Pneumatic Tire and Method for Producing the Same

Abstract

To provide a pneumatic tire that is helpful for simplifying manufacturing steps.SOLUTION: In a pneumatic tire 1, a reinforcement rubber layer 8 is arranged adjacently outside in a tire axial direction of a folded-back part of a carcass ply. The reinforcement rubber layer 8 is a laminate 10 in which a plurality of sheet-like rubber members 11 having different lengths in a tire radial direction are laminated in the tire axial direction. A method for manufacturing the pneumatic tire 1 includes a step of laminating the plurality of sheet-like rubber members 11 having the same thickness and having different lengths in the tire radial direction.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a pneumatic tire and a method for manufacturing the same.

Background Art

[0002] Patent Document 1 below describes a pneumatic tire including a carcass including a first ply, a filler, and an apex provided at a bead. The filler is located axially outside the folded portion of the first ply. This filler is said to suppress deformation of the apex and improve the durability of the pneumatic tire.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Generally, the filler as described above is extrusion-molded by a rubber extruder. The rubber extruder is provided with, for example, a die for forming the filler into a predetermined shape. For this reason, in order to manufacture a plurality of types of fillers according to the tire size, it is necessary to prepare and replace dies of different sizes, etc., and there has been a problem that the manufacturing process becomes complicated.

[0005] The present disclosure has been devised in view of the above actual situation, and the main object thereof is to provide a pneumatic tire useful for simplifying the manufacturing process.

Means for Solving the Problems

[0006] The present disclosure relates to a pneumatic tire, comprising a pair of bead portions each embedded with a bead core, and a carcass extending between the bead cores. The carcass includes a carcass ply including a main body portion extending between the bead cores and a folded-back portion that is folded back from the inner side in the tire axial direction around each bead core and extends outward in the tire radial direction. A reinforcing rubber layer is disposed in the bead portion adjacent to the outer side in the tire axial direction of the folded-back portion. The reinforcing rubber layer is a laminate in which a plurality of sheet-like rubber members having different lengths in the tire radial direction are laminated in the tire axial direction.

Advantages of the Invention

[0007] By adopting the above configuration or steps, the pneumatic tire and its manufacturing method of the present disclosure can simplify the manufacturing process.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0009] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. FIG. 1 is a right half tire meridian cross-sectional view including a tire rotation axis (not shown) in the normal state of the pneumatic tire (hereinafter sometimes simply referred to as "tire") 1 of the present embodiment. The present disclosure is used, for example, for the tire 1 of a commercial vehicle or a light truck. However, the present disclosure is not limited to such a tire 1.

[0010] Here, the "normal state" is a no-load state in which the tire 1 is rim-mounted on a normal rim R and adjusted to a normal internal pressure. Hereinafter, unless otherwise specified, the dimensions and the like of each part of the tire 1 are values measured in this normal state.

[0011] The "normal rim R" is a rim defined for each tire in a standard system including the standard on which the tire is based. For example, in the case of JATMA, it is the "standard rim", in the case of TRA, it is the "Design Rim", and in the case of ETRTO, it is the "Measuring Rim".

[0012] The "normal internal pressure" is the air pressure defined for each tire in a standard system including the standard on which the tire is based. In the case of JATMA, it is the "maximum air pressure", in the case of TRA, it is the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES", and in the case of ETRTO, it is the "INFLATION PRESSURE".

[0013] As shown in FIG. 1, the tire 1 of the present embodiment includes a pair of bead portions 4, 4 in which bead cores 5 are respectively embedded, and a carcass 6 extending between the bead cores 5, 5.

[0014] The carcass 6 includes a carcass ply 6A including a main body portion 6a extending between the bead cores 5, 5 and a folded-back portion 6b that is folded back around each bead core 5 from the inner side in the tire axial direction to the outer side and extends outward in the tire radial direction. In the present embodiment, the carcass 6 is formed of a single carcass ply 6A. The carcass 6 may be formed of, for example, a plurality of carcass plies (not shown).

[0015] In the bead portion 4, a reinforcing rubber layer 8 is disposed adjacent to the outer side in the tire axial direction of the folded-back portion 6b. The reinforcing rubber layer 8 enhances the rigidity of the bead portion 4 and improves durability.

