Pneumatic tires and molds for tire molding.

Abstract

This design suppresses crack formation on the bottom surface of the sipes while improving grip performance during the middle and end stages of wear. [Solution] The pneumatic tire 1 is a pneumatic tire having a tread having blocks 20a on which sipes 50 are formed. The sipes 50 have one of the following shapes on the block surface: a wave shape, a zigzag shape, or a shape including at least one bending point. The circumferential cross-sectional shape of the sipes 50 within the block 20a is the same as the sipe shape on the block surface from the block surface to a range of 65% to 80% of the sipe depth, and a flat straight region is formed along the longitudinal direction of the sipe in at least a portion of a predetermined height region from the bottom surface of the sipe.

Description

Technical Field

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

Background Art

[0002] Conventionally, a pneumatic tire having a tread pattern including a circumferential groove extending in the tire circumferential direction, an axial groove extending in the tire axial direction, and a plurality of blocks segmented by each groove is widely known. In Prior Art Document 1, a tire tread having a wave-shaped or zigzag sipe is described, in which the amplitude at the sipe bottom surface is smaller than that of the tread surface.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a tire having a sipe, due to stress or the like caused by the contact between the tire and the road surface, cracks occur at the sipe bottom surface, resulting in a problem that rubber pieces peel off from the tire. The phenomenon of rubber pieces peeling off from the tire is called chunk out. In the invention described in Prior Art Document 1, the occurrence of cracks at the sipe bottom surface is suppressed by making the amplitude of the sipe bottom surface smaller than the amplitude of the sipe surface. However, conventional tires including the tire described in Prior Art Document 1 have a large room for improvement in grip performance in the middle to late stages of wear. Furthermore, in addition to improving the grip performance, the tire is required to effectively suppress the occurrence of cracks at the sipe bottom surface.

Means for Solving the Problems

[0005] The pneumatic tire according to the present invention is a pneumatic tire having a tread having blocks on which sipes are formed, wherein the sipes have one of the following shapes on the surface of the block: a wave shape, a zigzag shape, or a shape including at least one bending point, and the circumferential cross-sectional shape of the sipes within the block is the same as the sipe shape on the surface of the block from the surface of the block to a range of 65% to 80% of the sipe depth, and a flat straight region is formed along the longitudinal direction of the sipe in at least a portion of a predetermined height region from the bottom surface of the sipe. [Effects of the Invention]

[0006] The pneumatic tire according to the present invention can suppress crack formation at the bottom surface of the sipes while improving grip performance during the middle and final stages of wear. [Brief explanation of the drawing]

[0007] [Figure 1] This figure shows the tread of a tire according to the first embodiment. [Figure 2] This is an enlarged perspective view of section X in Figure 1. [Figure 3] This is a cross-sectional view showing the section A-A in Figure 2. [Figure 4] Figure 3 is a cross-sectional perspective view showing the BB cross-section. [Figure 5] This is a circumferential cross-sectional view of a tire with sipes of different depths according to the first embodiment. [Figure 6] This is a radial cross-sectional view of the tire showing the bottom surface of the sipes. [Figure 7] This is a cross-sectional perspective view showing the sipe shape according to the second embodiment. [Figure 8] This is a circumferential cross-sectional view of a tire with sipes of different depths according to the second embodiment. [Figure 9] This is a circumferential cross-sectional view of a tire with sipes of different depths according to the third embodiment. [Figure 10] This figure illustrates the types of block surface shapes of sipes to which the present invention can be applied. [Figure 11] This is a diagram showing a mold for molding tires. [Figure 12] This is a perspective view showing a sipe blade in a tire molding die. [Modes for carrying out the invention]

[0008] 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.

[0009] The tire of this embodiment has a general configuration as a pneumatic tire, except for the tread, which is the part that contacts the road surface. Specifically, bead portions including a bead core and a bead filler are provided on both sides of the tire axial direction, and a carcass ply is provided extending from one bead portion to the other in the tire axial direction. A belt is provided on the outer diameter side of the carcass ply, and a tread 10 is provided on the outer diameter side of the belt. In addition, an inner liner is provided inside the carcass ply, and sidewall rubber is provided on both sides of the carcass ply in the tire axial direction. In addition to the above, several other rubber members are provided to constitute the tire 1.

