Pneumatic tires and molds for tire molding.

Abstract

This suppresses the reduction in the opening area of ​​the sipes during braking, thereby improving braking performance. [Solution] The pneumatic tire 1 comprises a block on which sipes 10 are formed. The sipes 10 extend along the length of the sipes 10 and include a first portion 11 and a second portion 12 arranged in a staggered pattern along the length, and a connecting portion 13 connecting these portions. In a plan view of the block, the angle between the first portion 11 and the connecting portion 13, and the angle between the second portion 12 and the connecting portion 13 are both acute angles.

Description

[Technical Field]

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

[0002] Conventionally, so-called corrugated sipes, which have a planar wave shape, are widely known. Since sipes greatly affect the driving performance of tires, much research has been done on the shape of sipes, and several sipes with special shapes other than corrugated ones have been proposed. For example, Patent Document 1 discloses a sipe (hereinafter sometimes referred to as a "trapezoidal sipe") that is formed in a zigzag shape such that the portion surrounded on three sides by the sipe exhibits a trapezoidal shape in plan view. The trapezoidal sipe disclosed in Patent Document 1 includes multiple portions that form the upper base of the trapezoid along the length direction of the sipe, and multiple portions that form the slanted sides of the trapezoid inclined with respect to the length direction of the sipe, and these portions are arranged alternately in the length direction to form a zigzag shape. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2019 / 020231 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, since sipes are thin, linear grooves, when braking, the openings of the sipes close, reducing the edge effect and water removal effect of the sipes, which in turn reduces the braking performance of the tire. The trapezoidal sipes disclosed in Patent Document 1 are thought to be able to suppress the reduction in edge effect and water removal effect during braking compared to, for example, corrugated sipes, but there is still much room for improvement. [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 first and second portions extending in the longitudinal direction of the sipe and arranged in a staggered pattern, and connecting portions connecting the respective portions, and in a plan view of the block, the angle formed by the first portion and the connecting portion, and the angle formed by the second portion and the connecting portion are both acute angles.

[0006] The mold for molding a tire 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, in a plan view of the blade, first and second bases extending in the longitudinal direction of the blade and arranged in a staggered pattern, and a connecting portion connecting the respective bases, and in a plan view of the sipe blade, the angle formed by the first base and the connecting portion, and the angle formed by the second base and the connecting portion are both acute angles. [Effects of the Invention]

[0007] According to the pneumatic tire of the present invention, the reduction in the opening area of ​​the sipes during braking can be suppressed, thereby improving braking 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 perspective view of a center block, which is an example of an embodiment. [Figure 3] This is a plan view of a center block, which is an example of an embodiment, showing a magnified view of the portion where the sipes are formed. [Figure 4] (a) A diagram showing an example of an embodiment with the sipe's opening open, and (b) a diagram showing the sipe's opening closed. [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]It is a perspective view of the sipe blade constituting the mold for molding shown in FIG. 5. [Figure 7] It is a figure showing a first modification example of the sipe. [Figure 8] It is a figure showing a second modification example of the sipe. [Figure 9] It is a figure showing the plan view shape of the sipe in the examples and comparative examples.

Mode for Carrying Out the Invention

[0009] Hereinafter, an example of an embodiment of a pneumatic tire and a tire molding die according to the present invention will be described in detail with reference to the drawings. The embodiment described below is merely an example, and the present invention is not limited to the following embodiments. Also, a form formed by selectively combining the respective components of the embodiment described below is included in the present invention.

[0010] FIG. 1 is a plan view of a pneumatic tire 1 which is an example of an embodiment, and shows a part of a tread 2 in an enlarged manner. As shown in FIG. 1, the pneumatic tire 1 includes a tread 2 which is a portion that contacts the road surface. The pneumatic tire 1 further includes a pair of sidewalls and a pair of beads which are portions fixed to the rim of the wheel (both not shown). The tread 2 includes blocks 3 in which siping is formed. The block 3 is a convex portion that protrudes toward the outer side in the tire radial direction, and may be called land in the tire industry. The block 3 has a ground contact surface 3S facing the outer side in the tire radial direction that 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 are, for example, formed in a continuous annular shape in the tire circumferential direction. A plurality of circumferential grooves 7 are formed in parallel with 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, connect to the plurality of circumferential grooves 7, and cross the rows of blocks 3. The widths of the circumferential grooves 7 and the transverse grooves 8 are, for example, 2.5 mm or more and 10.0 mm or less. In this specification, the groove width means the width at the ground contact surface 3S of the block 3.

[0012] The block 3 includes 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 a mediate block 6 disposed between the center block 4 and the shoulder blocks 5. The center block 4 is a block formed at the position closest to the tire equator CL, and is disposed on the tire equator CL in the present embodiment. The equator CL is a virtual line along the tire circumferential direction passing through the center in the tire axial direction of the tread 2. Further, the ground contact surface 3S of each shoulder block 5 includes a ground contact end E which is both ends in the tire axial direction of the region contacting the flat road surface.

[0013] As described above, sipes are formed in the block 3. The sipes are grooves in a thin line shape in plan view with a width smaller than that of the circumferential grooves 7 and the transverse grooves 8. In this specification, a thin groove with a width less than 1.5 mm, preferably 1.0 mm or less, is defined as a sip. Although details will be described later, a sip 10 is formed in the center block 4, and the sip 10 includes a first portion 11 and a second portion 12 that extend in the length direction thereof and are arranged in a staggered pattern, and a connecting portion 13 that connects the respective portions. In the plan view of the center block 4, the angles formed by the first portion 11 and the connecting portion 13, and the angles formed by the second portion 12 and the connecting portion 13 are both acute angles.