[0016] FIG. 2 is an enlarged view of the bead portion 4 in FIG. 1. As shown in FIG. 2, the reinforcing rubber layer 8 is a laminate 10 in which a plurality of sheet-like rubber members 11 having different lengths in the tire radial direction are laminated in the tire axial direction. Such a laminate 10 can simplify the manufacturing process. The reason for such simplification will be described later.

[0017] As shown in FIG. 1, in the tread portion 2 of the tire 1 of the present embodiment, a belt layer 7 having a well-known structure is formed on the outer side in the tire radial direction of the carcass 6. The tread portion 2 is not limited to such a mode, and various well-known structures are adopted.

[0018] In the bead portion 4 of the present embodiment, a bead apex rubber 9 extending outward in the tire radial direction from the bead core 5 and a sidewall rubber 3G disposed on the outer side in the tire axial direction of the reinforcing rubber layer 8 are provided. Further, in the bead portion 4, for example, a clinch rubber 4G adjacent to the inner side in the tire radial direction of the sidewall rubber 3G is provided. The sidewall rubber 3G and the clinch rubber 4G form the outer surface of the tire 1.

[0019] As shown in FIG. 2, in the present embodiment, the reinforcing rubber layer 8 has a thickness that decreases from the central side in the tire radial direction toward both sides in the tire meridian cross section. In the present embodiment, the reinforcing rubber layer 8 is formed such that the thickness changes in a stepped manner.

[0020] The laminate 10 is formed, for example, by laminating two sheet-like rubber members 11, 11. The laminate 10 is not limited to such a shape, and three or more sheet-like rubber members 11 may be laminated (shown in FIG. 5(c)).

[0021] The sheet-like rubber member 11 has a certain thickness T respectively. The reinforcing rubber layer 8 formed of such a sheet-like rubber member 11 is, for example, crescent-shaped, and has fewer portions with a small thickness compared to a conventional reinforcing rubber layer (not shown) having a portion where the thickness continuously increases, and its rigidity is maintained high, so the durability is improved. The thickness T of the sheet-like rubber member 11 is desirably 0.8 mm or more, more desirably 1.0 mm or more, desirably 2.0 mm or less, and more desirably 1.8 mm or less. In this specification, the "certain thickness" includes a portion where the thickness changes at 0.2 mm / mm or less in the direction orthogonal to the thickness of the sheet-like rubber member 11. Also, a portion 12 of 2.0 mm from the inner end 11i and the outer end 11e in the tire radial direction of the sheet-like rubber member 11 is excluded.

[0022] The reinforcing rubber layer 8 includes a maximum thickness portion 13 formed of a portion where a plurality of sheet-like rubber members 11 are laminated, and a minimum thickness portion 14 formed of a portion where the sheet-like rubber members 11 are not laminated. In this embodiment, the maximum thickness portion 13 is formed by laminating two sheet-like rubber members 11. The minimum thickness portion 14 is provided adjacent to both sides in the tire axial direction of the maximum thickness portion 13, for example. In other words, in this embodiment, the outer end portion 15 and the inner end portion 16 in the tire radial direction of the reinforcing rubber layer 8 are formed of the minimum thickness portion 14.

[0023] It is desirable that the difference (Ta - Tb) between the thickness Ta of the maximum thickness portion 13 and the thickness Tb of the minimum thickness portion 14 is 1 mm or more. Since the difference (Ta - Tb) is 1 mm or more, the rigidity of the maximum thickness portion 13 increases and the durability is improved. If the difference (Ta - Tb) is excessively large, the rigidity of the maximum thickness portion 13 may become too large, and for example, the riding comfort performance may deteriorate. From such a viewpoint, the difference (Ta - Tb) is desirably 3.5 mm or less, and more desirably 3.0 mm or less.

[0024] In order to effectively exert the above-mentioned effects, the ratio (Ta / Tb) of the thickness Ta to the thickness Tb is desirably 1.5 times or more, more desirably 1.8 times or more, desirably 2.5 times or less, and more desirably 2.3 times or less.

