JP2005067471A - Pneumatic tire for heavy load - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire for heavy load capable of enhancing the durability of a bead part. <P>SOLUTION: A carcass ply 6A comprises a toroidal body part 6a and a returned portion 6b returned from the inner side in the axial direction to the outside around a bead core 5 and having an outer end 6be extending inwardly in the axial direction on the outer side in the radial direction of the bead core 5 and terminating before the body part 6a. A cushion rubber 10 is filled in an area of a substantially triangular section surrounded by the returned portion 6b, an outer face 5o of the bead core and the body part 6a. The cushion rubber 10 is 3-12 mm in height h, and has a rubber composition in which the complex modulus of elasticity E*1 at 70°C is 3-13 MPa. A bead base rubber 11 arranged in an area in contact with a rim has a rubber composition in which the complex modulus of elasticity E*2 at 70°C is 11-30 MPa, and the loss tangent tanδ is 0.1-0.7. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

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

  For example, in a general heavy duty pneumatic tire, as shown in FIG. 3, at least one carcass ply a in which a steel cord or the like is covered with a topping rubber is bridged between a pair of bead cores b and b (note that In the figure, only one bead portion is shown, but the other bead portion is also configured symmetrically.) The carcass ply a includes a toroid-shaped main body portion a1 that extends from the tread portion through the sidewall portion to the bead core b, and a turn-back portion a2 that is connected to both ends and turned around the bead core b from the inner side to the outer side in the tire axial direction. It is out. Reference numeral d denotes a cord reinforcing layer disposed in a substantially U-shaped cross section.

  However, the outer end c of the folded portion a2 is not plated on the steel cord and has a low adhesive force with rubber. In particular, in a heavy-duty pneumatic tire in which a heavy load is applied during load running, rubber separation occurs at the outer end c due to bending deformation of the bead portion and the separation is caused by growth along the carcass ply a. It is easy to cause damage. Conventionally, Patent Document 1 below has been proposed to prevent such damage.

JP 2002-67628 A

  In the above-mentioned Patent Document 1, as shown in FIG. 4, the carcass ply a is folded around the bead core b from the main body a1 and both ends thereof from the inner side to the outer side in the tire axial direction. It is composed of a folded portion a2 that extends inward and terminates in front of the main body portion a1. Moreover, when forming such a folding | turning part a2, in order to make it easy to bend | fold in a carcass ply, it is also performed by necessity to provide a knotting (composition deformation location).

  Such a structure of the bead portion of the pneumatic tire is considered to be effective in suppressing separation damage and the like at the outer end c because the outer end c of the folded portion a2 is arranged in a region where distortion during load running is small. It is done.

  However, since Patent Document 1 does not specify the physical property value of rubber between the bead core 5 and the folded portion a2, there is room for further improvement in order to obtain effective bead durability. Further, in manufacturing, if the folded portion a2 is intended to be properly along the outer surface of the bead core b, the carcass ply a is wrinkled or waved in the vicinity of the outer end c of the folded portion a2 having a small inner diameter, as schematically shown in FIG. In addition to being prone to occur, the folded-up portion is likely to jump up and the moldability is poor. Further, the air may be vulcanized while containing air between the folded portion a2 and the bead core b. Such tires are likely to vary in manufacturing, and structural damage of the bead portion is likely to occur starting from an air reservoir between the bead core b and the folded portion a2.

  The present invention has been devised in view of the above problems, and limits the height and physical properties to a region having a substantially triangular cross section surrounded by the folded portion of the carcass ply, the outer surface of the bead core, and the main body of the carcass ply. A heavy-duty pneumatic tire that can improve the durability of the bead part based on limiting the physical properties of the bead base rubber disposed in the region from the bead bottom surface in contact with the rim to the bead outer surface. The purpose is to provide.

