JP2014189178A - Radial tire for heavy load - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve bead durability.SOLUTION: An outside surface 4Sb of a bead part 4 is provided with: a convex curved part 20 curving in a convex shape on the tire outside and having a maximum thickness point P1 of becoming a maximum thickness Tmax in a thickness T between a ply folding-back part 6b and the outside surface 4Sb of the bead part 4; and a concave curved part 21 curving in a concave shape and having a minimum thickness point P2 of becoming a minimum thickness Tmin in the thickness T. The maximum thickness point P1 is positioned outside in the radial direction more than a core maximum width line X of a bead core 5, and the minimum thickness point P2 is positioned on a line of the core maximum width line or on the inside in the radial direction more than the core maximum width line X.

Description

  The present invention relates to a heavy-duty radial tire having improved bead durability by specifying a thickness between a ply folded portion of a carcass and an outer surface of a bead portion.

  In the heavy duty radial tire, for example, a high internal pressure exceeding 700 kPa is filled. Therefore, at the time of internal pressure filling, the tire is strongly pressed against the rim flange, and the bead portion falls down and deforms outward in the tire axial direction so as to bend around the rim flange. When the vehicle is in contact with the road surface during driving and a load is applied, the deformation is further increased. At that time, a shear strain is generated between the bead apex rubber and the ply folded portion of the carcass, and this shear strain is repeated, whereby damage such as cord loose occurs at the outer end portion of the ply folded portion.

  In order to suppress this damage and improve the bead durability, the bead is increased by increasing the thickness of the bead apex rubber, increasing the rubber hardness of the bead apex rubber, or providing a bead reinforcement layer using a steel cord in the bead part. Rigidity is increased and bead deformation itself is suppressed. Patent Document 1 below also proposes reducing the size of the bead apex rubber so that the ply body portion and the ply folding portion of the carcass are brought close to each other, thereby suppressing the occurrence of distortion at the outer end portion of the ply folding portion. Yes.

  However, in view of the recent demand for longer life of tires based on tire retreading, further improvement in bead durability is desired.

Japanese Patent Laid-Open No. 11-192819

  Therefore, the present invention relates to a heavy-duty radial tire with improved bead durability based on specifying the thickness from the ply turn-up portion of the carcass to the outer surface of the bead portion.

The invention according to claim 1 of the present invention is a ply turn-up that is folded from the inner side to the outer side in the tire axial direction around the bead core on both sides of the ply main body part that extends from the tread part through the sidewall part to the bead core of the bead part. A heavy-duty radial tire having a carcass ply using a carcass ply using a steel carcass cord, and mounted on a 15 ° taper rim,
In the region range from the position of the bead heel point to the position of the radially outer end of the ply turn-up portion,
The outer surface in the tire axial direction of the bead portion has a maximum thickness point that is convexly convex toward the outer side of the tire and that the thickness T between the ply turn-up portion and the outer surface of the bead portion is the maximum thickness Tmax. A convex curved portion, and a concave curved portion that is concavely curved and has a minimum thickness point at which the thickness T is the minimum thickness T min,
Moreover, the thickness T gradually increases from the minimum thickness point to the maximum thickness point, and gradually decreases from the maximum thickness point to the position of the radially outer end of the ply turn-up portion,
The bead core has a hexagonal cross-section, and the maximum thickness point is located radially outward from a core maximum width line parallel to a radial inner surface of the bead core and passing through a maximum width position of the bead core, and the minimum The thickness point is characterized by being located on the line of the core maximum width line or radially inward of the core maximum width line.

  According to a second aspect of the present invention, the concave curved portion is an arc having a radius of curvature r1 of 20 to 50 mm.

  According to a third aspect of the present invention, the minimum thickness point is located on the radially outer side of the core inner surface line extending along the radial inner surface of the bead core 5.

  According to a fourth aspect of the present invention, the bead portion includes a chafer rubber that is exposed to the outer surface in a flange contact region that contacts the flange of the 15 ° taper rim, and the chafer rubber has a durometer C hardness. Is 70 to 95.

