JP7075203B2 - Pneumatic tires - Google Patents

Description

The present invention relates to a pneumatic tire. More specifically, a pneumatic tire with excellent durability and rolling resistance, which includes a pair of support rubbers arranged so as to sandwich the winding end of the chafer layer from both sides in the tire width direction, and silica in the tread rubber. Regarding.

Pneumatic tires with pad rubber on the bead are known. For example, Patent Documents 1 and 2 disclose a pneumatic tire in which a pad rubber is arranged on the outer surface side of a carcass ply tire corresponding to the outer side of the bead filler in the tire width direction. According to the pad rubber, strain concentration near the outer diameter side end of the bead filler due to load input from the rim flange during load rolling and / or deformation of the sidewall is suppressed, and the carcass ply wound up here. Separation is suppressed.

The pad rubber of Patent Document 1 is arranged over the tire inner surface side of the rim strip rubber and the sidewall rubber adjacent to the tire radial outer diameter side. The pad rubber of Patent Document 2 is arranged on the inner surface side of the tire of the rim strip rubber.

Japanese Patent No. 5442762 Japanese Patent No. 594486

In the pneumatic tire of Patent Document 2, a chafer layer wound up from the inner surface side of the tire to the outer surface side of the tire is arranged around the bead portion. In this case, during load rolling, strain tends to concentrate on the winding end of the chafer layer around the bead portion. However, in the pneumatic tire of Patent Document 2, since the pad rubber is arranged on the outer side in the tire radial direction with respect to the chafer layer, it does not effectively contribute to the suppression of strain concentration at the winding end portion of the chafer layer.

INDUSTRIAL APPLICABILITY The present invention improves durability and reduces tire rolling resistance in a pneumatic tire having a chafer layer in the bead portion and capable of suppressing concentration of strain near the winding end of the chafer layer. The problem is to decrease.

The present invention comprises a pair of bead cores, a pair of bead fillers connected to each of the pair of bead cores and extending toward the outer diameter side in the tire radial direction, a carcass ply spanned between the pair of bead cores, and the carcass ply. The sidewall rubber, which is arranged on the outer surface side of the tire and constitutes the outer surface of the tire, is folded back from the inner surface side of the tire to the outer surface side of the tire around the bead core and the bead filler, and is wound up on the outer surface of the carcass ply. A pair of support rubbers located between the sidewall rubber and the carcass ply and arranged so as to sandwich the winding end portion of the chafer layer from both sides in the tire width direction. Pneumatic tires comprising a tread rubber and characterized in that the modulus value of the pair of support rubbers is higher than the modulus value of the sidewall rubbers, the tread rubber provides a pneumatic tire containing silica. do.

According to the present invention, since the winding end portion of the chafer layer is sandwiched in the tire width direction by the support rubber having a higher modulus than the sidewall rubber, the strain concentration that may occur in the vicinity of the winding end portion is suppressed. .. As a result, the separation at the winding end of the chafer layer is suppressed. Further, by containing silica in the tread rubber, the rolling resistance of the tire can be reduced and the fuel efficiency can be improved.

Preferably, the pair of support rubbers are a pad rubber adjacent to the tire outer surface side with respect to the winding end portion of the chafer layer, and a tape rubber adjacent to the tire inner surface side with respect to the winding end portion of the chafer layer. And, it is composed of.

According to this configuration, since the tape rubber is arranged between the winding end portion of the chafer layer and the carcass ply, the step portion formed on the outer surface of the carcass ply by the tape rubber can be reduced. As a result, the winding end of the chafer layer can be easily wound along the outer surface of the carcass ply. As a result, while the winding end of the chafer layer is sandwiched between the tape rubber and the back pad rubber in the tire width direction, an excessive step is not formed in the vicinity of the winding end of the chafer layer. It is easy to suppress the occurrence of bears. As a result, the separation at the winding end of the chafer layer can be further suppressed.

On the other hand, when the back pad rubber is arranged between the winding end of the chafer layer and the carcass ply, a large step portion is formed by the back pad rubber on the outer surface of the carcass ply. Due to the stepped portion, air is likely to be generated between the member and the member arranged here.

Further, preferably, the position of the inner diameter end of the pad rubber in the tire radial direction is different from that of the inner diameter end of the tape rubber. More preferably, the outer diameter end of the pad rubber is different in position in the tire radial direction from the outer diameter end of the tape rubber.

According to this configuration, since the positions of the tire radial end portions of the pad rubber and the tape rubber where strain is likely to be concentrated are different in the tire radial direction, it is possible to suppress excessive strain concentration on the radial end portions.

Further, preferably, the winding end portion of the chafer layer is a tire reference from a position of 3% of the tire reference cross-sectional height inward in the tire radial direction to the outside in the tire radial direction with reference to the outer diameter side end portion of the bead core. It is located in the radial range at a position of 5% of the cross-sectional height.

