pneumatic tires

Abstract

To provide a pneumatic tire that achieves weight saving of the tire while maintaining good durability of a bead part.SOLUTION: A recessed part 20 continuous in a tire circumferential direction is provided in a tire outer surface of at least one sidewall part 2. When a straight line drawn so as to make contact with an outer contour of the sidewall part 2 and a bead part 3 is defined as a tangential line L1 in a meridian cross section, a point at which the tangential line L1 is in contact with the outer contour of the sidewall part 2 is defined as a point of contact P1, a straight line vertically crossing with a body part 4a of a carcass layer 4 through a winding-up end of the carcass layer 4 is defined as a vertical line L2, and a straight line vertically crossing with the body part 4a of the carcass layer 4 through the point of contact P1 is defined as a vertical line L3, an area A of a region enclosed by an outer contour and the tangent line L1 of the sidewall part 2 and the bead part 3, an area S of a region enclosed by the outer contour of the sidewall part 2 and the bead part 3 and the body part 4a and the vertical line L2 and the vertical line L3, and a thickness G1 of a bead filler 6 as measured along the vertical line L2 satisfy the relationship of 0.10×(G1-17)≤A / (S+A)≤0.05×(G1-10).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a pneumatic tire having recesses near the bead portions to reduce the tire weight. [Background technology]

[0002] In recent years, from the viewpoint of improving vehicle transportation efficiency, there has been a demand for lighter tires in order to increase actual load capacity. One method proposed for reducing tire weight is to provide recesses near the bead portions to reduce the amount of rubber in the bead portions (see, for example, Patent Document 1). However, providing such recesses poses a problem in that the durability of the bead portions decreases due to increased strain associated with the reduced amount of rubber. Therefore, even in pneumatic tires that have recesses near the bead portions to reduce tire weight, there is a demand for measures to suppress strain in the bead portions (especially near the carcass ends) and maintain good durability of the bead portions. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5390392 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a pneumatic tire that enables reduction in tire weight while maintaining good durability of the bead portion. [Means for solving the problem]

[0005] In order to achieve the above object, a pneumatic tire of the present invention includes a tread portion extending in a circumferential direction of the tire to form an annular shape, a pair of sidewall portions disposed on both sides of the tread portion, and a pair of bead portions disposed radially inward of the sidewall portions, and the pneumatic tire has a bead core disposed in each of the bead portions, a bead filler disposed radially outward of the bead core, and at least one carcass layer mounted between the pair of bead portions, the carcass layer comprising a main body portion wound up around the bead core and the bead filler disposed in each bead portion from the inner side to the outer side of the tire and positioned between the pair of bead portions, and a wound-up portion wound up on the outer side of the bead core and the bead filler in the width direction of the tire, and the pair of When the width between the bead portions is set to a specified rim width, at least one of the sidewall portions has a recessed portion that is continuous in the tire circumferential direction on the outer surface of the tire radially outward from the turned-up end of the carcass layer and radially inward from the tire maximum width position, and the contour line of the recessed portion in a meridian cross section is made up of a plurality of arcs with different radii of curvature, and when a straight line drawn tangent to the outer contours of the sidewall portions and the bead portions in the meridian cross section is defined as a tangent line L1, a point of contact between the tangent line L1 and the outer contour of the sidewall portions is defined as a tangent line P1, a straight line that passes through the turned-up end of the carcass layer and intersects with the main body portion perpendicularly is defined as a perpendicular line L2, and a straight line that passes through the tangent line P1 and intersects with the main body portion perpendicularly is defined as a perpendicular line L3, the area A (unit: mm) of the region surrounded by the outer contours of the sidewall portions and the bead portions and the tangent line L1 2 ] and the area S of the region surrounded by the outer contours of the sidewall portion and the bead portion, the main body portion, the perpendicular line L2 and the perpendicular line L3 [unit: mm 2 ] and the thickness G1 of the bead filler measured along the perpendicular line L2 [unit: mm] satisfy the relationship 0.10 × (G1-17) ≦ A / (S+A) ≦ 0.05 × (G1-10). [Effects of the Invention]

[0006] In the present invention, as described above, a continuous recess is provided in the tire circumferential direction near at least one bead portion, thereby reducing the amount of rubber near the bead portion and reducing the tire weight. Meanwhile, the recess is located radially outward from the turned-up end of the carcass layer in the sidewall portion and radially inward from the tire's maximum width position, and the area of ​​the recess (area A), the amount of rubber radially outward from the carcass end (area S), and the bead filler thickness G1 are set to satisfy the above-mentioned relationship. This allows for the dispersion of strain near the carcass end caused by the provision of the recess, thereby ensuring good durability of the bead portion.

[0007] In the present invention, when the point where the tangent line L1 and the outer contour of the bead portion meet is defined as a tangent point P2, it is preferable that the outer contours of the sidewall portion and the bead portion located between the tangent point P2 and the tangent point P3 be located outward in the tire width direction than a line L4 connecting the tangent point P2 and a point P3 that is spaced 10 mm outward from the tangent point P2 along the outer contour of the sidewall portion and the bead portion. This improves the shape of the recess (outer contour), ensures the amount of rubber near the carcass end, and is advantageous for improving the durability of the bead portion.