[0014] A pneumatic tire 1 equipped with a center block 4 on which sipes 10 are formed is suitable for a studless tire. The pneumatic tire 1 further includes corrugated sipes 40 formed on the shoulder block 5 and mediate block 6. 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 block 3, and the water-removing and edge effect of the sipes 10 and corrugated sipes 40. In particular, the sipes 10 effectively suppress the reduction in the opening area of ​​the sipes 10 during braking, thereby improving braking performance. 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.

[0015] The sipes 10 and corrugated sipes 40 extend in the axial direction of the tire. Multiple sipes 10 are formed on each of the center blocks 4, and multiple corrugated sipes 40 are formed on each of the shoulder blocks 5 and mediate blocks 6. The sipes 10 and corrugated sipes 40 formed on the center blocks 4 and mediate blocks 6 respectively traverse each block and communicate with two circumferential grooves 7 located on both sides of the tire axial direction of each block. Preferably, the corrugated sipes 40 formed on the shoulder blocks 5 also communicate with the circumferential grooves 7 and have a length that extends beyond the contact end E.

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

[0017] In the example shown in Figure 1, the sipes 10 are formed only on the center block 4, but the sipes 10 may be formed on all blocks 3. Alternatively, the sipes 10 may be formed on at least one of the shoulder blocks 5 or the mediate blocks 6. When the sipes 10 are formed on the mediate block 6, for example, they extend in the axial direction of the tire, traverse the block, and communicate with the two circumferential grooves 7. When the sipes 10 are formed on the shoulder block 5, for example, they extend in the axial direction of the tire from the circumferential groove 7 to the contact edge E, or beyond the contact edge E.

[0018] The block 3 on which the sipes 10 are formed is not particularly limited, but regardless of which block 3 they are formed on, the sipes 10 contribute to improving the braking performance of the tire. However, since a large load acts on the center block 4 during braking, the improvement in braking performance is particularly pronounced when the sipes 10 are applied to the center block 4. The tread pattern in Figure 1 includes two types of sipes, but all sipes may be sipes 10, or there may be three or more types.

[0019] 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.

[0020] The sipe 10 will be explained in detail below with reference to Figures 2 to 4. Figure 2 is a perspective view of the center block 4 on which the sipe 10 is formed. Figure 3 is a plan view of the center block 4, showing an enlarged view of the portion on which the sipe 10 is formed. Figure 4 shows (a) the state in which the opening 14 of the sipe 10 is open, and (b) the state in which the opening 14 of the sipe 10 is closed. Here, the opening 14 of the sipe 10 is an opening formed in the ground surface 3S of the center block 4.

[0021] As shown in Figures 2 and 3, the sipe 10 is formed in a zigzag shape and includes a first portion 11 and a second portion 12 that extend in its longitudinal direction and are arranged in a staggered pattern, and a connecting portion 13 that connects these portions. In this specification, the longitudinal direction of the sipe means the direction in which the sipe extends, and more specifically, the direction along a hypothetical line α, which is a straight line connecting both ends in the longitudinal direction. The sipe 10 has a plan view shape in which the first portion 11 is arranged on one side of the hypothetical line α and the second portion 12 is arranged on the other side, and the connecting portion 13 crosses the hypothetical line α and connects the first portion 11 and the second portion 12. The sipe 10 further includes straight portions 18 formed on the hypothetical line α at both ends in the longitudinal direction.

[0022] In a plan view of the center block 4, the sipe 10 is formed such that the angle between the first portion 11 and the connecting portion 13, and the angle between the second portion 12 and the connecting portion 13, are both acute angles. In this embodiment, these two angles are the same. In this specification, the term "same" includes not only cases where they are exactly the same, but also cases where they are considered substantially the same. In a plan view of the center block 4, the first portion 11 and the second portion 12 are formed in a substantially straight line and extend substantially parallel to the imaginary line α.

[0023] The sipe 10 has a plan view shape in which parts of the first portion 11 and the second portion 12 overlap in a direction perpendicular to the longitudinal direction of the sipe 10 (imaginary line α). The connecting portion 13 includes a first connecting portion 13A and a second connecting portion 13B that extend in different directions from each other, and the connecting portions 13A and 13B are arranged alternately in the longitudinal direction of the sipe 10. Note that the connecting portion 13A extending from one end of a single first portion 11 in the longitudinal direction, and the connecting portion 13B extending from the other end in the longitudinal direction, are each connected to a different second portion 12 (the same applies to the connecting portions 13A and 13B extending from the second portion 12).

[0024] As will be explained in more detail later, the connecting parts 13A and 13B are inclined in opposite directions with respect to the virtual line β, but in this embodiment, the inclination angle θ of the connecting parts 13A and 13B with respect to the virtual line β A ,θ B The same applies. Here, the imaginary line β is a straight line perpendicular to the imaginary line α in a plan view of the center block 4. The connecting parts 13A and 13B extending from one first part 11 are inclined so that they move closer to each other as they move away from the first part 11 (the same applies to the connecting parts 13A and 13B extending from the second part 12).

