pneumatic tires

Abstract

To provide a pneumatic tire which is excellent in brake performance on a dry road surface and a snow ice road surface.SOLUTION: A pneumatic tire 1 is a tire designated with a rotation direction, and has main grooves 20 and 21, and center blocks 32 and 34 alternately arranged with the main grooves 20 and 21 in a tire circumferential direction. The center blocks 32 and 34 have straight sipes 50, small-amplitude wavy sipes 51, and large-amplitude wavy sipes 52. The straight sipes 50 include terminal sipes arranged closest to both ends in a longitudinal direction of each of the blocks, among a plurality of sipes formed in the center blocks 32 and 34, and the small-amplitude wavy sipes 51 are arranged adjacent to the terminal sipes at least on an equator CL side of the center blocks 32 and 34.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire with a designated rotation direction. [Background technology]

[0002] Directional tires with a specified rotation direction have been known. For example, Patent Document 1 discloses a directional tire with a tread pattern including two main grooves along the tire circumferential direction, a plurality of inclined grooves extending in the tire circumferential direction, a plurality of transverse grooves extending in the tire axial direction, and a plurality of blocks defined by the grooves. Furthermore, each block of the tire of Patent Document 1 is formed with two types of sipes (straight sipes and wavy sipes) that differ in shape in a plan view. Patent Document 2 discloses two or more types of wavy sipes with different wave amplitudes as sipes formed in the tread blocks. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-167930 [Patent Document 2] International Publication No. 2017 / 0928974 Summary of the Invention [Problem to be solved by the invention]

[0004] The shape and arrangement of sipes formed on blocks significantly affect braking performance on snowy and icy roads as well as dry roads. For example, sipes contribute to improving snow performance by increasing the number of edges. However, if the number and arrangement of sipes are inappropriate, block rigidity will decrease, causing the blocks to collapse, reducing the contact area and significantly reducing dry performance. Enhancing edge effect and improving snow performance while maintaining good dry performance is not an easy task, and is a particularly important issue for all-season tires.

[0005] An object of the present invention is to provide a pneumatic tire that has excellent braking performance on dry road surfaces and on snow and ice surfaces. [Means for solving the problem]

[0006] The pneumatic tire according to the present invention is a pneumatic tire having a tread and a specified rotation direction, wherein the tread has main grooves extending from a ground contact edge side toward an equator side and having a greater inclination with respect to the tire axial direction on the equator side than on the ground contact edge side, and blocks formed along the main grooves and arranged alternately with the main grooves in the tire circumferential direction, the blocks including a first block located on the equator side and a second block located on the ground contact edge side, the first block having, in a plan view, a first sipe formed in a straight line, a second sipe formed in a wave shape, and a third sipe formed in a wave shape with a wave amplitude greater than that of the second sipe, the first sipe includes a terminal sipe of a plurality of sipes formed in the first block that is arranged closest to both longitudinal ends of the first block, and the second sipe is arranged adjacent to the terminal sipe at least on the equator side of the first block. [Effects of the Invention]

[0007] The pneumatic tire according to the present invention has excellent braking performance on dry road surfaces and on snowy and icy road surfaces, and is suitable as an all-season tire. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a perspective view showing a portion of a pneumatic tire that is an example of an embodiment. [Figure 2] 1 is a plan view of a pneumatic tire as an example of an embodiment. [Figure 3] FIG. 10 is a diagram showing the area where slits are formed in the center block. [Figure 4] FIG. 3 is an enlarged view of a part of the tread pattern (area A in FIG. 2). [Figure 5] FIG. 2 is a perspective view showing a part (area A) of the tread pattern. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an example of an embodiment of a pneumatic tire 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 embodiment. Furthermore, the present invention includes configurations obtained by selectively combining the respective components of the multiple embodiments and modified examples described below.

[0010] Fig. 1 is a perspective view showing a portion of a pneumatic tire 1 according to an embodiment, and also shows the internal structure of the tire. As shown in Fig. 1, the pneumatic tire 1 has a tread 10, which is the portion that comes into contact with the road surface. The tread 10 extends from the equator CL (see Fig. 2) side toward the tread edge side and has main grooves 20, 21 that are inclined at a larger angle with respect to the tire axial direction on the equator CL side than on the tread edge side, and blocks 30, 31 formed along the main grooves 20, 21, respectively. The main groove 20 and the blocks 30 extend from the equator CL side toward the tread edge E1, and the main groove 21 and the blocks 31 extend from the equator CL side toward the tread edge E2 side.

[0011] The equator CL refers to a line extending in the tire circumferential direction that passes through the exact center of the tread 10 in the tire axial direction (at a position equidistant from the ground contact edges E1, E2). In this specification, the ground contact edges E1, E2 are defined as both axial ends of the area that comes into contact with a flat road surface when a predetermined load is applied to an unused pneumatic tire 1 mounted on a standard rim and inflated to a standard internal pressure. In the case of passenger car tires, the predetermined load is a load equivalent to 88% of the normal load.

[0012] Here, a "regular rim" is a rim specified by the tire standard, and is a "standard rim" for JATMA and a "measuring rim" for TRA and ETRTO. "Regular internal pressure" is the "maximum air pressure" for JATMA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table for TRA, and "INFLATION PRESSURE" for ETRTO. The regular internal pressure is usually 180 kPa for passenger car tires, but 220 kPa for tires labeled "Extra Load" or "Reinforced." "Regular load" is the "maximum load capacity" for JATMA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table for TRA, and "LOAD CAPACITY" for ETRTO. For racing kart tires, the regular load is 392 N.

