Bladder for tire vulcanization and pneumatic tire

Abstract

To suppress occurrence of cracks at a base part of a ridge formed on an inner surface of a tire corresponding to grooves on an outer surface of a bladder.SOLUTION: There is provided a tire vulcanizing bladder 10 used for vulcanizing a green tire. An outer surface 12 of the bladder is provided with a groove 14, and a curvature radius R1 of an opening 22 in a cross section of the groove 14 is 0.8 mm or more.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a tire vulcanization bladder and a pneumatic tire. [Background technology]

[0002] The manufacturing process of pneumatic tires includes a vulcanization process in which a green tire (unvulcanized tire) is vulcanized and molded. In the vulcanization process, the green tire is set in a mold, and a tire vulcanization bladder (hereinafter simply referred to as a bladder) made of a rubber bag is inserted into the green tire. The bladder is then inflated to bring the inner surface of the green tire into close contact with the outer surface of the bladder, and the green tire is heated to vulcanize and mold it.

[0003] Conventionally, grooves have been formed on the outer surface of a bladder (see, for example, Patent Document 1). The grooves provided on the outer surface of the bladder are, for example, air-vent grooves intended to allow air to escape between the outer surface of the bladder and the inner surface of the tire. During vulcanization, the outer surface of the bladder is in close contact with the inner surface of the unvulcanized tire during vulcanization molding, and therefore ridges corresponding to the bladder grooves are formed on the inner surface of the tire after vulcanization molding. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-111661 Summary of the Invention [Problem to be solved by the invention]

[0005] Pneumatic tires are repeatedly deformed during use, which can cause cracks to form at the bases of the ridges on the inner surface of the tire.

[0006] In view of the above, an embodiment of the present invention aims to provide a tire vulcanization bladder that can suppress the occurrence of cracks at the base of ridges formed on the inner surface of a tire in correspondence with grooves on the outer surface of the bladder. [Means for solving the problem]

[0007] A tire vulcanization bladder according to an embodiment of the present invention is a bladder used for vulcanizing green tires, and has a groove on the outer surface of the tire bladder, with the opening of the groove having a radius of curvature of 0.8 mm or more in cross section.

[0008] In the tire vulcanization bladder, the radius of curvature of the corners of the groove bottom in the cross section of the groove may be smaller than the radius of curvature of the opening, and in that case, the radius of curvature of the corners of the groove bottom may be 0.5 mm or more.

[0009] In the tire vulcanization bladder, the cross-sectional shape of the groove may include a first arc portion that defines the opening, a second arc portion that defines a corner of the groove bottom, and a straight portion that is interposed between the first arc portion and the second arc portion and is tangent to the first arc portion and the second arc portion. In this case, the straight portion may be inclined so as to move away from the center of the width direction of the groove as it approaches the opening.

[0010] A pneumatic tire according to an embodiment of the present invention is vulcanized using the tire vulcanization bladder, and has ridges formed on the inner surface of the tire by the grooves of the tire vulcanization bladder. [Effects of the Invention]

[0011] According to this embodiment, by setting the radius of curvature of the opening in the cross section of the groove on the outer surface of the bladder to 0.8 mm or more, it is possible to suppress the occurrence of cracks at the base of the ridge formed on the inner surface of the tire corresponding to the groove. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view of a tire vulcanization bladder according to one embodiment. [Figure 2] FIG. 1 is a development view showing a part of the outer surface of the tire vulcanization bladder; [Figure 3] FIG. 3 is a cross-sectional view showing grooves in the tire vulcanization bladder. [Figure 4] FIG. 10 is a cross-sectional view showing grooves in a tire vulcanization bladder according to another embodiment. [Figure 5] 1 is a cross-sectional view of a pneumatic tire according to an embodiment; [Figure 6] FIG. 3 is a cross-sectional view showing a ridge of the pneumatic tire. [Figure 7] FIG. 10 is a cross-sectional view showing a ridge of a pneumatic tire according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0014] FIG. 1 shows a tire vulcanization bladder 10 (hereinafter simply referred to as bladder 10) according to one embodiment. Bladder 10 is a cylindrical rubber member with an axially central portion that protrudes outward in the axis-perpendicular direction. FIG. 1 is a cross-sectional view (meridian cross-section) of bladder 10 cut at one location in its circumferential direction. In FIG. 1, symbol X indicates the axial direction of bladder 10, which coincides with the axial direction of the tire to be vulcanized. Symbol Y indicates the outer side in the axis-perpendicular direction (i.e., the radially outer side). The rubber material constituting bladder 10 is not particularly limited, and examples thereof include butyl rubber and fluororubber.