[0010] Using Figure 1, we will explain the pneumatic tire 1 and the sipes 50 formed on the tread 10 of the pneumatic tire 1. Figure 1 is a diagram showing the surface of the tread 10 of the pneumatic tire 1. That is, Figure 1 is a view of the tread 10 of the pneumatic tire 1 from the outside in the radial direction of the tire. Hereinafter, "pneumatic tire 1" may be referred to as "tire 1".

[0011] As shown in Figure 1, the tire 1 comprises a tread 10 having at least one block 20, 21, 22 on which a sipe 50 is formed. More specifically, the tread 10 has a tread pattern in the portion that contacts the road surface, comprising a plurality of blocks 20, 21, 22, and is formed in an annular shape along the circumferential direction of the tire.

[0012] The tread 10 has a plurality of blocks 20, 21, 22 demarcated by circumferential grooves 30. The circumferential grooves 30 are grooves that extend along the circumferential direction of the tire. In the example shown in Figure 1, the circumferential grooves 30 are grooves parallel to the circumferential direction of the tire. The circumferential grooves 30 may also be grooves that are inclined with respect to the circumferential direction of the tire, or they may be zigzag-shaped grooves that extend along the circumferential direction of the tire. In the example shown in Figure 1, the circumferential grooves 30 have the same width, but are not limited to this. The dimensions such as the width of the circumferential grooves 30 are set appropriately based on the design policy of the tire 1.

[0013] The multiple blocks 20, 21, and 22 include a center block 20 located in the center in the tire width direction, mediate blocks 21 adjacent to both ends of the center block 20 in the tire axial direction, and shoulder blocks 22 located on the tire axial side of the mediate block 21. The center block 20 includes a tire equator CL, which is an imaginary line passing through the center of the tire axial direction and parallel to the tire circumferential direction.

[0014] Multiple blocks 20, 21, and 22 are divided in the circumferential direction of the tire by multiple axial grooves 40 provided in the tread 10, thereby forming small blocks 20a, 21a, and 22a. The axial grooves 40 are grooves that extend along the tire axis. In the example shown in Figure 1, the axial grooves 40 are grooves parallel to the tire axis. Note that the axial grooves 40 may also be grooves inclined with respect to the tire axis, or they may be zigzag-shaped grooves that extend along the tire axis. In the example shown in Figure 1, the axial grooves 40 have the same width, but are not limited to this. The dimensions such as the width of the axial grooves 40 are set appropriately based on the design policy of the tire 1. The axial grooves 40 have dimensions smaller than, for example, the width of the circumferential grooves 30.

[0015] On at least one surface of each of the small blocks 20a, 21a, and 22a, a plurality of sipes 50 extending substantially along the tire axis direction are formed. In this specification, a groove with a width less than 1.5 mm is defined as a sipe. The maximum width of the sipe is preferably 0.3 mm or more and 1.0 mm or less. Here, the surface of each of the small blocks 20a, 21a, and 22a is the surface that contacts the road surface. Each sipe 50 has the effect of improving grip performance by enhancing the edge effect of scraping snow and ice, and realizing good braking performance and handling stability on an icy or snowy road surface. Also, according to the sipe 50, since more water storage spaces can be created, the wet performance can be improved.

[0016] The plurality of sipes 50 have any one of a waveform, a zigzag shape, and a shape including at least one bending point on the surface of the small blocks 20a, 21a, and 22a. In this specification, the waveform means a waveform having a curved portion. Also, the zigzag shape means a shape having a bent portion, and includes a waveform having a bent portion. Note that the shape including at least one bending point is not limited to a waveform, and for example, is a shape composed of three straight lines and two bending points. Hereinafter, the case where the plurality of sipes 50 have a waveform will be exemplified and described. As shown in FIG. 1, the plurality of sipes 50 extend along the tire axis direction. Note that the sipe 50 may be formed to be inclined from the tire axis direction.