[0013] The pneumatic tire 1 is a directional tire with a specified rotation direction. FIG. 1 illustrates an arrow indicating the rotation direction of the tire. In this specification, the "rotation direction" of the tire refers to the rotation direction when the vehicle on which the tire is mounted moves forward. For convenience of explanation, the terms "left and right" are used in this specification, and these terms refer to the left and right as viewed from the direction of travel of the vehicle when the tire is mounted on the vehicle. The pneumatic tire 1 preferably has markings to indicate the mounting direction relative to the vehicle. For example, at least one of letters and an arrow indicating the rotation direction is provided on the side of the pneumatic tire 1.

[0014] The tread 10 has a tread pattern in which blocks 30, 31 are arranged in a staggered pattern along the tire circumferential direction. Most of the blocks 30, 31 are arranged on either side of the equator CL on either side of the tread 10. The blocks 30 are formed along the main grooves 20 and are arranged alternately with the main grooves 20 in the tire circumferential direction. The blocks 30 are pairs of blocks including a center block 32 (first block) located on the equator CL side and a shoulder block 33 (second block) located on the ground contact edge E1 side. A secondary groove 22 connecting the two main grooves 20 is formed between the center block 32 and the shoulder block 33, and the secondary groove 22 divides each block 30 into two blocks.

[0015] The blocks 31 are formed along the main grooves 21 and are arranged alternately with the main grooves 21 in the tire circumferential direction. The blocks 31 are pairs of blocks including a center block 34 (first block) located on the equator CL side and a shoulder block 35 (second block) located on the ground contact edge E2 side. A secondary groove 23 connecting the two main grooves 21 is formed between the center block 34 and the shoulder block 35, and the secondary groove 23 divides the block 31 into two blocks.

[0016] The pneumatic tire 1 includes a pair of sidewalls 11 that bulge outward in the tire axial direction, and a pair of beads 12. The beads 12 are fixed to the rim of a wheel and include a bead core 17 and a bead filler 18. The sidewalls 11 and the beads 12 are formed in an annular shape along the tire circumferential direction, and form the side surfaces of the pneumatic tire 1. The sidewalls 11 extend radially from both axial ends of the tread 10.

[0017] The pneumatic tire 1 may have side ribs 13 formed between the ground contact edges E1, E2 of the tread 10 and the portions of the sidewalls 11 that protrude most axially outward in the tire axial direction. The side ribs 13 protrude axially outward and are formed in an annular shape along the tire circumferential direction. The ground contact edges E1, E2 of the pneumatic tire 1 or the portions from their vicinity to the left and right side ribs 13 are also called shoulder or buttress regions. The tread 10 and the sidewalls 11 are generally made of different types of rubber. The shoulders may be made of the same rubber as the tread 10, or a different rubber.

[0018] The tread pattern of the pneumatic tire 1 will be described in detail below with reference to Fig. 2. Fig. 2 is a plan view of the pneumatic tire 1 (tread 10).

[0019] As shown in Fig. 2, the main grooves 20 are formed and spaced at arbitrary intervals in the tire circumferential direction. Similarly, the main grooves 21 are formed and spaced at arbitrary intervals in the tire circumferential direction. The tread 10 has a tread pattern in which the main grooves 20 and the majority of the blocks 30 are arranged closer to the ground contact edge E1 than the equator CL (the left region of the tread 10), and the majority of the main grooves 21 and the blocks 31 are arranged closer to the ground contact edge E2 than the equator CL (the right region of the tread 10). The blocks are portions that protrude outward in the tire radial direction and are generally also called lands.

[0020] The main groove 20 includes two types of main grooves 20A, 20B with different lengths. The main groove 20A is longer than the main groove 20B and is formed with a length that extends beyond the equator CL to the right region of the tread 10. The main groove 20B is formed in the left region of the tread 10 with a length that does not extend beyond the equator CL. The center blocks 32 formed along the main groove 20 include two types of center blocks 32A, 32B with different lengths. The center block 32A is longer than the center block 32B and is formed with a length that extends beyond the equator CL to the right region of the tread 10.

[0021] Similarly, the main groove 21 includes two types of main grooves 21A, 21B with different lengths. The center blocks 34 formed along the main groove 21 include two types of center blocks 34A, 34B with different lengths. The center blocks 32 are formed so that pairs of center blocks 32A, 32B are arranged at a variable pitch around the tire circumferential direction. The center blocks 34 are arranged as pairs of center blocks 34A, 34B with a variable pitch around the tire circumferential direction, and overlap with the center blocks 32 in the tire circumferential direction on and near the equator CL.

[0022] A pair of center blocks 32A, 32B and a pair of center blocks 34A, 34B are alternately arranged along the tire circumferential direction in the axial center of the tread 10. In the left region of the tread 10, the center block 32A, main groove 20B, center block 32B, and main groove 20A are arranged repeatedly in this order along the tire circumferential direction (the same applies to the right region). The pair of center blocks 32A, 32B and the pair of center blocks 34A, 34B are arranged in a staggered pattern along the equator CL.

[0023] The tread pattern of this embodiment is a pattern in which, in a plan view, blocks 30, 31 are arranged symmetrically on the left and right sides of the tire, shifted by a predetermined pitch in the circumferential direction with respect to the equator CL. The shape of the block 30 is the same as the shape of the block 31 when inverted with respect to the equator CL (the same applies to the main grooves 20, 21). If the block 31 inverted at the equator CL is slid in the circumferential direction of the tire, it will coincide with the block 30. The tread pattern of this embodiment has a good left-right balance and is effective in improving steering stability.

