Pneumatic tires and molds for tire molding.

Abstract

This improves wet grip performance and resistance to uneven wear, while also enhancing traction performance. [Solution] The sipe 10 has a first wall surface 11 and a second wall surface 12 facing each other. The first wall surface 11 is provided with one or more substantially triangular first projections 13, and the second wall surface 12 is provided with one or more substantially triangular second projections 14. The vertices 13a and 14a of the first projection 13 and the second projection 14 are offset in the depth direction of the sipe 10 so as not to face each other. The vertices 13a and 14a of the first projection 13 and the second projection 14 are located on the bottom side of the sipe 10 than the midpoints 13c and 14c of the bottom surfaces 13b and 14b of the projections 13 and 14. When a force in the substantially sipe width direction is applied to the block 3 to close the opening of the sipe 10, the first projection 13 comes into contact with the second wall surface 12 or the second projection 14 comes into contact with the first wall surface 11.

Description

Technical Field

[0001] The present invention relates to a pneumatic tire and a mold for molding a tire, and relates to the sipe structure of a pneumatic tire.

Background Art

[0002] Conventionally, pneumatic tires having blocks formed with sipes which are thin linear grooves are widely known. Sipes are generally formed straight in the depth direction, that is, perpendicular to the ground contact surface of the block. In this case, however, a large collapse of the block is likely to occur during braking or the like, and distortion tends to concentrate on a part of the bottom of the sipe, making cracks likely to occur. Since sipes greatly affect the running performance of a tire, sipes having a special shape have also been proposed. For example, Patent Document 1 discloses a widened sipe having a plurality of protrusions protruding from opposite wall surfaces of the sipe. The apex position of the protrusion of the widened sipe exists on the block surface side rather than the midpoint of the bottom surface of the protrusion.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Patent Document 1 describes an effect that the clogging of the sipe is suppressed by the protrusion and the braking performance on snow is improved. On the other hand, conventional tires including the tire disclosed in Patent Document 1 have great room for improvement in terms of the water removal effect on icy and snowy roads and the suppression of the collapse of blocks.

Means for Solving the Problems

[0005] The pneumatic tire according to the present invention is a pneumatic tire comprising a block on which sipes are formed, wherein the sipes have a first wall surface and a second wall surface that open on the surface of the block and face each other within the block, the first wall surface is provided with one or more substantially triangular first projections, and the second wall surface is provided with one or more substantially triangular second projections, the vertices of the first projections and the second projections are offset in the depth direction of the sipe so as not to face each other, the vertices of the first projections and the second projections are located on the bottom surface side of the sipe than the midpoint of the bottom surface of each projection, and when a force in the substantially sipe width direction that closes the opening of the sipe is applied to the block, the first projections come into contact with the second wall surface or the second projections come into contact with the first wall surface.

[0006] The tire molding die according to the present invention is a tire molding die equipped with a sipe blade for forming sipes in a block, wherein the sipe blade has a first side surface and a second side surface located opposite the first side surface, the first side surface is provided with two or more substantially triangular first protrusions, the second side surface is provided with two or more substantially triangular second protrusions, the first side surface is provided with a substantially triangular first groove formed by adjacent first protrusions, the second side surface is provided with a substantially triangular second groove formed by adjacent second protrusions, the bottoms of the first groove and the second groove are positioned offset in the height direction of the sipe blade so as not to face each other, the bottom of the first groove is located closer to the tip of the sipe blade than the midpoint of each of the tops of the first protrusions, and the bottom of the second groove is located closer to the tip of the sipe blade than the midpoint of each of the tops of the second protrusions. [Effects of the Invention]

[0007] The pneumatic tire according to the present invention improves wet grip performance through excellent water removal and reduces uneven wear resistance by suppressing block deformation. Furthermore, because the reaction force from the protrusions is directed towards the contact surface, the contact of the blocks is improved, resulting in improved traction performance. [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 AA in Figure 1. [Figure 3] This is an enlarged view of section B in Figure 2. [Figure 4] This is an illustrative diagram showing the behavior of the tire's contact patch during braking. [Figure 5] This figure shows another example of a sipe. [Figure 6] This is a diagram showing a mold for molding tires. [Figure 7] This diagram shows a sipe blade in a tire molding die. [Figure 8] This diagram shows a modified version of the sipe blade. [Figure 9] This figure shows the cross-sectional shape of the sipes according to the examples and comparative examples. [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 has circumferential grooves 7 and transverse grooves 8 that demarcate the blocks 3. The circumferential grooves 7 are grooves that extend in the circumferential direction of the tire and are formed, for example, in a continuous annular shape in the circumferential direction of the tire. Multiple circumferential grooves 7 are formed parallel to each other, forming multiple rows of blocks 3 that are aligned in the circumferential direction of the tire. In this embodiment, four circumferential grooves 7 are formed straight along the circumferential direction of the tire. The transverse grooves 8 are grooves that extend in the axial direction of the tire and are connected to multiple circumferential grooves 7, traversing the rows of blocks 3.