  The invention according to claim 1 of the present invention is a carcass made of a single carcass ply spanned between a pair of bead cores, and at least two of the carcass arranged radially outside the tire and inside the tread portion. A heavy-duty pneumatic tire provided with a belt layer composed of a belt ply, wherein the carcass ply includes a main body portion extending from the tread portion through the sidewall portion to the bead core of the bead portion, and the main body portion. A folded portion having an outer end that is folded around the bead core from the inner side in the tire axial direction to the outer side and extends outside in the tire radial direction of the bead core toward the inner side in the tire axial direction and terminates in front of the main body portion. And cushion rubber is disposed in a region having a substantially triangular cross section surrounded by the outer surface of the bead core and the main body. The bead core is made of a rubber composition having a height h of 3 to 12 mm perpendicular to the cross-sectional maximum width direction and a complex elastic modulus E * 1 of 3 to 13 MPa at 70 ° C., and is removed from the bead bottom surface in contact with the rim. The bead base rubber disposed in the region reaching the side surface is characterized by comprising a rubber composition having a complex elastic modulus E * 2 at 70 ° C. of 11 to 30 MPa and a loss tangent tan δ of 0.1 to 0.7. It is a heavy duty pneumatic tire.

  The complex elastic modulus and loss tangent tan δ were prepared as 4 mm wide × 30 mm long × 1.5 mm thick strip-shaped samples, using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co., Ltd. at the temperature of 70 ° C. It is a value measured under conditions of a frequency of 10 Hz, a static strain of 10%, and a dynamic strain of ± 2%.

  The invention according to claim 2 is the heavy duty pneumatic tire according to claim 1, wherein the cushion rubber is made of a rubber composition having a complex elastic modulus E * 1 of 3 to 7 MPa.

  According to a third aspect of the present invention, in the cushion rubber, a ratio (h / w) between the length w of the bottom in the tire radial direction and the height h is 0.25 to 0.75. The heavy-duty pneumatic tire according to claim 1 or 2, characterized in that

  According to a fourth aspect of the present invention, in the carcass ply, the minimum rubber thickness B between the outer end of the folded portion and the main body is 1 to 5 mm. The heavy-duty pneumatic tire according to any one of the above.

  According to a fifth aspect of the present invention, the folded portion includes a straight portion that is substantially linear from the maximum height position in the tire radial direction of the bead core to the outer end, and the straight portion is a tire. The pneumatic tire according to any one of claims 1 to 4, wherein the pneumatic tire rises at an angle α of 15 to 55 ° with respect to the axial line.

  In the heavy-duty pneumatic tire of the present invention, the folded portion of the carcass ply terminates in the tire radial direction outside of the bead core in the tire axial direction and before the main body of the carcass ply. Therefore, the outer end of the folded portion can be positioned in a region where the distortion is small even during load traveling. In addition, a cushion rubber having a limited height and physical property value is disposed in a region having a substantially triangular cross section surrounded by the folded portion, the outer surface of the bead core, and the main body portion. In addition to helping to reduce air accumulation, it is possible to relax and absorb the strain that acts on the folded portion during travel. Further, by limiting the complex elastic modulus E * 2 and loss tangent tan δ of the bead base rubber disposed in the region extending from the bottom surface of the bead in contact with the rim to the outer surface of the bead, the rubber is cured by heat and brought into contact with the rim. Cracks in the bead base rubber that tend to occur due to changes over time such as shear stress can be suppressed over a long period of time. Due to these synergistic effects, the heavy duty pneumatic tire of the present invention can greatly improve the durability of the bead portion.

  According to a third aspect of the present invention, the cushion rubber has a ratio (h / w) of the length w of the bottom in the tire radial direction to the height h in a range of 0.25 to 0.75. When it is limited to, the position of the outer end of the folded portion can be positioned in a more optimal region with less distortion, and the durability of the bead portion can be further improved.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a tubeless type heavy-duty radial tire (hereinafter simply referred to as a “tire”) used for a truck, bus, etc. in a normal state in which a normal rim J is assembled with a rim and filled with a normal internal pressure and is unloaded. 1) is exemplified. In FIG. 2, the rim is omitted and only the bead portion 4 is taken out and enlarged. 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 If so, use "Measuring Rim". In addition, “regular internal pressure” is the air pressure that each standard defines for each tire in the standard system including the standard on which the tire is based. The maximum air pressure is JATMA, the table is “TIRE LOAD LIMITS The maximum value described in "AT VARIOUS COLD INFLATION PRESSURES". If ETRTO, "INFLATION PRESSURE".