[0025] In a plan view of the center block 4, the sipe 10 is formed in a zigzag shape such that the portion enclosed on three sides by the first portion 11, the connecting portion 13A, and the connecting portion 13B has a trapezoidal shape with the first portion 11 as the base and the connecting portions 13A and 13B as the hypotenuses. More precisely, the portion enclosed by the imaginary line γ connecting adjacent second portions 12 in the longitudinal direction of the sipe 10, the first portion 11, the connecting portion 13A, and the connecting portion 13B forms a trapezoid. Similarly, the portion enclosed by the imaginary line γ connecting adjacent first portions 11 in the longitudinal direction of the sipe 10, the second portion 12, the connecting portion 13A, and the connecting portion 13B forms a trapezoid with the imaginary line γ as the top base and the second portion 12 as the bottom base.

[0026] As described above, Patent Document 1 discloses a trapezoidal sipe, but the trapezoidal sipe in Patent Document 1 differs from sipe 10 in that the portion corresponding to the first part 11 of sipe 10 is the upper base of the trapezoid. In the following, in order to distinguish it from the trapezoidal sipe in Patent Document 1, the above trapezoid of sipe 10 will be referred to as an "inverted trapezoid," and sipe 10 will be referred to as an "inverted trapezoidal sipe."

[0027] Because the sipe 10 is a thin, linear groove with a width of less than 1.5 mm, the opening 14 closes easily during braking. When the opening 14 closes, the edge that catches on the road surface decreases, and the water inlet also decreases, so the edge effect and water removal effect of the sipe 10 are reduced. However, the inverted trapezoidal sipe 10 has the characteristic that the opening 14 is more difficult to close compared to conventionally known corrugated sipes, trapezoidal sipes, etc. Therefore, the reduction in the edge effect and water removal effect during braking is suppressed by the sipe 10, and the braking performance of the tire is improved. As will be described in detail later, even when the sipe 10 is fully closed, a large opening area is secured at the connecting portion 13.

[0028] The sipe 10 is formed so that multiple inverted trapezoids are arranged in a row. The inverted trapezoids include a first inverted trapezoid and a second inverted trapezoid whose orientations are 180° apart from each other, and these two types of inverted trapezoids are arranged alternately along the length of the sipe 10. In other words, the sipe 10 has a plan view shape formed in a zigzag pattern to demarcate the first and second inverted trapezoids. The plan view shape of the sipe 10 refers to the shape of the sipe 10 when viewed perpendicular to the contact surface 3S of the center block 4.

[0029] Since straight sections 18 are formed on a virtual line α at both ends of the sipe 10 in the longitudinal direction, the portion connecting the straight section 18 to the first portion 11 or the second portion 12 is shorter than the connecting portion 13. Furthermore, since the straight section 18 extends straight in the depth direction from the opening 14 to the bottom of the sipe 10, an opening of the sipe 10 extending linearly in the height direction of the block is formed on the side surface of the center block 4 facing the circumferential groove 7. The grooves that define the center block 4 include the circumferential groove 7 and the transverse groove 8, but the sipe 10 extends in the tire axial direction and communicates only with the circumferential groove 7. For example, the length direction of the sipe 10 is parallel to the tire axial direction.

[0030] The sipes 10 may terminate at one or both ends in the longitudinal direction within the block, but considering the water removal performance of the sipes 10, it is preferable that both ends in the longitudinal direction connect to the circumferential grooves 7, as shown in Figure 2. Three sipes 10 are formed in the center block 4 at predetermined intervals so that their longitudinal directions are parallel to each other. The number of sipes 10 formed in one block is not particularly limited, but it is preferable that each sipe 10 is spaced at least 3.0 mm apart.

[0031] A drainage channel 15 is formed at the bottom of the sipe 10, to which the first portion 11, the second portion 12, and the connecting portion 13 are connected. The drainage channel 15 has a width greater than the width of the opening 14 of the sipe 10 formed on the ground surface 3S of the block, extends in the longitudinal direction of the sipe 10, and communicates with the circumferential groove 7. The drainage channel 15 is formed in a substantially circular tubular shape, and for example, its maximum diameter is more than 2 times but less than 5 times the width of the opening 14, preferably more than 3 times but less than 4 times. The drainage channel 15 is also formed straight along the entire length of the sipe 10.

[0032] The sipe 10 has a first section 11 and a second section 12 arranged in a staggered pattern, and is winding so that the first and second inverted trapezoids alternate. However, by providing a drainage channel 15, a good water removal effect can be ensured. In the following explanation, for convenience, the side of the sipe 10 with the opening 14 may be referred to as "upper" and the bottom side of the sipe 10 as "lower". Since both ends of the drainage channel 15 in the longitudinal direction are connected to the circumferential groove 7, water that enters the lower part of the sipe 10 is smoothly discharged into the circumferential groove 7 through the drainage channel 15.

[0033] The multiple first parts 11 that make up the sipe 10 are aligned on the same straight line and arranged at a predetermined interval D. Similarly, the multiple second parts 12 are aligned on the same straight line and arranged at a predetermined interval. The interval D between the first parts 11 is shorter than the length L of the first parts 11, and the interval between the second parts 12 is also shorter than the length of the second parts 12. The first parts 11 and the second parts 12 are arranged alternately in a staggered pattern, offset in the longitudinal direction of the sipe 10, but the longitudinal ends of each part overlap in a direction perpendicular to the longitudinal direction.