According to this configuration, the chafer layer is arranged so as to correspond to the contact portion with the rim flange in the bead portion of the pneumatic tire, and the winding end portion of the chafer layer is excessively on the outer diameter side in the tire radial direction. It can be suppressed from being positioned. As a result, the exposure of the carcass ply can be suppressed by the chafer layer even when the contact portion with the rim flange is worn.

Further, by limiting the height position of the winding end portion of the chafer layer in the tire radial direction, the winding end portion is easily arranged away from the portion of the sidewall portion having a large distortion, and the sidewall portion is deformed. The increase in strain caused by the above is suppressed. As a result, the separation at the winding end of the chafer layer is further suppressed.

If the winding end of the chafer layer is located inward in the tire radial direction with reference to the outer diameter side end of the bead core in excess of 3% of the tire reference cross-sectional height, the carcass ply will be generated when the bead part is worn. There is a risk of being exposed. Further, when the winding end portion of the chafer layer is located to the outer diameter side in the tire radial direction with respect to the outer diameter side end portion of the bead core exceeding 5% of the tire reference cross-sectional height, the winding end portion is located on the outer diameter side. Since it is close to the portion of the wall where the strain is large, the strain tends to increase excessively.

Further, preferably, the winding end portion of the chafer layer overlaps with the pair of support rubbers by 5 mm or more in the tire radial direction.

According to this configuration, since the winding end portion of the chafer layer is firmly supported by the support rubber over at least 5 mm in the tire radial direction, strain concentration is suitably suppressed.

Further, preferably, in the tire radial direction, the pad rubber is arranged in a radial range of 15% or more and 45% or less of the tire reference cross-sectional height.

According to this configuration, the pad rubber is located over a predetermined range in the tire radial direction while overlapping with the winding end portion of the chafer layer. As a result, the strain generated around the bead portion of the pneumatic tire can be dispersed in a predetermined range in the tire radial direction via the pad rubber, so that the strain at the winding end portion of the chafer layer can be suppressed. If the pad rubber is arranged in a radial range larger than 45% of the tire reference cross-sectional height, the proportion of the sidewall rubber in the sidewall portion is excessively reduced, resulting in deterioration of fuel efficiency.

Further, preferably, in the tire radial direction, the tape rubber is arranged in a radial range of 5% or more and 20% or less of the tire reference cross-sectional height.

According to this configuration, the tape rubber is located over a predetermined range in the tire radial direction while overlapping with the winding end portion of the chafer layer. As a result, the strain generated around the bead portion of the pneumatic tire can be dispersed in a predetermined range in the tire radial direction via the tape rubber, so that the strain at the winding end portion of the chafer layer can be suppressed.

According to the present invention, in a pneumatic tire provided with a chafer layer in the bead portion, concentration of strain at the winding end portion of the chafer layer can be suppressed, thereby improving durability. In addition, the rolling resistance of the tread rubber can be reduced to improve fuel efficiency.

A meridian half cross section of a pneumatic tire according to an embodiment of the present invention. FIG. 1 is an enlarged view showing the periphery of the bead portion of the pneumatic tire of FIG. The figure which shows the sidewall member schematically. A graph showing the thickness of the pad rubber.

Hereinafter, embodiments according to the present invention will be described with reference to the accompanying drawings. It should be noted that the following description is merely an example and is not intended to limit the present invention, its application, or its use. In addition, the drawings are schematic, and the ratio of each dimension is different from the actual one.

FIG. 1 is a meridian half-section view of a pneumatic tire 1 according to an embodiment of the present invention, showing only one side in the tire width direction with respect to the tire equatorial line CL. The pneumatic tire 1 includes a tread portion 10, a pair of sidewall portions 20 extending inward in the tire radial direction from the end portion of the tread portion 10 in the tire width direction, and a pair of sidewall portions 20 at the inner end portions in the tire radial direction. It is provided with a pair of bead portions 30 located at.

A carcass ply 4 is hung between the pair of bead portions 30 over the tire inner surface side of the tread portion 10 and the sidewall portion 20. In this embodiment, two layers of carcass ply 4 are arranged. A plurality of belt layers 7 and belt reinforcing layers 8 are wound between the tread portion 10 and the carcass ply 4 in the tire circumferential direction in order from the inside in the tire radial direction. An inner liner 3 is arranged on the inner surface side of the tire of the carcass ply 4.

The bead portion 30 includes a bead core 31 and a bead filler 32 connected to the bead core 31 and extending outward in the tire radial direction. The bead core 31 is formed by bundling a plurality of bead wires into an annular shape. The bead core 31 has an outer diameter side end surface 31a on the outer end surface in the tire radial direction. The bead filler 32 is formed by forming a rubber material having a triangular cross section in an annular shape along the outer diameter side end surface 31a of the bead core 31.