  In the figure, a tire 1 includes a tread portion 2, a pair of sidewall portions 3 extending inward in the tire radial direction from both ends thereof, and a bead portion that is positioned at an inner end of each sidewall portion 3 and is attached to a rim J. 4. The pneumatic tire 1 is provided with a toroidal carcass 6 spanned between the bead portions 4 and 4 and a belt layer 7 located outside the carcass 6 and inside the tread portion 2. Yes.

  The carcass 6 is composed of one carcass ply 6A. The carcass ply 6A includes a main body portion 6a that extends from the tread portion 2 through the side wall portion 3 to the bead core 5 of the bead portion 4, and is connected to the main body portion 6a and folded around the bead core 5 from the inner side to the outer side in the tire axial direction. In addition, the bead core 5 is provided with a folded portion 6b that extends inwardly in the tire radial direction and ends in front of the main body 6a. The main body portion 6a of the carcass ply 6A refers to a portion from the tread portion 2 to the tire axial direction line N passing through the position of the maximum radial height Hb (shown in FIG. 2) of the bead core 5 from the outer end. Up to 6be is defined as the folded portion 6b. In FIG. 2, reference sign BL is a bead base line passing through the rim diameter position.

  As the carcass ply 6A, a sheet-like one in which a carcass cord made of a steel cord is arranged with an angle range of, for example, 80 to 90 ° with respect to the tire equator C and covered on both sides with a topping rubber is used. In addition, an inner liner rubber layer (details not shown) is attached to the inner side of the carcass 6 so as to form a tire lumen surface and to be excellent in air impermeability.

  Examples of the belt layer 7 include those formed of at least two belt plies 7A to 7D in this example. Specifically, the innermost belt ply 7A in which the belt cord is inclined with respect to the tire equator C at an angle of, for example, about 60 ± 10 °, and the belt that is inclined with respect to the tire equator C at a small angle of 30 ° or less. The plies 7B, 7C, and 7D are overlapped with each other by providing one or more locations where the belt cord intersects between the plies. For example, a steel cord is preferably used for the belt cord of each belt ply.

  In this example, the bead core 5 is formed in a polygonal cross section (in this example, a horizontally long substantially hexagonal shape) by spirally winding a steel bead wire having a circular cross section a predetermined number of times. In the contour shape of the bead core 5, the inner surface 5i that is long on the inner side in the tire radial direction and the outer surface 5o that is long on the outer side (each surface is assumed to be an imaginary straight line that touches the uneven contour line formed by the cross-section circular wire). Is inclined at about 10 to 17 ° with respect to the tire axial line, and is substantially along the inclination of the rim sheet J1 of the regular rim J which is a 15 ° deep bottom rim. Further, as shown in FIG. 2, the bead core 5 has a maximum cross-sectional width BW parallel to the inner surface 5i and the outer surface 5o. The bead core 5 is made of a steel material in the present embodiment, but can be made of a substantially non-extensible material such as an aromatic polyamide.

  In the carcass ply 6 </ b> A of the present embodiment, the folded portions 6 b on both sides are folded back from the inner side in the tire axial direction by the bead core 5. Moreover, the folded-back portion 6b extends slightly obliquely from the outside in the tire radial direction of the bead core 5 to the inside in the tire axial direction and the outside in the tire radial direction so as to wrap the bead core 5. The outer end 6be of the folded portion 6b terminates in front of the carcass ply without contacting the main body portion 6a.

  A cushion rubber 10 is disposed in a region having a substantially triangular cross section surrounded by the folded portion 6b, the outer surface 5o of the bead core 5 and the main body portion 6a. The cushion rubber is made of a rubber composition having a height h of 3 to 12 mm perpendicular to the direction of the maximum cross-sectional width BW of the bead core 5 and a complex elastic modulus E * 1 at 70 ° C. of 3 to 13 MPa.

