer piece portion extending to the middle piece portion and extending along the folded sub portion. .   2. The heavy duty tire according to claim 1, wherein an outer end of the outer piece portion terminates at a distance of 1 mm or more and 12 mm or less along the turning sub-portion from the outer end of the folding sub-portion.   The heavy duty tire according to claim 1, wherein the carcass ply and the bead reinforcement layer are made of a steel cord ply.

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