A chafer layer 5 is arranged around the bead portion 30. The chafer layer 5 is arranged adjacent to the outer surface side of the carcass ply 4 (the side opposite to the bead portion 30), and is folded back from the inside to the outside in the tire width direction around the bead portion 30 together with the carcass ply 4. It is wound up to the outer diameter side in the tire radial direction. The chafer layer 5 is formed by arranging a plurality of nylon cords or steel cords side by side with a predetermined number of ends and covering them with rubber.

The chafer layer 5 has a winding end portion 5a located inside the tire width direction (the tire inner surface side of the bead portion 30) and a winding end portion 5b located outside the tire width direction (the tire outer surface side of the bead portion 30). Have. A tape rubber 6 is arranged between the winding end portion 5b of the chafer layer 5 and the carcass ply 4. The tape rubber 6 is a tape-shaped thin-walled member, and is configured to have a substantially constant thickness of, for example, 1 mm or less.

The sidewall portion 20 has a sidewall rubber 21, a rim strip rubber 22, a back pad rubber 23, and a belt under-belt pad rubber 24.

The sidewall rubber 21 constitutes the main body of the sidewall portion 20. Further, the sidewall rubber 21 forms the outer surface of the pneumatic tire 1, and rubber having excellent weather resistance, trauma resistance, and rolling resistance is adopted. The rim strip rubber 22 is located inside the sidewall portion 20 in the tire radial direction, and is a portion that comes into contact with the rim flange 40 when assembled to the wheel.

The back pad rubber 23 is adjacent to the sidewall rubber 21 and the rim strip rubber 22 over the inner surface side of the tire. The back pad rubber 23 is located on the inner surface side of the sidewall rubber 21, is not exposed to the outside air, is less likely to be distorted, and has excellent adhesiveness to the carcass ply 4. .. The lower belt pad rubber 24 is arranged so as to fill the space between the end portion of the belt layer 7 in the tire width direction and the carcass ply 4.

The sidewall portion 20 is configured such that the 100% modulus value decreases in the order of the underbelt pad rubber 24, the rim strip rubber 22, the back pad rubber 23, and the sidewall rubber 21. The 100% modulus value of each member 21 to 24 is, for example, 4.0 MPa or more and 5.5 MPa or less for the underbelt pad rubber 24, 4.0 MPa or more and 4.5 MPa or less for the rim strip rubber 22, and 3 for the back pad rubber 23. It is 5.5 MPa or more and 3.9 MPa or less, and the sidewall rubber 21 is configured to be 1.0 MPa or more and 2.4 MPa or less. Further, as the tape rubber 6, rubber having the same 100% modulus value as the back pad rubber 23 is adopted. The 100% modulus of each member is a value obtained by dividing the tensile force when 100% elongation is applied to the test piece specified in JIS K6251: 2010 3.7 by the initial cross-sectional area of the test piece. As the test piece, a dumbbell-shaped No. 3 type was used.

FIG. 3 schematically shows a sidewall member 20'for forming the sidewall portion 20. The sidewall portion 20 is formed by winding the sidewall member 20'around a molding drum (not shown) in a cylindrical shape and vulcanizing and molding the tire in a vulcanization die (not shown).

In the present embodiment, in the sidewall member 20', the sidewall rubber member 21', the rim strip rubber member 22', the back pad rubber member 23', and the under-belt pad rubber member 24'are integrally extruded through, for example, a base. It is formed. These members 21'to 24'are vulcanized and molded into a sidewall rubber 21, a rim strip rubber 22, a back pad rubber 23, and an underbelt rubber 24, respectively.

Since these members 21'to 24'are integrally formed with the sidewall member 20', the sidewall member 20'is wound around the molded drum as compared with the case where they are configured separately. You can easily do the work. In addition, these members 21'to 24' may be formed separately and wound around a molded drum.

Next, with reference to FIG. 2, the position in the tire radial direction of each member located around the bead portion 30 is used as a ratio to the tire reference cross-sectional height H0 with reference to the outer diameter side end surface 31a of the bead core 31. I will explain. When the ratio to the tire reference cross-sectional height H0 is a positive value, it means that the bead core 31 is located on the outer diameter side in the tire radial direction with respect to the outer diameter side end surface 31a, and when the ratio is a negative value. It means that the tire is located on the inner diameter side in the tire radial direction with respect to the outer diameter side end surface 31a.

As shown in FIG. 1, in the present specification, the tire reference cross-sectional height H0 is obtained by cutting a pneumatic tire in the tire radial direction within a predetermined range in the tire circumferential direction (for example, a range of 20 mm in the tire circumferential direction). The sample was measured with the pair of bead portions 30 set to the standard rim width, and the highest portion of the outer surface of the tread portion 10 from the outer diameter side end surface 31a of the bead core 31 (the intersection with the tire equatorial line CL). ) Means the height. Here, the standard rim width is a rim defined for each tire in the standard system including the standard on which the tire is based. For example, "standard rim" for JATTA and "Design Rim" for TRA. For ETRTO, use "Measuring Rim".