[0034] In this embodiment, the length L of each first portion 11 is the same, and the spacing D between each first portion 11 is also the same. Similarly, the length of each second portion 12 is the same as the length L of the first portion 11, and the spacing between each second portion 12 is the same as the spacing D between the first portions 11. Furthermore, each first portion 11 and each second portion 12 are formed at positions equidistant from the imaginary line α. In this case, similar functionality can be obtained along the length of the sipe 10, and it is also preferable from a design perspective. The number of first portions 11 and second portions 12 can be appropriately changed depending on the length of the sipe 10, and there may be one of each, but in this embodiment, multiple and equal numbers of each are formed.

[0035] The length L of the first portion 11 is, for example, 1.5 mm or more and 3.5 mm or 2.0 mm or more and 3.0 mm or less. If the length L is within this range, the reduction in edge effect and water removal effect during braking can be more effectively suppressed while ensuring a sufficient edge length along the tire axis. The spacing D is, for example, 50% or more and 80% or less of the length L, preferably 60% or more and 75% or less. Since the spacing D corresponds to the upper base of the inverted trapezoid, if the spacing D becomes too short, the block rigidity may decrease significantly locally, so it is preferable to ensure a spacing D of 1.2 mm or more. On the other hand, the spacing D is the inclination angle θ of the connecting portions 13A and 13B. A ,θ B Therefore, from the viewpoint of improving braking performance, it is preferable to ensure that the length L is 60% or more.

[0036] The depth of the sipe 10 is shallower than the depth of the circumferential groove 7, for example, 5.0 mm to 10.0 mm. The first section 11, the second section 12, the connecting section 13, and the straight section 18 are all formed to the same depth and connected to the drainage channel 15. The width of the sipe 10 is preferably 1.0 mm or less, and more preferably 0.3 mm to 0.6 mm. The first section 11, the second section 12, the connecting section 13, and the straight section 18 are formed to the same width as each other, and have a constant width along the entire length of the sipe 10.

[0037] At least one of the first portion 11 and the second portion 12 has a first wall surface on which a protrusion 16 is formed, and a second wall surface facing the first wall surface, on which a recess 17 is formed into which the protrusion 16 fits when the sipe 10 is closed. The fit of the protrusion 16 into the recess 17 can, for example, suppress the movement of the center block 4 along the length of the sipe 10, thereby reducing slippage on road surfaces with a low coefficient of friction. The height of the protrusion 16 and the depth of the recess 17 are preferably 30% to 70% of the width of the sipe 10, more preferably 40% to 60%, and in this embodiment, they are set to approximately half the width of the sipe 10 (for example, 50% ± 5%).

[0038] The protrusions 16 and recesses 17 may be formed only on a portion of the first portion 11 or the second portion 12, but it is preferable that they be formed on all wall surfaces of each portion. In this case, the above effect due to the interlocking of the protrusions and recesses becomes more pronounced. In this embodiment, the protrusions 16 and recesses 17 are formed in the longitudinal central portion of the first portion 11 and the second portion 12, extending from the opening 14 to the drainage channel 15. That is, the protrusions 16 are formed in a rib shape that is continuous in the depth direction of the sipe 10, and the recesses 17 are formed in a groove shape that is continuous in the depth direction of the sipe 10. In this case, the function of the protrusions and recesses is maintained even as wear of the center block 4 progresses, and the effect of the protrusions and recesses becomes more pronounced.

[0039] The amplitude W of the sipe 10, defined as the distance between the first portion 11 and the second portion 12 along a direction perpendicular to the longitudinal direction of the sipe 10, is, for example, 0.8 mm or more, preferably 1.0 mm or more, and more preferably 1.2 mm or more. The upper limit of the amplitude W is, for example, 2.5 mm, preferably 2.0 mm, and more preferably 1.8 mm. In this specification, the amplitude W is defined as the distance between the widthwise centers of the first portion 11 and the widthwise centers of the second portion 12 in the portion where the convex portion 16 and the concave portion 17 are not formed.

[0040] A suitable range for the amplitude W is 1.0 mm to 2.0 mm, or 1.2 mm to 1.8 mm. When the amplitude W is within this range, the improvement in braking performance becomes more pronounced while suppressing a decrease in block rigidity. The amplitude W is preferably smaller than the pitch P of the sipe 10, which will be described later, and more preferably 50% to 80% of the pitch P. In this case, a higher level of balance between block rigidity and good braking performance can be achieved.

[0041] In this embodiment, the amplitude W of the sipe 10 gradually decreases towards the bottom of the sipe 10. In this case, as wear of the center block 4 progresses, the amplitude W decreases, and the edge effect and water removal effect of the sipe 10 may decrease. On the other hand, even if the diameter of the drainage channel 15 is reduced to suppress the decrease in block rigidity, it becomes possible to smoothly connect the first portion 11 and the second portion 12 to the drainage channel 15.

[0042] The first part 11 and the second part 12 are further curved so that the amplitude W gradually decreases from the opening 14 towards the drain channel 15. The first part 11 and the second part 12 are curved such that the bottom region from a predetermined depth to the drain channel 15 is more curved than the opening-side region from the opening 14 to the predetermined depth so that the amplitude W gradually decreases towards the drain channel 15. The opening-side region may be curved with a first curvature or may be formed straight in the depth direction so as to maintain the amplitude W at the opening 14. The bottom region near the drain channel 15 is curved with a second curvature greater than the first curvature. In the bottom region, the first part 11 and the second part 12 are also curved in the longitudinal direction of the sipe 10, and the connecting portion 13 is twisted and the angle θ A , θ B is changing.