[0008] In the present invention, when the point where the tangent line L1 and the outer contour of the bead portion meet is defined as a contact point P2, the ratio G2 / G1 of the thickness G2 (unit: mm) of the bead filler measured on a line that passes through the contact point P2 and perpendicularly intersects with the main body portion to the thickness G1 satisfies the relationship of 0.55≦G2 / G1≦0.90, and the area S1 (unit: mm) of the region occupied by the bead filler in the area S is 2 It is preferable that the ratio S1 / S of the area S to the area S satisfies the relationship 0.25≦S1 / S≦0.50. This ensures a volume of bead filler that has excellent flex fatigue resistance and breaking characteristics, which is advantageous for improving the durability of the bead portion.

[0009] In the present invention, it is preferable that the bead filler has a two-layer structure consisting of an upper bead filler and a lower bead filler, and that the breaking elongation of the upper bead filler is 400% or more. By using a bead filler with such a high breaking elongation, breakage near the carcass end due to repeated strain during rolling is suppressed, which is advantageous for improving the durability of the bead portion.

[0010] At this time, the upper bead filler Measured under conditions of initial strain 10%, amplitude ±2%, frequency 20Hz, and 60°C The lower bead filler has an elastic modulus of 4.0 MPa or more and 8.0 MPa or less. Measured under conditions of initial strain 10%, amplitude ±2%, frequency 20Hz, and 60°C. The elastic modulus is preferably 14.0 MPa or more and 20.0 MPa or less, which improves the physical properties of the upper and lower bead fillers when the bead filler has a two-layer structure, and is advantageous for improving the durability of the bead portion.

[0011] Furthermore, it is preferable that the area S2 of the upper bead filler and the area S3 of the lower bead filler satisfy the relationship 0.30≦S3 / S2≦0.80. Providing the upper bead fillers and the lower bead fillers in such a balanced manner is advantageous in improving the durability of the bead portion.

[0012] In the present invention, it is preferable that the distance G3 between the turned-up end and the tire outer surface measured on the perpendicular line L2 is 7.0 mm or more and 14.0 mm or less, and the distance G4 between the turned-up end and the outer surface of the recess measured on an extension of the turned-up portion is 10.0 mm or more and 40.0 mm or less. This ensures a sufficient distance from the carcass end to the tire outer contour, disperses strain between the carcass end and the tire outer contour, and is advantageous for improving the durability of the bead portion.

[0013] In the present invention, a crack-preventing rubber may be arranged to cover the turned-up end, and the breaking elongation of the crack-preventing rubber may be set to 400% or more. By arranging the crack-preventing rubber in this way and increasing the breaking elongation of the crack-preventing rubber, it is possible to prevent breakage near the carcass end due to repeated strain during rolling, which is advantageous for improving the durability of the bead portion.

[0014] In the present invention, the breaking elongation of the side rubber constituting the sidewall portion is 450% or more, Measured under conditions of initial strain 10%, amplitude ±2%, frequency 20Hz, and 60°C. The elastic modulus is preferably 2.5 MPa or more and 5.5 MPa or less. Increasing the breaking elongation of the side rubber in this way can suppress breakage near the carcass end due to repeated strain during rolling, which is advantageous for improving the durability of the bead portion. In addition, increasing the elastic modulus of the side rubber can compensate for the reduced side rigidity caused by providing recesses, which is advantageous for reducing strain in the bead portion and improving durability.

[0015] In the present invention, an organic fiber reinforcement layer may be provided on the tire width direction outer side of the turned-up portion of the carcass layer, and the tire radially outer end of the organic fiber reinforcement layer may be located radially outward of the turned-up end, the tire radially inner end of the organic fiber reinforcement layer may be located radially inward of the center of the bead core, and the tire radially outer end of the organic fiber reinforcement layer may be spaced 6 mm or more from the recess. By providing the organic fiber reinforcement layer in this manner and setting its arrangement as described above, deformation due to flexing can be suppressed, which is advantageous for suppressing distortion near the carcass end and improving durability.

[0016] In the present invention, a steel reinforcing layer may be disposed along the outer surfaces of the main body portion and the turned-up portion of the carcass layer, with the end of the steel reinforcing layer facing the turned-up portion being disposed 5 mm to 25 mm radially inward from the position of the turned-up end, and the end of the steel reinforcing layer facing the main body portion being disposed 5 mm to 25 mm radially outward from the position of the turned-up end. Providing a steel reinforcing layer in this manner and arranging it as described above can improve side rigidity and suppress deformation of the bead portion due to flexing, which is advantageous for improving the durability of the bead portion.

[0017] In the present invention, the "specified rim width" refers to the width of the specified rim (the "applicable rim" specified by JATMA, the "design rim" specified by TRA, or the "measuring rim" specified by ETRTO). In the present invention, the breaking elongation of each part is a value (unit: %) measured at room temperature (23°C) in accordance with JIS K6251. The elastic modulus of each part at 60°C is a value (unit: MPa) measured in accordance with JIS K6394 using a viscoelasticity spectrometer under conditions of an initial strain of 10%, an amplitude of ±2%, a frequency of 20 Hz, and 60°C. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a meridian cross-sectional view showing an example of a pneumatic tire according to an embodiment of the present invention. [Figure 2] 1 is an explanatory diagram showing an enlarged view of a bead portion of a pneumatic tire according to an embodiment of the present invention. [Figure 3] FIG. 4 is an explanatory diagram showing an enlarged view of a bead portion of a pneumatic tire according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] The configuration of the present invention will be described in detail below with reference to the accompanying drawings.

