Pneumatic tires and molds for tire molding.

Abstract

This prevents the blocks from collapsing and cracks at the bottom of the sipes. [Solution] The pneumatic tire 1 comprises a block 3 on which sipes 10 are formed. The sipes 10 include a first portion 11 extending from an opening 14 formed in the contact surface 3S of the block 3 to a predetermined position in the depth direction, and a second portion 12 that is bent at a predetermined angle with respect to the depth direction at the predetermined position. Multiple second portions 12 are formed so as to branch off from the first portion 11, and the predetermined angles of adjacent second portions 12 are different from each other, forming a stepped shape from one side to the other in the length direction of the sipes 10.

Description

[Technical Field]

[0001] The present invention relates to a pneumatic tire and a mold for molding the pneumatic tire. [Background technology]

[0002] Conventionally, pneumatic tires equipped with blocks having sipes, which are thin, linear grooves, are widely known. Sipes are generally formed straight in the depth direction, that is, perpendicular to the contact surface of the block. However, in this case, large collapse of the block is likely to occur during braking, and strain is likely to concentrate on a part of the bottom of the sipe, making it prone to cracking. Since sipes greatly affect the driving performance of the tire, sipes with special shapes have also been proposed. For example, Patent Document 1 discloses a pneumatic tire equipped with sipes that branch in two directions at a predetermined position in the depth direction of the sipe. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2012-1030 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Patent Document 1 describes the effect of being able to maintain a good balance between dry grip performance and wet grip performance until the end of the tire's wear life. On the other hand, conventional tires, including the tire disclosed in Patent Document 1, still have considerable room for improvement in suppressing block deformation and cracks at the bottom of the sipes. [Means for solving the problem]

[0005] The pneumatic tire according to the present invention is a pneumatic tire comprising a block on which sipes are formed, wherein the sipes include a first portion from an opening formed on the contact surface of the block to a predetermined position in the depth direction, and a second portion that is bent at a predetermined angle with respect to the depth direction at the predetermined position, wherein a plurality of second portions are formed so as to branch off from the first portion, the predetermined angles of adjacent second portions are different from each other, and the sipes are formed in a stepped manner from one to the other in the length direction.

[0006] The tire molding die according to the present invention is a mold for molding a pneumatic tire equipped with a sipe blade for forming sipes in a block, wherein the sipe blade has a base portion that forms a portion from the contact surface of the block to a predetermined position in the depth direction of the sipe, and a plurality of branch portions that are bent at a predetermined angle relative to the base portion at the predetermined position and branch off from the base portion, wherein the predetermined angles of adjacent branch portions are different from each other, and the plurality of branch portions are formed in a stepped manner from one to the other in the length direction of the sipe blade. [Effects of the Invention]

[0007] According to the pneumatic tire of the present invention, block collapse and cracking at the bottom of the sipes can be effectively suppressed. [Brief explanation of the drawing]

[0008] [Figure 1] This is a plan view of a pneumatic tire, which is an example of an embodiment, showing a magnified view of a portion of the tread pattern. [Figure 2] This is a cross-sectional view taken by cutting a block in the tire axial direction at the center of the width direction of a sipe, which is an example of an embodiment. [Figure 3] This is a cross-sectional view along line AA in Figure 2. [Figure 4] This is a plan view of a sipe, which is an example of an embodiment, showing the change in shape during the wear process of the block. [Figure 5] This is a cross-sectional view of a mold for molding a pneumatic tire, which is an example of an embodiment. [Figure 6] Figure 5 is a perspective view of the sipe blades that make up the molding die. [Figure 7] This is a cross-sectional view of the block cut in the tire axial direction at the center of the width direction of the sipe, which is the second embodiment. [Figure 8] This is a perspective view of a sipe blade forming a sipe, which is a second embodiment. [Figure 9] This figure shows a modified example of the sipe blade shown in Figure 8. [Modes for carrying out the invention]

[0009] Hereinafter, with reference to the drawings, an example of an embodiment of the pneumatic tire and tire molding die according to the present invention will be described in detail. The embodiment described below is merely an example, and the present invention is not limited to the embodiments described below. Furthermore, forms obtained by selectively combining each component of the embodiments described below are included in the present invention.

[0010] Figure 1 is a plan view of a pneumatic tire 1, which is an example of an embodiment, and shows an enlarged view of a part of the tread 2. As shown in Figure 1, the pneumatic tire 1 includes a tread 2, which is the part that contacts the road surface. The pneumatic tire 1 further includes a pair of sidewalls and a pair of beads, which are the parts that are fixed to the rim of the wheel (neither of which are shown). The tread 2 includes blocks 3 on which sipes 10 are formed. The blocks 3 are protrusions that project outward in the radial direction of the tire, and are sometimes called "land" in the tire industry. The blocks 3 have a contact surface 3S that faces outward in the radial direction of the tire and contacts the road surface.