[0043] When the degree of curvature of the first part 11 and the second part 12 is small on the opening 14 side and large on the drain channel 15 side, it is possible to smoothly connect the first part 11 and the second part 12 to the drain channel 15 while suppressing a decrease in the amplitude W due to wear of the center block 4. Alternatively, if the first part 11 and the second part 12 are formed straight from the opening 14 to a predetermined depth, it is also possible to design so that a decrease in the amplitude W due to wear of the center block 4 does not substantially occur. The predetermined depth is, for example, a depth corresponding to the wear limit of the center block 4, and as a specific example, it is set in the range of 50% ± 5% of the depth of the sipe 10.

[0044] As described above, the connecting portions 13A and 13B are inclined in opposite directions with respect to the virtual line β orthogonal to the longitudinal direction of the sipe 10, but the inclination angles θ A , θ B of the connecting portions 13A and 13B with respect to the virtual line β are the same. The angle θ A , θ B is greater than 0°, and the larger the angle, the easier it is to suppress a decrease in the opening area of the sipe 10 during braking. On the other hand, the angle θ A , θ BIf the angle θ becomes too large, for example, the distance D between the first parts 11 and the distance between the second parts 12 may become too short, which can significantly reduce the block rigidity at the upper base of the inverted trapezoid. A ,θ B For example, the angle is 5° to 50°, preferably 10° to 40°, more preferably 15° to 35°, or 25° to 35°.

[0045] The pitch P of the sipe 10, defined as the distance between connecting portions 13 along the length of the sipe 10, is set to a length exceeding the amplitude W, preferably 1.5 mm or more, more preferably 1.8 mm or more. The upper limit of the pitch is, for example, 3.5 mm, preferably 3.0 mm, more preferably 2.5 mm. In this specification, the pitch P is defined as the distance between the widthwise centers of connecting portion 13A and the widthwise centers of connecting portion 13B on the imaginary line α.

[0046] A suitable range for the pitch P is 1.5 mm to 3.0 mm, or 1.8 mm to 2.5 mm. Within this range, the improvement in braking performance becomes more pronounced while suppressing a decrease in block rigidity. The pitch P may vary along the length of the sipe 10, but in this embodiment, all pitches are the same. This provides similar functionality along the length of the sipe 10 and is also preferable from a design perspective.

[0047] Figure 4 shows the open and closed states of the sipe 10's opening 14, as described above. As shown in Figure 4(a), the sipe 10's opening 14 is open when no load is acting on the center block 4. On the other hand, as shown in Figure 4(b), when a force in the circumferential direction of the tire (hereinafter sometimes referred to as "longitudinal force") acts on the center block 4 during braking, the opposing wall surfaces of the first portion 11 and the second portion 12 come into contact with each other, causing a part of the opening 14 to close. This state is referred to as the fully closed state of the sipe 10. At this time, the convex portion 16 of the first wall surface fits into the concave portion 17 of the second wall surface, restricting the movement of the center block 4 in the axial direction of the tire, and as a result, lateral skidding on snowy and icy road surfaces is suppressed.

[0048] In the case of sipe 10, although the opening area decreases when a large longitudinal force acts on the center block 4, the connecting portion 13 remains widely open even in the fully closed state. In contrast, as shown in the comparative example described later, a trapezoidal sipe, such as the one disclosed in Patent Document 1, cannot secure a large opening in the fully closed state. That is, during braking when a large longitudinal force acts, sipe 10, which is an inverted trapezoidal sipe, can secure a larger opening area compared to a trapezoidal sipe, effectively suppressing the reduction in edge effect and water removal effect. Until now, inverted trapezoidal sipes have not been proposed due to concerns about a decrease in block rigidity, but as a result of the inventors' studies, it has become clear that inverted trapezoidal sipes greatly improve braking performance on snow and ice surfaces.

[0049] The molding die 50 for the pneumatic tire 1 will be described in detail below with reference to Figures 5 and 6. Figure 5 is a cross-sectional view of the molding die 50. Figure 6 is a perspective view of the sipe blade 60 that constitutes the molding die 50.

[0050] 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, 70 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.

[0051] 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.

[0052] The sipe blade 60 is a thin, plate-shaped metal member for forming sipes 10 on the center block 4, 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. The sipe blade 60 is also attached so as to connect to two 55B and 55C. This forms sipes 10 with both ends in the longitudinal direction communicating with circumferential grooves 7.

[0053] The sipe blade 70 is a thin, plate-shaped metal member for forming corrugated sipes 40 on the shoulder block 5 and mediate block 6. Similar to the sipe blade 60, it is inserted into a groove formed in the main body 54 and attached to the tread molding surface 53. The sipe blade 70 is mounted so as to connect to the projection 55, thereby forming corrugated sipes 40 on the shoulder block 5 and mediate block 6 that communicate with the circumferential groove 7.

[0054] As shown in Figure 6, the sipe blade 60 has a first base portion 61, a second base portion 62, and a connecting portion 63 that connects the respective base portions. In a plan view of the sipe blade 60, the first base portion 61 and the second base portion 62 are arranged in a staggered pattern extending in the longitudinal direction of the blade, and the angles formed by the first base portion 61 and the connecting portion 63, and the angles formed by the second base portion 62 and the connecting portion 63 are both set to acute angles. In this embodiment, these two angles are the same. The sipe blade 60 also has straight portions 68 that are formed in a flat, plate-like shape along its longitudinal direction. The straight portions 68 are formed at both ends of the blade in the longitudinal direction.