[0012] Block 3 includes a center block 4 positioned in the axial center of the tread 2, shoulder blocks 5 positioned on both sides of the tread 2 in the axial direction, and a mediate block 6 positioned between the center block 4 and the shoulder blocks 5. The center block 4 is positioned on the tire equator CL. The equator CL is an imaginary line along the circumferential direction of the tire passing through the axial center of the tread 2. In addition, the contact surface 3S of each shoulder block 5 includes contact ends E, which are the axial ends of the area that contacts a flat road surface.

[0013] Block 3 has a sipe 10 formed therein, as described above. The sipe 10 is a narrow, linear groove in plan view, with a width smaller than the circumferential groove 7 and the transverse groove 8. In this specification, a sipe is defined as a narrow groove with a width of less than 1.5 mm, preferably 1.0 mm or less. As will be described in more detail later, the sipe 10 has a first wall surface 11 and a second wall surface facing each other within block 3, with a roughly triangular first projection 13 provided on the first wall surface 11 and a roughly triangular second projection 14 provided on the second wall surface 12. Furthermore, the vertices of the first projection 13 and the second projection 14 are offset in the depth direction of the sipe 10 so that they do not face each other. In addition, the vertices of the first projection 13 and the second projection 14 are located at the same point as, or below the midpoint of, the midpoint of the bottom surface of each projection 13, 14, on the bottom side of the sipe 10.

[0014] The sipes 10 are formed on the center block 4, shoulder block 5, and mediate block 6, and extend in the axial direction of the tire. Multiple sipes 10 are also formed on each of the blocks 3. The sipes 10 formed on the center block 4 and mediate block 6 traverse each block and communicate with two circumferential grooves 7 located on both sides of the axial direction of each block. The sipes 10 formed on the shoulder block 5 also communicate with the circumferential grooves 7 and preferably have a length that extends beyond the contact end E.

[0015] A pneumatic tire 1 having multiple blocks 3 on which sipes 10 are formed is suitable for a studless tire. The pneumatic tire 1 has excellent braking performance and handling stability on snowy and icy roads due to, for example, the edge effect of the blocks 3 and the water-removing and edge effect of the sipes 10. In addition, the sipes 10 having the first projection 13 and the second projection 14 effectively suppress the collapse of the blocks 3 and cracks at the bottom of the sipes 10, contributing to improved tire durability. If the collapse of the blocks 3 can be suppressed, for example, uneven wear of the blocks 3 will be reduced, and noise will also be reduced. Note that the tire on which the sipes 10 are formed is not limited to a studless tire, but may also be other tires such as an all-season tire.

[0016] For the rubber composition and internal structure of the pneumatic tire 1, a conventionally well-known configuration can be applied. 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 framework 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 FIG. 1, the sipe 10 is formed in all the blocks 3, but the sipe 10 may be formed only in some of the blocks 3. For example, the sipe 10 may be formed only in the center block 4 where a large force acts during braking, or only in the shoulder block 5 where a large force acts during turning. The block 3 in which the sipe 10 is formed is not particularly limited, but in any case where the sipe 10 is formed in the block 3, the sipe 10 effectively suppresses the collapse of the block 3 and the crack at the bottom of the sipe 10. In FIG. 1, only one type of sipe 10 is formed, but two or more types of sipers may be formed in the block 3, or a sipe having no first protrusion 13 and second protrusion 14 may be formed.

[0018] FIG. 1 shows an example of a suitable block pattern to which the sipe 10 is applied, but the block pattern to which the sipe 10 is applied is not limited thereto. For example, the center block 4 may be a rib-shaped block that is continuous in the tire circumferential direction and has no groove crossing the block other than the sipe 10. Also, the number of circumferential grooves 7 is not particularly limited, and the circumferential groove 7 may be formed on the tire equator CL. Further, the planar shape of the block 3 is not particularly limited, and the circumferential groove 7 and the transverse groove 8 may be formed in a zigzag shape, and irregularities may be formed on the edge of the block 3.