[0020] As shown in FIG. 1 , the pneumatic tire of the present invention includes a tread portion 1, a pair of sidewall portions 2 disposed on both sides of the tread portion 1, and a pair of bead portions 3 disposed radially inward of the sidewall portions 2. In FIG. 1 , the symbol CL indicates the tire equator. Although not depicted in FIG. 1 because it is a meridian cross-section, the tread portion 1, sidewall portions 2, and bead portions 3 each extend circumferentially in the tire direction and form an annular shape, thereby constituting the basic toroidal structure of a pneumatic tire. The following explanation using FIG. 1 is based primarily on the illustrated meridian cross-section, but each tire component also extends circumferentially in the tire direction and forms an annular shape. The illustrated meridian cross-section shows a state in which the width between the pair of bead portions 3 is set to the specified rim width when the tire is not mounted on a rim, and the following explanation will be about the structure in this state.

[0021] A carcass layer 4 is installed between the pair of left and right bead portions 3. This carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction, and is arranged around a bead core 5 disposed in each bead portion 3. Tire width direction The bead filler 6 is disposed on the outer periphery of the bead core 5, and is sandwiched between the main body portion 4a and the folded-back portion 4b of the carcass layer 4.

[0022] Multiple belt layers 7 (four layers in FIG. 1 ) are embedded on the outer periphery of the carcass layer 4 in the tread portion 1. Each belt layer 7 includes multiple reinforcing cords (steel cords) oriented in a predetermined direction. The multiple belt layers 7 include cross belt pairs. A cross belt pair is a combination of at least two belt layers in which the inclination angle of the reinforcing cords with respect to the tire circumferential direction is set in the range of 10° to 40° and the inclination direction of the reinforcing cords is reversed between the layers so that the reinforcing cords cross each other. In addition to the cross belt pairs, other optional layers may be provided, such as a high-angle belt layer in which the inclination angle of the reinforcing cords with respect to the tire circumferential direction is set in the range of 40° to 70°, a protective belt layer arranged in the outermost layer and having a width 85% or less of the other belt layers, or a circumferential reinforcing layer in which the reinforcing cords with respect to the tire circumferential direction are set in the range of 0° to 5°. For example, in FIG. 1 , one protective belt layer is arranged in the outermost layer and one high-angle belt layer is arranged in the innermost layer, and the other two layers are cross belt pairs. Furthermore, a belt reinforcing layer (not shown) may be provided on the outer peripheral side of the belt layer 7. The belt reinforcing layer may be made of, for example, organic fiber cords oriented in the tire circumferential direction. Belt Reinforcement Layer In the tire, the angle of the organic fiber cord relative to the tire circumferential direction is set to, for example, 0° to 5°.

[0023] In the tread portion 1, a tread rubber layer 11 is disposed on the outer peripheral side of the above-mentioned tire constituent members (carcass layer 4, belt layer 7, belt cover layer). A side rubber layer 12 is disposed on the outer peripheral side (outer side in the tire width direction) of the carcass layer 4 in the sidewall portion 2. A rim cushion rubber layer 13 is disposed on the outer peripheral side (outer side in the tire width direction) of the carcass layer 4 in the bead portion 3.

[0024] In the tire of the present invention, a recess 20 that is continuous in the tire circumferential direction is provided on the outer surface of at least one of the sidewall portion 2 and the bead portion 3. This recess 20 is located radially outward of the turned-up end of the carcass layer 4 and radially inward of the tire maximum width position P. In other words, a contact point P1 (described later) is located radially inward of the tire maximum width position P, and a contact point P2 (described later) is located radially outward of the turned-up end of the carcass layer 4. By providing such recess 20, the amount of rubber near the bead portion 3 can be reduced, thereby reducing the tire weight.

[0025] The contour line of the recess 20 in the meridian cross section is composed of multiple arcs with different radii of curvature and is smoothly curved. For example, the contour line of the recess 20 can be formed by a combination of an arc that is convex outward in the tire width direction and an arc that is convex inward in the tire width direction. In particular, of the multiple arcs that make up the contour line of the recess 20, the innermost arc in the tire radial direction and the outermost arc in the tire radial direction are preferably convex outward in the tire width direction.

[0026] As shown in FIG. 2, when a line drawn to be tangent to the outer contours of the sidewall portion 2 and the bead portion 3 in the meridian cross section is defined as a tangent line L1, a point where the tangent line L1 and the outer contour of the sidewall portion 2 meet is defined as a tangent line P1, a line passing through the turned-up end of the carcass layer 4 and perpendicularly intersecting with the main body portion 4a is defined as a perpendicular line L2, and a line passing through the tangent line P1 and perpendicularly intersecting with the main body portion 4a is defined as a perpendicular line L3, the area A (unit: mm 2 ] and the area S (unit: mm) of the region surrounded by the outer contours of the sidewall portion 2 and the bead portion 3, the main body portion 4a, the perpendicular lines L2 and L3 (the shaded portion in the figure). 2 ] and the thickness G1 (unit: mm) of the bead filler 6 measured along the perpendicular line L2 satisfy the relationship 0.10 × (G1-17) ≦ A / (S+A) ≦ 0.05 × (G1-10).