[0025] The outer end portion 15 desirably has a length L1 in the tire radius direction of 3 mm or more. Thereby, the difference in rigidity becomes small in the region from the maximum thickness portion 13 to the region where the reinforcing rubber layer 8 is not formed on the outer side in the tire radius direction, and damage starting from the reinforcing rubber layer 8 can be suppressed. If the length L1 is excessively large, there is a possibility that the manufacturing process cannot be simplified. For this reason, the length L1 is desirably 10 mm or less, and more desirably 8 mm or less.

[0026] The inner end portion 16 overlaps with the bead apex rubber 9 in the tire radius direction. Thus, the inner end portion 16 is adjacent in the tire axial direction to a portion having a large rigidity. Thereby, in the bead portion 4, a portion having an excessively large rigidity is reduced. Although not particularly limited, the length L2 in the tire radius direction of the inner end portion 16 formed at the minimum thickness portion 14 is desirably smaller than the length L1, more desirably 5 mm or less, and even more desirably 3 mm or less.

[0027] In the normal state, it is desirable that the maximum thickness portion 13 and the outer end 19 in the tire radius direction of the contact position between the tire 1 and the normal rim R are at the same position in the tire radius direction. The outer end 19 is a location where a large bending load acts during vehicle travel. By arranging the maximum thickness portion 13 at the same position in the tire radius direction as such an outer end 19, deformation at the outer end 19 is suppressed.

[0028] The distance L4 in the tire radius direction between the outer end 19 and the inner end 13i in the tire radius direction of the maximum thickness portion 13 is desirably 2% or more, more desirably 5% or more, desirably 20% or less, and more desirably 10% or less of the length L3 in the tire radius direction of the maximum thickness portion 13. Thereby, the above-mentioned effects are effectively exerted.

[0029] From the perspective of simplifying the manufacturing process and enhancing the durability of the tire 1, the length L3 of the maximum thickness portion 13 is desirably 10% or more, more desirably 15% or more, desirably 30% or less, and more desirably 25% or less of the tire cross-sectional height H (shown in FIG. 1). The "tire cross-sectional height H" is the distance in the tire radial direction from the bead base line BL to the outermost position in the tire radial direction. Also, the "bead base line BL" is a tire axial line passing through the rim diameter (refer to JATMA) position determined by the standard based on the tire 1.

[0030] The complex elastic modulus E*a of the reinforcing rubber layer 8 is desirably at least twice the complex elastic modulus E*b of the clinch rubber 4G. Thereby, the rigidity of the bead portion 4 is increased and the durability is improved. To ensure a good balance between the ride comfort performance and the durability, the complex elastic modulus E*a of the reinforcing rubber layer 8 is more desirably at least 2.2 times the complex elastic modulus E*b of the clinch rubber 4G, desirably at most 3 times, and more desirably at most 2.8 times.

[0031] Although not particularly limited, the complex elastic modulus E*a of the reinforcing rubber layer 8 is desirably 10 MPa or more, more desirably 20 MPa or more, desirably 70 MPa or less, and more desirably 50 MPa or less. In this specification, each complex elastic modulus E* is a value measured under the following conditions using a viscoelastic spectrometer such as "Implexor (registered trademark)" manufactured by GABO in accordance with JIS K6394. Initial strain: 10% Amplitude: ±2% Frequency: 10 Hz Deformation mode: Tension Temperature: 70 °C

[0032] As shown in FIG. 1, the bead apex rubber 9 is formed, for example, in a triangular shape in the tire meridian cross-section. Although not particularly limited, the outer end 9e of the bead apex rubber 9 in the tire radial direction overlaps with the maximum thickness portion 13 in the tire radial direction.

[0033] The complex elastic modulus E*c of the bead apex rubber 9 is preferably, for example, equal to or greater than the complex elastic modulus E*a of the reinforcing rubber layer 8. Although not particularly limited, the complex elastic modulus E*c of the bead apex rubber 9 is preferably 80% or more, more preferably 90% or more, preferably 120% or less, and more preferably 110% or less of the complex elastic modulus E*a of the reinforcing rubber layer 8. The bead apex rubber 9 preferably has the same formulation as the reinforcing rubber layer 8.

[0034] In the present embodiment, the inner end 3i in the tire radial direction of the sidewall rubber 3G overlaps with the maximum thickness portion 13 of the reinforcing rubber layer 8 in the tire radial direction. The inner end 3i of the sidewall rubber 3G is disposed, for example, on the outer side in the tire radial direction than the outer end 19 (shown in FIG. 2) of the contact position between the tire 1 and the regular rim R.