[0024] The main groove 20 and the blocks 30 have a curved shape in plan view that is convex toward the rear in the tire rotation direction. The main groove 21 and the blocks 31 also have a curved shape in plan view that is convex toward the rear in the tire rotation direction. The main grooves 20, 21 and the blocks 30, 31 are inclined with respect to the tire axial direction so that they are gradually positioned rearward in the tire rotation direction from the axial center of the pneumatic tire 1 toward both axial sides.

[0025] As described above, the main grooves 20, 21 have a larger inclination angle with respect to the tire axial direction on the equator CL side than on the ground contact edges E1, E2 sides. In other words, the main grooves 20, 21 gradually conform to the tire axial direction from the tire equator CL side toward the ground contact edges E1, E2, and the inclination with respect to the tire axial direction becomes gentler. The inclination angle of the main grooves 20, 21 with respect to the tire axial direction on the tire equator CL side is, for example, 30° to 60° or 40° to 50°.

[0026] The main groove 20 connects to the main groove 21 near the equator CL. The main groove 20 extends from the intersection with the main groove 21 toward the tread edge E1, beyond the tread edge E1, and is formed to extend to the left side rib 13. The main groove 21 extends from the intersection with the main groove 20 near the equator CL toward the tread edge E2, and is formed to extend to the right side rib 13 beyond the tread edge E2. As will be described in detail later, tie bars 36 that connect adjacent blocks are formed in the main grooves 20, 21.

[0027] The width of the main grooves 20, 21 may be constant throughout their entire length, but in this embodiment, they gradually increase from the equator CL side toward the tread edges E1, E2. The width of the main grooves 20, 21 may be greatest, for example, at or near the tread edges E1, E2, or at or near the intersections with the secondary grooves 22, 23. In this case, drainage and snow removal performance is improved, and the snow column shear force that grips and compacts snow is improved, resulting in good wet and snow performance. The pneumatic tire 1 has a main groove 20 that is wider than that of a summer tire.

[0028] The sub-grooves 22, 23 are grooves that are narrower in width (maximum width) than the main grooves 20, 21. The sub-groove 22 extends in the tire circumferential direction, dividing the blocks 30, and connects the main grooves 20A and 20B. The sub-groove 22 is inclined with respect to the tire circumferential direction so as to gradually move away from the ground contact edge E1 from the front to the rear in the tire rotation direction. Similarly, the sub-groove 23 divides the blocks 31, connects the main grooves 21A and 21B, and is inclined with respect to the tire circumferential direction so as to gradually move away from the ground contact edge E2 from the front to the rear in the tire rotation direction. The sub-grooves 22, 23 are formed, for example, to the same depth as the main grooves 20, 21.

[0029] The center blocks 32, 34 are formed with first slits 40, 41 that extend from the main grooves 20, 21, respectively, and terminate within the blocks. The center blocks 32, 34 are large blocks that extend long along the main grooves 20, 21, and the slits 40 are formed within a predetermined range from the center in the longitudinal direction. The slits 40 terminate within the blocks without dividing the center blocks 32, 34. This increases the edge while ensuring the rigidity of the blocks, making it possible to improve snow performance while maintaining good dry and wet performance.

[0030] The center blocks 32 and 34 are further formed with second and third slits. The center blocks 32A and 32B are each formed with second slits 42 and 43, respectively, extending from opposing positions across the main groove 20B and terminating within the block. The center block 32A is also formed with a third slit 46 between the slit 42 and the end of the block on the equator CL side. The center blocks 34A and 34B are each formed with second slits 44 and 45, respectively, and the center block 34A is formed with a third slit 47.

[0031] Sipes are formed in each block of the tread 10. Sipes are grooves that are narrower than the main grooves 20, 21 and the secondary grooves 22, 23, and form edges that catch snow and ice. Sipes also provide drainage through capillary action, contributing to improved braking, driving, and handling stability on snowy and icy roads. Generally, a groove with a groove width of 1.0 mm or less is defined as a sipe. In plan view, the center blocks 32, 34 have straight sipes 50 (first sipes) formed in a straight line, first wave-shaped sipes 51 (second sipes) formed in a wave shape, and second wave-shaped sipes 52 (third sipes) formed in a wave shape with a wave amplitude larger than that of the wave-shaped sipes 51.

[0032] The shoulder blocks 33 are arranged in a row at regular intervals in the tire circumferential direction on the contact edge E1 side of the tread 10. The row of shoulder blocks 33 is composed of blocks of one type having similar shapes. Similarly, the row of shoulder blocks 35 is also formed of blocks of one type arranged in a row at regular intervals in the tire circumferential direction. The shoulder blocks 33, 35 have a gently curved shape in plan view that follows the main grooves 20, 21, and the inclination angle with respect to the tire axial direction is slightly larger on the side of the secondary grooves 22, 23 than on the side rib 13 side.

[0033] Shoulder sipes 53, 54 are formed in each of the shoulder blocks 33, 35. The shoulder sipes 53 extend from the secondary groove 22 past the ground contact edge E1 to the buttress region, but are formed to a length that does not reach the side rib 13. Multiple shoulder sipes 53 (for example, three) are formed along the longitudinal direction of the shoulder block 33. Multiple shoulder sipes 54 are formed along the longitudinal direction of the shoulder block 35, and extend from the secondary groove 23 past the ground contact edge E2 to the buttress region. At least some of the shoulder sipes 53, 54 may be formed in a wavy shape.

[0034] The center blocks 32 and 34 will be described in further detail below with reference to Figures 3 to 5 as appropriate in addition to Figure 2. Figure 3 is a diagram for explaining the area in which the slits 40 are formed. Figure 4 is an enlarged view of region A in Figure 2, and Figure 5 is a perspective view of region A.