[0027] This structure makes it possible to maintain good durability of the bead portion 3, which is a concern when recesses 20 are provided near the bead portion to reduce the tire weight. That is, the recesses 20 are arranged radially outward of the turned-up end of the carcass layer 4 in the sidewall portion 2 and radially inward of the tire maximum width position P, and the area of ​​the recesses 20 (area A), the amount of rubber radially outward of the carcass end (area S), and the thickness G1 of the bead filler 6 are set to satisfy the above-mentioned relationship. Therefore, the thickness G1 of the bead filler 6 can be increased in proportion to the area of ​​the recesses 20, which distributes distortion near the carcass end caused by providing the recesses 20 and ensures good durability of the bead portion 3.

[0028] If the relationship between the area A, the area S, and the thickness G1 of the bead filler 6 is 0.10×(G1-17)>A / (S+A), there will be insufficient rubber to disperse strain, and the effect of improving the durability of the bead portion 3 will not be fully expected. If the relationship between the area A, the area S, and the thickness G1 of the bead filler 6 is A / (S+A)>0.05×(G1-10), the area of ​​the recess 20 will not be sufficient, and the effect of reducing tire weight will not be fully expected. The relationship between the area A, the area S, and the thickness G1 of the bead filler 6 preferably satisfies 0.10×(G1-16)≦A / (S+A)≦0.05×(G1-12). The value of the ratio A / (S+A) is not particularly limited, but is preferably 0.05 to 0.25.

[0029] 3, when the point where the tangent line L1 meets the outer contour of the bead portion 3 is defined as tangent point P2, it is preferable that the outer contours of the sidewall portion 2 and the bead portion 3 located between tangent point P2 and point P3 be positioned more outward in the tire width direction than a straight line L4 connecting point P2 and tangent point P3, which is 10 mm away from tangent point P2 radially outward along the outer contour of the sidewall portion 2 and the bead portion 3. This makes the outer contour between point P3 and tangent point P2 convex outward in the tire width direction, improving the shape (outer contour) of the recessed portion 20, which ensures the amount of rubber near the carcass end and is advantageous for improving the durability of the bead portion 3.

[0030] 3, it is preferable that the outer contours of the sidewall portions 2 and the bead portions 3 located between the tangent point P2 and the tangent point P4 be positioned more outward in the tire width direction than a straight line L5 connecting point P2 and point P4, which is 15 mm away from the tangent point P2 radially outward along the outer contours of the sidewall portions 2 and the bead portions 3. This also makes the outer contours between point P4 and the tangent point P2 convex outward in the tire width direction, improving the shape (outer contour) of the recessed portions 20, which ensures a sufficient amount of rubber near the carcass end and is advantageous for improving the durability of the bead portions 3.

[0031] As shown in Figure 2, the point where the tangent line L1 meets the outer contour of the bead portion 3 is defined as tangent point P2. The thickness of the bead filler 6 measured on a line passing through tangent point P2 and perpendicularly intersecting the main body portion 4a is defined as G2 (unit: mm). The ratio G2 / G1 of thickness G2 to thickness G1 preferably satisfies the relationship 0.55 ≦ G2 / G1 ≦ 0.90, more preferably 0.60 ≦ G2 / G1 ≦ 0.85. This ensures a volume of bead filler 6 with excellent flex fatigue resistance and fracture resistance, which is advantageous for improving the durability of the bead portion 3. If the G2 / G1 ratio is less than 0.55, the amount of rubber is insufficient to adequately suppress distortion near the carcass edge, resulting in a lack of durability. If the G2 / G1 ratio exceeds 0.90, the amount of rubber in the sidewalls may be insufficient, potentially increasing the risk of ozone cracking and other problems.

[0032] The area of ​​the region occupied by the bead filler 6 in the above-mentioned area S is S1 (unit: mm 2], the ratio S1 / S of area S1 to area S preferably satisfies the relationship 0.25≦S1 / S≦0.50, and more preferably 0.30≦S1 / S≦0.45. This ensures the volume of the bead filler 6, which has excellent flex fatigue resistance and breaking characteristics, and is advantageous for improving the durability of the bead portion 3. If S1 / S is less than 0.25, the amount of rubber is insufficient to sufficiently suppress distortion near the carcass end, and the effect of improving durability cannot be fully expected. If S1 / S exceeds 0.50, the amount of rubber in the side portion is insufficient, which may make failures such as ozone cracking more likely to occur.

[0033] 2, when the distance along the tire radial direction from the innermost point in the tire radial direction of the bead portion 3 (the tip of the bead toe) to the carcass end is H1 and the distance along the tire radial direction from the innermost point in the tire radial direction of the bead portion 3 (the tip of the bead toe) to the tangent point P is H2, the ratio H2 / H1 is preferably 1.1 or more and 1.5 or less. This improves the shape of each part of the bead portion 3, which is advantageous for improving the durability of the bead portion 3.

[0034] In the present invention, the bead filler 6 preferably has a two-layer structure consisting of an upper bead filler 6a and a lower bead filler 6b. When using such a two-layer bead filler 6, the breaking elongation of the upper bead filler 6a is preferably 400% or more, more preferably 450% or more. Using a bead filler 6 with such a high breaking elongation suppresses breakage near the carcass edge due to repeated strain during rolling, which is advantageous for improving the durability of the bead portion. If the breaking elongation of the upper bead filler 6a is less than 400%, the rubber around the carcass will easily break due to repeated strain, making it difficult to sufficiently improve the durability of the bead portion 3. The upper breaking elongation of the upper bead filler 6a is not particularly limited, but it is preferably set to, for example, 800% or less. The breaking elongation of the lower bead filler 6b is not particularly limited, but it is preferably set to, for example, 50% to 250%.