[0019] An example of an embodiment, the sump 10, will be described in detail with reference to FIGS. 2 and 3. FIG. 2 is a cross-sectional view taken along the line A-A of FIG. 1. FIG. 3 is an enlarged view of part B in FIG. 2. In FIG. 3, a virtual line α passing through each vertex 13a, 14a is shown for the purpose of explanation. Also, the bottom surfaces 13b, 14b and the midpoints 13c, 14c of each protrusion 13, 14 are shown.

[0020] As shown in FIGS. 2 and 3, the sump 10 has a first wall surface 11 and a second wall surface 12 that open on the surface of the block 3 and face each other inside the block 3. One or more substantially triangular first protrusions 13 are provided on the first wall surface 11. Also, one or more substantially triangular second protrusions 14 are provided on the second wall surface 12. Further, the vertices 13a, 14a of the first protrusion 13 and the second protrusion 14 are provided at positions shifted in the depth direction of the sump 10 and not facing each other. Furthermore, the vertices 13a, 14a of the first protrusion 13 and the second protrusion 14 are located at the same position as the midpoints 13c, 14c of the bottom surfaces 13b, 14b of each protrusion 13, 14 or on the bottom surface side of the sump 10 relative to the midpoints 13c, 14c. Thereby, the water floating on the road surface can be effectively drained. Specifically, since the vertices 13a, 14a of each protrusion 13, 14 face the bottom side of the sump 10, water can easily move from the opening of the sump 10 towards the bottom, and it is difficult to move from the bottom towards the opening. As a result, until the block 3 contacts the road surface and the opening of the sump 10 is blocked by falling over, the water on the road surface can be efficiently absorbed. The water absorbed by the sump 10 is drained from the side surface of the block 3 into the circumferential groove 7.

[0021] Although it will be described in detail later, each protrusion 13, 14 is arranged such that when a force in the substantially sump width direction for closing the opening of the sump 10 is applied to the block 3, the first protrusion 13 contacts the second wall surface 12 or the second protrusion 14 contacts the first wall surface 11. Therefore, the fall of the block 3 can be suppressed.

[0022] As described above, the vertices 13a and 14a of each projection 13 and 14 are located at the same depth as the midpoints 13c and 14c of the base surfaces 13b and 14b of each projection 13 and 14, or are located on the base side of the sipe 10 than the midpoints 13c and 14c. Here, we will explain the base surface 13b of the first projection 13 using the first projection 13 as an example. As shown in Figure 3, the base surface 13b of the first projection 13 is a virtual surface formed by connecting the two points furthest from the virtual line α of the first projection 13, and the center of the depth direction length of the sipe 10 on the base surface 13b is the midpoint 13c. That is, the vertex 13a of the first projection 13 is located at the same depth as the midpoint 13c of the base surface 13b, or is located on the base side of the sipe 10 than the midpoint 13c. The same applies to the second projection 14. In other words, the vertex 14a of the second projection 14 is located at the same depth as the midpoint 14c of the base surface 14b, or is located on the base surface side of the sipe 10 than the midpoint 14c.

[0023] The vertices 13a and 14a of the first projection 13 and the second projection 14 are positioned so as not to face each other, offset in the depth direction of the sipe 10. In this case, it is preferable that the vertex 13a of the first projection 13 is positioned midway between the vertices 14a of the two second projections 14. Similarly, it is preferable that the vertex 14a of the second projection 14 is also positioned midway between the vertices 13a of the two first projections 13. This ensures that the distance between the first wall surface 11 and the second wall surface 12 remains constant, allowing for more effective water removal.

[0024] It is preferable that the vertices 13a and 14a of the first projection 13 and the second projection 14 are formed so as to overlap in the depth direction of the sipe 10. That is, it is preferable that the vertices 13a and 14a are aligned on a straight line in the depth direction of the sipe 10. This allows for effective suppression of the collapse of the block 3 while maintaining the water removal performance of the sipe 10. The following explanation will use the case where the vertices 13a and 14a overlap in the depth direction of the sipe 10 as an example.

[0025] The first projection 13 and the second projection 14 each have a substantially triangular shape. More specifically, each projection 13 and 14 has a substantially triangular shape in the depth-direction cross-section of the sipe 10. In this specification, a substantially triangular shape means a shape with a sharply formed vertex, a shape with a rounded vertex, and a shape with a flat vertex. Here, a shape with a sharply formed vertex is a shape where the vertex is an acute-angled corner. A shape with a rounded vertex is a shape where the vertex consists of a curved surface, as shown in Figure 3. For example, a shape where the corners are chamfered with an R-chamfer. Furthermore, a shape with a flat vertex is a shape where the depth-direction length of the flat sipe 10 formed at the vertex is 25% or less of the depth-direction length L of the sipe 10 of the bottom surfaces 13b and 14b of each projection. That is, a trapezoidal shape where the length of the top surface is 25% or less of the length L of the bottom surfaces 13b and 14b.

