pneumatic tires

Abstract

To provide a pneumatic tire that can achieve a good balance of improved performance on ice and snow. [Solution] The tread 2 includes a plurality of ridges 6, including a rib-shaped central ridge 100 positioned on the tire equator E and extending continuously in an annular manner in the tire circumferential direction, and circumferential grooves 7 on both sides of the central ridge 100 in the tire axial direction, wherein the central ridge 100 has a first central sipe 110 having a portion extending in a direction intersecting the tire circumferential direction, and a second central sipe 120 having a portion extending in a direction intersecting the tire circumferential direction, the first central sipe 110 terminating within the central ridge 100, and the second central sipe 120 communicating with the circumferential grooves 7 and having a wavy shape at least on the tire surface, the total length of the second central sipe 120 on the surface of the central ridge 100 being longer than the total length of the first central sipe 110 on the surface of the central ridge 100.

Description

Technical Field

[0001] The present invention relates to pneumatic tires.

Background Art

[0002] Conventionally, pneumatic tires called studless tires are known, which have a large number of thin cuts called sipes on the tread surface that contacts the road surface, and braking performance and traction performance are ensured even on icy and snowy roads depending on the function of the sipes and the properties of the rubber. For example, Patent Document 1 shows that kind of pneumatic tire in which a large number of sipes are formed on the land at the center in the tire axial direction that is divided in the tire circumferential direction.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, improvement in ice driving performance has been particularly desired for studless tires, and for that purpose, it is necessary to increase the contact area of the tire. For example, when the land portion at the center in the tire axial direction as shown in the above Patent Document 1 is divided in the tire circumferential direction, it can be said that it is disadvantageous for increasing the contact area. Here, in addition to increasing the contact area, it has been considered to improve the snow driving performance as well as the ice driving performance by devising the arrangement and shape of the sipes.

[0005] Therefore, an object of the present invention is to provide a pneumatic tire capable of achieving a good balance in improving ice driving performance and snow driving performance.

Means for Solving the Problems

[0006] The pneumatic tire of the present invention comprises a tread including a plurality of ridges, including a rib-shaped central ridge positioned on the tire equator and extending continuously in an annular manner in the tire circumferential direction, and circumferential grooves on both sides of the central ridge in the tire axial direction, wherein the central ridge has a first central sipe having a portion extending in a direction intersecting the tire circumferential direction, and a second central sipe having a portion extending in a direction intersecting the tire circumferential direction, the first central sipe terminating within the central ridge, the second central sipe communicating with the circumferential groove and having a wavy shape at least on the tire surface, and the total length of the second central sipe on the surface of the central ridge is longer than the total length of the first central sipe on the surface of the central ridge. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a pneumatic tire that can achieve a good balance in improving ice driving performance and snow driving performance. [Brief explanation of the drawing]

[0008] [Figure 1] This is a perspective view of a tire (pneumatic tire) according to an embodiment, partially showing a portion of the tire in the circumferential direction. [Figure 2] This is a partially enlarged front view showing the tread surface of a tire according to an embodiment. [Figure 3] This is an enlarged view of the area shown in III in Figure 1. [Figure 4] This is a plan view showing the first central sipe of the tire according to the embodiment. [Figure 5] This is a cross-sectional view of the tire showing the first central sipe. [Figure 6] This is a cross-sectional view taken from VI-VI in Figure 4. [Figure 7A] This is a schematic cross-sectional diagram illustrating the deformation process of the first central sipe that contacts the road surface, showing the initial state of tire pressure. [Figure 7B] This diagram shows the state immediately after the initial stage of tire compression during the process described above. [Figure 7C] This figure shows the state of the tire during the mid-stage of contact with the ground during the process described above. [Figure 7D] This figure shows the state immediately after the mid-stage of tire contact during the process described above. [Figure 7E] This diagram shows the state of the tire when it is being kicked out during the process described above. [Figure 8] This is an enlarged view of Figure 7B. [Figure 9] This figure shows the contact surface shape of a tire according to an embodiment and illustrates the rectangularity of the contact surface shape. [Figure 10] This is a schematic cross-sectional view showing a tire molding die for forming a tire according to the embodiment. [Modes for carrying out the invention]

[0009] The embodiments will be described below with reference to the drawings. Figure 1 is a partial perspective view showing a part of the circumferential direction of tire 1 as a pneumatic tire according to the embodiment. Tire 1 according to the embodiment is, for example, a pneumatic tire for a passenger car. The configuration of tire 1 according to the embodiment can be used for various vehicles other than passenger cars, such as light trucks, trucks, and buses.

[0010] As shown in Figure 1, the tire 1 comprises a tread 2 which includes the outer circumference of the tire and is the part that contacts the road surface, a pair of beads 3 which are the parts that are fitted onto the rim of a tire wheel (not shown), a pair of sidewalls 4 which are positioned between the tread 2 and each bead 3 and constitute the side wall surface of the tire, and a shoulder 5 between each sidewall 4 and the tread 2. The tread 2 includes a tread surface 2A which contacts the road surface, and a tread pattern 2B is formed on the tread surface 2A by a plurality of types of grooves and other features. The tread pattern 2B in this embodiment is asymmetrical in the tire axial direction. Each of the pair of sidewalls 4 has a buttress 8 on its radially outer side where it transitions to the shoulder 5.

[0011] FIG. 2 is a partially enlarged front view of the tire 1, showing the tread surface 2A, a pair of sidewalls 4, a pair of shoulders 5 and a pair of battless 8. FIG. 3 is an enlarged view of the portion indicated by III in FIG. 2. In FIGS. 2 and 3, the tire axial direction X, the tire circumferential direction C and the tire equator E are shown. The tire equator E is a virtual line extending along the tire circumferential direction at the center in the tire axial direction. In FIGS. 2 and 3, one side (the right side in FIGS. 2 and 3) in the tire axial direction X is indicated by an arrow X1, and the other side (the left side in FIGS. 2 and 3) is indicated by an arrow X2. Also, in FIGS. 2 and 3, one side (the lower side in FIG. 1) in the tire circumferential direction C is indicated by an arrow C1, and the other side (the upper side in FIG. 1) is indicated by an arrow C2. Regarding these reference signs, the same applies to FIG. 4.