[0035] When using a two-layer bead filler 6 as described above, the elastic modulus of the upper bead filler 6a at 60°C is preferably 4.0 MPa to 8.0 MPa, more preferably 4.5 MPa to 7.5 MPa. The elastic modulus of the lower bead filler 6b at 60°C is preferably 14.0 MPa to 20.0 MPa, more preferably 15.0 MPa to 19.0 MPa. This improves the physical properties of the upper bead filler 6a and the lower bead filler 6b when the bead filler 6 has a two-layer structure, which is advantageous for improving the durability of the bead portion. If the elastic modulus of the upper bead filler 6a and the lower bead filler 6b at 60°C is lower than the above-mentioned range, the deformation of the bead portion 3 under load increases, and the distortion of the carcass edge also increases, resulting in a lack of durability improvement. If the elastic modulus at 60° C. of the upper bead filler 6a and the lower bead filler 6b is higher than the above range, the breaking elongation of the bead filler 6 cannot be improved, and the effect of improving durability cannot be expected to be sufficient.

[0036] When using a bead filler 6 having a two-layer structure as described above, the area S2 of the upper bead filler 6a and the area S3 of the lower bead filler 6b preferably satisfy the relationship 0.30≦S3 / S2≦0.80, and more preferably satisfy the relationship 0.40≦S3 / S2≦0.70. 6 a and lower bead filler 6 By providing the upper bead filler b in a well-balanced manner, it is advantageous to improve the durability of the bead portion 3. 6 When the breaking elongation of a is large, the upper bead filler 6 The large area of ​​a can disperse strain near the carcass end, improving the durability of the bead portion 3. 6 When the elastic modulus of b is high, deformation of the entire bead portion 3 under load is suppressed, and the durability of the bead portion 3 can be improved. By setting the area as described above, 6 a and lower bead filler 6The area of ​​b is well balanced, the above-mentioned effects can be effectively achieved, and the durability of the bead portion 3 can be improved overall.

[0037] As shown in FIG. 3 , let G3 be the distance between the turned-up end and the tire outer surface measured on the perpendicular line L2, and G4 be the distance between the turned-up end and the outer surface of the recess 20 measured on the extension line of the turned-up portion 4b. Distance G3 is preferably 7.0 mm to 14.0 mm, more preferably 8.0 mm to 13.0 mm, and distance G4 is preferably 10.0 mm to 40.0 mm, more preferably 15.0 mm to 37.0 mm. This ensures a sufficient distance from the carcass end to the tire outer contour, dispersing strain between the carcass end and the tire outer contour, which is advantageous for improving the durability of the bead portion 3. If distances G3 and G4 are smaller than the respective ranges, the amount of rubber cannot be sufficiently secured, dispersing strain at the carcass end, and the effect of improving durability cannot be fully expected. If distances G3 and G4 are larger than the respective ranges, the effect of reducing tire weight cannot be fully expected.

[0038] In the present invention, the breaking elongation of the rubber constituting the side rubber layer 12 is preferably 450% or more, more preferably 500% or more. The elastic modulus of the rubber constituting the side rubber layer 12 at 60°C is preferably 2.5 MPa or more and 5.5 MPa or less, more preferably 3.5 MPa or more and 5.0 MPa or less. Increasing the breaking elongation of the side rubber in this way can suppress breakage near the carcass end due to repeated strain during rolling, which is advantageous for improving the durability of the bead portion. Furthermore, increasing the elastic modulus of the side rubber can compensate for the reduced side rigidity caused by providing recesses, which is advantageous for reducing strain in the bead portion and improving durability. If the breaking elongation of the rubber constituting the side rubber layer 12 is less than 450%, the rubber around the carcass will easily break due to repeated strain during rolling, making it difficult to sufficiently improve the durability of the bead portion 3. The upper limit of the breaking elongation of the side rubber layer 12 is not particularly limited, but it is preferably 800% or less, for example. If the elastic modulus at 60°C of the rubber constituting the side rubber layer 12 is less than 2.5 MPa, sufficient side rigidity cannot be ensured, and if it exceeds 5.5 MPa, the breaking elongation of the side rubber layer 12 cannot be maintained at a good level, and the effect of improving durability cannot be fully expected.

[0039] In the present invention, as shown in FIG. 3 , the crack-suppressing rubber layer 14 can be disposed so as to cover the turned-up end of the carcass layer 4. The crack-suppressing rubber layer 14 is preferably disposed so as to be in contact with both the side rubber layer 12 and the rim cushion rubber layer 13. Furthermore, when a steel reinforcing layer 21 (described later) is provided, the crack-suppressing rubber layer 14 is preferably disposed so as to cover not only the turned-up end of the carcass layer 4 but also the end of the steel reinforcing layer 21. Similarly, when an organic fiber reinforcing layer 22 (described later) is provided, the crack-suppressing rubber layer 14 is preferably disposed so as to cover not only the turned-up end of the carcass layer 4 but also the end of the organic fiber reinforcing layer 22. When such a crack-suppressing rubber layer 14 is provided, its breaking elongation is preferably set to 400% or more, more preferably 450% or more. Increasing the breaking elongation of the crack-suppressing rubber layer 14 in this way can prevent breakage near the carcass end due to repeated strain during rolling, which is advantageous for improving the durability of the bead portion. If the elongation at break of the crack-preventing rubber layer 14 is less than 400%, the rubber around the carcass will easily break due to repeated strain during rolling, making it difficult to sufficiently improve the durability of the bead portion 3. There is no particular upper limit to the elongation at break of the crack-preventing rubber layer 14, but it is preferable to set it to, for example, 800% or less.