[0035] The following describes the block shape and the configuration of the slits and sipes formed in the block, mainly using the center block 32 on the tread edge E1 side as an example. Note that, as mentioned above, the center block 34 on the tread edge E2 side has a configuration inverted from the center block 32 at the equator CL, and therefore the following description of the configuration of the center block 32 also applies to the configuration of the center block 34.

[0036] As shown in Figure 2, the center blocks 32, 34 are formed on both the left and right sides of the equator CL within a predetermined range from the equator CL. By forming the large center blocks 32, 34 in the axial center of the tread 10, excellent braking performance and handling stability on dry roads are achieved. Furthermore, as described above, by forming the slits 40, 41 at a length that does not divide the center blocks 32, 34, it is possible to increase the edge area while maintaining the rigidity of the blocks, thereby achieving good dry / wet and snow performance.

[0037] To improve a tire's snow performance, it is necessary to increase the groove area, the number of sipes, or the edges by dividing the tread into multiple blocks. However, this reduces block rigidity, making it difficult to ensure good dry performance. In the pneumatic tire 1, large center blocks 32, 34 with slits 40 are provided, ensuring a large contact area and high block rigidity, achieving good dry performance, while increasing the edges improves snow performance. While it is possible to ensure block rigidity by forming tie bars in the grooves, this would result in problems such as a reduced contact area and poor drainage.

[0038] The width (length along the tire axis) of the first region R1, which is the region from the end X1 of the center block 32 on the side of the ground contact edge E1 to the end X2 of the center block 34 on the side of the ground contact edge E2, is preferably 50% to 70% of the ground contact width D of the tread 10. The ground contact width D is the length along the tire axis between the ground contact edges E1 and E2. That is, the width of each of the second regions R2, which is the region from the end X1 of the center block 32 to the equator CL and the region from the end X2 of the center block 34 to the ground contact edge E2, is preferably 15% to 25% of the ground contact width D. The ground contact area of ​​the first region R1 is preferably equal to or slightly larger than the ground contact area of ​​the second region R2. In this case, braking performance and handling stability are more significantly improved while maintaining good cornering power characteristics, etc.

[0039] In this embodiment, the length from the equator CL to the end X1 of the center block 32 is the same as the length from the equator CL to the end X2 of the center block 34. Center blocks 32A and 34A are formed on the equator CL, and the center blocks 32A and 34A are arranged alternately along the equator CL. The center blocks 32B and 34B do not overlap in the tire circumferential direction, but are formed separately on the left and right sides of the equator CL. The ends X1 of the center blocks 32A and 32B and the ends X2 of the center blocks 34A and 34B are aligned in the tire circumferential direction.

[0040] As described above, the center block 32 has slits 40 formed therein that extend from the main groove 20 and terminate within the block. In the center block 32A, the slits 40 are formed from the main groove 20A located rearward of the block in the tire rotation direction. Similarly, in the center block 32B, the slits 40 are formed from the main groove 20B located rearward of the block in the tire rotation direction. From the viewpoints of wear resistance, braking performance, etc., it is preferable that the slits 40 be formed on the rear side of the center block 32 in the tire rotation direction.

[0041] In this embodiment, each of the center blocks 32A and 32B has one first slit 40 of the same shape, size, and depth. On the other hand, the second slits 42 and 43 and the third slit 46 are formed with different lengths. As will be described in detail later, the slits 42, 43, and 46 are preferably formed shallower than the slit 40. Note that different first slits may be formed in each of the center blocks 32A and 32B.

[0042] As shown in Figure 3, the slit 40 is formed between the axial center WC of the center block 32A and a point WS located on the equator CL side by a distance (0.3W) equivalent to 30% of the axial length W of the block. The axial center WC is equidistant from both longitudinal ends Xa and Ya of the center block 32A. Forming the slit 40 in this range achieves both high block rigidity and edge effect at a higher level.

[0043] 3 shows the WC and WS of the center block 32A, the slits 40 of the center block 32B are also formed in the same positions as those of the center block 32A. In this embodiment, the slits 40 of the center block 32B are formed closer to the tire axial center WC of the block than the slits 40 of the center block 32A.

[0044] In the center block 32A, the slit 42 is formed closer to the end Xa than the axial center WC, and the slit 44 is formed closer to the end Ya than the point WS. The slit 43 in the center block 32B is formed closer to the end Xb than the axial center of the block. Note that no slits are formed in the center block 32B closer to the equator CL than the slit 40. The axial length W of the center block 32A is, for example, 25% to 35% of the contact width D. The axial length of the center block 32B is shorter than the length W, for example, 70% to 95% of the length W.

[0045] 4 and 5, the center block 32A is a generally rectangular block in plan view, and edges Fa3 and Fa4 along the main grooves 20A and 20B are gently curved so as to convex rearward in the tire rotation direction. Similarly, the center block 32B is generally rectangular in plan view, but its longitudinal length is shorter than that of the center block 32A. Edges Fb3 and Fb4 of the center block 32B are gently curved along the main grooves 20A and 20B. Edges Fa1, Fa2, Fb1, and Fb2 located at both longitudinal ends of the center blocks 32A and 32B are inclined relative to the tire circumferential direction, with the inclination angle of edges Fa2 and Fb2 being larger than that of edges Fa1 and Fb1.

[0046] The edges Fa2 and Fb2 of the center blocks 32A and 32B on the equator CL side are formed along the main groove 21A extending from the tread edge E2 side and face the center block 34A across the main groove 21A. The center blocks 32B and 34A are connected by a tie bar 36, which is a raised portion formed in the main groove 21A. The edges of the center blocks 34A and 34B on the equator CL side face the center block 32A across the main groove 20A. In other words, the edge Fa3 of the center block 32A faces the center blocks 34A and 34B across the main groove 20A.