[0035] The complex elastic modulus E*c of the sidewall rubber 3G is preferably smaller than the complex elastic modulus E*b of the clinch rubber 4G. The complex elastic modulus E*c of the sidewall rubber 3G is preferably 3 MPa or more, more preferably 4 MPa or more, preferably 8 MPa or less, and more preferably 7 MPa or less.

[0036] The clinch rubber 4G is adjacent to the outside in the tire axial direction of the reinforcing rubber layer 8, for example. The outer end 4e in the tire radial direction of the clinch rubber 4G is disposed, for example, on the outer side in the tire radial direction than the outer end 13e in the tire radial direction of the maximum thickness portion 13 of the reinforcing rubber layer 8. In the present embodiment, the inner end 4i in the tire radial direction of the clinch rubber 4G is disposed on the inner side in the tire radial direction than the inner end 13i in the tire radial direction of the maximum thickness portion 13.

[0037] Next, a method for manufacturing such a tire 1 will be described. FIG. 3(a) is a flowchart of the method for manufacturing the tire 1 of the present embodiment. As shown in FIG. 3(a), the method for manufacturing the tire 1 of the present embodiment includes a laminate forming step S1 of forming a laminate 10, a green tire forming step S2 of forming a green tire (not shown) using the laminate 10, and a vulcanization step S3 of vulcanizing and molding the green tire. Well-known methods can be appropriately employed in the green tire forming step S2 and the vulcanization step S3.

[0038] FIG. 3(b) is a flowchart of the laminate forming step S1 of the present embodiment. As shown in FIG. 3(b), the laminate forming step S1 includes a first step S11, a second step S12, and a third step S13. The first step S11 is a step of forming a sheet stock 20 (shown in FIG. 4(a)). The second step S12 is a step of cutting out and preparing a sheet-shaped rubber member 11 from the sheet stock 20. The third step S13 is a step of laminating the plurality of cut-out sheet-shaped rubber members 11.

[0039] FIG. 4(a) is a perspective view of the sheet stock 20 for schematically explaining the first step S11 and the second step S12. As shown in FIG. 4(a), in the first step S11, for example, the sheet stock 20 is extrusion-molded from a well-known rubber extruder (not shown). The sheet stock 20 extruded from the rubber extruder has a certain thickness t. The thickness t of the sheet stock 20 (sheet-shaped rubber member 11) is, for example, 1.0 to 3.0 mm.

[0040] Next, the second step S12 is performed. In the second step S12 of the present embodiment, for example, the sheet stock 20 is cut by a well-known cutting tool 21 such as a cutter blade to form the sheet-like rubber member 11. In the present embodiment, the sheet stock 20 is formed into two sheet-like rubber members 11a and 11b having different lengths (the lengths in the width direction of the sheet stock 20) by cutting. Thus, in the laminate forming step S1 of the present embodiment, since the sheet stock 20 is cut, even in the case of the reinforcing rubber layer 8 having different tire sizes, the sheet-like rubber member 11 having a desired length can be taken out, so that the manufacturing is simplified. Note that the width W of the sheet stock 20 is preferably, for example, the sum of the lengths (forming the lengths in the tire radial direction) of the plurality of sheet-like rubber members 11 to be laminated. Thereby, since the laminate 10 can be formed from one sheet stock 20, the manufacturing is further simplified.

[0041] Next, the third step S13 is performed. FIG. 4(b) is a perspective view of the laminate 10 for schematically explaining the third step S13. As shown in FIG. 4(b), in the third step S13 of the present embodiment, a plurality of sheet-like rubber members 11a and 11b having the same thickness and different lengths in the tire radial direction are laminated to form the laminate 10. As the lamination method of the sheet-like rubber member 11, a well-known technique is adopted. Also, before vulcanization, the ends of the sheet-like rubber member 11 are less likely to deform.