[0012] The grooves forming the tread pattern 2B include circumferential grooves, slits, lug grooves, sipes, etc. including main grooves and sub-grooves as will be described later. The circumferential grooves are basically grooves along the tire circumferential direction, and the slits, lug grooves and sipes are basically grooves extending in a direction intersecting the tire circumferential direction. The widths of these grooves are such that the width of the main groove is the largest and the width of the sipe is the smallest. The widths of various sipes in the embodiment are, for example, about 0.3 mm or more and less than 1.0 mm, and the depths are, for example, about 5 mm or more and 11 mm or less, but are not limited thereto. The widths of each of the sub-grooves, slits and lug grooves are basically common in that they are smaller than the main groove and larger than the sipe, but may have the same width or may have differences.

[0013] As shown in FIG. 2, the tread 2 includes a plurality of lands 6 arranged in the tire axial direction and a plurality of circumferential grooves 7 extending in the tire circumferential direction for partitioning the plurality of lands 6 in the tire axial direction. Each of the plurality of lands 6 extends in the tire circumferential direction. The battless 8 includes a first battless 8A on one side X1 in the tire axial direction and a second battless 8B on the other side X2 in the tire axial direction.

[0014] The plurality of lands 6 includes a central land 100 that is on the tire equator E and disposed at the center in the tire axial direction, a first intermediate land 200 disposed on one side X1 in the tire axial direction of the central land 100, a second intermediate land 300 disposed on the other side X2 in the tire axial direction of the central land 100, a first shoulder land 400 disposed on one side X1 in the tire axial direction of the first intermediate land 200, and a second shoulder land 500 disposed on the other side X2 in the tire axial direction of the second intermediate land 300. Each of the first shoulder land 400 and the second shoulder land 500 is an example of the shoulder land according to the present disclosure disposed at both ends in the tire axial direction of the tread 2. Each of the first intermediate land 200 and the second intermediate land 300 is an example of the intermediate land according to the present disclosure disposed between the central land and the shoulder land.

[0015] The maximum widths of the first intermediate land 200 and the second intermediate land 300 in the embodiment are substantially the same and are larger than the maximum width of the central land 100. The widths of the first shoulder land 400 and the second shoulder land 500 in the embodiment are substantially the same and are larger than the widths of the first intermediate land 200 and the second intermediate land 300. Note that the width of each land 6 is not limited in this way and may be arbitrary.

[0016] The plurality of circumferential grooves 7 includes a sub-groove 600 between the central land 100 and the first intermediate land 200, a first main groove 700 between the central land 100 and the second intermediate land 300, a second main groove 800 between the first intermediate land 200 and the first shoulder land 400, and a third main groove 900 between the second intermediate land 300 and the second shoulder land 500. The maximum width of each of the main grooves 700, 800, 900 is, for example, about 4 mm or more and 8 mm or less, and the depth is, for example, about 8 mm or more and 9.5 mm or less, but is not limited thereto. The sub-groove 600 has a maximum width and depth smaller than those of each of the main grooves 700, 800, 900. For example, the maximum width is about 2 to 5 mm, and the depth is about 6 mm or more and 7.5 mm or less, but is not limited thereto.

[0017] The secondary groove 600 of the embodiment has an overall zigzag shape. The first main groove 700 of the embodiment is a groove that is straight along the circumferential direction of the tire and has a substantially constant width. The second main groove 800 and the third main groove 900 of the embodiment have a zigzag shape. The groove shape of these circumferential grooves 7 on the tread surface 2A is not limited and may be arbitrary.

[0018] As shown in Figure 3, the central landmass 100 comprises a plurality of first central sipes 110, a plurality of second central sipes 120, and a plurality of third central sipes 130.

[0019] Multiple first central sipes 110 are arranged in a substantially central region in the width direction of the central ridge 100. Multiple first central sipes 110 are spaced apart in the circumferential direction of the tire. Figure 4 is an enlarged plan view of the first central sipe 110. As shown in Figure 4, the first central sipe 110 has a surface shape on the tread surface 2A that can be described as substantially S-shaped or crank-shaped, and includes a central straight section 111 extending in the axial direction of the tire, a first end straight section 112 extending from one end X1 on the axial side of the central straight section 111 to one end C1 in the circumferential direction of the tire, and a second end straight section 113 extending from the other end X2 on the axial side of the central straight section 111 to the other end C2 in the circumferential direction of the tire. The central straight section 111 is the portion that intersects with the circumferential direction of the tire. The first central sipe 110 does not communicate with either the secondary grooves 600 or the first main groove 700 on either side of the tire axial direction, and both ends terminate within the central land 100.

[0020] The length of the central straight section 111 is, for example, about 5 mm, and preferably between 3 mm and 10 mm. The lengths of the first end straight section 112 and the second end straight section 113 are, for example, about 2.1 mm, and preferably between 1.5 mm and 3 mm.

[0021] As described above, the multiple first central sipes 110 of the embodiment are arranged in a substantially central region in the width direction of the central land 100. This central region may be located within a region that occupies up to 60% of the width of the central land 100, and preferably within a region that occupies 40% of that width.

[0022] The axial length of the first central sipe 110 is preferably 20% to 60% of the width of the central sipe 100.

[0023] As shown in Figure 3, the multiple second central sipes 120 are located on one side X1 and the other side X2 of the first central sipe 110 in the tire axial direction. The multiple second central sipes 120 are spaced apart in the tire circumferential direction. The second central sipes 120 have a wavy surface shape on the tread surface 2A. The overall extending direction of the second central sipes 120 is inclined to extend towards one side C1 in the tire circumferential direction as it moves from the end of the other side X2 in the tire axial direction toward the end of the one side X1 in the tire axial direction. The second central sipes 120 located on one side X1 in the tire axial direction of the first central sipe 110 communicate with the secondary groove 600. The second central sipes 120 located on the other side X2 in the tire axial direction of the first central sipe 110 communicate with the first main groove 700.

[0024] The second central sipe 120 is preferably a 3D sipe. A 3D sipe, as used herein, is a sipe that is three-dimensional in the direction of extension of the second central sipe 120 (the length direction from one end to the other) by being bent in a wave-like shape, and also has a bent portion in the sipe depth direction, making it three-dimensional.