[0047] The center block 32A is connected to the center block 34B by a tie bar 36 formed in the main groove 20A. The center block 32A and the center block 32B are connected by a tie bar 36 in the main groove 20B, and the center block 34A and the center block 34B are connected by a tie bar 36 in the main groove 21B. The tie bars 36 are formed at the tip of each main groove on the equator CL side. The length of the tie bar 36 along the main groove is, for example, shorter than the length of the slit 40 from the tip of each main groove.

[0048] That is, adjacent center blocks separated by each main groove are connected to each other via tie bars 36 on the equator CL side. That is, because the center blocks are connected in the tire circumferential direction, block rigidity is increased near the equator CL, more effectively improving dry performance. Furthermore, because the tie bars 36 are formed only at the ends of each main groove, good drainage and snow removal performance is ensured. The tie bars 36 are preferably formed at a height of 30% to 70% or 40% to 60% of the depth of the main groove.

[0049] As described above, the slits 40 are formed between the axial center WC of the center blocks 32A, 32B and a point WS (see FIG. 3) on the equator CL side. The slits 40 are preferably formed from the rear side in the tire rotation direction, i.e., from the edge Fa3, Fb3 side of the center blocks 32A, 32B. In this case, the effects of improving wear resistance and braking performance are more pronounced. The slits 40 are formed, for example, to a depth of 10% to 100% of the depth of the main grooves 20A, 20B.

[0050] The depth of the slit 40 is preferably 40% to 100% of the depth of the main grooves 20A, 20B, more preferably 50% to 100%, and particularly preferably 50% to 80%. The slit 40 is preferably formed deeper than the slits 42, 43, and 46. The main grooves 20A, 20B are formed to the same depth, for example, to a constant depth in the first region R1.

[0051] The slits 40 may be formed in a rectangular shape in plan view, but in this embodiment, from the viewpoints of block durability, design, snow removal performance, etc., they have a tapered shape that gradually narrows toward the tip of the block. The length of the slits 40 may be any length that does not cross the center blocks 32A, 32B, but is preferably 50% to 80% of the block width at the portion where the slits 40 are formed. In addition, the depth of the slits 40 may be deepest at the openings connected to the main grooves 20A, 20B and gradually shallower toward the tip of the block.

[0052] The slits 40 are inclined with respect to the tire circumferential direction and the tire axial direction. In this case, the edge effect acts in both the tire circumferential direction and the tire axial direction, and the effect of improving braking performance and steering stability on snowy and icy road surfaces is more pronounced. For example, the slits 40 are inclined more greatly with respect to the tire axial direction. An example of the inclination angle of the slits 40 with respect to the tire axial direction is 50° to 70°.

[0053] The slits 40 of the center blocks 32A and 32B are both formed on an extension of the main groove 21A. Similarly, the slits 41 of the center blocks 34A and 34B are formed on an extension of the main groove 20A. This provides a stable edge effect, and because the slits 40 of the center block 32A are positioned opposite the main groove 21A across the main groove 20A, effective snow pockets are formed, resulting in a more significant improvement in snow performance. The width of the slits 40 is not particularly limited, but it is preferably equal to or smaller than the width at the tip of the main groove 21A.

[0054] The center blocks 32A and 32B are each formed with second slits 42 and 43, which extend from opposing positions across the main groove 20B, i.e., from the edges Fa4 and Fb3 of each block, and terminate within the block. Arranging the slits 42 and 43 facing each other efficiently creates large snow pockets, resulting in a more pronounced improvement in snow performance. Similarly to the slit 40, the slits 42 and 43 also increase the edge area. The slit 42 is formed on the front side of the center block 32A in the tire rotation direction, and the slit 43 is formed on the rear side of the center block 32B in the tire rotation direction.

[0055] The slits 42, 43 are formed between the slit 40 and one longitudinal end Xa, Xb of each block on the ground contact end E1 side. In this embodiment, the slits 42, 43 are formed at positions approximately equidistant from the equator CL and the ground contact end E1. From the standpoint of block rigidity, durability, etc., the slits 42, 43 are preferably formed at positions away from the slit 40 and the ends Xa, Xb, or may be formed exactly halfway between the slit 40 and the ends Xa, Xb.

[0056] The slits 42, 43 may be long enough so as not to cross the blocks, but preferably have a length that is 30% to 80% of the block width at the portion where the slits 42, 43 are formed. The slits 42, 43 may be formed to have the same length, but in this embodiment, the slit 42 is longer than the slit 43. For example, the slit 42 has a length that is 50% to 80% of the block width, and the slit 43 has a length that is 30% to 50% of the block width. In this case, it becomes easier to achieve both high block rigidity and good snow performance.

[0057] The slits 42 and 43 may be formed to the same depth as the slit 40, but are preferably formed shallower than the slit 40 from the viewpoint of the rigidity, durability, etc. of the block. The slits 42 and 43 are preferably formed to a depth of 15% to 30% of the depth of the main grooves 20A and 20B. Like the slit 40, the slits 42 and 43 have a tapered shape that gradually narrows toward the end within the block. The depth of the slits 42 and 43 is deepest at the openings connected to the main grooves 20A and 20B and gradually shallows toward the end within the block. The width of the slits 42 and 43 is not particularly limited, but is preferably equal to or smaller than the width of the slit 40.