[0017] The shapes of the sipes 50 formed in each of the small blocks 20a, 21a, and 22a may be the same shape or may be different from each other. In the example shown in FIG. 1, the sipe 50 formed in the small block 21a has the same shape as the sipe 50 formed in the small block 20a. The sipe 50 formed in the small block 22a has a larger length and more waves than the sipe 50 formed in the small block 20a, but the basic shape is the same.

[0018] The sipes 50 formed on each block 20, 21, and 22 may be formed to connect adjacent circumferential grooves 30 in the tire axial direction, as shown in Figure 1, by extending to both ends of each block 20, 21, and 22 in the tire axial direction. Alternatively, the sipes 50 may be formed from one end of each block 20, 21, and 22 in the tire axial direction and closed within the block. Furthermore, multiple sipes 50 are formed separately in the tire circumferential direction within each block. The shape of the sipes 50 formed on each block 20, 21, and 22 may be similar, as shown in Figure 1. However, different shapes may be used for each block.

[0019] In the example shown in Figure 1, three sipes 50 are formed in each of the small blocks 20a, 21a, and 22a. However, the number of sipes 50 per small block is not particularly limited.

[0020] The number of sipes 50 formed on each block 20, 21, and 22 may be the same as shown in Figure 1, but different numbers may be formed on each block. For example, it is preferable that the number of sipes 50 formed on the center block 20 is greater than the number of sipes 50 formed on the mediate block 21, and also greater than the number of sipes 50 formed on the shoulder block 22. In this case, the number of sipes 50 formed on the mediate block 21 and the shoulder block 22 may be the same, but it is preferable that the number of sipes 50 formed on the mediate block 21 is greater than the number of sipes 50 formed on the shoulder block 22. That is, it is preferable that the number of sipes 50 increases in the order of shoulder block 22, mediate block 21, and center block 20. With the above configuration, since many sipes 50 are formed on the center block 20, which is subjected to a large load during braking, the grip performance on that block can be improved. As a result, the grip performance of the entire pneumatic tire can be improved.

[0021] The sipe 50 will be described in detail with reference to Figures 2 and 3. Figure 2 is an enlarged perspective view of section X in Figure 1. Figure 3 is a cross-sectional view taken along line A-A in Figure 2. Figure 3 is a cross-sectional view of a virtual line passing through the center of the sipe 50 in the width direction, as shown in Figure 2. In the following, the sipe 50 formed on the small block 20a will be described as an example.

[0022] As shown in Figure 2, the sipe 50 has a wave shape on the surface of the small block 20a. In detail, the sipe 50 has a wave shape with a constant wavelength and amplitude. However, if the sipe 50 has a wave shape, wave shapes with different wavelengths and amplitudes may be used. Here, the wavelength represents the longitudinal distance of the sipe 50 from the peak of one wave-shaped peak to the peak of an adjacent peak. The amplitude represents the widthwise distance of the sipe 50 from the center line passing through the center of the widthwise center of the sipe 50 to the peak of the wave-shaped peak.

[0023] As shown in Figure 3, the sipe 50 has a first wall surface 51 and a second wall surface 52 that face each other within the small block 20a. As shown in Figure 2, the first wall surface 51 and the second wall surface 52 have a wave shape that extends along the tire axis direction when viewed from the outside in the radial direction of the tire. As will be described in detail later, in the first embodiment, it is preferable that the first wall surface 51 and the second wall surface 52 have the same shape from the surface of the block to a range of 65% to 80% of the sipe depth.

[0024] It is preferable that the sipe 50 has straight sections 53 at both ends in the tire axial direction. That is, the sipe 50 has straight sections 53 at both ends in the tire axial direction of the small block 20a. Furthermore, it is preferable that the straight sections 53 located at both ends in the tire axial direction of the sipe 50 are located on the same straight line, for example, on the widthwise centerline of the sipe 50. By having straight sections 53 at both ends in the tire axial direction of the sipe 50, it is possible to suppress a decrease in rigidity at the tire axial end of the small block 20a. In particular, by having straight sections 53 in the sipe 50, it becomes easier to set the sipe setting angle at the tire axial end of the small block 20a to be larger than that of a wave shape, thereby suppressing a decrease in rigidity at that end. Here, the sipe setting angle refers to the inclination angle of the sipe 50 with respect to the tire axial direction. As a result, chunking out at the tire axial end of the small block 20a can be suppressed.