[0011] The tread 2 is formed with circumferential grooves 7 and transverse grooves 8 that partition the blocks 3. The circumferential grooves 7 are grooves extending in the tire circumferential direction, and for example, are formed continuously and annularly in the tire circumferential direction. A plurality of circumferential grooves 7 are formed parallel to each other, forming a plurality of rows of blocks 3 arranged in the tire circumferential direction. In the present embodiment, four circumferential grooves 7 are formed straight along the tire circumferential direction. The transverse grooves 8 are grooves extending in the tire axial direction, connecting to the plurality of circumferential grooves 7 and crossing the rows of blocks 3.

[0012] The blocks 3 include a center block 4 disposed at the center in the tire axial direction of the tread 2, shoulder blocks 5 disposed on both sides in the tire axial direction of the tread 2, and intermediate blocks 6 disposed between the center block 4 and the shoulder blocks 5. The center block 4 is disposed on the tire equator CL. The equator CL is an imaginary line along the tire circumferential direction passing through the center in the tire axial direction of the tread 2. Also, the ground contact surface 3S of each shoulder block 5 includes ground contact ends E that are both ends in the tire axial direction of the region contacting the flat road surface.

[0013] As described above, the blocks 3 are formed with sipes 10. The sipes 10 are thin grooves in a plan view that are narrower than the circumferential grooves 7 and the transverse grooves 8. In this specification, a thin groove with a width of less than 1.5 mm, preferably 1.0 mm or less, is defined as a sip. Although details will be described later, the sipes 10 include a first portion from an opening formed in the ground contact surface 3S of the block 3 to a predetermined position in the depth direction, and a second portion that is bent at a predetermined angle with respect to the depth direction at the predetermined position and is formed in a plurality so as to branch from the first portion. The second portion is formed in a stepped shape from one side to the other side in the length direction of the sipes 10.

[0014] The sipe 10 is formed in the center block 4, the shoulder block 5, and the intermediate block 6, and extends in the tire axial direction. Also, a plurality of sip es 10 are formed in each of the blocks 3. The sip es 10 formed in the center block 4 and the intermediate block 6 cross each block and communicate with two circumferential grooves 7 located on both sides in the tire axial direction of each block, respectively. Also, the sipe 10 formed in the shoulder block 5 preferably also communicates with the circumferential groove 7 and has a length exceeding the ground contact end E. In this case, while the water drainage performance by the sipe 10 is improved, the collapse of the block 3 is likely to occur.

[0015] The pneumatic tire 1 including a plurality of blocks 3 in which sip es 10 are formed is suitable for a studless tire. The pneumatic tire 1 is excellent in braking performance and handling stability on snow and ice roads due to, for example, the edge effect of the block 3 and the water drainage effect and edge effect by the sipe 10. In addition, the sipe 10 having the second part effectively suppresses the collapse of the block 3 and cracks at the bottom of the sipe 10, contributing to an improvement in the durability of the tire. If a large collapse of the block 3 can be suppressed, for example, uneven wear of the block 3 is reduced and noise is also reduced. Note that the tire in which the sipe 10 is formed is not limited to a studless tire, and may be other tires such as an all-season tire.

[0016] Conventionally known configurations can be applied to the rubber composition and internal structure of the pneumatic tire 1. The pneumatic tire 1 includes, for example, a carcass, a belt, and a cap ply. The carcass is a cord layer covered with rubber and serves as the skeleton of the tire that withstands loads, impacts, air pressure, etc. The carcass is composed of two carcass plies and has a radial structure in which carcass cords are arranged in a direction orthogonal to the tire circumferential direction. An inner liner, which is a rubber layer for holding air pressure, is provided inside the carcass. The belt is a reinforcing band disposed between the rubber constituting the tread 2 and the carcass.

[0017] In the example shown in Figure 1, sipes 10 are formed on all blocks 3, but sipes 10 may be formed on only some of the blocks 3. For example, sipes 10 may be formed only on the center block 4, which is subjected to large forces during braking, or only on the shoulder blocks 5, which are subjected to large forces during turning. The blocks 3 on which sipes 10 are formed are not particularly limited, but in any case, the sipes 10 effectively suppress the collapse of the block 3 and cracking at the bottom of the sipes 10. In Figure 1, only one type of sipe 10 is formed, but two or more types of sipes may be formed on the block 3, or sipes that do not include the second part described above may be formed.

[0018] Figure 1 shows an example of a suitable block pattern to which the sipes 10 are applied, but the block pattern to which the sipes 10 are applied is not limited thereto. For example, the center block 4 may not have grooves crossing the block other than the sipes 10, and may be a rib-shaped block continuous in the circumferential direction of the tire. Also, the number of circumferential grooves 7 is not particularly limited, and the circumferential grooves 7 may be formed on the tire equator CL. Furthermore, the plan view shape of the block 3 is not particularly limited, and the circumferential grooves 7 and transverse grooves 8 may be formed in a zigzag pattern, and irregularities may be formed on the edges of the block 3.

[0019] The sipe 10 will be described in detail below with reference to Figures 2 to 4. Figure 2 is a cross-sectional view of block 3 cut in the tire axial direction at the center of the width direction of the sipe 10. Figure 3 is a cross-sectional view taken along line AA in Figure 2. In this specification, the length direction of the sipe means the direction in which the sipe extends, and for example, in the case of a sipe having a planar wave shape, it is the direction along the straight line connecting the two ends in the length direction. The width direction of the sipe is the direction perpendicular to the length direction in a plan view of the sipe.