[0026] The height of each projection 13, 14 and the length L of the base surfaces 13b, 14b are not particularly limited. Here, the height of each projection 13, 14 refers to the distance in the width direction of the sipe 10 from the base surfaces 13b, 14b to the vertices 13a, 14a. It is preferable that the sum of the heights of each projection 13, 14, i.e., the distance between the base surfaces 13b and 14b, is the same as or smaller than the length L of each base surface 13b, 14b. This makes it easier for each projection 13, 14 to contact the opposing wall surfaces 11, 12, thereby more effectively suppressing the collapse of the block 3.

[0027] The first projection 13 and the second projection 14 preferably have a shape symmetrical with respect to the imaginary line α, as shown in Figure 3. More specifically, assuming that the depth-direction displacement of each projection 13 and 14 in the sipe 10 is adjusted so that they face each other, they have a shape symmetrical with respect to the imaginary line α. In other words, the first projection 13 preferably has a shape that is an inversion of the second projection 14 with respect to the imaginary line α as the axis. That is, it is preferable that the various dimensions of the first projection 13 and the second projection 14 are the same. With this, a reaction force of a similar magnitude can be obtained whether a force is applied to the block 3 from one direction in the width direction of the sipe 10 or from the other direction in the width direction of the sipe 10. As a result, a similar degree of collapse suppression effect can be obtained in both directions.

[0028] It is preferable that the first projection 13 and the second projection 14 extend continuously in the longitudinal direction of the sipe 10. That is, it is preferable that the first projection 13 and the second projection 14 are formed from one end to the other in the longitudinal direction of the sipe 10. This allows for the acquisition of a reaction force including a component in the direction of the contact surface 3S over the entire longitudinal region of the sipe 10, thereby more effectively suppressing the collapse of the block 3. Furthermore, the formation of each projection 13 and 14 from one end to the other in the longitudinal direction of the sipe 10 improves drainage into the circumferential groove 7, thereby more effectively removing water.

[0029] The first wall surface 11 is provided with three first protrusions 13, for example, as shown in Figure 2. The second wall surface 12 is provided with three second protrusions 14, for example, as shown in Figure 2. It is preferable that the number of protrusions 13 and 14 on the first wall surface 11 and the second wall surface 12 are the same. This allows the space of the sipe 10 to be kept uniform, making it possible to remove water more effectively.

[0030] The first projection 13 and the second projection 14 have a long side and a short side that form their respective vertices 13a and 14a, and it is preferable that each side is inclined in the depth direction of the sipe 10. In this case, each side is also inclined in the width direction of the sipe 10. Since the respective vertices 13a and 14a of each projection 13 and 14 are located on the bottom side of the sipe 10, the long side is located on the opening side of the sipe 10 and the short side is located on the bottom side of the sipe 10. With the above shape, water flows easily from the opening of the sipe 10 toward the bottom surface of the sipe 10, so water can be removed more effectively.

[0031] The inclination angles of the long and short sides of each projection 13,14 with respect to the imaginary line α are preferably such that the angle θx of the long side is less than the angle θy of the short side. Furthermore, the angle θy of the short side is preferably 75°±5°. This makes it easier for the mold to come out of the block 3 when forming the sipes 10. As a result, the productivity of pneumatic tires is improved.

[0032] The length of the longer side of each projection 13, 14 is preferably 1.5 to 3.0 times the length of the shorter side. This ensures that when a force is applied to close the opening of the sipe 10, the length of the longer sides of the opposing projections 13, 14 that come into contact is maintained, thereby effectively suppressing the collapse of the block 3. As a result, the rigidity of the block 3 is improved.

[0033] Preferably, the vertex 13a of the first projection 13 is formed to face the long side of the second projection 14, and preferably, the vertex 14a of the second projection 14 is formed to face the vertex of the first projection 13. According to this, when a force is applied in approximately the width direction of the sipe that closes the opening of the sipe 10, the vertex 13a of the first projection 13 is likely to come into contact with the long side of the second projection 14, and the vertex 14a of the second projection 14 is likely to come into contact with the long side of the first projection 13. As a result, it is easy to obtain a reaction force including a component in the direction of the contact surface 3S from the first projection 13 and the second projection 14, so that the collapse of the block 3 can be effectively suppressed. This makes it possible to improve the resistance to uneven wear and the traction performance.