[0025] The sipe 50 will be described in more detail with further reference to Figures 4 to 6. Figure 4 is a schematic cross-sectional view showing the BB cross-section of Figure 3. Figure 5 shows circumferential cross-sectional views of the sipe 50 at different depths. Figure 6 shows the bottom surface of the sipe 50.

[0026] Figure 4 shows cross-sectional views obtained by cutting along the center line b that passes through the center of the width of the sipe 50 in each region shown in Figure 3. The center line b has a roughly S-shape in the tire radial direction, but is also deformed in the tire axial direction according to the shape viewed from the outside in the tire radial direction of each region. In detail, in regions of the same shape, the center line b is set along the shape of the surface of the small block 20a of the sipe 50, which is the center of the sipe 50. In the transition region, the center line b is set along the shape of the transition region, which is the center of the width of the sipe 50. Furthermore, as will be described in more detail later, in this embodiment a flat surface is formed over the entire surface of the straight region 50a, so in the straight region 50a, a straight center line b is set along the center of the sipe 50. Figure 4 shows cross-sectional views obtained by cutting along the center line b for each of these regions.

[0027] As shown in Figure 4, the sipe 50 has the same shape from the surface of the small block 20a to a predetermined region in the depth direction of the sipe 50. Here, the predetermined region is the area from the surface of the small block 20a to 65% to 80% of the depth of the sipe 50. In detail, the circumferential cross-sectional shape of the sipe 50 within the small block 20a has the same shape as the sipe shape on the surface of the small block 20a as viewed from the outside in the radial direction of the tire, up to the range from the surface of the small block 20a to 65% to 80% of the sipe depth (same shape region). In this case, it is preferable that the first wall surface 51 and the second wall surface 52 have the same shape as the shape on the surface of the small block 20a as viewed from the outside in the radial direction of the tire, up to the predetermined region, and the distance between the first wall surface 51 and the second wall surface 52 is also the same as the distance on the surface of the small block 20a up to the predetermined region. By having the above configuration, the wave shape of the sipe 50 is maintained even in the final stages of wear, so that grip performance can be improved.

[0028] As shown in Figure 4, a flat, straight region 50a is formed along the longitudinal direction of the sipe 50 in at least a portion of the region from the bottom surface of the sipe 50 to a predetermined height. More specifically, a flat shape along the longitudinal direction of the sipe 50 is formed on at least one of the first wall surface 51 and the second wall surface 52 in the region from the bottom surface of the sipe 50 to a predetermined height. This makes it possible to more effectively suppress the occurrence of cracks at the bottom surface of the sipe 50 and suppress chunking out.

[0029] The predetermined height region is preferably a region from the bottom surface of the sipe 50 to a height of 3% to 15% of the depth of the sipe 50. This allows for more effective suppression of crack formation.

[0030] It is preferable that the straight region 50a is formed over the entire surface of the predetermined height region. In this case, the first wall surface 51 and the second wall surface 52 near the bottom surface of the sipe 50 are formed substantially parallel to each other. That is, the bottom surface of the sipe 50 is formed in a straight line shape. Because the bottom surface of the sipe 50 is in a straight line shape, distortion and stress concentration are less likely to occur compared to a wave shape. In particular, if the bottom surface of the sipe 50 is wave-shaped, a lot of distortion is likely to occur at the bottom surface of the sipe regardless of whether the force applied is in the direction of the tire axis or in a direction inclined from the tire axis. However, if the bottom surface of the sipe 50 is in a straight line shape, distortion is likely to occur at the bottom surface of the sipe when a force is applied from the circumferential direction of the tire, but regardless of whether the force applied is in the direction of the tire axis or in a direction inclined from the tire axis, the amount of distortion at the bottom surface of the sipe will be less than the amount of distortion that occurs when a force is applied from the circumferential direction of the tire. As a result, crack formation at the bottom surface of the sipe can be suppressed more effectively, and therefore chunking out can be suppressed more effectively. In the following explanation, we will use the example of a case where a straight region 50a is formed over the entire surface of a predetermined height range from the bottom surface of the sipe 50.