[0020] As shown in Figures 2 and 3, the sipe 10 includes a first portion 11 extending from an opening 14 formed in the contact surface 3S of the block 3 to a predetermined position P in the depth direction, and a second portion 12 that is bent at an angle θ with respect to the depth direction at the predetermined position P. Multiple second portions 12 are formed so as to branch off from the lower end of the first portion 11, which is formed straight along the tire axis direction. Hereinafter, for the sake of explanation, the side of the sipe 10 with the opening 14 may be referred to as "upper," and the side of the sipe 10 with the bottom 15 may be referred to as "lower." In the depth direction (vertical direction), at least a portion of the sipe 10 is not formed straight to the bottom 15, but has a bent shape along the way.

[0021] The sipe 10 has a structure in which adjacent second parts 12 bend at different angles θ relative to the depth direction, and multiple second parts 12 are formed in a stepped manner from one end to the other along the length of the sipe 10. Conventional sipes are formed straight from the opening to the bottom, but in this case, strain is concentrated particularly at the corners of the bottom of the sipe, making it prone to cracking. In contrast, the sipe 10 has a shape in which the lower part of the sipe 10 branches out and widens in the width direction. Therefore, the strain acting on the bottom 15 of the sipe 10 can be dispersed, and the occurrence of cracks can be effectively suppressed. Furthermore, because multiple second parts 12 are formed in a stepped manner, multiple wall surfaces are formed along the width direction of the sipe 10, which can effectively suppress the collapse of the block 3.

[0022] The sipe 10 preferably has three or more second portions 12, and more preferably four or more. The sipe 10 has a plurality of bent portions 16 at a predetermined position P in the depth direction. The bent portion 16 (determined position P) is the boundary between the first portion 11 and the second portion 12. As will be described in detail later, a straight region without bent portions 16 is formed in the longitudinal center of the sipe 10, extending straight from the opening 14 to the bottom. Of the straight region, the portion from the predetermined position P to the bottom of the sipe 10 is called the straight portion 13. The plurality of second portions 12 include a first type that bends to one side in the width direction of the first portion 11, and a second type that bends to the other side in the width direction of the first portion 11.

[0023] In this embodiment, the second portions 12A and 12B of the first type are formed on one end of the sipe 10 in the longitudinal direction, and the second portions 12C and 12E of the second type are formed on the other end in the longitudinal direction. The straight portion 13 is located between the second portions 12B and 12C. The lower part of the sipe 10 is formed in a stepped manner along the longitudinal direction of the sipe 10, with the second portions 12A and 12B, the straight portion 13, and the second portions 12C and 12D in that order, and extends to both sides in the width direction of the first portion 11. In addition, the widthwise center of the bottom 15 of the four second portions 12 and the widthwise center of the bottom of the straight portion 13 are located at the same depth P2. In this specification, “same” includes not only cases where they are exactly the same, but also cases where they are considered substantially the same.

[0024] The plan view shape of the sipe 10 may be a non-linear shape such as a wave shape, but in this embodiment it is linear. The plan view shape of the sipe 10 refers to the shape of the sipe 10 when viewed perpendicular to the ground surface 3S of the block 3. Since the first portion 11 is formed along the entire length of the sipe 10, the plan view shape of the sipe 10 depends on the plan view shape of the first portion 11. Three linear sipes 10 are formed on the block 3 parallel to each other and at a predetermined interval. The number of sipes 10 formed on one block 3 is not particularly limited, but it is preferable that each sipe 10 is formed at an interval of 4.0 mm or more.

[0025] As described above, the sipe 10 communicates with the circumferential groove 7 that demarcates the block 3. The grooves that demarcate the block 3 include the circumferential groove 7 and the transverse groove 8, but the sipe 10 is formed, for example, substantially parallel to the transverse groove 8 and communicates only with the circumferential groove 7. The sipe 10 may terminate at one or both ends in the longitudinal direction within the block 3, but considering the water removal performance of the sipe 10, it is preferable that both ends in the longitudinal direction connect to the circumferential groove 7, as shown in Figure 2. The sipe 10 formed on the shoulder block 5 preferably extends from the circumferential groove 7 to a position beyond the contact edge E of the tread 2. On the other hand, if the sipe 10 communicates with the groove, the rigidity of the block 3 decreases and the block 3 is more prone to collapsing, but the function of the multiple second parts 12 effectively suppresses the collapsing of the block 3.

[0026] The sipe 10 is formed such that the first portion 11 communicates with the circumferential groove 7, while the second portion 12 does not communicate with the circumferential groove 7. That is, the second portion 12 is not formed in the region adjacent to the circumferential groove 7 of the block 3. The second portion 12 is formed towards the longitudinal center of the sipe 10 from a position a predetermined length away from the circumferential groove 7, and a shallow bottom portion with a shallower depth is formed in the region adjacent to the circumferential groove 7. In other words, the sipe 10 extends straight in the depth direction from the opening 14 to the bottom within a predetermined length from both ends in the longitudinal direction. In this case, good water removal performance can be ensured while suppressing a decrease in the rigidity of the block 3.