[0034] Grooves 15 and 16 may be formed on each wall surface 11 and 12 by projections 13 and 14. More specifically, on the first wall surface 11, a first groove 15 may be formed between adjacent first projections 13 in the depth direction of the sipe 10. Also, on the second wall surface 12, a second groove 16 may be formed between adjacent second projections 14 in the depth direction of the sipe 10. Each groove 15 and 16 is an expanded region that is wider than the width of the bottom side and the surface side of the sipe 10. The grooves 15 and 16 can increase the volume of the sipe 10. Here, the volume of the sipe 10 refers to the size of the internal space of the sipe 10. Since the water removal performance is improved because the amount of water that the sipe 10 can absorb increases as the volume of the sipe 10 increases.

[0035] The long and short sides of each groove 15, 16 may correspond to the long and short sides of each projection 13, 14. That is, the shape of each groove 15, 16 may be the same as the shape of each projection 13, 14. More specifically, the shape formed by the imaginary line α, long side, and short side in each groove 15, 16 is the same as the shape formed by the bottom surfaces 13b, 14b, long side, and short side in each projection 13, 14. That is, each groove 15, 16 may be approximately triangular in shape.

[0036] Furthermore, each groove 15, 16 may be provided at a position other than between adjacent protrusions 13, 14. For example, each groove 15, 16 may be provided between the opening of the sipe 10 and each protrusion 13, 14. Alternatively, each groove 15, 16 may be provided between the bottom of the sipe 10 and each protrusion 13, 14. This would further increase the volume of the sipe 10, thereby improving the water removal performance.

[0037] The first projection 13 and the second projection 14 are positioned such that when a force is applied to the block 3 in approximately the width direction of the sipe that closes the opening of the sipe 10, the first projection 13 contacts the second wall surface 12 or the second projection 14 contacts the first wall surface 11. As a result, each projection 13 and 14 contacts the opposing wall surfaces 11 and 12, thereby generating a reaction force that includes a component in the direction of the contact surface 3S, and thus suppressing the collapse of the block 3. This improves the rigidity of the block and suppresses uneven wear.

[0038] Referring further to Figure 4, the effect of suppressing the collapse of the block 3 having the sipe 10, which is an example of an embodiment, will be explained in detail. Figure 4 is an illustrative diagram showing the behavior of the tire's contact area during braking. Figure 4(A) is a diagram showing the behavior of the block 3 during braking, and Figure 4(B) is an enlarged view of part C of Figure 4(A).

[0039] As shown in Figure 4(A), during braking, a force is applied to the contact surface 3S of block 3 in the direction of arrow X from the road surface 100, opposite to the direction of vehicle travel (arrow Y). The sipe 10 closes when a force opposite to the direction of vehicle travel is applied to the contact surface 3S. This force also causes block 3 to tilt so that its inner side is forward of the contact surface 3S in the direction of travel. At this time, the second projection 14 of the second wall surface 12 contacts the long side of the first projection 13 of the first wall surface 11, resulting in a reaction force from the first wall surface 11 that includes a component in the direction of the contact surface 3S, as shown in Figure 4(B). As a result, this reaction force suppresses the tilting of block 3. Consequently, block rigidity is improved, and resistance to uneven wear is enhanced. Furthermore, because the reaction force includes a component in the direction of the contact surface 3S, the contact area of ​​block 3 can be sufficiently secured, improving traction performance.

[0040] As described above, the pneumatic tire 1 equipped with blocks 3 on which sipes 10 are formed improves wet grip performance due to its excellent water removal effect and improves resistance to uneven wear by suppressing block deformation. By providing projections 13 and 14 on each wall surface 11 and 12 of the sipes 10, water on the road surface can be efficiently removed, thereby improving wet grip performance. In addition, the projections 13 and 14 suppress deformation of the blocks 3 during braking. This improves the resistance to uneven wear of the blocks 3. Furthermore, during braking, the reaction force from the projections 13 and 14 is directed towards the contact surface, improving the contact of the blocks 3 and enhancing traction performance.

[0041] 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 extend in the tire axial direction, it is also possible to form the sipes 10 along a direction intersecting the tire axial direction and circumferential direction, or along the tire circumferential direction.