[0055] The first base portion 61, the second base portion 62, the connecting portion 63, and the straight portion 68 are the parts that form the first portion 11, the second portion 12, the connecting portion 13, and the straight portion 18 of the sipe 10, respectively, and in this embodiment, they are formed with the same height and thickness. The height direction of the sipe blade 60 corresponds to the depth direction of the sipe 10, and the thickness direction of the blade corresponds to the width direction of the sipe 10. The distance between the first base portion 61 and the second base portion 62 (hereinafter simply referred to as "distance") along the direction perpendicular to the length direction of the sipe blade 60 determines the amplitude W of the sipe 10.

[0056] The connecting portion 63 includes a first connecting portion 63A and a second connecting portion 63B that extend in different directions from each other, and the connecting portions 63A and 63B are arranged alternately in the longitudinal direction of the sipe blade 60. The connecting portions 63A and 63B extending from a single first base 61 are inclined with respect to the first base 61 such that they move closer to each other as they move away from the first base 61 (the same applies to the connecting portions 63A and 63B extending from the second base 62). The inclination angle of the connecting portions 63A and 63B corresponds to the angle θ of the sipe 10. A ,θ B To decide.

[0057] The sipe blade 60 further has a rod portion 65 to which a first base portion 61, a second base portion 62, a connecting portion 63, and a straight portion 68 are connected. The rod portion 65 is the part that forms the drainage channel 15. The rod portion 65 is formed in a substantially round bar shape or a substantially cylindrical shape and extends straight in the longitudinal direction of the sipe blade 60.

[0058] At least one of the first base portion 61 and the second base portion 62 has a first wall surface on which a protruding portion 66 is formed and a second wall surface on which a recessed portion 67 is formed. The protruding portion 66 and the recessed portion 67 are formed in positions that overlap in the thickness direction of the base portion. The protruding portion 66 is the portion that forms the recess 17 of the sipe 10, and the recessed portion 67 is the portion that forms the protruding portion 16 of the sipe 10. In this embodiment, the protruding portion 66 and the recessed portion 67 are formed along the entire length in the height direction (from the upper end to the lower end) of all base portions. This forms a continuous protruding portion 16 and recess 17 in the depth direction of the sipe 10. In addition, the distance between the first base portion 61 and the second base portion 62 gradually decreases toward the rod portion 65.

[0059] The first base 61 and the second base 62 are further curved such that the distance between them gradually decreases from the upper end towards the lower end connected to the rod portion 65. The degree of curvature of each base increases as it approaches the rod portion 65. The first base 61 and the second base 62 may be curved with a first curvature from the upper end up to a predetermined height, and then curved with a second curvature greater than the first curvature from the predetermined height up to the rod portion 65. Alternatively, they may be formed straight in the height direction up to a predetermined height so as to maintain the distance at the upper end.

[0060] The following sections will provide a detailed explanation of sipes 20 and 30, which are modified versions of sipe 10, with reference to Figures 7 and 8. The following sections will primarily focus on the differences from sipe 10, omitting redundant explanations.

[0061] As shown in Figure 7, the sipe 20 includes a first section 21, a second section 22, a connecting section 23, a drainage channel 25, and a straight section 28, and is similar to the sipe 10 in that a convex section 26 and a concave section 27 are formed on the first section 21 and the second section 22. Also, similar to the sipe 10, the connecting section 23 includes connecting sections 23A and 23B, and in a plan view of block 3, the section enclosed on three sides by the first section 21, the connecting section 23A, and the connecting section 23B is formed in a zigzag shape, exhibiting an inverted trapezoid shape with the first section 21 as the base and the connecting sections 23A and 23B as the hypotenuses. On the other hand, the sipe 20 differs from the sipe 10 in that the first section 21, the second section 22, and the connecting section 23 are formed straight in the depth direction.

[0062] In other words, the amplitude of the sipe 20 does not change in the depth direction. Therefore, even if wear of the block 3 progresses, the amplitude of the sipe 20 does not decrease, and the function of the sipe 20 is less likely to deteriorate. However, the drainage channel 25 to which the first part 21, the second part 22, and the connecting part 23 are connected needs to have a larger diameter than the drainage channel 15 of the sipe 10. In this case, the block rigidity is more likely to decrease compared to when the sipe 10 is applied. A structure like the sipe 10, in which the first part 11 and the second part 12 are greatly curved on the drainage channel 15 side, is useful from the viewpoint of smoothly connecting each part to the drainage channel 15 with a small diameter while suppressing the decrease in amplitude due to block wear.

[0063] As shown in Figure 8, the sipe 30 includes a first portion 31, a second portion 32, a connecting portion 33, a drainage channel 35, and a straight portion 38, and is similar to sipes 10 and 20 in that, in a plan view of block 3, the portion enclosed on three sides by the first portion 31 (second portion 32), the connecting portion 33A, and the connecting portion 33B is formed in a zigzag shape, exhibiting an inverted trapezoid shape. Also, similar to the case of sipe 10, the amplitude of sipe 30 gradually decreases towards the bottom of sipe 30. On the other hand, sipe 30 differs from sipe 10 in that, from the opening 34 toward the drainage channel 35, the first portion 31 and the second portion 32 are inclined toward each other at a certain angle.

[0064] The sipe 30 is similar to the sipe 10 in that its first portion 31 and second portion 32 each have a first wall surface on which a protrusion 36 is formed, and a second wall surface facing the first wall surface, on which a recess 37 is formed into which the protrusion 36 fits when the sipe 30 is closed. On the other hand, while the protrusion 16 and recess 17 of the sipe 10 are formed along the entire length in the depth direction, the protrusion 36 and recess 37 are formed in multiples with spacing in the depth direction. In the example shown in Figure 8, two protrusions 36 are formed on the first wall surface of the first portion 31 and the second portion 32 at a predetermined distance in the depth direction, away from the opening 34 and the drainage channel 35. In this case as well, when braking, the protrusion 36 fits into the recess 37, thereby suppressing skidding on snowy and icy road surfaces.