[0027] The predetermined length range in which the second portion 12 is not formed is, for example, set to the same length from both ends of the sipe 10 in the longitudinal direction. The predetermined length is not particularly limited, but a preferred example is set to a length equivalent to half the length of one second portion 12 along the longitudinal direction of the first portion 11, and less than or equal to the length of two or one second portion 12. In this case, excellent water removal performance and block rigidity can be achieved at a higher level, and the function of the second portion 12 can also be fully demonstrated.

[0028] The predetermined position P where the bent portion 16 is formed is preferably within a range of 50% ± 10% of the depth of the sipe 10. The predetermined position P (bent portion 16) may be different in each second portion 12, but in this embodiment, all bent portions 16 are at the same depth. Multiple bent portions may be formed in the depth direction of the sipe 10, but in this specification, the position of the bent portion closest to the opening 14 is defined as the predetermined position P which is the boundary between the first portion 11 and the second portion 12. The depth of the sipe 10 means the length from the opening 14 along the direction perpendicular to the ground surface 3S of the block 3, and unless otherwise specified, it is the length from the opening 14 to the center of the width direction of the bottom 15 of the second portion 12.

[0029] The predetermined position P is more preferably located within a range of 50% ± 5% of the depth of the sipe 10, for example, set at 50% of the depth of the sipe 10. In this case, the depth D1 of the first part 11 and the depth D2 of the second part 12 are the same. If the predetermined position P is located within the above range, it is possible to more effectively suppress the collapse of the block 3 and cracks at the bottom of the sipe 10 while ensuring appropriate block rigidity. For example, if the predetermined position P is too close to the opening 14 of the sipe 10, the collapse of the block 3 will be suppressed too much, causing the block 3 to become immobile and worsening the road surface following ability of the block 3. As a result, the block 3 may not grip the road surface easily, and the edge effect may decrease. On the other hand, if the predetermined position P is too deep, it is possible that the function of the second part 12 will not be fully realized.

[0030] Figure 4 is a plan view of the sipe 10, showing the change in shape of block 3 during the wear process. Figure 4(a) shows block 3 of an unused pneumatic tire 1, and Figure 4(e) shows block 3 in its most worn state.

[0031] As shown in Figure 4(a), the sipe 10 is formed in a straight line in plan view when the pneumatic tire 1 is not in use. As the block 3 wears down and the contact surface 3S decreases, the first portion 11 of the sipe 10 disappears, and the second portion 12 and the straight portion 13 become visible on the contact surface 3S. As will be described in detail later, the base portion of the second portion 12 near a predetermined position P is connected to the adjacent second portion 12, and communicates in the longitudinal direction of the sipe 10. Therefore, as shown in Figure 4(b), when the block 3 has worn down to the point where the second portion 12 is slightly exposed, the sipe 10 has the same straight shape as when it was not in use.

[0032] As shown in Figures 4(c) to 4(e), as block 3 wears down beyond the predetermined position P of sipe 10, sipe 10 is divided into multiple parts and gradually expands in a direction perpendicular to the length direction (the width direction of sipe 10), and the overlap between adjacent second parts 12 decreases. That is, as block 3 wears down, sipe 10 is divided into shorter second parts 12, and the lower part of sipe 10 is divided into multiple smaller parts. This branching structure of sipe 10 effectively suppresses strain concentration by dispersing the strain acting on the bottom 15, and as a result, crack formation is prevented.

[0033] The following provides a more detailed explanation of Part 11 and Part 212 of Sipe 10.

[0034] As shown in Figures 2 to 4, the first portion 11 extends straight in the depth direction of the sipe 10. The first portion 11 may be curved overall with respect to the depth direction of the sipe 10, for example, but in this embodiment, it is formed perpendicular to the ground surface 3S from the opening 14 to a predetermined position P. The predetermined position P of the sipe 10 where the bent portion 16 is formed is located slightly deeper than both ends of the first portion 11 in the longitudinal direction. That is, the depth of the first portion 11 is not constant along its entire length, but is slightly deeper in the area where the second portion 12 is formed.

[0035] A preferred example of the depth (D1+D2) of the sipe 10 is 4.0 mm to 14.0 mm, more preferably 6.0 mm to 10.0 mm. The first portion 11 has the same width along its entire length, for example. A preferred example of the width of the first portion 11 is 0.3 mm to 1.2 mm, more preferably 0.3 mm to 1.0 mm. In this embodiment, the widths of the first portion 11 and the second portion 12 are the same, and the width of the sipe 10 is constant from the opening 14 to the bottom 15. The widths of each second portion 12 are also the same.