[0015] The bladder 10, together with a mold (not shown), constitutes a tire vulcanizing apparatus. The bladder 10 expands when a shaping gas or a heating medium (e.g., steam) is supplied, and is pressed against the inner surface of the green tire during vulcanization. When pressed against the inner surface of the green tire, the bladder 10 forms a horseshoe shape that conforms to the inner surface shape of the pneumatic tire. Clamped portions 11, 11 are provided at both ends of the bladder 10 in the axial direction X. The bladder 10 is incorporated into the tire vulcanizing apparatus by gripping the clamped portions 11 with the clamping portions of the tire vulcanizing apparatus. Note that known structures can be applied to the mold and tire vulcanizing apparatus, and are not particularly limited.

[0016] As shown in Fig. 1, a plurality of air-releasing grooves 14 are provided on the outer surface 12 of the bladder 10. As shown in Fig. 2, the grooves 14 extend in a direction (i.e., the axial direction X) that intersects with the circumferential direction Z of the bladder 10. Therefore, air present between the green tire and the bladder 10 during vulcanization can escape to the outside through the grooves 14.

[0017] Groove 14 is not provided at axial center 16 of bladder 10, which corresponds to the equatorial plane of the tire to be molded. Instead, groove 14 is provided so as to extend from starting point 18, which is located at a predetermined distance G1 from axial center 16, to both sides in axial direction X. The predetermined distance G1 from axial center 16 to starting point 18 may be, for example, 5 to 30 mm or 10 to 20 mm. Groove 14 extends outward in axial direction X from starting point 18 and terminates before reaching clamped portion 11. A distance G2 (see FIG. 1 ) between end point 20 of groove 14 and clamped portion 11 may be, for example, 5 to 30 mm or 10 to 30 mm.

[0018] Grooves 14 may be provided parallel to the axial direction X of bladder 10, but in this example, they are provided at an angle relative to axial direction X as shown in Figure 2. The angle of inclination θ of grooves 14 relative to axial direction X (strictly speaking, the angle of inclination relative to the meridian direction along outer surface 12 of bladder 10) may be, for example, 10° to 60°, and preferably 35° to 55°. Note that in this example, grooves 14 extend linearly in the developed view shown in Figure 2, but they may also extend in a curved manner.

[0019] A plurality of grooves 14 are provided at intervals in the circumferential direction Z of the bladder 10. The grooves 14 may be arranged at equal intervals in the circumferential direction Z, or may be arranged at staggered intervals. The interval between the widthwise centerlines of the grooves 14 may be, for example, 5 to 30 mm, and preferably 10 to 15 mm.

[0020] FIG. 3 is a cross-sectional view of bladder 10 showing the cross-sectional shape of groove 14. Groove 14 is formed to have a constant cross-sectional shape in the direction of extension. The radius of curvature R1 of opening 22 in the cross-section of groove 14 is set to 0.8 mm or more (R1≧0.8 mm). Specifically, in a cross-section perpendicular to the direction of extension of groove 14, both corners of opening 22 that opens to outer surface 12 of bladder 10 (i.e., the portions where the side walls of groove 14 intersect with outer surface 12 of bladder 10) are formed in an arc shape with a radius of curvature R1 of 0.8 mm or more. Here, the center of the circle of curvature with radius of curvature R1 is located inside bladder 10.

[0021] By making the radius of curvature R1 of the opening 22 0.8 mm or more in this way, the radius of curvature at the base of the ridge formed on the tire inner surface corresponding to the groove 14 becomes larger, making it possible to suppress the occurrence of cracks at the base. The larger the radius of curvature R1, the better the effect of suppressing the occurrence of cracks, so there is no particular upper limit, and it may be, for example, 2.0 mm or less, 1.5 mm or less, or 1.2 mm or less.