[0025] Preferably, the sum of the sipe lengths of all the second central sipes 120 on the surface of the central landmass 100, i.e., the total length, is longer than the sum of the sipe lengths of the first central sipes 110 on the surface of the central landmass 100, i.e., the total length. Here, sipe length refers to the total length tracing the shape of the sipes on the surface of the central landmass 100.

[0026] Multiple third central sipes 130 are located on one side X1 of the tire axial direction of the first central sipe 110. The third central sipes 130 have a wavy surface shape on the tread surface 2A. The third central sipes 130 are located between a predetermined pair of second central sipes 120 that are adjacent in the tire circumferential direction, among the second central sipes 120 located on one side X1 of the tire axial direction of the first central sipe 110. The overall extension direction of the third central sipes 130 is substantially parallel to that of the second central sipes 120. The third central sipes 130 are adjacent to the sub-grooves 600 but do not communicate with the sub-grooves 600, and both ends terminate within the central land 100.

[0027] In this embodiment, the width of the second central sipe 120 and the width of the third central sipe 130 are approximately the same, and the width of the first central sipe 110 is greater than the widths of the second central sipe 120 and the third central sipe 130, but this is not limited to this.

[0028] As shown in Figures 2 and 3, the central land bridge 100 includes a plurality of first central slits 140 and a plurality of second central slits 150 extending in a direction intersecting the tire circumferential direction. Each of the first central slits 140 and the second central slits 150 is spaced apart in the tire circumferential direction. The width of the first central slits 140 and the second central slits 150 is, for example, approximately 3.0 mm to 6 mm, but is not limited thereto. The depth is, for example, approximately 7.0 mm to 8.5 mm for the first slits 140 and approximately 4.0 mm to 5.5 mm for the second slits 150, but is not limited thereto.

[0029] The first central slit 140 has one end X1 on the tire axial direction that communicates with the sub-groove 600. The first central slit 140 extends from the end communicating with the sub-groove 600 to the other end X2 on the tire axial direction, and terminates just before reaching the first main groove 700. As a result, the central ridge 100 has a rib shape that extends continuously in an annular manner in the tire circumferential direction. The first central slit 140 is inclined with respect to the tire axial direction so that it extends to the other end C2 on the tire circumferential direction as it moves from the end communicating with the sub-groove 600 toward the other end X2 on the tire axial direction. The end portion of the first central slit 140 toward the other end X2 on the tire axial direction has a hook-shaped portion 141 that extends toward the one end C1 on the tire circumferential direction as it moves toward the other end X2 on the tire axial direction. The first central slit 140 extends across the tire equator E. In the first central slit 140 of this embodiment, the tire equator E passes near the starting end of the hook-shaped portion 141.

[0030] The second central slit 150 has one end X2 on the other side of the tire axial direction that communicates with the first main groove 700. The second central slit 150 extends from one end communicating with the first main groove 700 toward one side X1 in the tire axial direction and terminates just before reaching the sub-groove 600. The second central slit 150 is inclined with respect to the tire axial direction so that as it moves from one end communicating with the first main groove 700 toward one side X1 in the tire axial direction, it extends toward one side C1 in the tire circumferential direction. The second central slit 150 extends across the tire equator E.

[0031] The first central slit 140 and the second central slit 150 are arranged alternately in the circumferential direction of the tire. A predetermined number of first central sipes 110, second central sipes 120, and third central sipes 130 are arranged between adjacent first central slits 140 and second central slits 150 in the circumferential direction of the tire.

[0032] As shown in Figures 2 and 3, the first intermediate ridge 200 includes a plurality of first intermediate blocks 210 arranged in the circumferential direction of the tire, and a plurality of first intermediate slits 220 extending in a direction intersecting the circumferential direction of the tire. The plurality of first intermediate slits 220 are spaced apart in the circumferential direction of the tire. The first intermediate slits 220 traverse the first intermediate ridge 200 and communicate with the secondary groove 600 and the second main groove 800. The width and depth of the first intermediate slits 220 are equivalent to those of the first central slit 140.

[0033] As shown in Figure 3, the first intermediate slit 220 has a first bent portion 221 that protrudes to one side C1 in the tire circumferential direction. The first bent portion 221 is formed in the first intermediate slit 220 at a position closer to one side X1 in the tire axial direction. The first intermediate slit 220 has a first inclined portion 222 that extends from the first bent portion 221 to the second main groove 800, and a second inclined portion 223 that extends from the first bent portion 221 to the sub-groove 600. When viewed from the first bent portion 221 as the starting point, the first inclined portion 222 and the second inclined portion 223 are inclined with respect to the tire axial direction such that they extend to the other side C2 in the tire circumferential direction as they extend away from the first bent portion 221 in the tire axial direction. The first intermediate slit 220 has a first protruding recess 224 on one side C1 in the tire circumferential direction of the first bent portion 221 that protrudes to one side X1 in the tire axial direction.

[0034] Each of the multiple first intermediate blocks 210 is partitioned into a substantially rectangular shape by a sub-groove 600, a second main groove 800, and a pair of first intermediate slits 220 adjacent to each other in the circumferential direction of the tire. The first intermediate slits 220 are an example of block-forming grooves according to the present disclosure. The first intermediate block 210 is an example of a block according to the present disclosure partitioned in the circumferential direction of the tire by the block-forming grooves. The first central slit 140 of the central base 100 extends on the extension of the first intermediate slits 220, with the sub-groove 600 in between.

[0035] As shown in Figure 3, the sub-groove 600 is composed of a plurality of segmented grooves 610 formed in each first intermediate block 210 and divided in the tire circumferential direction, which are continuous in the tire circumferential direction via the first intermediate slit 220. Each of the segmented grooves 610 is inclined with respect to the tire circumferential direction such that it extends towards one side X1 in the tire axial direction as it moves from the other side C2 in the tire circumferential direction toward one side C1 in the tire circumferential direction.

[0036] As shown in Figure 3, the first intermediate block 210 has a pair of notches, a first notch 211 and a second notch 212, located approximately in the center of the tire circumferential direction and approximately opposite to each other in the tire axial direction. The first notch 211 is formed on the edge of the first intermediate block 210 on one side X1 in the tire axial direction and communicates with the second main groove 800. The second notch 212 is formed on the edge of the first intermediate block 210 on the other side X2 in the tire axial direction and communicates with the sub-groove 600.