[0042] FIG. 5(a) is an end view of the laminate 10 manufactured in the third step S13 of the present embodiment. As shown in FIG. 5(a), the laminate 10 of the present embodiment is formed of two sheet-like rubber members 11. The sheet-like rubber member 11 includes a first sheet-like rubber member 11A having a large length and a second sheet-like rubber member 11B having a length smaller than that of the first sheet-like rubber member 11A. The laminate 10 of the present embodiment is formed such that both ends 25 of the second sheet-like rubber member 11B are placed closer to the center than both ends 24 of the first sheet-like rubber member 11A. And in the green tire forming step S2, the green tire is formed such that the first sheet-like rubber member 11A is on the inner side in the tire axial direction than the second sheet-like rubber member 11B.

[0043] Figure 5(b) is an end view of the laminate 10 of another embodiment manufactured in the third step S13 of the present embodiment. The same components as those of the present embodiment may be denoted by the same reference numerals, and detailed descriptions thereof may be omitted. As shown in FIG. 5(b), in the laminate 10 of this embodiment, one end 25i of the second sheet-like rubber member 11B is formed so as to be placed on one end 24i of the first sheet-like rubber member 11A. Further, the other end 25e of the second sheet-like rubber member 11B is formed so as to be placed closer to the center than the other end 24e of the first sheet-like rubber member 11A. Then, in the green tire forming step S2, the green tire is formed such that one end 24i of the first sheet-like rubber member 11A is located inside the other end 24e of the first sheet-like rubber member 11A in the tire radial direction.

[0044] Figure 5(c) is an end view of the laminate 10 of yet another embodiment manufactured in the third step S13 of the present embodiment. The same components as those of the present embodiment may be denoted by the same reference numerals, and detailed descriptions thereof may be omitted. As shown in FIG. 5(c), the laminate 10 of this embodiment further includes a third sheet-like rubber member 11C that is shorter than the second sheet-like rubber member 11B. In the laminate 10, for example, both ends 26 of the third sheet-like rubber member 11C are formed so as to be placed closer to the center than both ends 25 of the second sheet-like rubber member 11B. As a result, the laminate 10 of this embodiment includes a portion 27 where three or more sheet-like rubber members 11 are laminated and a portion 28 where two sheet-like rubber members 11 are laminated. In the laminate 10 of this embodiment, the portion 28 where two sheet-like rubber members 11 are laminated is provided adjacent to both sides of the portion 27 where three or more sheet-like rubber members 11 are laminated, for example. Further, a portion 29 where the sheet-like rubber members 11 are not laminated is formed at one end 10i of the laminate 10. Then, in the green tire forming step S2, the green tire is formed such that one end 24i of the first sheet-like rubber member 11A is located inside the other end 24e of the first sheet-like rubber member 11A in the tire radial direction.

[0045] As described above in detail for one embodiment of the present disclosure, the present disclosure is not limited to the above specific embodiments and can be implemented with various modifications.

Example

[0046] A pneumatic tire having the basic structure of FIG. 1 was prototyped based on the specifications in Table 1. Then, the durability of each test tire was tested. The common specifications and test methods of each test tire are as follows.

[0047] <Durability> After the test tire was attached to a well-known drum tester, it was run under the following conditions, and the running distance until damage occurred in the bead portion was measured. The results were shown as an index with Comparative Example 1 being 100. The larger the numerical value, the better the durability. 95 or more is considered a pass. Tire size: 225 / 85R16 Rim: 6.0J Load: 18.95 (kN) Speed: 80 (km / h) E*b: 10.0 (MPa) The test results are shown in Table 1. The reinforcing rubber layer of the comparative example is not a laminate but is in the shape as extruded from a rubber extruder. Also, the reinforcing rubber layers of the comparative example and the examples are both the same in terms of their length in the tire radial direction, the thickness of the maximum thickness portion, and their length in the tire radial direction. The "profile" of Comparative Example 1 shows a crescent shape in which the thickness of the reinforcing rubber layer continuously increases from the inner end and the outer end in the tire radial direction toward the center side.

[0048]

Table 1

[0049] As a result of the test, it is understood that the tires of the examples have improved durability compared to the tires of the comparative examples. Also, the tires of the examples are more simplified in manufacturing compared to the tires of the comparative examples. In particular, the test tires of Examples 1 to 3 have a high degree of simplification.

[0050] [The present disclosure] The present disclosure is as follows.