[0022] In this example, the radius of curvature R2 of the corner 24A of the groove bottom 24 in the cross-section of the groove 14 is also formed to be smaller than the radius of curvature R1 of the opening 22 (R2 < R1). Specifically, in a cross-section perpendicular to the extending direction of the groove 14, the corners 24A, 24A on both sides of the groove bottom 24 (i.e., the portions where the side wall of the groove 14 and the groove bottom 24 intersect) are formed in an arc shape with a radius of curvature R2, and the radius of curvature R2 is smaller than the radius of curvature R1 of the opening 22. Here, the center of the curvature circle with the radius of curvature R2 is located outside the bladder 10, specifically, inside the groove 14 (inside the space). Thus, by making the radius of curvature R1 of the opening 22 larger than the radius of curvature R2 of the groove bottom 24, the above-mentioned effect of suppressing the generation of cracks can be enhanced.

[0023] The radius of curvature R2 of the corner 24A of the groove bottom 24 may be 0.2 mm or more, but preferably 0.5 mm or more. By having the radius of curvature R2 be 0.5 mm or more, the above-mentioned effect of suppressing the generation of cracks can be further enhanced.

[0024] As shown in FIG. 3, in this example, the cross-sectional shape of the groove 14 includes a first arc portion 26 with a radius of curvature R1 that defines the opening 22, a second arc portion 28 with a radius of curvature R2 that defines the corner 24A of the groove bottom 24, and a straight portion 30 interposed between the first arc portion 26 and the second arc portion 28. Specifically, in a cross-section perpendicular to the extending direction of the groove 14, the groove 14 includes, in order from the opening side, a pair of first arc portions 26, 26 with a radius of curvature R1, a pair of straight portions 30, 30 that define both side walls of the groove 14, a pair of second arc portions 28, 28 with a radius of curvature R2, and a straight portion 32 that defines the central portion of the groove bottom 24. The first arc portion 26 is in contact with the straight portion that defines the outer surface 12 of the bladder 10 at one end thereof and is in contact with the straight portion 30 that defines the side wall of the groove 14 at the other end thereof. The second arc portion 28 is in contact with the straight portion 30 that defines the side wall of the groove 14 at one end thereof and is in contact with the straight portion 32 that defines the central portion of the groove bottom 24 at the other end thereof. Note that in one embodiment, the straight portion 30 and / or the straight portion 32 may not be provided.

[0025] In this way, by forming a cross-sectional shape in which the first arcuate portion 26 and the second arcuate portion 28 are connected by the linear portion 30 tangent to both, it becomes easier to ensure the depth of the groove 14 and also improves the flow of rubber during vulcanization. Here, rubber flow refers to the flow of unvulcanized rubber that makes up the green tire during vulcanization, and in this example, it means that the unvulcanized rubber can easily enter the groove 14.

[0026] 3, the linear portion 30 tangent to the first arc portion 26 and the second arc portion 28 is inclined so as to move away from the widthwise center of the groove 14 as it approaches the opening 22. In other words, the width of the groove 14 is inclined so as to increase from the groove bottom 24 side toward the opening 22 side. This can further enhance the effect of suppressing the occurrence of cracks.

[0027] The height H1 of the first arcuate portion 26 (the dimension of the first arcuate portion 26 in the depth direction of the groove 14) may be, for example, 0.3 to 1.0 mm, 0.3 to 0.8 mm, or 0.4 to 0.6 mm.

[0028] The depth H of the groove 14 may be, for example, 0.5 mm or more, 0.8 mm or more, or 2.0 mm or less, or 1.5 mm or less. The width W of the groove 14 may be, for example, 0.5 to 2.0 mm, or 0.8 to 1.5 mm. Here, the width W of the groove 14 is the width of the groove bottom 24 when it is assumed that the corners 24A of the groove bottom 24 are not curved, and is the distance between the intersections of imaginary lines L1, L1 extending from a pair of straight line portions 30, 30 and a reference line L2 of the groove bottom 24, as shown in FIG. 3 .

[0029] The thickness T of the bladder 10 may be, for example, 4 to 10 mm, or 5 to 7 mm.