[0037] The first intermediate block 210 includes a plurality of first intermediate sipes 213 extending in a direction intersecting the tire circumferential direction. The first intermediate sipes 213 have a wavy surface shape on the tread surface 2A. Overall, the first intermediate sipes 213 are curved so as to be convex on one side C1 in the tire circumferential direction, but the proportion of the inclined portion relative to the tire axial direction on the other side X2 in the tire axial direction is longer.

[0038] The first intermediate sipe 213 includes one end X1 on one side in the tire axial direction communicating with the first notch 211, extending from that end toward the sub-groove 600 and terminating just before reaching the sub-groove 600, one end X2 on the other side in the tire axial direction communicating with the second notch 212, extending from that end toward the second main groove 800 and terminating just before reaching the second main groove 800, and one that communicates with the sub-groove 600 and the second main groove 800. However, the sipe pattern formed by the shape and arrangement of these multiple first intermediate sipes 213 is common to each first intermediate block 210.

[0039] As shown in Figures 2 and 3, the second intermediate platform 300 includes a plurality of second intermediate blocks 310 arranged in the circumferential direction of the tire, a plurality of second intermediate slits 320 extending in a direction intersecting the circumferential direction of the tire, a plurality of third intermediate slits 330, and a plurality of fourth intermediate slits 340. The width of each slit 320, 330, and 340 is, for example, about 2.5 mm to 5.0 mm, and the depth is, for example, about 7.0 mm to 8.5 mm for slit 320 and about 4.0 mm to 5.5 mm for slits 330 and 340, but is not limited to these.

[0040] Multiple second intermediate slits 320 are arranged at intervals in the circumferential direction of the tire. The second intermediate slits 320 traverse the second intermediate groove 300 and communicate with the first main groove 700 and the third main groove 900.

[0041] As shown in Figure 3, the second intermediate slit 320 has a second bend 321 and a third bend 322 at each end in the tire axial direction. The second bend 321 is formed at the end on one side X1 in the tire axial direction and protrudes to the other side C2 in the tire circumferential direction. The third bend 322 is formed at the end on the other side X2 in the tire axial direction and protrudes to the one side C1 in the tire circumferential direction. The second intermediate slit 320 has a third inclined portion 323 extending from the second bend 321 to the first main groove 700, a fourth inclined portion 324 extending from the third bend 322 to the third main groove 900, and a fifth inclined portion 325 connecting the second bend 321 and the third bend 322.

[0042] The fifth inclined portion 325 is the main part of the second intermediate slit 320 and is longer than the third inclined portion 323 and the fourth inclined portion 324. The fifth inclined portion 325 is inclined with respect to the tire axis so as it extends toward one side C1 in the tire circumferential direction from the second bend portion 321 toward the third bend portion 322. The lengths of the third inclined portion 323 and the fourth inclined portion 324 are approximately the same and are inclined in the opposite direction to the fifth inclined portion 325.

[0043] The second intermediate slit 320 has a second protruding recess 326 on the other side C2 in the tire circumferential direction of the second bent portion 321 that protrudes to the other side X2 in the tire axial direction, and a third protruding recess 327 on one side C1 in the tire circumferential direction of the third bent portion 322 that protrudes to the one side X1 in the tire axial direction.

[0044] Each of the multiple second intermediate blocks 310 is partitioned into a substantially rectangular shape by a first main groove 700, a third main groove 900, and a pair of second intermediate slits 320 adjacent to each other in the tire circumferential direction. The second intermediate slits 320 are an example of block-forming grooves according to the present disclosure. The second intermediate block 310 is an example of a block according to the present disclosure partitioned in the tire circumferential direction by the block-forming grooves.

[0045] As shown in Figure 2, the second intermediate block 310 is arranged alternately in the circumferential direction of the tire, with some having a third intermediate slit 330 and others having a fourth intermediate slit 340.

[0046] As shown in Figure 3, the third intermediate slit 330 is formed on the edge of the second intermediate block 310 on one side X1 in the tire axial direction. The third intermediate slit 330 is bent in a hook shape. The third intermediate slit 330 communicates with the first main groove 700, and the end opposite to the communicating end is formed in a tapered shape and terminates within the second intermediate block 310. The fourth intermediate slit 340 is formed on the edge of the second intermediate block 310 on the other side X2 in the tire axial direction. The fourth intermediate slit 340 has the same shape as the third intermediate slit 330 and is bent in a hook shape, but the direction of bending is opposite to that of the third intermediate slit 330. The fourth intermediate slit 340 communicates with the third main groove 900, and the end opposite to the communicating end is formed in a tapered shape and terminates within the second intermediate block 310.

[0047] The second intermediate block 310 includes a plurality of second intermediate sipes 311 extending in a direction intersecting the tire circumferential direction. The second intermediate sipes 311 have a wavy surface shape on the tread surface 2A. There are multiple types of second intermediate sipes 311, differing in their length, direction of extension, position, and the grooves or slits they communicate with. For example, some second intermediate sipes 311 have a substantially straight extension direction, while others have a curved extension direction. Furthermore, some second intermediate sipes 311 terminate within the second intermediate block 310 by communicating only with the first main groove 700 or only with the third main groove 900. In addition, some second intermediate sipes 311 communicate with either the first main groove 700 or the third main groove 900 and with the second intermediate slit 320. However, the sipe pattern formed by the shape and arrangement of these multiple second intermediate sipes 311 is common to each second intermediate block 310.

[0048] As shown in Figure 2, the first shoulder block 400 includes a plurality of first shoulder blocks 410 arranged in the circumferential direction of the tire, and a plurality of first lug grooves 420 extending in a direction intersecting the circumferential direction of the tire. The width of the first lug grooves 420 is, for example, about 3.5 mm to 6.0 mm, and the depth is, for example, about 6.5 mm to 8.5 mm, but is not limited thereto.

[0049] Multiple first lug grooves 420 are arranged at intervals in the circumferential direction of the tire. The first lug grooves 420 traverse the first shoulder ridge 400 and the first buttress 8A and communicate with the second main groove 800 and the first annular groove 9A. The first annular groove 9A is an annular groove along the circumferential direction of the tire and is formed on the radially inward side of the first buttress 8A.