[0058] The slits 42, 43 are inclined with respect to the tire circumferential direction and the tire axial direction. In this case, an edge effect is exerted in both the tire circumferential direction and the tire axial direction. The slits 42, 43 are formed, for example, parallel to the slit 40 or closer to the tire circumferential direction than the slit 40, and are inclined more with respect to the tire axial direction. An example of the inclination angle of the slits 42, 43 with respect to the tire axial direction is 50° to 70°.

[0059] The center block 32A has a slit 46 formed between the slit 40 and the other longitudinal end Ya on the equator CL side. The slit 46 is formed on the rear side of the center block 32A in the tire rotation direction, extends from the main groove 20A, and terminates within the block. Like the slit 40, the slit 46 is inclined with respect to the tire circumferential direction and tire axial direction, and is formed, for example, parallel to the slit 40. Note that no slit is formed in the center block 32B on the equator CL side of the slit 40.

[0060] Like slits 40 and the like, slits 46 have a tapered shape that gradually narrows toward the end within the block. The depth of slit 46 is deepest at the opening portion connected to main grooves 20A, 20B and gradually shallows toward the end within the block. Slit 46 may be formed to the same depth as slit 40, but is preferably formed to a depth that is 15% to 30% of the depth of main grooves 20A, 20B. The length of slit 46 may be shorter than the length of slit 40 and may be 20% to 50% of the width of the block at the portion where slit 46 is formed.

[0061] The slits 46 are formed on an extension of the main groove 21B. Like other slits, the slits 46 contribute to the formation of snow pockets and the improvement of edge effect while suppressing a decrease in block rigidity. The width of the slits 46 is not particularly limited, but is preferably equal to or smaller than the width at the tip of the main groove 21B.

[0062] As described above, a plurality of sipes are formed in the center blocks 32A and 32B. The plurality of sipes includes, in a plan view, straight sipes 50 formed in a straight line, first wave-shaped sipes 51 formed in a wave shape, and second wave-shaped sipes 52 formed in a wave shape with a larger wave amplitude than the wave-shaped sipes 51. While wave-shaped sipes contribute to an increase in edge compared to straight sipes, they tend to further reduce block rigidity. For this reason, as will be described in detail later, it is necessary to appropriately determine the formation locations of the wave-shaped sipes.

[0063] To improve a tire's snow performance, it is necessary to increase the edge by increasing the number of sipes or forming longer sipes. However, increasing the number of sipes reduces block rigidity and reduces the contact area due to block collapse. Block collapse reduces dry and wet performance, and excessive collapse can also lead to reduced snow performance. Furthermore, if the sipes are formed into a wave shape and the sipe length is increased, the high ground contact pressure acting on the acute angles of the waves can cause block damage. In the pneumatic tire 1, high block rigidity and edge effect are achieved at a high level by appropriately arranging the straight sipes 50 and two types of wave sipes 51 and 52.

[0064] The waves of the wavy sipes 51, 52 are convex portions in a direction perpendicular to the longitudinal direction of the sipe, and are formed in a generally triangular shape in a plan view. The wavy sipes 51, 52 have straight portions formed in a straight line and wave portions with multiple repeated waves. The straight portions are formed at both ends of the wavy sipes 51, 52 in the longitudinal direction, and the wave portions are formed between the straight portions. The wave portions are formed by bending the sipe in a zigzag shape so that they are convex on both sides of a center line α (see FIG. 4) connecting both ends of the sipe in the longitudinal direction. In this specification, the amplitude of the wavy sipe means the distance from the center line α to the peak P of the largest wave.

[0065] The amplitude of the wavy sipes 51 is, for example, constant for each wave, and the wavy portions of the wavy sipes 51 are formed regularly at a constant cycle. An example of the amplitude of the wavy sipes 51 is 0.5 mm to 3.0 mm. Similarly, for the wavy sipes 52, the multiple waves have a constant amplitude, and the wavy portions are formed regularly at a constant cycle. The amplitude of the wavy sipes 52 is larger than the amplitude of the wavy sipes 51, for example, two to five times the amplitude of the wavy sipes 51. An example of the amplitude of the wavy sipes 52 is 1.0 mm to 5.0 mm.

[0066] Each sipe is preferably formed deeper than the slits 42, 43, 46, for example, 50% to 90% of the depth of the main grooves 20A, 20B. The depth of the straight sipe 50 may be shallower than the depth of the wavy sipes 51, 52. A suitable example of the depth of the straight sipe 50 is 50% to 70% of the depth of the main grooves 20A, 20B.

[0067] The straight sipes 50 include terminal sipes that are located closest to both longitudinal ends of each block among the multiple sipes formed in the center blocks 32A, 32B. In other words, the sipes formed closest to both longitudinal ends of each block are straight sipes 50. Since large ground pressure is likely to act on both longitudinal ends of the center blocks 32A, 32B and particularly high durability is required, it is preferable to arrange the straight sipes 50 to impart an edge effect while suppressing a decrease in block rigidity.

[0068] Terminal sipes (straight sipes 50) on the equator CL side of the center blocks 32A, 32B are formed from edges Fa2, Fb2 along the main groove 21A to edges Fa4, Fb4 along the main grooves 20A, 20B, respectively. Terminal sipes on the ground contact edge E1 side of each block are formed from edges Fa3, Fb3 along the main grooves 20A, 20B to edges Fa1, Fb1 along the secondary groove 22, respectively. Sipes other than the terminal sipes are also formed to traverse the blocks in the same manner, except for some sipes formed near the slits 40.

[0069] Each center block 32A, 32B has a plurality of sipes spaced apart along the length of the block, with straight sipes 50 serving as terminal sipes. The spacing between each sipe is constant, and adjacent sipes are parallel to each other in the longitudinal direction. As will be described in more detail later, the inclination of the sipes relative to the tire axial direction varies between the equator CL side and the tread edge E1 side, separated by a slit 40.