[0031] The sipes 50, having a wave-like shape, a zigzag shape, and a shape including at least one bending point on the surface of the small block 20a, enhance the edge effect that scratches snow and ice, thereby improving grip performance and achieving good braking performance and handling stability on icy and snowy roads. In other words, the shape of the sipes 50 on the contact surface is the shape that enables grip performance in tire 1. The shape of the sipes 50 that enables grip performance (wave-like shape in this embodiment) must be formed at least 50% of the depth of the sipes 50 from the block surface, as specified by JATMA, for winter tires. By setting the same shape area of ​​the sipes 50 at least 65% of the depth of the sipes 50 from the surface of the small block 20a, the above specification is sufficiently met, and it is possible to maintain sufficient grip performance. In other words, even if the surface of the small block 20a is worn, the edge effect of the sipes 50 can still be exerted, improving grip performance on icy and snowy roads. Furthermore, by ensuring that the area of ​​sipe 50 with the same shape accounts for 80% or less, crack formation can be effectively suppressed, thereby preventing chunking out.

[0032] If we define the same-shape region as the area from the surface of the small block 20a to a depth of 65% to 80% of the sipe 50 in the tire's circumferential cross-sectional shape that is the same as the shape on the surface of the sipe 50, then the sipe 50 has a transition region between the same-shape region and the straight region 50a, which gradually deforms from the same-shape region toward the straight region 50a. The transition region is the area located between the same-shape region and the straight region 50a, and its amplitude is smaller compared to the shape of the sipe 50 on the surface of the small block 20a.

[0033] Referring to Figure 5, the circumferential cross-sectional shape of the sipe 50 will be explained in detail. In Figure 5, Figure 5(A) shows a CC cross-sectional view of the same-shape region, Figure 5(B) shows a DD cross-sectional view of the transition region, and Figure 5(C) shows an FF cross-sectional view of the straight region 50a. As shown in Figure 5(B), in the transition region, the amplitude of the sipe 50 decreases from the amplitude of the same-shape region shown in Figure 5(A) towards the bottom surface of the sipe. The transition region transitions to the straight region 50a shown in Figure 5(C) when the amplitude becomes 0. The formation of a transition region in the sipe 50 prevents a sudden change in shape from the wave shape of the same-shape region to the flat shape of the straight region 50a, and suppresses stress concentration caused by abrupt shape changes, thereby effectively suppressing chunking out.

[0034] The bottom shape of the sipe 50 will be described in detail with further reference to Figure 6. The bottom shape of the sipe 50 may be formed such that the bottom of the straight portion 53 formed at both ends of the sipe 50 in the tire axial direction becomes shallower, as shown in Figure 6. This makes it possible to suppress the occurrence of cracks at both ends of the small block 20a in the tire axial direction. Furthermore, it is preferable that the sipe 50 is formed so that the sipe depth gradually becomes shallower. This suppresses stress concentration compared to the case where the sipe depth is changed abruptly, thereby suppressing the occurrence of cracks and chunking out.

[0035] The pneumatic tire 1 according to the second embodiment will be described in detail with reference to Figures 7 and 8. The tire 1 according to the second embodiment is the same as the tire 1 according to the first embodiment, except that the shape of the sipes, particularly the shape of the sipe walls, is different. Figure 7 is a schematic cross-sectional view showing the wall surface of the sipe 60 according to the second embodiment, and corresponds to Figure 4 of the first embodiment. Figure 8 is a cross-sectional view of the sipe 60 according to the second embodiment in the tire circumferential direction, and corresponds to Figure 5 of the first embodiment.

[0036] In the second embodiment, the sipe 60 is formed with a displacement in the longitudinal direction within the small block 20a depending on its depth. The shape of the sipe 60 on the surface of the small block 20a is one of the following: a wave shape, a zigzag shape, or a shape including at least one inflection point. In the following description, the wave shape will be used as an example, as shown in Figure 8. As shown in Figure 7, the sipe 60 is formed with a displacement in the longitudinal direction within the block, but the shape of the sipe 60 within the small block 20a is the same as the shape of the sipe 60 on the surface of the small block 20a. That is, the wave shape of the sipe 60 within the block is formed with a phase difference from the wave shape on the surface of the small block 20a.