  The inventors made a plurality of heavy-duty pneumatic tires by changing the height h of the cushion rubber 10 and confirmed its moldability and bead durability. As a result, if the height h is smaller than 3 mm, the folded portion 6b easily jumps up from the bead core 5 as described above, and the rubber volume between the folded portion 6b and the bead core 5 is reduced. It was found that the amount of cushion rubber sufficient to absorb wrinkles and undulations near the edges could not be secured, and air and the like were easily sealed on the outer surface of the bead core 5 during molding, and peeling was likely to occur at the interface between the two. . On the other hand, if the height h of the cushion rubber exceeds 12 mm, the outer end 6be of the folded portion 6b is likely to be located in a large strain area during travel. Is likely to occur. Particularly preferably, when the height h of the cushion rubber 10 is larger than 5 mm and smaller than 10 mm, a more remarkable improvement in durability and excellent moldability can be obtained.

  The cushion rubber 10 is made of a rubber composition having a complex elastic modulus E * 1 at 70 ° C. of 3 to 13 MPa. The folded portion 6b of the present embodiment extends the outside of the bead core 5 in the tire radial direction obliquely outward in the tire axial direction. Therefore, the cushion rubber 10 receives a load in the tire radial direction during load traveling through the folded portion 6b. Here, by optimizing the elastic modulus of the cushion rubber 10, the vibration of the folded portion 6b during traveling, in particular, the movement of the outer end 6be of the folded portion 6b is absorbed and mitigated, and the damage from the outer end 6be is effective. Can be prevented. As described in Examples below, the complex elastic modulus E * 1 of the cushion rubber 10 is particularly preferably 3 to 7 MPa, and more preferably 4 to 6 MPa.

  The cushion rubber 10 is not particularly limited, but the ratio (h / w) between the length w of the bottom in the tire radial direction inner side (measured in parallel with the outer surface 5o of the bead core) and the height h. Is preferably 0.25 to 0.75, more preferably 0.3 to 0.7. Thus, when the ratio (h / w) of the cushion rubber is limited, it helps to position the outer end 6be of the folded portion 6b to a region where the distortion is smaller, and the durability of the bead portion. Can be improved.

  In the present embodiment, the minimum rubber thickness B between the outer end 6be of the folded portion 6b and the main body portion 6a is set to 1 to 5 mm. When the minimum rubber thickness B is less than 1 mm, the carcass cords of the main body portion 6a and the folded portion 6b approach each other, and rubber peeling is likely to occur. Conversely, if the minimum rubber thickness B exceeds 5 mm, the folded portion The adhesion length between the portion 6a and the rubber tends to be reduced, and the durability of the bead portion 4 is similarly reduced, such as the folded portion 6b being easily pulled out into a lip shape by the carcass cord tension acting on the main body portion 6a. There is a tendency to make it. From this point of view, it is particularly preferable that the minimum rubber thickness B is 1.5 to 6.0 mm, more preferably 2.0 to 4.0 mm.

  Further, the folded portion 6b of the present embodiment is formed as a linear portion 9 in which the position from the maximum height Hb of the bead core 5 in the tire radial direction to the outer end 6be of the folded portion is substantially linear. Such a straight portion 6b does not need to bend the carcass cord of the turned-up portion 6b, and thus does not require processing such as staking, and is excellent in moldability at the time of manufacture. It is desirable that the straight portion 9 rises outward in the tire radial direction toward the inner side in the tire axial direction at an angle α of, for example, about 15 to 55 °, more preferably about 40 to 55 ° with respect to the tire axial direction line N.

  The folded portion 6b includes a bending deformation force of the steel cord that causes the folded portion 6b to fall into the cushion rubber 10 and an axial force along the longitudinal direction of the steel cord. Can be shared. Since the former force is further borne by the cushion rubber 10, it helps to improve the compressive load resistance performance in the tire radial direction in the bead portion 4.