[0050] The first shoulder block 410 is provided extending from the first shoulder base 400 to the first buttress 8A. The first shoulder block 410 is divided into a substantially rectangular shape in plan view by a second main groove 800, a first annular groove 9A, and a pair of first lug grooves 420 adjacent to each other in the circumferential direction of the tire. The first lug grooves 420 are an example of block-forming grooves according to the present disclosure. The first shoulder block 410 is an example of a block according to the present disclosure divided in the circumferential direction of the tire by the block-forming grooves.

[0051] The first shoulder block 410 includes a first shoulder slit 411 and a plurality of first shoulder sipes 412. Both the first shoulder slit 411 and the first shoulder sipes 412 extend in a direction intersecting the circumferential direction of the tire.

[0052] The first shoulder slit 411 has a shape that is bent in a roughly Z-shape. The first shoulder slit 411 does not communicate with any grooves other than the sipes and terminates within the first shoulder block 410. The width of the first shoulder slit 411 is, for example, about 0.5 mm to 2.0 mm, and the depth is, for example, about 0.5 mm to 2.0 mm, but is not limited to these values.

[0053] Multiple first shoulder sipes 412 are arranged at intervals in the circumferential direction of the tire. Each first shoulder sipe 412 has a wavy shape. Each first shoulder sipe 412 communicates with the second main groove 800, extends from its communicating end toward the shoulder 5, and communicates with the dimples 414 provided on the shoulder 5.

[0054] The region of the first buttress 8A in the first shoulder block 410 includes a pair of opposing first hook-shaped grooves 81 and second hook-shaped grooves 82 in the tire axial direction, and a shoulder groove 86 provided near the shoulder 5. The second hook-shaped groove 82 is located on the other side X2 in the tire axial direction of the first hook-shaped groove 81. The widths of the first hook-shaped groove 81, the second hook-shaped groove 82, and the shoulder groove 86 are, for example, about 1.0 mm to 3.5 mm, and the depths are, for example, about 0.5 mm to 1.5 mm, but are not limited thereto.

[0055] The first hook-shaped groove 81 and the second hook-shaped groove 82 have the same shape. Each of the hook-shaped grooves 81 and 82 has a hook-shaped bent tip portion 81b and 82b at the end of a circumferentially inclined groove portion 81a and 82a that is inclined with respect to the circumferential direction of the tire. The hook-shaped grooves 81 and 82 are arranged in the first shoulder block 410 in a manner in which the tip portions 81b and 82b engage with each other, and the circumferentially inclined groove portions 81a and 82a are parallel, and are arranged in opposite directions in the circumferential direction of the tire. The first hook-shaped groove 81, located on one side X1 in the axial direction of the tire, has its base end in communication with the first annular groove 9A and the first lug groove 420, and its tip portion 81b terminates within the first shoulder block 410. The second hook-shaped groove 82, located on the other side X2 of the tire axial direction, has its base end in communication with a first lug groove 420 that is different from the first lug groove 420 that the base end of the first hook-shaped groove 81 communicates with.

[0056] The shoulder groove 86 is located within the first shoulder block 410 on one side C1 in the tire circumferential direction of the second hook-shaped groove 82. The shoulder groove 86 communicates with the first lug groove 420, which is connected to the base end of the first hook-shaped groove 81, and extends from that communicating end to the other side C2 in the tire circumferential direction, terminating without reaching the second hook-shaped groove 82.

[0057] As shown in Figure 2, the configuration of the second shoulder ramp 500 and the second buttress 8B on the other side X2 in the tire axial direction from the third main groove 900 is almost point-symmetric to the configuration of the first shoulder ramp 400 and the first buttress 8A on the other side X1 in the tire axial direction from the second main groove 800 described above, and has a similar configuration as follows. Note that the width and depth of the corresponding slits and grooves are approximately the same due to the point symmetry.

[0058] The second shoulder block 500 includes a plurality of second shoulder blocks 510 arranged in the circumferential direction of the tire, and a plurality of second lug grooves 520 extending in a direction intersecting the circumferential direction of the tire.

[0059] Multiple second lug grooves 520 are arranged at intervals in the circumferential direction of the tire. The second lug grooves 520 traverse the second shoulder land 500 and the second buttress 8B and communicate with the third main groove 900 and the second annular groove 9B. The second annular groove 9B is an annular groove along the circumferential direction of the tire and is formed on the radially inward side of the second buttress 8B.

[0060] The second shoulder block 510 is provided extending from the second shoulder base 500 to the second buttress 8B. The second shoulder block 510 is divided into a substantially rectangular shape in plan view by a third main groove 900, a second annular groove 9B, and a pair of second lug grooves 520 adjacent in the circumferential direction of the tire. The second lug grooves 520 are an example of block-forming grooves according to the present disclosure. The second shoulder block 510 is an example of a block according to the present disclosure divided in the circumferential direction of the tire by the block-forming grooves.

[0061] The second shoulder block 510 includes a second shoulder slit 511 and a plurality of second shoulder sipes 512. Both the second shoulder slit 511 and the second shoulder sipes 512 extend in a direction intersecting the circumferential direction of the tire.

[0062] The second shoulder slit 511 has a shape that is bent in a roughly Z-shape. The second shoulder slit 511 does not communicate with any grooves other than the sipe and terminates within the second shoulder block 510.

[0063] Multiple second shoulder sipes 512 are arranged at intervals in the circumferential direction of the tire. The second shoulder sipes 512 have a wavy shape. The second shoulder sipes 512 communicate with the third main groove 900, extend from the end communicating with it toward the shoulder 5, and communicate with the dimples 514 provided on the shoulder 5.

[0064] The region of the second buttress 8B in the second shoulder block 510 includes a pair of third hook-shaped grooves 83 and a fourth hook-shaped groove 84 facing each other in the tire axial direction, and a shoulder groove 87 provided near the shoulder 5. The fourth hook-shaped groove 84 is located on one side X1 in the tire axial direction of the third hook-shaped groove 83.