[0037] Referring to Figure 8, the circumferential cross-sectional shape of the sipe 60 will be explained in detail. In Figure 8, Figure 8(A) shows the shape of the sipe 60 on the surface of the small block 20a, Figure 8(B) shows a GG cross-section in the same shape region, Figure 8(C) shows an HH cross-section in the transition region, and Figure 8(D) shows a II cross-section in the straight region. As shown in Figure 8(B), the shape of the sipe 60 in the same shape region is formed with a displacement in the longitudinal direction of the sipe 60 from the shape of the sipe 60 on the surface of the small block 20a. By forming the sipe 60 with a displacement in the longitudinal direction as shown in Figure 8(B), when a force is applied in the axial direction of the tire, the walls of the sipe 60 come into contact with each other at the center in the depth direction, which suppresses the generation of distortion on the bottom surface of the sipe 60.

[0038] The above embodiments can be modified as appropriate without impairing the objectives of the present invention. For example, in the first and second embodiments, a straight region was described for the entire area from the bottom surface of the sipes 50 and 60 to a predetermined height region, but as shown in Figure 9(C), a part of the predetermined height region may be a straight region. Figure 9 is a cross-sectional view of a sipe 70 at different depths according to a modified example. Figure 9(A) is a cross-sectional view of the tire in the same shape region, Figure 9(B) is a cross-sectional view of the tire in the transition region, and Figure 9(C) is a cross-sectional view of the tire in the tire from the bottom surface of the sipe to a predetermined height region. In the area from the bottom surface of the sipe 70 to a predetermined height region, as shown in Figure 9(C), a part of it may be a flat region along the tire axis direction. That is, the area other than the flat region within the predetermined height region does not need to change shape from the block surface to the bottom surface of the sipe. According to this, the space at the bottom of the sipe can be increased, so when force is applied, the wall surface does not come into contact with the bottom of the sipe 70, thereby suppressing stress concentration and strain generation, and thus suppressing crack formation.

[0039] Furthermore, while the first and second embodiments described the case where the sipes 50 and 60 on the surface of the small block 20a are wave-shaped, the sipe shape is not limited to this. For example, multiple shapes can be used, as shown in Figure 10. For example, as shown in Figure 10(A), the sipe 80 may have a zigzag shape, or as shown in Figure 10(B), the sipe 90 may include multiple right-angle shapes. In this specification, the sipe 90 is classified as a sipe having a zigzag shape. Moreover, the sipe 100 may have two bending points, as shown in Figure 10(C). The shape of the sipe on the block surface of the present invention is not limited to the shapes described above. Furthermore, the shape of the sipe on the block surface of the present invention may be composed of a combination of the shapes described above.

[0040] An example of an embodiment, a tire molding die 120, will be described in detail using Figures 11 and 12. Figure 11 is a schematic diagram showing the tire molding die 120. Figure 12 is a perspective view showing the sipe blade 130. Note that in Figure 11, the side shape (wave shape) of the sipe blade 130 is not shown for clarity.

[0041] The tire molding die 120 includes a tread die 121 for molding the surface of the tread 10 and a side die 122 for molding the surface of the sidewall.

[0042] The tread mold 121 has a main body portion 124 having a tread molding surface 123, a projection 125 protruding from the tread molding surface 123, and a sipe blade 130 protruding from the tread molding surface 123 and provided between the projections 125.

[0043] The sipe blade 130 forms the sipes 50 of the tire 1. The sipe blade 130 protrudes from the tread molding surface 123 in the tire radial direction between the projections 125. As shown in Figure 11, the sipe blade 130 protrudes from the tread molding surface 123 and is formed to connect adjacent projections 125. The sipe blade 130 is fixed to the tread mold 121 by inserting its base end 131 into a fixing hole formed in the tread mold 121.

[0044] The main body 124 is made of a metal material, for example, an aluminum alloy. Suitable aluminum alloys include, for example, AC4 series and AC7 series. The projection 125 is the part that forms the circumferential groove 30 on the tire 1. The projection 125 is formed from the same metal material as the main body 124.