[0042] Furthermore, although the above embodiment was described using the example of a case where the sipe 10 has a linear shape on the surface of the block 3, the shape of the sipe as viewed from the outside in the radial direction of the tire is not limited to a linear shape. The shape of the sipe as viewed from the outside in the radial direction of the tire may be, for example, a wave shape or a shape having one or more inflection points. When the shape of the sipe is a wave shape in plan view, the length of the sipe increases, and the length of each projection 13, 14 also increases, so the block rigidity is improved. As a result, the resistance to uneven wear is improved.

[0043] In the above embodiments, examples were given in which the sipe 10 has the shape shown in Figures 2 and 3, but the shape of the sipe is not limited thereto. For example, as shown in Figure 5(A), the sipe 20 may have vertices 13a and 14a at the same positions as the midpoints 13c and 14c of the bottom surfaces 13b and 14b of each projection 13 and 14. In this case, the lengths of the sides forming the vertices 13a and 14a may be the same. Also, as shown in Figure 5(B), the sipe 30 may have two projections 13 and 14 on each wall surface 11 and 12. In this case, each projection 13 and 14 is formed continuously in the depth direction of the sipe 10. As shown in Figure 5(C), the sipe 40 may have planar vertices 13a and 14a. In this case, the length L1 of the plane formed on the vertices 13a and 14a is 25% or less of the length L of the bottom surfaces 13b and 14b.

[0044] The tire molding die 50 will be described in detail with reference to Figures 6 and 7. Figure 6 is a cross-sectional view showing a tire molding die 50 as an example of an embodiment. Figure 7 is a perspective view showing the sipe blade 60 that constitutes the tire molding die 50. Figure 7(A) is a perspective view of the sipe blade 60, and Figure 7(B) is a DD cross-section of Figure 7(A).

[0045] As shown in Figure 6, the tire 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.

[0046] 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 tire 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.

[0047] 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.

[0048] 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.

[0049] As shown in Figure 7, the sipe blade 60 has a first side surface 61 and a second side surface 62 located opposite the first side surface 61. The first side surface 61 is provided with two or more substantially triangular first protrusions 63, and the second side surface 62 is provided with two or more substantially triangular second protrusions 64. In addition, the first side surface 61 is provided with a substantially triangular first groove 65 formed by adjacent first protrusions 63, and the second side surface 62 is provided with a substantially triangular second groove 66 formed by adjacent second protrusions 64. The sipe blade 60 forms the projections 13 and 14 of the sipe 10 by the grooves 65 and 66.

[0050] As shown in Figure 7(B), the bottom portions 65a and 66a of the first groove 65 and the second groove 66 are positioned offset in the height direction of the sipe blade 60 so that they do not face each other. This causes the projections 13 and 14 of the sipe 10 to be offset in the depth direction of the sipe 10 so that they do not face each other.

[0051] The bottom 65b of the first groove 65 is positioned at the same time as, or closer to the tip of the sipe blade 60 than, the midpoint 63c of each apex 63a of the first protrusion 63. Here, the midpoint 63c is the center point of the line connecting adjacent apex 63a in the height direction of the sipe blade 60. Similarly, the bottom 66b of the second groove 66 is positioned at the same time as, or closer to the tip of the sipe blade 60 than, the midpoint 64c of each apex 64a of the second protrusion 64. As a result, in the sipe 10, each apex 13a, 14a of each projection 13, 14 is positioned at the same time as, or closer to the bottom of the sipe 10 than, the midpoint 13c, 14c of the bottom surface of each projection 13, 14.

[0052] Figure 8 is a perspective view of a modified example of the sipe blade 60, the sipe blade 60x.

[0053] The sipe blade 60x differs from the sipe blade 60 in that its plan view shape is wave-shaped. The sipe blade 60x is used to form sipes that have a plan view wave shape. The cross-sectional shape of the sipe blade 60x in the width direction is the same as that of the sipe blade 60. The first wall surface 61x and the second wall surface 62x of the sipe blade 60x also have a wave shape. Furthermore, the sipe blade 60x may be combined with the sipe blade 60. For example, the sipe may be configured with sipe blades 60 at both ends in the longitudinal direction and sipe blade 60x in the longitudinal central region of the sipe. [Examples]

[0054] The present invention will be further described below with reference to examples, but the present invention is not limited to these examples.

[0055] <Example 1> A test tire A1 (tire size: 225 / 60R18 100H) was fabricated with a tread pattern containing multiple center blocks, shoulder blocks, and mediate blocks, each demarcated by circumferential and lateral grooves. Three sipes X1 were formed in each block.