In FIG. 2, the height position H1 of the winding end portion 5b of the chafer layer 5 is located in a range of -3% or more and 5% or less of the tire reference cross-sectional height H0 with respect to the outer diameter side end surface 31a of the bead core 31. ing.

In the back pad rubber 23, the height position H2 of the inner diameter side end portion 23a in the tire radial direction is 5 mm or more on the tire inner diameter side with respect to the winding end portion 5b of the chafer layer 5, and is on the outer diameter side end surface 31a of the bead core 31. On the other hand, it is located in the range of -5% or more and 3% or less of the tire reference cross-sectional height H0. Further, in the back pad rubber 23, the height position H3 of the outer diameter side end portion 23b is located in a range of 16% or more and 45% or less of the tire reference cross-sectional height H0 with respect to the outer diameter side end surface 31a of the bead core 31. There is. The back pad rubber 23 is arranged in a height range R1 of 15% or more and 45% or less of the tire reference cross-sectional height H0.

In the tape rubber 6, the height position H4 of the inner diameter side end portion 6a in the tire radial direction is on the inner diameter side of the tire with respect to the inner diameter side end portion 23a of the back pad 23, and the tire reference to the outer diameter side end surface 31a of the bead core 31. It is located in the range of -6% or more and 2% or less of the cross-sectional height H0, and the height position H5 of the outer diameter side end portion 6b is the tire reference cross-sectional height H0 with respect to the outer diameter side end surface 31a of the bead core 31. It is located in the range of 10% or more and 15% or less of. The tape rubber 6 is arranged in a height range R2 of 5% or more and 20% or less of the tire reference cross-sectional height H0.

Further, the height position H6 of the outer diameter side end portion 32a of the bead filler 32 is inside the outer diameter side end portion 23b of the back pad rubber 23 in the tire radial direction, and the tire is relative to the outer diameter side end surface 31a of the bead core 31. It is located in the range of 8% or more and 40% or less of the reference cross-sectional height H0.

That is, the winding end portion 5b of the chafer layer 5 is supported in the tire width direction by a pair of support rubbers composed of a tape rubber 6 and a back pad rubber 23 arranged adjacent to the chafer layer 5 in the tire width direction.

Next, the back pad 23 will be described in detail.

In the back pad rubber 23, the inner surface _23c (PS to PE in _FIG . 2) abutting on the outer surface of the chafer layer 5, the tape rubber 6, and the carcass ply 4 extends substantially parallel to the inner surface 23c, and the sidewall is formed. The rubber 21 and the rim strip rubber 22 are formed in a trapezoidal shape that is longer in the tire radial direction than the outer surface 23d ₍ P1 to P4 in FIG. ₂ ) that is in contact with the inner surface. The back pad rubber 23 has a constant thickness portion 231 in which the portion corresponding to the outer surface 23d has a substantially constant thickness, and a pair of thickness tapering portions whose thickness gradually decreases as the tire diameter direction is separated from both ends in the tire radial direction. It has 232 and.

In FIG. 2, the portions shown by PS to _{P 1} are the thickness gradual reduction portions 232 located on the inner diameter side in the tire radial direction, and the portions located at P ₁ to P ₄ are the constant thickness portions 231 and P ₄ to. The portion indicated by _PE is the thickness gradual reduction portion 232 located on the outer diameter side in the tire radial direction. That is, inflection _points P1 and P4 that transition to the thickness gradual decrease portion 232 exist at both ends in the tire radial direction _on the tire outer surface side of the thickness constant portion 231.

The constant thickness portion 231 is located outside the winding end portion 5b of the chafer layer 5 in the tire radial direction, that is, the thickness tapering portion 232 located inside the tire radial direction is located at the winding end portion 5b of the chafer layer 5. It is located adjacent to each other.

FIG. 4 is a graph showing the thickness T (mm) of the back pad rubber 23. The thickness T of the back pad rubber 23 is shown as the thickness in the direction perpendicular to the carcass ply 4. The graph shows the carcass from one end to the other end of the rear pad rubber 23 in the tire radial direction (in this embodiment, from the inner diameter side end 23a (PS) to the outer diameter side end _23b ( _PE )). The thickness T at each position of the distance d (mm) along the outer surface of the ply 4 is shown, that is, the thickness T is shown as a thickness function T (d) which is a function of the distance d. In addition, the slope A of the function T (d) is also shown.

As shown in FIG. 4, the thickness constant portion 231 means a portion where the absolute value of the inclination A of the function T (d) is 0.2 mm / mm or less, and the thickness gradual decrease portion 232 is the function T ( d) means a portion where the absolute value of the inclination A is larger than 0.2 mm / mm. That is, according to the function _T (d), the thickness of the thickness gradually decreasing portion 232 on the inner diameter _side increases from PS to P1. In the constant thickness portion 231, although the thickness is substantially constant from P ₁ to P ₄ , the thickness slightly decreases from P ₁ to P ₂ , and the thickness slightly increases from P ₂ to P ₃ , and P ₃ to The thickness is slightly reduced toward _P4 . Further, in the thickness gradual reduction portion 232 on the outer diameter side, the thickness decreases from _P4 to _PE .