[0045] The sipe blade 130 will be described in detail with reference to Figure 12. The sipe blade 130 is made of a thin metal material, which may be made of stainless steel, for example. Suitable stainless steels include SUS303, SUS304, SUS630, SUS631, etc. When using a 3D molding machine, SUS304L, SUS630 equivalent material 17-4PH, etc. are suitable.

[0046] The general method for processing the Sipe Blade 130 involves using a press molding machine to form its shape. Alternatively, a 3D modeling machine may be used to create complex shapes that are difficult to achieve with conventional machining.

[0047] As described above, the sipe blade 130 protrudes from the tread molding surface 123 of the tread mold 121. The sipe blade 130 has one of the following shapes at its base end 131 relative to the tread molding surface 123: a wave shape, a zigzag shape, or a shape having at least one inflection point. This makes it possible to form sipes 50 having the above shapes on the surface of the tread 10 of the tire 1.

[0048] The sipe blade 130 has the same shape as the sipe blade 130 at the base end 131 from the base end 131 up to a range of 65% to 80% in the height direction of the sipe blade 130. That is, when the sipe blade 130 is fixed to the tread mold 121, the shape of the sipe blade 130 is the same as the sipe blade 130 at the base end 131 from the tread molding surface 123 up to a range of 65% to 80% in the height direction of the sipe blade 130. This creates a region of the sipe 50 with the same shape.

[0049] The sipe blade 130 may have straight sections 133 at both ends in the axial direction of the tire. This allows for the formation of the straight sections 53 of the sipe 50.

[0050] The sipe blade 130 has a flat, straight region formed along its longitudinal direction on at least a portion of both sides of the sipe blade 130 in a predetermined height range from the tip 132. Here, the predetermined height range refers to the length range in the tire radial direction of the sipe blade 130 provided in the tire molding die 120. Alternatively, as shown in Figure 12, the straight region may be formed over the entire predetermined height range from the tip 132 of the sipe blade 130. The straight region of the sipe 50 is formed by the above configuration of the sipe blade 130.

[0051] With the tire molding die 120 having the sipe blade 130 described above, it is possible to create a tire that can more effectively suppress the occurrence of cracks on the bottom surface of the sipes while improving grip performance in the middle and end stages of wear. [Examples]

[0052] The present invention will be further described below with reference to examples, but the present invention is not limited to these examples.

[0053] <Example 1> [Air-filled tires] A test tire (tire size: 225 / 60R18 100H) was fabricated with a tread pattern containing multiple center blocks, mediate blocks, and shoulder blocks, each demarcated by circumferential grooves and axial grooves. Three sipes were formed in each of the center blocks, mediate blocks, and shoulder blocks, with the longitudinal direction of the sipes aligned with the axial direction of the tire.

[0054] The sipes have a wave-like shape on the block surface, and the circumferential cross-sectional shape of the sipes within the block is identical to the sipe shape on the block surface (identical shape region) from the block surface to 65% of the sipe depth. In addition, a flat straight region is formed along the longitudinal direction of the sipe across the entire surface of a predetermined height region from the bottom surface of the sipe. The predetermined height region is the region from the bottom surface of the sipe to 5% of the sipe depth in the sipe height direction. Furthermore, a transition region with gradually decreasing amplitude is formed between the identical shape region and the straight region of the sipe.

[0055] <Example 2> The same tire as in Example 1 was used, except that the same shaped region was formed up to 70% of the sipe depth.

[0056] <Example 3> The same tire as in Example 1 was used, except that the same shaped region was formed up to 80% of the sipe depth.

[0057] <Comparative Example 1> The same tire as in Example 1 was used, except that the same shaped region was formed up to 100% of the sipe depth.

[0058] [Chunking performance test] The test tires were prepared and tested under the conditions of the FMVSS139 durability test. Subsequently, the durability test was conducted by running the tires on a drum until they failed. The durability performance was evaluated by adjusting the air pressure of the test tires to 180 kPa and running them at 120 km / h for 4 hours with a load of 85% of the normal load. After 4 hours of running, the load was increased by 5% and the tires were run at 120 km / h for 6 hours. After 6 hours of running, the load was further increased by 10% and the tires were run at 120 km / h for 24 hours. In this way, the load was gradually increased and the durability performance was evaluated using the distance traveled until the tread chunked out. Chunking out refers to the phenomenon of the tread rubber delaminating near the sipes.