[0056] Furthermore, the tread patterns of the test tires in the other embodiments and comparative examples are the same as those of test tire A1, except for the sipes formed on each block. Figure 9 shows the plan view shape of the sipes formed on the center block of each test tire.

[0057] The sipe X1 has a first wall surface and a second wall surface that open on the surface of the block and face each other inside the block. The first wall surface is provided with three roughly triangular first projections. The second wall surface is provided with three roughly triangular second projections. The vertices of the first and second projections are offset in the depth direction of the sipe so that they do not face each other. Furthermore, the vertices of the first and second projections are located closer to the bottom surface of the sipe than the midpoint of the bottom surface of each projection. In addition, the projections are arranged so that when a force is applied to the block in the direction of the width of the sipe to close the opening of the sipe, the first projection will contact the second wall surface or the second projection will contact the first wall surface.

[0058] The specifications of the Sipe X1 are as follows. These specifications, along with the evaluation results of the test tires, are shown in Table 1. Table 1 also includes the specifications of sipes from other examples and comparative examples. Vertex position: bottom side of the sipe Length: 2.0mm Height: 2.0mm Length of the longest side: 1.82 mm Short side length: 1.04 mm Long side angle θx: 33.4° Short side angle θy: 75.0°

[0059] Here, length is the length of the base of each projection, height is the distance from the base of the first projection to the base of the second projection, and the angles θx of the longer side and θy of the shorter side represent the inclination angles from the imaginary line α.

[0060] <Example 2> Test tire A2 was manufactured in the same manner as in Example 1, except that the sipe formed on the block was replaced with sipe X2 as shown in Figure 9. The specifications of sipe X2 are shown in Figure 9 and Table 1.

[0061] <Example 3> Test tire A3 was manufactured in the same manner as in Example 1, except that the sipe formed on the block was replaced with sipe X3 as shown in Figure 9. The specifications of sipe X3 are shown in Figure 9 and Table 1.

[0062] <Comparative Example 1> Test tire B1 was manufactured in the same manner as in Example 1, except that the sipe formed on the block was replaced with sipe Y1 as shown in Figure 9. The specifications of sipe Y1 are shown in Figure 9 and Table 1.

[0063] <Comparative Example 2> Test tire B2 was manufactured in the same manner as in Example 1, except that the sipe formed on the block was replaced with sipe Y2 as shown in Figure 9, instead of sipe X1. The specifications of sipe Y2 are shown in Figure 9 and Table 1. Note that when a force is applied to close the sipe opening, each projection of sipe Y2 does not come into contact with the opposing wall surface.

[0064] For each test tire in the examples and comparative examples, the resistance to uneven wear and the wet grip performance were evaluated using the methods described below. The evaluation results are shown in Table 1. Table 1 also shows the volume of the sipes for each test tire. The volume of the sipes is a relative value with the volume of test tire B1 of Comparative Example 1 set to 100. The evaluation results shown in Table 1 are relative values ​​with the evaluation result of test tire B1 of Comparative Example 1 set to 100.

[0065] [Evaluation of resistance to uneven wear] For each of the test tires A1-A3 and B1-B2, a real vehicle (with two occupants) equipped with the test tire was driven, and after 20,000 km of driving, the difference in wear between the pressure-bearing side and the push-off side of the tread blocks was measured, and the reciprocal of this difference was calculated. The results of Comparative Example 1 were evaluated using an index with 100, and a higher value indicates better resistance to uneven wear.

[0066] [Evaluation of wet grip performance] Test tires A1-A3 and B1-B2 were fitted to all wheels of a test vehicle (front-wheel drive, 2000cc engine) with an air pressure of 230kPa, and the vehicle was driven on a wet surface (water-sprayed asphalt). The braking distance from an initial speed of 40km / h was measured. The results are expressed as an index with Comparative Example 1 set to 100, and a higher value indicates a shorter braking distance and superior wet grip performance.

[0067] [Table 1]

[0068] As shown in Table 1, it can be confirmed that Examples 1-3 show improved resistance to uneven wear and improved wet grip performance compared to Comparative Example 1. In the test tires of Examples 1-3, each protrusion receives a reaction force including a component in the direction of the contact surface from the opposing wall surface during braking, thereby suppressing block collapse and improving resistance to uneven wear. In addition, because the apex of each protrusion is located at the same time as or below the midpoint of the bottom surface of the sipe, water removal performance is improved, and wet grip performance is improved. In Comparative Example 2, although the increased volume improves water removal performance and wet grip performance, when a force is applied to close the sipe opening, each protrusion does not contact the opposing wall surface, so collapse cannot be suppressed. As a result, block rigidity decreases, and resistance to uneven wear decreases. In other words, it can be confirmed that Examples 1-3 achieve both resistance to uneven wear and improved wet grip performance compared to Comparative Example 2.