The constant thickness portion 231 is set in a height range of 7% or more and 26% or less with respect to the tire reference cross-sectional height H0. Further, the thickness gradual reduction portion 232 is preferably set so that the absolute value of the inclination of the function T (d) is 0.6 mm / mm or less, whereby the contact area of the thickness gradual reduction portion 232 with the sidewall rubber 21 is set. Easy to secure.

According to the pneumatic tire 1 described above, the following effects are obtained.

(1) Since the winding end portion 5b of the chafer layer 5 is sandwiched in the tire width direction by the tape rubber 6 and the back pad rubber 23 having higher modulus than the sidewall rubber 21, distortion that may occur in the vicinity of the winding end portion 5b. Is suppressed. As a result, the separation at the winding end portion 5b of the chafer layer 5 is suppressed.

(2) Since the tape rubber 6 is arranged between the winding end portion 5b of the chafer layer 5 and the carcass ply 4, the step portion formed on the outer surface of the carcass ply 4 can be reduced by the tape rubber 6. As a result, the winding end portion 5b of the chafer layer 5 can be easily wound along the outer surface of the carcass ply 4. As a result, while the winding end portion 5b of the chafer layer 5 is sandwiched between the tape rubber 6 and the back pad rubber 23 in the tire width direction, an excessive step portion is not formed in the vicinity of the winding end portion 5b of the chafer layer 5. It is easy to suppress the occurrence of bears due to the steps. As a result, the separation at the winding end portion 5b of the chafer layer 5 can be further suppressed.

On the other hand, when the back pad rubber 23 is arranged between the winding end portion 5b of the chafer layer 5 and the carcass ply 4, a large step portion is formed by the back pad rubber 23 on the outer surface of the carcass ply 4. Therefore, a bear is likely to occur between the member and the member arranged here due to the step portion.

(3) Since the positions of the tire radial ends of the back pad rubber 23 and the tape rubber 6 where strain is easily concentrated are different in the tire radial direction, it is possible to suppress excessive strain concentration on the radial ends.

(4) The height position H1 of the winding end portion 5b of the chafer layer 5 is located within a range of -3% or more and 5% or less of the tire reference cross-sectional height H0 with respect to the outer diameter side end surface 31a of the bead core 31. There is. As a result, the chafer layer 5 is arranged so as to correspond to the contact portion with the rim flange 40 in the bead portion 30 of the pneumatic tire 1, and the winding end portion 5b of the chafer layer 5 is excessively removed in the tire radial direction. It can be suppressed to be located on the radial side. As a result, even if the rest strip rubber 22 is worn at the contact portion with the rim flange 40, the exposure of the carcass ply 4 can be suppressed by the chafer layer 5.

Further, by limiting the height position of the winding end portion 5b of the chafer layer 5 in the tire radial direction, the winding end portion 5b can be easily arranged away from the portion of the sidewall portion 20 having a large distortion, and the sidewall portion 5b can be easily arranged. The increase in strain caused by the deformation of the portion 20 is suppressed. As a result, the separation at the winding end portion 5b of the chafer layer 5 is further suppressed.

If the winding end portion 5b of the chafer layer 5 is located inward in the tire radial direction with respect to the outer diameter side end surface 31a of the bead core 31 to the inner diameter side by 3% or more of the tire reference cross-sectional height, the carcass is generated when the bead portion 30 is worn. There is a risk that the ply 4 will be exposed. Further, when the winding end portion 5b of the chafer layer 5 is located to the outer diameter side in the tire radial direction with respect to the outer diameter side end surface 31a of the bead core 31 by 5% or more of the tire reference cross-sectional height, the winding end portion 5b is located. Since it is close to the portion of the sidewall portion 20 where the strain is large, the strain tends to increase excessively.

(5) Since the winding end portion 5b of the chafer layer 5 is firmly supported by the tape rubber 6 and the back pad rubber 23 over at least 5 mm in the tire radial direction, strain concentration is suitably suppressed.

(6) Since the back pad rubber 23 is arranged in the height range R1 of 15% or more and 45% or less of the tire reference cross-sectional height H0, the back pad rubber 23 is positioned so as to overlap the winding end portion 5b of the chafer layer 5. It will be located over a predetermined range in the tire radial direction. As a result, the strain generated around the pneumatic tire 1 bead portion 30 can be dispersed in a predetermined range in the tire radial direction via the back pad rubber 23, so that the strain of the winding end portion 5b of the chafer layer 5 can be suppressed. .. If the back pad rubber 23 is arranged in a radial range larger than 45% of the tire reference cross-sectional height H0, the proportion of the sidewall rubber 21 in the sidewall portion 20 is excessively reduced, resulting in poor fuel efficiency. do.