[0059] [Evaluation of chunking performance] Table 1 shows the chunk-out performance of the tires in the examples and comparative examples. The chunk-out performance test described above was performed on the test tires of the examples and comparative examples, and the time until chunk-out occurred was measured. Chunk-out performance is expressed as an index with Comparative Example 1 set to 100, representing the time until the tread rubber chunks out. A higher value indicates that cracks are less likely to occur at the bottom of the sipes, and chunk-out is less likely to occur.

[0060] [Table 1]

[0061] As shown in Table 1, it can be confirmed that the time until chunking out occurs is increased in Examples 1 to 3 compared to Comparative Example 1. In other words, the pneumatic tires of Examples 1 to 3 can effectively suppress the occurrence of chunking out. Furthermore, since the same shaped region is formed for more than 65% of the sipe depth, the wave shape is maintained even in the middle and end stages of wear, thereby improving grip performance. From the above, the pneumatic tires of Examples 1 to 3 can suppress crack formation at the bottom surface of the sipes while improving grip performance on icy and snowy roads in the middle and end stages of wear. [Explanation of symbols]

[0062] 1 pneumatic tire, 10 tread, 20 center block, 21 mediate block, 22 shoulder block, 20a, 21a, 22a small blocks, 30 circumferential groove, 40 axial groove, 50, 60, 70, 80, 90, 100 sipe, 51 first wall surface, 52 second wall surface, 53, 133 straight section, 120 tire molding die, 121 tread die, 122 side die, 123 tread molding surface, 124 main body, 130 sipe blade, 131 base end, 132 tip, CL tire equator

Claims

1. A pneumatic tire having a tread with blocks having sipes formed therein The sipe has one of the following shapes on the block surface: a wave shape, a zigzag shape, or a shape including at least one inflection point. The circumferential cross-sectional shape of the sipe within the block is the same as the sipe shape on the block surface from the block surface to a range of 65% to 80% of the sipe depth. A pneumatic tire in which a flat, straight region is formed along the longitudinal direction of the sipe in at least a portion of a predetermined height region from the bottom surface of the sipe.

2. The pneumatic tire according to claim 1, wherein the predetermined height region is a region from the bottom surface of the sipe to a height of 3% to 15% of the sipe depth.

3. The pneumatic tire according to claim 1, wherein a flat straight region is formed along the longitudinal direction of the sipe across the entire area of ​​the predetermined height region from the bottom surface of the sipe.

4. The pneumatic tire according to claim 1, wherein, when the region from the surface of the block to a range of 65% to 80% of the sipe depth in which the tire circumferential cross-sectional shape of the sipe is the same as the sipe shape is defined as the same-shape region, the tire has a transition region between the same-shape region and the straight region that gradually deforms from the same-shape region toward the straight region.

5. The block includes a center block provided in the tread at the center in the tire axial direction, shoulder blocks provided on both sides in the tire axial direction, and a mediate block provided between the shoulder block and the center block. The number of sipes formed in the mediate block is Less than the number of sipes formed in the center block, The pneumatic tire according to claim 1, wherein the number of sipes formed on the shoulder block is the same as or greater than the number of sipes formed on the shoulder block.

6. The sipe has straight sections at both ends in the longitudinal direction, The pneumatic tire according to any one of claims 1 to 5, wherein the straight section has a shallower sipe depth compared to other areas of the sipe.

7. A tire molding die comprising a tread mold for shaping the surface of a tire tread, and a sipe blade protruding from the tread mold for forming sipes in the blocks of the tread, The sipe blade has one of the following shapes at its base end relative to the tread mold: a wave shape, a zigzag shape, or a shape having at least one bending point. The circumferential cross-sectional shape of the sipe blade is the same as the shape of the sipe blade at the base end, from the base end up to a range of 65% to 80% of the height of the sipe blade. A mold for molding tires, wherein a flat, straight region is formed along the longitudinal direction of the sipe blade on at least a portion of the side surface of the sipe blade in a region of a predetermined height from the tip of the sipe blade.

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