[0070] Small-amplitude wavy sipes 51 are arranged adjacent to the terminal sipes on the equator CL side of the center blocks 32A, 32B. Of the longitudinal ends of each block, greater ground pressure acts particularly on the end on the equator CL side. Therefore, by arranging the straight sipes 50 and then the wavy sipes 51, it becomes easier to enhance the edge effect while ensuring the durability of the blocks. A large-amplitude wavy sipe 52 is arranged adjacent to the wavy sipe 51 on the opposite side of the terminal sipe.

[0071] Large-amplitude wavy sipes 52 are arranged adjacent to the terminal sipes on the ground-contact edge E1 side of the center blocks 32A, 32B. Because the ground pressure is lower at the end of each block on the ground-contact edge E1 side than on the equator CL side, it is preferable to increase the sipe length and increase the edge length to improve snow performance. In this embodiment, straight sipes 50 and wavy sipes 52 are arranged in this order from the end on the ground-contact edge E1 side, and multiple wavy sipes 52 are arranged continuously up to the vicinity of the slits 40.

[0072] Sipes are connected to the slits 40. From the viewpoint of ensuring block rigidity, etc., the sipes connected to the slits 40 are preferably straight sipes 50 or small-amplitude wave-shaped sipes 51. In this embodiment, two straight sipes 50 are connected to the slits 40 of the center block 32A, and one straight sipe 50 and one wave-shaped sipe 51 are connected to the slits 40 of the center block 32B. The straight sipes 50 and the small-amplitude wave-shaped sipes 51 are formed up to the edges of the slits 40, but are not formed inside the slits 40. On the other hand, the large-amplitude wave-shaped sipes 52 cross the slits 42, 43, and 46 and are also formed inside each slit.

[0073] In the center block 32A, straight sipes 50, small amplitude wave-shaped sipes 51, and large amplitude wave-shaped sipes 52 are arranged in this order from the slit 40 side. In the portion closer to the equator CL than the slit 40, the wave-shaped sipes 51 adjacent to the straight sipes 50 do not connect to the slit 40 and terminate within the block. In the equator CL side portions of the center blocks 32A and 32B, a group of sipes is formed that is arranged in this order from the slit 40 side: straight sipe 50, wave-shaped sipe 51, two wave-shaped sipes 52, wave-shaped sipe 51, and straight sipe 50 (terminal sipe).

[0074] The center block 32A has a sipe group formed on its ground-contact edge E1 side in the following order from the slit 40: a straight sipe 50, a wavy sipe 51, five wavy sipes 52, and a terminal sipe. On the other hand, the center block 32B has a sipe group formed on its ground-contact edge E1 side in the following order from the slit 40: a wavy sipe 51, four wavy sipes 52, and a terminal sipe. That is, the sipe group of the center block 32B has one less straight sipe 50 and one less wavy sipe 52 than the center block 32A.

[0075] In both center blocks 32A and 32B, the sipes formed closer to the equator CL than the slits 40 are aligned more in the tire axial direction than the sipes formed closer to the tread edge E1 than the slits 40. The sipes on the equator CL side are aligned parallel to the tire axial direction, and are inclined at an angle of, for example, 5° to 20° relative to the tire axial direction. This provides a more pronounced improvement in braking performance and handling stability. [Example]

[0076] The present invention will be further explained below with reference to examples, but the present invention is not limited to these examples.

[0077] Example 1 A pneumatic tire A1 (tire size: 205 / 55R16 91H) was manufactured having the tread pattern shown in Figures 1 to 5. As described above, the terminal sipes of each center block were straight sipes, and the sipes adjacent to the terminal sipes were small-amplitude wavy sipes on the equator CL side and large-amplitude wavy sipes on the tread edge side.

[0078] <Comparative Example 1> Except for changing the sipe formation pattern of the center block, a pneumatic tire B1 was produced in the same manner as in Example 1. The terminal sipes of each center block were a mixture of straight sipes and small-amplitude wavy sipes, and the sipes on the ground-contact edge side adjacent to the terminal sipes were changed to small-amplitude wavy sipes.

[0079] The snow braking performance and dry braking performance of the pneumatic tires A1 and B1 were evaluated by the following method, and the evaluation results are shown in Table 1. The evaluation results in Table 1 are relative values, with the value of pneumatic tire B1 being set at 100.

[0080] [Snow braking performance evaluation] An actual vehicle (with two occupants) fitted with test tires (pneumatic tires A1 and B1) was driven on snow, and braking force was applied at 40 km / h to activate the ABS, and the braking distance was measured and the reciprocal was calculated. The results for pneumatic tire B1 of Comparative Example 1 were evaluated using an index of 100, with a higher index indicating better snow braking performance (the same applies below).

[0081] [Dry braking performance evaluation] A real vehicle (with two occupants) fitted with test tires was driven on a dry road surface, and the braking distance was measured when braking force was applied at 100 km / h to activate the ABS, and the reciprocal of this distance was calculated.

[0082] [Table 1]

[0083] As described above, the pneumatic tire 1 (pneumatic tire A1 of the embodiment) having the above configuration has excellent braking performance on snowy and icy road surfaces and dry road surfaces. The pneumatic tire 1 is a directional tire with a specified rotation direction, and is suitable as an all-season tire.