[0036] As described above, the first portion 11 is formed straight in the longitudinal direction. Furthermore, the first portion 11 extends along the axial direction of the pneumatic tire 1. In this case, the edge length of the sipe 10 along the axial direction of the pneumatic tire 1 can be made longer, and a good edge effect is achieved. If the sipe 10 has a non-linear shape such as a planar view wave shape, for example, its shape may be reflected across the second portion 12 and the straight portion 13, and it may gradually approach a linear shape toward the lower end (predetermined position P) of the first portion 11, with only the first portion 11 being formed in a non-linear shape.

[0037] As described above, multiple second parts 12 are formed so as to branch off from the first part 11. Among the multiple second parts 12, adjacent second parts 12 have different degrees of curvature at the bent portion 16. As a result, the multiple second parts 12 are formed in a stepped manner along the length direction of the sipe 10. The multiple second parts 12 may be curved only on one side in the width direction of the first part 11, but preferably include a first type that is curved on one side in the width direction of the first part 11 and a second type that is curved on the other side in the width direction of the first part 11. That is, the lower part of the sipe 10 spreads out on both sides in the width direction of the sipe 10.

[0038] Preferably, the first and second types of the second part 12 each include multiple second parts 12. In this embodiment, two second parts 12A and 12B are bent on one side in the width direction of the first part 11, and two second parts 12C and 12D are bent on the other side in the width direction of the first part 11. The second parts 12A and 12B are classified as the first type (hereinafter referred to as the "first group"), and the second parts 12C and 12D are classified as the second type (hereinafter referred to as the "second group"). In this case, the strain acting on the bottom 15 of the sipe 10 can be distributed more evenly and effectively, and since multiple load-bearing wall surfaces of the sipe 10 are formed on both sides in the width direction, the effect of suppressing the collapse of the block 3 and cracking of the bottom 15 becomes more pronounced.

[0039] Multiple second sections 12 are connected to each other by at least a portion of adjacent second sections 12, communicating in the longitudinal direction of the sipe 10. That is, multiple second sections 12 are arranged adjacent to each other without any gaps between them. In this embodiment, second sections 12B and 13C are also connected to the straight section 13, and the first group, the straight section 13, and the second group are arranged adjacent to each other in the longitudinal direction of the sipe 10 in this order. In this case, compared to the case where each second section 12 and the straight section 13 are formed separately, the water removal performance of the sipe 10 is improved, and the effect of suppressing the collapse of the block 3 is also improved due to the interaction of the wall surfaces of the second sections 12.

[0040] The second portion 12 overlaps with adjacent second portions 12 and straight portions 13 as it moves away from the base 15 and closer to a predetermined position P. The second portion 12 may be in communication with adjacent second portions 12 across the base 15, or it may be completely separated from adjacent second portions 12 in the vicinity of the base 15.

[0041] The length of the second portion 12 along the length of the sipe 10 can be changed according to the length of the sipe 10, etc., but a suitable length is 2.0 mm to 6.0 mm. The length of each second portion 12 is, for example, 20% or less, or 15% or less, of the length of the first portion 11. By branching the lower part of the sipe 10 into multiple shorter second portions 12, the strain acting on the bottom 15 can be distributed more effectively. The lengths of the second portions 12 may differ from each other as long as the lengths are within the above range, but in this embodiment, all second portions 12 have the same length. The straight portion 13 also has the same length as the second portions 12.

[0042] As described above, the second section 12 is bent at an angle θ with respect to the depth direction of the sipe 10, and the angle θ differs between adjacent second sections 12. Figure 3 shows the angle θ of the second sections 12A and 12B with respect to the depth direction of the sipe 10 (wall surface of the straight section 13). A ,θ B This shows that the second portion 12 may be gently curved from the bent portion 16 at a predetermined position P toward the bottom 15, or it may be formed in a stepped shape, but in this embodiment, each second portion 12 is inclined at a constant angle θ from the bent portion 16 toward the bottom 15.

[0043] The inclination angle θ of the second part 12 is preferably between 3.5° and 30.0°, and more preferably between 7.5° and 15.0°. If the angle θ is within this range, the effect of suppressing the collapse of the block 3 and cracking of the bottom 15 becomes more pronounced. If the angle θ exceeds 30°, it is expected that it will become difficult to remove the sipe blades 60 (see Figure 6 below) from the tire after the rubber vulcanization, and to set the vent holes for releasing air. In other words, if the angle θ is 30° or less, these manufacturing problems are less likely to occur. Furthermore, a configuration in which the second part 12 is not formed at both longitudinal ends of the first part 11 also has the effect of facilitating the removal of the blades and the setting of vent holes.

[0044] In this embodiment, the angle θ of the second portion 12A A The angle θ of the second part 12B B It is getting bigger. Also, the angle θ of the second part 12DD is the angle θ of the second part 12C C is larger (none of them are shown). That is, the farther away from the straight part 13, in other words, the farther away from the center in the length direction of the sipe 10, the larger the angle θ becomes. The second part 12D is inclined in the opposite direction to the second part 12A, but the angle θ D is the angle θ A and is the same angle as the angle θ of the second part 12C, and the angle θ C of the second part 12C is the same angle as the angle θ B of the second part 12B. The sipe 10 is, for example, rotationally symmetric twice with respect to a virtual line passing through the center in the length direction and the width direction of the first part 11.