  In this specification, the dimension of each part of the tire is a value specified when the bead part is held in accordance with the rim width defined by the tire size in the non-rim assembled state.

  The durometer C hardness is a rubber hardness measured under an environment of 23 ° C. by durometer type C based on JIS-K6253.

  As described above, according to the present invention, a convex curved portion having a maximum thickness point at which the thickness between the ply folded portion of the carcass and the outer surface of the bead portion is the maximum thickness Tmax on the outer surface of the bead portion; And a concave curved portion having a minimum thickness point at which the thickness T is the minimum thickness T min. The maximum thickness point is positioned radially outward from the core maximum width line, and the minimum thickness point is positioned on the core maximum width line or radially inward of the core maximum width line. Yes.

  By providing such a concave curved portion, the carcass tends to fall to the flange side during internal pressure filling as compared with a conventional tire not provided with the concave curved portion. On the other hand, by providing the convex curved portion, the fall of the carcass toward the flange side when a load is applied can be reduced. That is, as compared with the conventional tire, the carcass collapses at the time of internal pressure filling, but the amount of collapse between the internal pressure filling and the load application can be reduced. As a result, the amount of repeated change in strain at the outer end of the ply folded portion of the carcass can be reduced, and the bead durability can be improved.

It is sectional drawing which shows one Example of the radial tire for heavy loads of this invention. It is sectional drawing which expands and shows the bead part. It is sectional drawing which shows the shape of the outer surface of a bead part. It is a graph which illustrates notionally the operation effect of the present invention.

Hereinafter, embodiments of the present invention will be described in detail.
As shown in FIG. 1, the tire 1 of the present embodiment is a tubeless heavy-duty radial tire mounted on a 15 ° taper rim R, and a bead core 5 of a bead portion 4 from a tread portion 2 to a sidewall portion 3. Toroidal carcass 6 and a belt layer 7 disposed radially outside the carcass 6 and inside the tread portion 2.

  The carcass 6 is formed of a carcass ply 6A in which steel carcass cords are arranged at an angle of 80 to 90 ° with respect to the tire circumferential direction. The carcass ply 6 </ b> A includes a series of ply folding portions 6 b that are folded from the inner side to the outer side in the tire axial direction around the bead core 5 at both ends of the toroidal ply main body portion 6 a that extends between the bead cores 5 and 5. A radial height H6 from the bead base line BL of the ply folded portion 6b in the radial direction (sometimes referred to as a folded end) 6E is substantially the same as that of the conventional tire. The flange height Hf of the taper rim R is set to 2.5 to 3.0 times, for example, 2.9 times. The bead base line BL means a tire axial direction line passing through a bead heel point 4h that is an outer end in the tire axial direction of the bottom surface of the bead portion 4 (hereinafter sometimes referred to as “bead bottom surface”) 4Sa.

  The belt layer 7 is formed of a plurality of belt plies using steel belt cords. The belt layer 7 of this example includes a first belt ply 7A on the innermost side in the radial direction in which belt cords are arranged at an angle of, for example, 50 ± 10 ° with respect to the tire circumferential direction, and a belt cord that is sequentially stacked on the outer side. Is formed from second to fourth belt plies 7B to 7D arranged at an angle of 10 to 30 °, for example. The belt layer 7 has one or more places where the belt cords cross each other between the plies. As a result, the belt rigidity is increased and the entire width of the tread portion 2 is strongly reinforced.

  Also, the bead portion 4 has a bead apex rubber 8 that tapers from the bead core 5 radially outwardly between the ply body portion 6a and the ply turn-up portion 6b of the carcass 6, as in the conventional tire. A bead reinforcement layer 9 that covers the outside of the bead apex rubber 8 via the carcass 6 is disposed.