  A bead apex 12 that is tapered and extends outward in the tire radial direction is disposed outside the folded portion 6b in the tire radial direction. The bead apex 12 has a sufficiently large height in the tire radial direction as compared with the cushion rubber 10, and effectively increases the bending rigidity of the bead portion 4. As the bead apex 12, a rubber composition having a complex elastic modulus E * 3 of, for example, 20 to 50 MPa, more preferably 30 to 45 MPa is used. If the complex elastic modulus E * 3 of the bead apex 12 is less than 20 MPa, the bending rigidity of the bead portion 4 cannot be effectively increased, and the durability tends to deteriorate due to heat generation due to a large bending deformation, On the other hand, if it exceeds 50 MPa, the bending rigidity of the bead portion 4 is remarkably increased, and the shock absorption tends to be lowered and the riding comfort tends to be impaired.

  In the bead portion 4, a bead base rubber 11 is disposed in a region from the bead bottom surface 4 b in contact with the rim J to the bead outer surface 4 a. The bead base rubber 11 of the present embodiment includes a main portion 11a extending over the bead bottom surface 4b, an inner portion 11b covering the bead toe extending radially outward in the tire axial direction inside the main portion 11a, and the main portion 11a. The thing of the cross-sectional substantially U shape including the outer side part 11c which covers the bead outer side surface 4a extended in the tire radial direction outward from a tire axial direction outer side is illustrated.

  The bead base rubber 11 generates a large amount of friction with the rim J during traveling, and thus receives a large shear force on the surface and generates heat. The exotherm causes the rubber to cure and the shear force causes cracks in the cured rubber. In the present embodiment, a rubber composition capable of suppressing such cracks over a long period of time is employed for the bead base rubber 11. Specifically, by using a rubber composition having a complex elastic modulus E * 2 at 70 ° C. of 11 to 30 MPa and a loss tangent tan δ of 0.1 to 0.7, the bead bottom surface 4b or the bead contacting the rim J The generation of cracks on the outer side surface 4a is suppressed.

  If the complex elastic modulus E * 2 is smaller than 11 MPa, cracks tend to occur in the bead base rubber 11 due to long-term running. Conversely, if the complex elastic modulus E * 2 is larger than 30 MPa, chipping or the like is likely to occur during rim assembly. Neither is preferred. Particularly preferably, the complex elastic modulus E * 2 is larger than E * 1, and is preferably 15 to 25 MPa, more preferably 17 to 23 MPa.

  Further, if the loss tangent tan δ of the bead base rubber 11 is smaller than 0.1, vibration during traveling tends to occur, and air leakage tends to occur, and conversely, if larger than 0.7, Both are unfavorable because they tend to accumulate and easily cure. It is particularly preferable that the loss tangent tan δ of the bead base rubber 11 is 0.2 to 0.5, and more preferably 0.2 to 0.4.

  Further, in the heavy duty pneumatic tire 1 of the present embodiment, the cord reinforcing layer d as shown in FIG. In the tire 1 of the present embodiment, the folded portion 6b of the carcass ply 6A is located in a region where the distortion during running is small, and therefore it is not necessary to cover it with a cord reinforcing layer. Rather, the provision of the conventional cord reinforcing layer d is not preferable because the outer end thereof becomes a starting point of new damage. Further, since the bead bottom surface 4b is covered with the bead base rubber 11 defining the above-described rubber physical properties, durability can be maintained without providing the cord reinforcing layer d.

  A heavy-duty pneumatic radial tire with a 5 rib pattern having a basic configuration of FIGS. 1, 3 and 4 and having a tire size of 11R22.5 is manufactured based on the specifications shown in Table 1, and the bead strength and bead are determined according to the following procedure. Tests were conducted for durability, defect rate during manufacture, and bead base aging. Each tire has the same bead apex height. In addition, the length W of the bottom side of the cushion rubber was set to 12 mm for those having cushion rubber. In Example 7, a cord reinforcing layer having a U-shaped cross section is provided, and in other Examples 1 to 6 and Comparative Examples 2 to 7, no reinforcing ply other than the carcass ply is provided in the bead portion. .