[0065] The third hook-shaped groove 83 and the fourth hook-shaped groove 84 have the same shape. Each of the hook-shaped grooves 83 and 84 has a hook-shaped bent tip portion 83b and 84b at the end of a circumferentially inclined groove portion 83a and 84a that is inclined with respect to the tire circumferential direction. The hook-shaped grooves 83 and 84 are arranged in the second shoulder block 510 in opposite directions in the tire circumferential direction, with the tip portions 83b and 84b engaging with each other and the circumferentially inclined groove portions 83a and 84a being parallel. The third hook-shaped groove 83, located on the other side X2 in the tire axial direction, has its base end communicating with the second annular groove 9B and the second lug groove 520, and its tip portion 83b terminates within the second shoulder block 510. The fourth hook-shaped groove 84, located on one side X1 of the tire axial direction, has its base end in communication with a second lug groove 520 that is different from the second lug groove 520 to which the base end of the third hook-shaped groove 83 communicates.

[0066] The shoulder groove 87 is located within the second shoulder block 510 on the other side C2 in the tire circumferential direction of the fourth hook-shaped groove 84. The shoulder groove 87 communicates with the second lug groove 520, which is connected to the base end of the third hook-shaped groove 83, and extends from that communicating end to one side C1 in the tire circumferential direction, terminating without reaching the fourth hook-shaped groove 84.

[0067] As mentioned above, the central rib 100 of the embodiment has a rib shape that extends continuously in an annular manner in the circumferential direction of the tire. This ensures a contact length of the central rib 100 and increases the contact area, thereby improving ice driving performance. In addition, the first central sipe 110 provided on the central rib 100 improves the water removal effect, which also improves ice driving performance. The first central sipe 110 will be described in detail below.

[0068] Figure 5 is a cross-sectional view of a tire showing the first central sipe 110 located on the central land surface 100, and in Figure 5, VA shows an enlarged view of the cross-section of multiple first central sipes 110 in the sipe depth direction (tire radial direction).

[0069] Figure 6 is a cross-sectional view of the VI-VI section of Figure 4, in which the opening 110a of the first central sipe 110 is positioned on the lower side and the bottom 110b is positioned on the upper side. Figure 6 shows a cross-sectional view of the first central sipe 110 in the sipe width direction when the tire 1 is unloaded. As shown in Figure 6, the first central sipe 110 is formed between the first wall surface 160 and the second wall surface 170, which are opposite each other in the central landform 100. In other words, the first central sipe 110 as a groove has an opening 110a, a bottom 110b, a first wall surface 160, and a second wall surface 170, with a space between the first wall surface 160 and the second wall surface 170. The first central sipe 110 is also a 3D sipe, similar to the second central sipe 120.

[0070] The first wall surface 160 is provided at two locations spaced apart in the sipe depth direction (vertical direction in Figure 6) and has a first protrusion 161 extending in the sipe length direction and a first recess 162 positioned between the first protrusions 161. Each of the first protrusions 161 projects toward the second wall surface 170. The first protrusions 161 and the first recess 162 are provided along the entire length of the first central sipe 110 in the extending direction.

[0071] The second wall surface 170 has second recesses 171 facing each of the first protrusions 161 of the first wall surface 160, and a second protrusion 172 positioned between these second recesses 171 and facing the first recess 162 of the first wall surface 160. The second protrusions 172 project toward the first wall surface 160. The second recesses 171 and the second protrusions 172 are provided along the entire length of the first central sipe 110 in the extending direction.

[0072] As shown in Figure 6, the first central sipe 110 has a straight space 110s in its sipe widthwise cross-section that extends linearly from the opening 110a to the bottom 110b in an unloaded state. This straight space 110s allows for a clear view of the bottom 110b from the opening 110a to the bottom 110b in the sipe depth direction, without being obstructed by the first protrusion 161 of the first wall surface 160 and the second protrusion 172 of the second wall surface 170.

[0073] In the first central sipe 110, the distance between the first wall surface 160 and the second wall surface 170 is approximately equal from the opening 110a to the bottom 110b. The distance between the first wall surface 160 and the second wall surface 170 referred to here is the distance in the sipe width direction between the main first wall surface 160 and the second wall surface 170, between the portion of the first wall surface 160 where the first protrusion 161 and the first recess 162 are not provided, and between the portion of the second wall surface 170 where the second recess 171 and the second protrusion 172 are not provided, as well as the distance in the sipe width direction between the first protrusion 161 and the second recess 171, and the distance in the sipe width direction between the first recess 162 and the second protrusion 172. At both ends of the first recess 162 and the second recess 171 in the depth direction, the gap between them and the opposing wall surface is partially larger, but the spacing in the width direction of the sipe in that portion is excluded from the spacing between the first wall surface 160 and the second wall surface 170, which is considered to have equal spacing.

[0074] The spacing between the first wall surface 160 and the second wall surface 170, i.e., the sipe width of the first central sipe 110, is, for example, about 0.6 mm, and preferably between 0.5 mm and 1.0 mm. The protruding height of the first protrusion 161 and the second protrusion 172 is, for example, about 0.3 mm, and preferably between 0.2 mm and 0.5 mm. The width of the straight space 110s is, for example, about 0.3 mm, and preferably between 0.1 mm and 0.5 mm.

[0075] Preferably, the length of the first protrusion 161 of the first wall surface 160 in the sipe depth direction is 40% or more and 70% or less of the length of the second recess 171 of the second wall surface 170 in the sipe depth direction.

[0076] The operation of the first central sipe 110 having this configuration will now be explained. Figures 7A to 7E schematically show the deformation process when the central contact surface 100 of a rotating tire 1, which rotates in the G direction, makes contact with the road surface R while the vehicle is traveling forward on the road surface R. Here, the central straight portion 111 extending in the tire axis direction of the three first central sipes 110 arranged in the circumferential direction of the tire is shown. The contact surface of the tire 1 has a tire-pressing side (first contact side) that makes contact with the road surface R first, and a tire-kicking side (rear contact side) that moves away from the road surface R. In the embodiment of the tire 1, the first wall surface 160 is located on the tire-pressing side, and the second wall surface 170 is located on the tire-kicking side.

[0077] Figures 7A and 7B show the state when the tire is pressed down, illustrating how the width of the central sipe 110 narrows from the side where the tire is pressed down (right side). Figure 8 is an enlarged view of Figure 7B.