[0051] The present disclosure (1) is a pneumatic tire including a pair of bead portions each embedded with a bead core, and a carcass extending between the bead cores. The carcass includes a carcass ply including a main body portion extending between the bead cores and a folded-back portion folded back from the inner side in the tire axial direction around each bead core and extending outward in the tire radial direction. A reinforcing rubber layer is disposed in the bead portion adjacent to the outer side in the tire axial direction of the folded-back portion. The reinforcing rubber layer is a laminate in which a plurality of sheet-like rubber members having different lengths in the tire radial direction are laminated in the tire axial direction.

[0052] The present disclosure (2) is the pneumatic tire according to the present disclosure (1), wherein the reinforcing rubber layer has a thickness that decreases from the center side to both sides in the tire radial direction.

[0053] The present disclosure (3) is the pneumatic tire according to the present disclosure (1) or (2), wherein the reinforcing rubber layer includes a maximum thickness portion formed of a portion where the plurality of sheet-like rubber members are laminated and a minimum thickness portion formed of a portion where the sheet-like rubber members are not laminated, and a difference (Ta - Tb) between a thickness Ta of the maximum thickness portion and a thickness Tb of the minimum thickness portion is 1 mm or more.

[0054] The present disclosure (4) is the pneumatic tire according to the present disclosure (3), wherein a ratio (Ta / Tb) of the thickness Ta to the thickness Tb is 1.5 to 2.5 times.

[0055] The present disclosure (5) is the pneumatic tire according to the present disclosure (3) or (4), wherein an outer end portion in the tire radial direction of the reinforcing rubber layer is the minimum thickness portion.

[0056] The present disclosure (6) is the pneumatic tire according to the present disclosure (5), wherein the outer end portion has a length of 3 mm or more in the tire radial direction.

[0057] The present disclosure (7) is a pneumatic tire in any combination with any one of the present disclosures (3) to (6), wherein an inner end portion in the tire radial direction of the reinforcing rubber layer is the minimum thickness portion.

[0058] The present disclosure (8) is a pneumatic tire in any combination with any one of the present disclosures (3) to (6), wherein an inner end portion in the tire radial direction of the reinforcing rubber layer is the maximum thickness portion.

[0059] The present disclosure (9) is a pneumatic tire in any combination with any one of the present disclosures (3) to (8), wherein in a non-loaded state where it is mounted on a standard rim and filled with a standard internal pressure, the maximum thickness portion and an outer end in the tire radial direction of a contact position between the pneumatic tire and the standard rim are at the same position in the tire radial direction.

[0060] The present disclosure (10) is a pneumatic tire in any combination with any one of the present disclosures (1) to (9), wherein the laminate includes a portion where three or more of the sheet-like rubber members are laminated and a portion where two of the sheet-like rubber members are laminated.

[0061] The present disclosure (11) is a pneumatic tire in any combination with any one of the present disclosures (1) to (10), wherein a clinch rubber is disposed outside the reinforcing rubber layer in the tire axial direction, and a complex elastic modulus of the reinforcing rubber layer is two times or more that of the clinch rubber.

[0062] The present disclosure (12) is a method for manufacturing the pneumatic tire according to any one of the present disclosures (1) to (11), including a step of molding the laminate, and the step includes laminating a plurality of sheet-like rubber members having the same thickness and different lengths in the tire radial direction.

[0063] The present disclosure (13) is a method for manufacturing a pneumatic tire according to the present disclosure (12), wherein each of the sheet-like rubber members has a constant thickness.

[0064] The present disclosure (14) is a method for manufacturing a pneumatic tire according to the present disclosure (12) or (13), including a step of preparing the plurality of sheet-like rubber members by cutting them out from a sheet stock having a constant thickness.

[0065] The present disclosure (15) is a method for manufacturing a pneumatic tire in any combination with any one of the present disclosures (12) to (14), wherein the thickness of the sheet-like rubber member is 1.0 to 3.0 mm.