[0045] In adjacent second parts 12, the difference in the angle θ is preferably 15.0° or less. In this case, sufficient overlap between adjacent second parts 12 can be ensured, and the water removal performance by the sipe 10 is improved. On the other hand, if the difference in the angle θ becomes too small, it becomes difficult to widen the sipe 10 significantly in the width direction, especially when the length of the sipe 10 is short. Therefore, the difference in the angle θ is preferably 5.0° or more. For example, the angle θ A of the second part 12A is 15.0° or more and 25.0° or less, and the angle θ B of the second part 12B is 5.0° or more and 15.0° or less. Also, the difference between the angles θ A , θ B is 8.0° or more and 12.0° or less.

[0046] Hereinafter, the mold 50 for molding the pneumatic tire 1 will be described in detail while referring to FIGS. 5 and 6. FIG. 5 is a cross-sectional view of the mold 50 for molding. FIG. 6 is a perspective view of the sipe blade 60 constituting the mold 50 for molding.

[0047] As shown in Figure 5, the molding die 50 includes a tread die 51 for molding the surface of the tread 2 of the pneumatic tire 1, and a pair of side dies 52 for molding the surface of the sidewall. The tread die 51 and the side dies 52 are made of a metal such as an aluminum alloy. The tread die 51 includes a main body 54 that includes a tread molding surface 53 for molding the tread pattern, a plurality of protrusions 55 protruding from the tread molding surface 53, and sipe blades 60 that protrude from the tread molding surface 53 and are positioned between each of the protrusions 55. The tread die 51 also has protrusions (not shown) for molding lateral grooves 8.

[0048] The protrusions 55 are the parts that form the circumferential grooves 7 of the pneumatic tire 1. Multiple rib-shaped protrusions 55 are formed parallel to each other on the tread molding surface 53. Each protrusion 55 is integrally molded with the main body 54, for example. In this embodiment, four protrusions 55A, 55B, 55C, and 55D are formed sequentially from one side in the width direction of the tread mold 51. The molding die 50 forms a center block 4 between protrusions 55B and 55C, a mediate block 6 between protrusions 55A and 55B and protrusions 55C and 55D, and a shoulder block 5 further outward in the width direction of the tread mold 51 than protrusions 55A and 55D.

[0049] The sipe blade 60 is a thin, plate-like metal member for forming sipes 10 on block 3 and is attached to the tread molding surface 53. The sipe blade 60 is made of, for example, stainless steel. The sipe blade 60 is inserted into a groove (not shown) formed in the body 54 of the tread mold 51, and is erected on the tread molding surface 53 with a portion of the blade embedded in the body 54.

[0050] The sipe blades 60 are mounted so as to connect to the two protrusions 55. This forms sipes 10 on the center block 4 and mediate block 6, with both longitudinal ends communicating with the circumferential grooves 7. Additionally, the sipe blades 60 extending outward in the width direction from the protrusions 55A and 55D on the tread mold 51 form sipes 10 on the shoulder block 5, with one longitudinal end communicating with the circumferential grooves 7.

[0051] As shown in Figure 6, the sipe blade 60 has a base portion 61 that forms the portion from the contact surface 3S of the block 3 to a predetermined position in the depth direction of the sipe 10, and a plurality of branch portions 62 that are bent at a predetermined angle relative to the base portion 61 at the predetermined position and branch off from the base portion 61. The base portion 61 is the portion that forms the first portion 11 of the sipe 10, and the branch portions 62 are the portions that form the second portion 12 of the sipe 10. The plurality of branch portions 62 are formed in a stepped manner from one side to the other in the length direction of the sipe blade 60, with adjacent branch portions 62 having different inclination angles.

[0052] The sipe blade 60 has a shape in which multiple branch portions 62 protrude from a base portion 61. The branch portions 62 protrude from the base portion 61 except for both ends in the longitudinal direction. The multiple branch portions 62 include four branch portions 62A, 62B, 62C, and 62D. Branch portion 62A forms the second portion 12A of the sipe 10, branch portion 62B forms the second portion 12B, branch portion 62C forms the second portion 12C, and branch portion 62D forms the second portion 12D. In addition, an extension portion 63 is provided between branch portions 62B and 62C to form a straight portion 13.

[0053] The base portion 61 extends straight in the length, width (thickness), and height directions of the sipe blade 60 and is formed in the shape of a flat rectangular plate. The height direction of the sipe blade 60 corresponds to the depth direction of the sipe 10. Since the end of the base portion 61 is inserted into the main body 54, the height of the base portion 61 is slightly longer than the depth of the first portion 11 of the sipe 10. The length of the base portion 61 is also slightly longer than the length of the first portion 11. If the first portion 11 has a non-linear shape such as a planar wave shape, the base portion 61 is also formed in the shape of a plate with irregularities corresponding to the wave shape, etc.