[0084] The tread pattern of the pneumatic tire 1 has straight sipes 50 and two types of wavy sipes 51, 52 formed in a specific pattern in large center blocks 32, 34 extending long along the main grooves 20, 21, achieving both high block rigidity and a high level of edge effect. The pneumatic tire 1 can effectively increase the edges while ensuring high block rigidity and a large contact area, thereby improving snow performance while maintaining good dry and wet performance. As is clear from the comparative example, if the sipe formation pattern is inappropriate, dry and snow performance will be significantly reduced.

[0085] The above-described embodiment can be appropriately modified without departing from the scope of the present invention. For example, in the tread pattern of the pneumatic tire according to the present invention, the configuration of the first to third slits is particularly useful for improving snow performance, but it is possible to achieve the objectives of the present invention by changing these configurations to other configurations. As long as the objectives of the present invention are not impaired, grooves that cross the blocks may be formed in place of the first slits for at least some of the center blocks. [Explanation of symbols]

[0086] 1 pneumatic tire, 10 tread, 11 sidewall, 12 bead, 13 side rib, 14 carcass, 15 belt, 16 inner liner, 17 bead core, 18 bead filler, 20, 20A, 20B, 21, 21A, 21B main groove, 22, 23 secondary groove, 30, 31 block, 32, 32A, 32B, 34, 34A, 34B center block, 33, 35 shoulder block, 36 tie bar, 40, 41, 42, 43, 44, 45, 46, 47 slit, 50 straight sipe, 51, 52 wave-shaped sipe, 53, 54 shoulder sipe, CL tire equator, E1, E2 ground contact edge, R1 first region, R2 second region

Claims

1. A pneumatic tire having a tread and a designated direction of rotation, The tread is a main groove extending from the equator side toward the tread edge side, the main groove having a greater inclination with respect to the tire axial direction on the equator side than on the tread edge side; blocks formed along the main grooves and arranged alternately with the main grooves in the tire circumferential direction; and the blocks include a first block located on the equator side and a second block located on the ground contact end side, The first block has, in a plan view, a first sipe formed in a straight line, a second sipe formed in a wave shape, and a third sipe formed in a wave shape and having a wave amplitude larger than that of the second sipe, The first sipes include terminal sipes that are arranged closest to both ends of the first block in the longitudinal direction among the plurality of sipes formed in the first block, and the second sipes are arranged adjacent to the terminal sipes at least on the equator side of the first block, the third sipe is disposed adjacent to the terminal sipe on the ground contact end side of the first block.

2. a slit extending from the main groove and terminating within the first block is formed in the first block; 2. The pneumatic tire according to claim 1, wherein the slit is formed between an axial center of the first block and a point located on the equator side by a length equivalent to 30% of the axial length of the first block.

3. A pneumatic tire having a tread and a designated direction of rotation, The tread is a main groove extending from the equator side toward the tread edge side, the main groove having a greater inclination with respect to the tire axial direction on the equator side than on the tread edge side; blocks formed along the main grooves and arranged alternately with the main grooves in the tire circumferential direction; and the blocks include a first block located on the equator side and a second block located on the ground contact end side, The first block has, in a plan view, a first sipe formed in a straight line, a second sipe formed in a wave shape, and a third sipe formed in a wave shape and having a wave amplitude larger than that of the second sipe, The first sipes include terminal sipes that are arranged closest to both ends of the first block in the longitudinal direction among the plurality of sipes formed in the first block, and the second sipes are arranged adjacent to the terminal sipes at least on the equator side of the first block, a slit extending from the main groove and terminating within the first block is formed in the first block; The pneumatic tire, wherein the sipe connected to the slit is the first sipe or the second sipe.

4. A pneumatic tire having a tread and a designated direction of rotation, The tread is a main groove extending from the equator side toward the tread edge side, the main groove having a greater inclination with respect to the tire axial direction on the equator side than on the tread edge side; blocks formed along the main grooves and arranged alternately with the main grooves in the tire circumferential direction; and the blocks include a first block located on the equator side and a second block located on the ground contact end side, The first block has, in a plan view, a first sipe formed in a straight line, a second sipe formed in a wave shape, and a third sipe formed in a wave shape and having a wave amplitude larger than that of the second sipe, The first sipes include terminal sipes that are arranged closest to both ends of the first block in the longitudinal direction among the plurality of sipes formed in the first block, and the second sipes are arranged adjacent to the terminal sipes at least on the equator side of the first block, a slit extending from the main groove and terminating within the first block is formed in the first block, and the first sipe, the second sipe, and the third sipe are arranged in this order from the slit side.

5. The pneumatic tire according to any one of claims 2 to 4, wherein a group of sipes formed in a portion closer to the equator than the slits are formed so as to be aligned in the tire axial direction compared to a group of sipes formed in a portion closer to the ground contact edge than the slits.

6. A pneumatic tire having a tread and a designated direction of rotation, The tread is a main groove extending from the equator side toward the tread edge side, the main groove having a greater inclination with respect to the tire axial direction on the equator side than on the tread edge side; blocks formed along the main grooves and arranged alternately with the main grooves in the tire circumferential direction; and the blocks include a first block located on the equator side and a second block located on the ground contact end side, The first block has, in a plan view, a first sipe formed in a straight line, a second sipe formed in a wave shape, and a third sipe formed in a wave shape and having a wave amplitude larger than that of the second sipe, The first sipes include terminal sipes that are arranged closest to both ends of the first block in the longitudinal direction among the plurality of sipes formed in the first block, and the second sipes are arranged adjacent to the terminal sipes at least on the equator side of the first block, a slit extending from the main groove and terminating within the first block is formed in the first block; A pneumatic tire, wherein a group of sipes formed in a portion closer to the equator than the slits are formed to extend along the tire axial direction, compared to a group of sipes formed in a portion closer to the ground contact edge than the slits.

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