Explanation of Signs

[0066] 1 Pneumatic tire 6A Carcass ply 6b Folded-back portion 8 Reinforcing rubber layer 10 Laminate 11 Sheet-like rubber member

Claims

1. A pneumatic tire comprising: a pair of bead portions each having a bead core embedded therein, and a carcass extending between the bead cores; the carcass includes a carcass ply including a main body portion extending between the bead cores and a folded-back portion that is folded back from the inner side in the tire axial direction around each bead core and extends outward in the tire radial direction; a reinforcing rubber layer is disposed in the bead portion adjacent to the outer side in the tire axial direction of the folded-back portion; the reinforcing rubber layer is a laminate in which a plurality of sheet-like rubber members having different lengths in the tire radial direction are laminated in the tire axial direction; the inner end and the outer end of the sheet-like rubber member in the tire radial direction are adjacent to the folded-back portion; the reinforcing rubber layer includes a minimum thickness portion formed by a portion where the sheet-like rubber members are not laminated; the reinforcing rubber layer includes an outer end portion and an inner end portion in the tire radial direction formed by the minimum thickness portion; the length of the inner end portion in the tire radial direction is smaller than the length of the outer end portion in the tire radial direction; A pneumatic tire.

2. The pneumatic tire according to claim 1, wherein the reinforcing rubber layer has a thickness that decreases from the center side in the tire radial direction toward both sides.

3. The reinforcing rubber layer includes a maximum thickness portion formed by a portion where the plurality of sheet-like rubber members are laminated and a minimum thickness portion formed by a portion where the sheet-like rubber members are not laminated; The pneumatic tire according to claim 1 or 2, wherein a difference (Ta - Tb) between the thickness Ta of the maximum thickness portion and the thickness Tb of the minimum thickness portion is 1 mm or more.

4. The pneumatic tire according to claim 3, wherein a ratio (Ta / Tb) of the thickness Ta to the thickness Tb is 1.5 to 2.5 times.

5. The pneumatic tire according to claim 3 or 4, wherein an outer end portion of the reinforcing rubber layer in the tire radial direction is the minimum thickness portion.

6. The pneumatic tire according to claim 5, wherein the outer end portion has a length in the tire radial direction of 3 mm or more.

7. The pneumatic tire according to any one of claims 3 to 6, wherein an inner end portion of the reinforcing rubber layer in the tire radial direction is the minimum thickness portion.

8. The pneumatic tire according to any one of claims 3 to 6, wherein an inner end portion of the reinforcing rubber layer in the tire radial direction is the maximum thickness portion.

9. In a state where the tire is mounted on a regular rim and filled with a regular internal pressure and is unloaded, the maximum thickness portion and the outer end in the tire radial direction of the contact position between the pneumatic tire and the regular rim are at the same position in the tire radial direction. The pneumatic tire according to any one of claims 3 to 8.

10. The laminate includes a portion where three or more of the sheet-like rubber members are laminated and a portion where two of the sheet-like rubber members are laminated. The pneumatic tire according to any one of claims 1 to 9.

11. A clinch rubber is disposed outside the reinforcing rubber layer in the tire axial direction. The complex elastic modulus of the reinforcing rubber layer is two times or more the complex elastic modulus of the clinch rubber. The pneumatic tire according to any one of claims 1 to 10.

12. The sheet-like rubber member includes a first sheet-like rubber member having a large length and a second sheet-like rubber member having a smaller length than the first sheet-like rubber member. The second sheet-like rubber member is located outside the first sheet-like rubber member in the tire axial direction. The pneumatic tire according to any one of claims 1 to 11.

13. A method for manufacturing the pneumatic tire according to claims 1 to 12, including a step of molding the laminate. The step includes laminating a plurality of sheet-like rubber members having the same thickness and different lengths in the tire radial direction, and making the inner end portion in the tire radial direction formed at the minimum thickness portion composed of the portion where the sheet-like rubber members of the laminate are not laminated smaller in length in the tire radial direction than the outer end portion in the tire radial direction formed at the minimum thickness portion. The method further includes a green tire forming step of arranging the inner end and the outer end in the tire radial direction of the sheet-like rubber member adjacent to the folded-back portion of the carcass. A method for manufacturing a pneumatic tire.

14. Each of the sheet-like rubber members has a constant thickness. The method for manufacturing a pneumatic tire according to claim 13.

15. The method for manufacturing a pneumatic tire according to claim 13 or 14 includes a step of preparing the plurality of sheet-like rubber members by cutting them out from a sheet stock having a constant thickness.

16. The thickness of the sheet-like rubber member is 1.0 to 3.0 mm. The method for manufacturing a pneumatic tire according to any one of claims 13 to 15. ​ ​ ​ ​ ​ ​ ​ ​

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