[0054] The branched portion 62 includes branched portions 62A and 62B that are bent to one side in the width direction of the base portion 61, and branched portions 62C and 62D that are bent to the other side in the width direction of the base portion 61. This forms a second portion 12 that extends to both sides in the width direction of the sipe 10. A portion that extends straight in the height direction is formed in the center of the length direction of the sipe blade 60, and the branched portions 62A and 62B, the extension portion 63, and the branched portions 62C and 62D are arranged adjacent to each other in the length direction of the sipe blade 60 from one side to the other. Of the portion that extends straight in the height direction, the portion that extends from the rectangular plate-shaped base portion 61 is called the extension portion 63.

[0055] The inclination angle of the branch portion 62 with respect to the height direction of the sipe blade 60 (the predetermined angle described above) is preferably 3.5° to 30.0°, and more preferably 7.5° to 15.0°. Furthermore, for adjacent branch portions 62, the angles may differ, but the difference between them is preferably 5.0° to 15.0°. In this embodiment, each branch portion 62 extends straight from the bent portion at the base to the tip at a predetermined angle. The lengths of each branch portion 62 and extension portion 63 along the length direction of the sipe blade 60 are, for example, 2.0 mm to 6.0 mm and are the same as each other. The height of each branch portion 62 and extension portion 63 is lower than the height of the base portion 61 and is the same as each other.

[0056] The sipe 20 and sipe blade 70, which are the second embodiment, will be described in detail below with reference to Figures 7 and 8. Figure 7 is a cross-sectional view of block 3 cut in the tire axial direction at the center of the width direction of the sipe 20. Figure 8 is a perspective view of the sipe blade 70 that forms the sipe 20. Below, the differences from the sipe 10 and sipe blade 60 will be mainly explained, and redundant explanations will be omitted.

[0057] As shown in Figure 7, the sipe 20 includes a first portion 21 extending from an opening 24 formed in the contact surface 3S of the block 3 to a predetermined position in the depth direction, and a second portion 22 that is bent at a predetermined angle with respect to the depth direction at the predetermined position, and is similar to the sipe 10 in that multiple bent portions 26 are formed at the same depth. Furthermore, the multiple second portions 22 include a first group that bends to one side in the width direction of the first portion 21, and a second group that bends to the other side in the width direction of the first portion 21. Similarly, in the case of the sipe 20, by branching the bottom 25, the strain acting on the bottom 25 can be dispersed, and the concentration of strain can be effectively suppressed.

[0058] On the other hand, sipe 20 differs from sipe 10 in that it has six second parts 22, with three in the first group and three in the second group. Of the second parts 22A, 22B, and 22C that make up the first group, the second part 22B, located in the middle, is inclined at the largest angle with respect to the depth direction of sipe 20. Similarly, of the second parts 22D, 22E, and 22F that make up the second group, the second part 22E, located in the middle, is inclined at the largest angle with respect to the depth direction of sipe 20. Second parts 22B and 22E are curved in opposite directions, but for example, their inclination angles are the same. Also, the inclination angles of second parts 22A, 22C, 22D, and 22F may be the same as each other.

[0059] Furthermore, the sipe 20 shares with the sipe 10 the characteristic of having a straight region extending straight from the opening 24 to the bottom in the longitudinal center, without a bent portion 26, and a straight portion 23 sandwiched between the second portions 22C and 22D. On the other hand, the sipe 20 differs from the sipe 10 in that it does not have shallow bottom portions at both ends in the longitudinal direction, and straight regions are formed at both ends in the longitudinal direction, and it has straight portions 27 and 28 adjacent to the second portions 22A and 22F, respectively. As a result, the opening area of ​​the sipe 20 relative to the circumferential groove 7 is increased, and the water removal performance of the sipe 20 is improved.

[0060] The sipe 20 may have only the first group, but preferably it has a shape in which the first group and the second group are arranged alternately in the longitudinal direction of the sipe 20. In the example shown in Figure 7, there is one first group and one second group, but multiple of each may be provided. When there are multiple first groups and multiple second groups, the first group may be continuous in the longitudinal direction of the sipe 20, but it is preferable that the first group and the second group are arranged alternately. In this case, the effect of suppressing the collapse and cracking of the block 3 becomes more pronounced.

[0061] As shown in Figure 8, the sipe blade 70 is similar to the sipe blade 60 in that it has a base portion 71 that forms the portion from the contact surface 3S of the block 3 to a predetermined position in the depth direction of the sipe 20, and a plurality of branch portions 72 that are bent at a predetermined angle relative to the base portion 71 at the predetermined position and branch off from the base portion 71. The base portion 71 is the portion that forms the first portion 21 of the sipe 20, and the branch portions 72 are the portions that form the second portion 22 of the sipe 20. The plurality of branch portions 72 are formed in a stepped manner from one to the other in the longitudinal direction of the sipe blade 70, with predetermined angles of adjacent branch portions 72 being different from each other.

[0062] On the other hand, the sipe blade 70 differs from the sipe blade 60 in that it has a total of six branch sections 72, including three branch sections 72A, 72B, and 72C that are bent to one side in the width direction of the base 71, and three branch sections 72D, 72E, and 72F that are bent to one side in the width direction of the base 71. The sipe blade 70 further has extensions 73, 77, and 78 that form straight sections 23, 27, and 28 at the center and both ends in the length direction, respectively.