[0030] FIG. 4 shows a modified example of groove 14A provided on outer surface 12 of bladder 10. In this example, linear portions 30A tangent to first arcuate portion 26 and second arcuate portion 28 are formed perpendicular to outer surface 12 of bladder 10. Thus, linear portions 30A, 30A defining both side walls of groove 14A may be formed as vertical side walls without being inclined. However, the embodiment shown in FIG. 3, which has inclined linear portions 30, is superior in terms of the effect of suppressing the occurrence of cracks.

[0031] As a method for manufacturing a pneumatic tire using the bladder 10, known tire manufacturing methods can be adopted, except for the bladder used. That is, for example, after a green tire is produced, a vulcanization process is performed to vulcanize and mold the green tire. In the vulcanization process, a tire vulcanization apparatus equipped with a mold (not shown) and the bladder 10 is used. The green tire is set in the mold, and the bladder 10 is inserted inside the green tire. Then, shaping is performed by supplying a shaping gas into the bladder 10 to closely fit the outer surface of the bladder 10 to the inner surface of the green tire. Next, the mold is heated, and a high-temperature heating medium is supplied into the bladder 10 to heat the green tire and vulcanize and mold it. After vulcanization is complete, the mold is opened and the bladder 10 is evacuated, and the vulcanized tire is removed. This results in a pneumatic tire.

[0032] Figure 5 is a diagram showing an example of a pneumatic tire 50 (hereinafter simply referred to as the tire 50) obtained in this manner. The tire 50 has a pair of left and right bead portions 52, 52 fixed to a rim, a pair of left and right sidewalls 54, 54 continuing radially outward from the pair of bead portions 52, 52, respectively, and a tread 56 extending across the pair of sidewalls 54, 54 and forming a contact surface. Figure 5 is a cross-sectional view of the tire 50 taken along a meridian including the tire rotation axis.

[0033] In the figure, the symbol CL indicates the tire equatorial plane, which corresponds to the tire axial center. The tire axial direction refers to the direction parallel to the tire rotation axis, and is indicated by the symbol AD ​​in the figure. The tire radial direction refers to the direction perpendicular to the tire rotation axis, and is indicated by the symbol RD in the figure. The tire circumferential direction refers to the direction of rotation around the tire rotation axis.

[0034] The tire 50 includes a pair of left and right bead cores 58, 58, a carcass ply 60 that is toroidally wound between the pair of bead cores 58, 58, and a belt 62 that is disposed on the outer side in the tire radial direction RD of the crown portion of the carcass ply 60. In this embodiment, the structure of the tire 50 other than the inner surface 64 is not particularly limited.

[0035] The tire 50 according to this embodiment has a plurality of ridges 66 formed on its inner surface 64 by the grooves 14 of the bladder 10. The ridges 66 are formed by vulcanization molding in a state in which the outer surface 12 of the bladder 10, which has the grooves 14, is in close contact with the inner surface 64 of the unvulcanized tire, and are formed in a shape that is an inverted version of the grooves 14.

[0036] Therefore, the ridges 66 extend in a direction intersecting the tire circumferential direction (i.e., in the tire axial direction AD). As shown in Fig. 5, the ridges 66 are not provided at a center 67 in the axial direction AD, which corresponds to the equatorial plane CL, but rather have a starting point 69 located at a position spaced a predetermined distance G3 from the center 67, and extend outward from the starting point 69 in the axial direction AD to the bead toe of the bead portion 52. The predetermined distance G3 from the center 67 to the starting point 69 may be, for example, 5 to 30 mm or 10 to 20 mm.

[0037] The ridges 66 may be provided parallel to the axial direction AD of the tire 50, but in this example, they are provided at an incline with respect to the axial direction AD, similar to the grooves 14 described above. The inclination angle of the ridges 66 with respect to the axial direction AD (strictly speaking, the inclination angle with respect to the meridian direction along the inner surface 64 of the tire 50) may be, for example, 10° to 60°, and preferably 35° to 55°. The ridges 66 may extend linearly or curvedly in a developed view.

[0038] Similar to the grooves 14, a plurality of ridges 66 are provided at intervals in the circumferential direction of the tire 50. The ridges 66 may be arranged at equal intervals in the circumferential direction of the tire 50, or may be arranged at staggered intervals. The interval between the center lines of the ridges 66 in the width direction may be, for example, 5 to 30 mm, and preferably 10 to 15 mm.