  As shown in FIG. 2 in an enlarged manner, the bead apex rubber 8 of this example is formed of a radially inner apex portion 8A made of hard rubber and a radially outer apex portion 8B made of soft rubber. . The bead apex rubber 8 having a two-layer structure can be deformed following the large strain of the sidewall portion 3 while increasing the bending rigidity of the bead portion 4, and is useful for suppressing damage on the outer end side. The rubber hardness of the inner apex portion 8A is about 75 to 95 in terms of durometer A hardness, and the rubber hardness of the outer apex portion 8B is about 30 to 70 in terms of durometer A hardness. The durometer A hardness is a value measured in a 23 ° C. environment by durometer type A based on JIS-K6253. The radially outer end 6E of the ply turn-up portion 6b terminates in contact with the outer surface of the outer apex portion 8B.

  The bead reinforcing layer 9 is formed of a single reinforcing ply in which steel reinforcing cords are arranged at an angle of, for example, 15 to 75 ° with respect to the tire circumferential direction. The bead reinforcing layer 9 increases the bead rigidity in cooperation with the bead apex rubber 8 and improves the handling stability under a high load. The bead reinforcement layer 9 of this example includes an outer piece portion 9o along the tire axial direction outer surface of the ply turn-up portion 6b, an inner piece portion 9i along the tire axial direction inner surface of the ply main body portion 6a, and a bottom piece portion 9a that connects between them. A U-shaped cross section consisting of The radial heights Hi and Ho from the bead base line BL of the inner piece portion 9i and the outer piece portion 9o are respectively larger than the flange height Hf and higher than the height H6 of the ply turn-up portion 6b. It is small.

  The bead core 5 has a hexagonal cross section in which bead wires are wound in multiple rows and stages. The radial inner surface 5S of the bead core 5 is inclined with respect to the bead base line BL at an angle θ of 15 to 20 °, for example, and becomes an inclination angle close to the rim seat Rs of the 15 ° taper rim R, whereby the rim fitting force is increased. Increased over a wide range. A known wrapping layer 11 is disposed around the bead core 5 for the purpose of preventing the bead wire from being scattered.

  The bead portion 4 is provided with a chafer rubber 10 for preventing rim deviation. The chafer rubber 10 is exposed at a tire axial direction outer side surface (hereinafter also referred to as a bead outer side surface) 4Sb of the bead portion 4 at least in the flange contact region F. The flange contact area F means an area that can come into contact with the flange Rf of the 15 ° taper rim R in a traveling state including when a load is applied. The chafer rubber 10 of the present example includes a chafer main portion 10A extending radially inward and outward on the outside of the carcass 6, and a chafer bottom portion 10B bent from the radially inner end of the chafer main portion 10A and extending along the bead bottom surface 4Sa. It has a substantially L-shaped cross section. The radially inner portion of the chafer main portion 10A is exposed in the flange contact region F. The radially outer portion of the chafer main portion 10A is adjacent to the sidewall rubber 3G. The interface K between the chafer rubber 10 and the side wall rubber 3G extends from the one end Qa on the bead outer surface 4Sb to the other end Qb on the outer surface of the bead apex rubber 8 in a radially outward direction.

  As shown in FIG. 3 in an enlarged manner, the bead outer surface 4Sb of the tire 1 has a tire in a region range L from the position of the bead heel point 4h to the position of the radially outer end 6E of the ply turn-up portion 6b. A convex curved portion 20 that curves outwardly and a concave curved portion 21 that curves concavely are arranged.

  The “position of the bead heel point 4h” is a height position of the tire axial direction line L1 passing through the bead heel point 4h (that is, corresponding to the bead base line BL). The “position of the outer end 6E” means the height position of the tire axial line L2 passing through the outer end 6E. The “region range L” means a region between the tire axial lines L1 and L2.

  The convex curved portion 20 is curved in a convex shape toward the tire outer side, and has a maximum thickness point P1 at which the thickness T between the ply folded portion 6b and the bead outer side surface 4Sb becomes the maximum thickness Tmax. . The concave curved portion 21 is curved in a concave shape and has a minimum thickness point P2 at which the thickness T becomes the minimum thickness Tmin. For comparison, the contour shape J of the bead outer surface of the conventional tire A is illustrated by a one-dot chain line.