[0063] Figure 9 is a perspective view of a modified example of the sipe blade 70, the sipe blade 70x.

[0064] As shown in Figure 9, the sipe blade 70x differs from the sipe blade 70 in that it includes four branch sections 72Ax, 72Bx, 72Cx, and 72Dx bent on one side in the width direction of the base 71, and four branch sections 72Ex, 72Fx, 72Gx, and 72Hx bent on the other side in the width direction of the base 71. The sipe blade 70x does not have an extension 73 in the center in the length direction, and has a shape in which a total of eight branch sections 72x are arranged continuously in the length direction of the sipe blade 70x. The inclination angles of adjacent branch sections 72x are different, with branch sections 72Bx and 72Gx being inclined at the largest angle with respect to the height direction of the blade.

[0065] In the sipes formed using the sipe blade 70x, no straight region is formed in the longitudinal center, and eight second portions are continuously formed in the area excluding both ends in the longitudinal direction. The eight second portions include four second portions that constitute a first group that curves to one side in the width direction of the first portion, and four second portions that constitute a second group that curves to the other side in the width direction of the first portion.

[0066] As described above, in a pneumatic tire 1 equipped with multiple blocks 3 on which sipes 10 and 20 are formed, the collapse of the blocks 3 and cracking of the bottom of the sipes 10 and 20 are effectively suppressed. As a result, uneven wear and cracking of the blocks 3 are less likely to occur, and excellent durability is obtained. In addition, the sipes 10 and 20 also contribute to noise reduction. Because the second portion of the sipes 10 and 20 has a shape that extends in the width direction of the sipe 10, the strain acting on the bottom of the sipes 10 and 20 can be dispersed, thereby preventing the occurrence of cracks. Furthermore, the multiple second portions formed in a stepped shape form multiple load-bearing walls, preventing large collapse of the blocks 3 during braking and turning.

[0067] The above embodiments can be modified as appropriate without impairing the objectives of the present invention. For example, although the above embodiments describe a tread pattern in which the sipes 10 and 20 extend in the tire axial direction, it is also possible to form the sipes 10 and 20 along directions intersecting the tire axial direction and circumferential direction, or along the tire circumferential direction. [Explanation of Symbols]

[0068] 1 Pneumatic tire, 2 Tread, 3 Block, 3S Contact surface, 4 Center block, 5 Shoulder block, 6 Mediate block, 7 Circumferential groove, 8 Lateral groove, 10,20 Sipes, 11,21 First section, 12,12A~12D,22,22A~22F Second section, 13,23,27,28 Straight section, 14,24 Opening, 15,15,25 Bottom, 16,26 Bent section, 50 Molding die, 51 Tread die, 52 Side die, 53 Tread molding surface, 54 Main body, 55 Protrusion, 60,70 Sipe blade, 61,71 Base, 62,62A~62D,72,72A~72F,72x,72Ax~72Hx Branch section, 63,73,77,78 Extension, CL: tire equator, E: contact point

Claims

1. A pneumatic tire having blocks with sipes formed therein The sipe includes a first portion from an opening formed in the contact surface of the block to a predetermined position in the depth direction, and a second portion that is bent at a predetermined angle with respect to the depth direction at the predetermined position. A pneumatic tire in which the second portion is formed in multiple ways so as to branch off from the first portion, the predetermined angles of adjacent second portions are different from each other, and the sipe is formed in a stepped manner from one side to the other in the longitudinal direction.

2. The pneumatic tire according to claim 1, wherein the plurality of the second portions are connected to each other by at least a portion of adjacent second portions and communicate in the longitudinal direction of the sipe.

3. The sipe communicates with the grooves that demarcate the block, The pneumatic tire according to claim 1, wherein the second portion is not formed in the region adjacent to the groove.

4. The pneumatic tire according to claim 1, wherein the plurality of second portions include a first type that curves to one side in the width direction of the first portion and a second type that curves to the other side in the width direction of the first portion.

5. The pneumatic tire according to claim 4, wherein the first type and the second type are arranged alternately in the longitudinal direction of the sipes.

6. The pneumatic tire according to claim 1, wherein the length of each second portion along the longitudinal direction of the sipe is 2.0 mm or more and 6.0 m or less.

7. The pneumatic tire according to claim 1, wherein the predetermined angle is 3.5° or more and 30.0° or less.

8. The pneumatic tire according to claim 7, wherein the difference in the predetermined angle between adjacent second portions is 15.0° or less.

9. The pneumatic tire according to claim 1, wherein the predetermined position is within a range of 50% ± 10% of the depth of the sipe.

10. A mold for forming pneumatic tires, equipped with sipe blades for forming sipes in a block, The sipe blade has a base portion that forms a portion from the contact surface of the block to a predetermined position in the depth direction of the sipe, and a plurality of branch portions that are bent at a predetermined angle relative to the base at the predetermined position and branch off from the base. A molding die in which a plurality of the aforementioned branch portions have different predetermined angles between adjacent branch portions and are formed in a stepped manner from one end to the other in the longitudinal direction of the sipe blade.

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