[0039] FIG. 6 is a cross-sectional view showing the cross-sectional shape of the ridge 66, which is formed to have a constant cross-sectional shape in its extension direction. Because the ridge 66 has a shape that is an inversion of the groove 14 of the embodiment shown in FIG. 3, the radius of curvature R3 of the root portion 68 in the cross section of the ridge 66 is formed to be 0.8 mm or more (R3≧0.8 mm). More specifically, in a cross section perpendicular to the extension direction of the ridge 66, the root portions 68 on both sides of the ridge 66 relative to the inner surface 64 of the tire 50 (i.e., the portions where the sidewalls of the ridge 66 intersect with the inner surface 64 of the tire 50) are formed in an arc shape with a radius of curvature R3 of 0.8 mm or more. Here, the center of the circle of curvature with radius of curvature R3 is located outside the tire 50.

[0040] In this way, by setting the radius of curvature R3 of the ridge 66 to 0.8 mm or more, it is possible to suppress the occurrence of cracks at the base 68 of the ridge 66. The larger the radius of curvature R3, the better the effect of suppressing the occurrence of cracks, so there is no particular upper limit, but it may be, for example, 2.0 mm or less, 1.5 mm or less, or 1.2 mm or less.

[0041] In this example, the radius of curvature R4 of the corner 70A of the top 70 in the cross-section of the ridge 66 is also formed to be smaller than the radius of curvature R3 of the base 68 (R4 < R3). Specifically, in a cross-section perpendicular to the extending direction of the ridge 66, the corners 70A, 70A on both sides of the top 70 (i.e., the portions where the side wall of the ridge 66 and the top 70 intersect) are formed in an arc shape with a radius of curvature R4, and this radius of curvature R4 is smaller than the radius of curvature R3 of the base 68. Here, the center of the curvature circle with the radius of curvature R4 is located inside the tire 50, specifically inside the ridge 66. By making the radius of curvature R3 of the base 68 larger than the radius of curvature R4 of the top 70 in this way, the effect of suppressing the occurrence of the above cracks can be enhanced.

[0042] The radius of curvature R4 of the corner 70A of the top 70 of the ridge 66 may be 0.2 mm or more, but is preferably 0.5 mm or more. By having the radius of curvature R4 be 0.5 mm or more, the effect of suppressing the occurrence of the above cracks can be further enhanced.

[0043] As shown in FIG. 6, in this example, the cross-sectional shape of the ridge 66 includes a third arc portion 72 that defines the base 68, a fourth arc portion 74 that defines the corner 70A of the top 70, and a straight portion 76 interposed between the third arc portion 72 and the fourth arc portion 74. Specifically, in a cross-section perpendicular to the extending direction of the ridge 66, the ridge 66 includes, in order from the base side, a pair of third arc portions 72, 72 having a radius of curvature R3, a pair of straight portions 76, 76 that define both side walls of the ridge 66, a pair of fourth arc portions 74, 74 having a radius of curvature R4, and a straight portion 78 that defines the central portion of the top 70. One end of the third arc portion 72 contacts a straight portion that defines the inner surface 64 of the tire 50, and the other end contacts the straight portion 76 that defines the side wall of the ridge 66. One end of the fourth arc portion 74 contacts the straight portion 76 that defines the side wall of the ridge 66, and the other end contacts the straight portion 78 that defines the central portion of the top 70. Note that in one embodiment, the straight portion 76 and / or the straight portion 78 may not be provided.

[0044] 6, the straight line portion 76 tangent to the third arc portion 72 and the fourth arc portion 74 is inclined so as to move away from the center of the width of the ridge 66 as it approaches the base portion 68. In other words, the width of the ridge 66 is inclined so as to increase from the peak portion 70 side toward the base portion 68 side. This further enhances the effect of suppressing the occurrence of cracks.

[0045] The height H2 of the third arcuate portion 72 may be, for example, 0.3 to 1.0 mm, 0.3 to 0.8 mm, or 0.4 to 0.6 mm.