[0065] As described above, with a pneumatic tire 1 equipped with a center block 4 on which sipes 10 are formed, the reduction in the opening area of ​​the sipes 10 during braking is effectively suppressed, improving braking performance on snowy and icy roads. With sipes 10 that are inverted trapezoidal, a large opening area is secured at the connecting portion 13 even when fully closed, allowing for edge effect and water removal effect. As a result, the braking performance of the pneumatic tire 1 on snowy and icy roads can be greatly improved.

[0066] In particular, the amplitude W and angle θ of sipe 10. A ,θ B By setting the pitch and other parameters to a suitable range, it is possible to more effectively improve braking performance while suppressing a decrease in block rigidity. The sipes 10 suppress the movement of the blocks when longitudinal forces are applied, reducing slippage on road surfaces with a low coefficient of friction. In addition, the convex portion 16 of the sipes 10 fits into the concave portion 17, restricting the movement of the blocks in the axial direction of the tire, suppressing lateral slippage and further improving braking performance. The sipes 20 and 30 also provide the same braking performance improvement effect as the sipes 10. [Examples]

[0067] The present invention will be further described below with reference to examples, but the present invention is not limited to these examples.

[0068] <Example 1> A test tire A1 (tire size: 225 / 60R18 100H) was fabricated, featuring a tread pattern containing multiple center blocks, shoulder blocks, and mediate blocks, each demarcated by circumferential and transverse grooves. Three inverted trapezoidal sipes X1 were formed on each center block, with the length of the sipes aligned with the tire axis. Additionally, three corrugated sipes were formed on each shoulder block and mediate block, with the length of the sipes aligned with the tire axis.

[0069] 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 the center block. Figure 9 shows the plan view shape of the sipes formed on the center block of each test tire.

[0070] The specifications for the inverted trapezoidal sipe X1 are as follows. These specifications, along with the evaluation results of the test tires, are shown in Table 1. Note that in Table 1, "sipe" refers to the sipe formed on the center block. Type: Inverted trapezoid Pitch P: 2.0mm Amplitude W: 1.5mm Angle θ: 18°

[0071] As described above, an inverted trapezoidal sipe is a sipe in which the portion enclosed on three sides by the first portion and the two connecting portions forms a first trapezoid (the first inverted trapezoid described above) with the first portion as the base and the connecting portions as the hypotenuses, and the portion enclosed on three sides by the second portion and the two connecting portions forms a second inverted trapezoid (the second inverted trapezoid described above) with the second portion as the base and the connecting portions as the hypotenuses, and the first and second inverted trapezoids are arranged alternately in the length direction. The angle θ is the inclination angle of the connecting portion with respect to the direction perpendicular to the length direction of the sipe, and in this embodiment, the angle θ is the same at each connecting portion. The pitch P and amplitude W are as described above.

[0072] <Examples 2-4> Test tires A2 to A4 were manufactured in the same manner as in Example 1, except that the sipes on the center block were replaced with inverted trapezoidal sipes X2 to X4 as shown in Figure 9. The specifications of the inverted trapezoidal sipes X2 to X4 are shown in Figure 9 and Tables 1 to 3.

[0073] <Comparative Example 1> Test tire B1 was manufactured in the same manner as in Example 1, except that the sipes on the center block were replaced with the square sipes Y1 shown in Figure 9. The specifications of the square sipes Y1 are shown in Figure 9 and Table 1.

[0074] <Comparative Examples 2, 3> Test tires B2 and B3 were manufactured in the same manner as in Example 1, except that the sipes on the center block were replaced with trapezoidal sipes Y2 and Y3 as shown in Figure 9. The specifications of trapezoidal sipes Y2 and Y3 are shown in Figure 9 and Table 1. Trapezoidal sipes Y2 and Y3 differ from inverted trapezoidal sipes X1 to X4 in that the parts corresponding to the first and second parts of inverted trapezoidal sipe X1 become the upper base of the trapezoid.

[0075] <Comparative Examples 4, 5> Test tire B1 was manufactured in the same manner as in Example 1, except that the sipes on the center block were replaced with square sipes instead of the inverted trapezoidal sipes X1. The plan view shape of the square sipes is the same as that of the square sipes Y1 in Comparative Example 1. The specifications of the square sipes are shown in Tables 2 and 3, respectively.

[0076] For each test tire in the examples and comparative examples, the clearance ratio in the fully closed state and braking performance were evaluated using the method described below. The evaluation results are shown in Tables 1 to 3. The evaluation results for the fully closed clearance ratio shown in Table 1 are relative values ​​with the evaluation result of test tire B1 of Comparative Example 1 set to 1.00, and the evaluation results for braking performance are relative values ​​with the evaluation result of test tire B1 set to 100. Furthermore, the evaluation results shown in Table 2 are relative values ​​based on the evaluation result of test tire B4 of Comparative Example 4, and the evaluation results shown in Table 3 are relative values ​​based on the evaluation result of test tire B5 of Comparative Example 5.