[0078] As shown in Figure 8, when the tire is pressed down, the rubber of the central rim 100 on the tire-pressing side deforms more than the first wall surface 160 on the tire-pressing side, causing the first wall surface 160 to approach the second wall surface 170 and reducing the width of the first central sipe 110. At this time, the first protrusion 161 fits into the second recess 171, and the second protrusion 172 fits into the first recess 162. Furthermore, of the two first protrusions 161, the first protrusion 161 on the opening 110a side comes into contact with the second protrusion 172, and the first protrusion 161 on the bottom 110b side comes into contact with the edge 171c of the second recess 171 on the bottom 110b side. In this state, in the tire 1 of the embodiment, a gap 105 is formed between the first protrusion 161 and the second protrusion 172 in the sipe depth direction.

[0079] As shown in Figure 7C, during the mid-tire contact period when the sipe depth direction of the first central sipe 110 is approximately perpendicular to the road surface R, the first wall surface 160 and the second wall surface 170 are separated, the first protrusion 161 does not fit into the second recess 171, and the first recess 162 does not fit into the second protrusion 172.

[0080] Figures 7D to 7E show the tire kick-out process. During this process, the rubber of the central land 100 on the tire kick-out side (left side) of the second wall 170 deforms, causing the second wall 170 to separate from the first wall 160 and increasing the width of the first central sipe 110.

[0081] In this embodiment, the first central sipe 110 comes into contact with each other due to tire deformation that occurs when the tire is pressed down, as described above. As a result, the opening 110a of the first central sipe 110 remains open, making it difficult for blockage to occur on the tire surface. Therefore, a water-removing effect is ensured as moisture enters the first central sipe 110 from the opening 110a, resulting in improved ice driving performance.

[0082] There are no particular restrictions on the dimensions of the first central sipe 110, but as shown in Figure 6, for example, the spacing Wa in the sipe width direction between the first protrusion 161 and the second recess 171 is 0.6 mm, and the maximum spacing Wb between the first protrusion 161 and the edge 171c of the second recess 171, which are in contact with each other, is 0.5 mm. These dimensions are just examples, and it is preferable that the ratio of Wa to Wb, Wb / Wa, is, for example, 0.5 or more and 1 or less. By having such a dimensional relationship, the first protrusion 161 can easily come into contact with the edge 171c of the second recess 171, and the water removal effect described above can be ensured.

[0083] The tread 2, including the central ridge 100, is made of tread rubber, and the hardness of this tread rubber is preferably 50 to 65 on the durometer hardness type A of JIS K6253-3:2012. When the tread rubber has such hardness, the first convex portion 161 can easily come into proper contact with the edge 171c of the second concave portion 171, thereby ensuring the water removal effect described above.

[0084] Figure 9 is a diagram showing an example of the contact surface shape of the tread surface 2A of the tire 1 of the embodiment, and is a diagram for explaining the rectangularity of the contact surface. Figure 9 is a diagram corresponding to the contact mark left by the tire 1 when it makes contact with the ground. In Figure 9, L1 is shown as the tread contact length in the circumferential direction of the tire on the tire equator E, and L2 is shown as the tread contact length in the circumferential direction of the tire at a position 10 mm inward from both ends of the contact width W1, and the rectangularity is L2 / L1. Note that the actual L2 may differ on the left and right sides, so the average of both is taken.

[0085] In the embodiment, when tire 1 is mounted on a standard rim and filled to the standard internal pressure, the rectangular ratio L2 / L1 at 70% of the maximum load is between 70% and 92%. This relatively high rectangular ratio of the contact surface, resulting in a square-shaped contact surface, improves ice driving performance due to the increased contact area.

[0086] Figure 10 shows one embodiment of a tire molding die used for vulcanizing the tire 1 of the embodiment. Figure 10 is a meridian cross-sectional view of the tire molding die 10 along the axial direction of the tire 1 being molded.

[0087] The tire molding die 10 shown in Figure 10 comprises a plurality of sectors 11 arranged circumferentially along the outer circumference of the tire 1, a pair of side plates 12 positioned on both sides of the axial direction of the annular body formed by the combination of the plurality of sectors 11, and a pair of bead rings (not shown). During vulcanization molding, an unvulcanized tire, which will become the tire 1, is set inside the tire molding die 10. The combination of sectors 11, side plates 12, and bead rings forms the mold for forming the tire 1, and the outer surface of the entire tire 1 is formed by the inner surface of the mold, i.e., the inner surface 11a of the sectors 11, the inner surface 12a of the side plates 12, and the inner surface of the bead rings. Also, during vulcanization molding, a bladder (not shown) is placed inside the unvulcanized tire to press the unvulcanized tire against the inner surface of the tire molding die 10. The plurality of sectors 11 mainly form the tread 2, shoulder 5, and buttress 8, and the pair of side plates 12 mainly form the sidewall 4. The pair of bead rings forms the bead 3, and the bladder forms the entire inner surface of the tire 1.

[0088] The tire molding die 10 vulcanizes the unvulcanized tire to form the overall rubber shape of the tire 1, and also forms a tread pattern 2B on the tread 2.

[0089] The tire 1 according to the embodiment described above provides the following effects.

[0090] (1) The tire 1 according to the embodiment is a pneumatic tire comprising a plurality of ridges 6 including a rib-shaped central ridge 100 arranged on the tire equator E and extending in an annular manner continuously in the tire circumferential direction, and a tread 2 including circumferential grooves 7 on both sides of the tire axial direction of the central ridge 100, wherein the central ridge 100 has a first central sipe 110 having a portion that extends in a direction intersecting the tire circumferential direction, and a second central sipe 120 having a portion that extends in a direction intersecting the tire circumferential direction, the first central sipe 110 ending within the central ridge 100, the second central sipe 120 communicating with the circumferential grooves 7 and having a wave-shaped shape at least on the tire surface, and the total length of the second central sipe 120 on the surface of the central ridge 100 is longer than the total length of the first central sipe 110 on the surface of the central ridge 100.