Further, the height position H6 of the outer diameter side end portion 32a of the bead filler 32 is located inside the outer diameter side end portion 23b of the back pad rubber 23 in the tire radial direction. As a result, the strain that may occur in the vicinity of the outer diameter side end portion 32a of the bead filler 32 is suppressed by the back pad rubber 23. Therefore, in the vicinity of the bead portion 30, not only the winding end portion of the chafer layer 5 but also the separation in the vicinity of the outer diameter side end portion 32a of the bead filler 32 is suitably suppressed.

(7) Since the tape rubber 6 is arranged in the height range R2 of 5% or more and 20% or less of the tire reference cross-sectional height H0, the tire is located overlapping the winding end portion 5b of the chafer layer 5. It will be located over a predetermined range in the radial direction. As a result, the strain generated around the bead portion 30 of the pneumatic tire 1 can be dispersed in a predetermined range in the tire radial direction via the tape rubber 6, so that the strain of the winding end portion 5b of the chafer layer 5 is suppressed. To.

(8) Since the back pad rubber 23 has a constant thickness portion 231 over a height range of 7% or more and 26% or less of the tire reference cross-sectional height H0, distortion generated around the bead portion 30 of the pneumatic tire 1 is generated. , Can be dispersed in a predetermined range in the tire radial direction via the back pad rubber 23. As a result, the strain at the winding end portion 5b of the chafer layer 5 is further reduced.

When the height range of the constant thickness portion 231 is smaller than 7% of the tire reference cross-sectional height H0, the strain dispersion effect of the constant thickness portion 231 is reduced. When the height range of the constant thickness portion 231 is larger than 26% of the tire reference cross-sectional height H0, the proportion of the back pad rubber 23 in the sidewall portion 20 is excessively increased and the proportion of the sidewall rubber 21 is excessively small. Therefore, the effect of improving the rolling resistance of the sidewall rubber 21 is diminished, and the fuel efficiency is likely to deteriorate.

(9) The constant thickness portion 231 is a portion where the absolute value of the inclination is 0.2 mm / mm or less in the thickness function T (d) of the back pad rubber 23. As a result, since the thickness change of the constant thickness portion 231 is sufficiently small, the strain generated around the bead portion 30 can be easily dispersed widely in the tire radial direction.

(10) Since the constant thickness portion 231 of the back pad is not located at the winding end portion 5b of the chafer layer 5, the rim strip rubber 22 arranged on the tire outer surface side of the winding end portion 5b of the chafer layer 5 Easy to secure capacity.

(11) The thickness gradual reduction portion 232 is a portion where the absolute value of the inclination A is larger than 0.2 mm / mm and 0.6 mm / mm or less in the thickness function T (d) of the back pad rubber 23. As a result, it is possible to suppress the separation in the thickness gradual decrease portion 232 while suppressing the thickness gradual decrease portion 232 from becoming excessively long.

That is, if the absolute value of the inclination A of the thickness gradual decrease portion 232 is 0.2 mm / mm or less, the thickness gradual decrease portion 232 becomes long, and the proportion of the sidewall rubber 21 in the sidewall portion 20 becomes excessively small. Therefore, the effect of improving the rolling resistance of the sidewall rubber 21 is diminished, and the fuel efficiency tends to deteriorate. Further, when the absolute value of the inclination A of the thickness gradual reduction portion 232 is larger than 0.6 mm / mm, the thickness gradual reduction portion 232 becomes short, so that the contact area of the thickness gradual reduction portion 232 with the sidewall rubber 21 decreases, and as a result, the contact area with the sidewall rubber 21 decreases. The adhesiveness of the back pad rubber 23 at the thickness gradually decreasing portion 232 tends to decrease, and the separation resistance tends to deteriorate.

In the above embodiment, the case where the tape rubber 6 and the back pad rubber 23 are made of the same rubber material has been described as an example. However, the tape rubber 6 and the back pad rubber 23 may each have a higher modulus than the sidewall rubber 21, and rubbers different from each other may be adopted.

The pneumatic tire of the present invention described above includes a tread rubber made of a rubber composition, and the present invention also relates to the rubber composition constituting the tread rubber.
The rubber composition of the present invention contains (A) a diene-based rubber, (B) silica, and (C) an additive.

(A) Diene-based rubber Examples of the diene-based rubber used in the rubber composition of the present invention include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), and styrene-. Examples thereof include isoprene rubber, butadiene-isoprene rubber, styrene-butadiene-isoprene rubber, and nitrile rubber (NBR), and one or a combination of two or more of these can be used. More preferably, it is at least one selected from styrene butadiene rubber (SBR), butadiene rubber (BR) and natural rubber (NR).