<Bead strength>
After assembling each test tire on a rim of 7.50 × 22.5, water was injected into the tire and the pressure when the tire burst was measured. The results are indicated by an index with the pressure of Comparative Example 1 being 100, and the larger the value, the better the bead strength.

<Bead durability>
After assembling each test tire on a 7.50 x 22.5 rim, it is filled with JATMA standard air pressure, and a load three times the maximum load capacity of JATMA standard is applied, and the drum is run at a speed of 30 km / H. The time until the tire was damaged was measured. The results are expressed as an index with the time of Comparative Example 1 being 100, and the larger the value, the better the bead durability.

<Defect rate during production>
Each of the test tires was made on a trial basis, and the occurrence rate of defective products was measured. The defective product was obtained by scanning the meridional section of the tire with a CT scanner and trapping air between the bead core and the folded portion. The smaller the numerical value, the lower the defect rate and the better.

<Time-dependent change of bead base>
Each test tire is assembled on a rim of 7.50 x 22.5, filled with normal internal pressure, mounted on the rear wheel of a 20-ton dump truck with a constant load, and after running 100,000 km, the tire Was removed from the rim, and the change in the angle of the bottom surface of the bead from when it was new was measured. The smaller the value, the smaller the bead base angle change and the better.
Tables 1 and 2 show the test results.

  As a result of the test, it can be seen that the tires of the examples significantly improved the strength and durability of the bead portion. In addition, it can be confirmed that defects at the time of manufacture are greatly improved.

It is sectional drawing of the normal state of the pneumatic tire of this embodiment. It is the expanded sectional view which expanded the bead part. It is an expanded sectional view of the bead part of the conventional pneumatic tire. It is an expanded sectional view of the bead part of the conventional pneumatic tire of other examples. It is a partial expansion perspective view of the bead core vicinity.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 6A Carcass ply 6a Main part 6b Folding part 6be Folding part outer end 10 Cushion rubber 11 Bead base rubber

Claims (5)

A carcass made of one carcass ply spanned between a pair of bead cores, and a belt layer made of at least two belt plies arranged on the outer side in the tire radial direction of the carcass and inside the tread portion are provided. A heavy duty pneumatic tire,
The carcass ply has a main body part extending from the tread part through the sidewall part to the bead core of the bead part,
A folded portion having an outer end that extends from the inner side in the tire axial direction to the outer side and is connected to the main body portion; With
Cushion rubber is arranged in a region having a substantially triangular cross section surrounded by the folded portion, the outer surface of the bead core and the main body portion,
The cushion rubber is made of a rubber composition having a height h of 3 to 12 mm perpendicular to the cross-sectional maximum width direction of the bead core and a complex elastic modulus E * 1 at 70 ° C. of 3 to 13 MPa.
The bead base rubber disposed in the region extending from the bottom surface of the bead in contact with the rim to the outer surface of the bead has a rubber composition having a complex elastic modulus E * 2 at 70 ° C. of 11 to 30 MPa and a loss tangent tan δ of 0.1 to 0.7. A heavy-duty pneumatic tire characterized by comprising a thing.   The heavy-duty pneumatic tire according to claim 1, wherein the cushion rubber is made of a rubber composition having a complex elastic modulus E * 1 of 3 to 7 MPa.   3. The cushion rubber according to claim 1, wherein a ratio (h / w) between a length w of a bottom side in the tire radial direction and the height h is 0.25 to 0.75. The heavy-duty pneumatic tire described.   4. The heavy-duty pneumatic according to claim 1, wherein the carcass ply has a minimum rubber thickness B of 1 to 5 mm between an outer end of the folded portion and the main body portion. tire.   The folded portion is a straight portion that is substantially linear from the maximum height position of the bead core in the tire radial direction to the outer end, and the straight portion is 15 to 55 with respect to the tire axial line. The pneumatic tire according to any one of claims 1 to 4, wherein the pneumatic tire rises at an angle α of °.

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