[0091] In this embodiment, the central ridge 100 has a rib shape that extends continuously in an annular manner in the circumferential direction of the tire. This ensures a contact length of the central ridge 100, increasing the contact area and improving ice driving performance. In addition, the rib shape of the central ridge 100 suppresses twisting during cornering, improving initial response. In the central ridge 100, multiple first central sipes 110 and second central sipes 120 are provided to ensure an edge effect. The first central sipes 110, which terminate within the central ridge 100, adjust the rigidity around the first central sipes 110 to be low. On the other hand, the second central sipes 120, which communicate with the circumferential groove 7, have a wave shape rather than a straight shape that makes it easy for the edge of the central ridge 100 to collapse. This makes it difficult for the edge to collapse, and the rigidity is adjusted to be high. As a result of these factors, the rigidity of the central ridge 100 is made uniform, and as a result, the contact pressure of the central ridge 100 is made uniform, improving ice driving performance. As described above, the central ridge 100 is provided with multiple first central sipes 110 and second central sipes 120 to ensure an edge effect, thereby ensuring snow driving performance. In addition, the total length of the second central sipes 120 on the surface of the central ridge 100 is longer than the total length of the first central sipes 110 on the surface of the central ridge 100, resulting in a balanced improvement in both ice driving performance and snow driving performance.

[0092] (2) In the tire 1 of the embodiment described in (1) above, the second central sipe 120 is preferably a 3D sipe.

[0093] This results in even greater rigidity and superior edge performance on ice.

[0094] (3) In the tire 1 according to the embodiments of (1) and (2) above, the base 6 includes a central base 100, a first shoulder base 400 and a second shoulder base 500 as shoulder bases arranged at both ends of the tread 2 in the tire axial direction, and a first intermediate base 200 and a second intermediate base 300 as intermediate bases arranged between the central base 100 and the shoulder bases, respectively, each of which has a first intermediate block 210 and a second intermediate block 310 as a plurality of blocks partitioned in the tire circumferential direction by a first intermediate slit 220 and a second intermediate slit 320 as block-forming grooves extending in a direction intersecting the tire circumferential direction, and each of which has a first shoulder block 410 and a second shoulder block 510 as a plurality of blocks partitioned in the tire circumferential direction by a first lug groove 420 and a second lug groove 520 as block-forming grooves extending in a direction intersecting the tire circumferential direction.

[0095] As a result, drainage is improved at each intermediate and shoulder section of the road, and the shear force in the snow is increased during snow driving, improving snow driving performance.

[0096] (4) In the tire 1 according to the embodiment described in (1) to (3) above, it is preferable that the first central sipe 110 is provided at least on the central land surface 100.

[0097] As a result, the rigidity around the first central sipe 110 is adjusted to be lower, especially within the central land area 100 where ground pressure tends to be high. This allows for a moderate reduction in ground pressure, and as a result, the ground pressure of the entire tire is made more uniform. The first central sipe 110 may be provided not only in the central land area 100, but also in either or both of the first intermediate land area 200 and the second intermediate land area 300.

[0098] (5) In the tire 1 according to the embodiment described in (1) to (4) above, the ratio of the tire axial length of the first central sipe 110 to the width of the central ridge 100 is preferably 20% or more and 60% or less.

[0099] This makes it easier for the above-mentioned effects of the first central sipe 110 to be achieved.

[0100] (6) In the tire 1 according to the embodiment described in (1) to (5) above, the first central sipe 110 is preferably located in the central region in the width direction of the central land 100.

[0101] As a result, the first central sipe 110 adjusts the rigidity of the central region of the central land surface 100 to be low, and the second central sipe 120 adjusts the rigidity of the area near the edge of the central land surface 100 to be high. Consequently, the ground pressure of the central land surface 100 is made uniform, improving ice driving performance.

[0102] Furthermore, the present invention is not limited to the embodiments described above, and modifications, improvements, etc., made to the extent that the objectives of the present invention can be achieved are also included within the scope of the present invention.

[0103] For example, the first central sipe 110 only needs to be located on the central landmass 100, and may be located on either or both of the first intermediate landmass 200 and the second intermediate landmass 300.

[0104] The circumferential groove 7 has one sub-groove 600 and multiple main grooves (first main groove 700, second main groove 800, third main groove 900), but the circumferential groove 7 may consist entirely of main grooves, or it may have multiple sub-grooves. [Explanation of symbols]

[0105] 1. Tire (pneumatic tire) 2 tread 6 land 7 Circumferential groove 100 Chuo Riku 110 First Central Sipe 120 Second Central Sipe 200 1st Intermediate Landing (Intermediate Landing) 210 First Intermediate Block (Block) 220 First intermediate slit (block forming groove) 300 Second Intermediate Landing (Intermediate Landing) 310 Second Intermediate Block (Block) 320 Second intermediate slit (block forming groove) 400 First Shoulder Land (Shoulder Land) 410 First shoulder block (block) 420 First lug groove (block forming groove) 500 Second Shoulder Land (Shoulder Land) 510 Second shoulder block (block) 520 Second lug groove (block forming groove) E-Tire Equator C Tire circumferential direction X Tire Axle

Claims

1. Multiple landmasses, including a central landmass in the shape of a rib that is positioned on the tire equator and extends continuously in a ring shape in the circumferential direction of the tire, A pneumatic tire having a tread including circumferential grooves on both sides of the tire axial direction of the central land, The central ridge has a first central sipe having a portion extending in a direction intersecting the tire circumferential direction, and a second central sipe having a portion extending in a direction intersecting the tire circumferential direction. The first central sipe terminates within the central land area. The second central sipe communicates with the circumferential groove and has a wave-like shape at least on the tire surface. A pneumatic tire in which the total length of the second central sipe on the surface of the central landmass is longer than the total length of the first central sipe on the surface of the central landmass.

2. The pneumatic tire according to claim 1, wherein the second central sipe is a 3D sipe.

3. The land includes the central land, shoulder land positioned at both ends of the tread in the tire axial direction, and intermediate land positioned between the central land and the shoulder land, The pneumatic tire according to claim 1 or 2, wherein each of the intermediate land and the shoulder land has a plurality of blocks partitioned in the circumferential direction of the tire by block-forming grooves extending in a direction intersecting the circumferential direction of the tire.

4. The pneumatic tire according to claim 3, wherein the first central sipe is provided at least on the central land.

5. The pneumatic tire according to claim 4, wherein the ratio of the tire axial length of the first central sipe to the width of the central ridge is 20% or more and 60% or less.

6. The pneumatic tire according to claim 1 or 2, wherein the first central sipe is located in the central region in the width direction of the central land.

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