[0077] [Evaluation of the fully closed clearance ratio] The ratio of the opening area of ​​the sipes formed on the center block of each test tire in the fully closed state was determined, and the relative value (fully closed gap ratio) with respect to the sipes of the comparative example used as the evaluation standard was calculated. The fully closed state, as described above, means the state in which a longitudinal force acts on the center block and the walls of opposing sipes in the circumferential direction of the tire are in contact with each other.

[0078] [Evaluation of braking performance] We drove a real vehicle (with two occupants) equipped with each test tire on an icy road, measured the braking distance when braking force was applied at a speed of 50 km / h and the ABS was activated, and calculated the reciprocal of the braking distance. A higher number indicates better braking performance.

[0079] [Table 1]

[0080] [Table 2]

[0081] [Table 3]

[0082] As shown in Tables 1 to 3, all of the test tires A1 to A4 in the examples exhibit superior braking performance compared to the comparative example test tire used as the evaluation standard. The tires in the examples have a larger fully closed clearance ratio than the comparative example tire. As a result, it is believed that the edge effect and water-removal effect of the sipes are fully utilized even during braking when large longitudinal forces are applied to the center block.

[0083] Furthermore, test tires A1 and A2 exhibit even better braking performance compared to test tires A3 and A4. This indicates that the amplitude W and pitch P of the inverted trapezoidal sipes significantly affect braking performance. For example, while a larger amplitude W is thought to improve edge effect and water removal effect, if it becomes too large, block rigidity decreases, which can actually reduce braking performance. As mentioned above, an example of a suitable range for amplitude W is 1.0 mm to 2.0 mm, or 1.2 mm to 1.8 mm. Similarly, an example of a suitable range for pitch P is 1.5 mm to 3.0 mm, or 1.8 mm to 2.5 mm. [Explanation of symbols]

[0084] 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 sipe, 11, 21, 31 first part, 12, 22, 32 second part, 13, 13A, 13B, 23, 23A, 23B, 33, 33A, 33B connecting part, 14, 34 opening, 15, 25, 35 drainage channel, 16, 26, 36 protrusion, 17, 27, 37 recess, 18, 28, 38 straight part, 40 corrugated sipe, 50 molding die, 51 tread die, 52 side die, 53 tread molding surface, 54 main body, 55 projection, 60, 70 sipe blade, 61 first base, 62 Second base, 63 connecting section, 65 rod section, 66 convex section, 67 concave section, 68 straight section, CL tire equator, E ground contact end, α,β,γ imaginary lines

Claims

1. A pneumatic tire having blocks with sipes formed therein The sipe includes first and second portions that extend in the longitudinal direction of the sipe and are arranged in a staggered pattern, and connecting portions that connect each of the portions. A pneumatic tire in which, in a plan view of the block, the angle between the first portion and the connecting portion, and the angle between the second portion and the connecting portion, are both acute angles.

2. The pneumatic tire according to claim 1, wherein parts of the first and second portions overlap in a direction perpendicular to the longitudinal direction.

3. In a plan view of the block, the inclination angle θ of the connecting portion with respect to the direction perpendicular to the longitudinal direction of the sipe is 10° or more and 40° or less, as described in claim 1 or 2.

4. The aforementioned connecting portion includes the first and second connecting portions. In a plan view of the block, the inclination angle θ1 of the first connecting portion and the inclination angle θ2 of the second connecting portion with respect to the direction perpendicular to the longitudinal direction of the sipe are the same angle and are between 10° and 40°, as described in claim 1 or 2.

5. The pneumatic tire according to claim 1 or 2, wherein at least one of the first and second portions has a first wall surface on which a protrusion is formed, and a second wall surface facing the first wall surface and having a recess in which the protrusion fits when the sipe is closed.

6. The pneumatic tire according to claim 1 or 2, wherein the amplitude of the sipe, defined as the distance between the first portion and the second portion along a direction perpendicular to the longitudinal direction of the sipe, gradually decreases toward the bottom of the sipe.

7. A drainage channel is formed at the bottom of the sipe, to which the first portion, the second portion, and the connecting portion are connected. The pneumatic tire according to claim 6, wherein the bottom region from a predetermined depth to the drainage channel is more curved than the opening region from the opening formed on the contact surface of the block to the predetermined depth, such that the amplitude of the sipe gradually decreases toward the drainage channel.

8. The pneumatic tire according to claim 6, wherein the amplitude of the sipe is 1.0 mm or more and 2.0 mm or less.

9. The pneumatic tire according to claim 1 or 2, wherein the repeating pitch, defined as the distance between the connecting portions along the longitudinal direction of the sipe, is 1.5 mm or more and 3.0 mm or less.

10. The pneumatic tire according to claim 1 or 2, wherein the sipe communicates with grooves that demarcate the block.

11. A drainage channel is formed at the bottom of the sipe, to which the first portion, the second portion, and the connecting portion are connected. The pneumatic tire according to claim 10, wherein the drainage channel has a width greater than the opening width of the sipe, extends in the longitudinal direction of the sipe, and communicates with the groove.

12. The block includes a center block formed at the position closest to the tire equator, The pneumatic tire according to claim 1 or 2, wherein the sipes are formed in the center block.

13. A mold for forming pneumatic tires, equipped with sipe blades for forming sipes in a block, The sipe blade has, in a plan view of the blade, first and second bases that extend in the longitudinal direction of the blade and are arranged in a staggered pattern, and a connecting portion that connects each of the bases. A molding die in which, in a plan view of the sipe blade, the angle between the first base and the connecting portion, and the angle between the second base and the connecting portion, are both acute angles.

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