[0040] In the present invention, as shown in FIG. 2 , a steel reinforcing layer 21 can be disposed along the outer surfaces of the main body portion 4a and the turned-up portion 4b of the carcass layer 4. When the steel reinforcing layer 21 is disposed, the end of the steel reinforcing layer 21 on the turned-up portion 4b side is preferably spaced radially inward from the position of the turned-up end, and the distance along the tire radial direction between the end of the steel reinforcing layer 21 on the turned-up portion 4b side and the turned-up end is preferably 5 mm to 25 mm, more preferably 7 mm to 20 mm. Furthermore, the end of the steel reinforcing layer 21 on the main body portion 4a side is preferably spaced radially outward from the position of the turned-up end, and the distance along the tire radial direction between the end of the steel reinforcing layer 21 on the main body portion 4a side and the turned-up end is preferably 5 mm to 25 mm, more preferably 7 mm to 20 mm. Providing the steel reinforcing layer 21 in this manner and arranging it as described above improves side rigidity and suppresses deformation of the bead portion due to flexure, which is advantageous for improving the durability of the bead portion.

[0041] In the present invention, as shown in FIG. 2, an organic fiber reinforcement layer 22 can also be disposed on the tire width direction outer side of the turned-up portion 4b of the carcass layer 4. When the above-described steel reinforcement layer 21 is provided, the organic fiber reinforcement layer 22 is preferably disposed on the outer peripheral side (outer side in the tire width direction) of the steel reinforcement layer 21 as shown in the figure. When the organic fiber reinforcement layer 22 is provided, its radially outer end is preferably located radially outward of the turned-up end, and its radially inner end is preferably located radially inward of the center of the bead core 5. Furthermore, the radially outer end of the organic fiber reinforcement layer 22 is preferably spaced 6 mm or more from the recess. By providing the organic fiber reinforcement layer 22 in this manner and arranging it as described above, deformation due to flexure can be suppressed, which is advantageous for suppressing distortion near the carcass end and improving durability.

[0042] The present invention will be further explained below with reference to examples, but the scope of the present invention is not limited to these examples. [Example]

[0043] Thirty-five types of pneumatic tires, Conventional Example 1, Comparative Example 1, and Examples 1 to 33, were manufactured, each having a tire size of 11R22.5 and the basic structure shown in FIG. 1, with the structures in the vicinity of the bead portions set as shown in Tables 1 to 3.

[0044] Regarding the "presence or absence of recesses" in Tables 1 to 4, cases where a recess that is continuous in the tire circumferential direction is present on the outer surface of the tire radially outward from the turned-up end of the carcass layer in the sidewall portion and radially inward from the maximum tire width position is indicated as "present," and cases where such a recess is not present are indicated as "absent," as shown in Figure 1. Note that cases where a recess is provided in only one sidewall portion are indicated as "present (one side)" (when a recess is provided in only one sidewall portion, the numerical values ​​for the side with the recess are entered for other items).

[0045] "G1" in Tables 1 to 4 is the thickness G1 (unit: mm) of the bead filler measured along a straight line (perpendicular line L2) that passes through the turned-up end of the carcass layer and intersects perpendicularly with the main body of the carcass layer. "A / (S+A)" in Tables 1 to 4 is the area A (unit: mm) of the region enclosed by the outer contour of the sidewall and bead portions and the tangent line L1 (a straight line drawn so as to be tangent to the outer contour of the sidewall and bead portions). 2 ], the area S (unit: mm) of the region surrounded by the outer contours of the sidewall and bead portions, the main body portion, and the above-mentioned perpendicular lines L2 and L3 (straight lines passing through the point where the above-mentioned tangent line L1 and the outer contour of the sidewall portion meet (contact point P1) and perpendicular to the main body portion of the carcass layer). 2 ] is the area ratio calculated from

[0046] The column "Outer contour shape relative to line L4" in Tables 1 to 4 shows the curved shape of the outer contour relative to line L4 (the direction of the convexity relative to line L4) when a point P3, which is 10 mm away from line L4 radially outward along the outer contour of the sidewall and bead portions, is drawn from tangent point P2, where the point where the tangent line L1 meets the outer contour of the bead portion, to line L4. When the outer contour of the sidewall and bead portions located between tangent point P2 and point P3 and line L4 is located on the outer side in the tire width direction, it is shown as "outer," and all other cases as "inner."

[0047] "S1 / S" in Tables 1 to 4 is the area S1 (unit: mm 2 ] to the area S. "G2 / G1" in Tables 1 to 4 is the ratio of the bead filler thicknesses G1 and G2 measured at different positions, where G1 is the thickness of the bead filler measured along a straight line (perpendicular line L2) that passes through the turned-up end of the carcass layer and intersects perpendicularly with the main body of the carcass layer, and G2 is the thickness of the bead filler measured on a straight line that passes through the aforementioned contact point P2 and intersects perpendicularly with the main body of the carcass layer.