When styrene butadiene rubber (SBR), butadiene rubber (BR) and natural rubber (NR) are used in combination as one embodiment of the present invention, styrene butadiene rubber (SBR) is contained in 100 parts by mass of these diene rubbers in total. It is preferable to contain 0 to 100 parts by mass of butadiene rubber (BR), 0 to 50 parts by mass of natural rubber (NR), and 0 to 50 parts by mass of natural rubber (NR).

Further, the diene rubber used in the rubber composition of the present invention comprises a group consisting of a hydroxyl group, an amino group, a carboxyl group, an alkoxy group, an alkoxysilyl group, and an epoxy group in the molecular end or the molecular chain of the above rubber. A modified diene rubber having at least one selected functional group introduced therein may be used. Here, as the amino group, a primary amino group, a secondary amino group or a tertiary amino group can be introduced. Further, as the carboxyl group, an acid anhydride group can also be introduced. Further, as the alkoxyl group, an alkoxyl group having 1 to 4 carbon atoms can be introduced, and as the alkoxysilyl group, at least three hydrogens of the silyl group such as a trialkoxysilyl group and an alkyldialkoxysilyl group can be introduced. It is possible to introduce one hydrogen substituted with an alkoxyl group. These functional groups interact with silanol groups on the surface of silica and contribute to the improvement of silica dispersibility. As the modified diene rubber, modified SBR and / or modified BR are preferable. In one embodiment, the diene-based rubber may be the modified diene-based rubber alone, or may be a mixture of the modified diene-based rubber and the unmodified diene-based rubber. In one embodiment, 20 to 80 parts by mass of the modified diene rubber (for example, modified SBR) and 20 to 20 parts by mass of the unmodified diene rubber (for example, SBR, BR and / or NR) out of 100 parts by mass of the total diene rubber. It may contain 80 parts by mass.

(B) Silica The silica contained in the rubber composition of the present invention is not particularly limited, but wet silica such as wet precipitation method silica and wet gel method silica is preferably used. The colloidal characteristics of silica are not particularly limited, but the nitrogen adsorption specific surface area (BET) by the BET method is preferably 90 to 250 m ² / g, more preferably 100 to 230 m ² / g. This BET value is measured according to the BET method described in ISO 5794.

The blending amount of silica is usually 10 to 150 parts by mass, preferably 20 to 120 parts by mass, and more preferably 40 to 100 parts by mass with respect to 100 parts by mass of the total diene rubber contained in the rubber composition.

In addition, a silane coupling agent can be added to improve the dispersibility of silica. Examples of this silane coupling agent include sulfide silane and mercaptosilane. The blending amount of the silane coupling agent is not particularly limited, but is usually 3 to 15% by mass, preferably 5 to 10% by mass, based on the blending amount of silica.
(C) Additives Further, in the rubber composition of the present invention, in addition to the above components, carbon black, process oil, zinc oxide, stearic acid, antiaging agent, wax, sulfur, vulcanization accelerator and the like are added to the tire. Various additives generally used in the rubber composition constituting the above can be blended.

The blending amount of the additive is 10 to 100 parts by mass, preferably 30 to 80 parts by mass with respect to a total of 100 parts by mass of the diene rubber contained in the rubber composition.

The rubber composition of the present invention can be produced by kneading the above-mentioned components (A) to (C) according to a conventional method using a mixer such as a Banbury mixer, a kneader, or a roll. That is, in the first mixing step, the diene rubber is mixed with silica and, if desired, a silane coupling agent, and other additives other than the vulcanizing agent and the vulcanization accelerator, and the mixture is added to the mixture in the final step. A rubber composition can be prepared by adding sulfur and a vulcanization accelerator.

Next, examples of the present invention will be shown, but the present invention is not limited to these examples.

[raw materials]
The raw materials used in the compositions of the Examples are as follows.

-SBR1: Emulsified polymerized styrene-butadiene rubber, "SBR1502" manufactured by JSR Corporation
-SBR2: Modified styrene-butadiene rubber, "HPR350" manufactured by JSR Corporation
-BR: Butadiene rubber, "BR150B" manufactured by Ube Kosan Co., Ltd.
・ NR: Natural rubber, "RSS # 3"
-Silica: "Ultrasil VN3" manufactured by Evonik Japan Co., Ltd.
・ Carbon black: "Seast 3" manufactured by Tokai Carbon Co., Ltd.
-Process oil: "Process NC140" manufactured by JXTG Energy Co., Ltd.
・ Zinc Oxide: "Zinc Oxide No. 3" manufactured by Mitsui Kinzoku Co., Ltd.
-Stearic acid: "Lunac S-20" manufactured by Kao Corporation
・ Anti-aging agent: "Nocrack 6C" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
・ Wax: "Ozoace-0355" manufactured by Nippon Seiro Co., Ltd.
・ Silane coupling agent: "Si69" manufactured by Evonik Japan Co., Ltd.
・ Sulfur: "Powdered sulfur" manufactured by Tsurumi Chemical Co., Ltd.
・ Vulcanization accelerator: "Soxinol CZ" manufactured by Sumitomo Chemical Co., Ltd.