[0046] The height H0 of the ridge 66 may be, for example, 0.5 mm or more, 0.8 mm or more, or 2.0 mm or less, or 1.5 mm or less. The width W0 of the ridge 66 may be, for example, 0.5 to 2.0 mm, or 0.8 to 1.5 mm. Here, the width W0 of the ridge 66 is the width of the apex 70 when it is assumed that the corners 70A of the apex 70 are not curved, and is the distance between the intersections of imaginary lines L3, L3 extending from a pair of straight line portions 76, 76, respectively, and a reference line L4 of the apex 70, as shown in FIG. 6 .

[0047] Fig. 7 is a cross-sectional view showing the cross-sectional shape of a ridge 66A formed by the groove 14A of the embodiment shown in Fig. 4. The ridge 66A has an inverted shape of the groove 14A, and therefore the linear portions 76A tangent to the third arc portion 72 and the fourth arc portion 74 are formed perpendicular to the inner surface 64 of the tire 50. In this way, the linear portions 76A, 76A defining both side walls of the ridge 66A may be formed as vertical side walls without being inclined.

[0048] In this embodiment, the thickness of the bladder and the dimensions of the grooves, such as the inclination angle, spacing, radius of curvature, width, and depth, are values ​​measured in a free state without the bladder being mounted in a tire vulcanizing apparatus, while the dimensions of the ridges of the pneumatic tire, such as the inclination angle, spacing, radius of curvature, width, and height, are values ​​measured in a free state without the pneumatic tire being mounted on a rim. [Example]

[0049] Examples will be described to demonstrate the effects of this embodiment. In Example 1, a bladder was prototyped with grooves 14 having the cross-sectional shape shown in FIG. 3, and a pneumatic tire was prototyped using the bladder. In Example 2, a bladder was prototyped with grooves 14A having the cross-sectional shape shown in FIG. 4, and a pneumatic tire was prototyped using the bladder. The tire size was 11R22.5 16PR. The radii of curvature R1, R2, width W, depth H, bladder thickness T, and number of grooves (number of grooves around the entire circumference of the bladder) for the grooves 14, 14A are as shown in Table 1 below. In Comparative Example 1, a pneumatic tire was prototyped in the same manner as in Example 1, except that the radii of curvature R1 and R2 were changed as shown in Table 1.

[0050] The state of cracks occurring at the base of the ridge on the inner surface of the tire was evaluated for the prototype tires of Examples 1 and 2 and Comparative Example 1. The prototype tires were mounted on a truck, and the inner surface of the tire was observed after running 100,000 km, and evaluated according to the following criteria. ○: No cracks occurred at the base of the ridge △: A small crack occurred at the base of the ridge, but it does not affect use. ×: A crack larger than the above-mentioned microcrack occurs at the base of the ridge.

[0051] [Table 1]

[0052] As shown in Table 1, Examples 1 and 2, in which the radius of curvature R1 was 0.8 mm or more, were superior to Comparative Example 1 in the effect of suppressing crack occurrence. [Explanation of symbols]

[0053] 10... tire vulcanization bladder, 12... outer surface, 14, 14A... groove, 22... opening, 24... groove bottom, 24A... corner portion, 26... first arc portion, 28... second arc portion, 30... straight portion, 50... pneumatic tire, 64... inner surface, 66... ​​ridge, R1... radius of curvature of opening, R2... radius of curvature of groove bottom

Claims

1. A tire vulcanization bladder used for vulcanizing a green tire, the tire vulcanization bladder having grooves on its outer surface, the grooves having a depth of 0.8 mm or more and 2.0 mm or less, the openings of the grooves in their cross sections having a radius of curvature of 0.8 mm or more, the corners of the groove bottoms in their cross sections having a radius of curvature of 0.5 mm or more, and the radius of curvature of the corners of the groove bottoms being smaller than the radius of curvature of the openings.

2. 2. The tire vulcanization bladder according to claim 1, wherein the cross-sectional shape of the groove includes a first arc portion that defines the opening, a second arc portion that defines a corner portion of the groove bottom, and a straight line portion that is interposed between the first arc portion and the second arc portion and is tangent to the first arc portion and the second arc portion.

3. 3. The tire vulcanization bladder according to claim 2, wherein the linear portion is inclined so as to move away from the center of the groove in the width direction as it approaches the opening.

4. A pneumatic tire vulcanized and molded using the tire vulcanization bladder according to any one of claims 1 to 3, and having ridges molded on an inner surface of the tire by the grooves of the tire vulcanization bladder.

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