  Here, when the maximum core width line parallel to the radial inner surface 5S of the bead core 5 and passing through the maximum width position of the bead core 5 is X, the maximum thickness point P1 is more radial than the maximum core width line X. Located outside. On the other hand, the minimum thickness point P2 is located on the core maximum width line X or on the inner side in the radial direction from the core maximum width line X. The thickness T gradually increases from the minimum thickness point P2 to the maximum thickness point P1, and from the maximum thickness point P1 to the position L2 of the radially outer end 6E of the ply turn-up portion 6b, The thickness T is gradually reduced.

  By providing such a concave curved portion 21 on the bead outer surface 4Sb, the carcass 6 tends to fall to the flange side during internal pressure filling as compared with the conventional tire A not provided with the concave curved portion 21. . On the other hand, by providing the convex curved portion 20 on the bead outer side surface 4Sb, the fall of the carcass 6 toward the flange side when a load is applied can be reduced. That is, as conceptually shown in FIG. 4, in the tire 1 of the present embodiment, compared to the conventional tire A (indicated by the alternate long and short dash line), the carcass 6 collapses at the time of internal pressure filling, but at the time of internal pressure filling. On the contrary, the fall amount Δ during the period from when the load is applied to when the load is applied can be reduced. As a result, it is possible to reduce the repeated change in strain at the outer end 6E of the ply folding portion 6b of the carcass 6 and to improve the bead durability.

  For this purpose, the difference (Tmax−Tmin) between the maximum thickness Tmax and the minimum thickness Tmin is preferably in the range of 3 to 9 mm. When the difference (Tmax−Tmin) is less than 3 mm, it is difficult to sufficiently exhibit the above effects. On the contrary, if the difference (Tmax−Tmin) exceeds 9 mm, a gap is generated at the time of fitting, causing a disadvantage that rim displacement occurs during running. Therefore, the lower limit of the difference (Tmax−Tmin) is preferably 4 mm or more, and the upper limit is preferably 6 mm or less.

  The concave curved portion 21 is preferably formed by an arc having a curvature radius r1 of 20 to 50 mm. When the curvature radius r1 exceeds 50 mm, the fall of the carcass 6 at the time of internal pressure filling becomes small, and it becomes difficult to reduce the amount of fall between the time of internal pressure filling and the time of loading. On the other hand, when the radius of curvature r1 is less than 20 mm, stress concentrates on the concave curved portion 21, and there is a possibility that new damage (such as cracks) starting from the concave curved portion 21 may be caused. From such a viewpoint, the lower limit value of the curvature radius r1 is preferably 30 mm or more, and the upper limit value is preferably 40 mm or less.

  Moreover, it is preferable that the concave curved portion 21 and the convex curved portion 20 are formed smoothly and continuously in an S shape. The convex curved portion 20 is formed in the flange contact area F. In other words, the convex curved portion 20 is formed by the hard chafer rubber 10. The convex curved portion 20 is smoothly connected to the interface K. The convex curved portion 20 is also preferably formed by an arc, and the curvature radius r2 is preferably in the range of 40 to 70 mm.

  The minimum thickness point P2 is preferably located on the radially outer side of the core inner surface line Y extending along the radial inner surface 5S of the bead core 5. When the minimum thickness point P2 is positioned on the core inner surface line Y or radially inward of the core inner surface line Y, it is difficult to reduce the fall of the carcass 6 toward the flange side when a load is applied.

  It is also preferable to form the chafer rubber 10 from an ultra-hard rubber having a durometer C hardness of 70 to 95 in order to reduce the amount of collapse between the time when the internal pressure is filled and the time when a load is applied. However, if the rubber hardness exceeds 95 (durometer C hardness), the rubber is hardened and the chafer rubber 10 tends to be damaged such as rubber cracks. On the other hand, if it is less than 70 (durometer C hardness), the bead durability improving effect tends to be lowered. The rubber hardness of the chafer rubber 10 is usually about 70 to 85 in terms of durometer A hardness.