[0048] "Breaking elongation (upper BF)" in Tables 1 to 4 is the breaking elongation of the upper bead filler in a two-layer bead filler. "Breaking elongation (side)" in Tables 1 to 4 is the breaking elongation of the side rubber that constitutes the sidewall portion. "Elongation at break (cr)" is the elongation at break of the rubber that constitutes the crack-suppressing rubber layer. All values ​​are measured at room temperature (23°C) in accordance with JIS K6251 for the rubber that makes up each part (unit: %).

[0049] In Tables 1 to 4, "Modulus of Elasticity (Upper BF)" is the modulus of elasticity at 60°C of the upper bead filler in a two-layer bead filler, and "Modulus of Elasticity (Lower BF)" is the modulus of elasticity at 60°C of the lower bead filler in a two-layer bead filler. "Modulus of Elasticity (side)" is the modulus of elasticity at 60°C of the side rubber that constitutes the sidewall. .stomach All values ​​are measured for the rubber constituting each part using a viscoelasticity spectrometer in accordance with JIS K6394 under conditions of an initial strain of 10%, amplitude of ±2%, frequency of 20 Hz, and 60°C (unit: MPa).

[0050] "S3 / S2" in Tables 1 to 4 is the ratio of the area S2 of the upper bead filler to the area S3 of the lower bead filler. "G3" in Tables 1 to 4 is the distance between the turned-up end and the outer surface of the tire measured on the aforementioned perpendicular line L2. "G4" in Tables 1 to 4 is the distance between the turned-up end and the outer surface of the recess measured on the extension of the turned-up portion.

[0051] In the column "Presence or absence of organic fiber reinforcement layer" in Tables 1 to 4, cases where an organic fiber reinforcement layer is provided on the tire width direction outer side of the turned-up portion of the carcass layer are indicated as "present," and cases where such an organic fiber reinforcement layer is not provided are indicated as "absent." When an organic fiber reinforcement layer is provided, the outer end of this organic fiber reinforcement layer in the tire radial direction is located outer than the turned-up end in the tire radial direction, the inner end of the organic fiber reinforcement layer in the tire radial direction is located inner than the center of the bead core in the tire radial direction, and the outer end of the organic fiber reinforcement layer in the tire radial direction is separated from the recess by 6 mm or more.

[0052] In the column "Presence or Absence of Steel Reinforcing Layer" in Tables 1 to 4, cases where a steel reinforcing layer was arranged along the outer surface of the main body portion and the turned-up portion of the carcass layer were indicated as "present," and cases where such a steel reinforcing layer was not arranged were indicated as "absent." When a steel reinforcing layer is provided, the end of this steel reinforcing layer on the turned-up portion side is positioned 5 mm to 25 mm away from the position of the turned-up end toward the inner side in the tire radial direction, and the end of the steel reinforcing layer on the main body side is positioned 5 mm to 25 mm away from the position of the turned-up end toward the outer side in the tire radial direction.

[0053] These test tires were evaluated for tire weight reduction and durability using the following evaluation methods, and the results are shown in Tables 1 to 4.

[0054] Tire weight reduction The weight (kg) of each test tire was measured, and the weight reduction (absolute value of the difference in weight from the tire of Conventional Example 1) compared to Conventional Example 1, which had no recesses, was calculated. The evaluation results show the actual value of the calculated weight reduction (kg). The larger this value, the greater the effect of reducing tire weight.

[0055] durability Each test tire was mounted on a JATMA-specified rim, mounted on a drum testing machine with a drum diameter of 1707 mm, inflated to the maximum JATMA-specified air pressure, and run at a speed of 45 km / h under the maximum JATMA-specified load, measuring the distance at which bead bulging or separation was detected. The evaluation results were expressed as an index, with Conventional Example 1 being set at 100, and the higher the index value, the longer the running distance until bead bulging or separation was detected, indicating superior bead durability. An index value of 90 or higher means that sufficient durability was obtained compared to Conventional Example 1, which does not have recesses.

[0056] [Table 1]

[0057] [Table 2]

[0058] [Table 3]

[0059] [Table 4]

[0060] As is clear from Tables 1 to 4, it was possible to reduce the tire weight while maintaining good durability in all of Examples 1 to 33. In contrast, in Comparative Example 1, although the tire weight could be reduced by providing recesses, durability deteriorated. [Explanation of symbols]

[0061] 1 Tread section 2 Sidewall 3 Bead section 4 carcass layers 4a Main body 4b Folded part 5 bead core 6 Bead filler 6a Upper bead filler 6b Lower bead filler 7 Belt Layer 11 Tread rubber layer 12 Side rubber layer 13 Rim cushion rubber layer 14 Crack suppression rubber layer 20 recess 21 Steel reinforcement layer 22 Organic fiber reinforcement layer P Maximum tire width position CL Tire Equator