[Evaluation method]
-Rolling resistance: The rolling resistance was measured when the vehicle was run at 23 ° C. and 80 km / h with a single-screw drum tester for measuring rolling resistance at an air pressure of 230 kPa and a load of 450 kgf. The results are shown as an index with the value of Comparative Example 1 as 100. The smaller the index, the smaller the rolling resistance, and therefore the better the fuel efficiency.
-Durability: A steel drum with a diameter of 1707 mm was run at a speed of 80 km / h until a tire failed at an air pressure of 0 kPa and a load load of 4.0 kN. It is shown as an index with the mileage of Comparative Example 1 as 100. The larger the index, the better the durability.

Using a Banbury mixer, add other compounding agents to the diene rubber (SBR, BR, NR) except sulfur and vulcanization accelerator in the first mixing step according to the composition (parts by mass) shown in Table 1 below. In the final mixing step, sulfur and a vulcanization accelerator were added to the obtained kneaded product and kneaded to prepare a rubber composition. The obtained rubber composition is subjected to rolling resistance and durability according to the above evaluation method, for example, using a tire (tire size: 235 / 65R16C 115 / 113R) manufactured by vulcanization molding at 140 to 180 ° C. evaluated. The results are shown in Table 1. As the support rubber, a general rubber composition containing BR and NR as main components and carbon black and other raw materials as appropriate as the diene rubber was used.

From the rubber composition of Comparative Example 2 provided with a pair of support rubbers arranged so as to sandwich the winding end portion of the chafer layer from both sides in the tire width direction with respect to the tire manufactured from the rubber composition of Comparative Example 1. In the manufactured tires, improvement in durability was observed, but rolling resistance increased. On the other hand, in the tire manufactured from the rubber composition of Comparative Example 3 in which silica was blended with respect to the rubber composition of Comparative Example 1, the rolling resistance was reduced and the improvement of fuel efficiency could be expected, but the durability was lowered. did. Therefore, in the tires of Examples 1 to 6 provided with a pair of support rubbers produced from a rubber composition obtained by blending silica with the rubber composition of Comparative Example 1, the tires roll while maintaining or improving the durability. It was expected that the resistance would decrease and the fuel efficiency would improve.

4 Carcasply 5 Chafer layer 5b Winding end 6 Tape rubber 10 Tread part 11 Tread rubber 20 Side wall part 21 Side wall rubber 22 Rim strip rubber 23 Back pad rubber 231 Thickness constant part 232 Thickness tapering part 24 Under belt pad rubber 30 Bead part 31 Bead core 31a Outer diameter side end face 32 Bead filler H0 Tire standard cross-sectional height

Claims (7)

With a pair of bead cores,
A pair of bead fillers that are connected to each of the pair of bead cores and extend to the outer diameter side in the tire radial direction.
The carcass ply hung between the pair of bead cores,
The sidewall rubber, which is arranged on the tire outer surface side of the carcass ply and constitutes the tire outer surface,
A chafer layer that is folded back from the inner surface side of the tire to the outer surface side of the tire around the bead core and the bead filler and wound up on the outer surface of the carcass ply.
A pair of support rubbers located between the sidewall rubber and the carcass ply and arranged so as to sandwich the winding end of the chafer layer, which is a portion, from both sides in the tire width direction, and a tread rubber. Here, the winding end of the chafer layer is a tire from a position of 3% of the tire reference cross-sectional height inward in the tire radial direction to the outside in the tire radial direction with reference to the outer diameter side end of the bead core. Located in the radial range at 5% of the reference cross-sectional height,
A pneumatic tire in which the tread rubber contains silica in a pneumatic tire characterized in that the modulus values of both of the pair of support rubbers are higher than the modulus values of the sidewall rubbers. The pair of support rubbers
With respect to the winding end of the chafer layer, the pad rubber adjacent to the outer surface side of the tire and
The pneumatic tire according to claim 1, which is composed of a tape rubber adjacent to the winding end portion of the chafer layer on the inner surface side of the tire. The pneumatic tire according to claim 2, wherein the inner diameter end of the pad rubber is different from the inner diameter end of the tape rubber in a position in the tire radial direction. The pneumatic tire according to claim 2 or 3, wherein the outer diameter end of the pad rubber is different from the outer diameter end of the tape rubber in the position in the tire radial direction. The pneumatic tire according to any one of claims 1 to 4 , wherein the winding end portion of the chafer layer overlaps both of the pair of support rubbers by 5 mm or more in the tire radial direction. The air-filled portion according to any one of claims 2 to 5 , wherein all the parts of the pad rubber are arranged in a radial range of 15% or more and 45% or less of the tire reference cross-sectional height in the tire radial direction. tire. The air-filled portion according to any one of claims 2 to 6 , wherein all the parts of the tape rubber are arranged in a radial range of 5% or more and 20% or less of the tire reference cross-sectional height in the tire radial direction. tire.

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