[0069] Furthermore, test tire A1 exhibits even better resistance to uneven wear compared to test tires A2 and A3. This suggests that the shape and number of sipes affect resistance to uneven wear. Comparing test tire A1 and test tire A2, test tire A1 has more protrusions than test tire A2, resulting in superior resistance to uneven wear. Comparing test tire A1 and test tire A3, each protrusion on test tire A1 is positioned to face the long side of the protrusion formed on the opposing wall surface, making it easier to obtain reaction force. As a result, it effectively suppresses deformation and exhibits superior resistance to uneven wear. In addition, test tire A2 exhibits even better wet grip performance compared to test tires A1 and A3. This suggests that the volume of the sipes affects wet grip performance. That is, a larger volume allows more water to be removed, improving wet grip performance. [Explanation of Symbols]

[0070] 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, 30, 40 sipe, 11 first wall surface, 12 second wall surface, 13 first projection, 14 second projection, 13a, 14a apex, 13b, 14b bottom surface, 13c, 14c midpoint, 15 first groove, 16 second groove, 50 molding die, 51 tread die, 52 side die, 53 tread molding surface, 54 main body, 55 projection, 60, 60x sipe blade, 61 first side surface, 62 second side surface, 63 first convex part, 64 second convex part, 63a, 64a apex, 63c, 64c midpoint of each apex, 65 first groove part, 66 Second groove, 100 road surface, CL tire equator, E contact point, α virtual line

Claims

1. A pneumatic tire having blocks with sipes formed therein The sipe has a first wall surface and a second wall surface that open on the surface of the block and face each other within the block. The first wall surface is provided with one or more roughly triangular first protrusions, The second wall surface is provided with one or more substantially triangular second protrusions. The vertices of the first projection and the second projection are positioned so as to be offset from each other in the depth direction of the sipe and not facing each other. The vertices of the first and second projections are located on the bottom surface side of the sipe, A pneumatic tire in which, when a force is applied to the block in a direction substantially in the width direction of the sipe that closes the opening of the sipe, the first projection comes into contact with the second wall surface or the second projection comes into contact with the first wall surface.

2. The first projection and the second projection extend continuously in the longitudinal direction of the sipe, as described in claim 1.

3. The pneumatic tire according to claim 1, wherein the first projection and the second projection have a long side and a short side that form a vertex, and each side is inclined with respect to the depth direction of the sipe.

4. The pneumatic tire according to claim 3, wherein the angle of inclination of each side with respect to a virtual line α along the depth direction of the sipe, passing through the vertices of each projection, is such that the angle of the longer side θx < the angle of the shorter side θy, and θy is 75° ± 5°.

5. The pneumatic tire according to claim 4, wherein the first projection and the second projection have shapes that are symmetrical with respect to a virtual line α.

6. The pneumatic tire according to claim 4, wherein the vertex of the first projection faces the long side of the second projection, and the vertex of the second projection faces the long side of the first projection.

7. The pneumatic tire according to claim 5, wherein the length of the longer side is 1.5 times or more and 3.0 times or less the length of the shorter side.

8. The pneumatic tire according to claim 1, wherein the vertices of the first projection and the second projection overlap in the depth direction of the sipe.

9. The pneumatic tire according to any one of claims 1 to 8, wherein the first projection and the second projection are each two in number and are formed continuously in the depth direction of the sipe.

10. A mold for forming tires, equipped with sipe blades for forming sipes in a block, The sipe blade has a first side surface and a second side surface located opposite to the first side surface. The first side surface is provided with two or more roughly triangular first protrusions, The second side surface is provided with two or more substantially triangular second protrusions, The first side surface is provided with a substantially triangular first groove formed by the adjacent first protrusions, The second side surface is provided with a substantially triangular second groove formed by the adjacent second protrusions. The bottoms of the first groove and the second groove are positioned so as not to face each other, offset in the height direction of the sipe blade. The bottom of the first groove is located closer to the tip of the sipe blade than the midpoint of each peak of the first protrusion. The bottom of the second groove is located closer to the tip of the sipe blade than the midpoint of each apex of the second protrusion. Mold for tire molding.

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