Claims

1. A pneumatic tire comprising a tread portion extending in a circumferential direction of the tire and forming an annular shape, a pair of sidewall portions disposed on both sides of the tread portion, and a pair of bead portions disposed radially inward of the sidewall portions, a bead core disposed in each of the bead portions, a bead filler disposed radially outward of the bead core, and at least one carcass layer mounted between the pair of bead portions, The carcass layer comprises a main body portion wound up around the bead core and the bead filler disposed in each bead portion from the inside to the outside of the tire and positioned between the pair of bead portions, and a wound-up portion wound up on the outside of the bead core and the bead filler in the tire width direction, When the width between the pair of bead portions is set to the specified rim width in an unassembled state, a tire outer surface provided with a recess that is continuous in the tire circumferential direction, the recess being located radially outward of a turned-up end of the carcass layer of at least one of the sidewall portions and radially inward of a maximum tire width position, the contour line of the recess being formed by a plurality of arcs having different radii of curvature in a meridian cross section, When a line drawn tangent to the outer contours of the sidewall portion and the bead portion in a meridian cross section is defined as a tangent line L1, a point where the tangent line L1 and the outer contour of the sidewall portion are tangent to a tangent line P1, a line passing through the turned-up end of the carcass layer and perpendicularly intersecting the main body portion is defined as a perpendicular line L2, and a line passing through the tangent line P1 and perpendicularly intersecting the main body portion is defined as a perpendicular line L3, The area A (unit: mm) of the region surrounded by the outer contours of the sidewall portion and the bead portion and the tangent line L1 ２ ] and the area S [unit: mm ２ and a thickness G1 (unit: mm) of the bead filler measured along the perpendicular line L2 satisfy the relationship 0.10 × (G1-17) ≦ A / (S+A) ≦ 0.05 × (G1-10).

2. 2. The pneumatic tire according to claim 1, wherein when a point where the tangent line L1 and the outer contour of the bead portion meet is defined as a contact point P2, the outer contours of the sidewall portion and the bead portion located between the contact point P2 and a point P3 that is spaced 10 mm radially outward from the contact point P2 along the outer contour of the sidewall portion and the bead portion and that is located between the contact point P2 and the point P3 are located outward in the tire width direction than a straight line L4 that connects the contact point P2 and a point P3.

3. When the point where the tangent line L1 and the outer contour of the bead portion meet is defined as a contact point P2, the ratio G2 / G1 of the thickness G2 (unit: mm) of the bead filler measured on a line that passes through the contact point P2 and perpendicularly intersects with the main body portion to the thickness G1 satisfies the relationship of 0.55≦G2 / G1≦0.90, and the area S1 (unit: mm) of the region occupied by the bead filler in the area S is ２ 3. The pneumatic tire according to claim 1, wherein a ratio S1 / S of the area S to the area S satisfies the relationship 0.25≦S1 / S≦0.

50.

4. The pneumatic tire according to any one of claims 1 to 3, characterized in that the bead filler has a two-layer structure consisting of an upper bead filler and a lower bead filler, and the upper bead filler has a breaking elongation of 400% or more.

5. 5. The pneumatic tire according to claim 4, wherein the upper bead filler has an elastic modulus of 4.0 MPa or more and 8.0 MPa or less, measured under conditions of an initial strain of 10%, an amplitude of ±2%, a frequency of 20 Hz, and 60°C, and the lower bead filler has an elastic modulus of 14.0 MPa or more and 20.0 MPa or less, measured under conditions of an initial strain of 10%, an amplitude of ±2%, a frequency of 20 Hz, and 60°C.

6. 6. The pneumatic tire according to claim 4, wherein the area S2 of the upper bead filler and the area S3 of the lower bead filler satisfy the relationship 0.30≦S3 / S2≦0.

80.

7. 7. The pneumatic tire according to claim 1, wherein a distance G3 between the turned-up end and the tire outer surface measured on the perpendicular line L2 is 7.0 mm or more and 14.0 mm or less, and a distance G4 between the turned-up end and the outer surface of the recessed portion measured on an extension line of the turned-up portion is 10.0 mm or more and 40.0 mm or less.

8. The pneumatic tire according to any one of claims 1 to 7, characterized in that the side rubber constituting the sidewall portion has a breaking elongation of 450% or more, and an elastic modulus measured under conditions of an initial strain of 10%, an amplitude of ±2%, a frequency of 20 Hz, and 60°C of 2.5 MPa or more and 5.5 MPa or less.

9. The pneumatic tire according to any one of claims 1 to 8, characterized in that a crack-preventing rubber layer is disposed so as to cover the turned-up end, and the elongation at break of the crack-preventing rubber layer is 400% or more.

10. 10. The pneumatic tire according to claim 1, further comprising an organic fiber reinforcement layer on the outer side in the tire width direction of the turned-up portion of the carcass layer, wherein an outer end of the organic fiber reinforcement layer in the tire radial direction is located outer than the turned-up end in the tire radial direction, an inner end of the organic fiber reinforcement layer in the tire radial direction is located inner than the center of the bead core in the tire radial direction, and the outer end of the organic fiber reinforcement layer in the tire radial direction is spaced 6 mm or more from the recess.

11. 11. The pneumatic tire according to claim 1, wherein a steel reinforcing layer is disposed along outer surfaces of the main body portion and the turned-up portion of the carcass layer, an end of the steel reinforcing layer facing the turned-up portion is disposed at a position 5 mm to 25 mm away from the position of the turned-up end toward the inner side in the tire radial direction, and an end of the steel reinforcing layer facing the main body portion is disposed at a position 5 mm to 25 mm away from the position of the turned-up end toward the outer side in the tire radial direction.

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