  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 was prototyped according to the specifications shown in Table 1, and the bead durability of each sample tire was tested and compared. Except as described in Table 1, the specifications are substantially the same. The common specifications are as follows.
・ Tire size: 11R22.5
・ Tire cross-section height H: 239.8 mm
・ Rim size: 22.5 × 7.50,
・ Flange height Hf: 12.7mm
-Number of carcass plies: 1 piece Cord material: Steel Cord arrangement angle: 90 degrees (direction of circumference)
Ply turn-up height H6: 37 mm
Belt layer Number of plies: 4 Cord material: Steel Cord arrangement angle: Right 50 degrees / Right 18 degrees / Left 18 degrees / Left 18 degrees (direction of circumference)
(The order is from the inner ply to the outer ply. “Right” indicates a right-up in plan view, and “left” indicates a left-up in plan view.)
・ Bead reinforcement cord layer (U-shaped)
Number of plies: 1 Cord material: Steel Cord arrangement angle: 25 degrees (direction of circumference)
Inner piece height Hi: 27 mm
Outer piece height Ho: 27 mm
・ Bead apex rubber Height H8: 80mm
Inner apex rubber hardness (durometer A hardness): 80
Rubber hardness of outer apex part (durometer A hardness): 40

  Further, the contour shape J (shown in FIG. 3) other than the convex curved portion and the concave curved portion on the outer surface of the bead is substantially the same for each tire. In the table, δa means the maximum protrusion amount of the convex curved portion from the contour shape J, and δb means the maximum concave amount of the concave curved portion.

<Bead durability>
Using a drum testing machine, each sample tire was run at a speed of 20 km / h under the conditions of a rim (7.50 × 22.5), internal pressure (800 kPa), and load (88.26 kN), and the bead portion was damaged. The distance traveled until the occurrence of the problem was expressed as an index with Comparative Example 1 taken as 100. The larger the value, the better the bead durability. In the bead damage that occurred, “A” means that a cord loose occurred at the folded end of the carcass. “B” means that a rubber crack (crack) occurred on the outer surface of the bead portion.

DESCRIPTION OF SYMBOLS 1 Radial tire for heavy loads 2 Tread part 3 Side wall part 4 Bead part 4h Bead heel point 4Sb Outer side surface 5 Bead core 5S Radial inner surface 6 Carcass 6A Carcass ply 6a Ply main part 6b Ply folding | turning part 10 Chafer rubber 20 Convex curve part 21 Concave curve part L Range P1 Maximum thickness point P2 Minimum thickness point X Core maximum width line Y Core inner surface line

Claims (4)

A steel carcass cord is used that has a ply turn-up part that is turned from the inside to the outside in the tire axial direction around the bead core on both sides of the ply body part extending from the tread part through the sidewall part to the bead core of the bead part. A heavy duty radial tire having a carcass made of a carcass ply and mounted on a 15 ° taper rim,
In the region range from the position of the bead heel point to the position of the radially outer end of the ply turn-up portion,
The outer surface in the tire axial direction of the bead portion has a maximum thickness point that is convexly convex toward the outer side of the tire and that the thickness T between the ply turn-up portion and the outer surface of the bead portion is the maximum thickness Tmax. A convex curved portion, and a concave curved portion that is concavely curved and has a minimum thickness point at which the thickness T is the minimum thickness T min,
Moreover, the thickness T gradually increases from the minimum thickness point to the maximum thickness point, and gradually decreases from the maximum thickness point to the position of the radially outer end of the ply turn-up portion,
The bead core has a hexagonal cross-section, and the maximum thickness point is located radially outward from a core maximum width line parallel to a radial inner surface of the bead core and passing through a maximum width position of the bead core, and the minimum The thickness point is located on the core maximum width line or radially inward of the core maximum width line, the heavy duty radial tire characterized by the above.   The radial tire for heavy loads according to claim 1, wherein the concave curved portion is an arc having a radius of curvature r1 of 20 to 50 mm.   3. The heavy duty radial tire according to claim 1, wherein the minimum thickness point is located radially outside a core inner surface line extending along a radial inner surface of the bead core 5. The bead portion includes a chafer rubber that is exposed to the outer surface in a flange contact area that contacts the flange of the 15 ° taper rim on the outside of the carcass, and the chafer rubber has a durometer C hardness of 70 to 95. The heavy duty radial tire according to any one of claims 1 to 3.

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