tire

Abstract

To provide a tire improved in on-ice gripping performance.SOLUTION: A tire 1 has land parts 4 on a tread surface 2, and in the land part 4, a sipe unit 8 having a connection point P and composed of three or more sipes 7 radially extending from the connection point P is disposed. Each of the three or more sipes 7 in the sipe unit 8 has both ends in an extending direction of the sipe 7 which extend so as to terminate in the land part 4. The three or more sipes 7 in the sipe unit 8 includes a first sipe 7A extending from the connection point P to one side in a tire width direction, and a second sipe 7B extending from the connection point P to the other side in the tire width direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a tire. [Background technology]

[0002] Conventionally, tires, particularly studless tires, have been provided with narrow grooves called sipes in the land portion of the tread to improve the tire's grip on ice. These sipes allow water that wells up when the ice melts on the tire's contact surface to be expelled outside the contact surface, thereby improving the tire's grip on ice.

[0003] For example, Patent Document 1 proposes a technology that aims to improve grip performance on ice by arranging sipes at a high density while suppressing a decrease in rigidity of the land portion. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2005-186827 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the conventional technology has not been able to achieve a sufficient balance between the rigidity of the land portion and the water evacuation by the sipes, and there is still a demand for further improvement in the grip performance of tires on ice.

[0006] SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a tire with improved grip performance on ice. [Means for solving the problem]

[0007] The tire of the present invention is a tire having a land portion on the tread surface, in which a sipe unit is arranged having a connection point and consisting of three or more sipes extending radially from the connection point, each of the three or more sipes in the sipe unit extending so that both ends in the extension direction of the sipe terminate within the land portion, and the three or more sipes in the sipe unit include a first sipe extending from the connection point to one side in the tire width direction and a second sipe extending from the connection point to the other side in the tire width direction. According to the tire of the present invention, the tire's grip performance on ice can be improved.

[0008] In the tire according to the present invention, it is preferable that each of the first sipes and the second sipes extends linearly so that the angle φ formed with the tire width direction satisfies 0°<φ<45°. In a tire having such a configuration, the sipe unit not only contributes to improving the braking force and driving force in the tire circumferential direction, but also to improving the lateral grip performance (cornering force) in the tire width direction.

[0009] In the tire according to the present invention, it is preferable that the three or more sipes in the sipe unit include a third sipe extending from the connecting point along the tire circumferential direction, and that the third sipe extends from the connecting point on a side opposite to the first sipe and the second sipe in the tire width direction. A tire having such a configuration can further improve the grip performance on ice.

[0010] In the tire according to the present invention, it is preferable that the length of the third sipes is shorter than the length of the first sipes and the second sipes. In a tire having such a configuration, the sipe unit is more likely to contribute to improving the braking force and driving force in the tire circumferential direction.

[0011] In the tire according to the present invention, it is preferable that in the land portion, a plurality of the sipe units are repeatedly arranged in the tire circumferential direction to form a sipe unit row, and the plurality of sipe units that form the sipe unit row are arranged so that the third sipes are aligned on a straight line extending along the tire circumferential direction. A tire having such a configuration can further improve the grip performance on ice of the tire.

[0012] In the tire according to the present invention, the land portion preferably includes a plurality of sipe unit rows arranged side by side in the tire width direction, and a plurality of sipe units constituting a first sipe unit row among the plurality of sipe unit rows are preferably arranged so that each of the third sipes extends from the connecting point to one side in the tire circumferential direction, and a plurality of sipe units constituting a second sipe unit row adjacent to the first sipe unit row are preferably arranged so that each of the third sipes extends from the connecting point to the other side in the tire circumferential direction. A tire having such a configuration can further improve the grip performance on ice of the tire.

[0013] In the tire according to the present invention, it is preferable that at least one of the plurality of sipe units constituting the first sipe unit row and at least one of the plurality of sipe units constituting the second sipe unit row are arranged such that a portion of each sipe unit in the tire width direction faces the other sipe unit in the tire circumferential direction. With a tire having such a configuration, it is possible to widen the range in which the sipe units can exert their edge effect and water removal effect while maintaining the sipe density in the land portion.

[0014] In the tire according to the present invention, when the length of the sipe unit in the tire width direction is W (mm) and the depth of the sipe is h (mm), W×h is 150 (mm 2 ) or less, where n is the number of sipe units in the land portion, T (mm) is the total length of the sipes constituting the sipe unit in the tire width direction, BW (mm) is the maximum width of the land portion in the tire width direction, and2 When the equivalent circumferential length of the land portion is defined as BL (mm), calculated by dividing the maximum width BW by the equivalent number of sipes N, the average circumferential spacing of the sipes is defined as BL / (N+1), and the circumferential sipe density SD is defined as the reciprocal of the average sipe spacing, SD = (N+1) / BL = ((T×n / BW)+1) / BL, it is preferable that SD be 0.15 (1 / mm) or greater. A tire having such a configuration can further improve the grip performance on ice. [Effects of the Invention]

[0015] According to the present invention, a tire with improved grip performance on ice can be provided. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a development view that schematically shows a tread pattern of a tire according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing the lifting of block land portions around sipes. [Figure 3] FIG. 3 is a schematic diagram showing the arrangement of the sipe units shown in FIG. [Figure 4] FIG. 4 is a schematic diagram showing the arrangement of the sipe units in the case where the sipe unit shown in FIG. 1 does not include the third sipe. [Figure 5] FIG. 5 is a cross-sectional view showing the AA' cross section shown in FIG. [Figure 6] FIG. 6 is a schematic diagram showing the arrangement of sipe units in which sipes are connected by shallow grooves in one embodiment of the present invention. [Figure 7] FIG. 7 is a cross-sectional view showing the cross section BB' shown in FIG. [Figure 8] FIG. 8 is a schematic diagram showing the arrangement of a modified example of the sipe unit in one embodiment of the present invention. [Figure 9] FIG. 9 is a table showing examples and comparative examples. [Figure 10] FIG. 10 is a diagram showing the block rigidity and sipe density in the example and comparative example shown in FIG. [Figure 11] FIG. 11 is a diagram showing the contact area and sipe density in the example and comparative example shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of a tire according to the present invention will be described with reference to the drawings. The same reference numerals are used to designate common components and parts in the drawings. However, please note that the drawings are schematic and that the ratios of dimensions may differ from those of the actual tire.

[0018] In this specification, "tire width direction" refers to a direction parallel to the tire's rotational axis, "tire radial direction" refers to a direction perpendicular to the tire's rotational axis, and "tire circumferential direction" refers to the direction in which the tire rotates around the tire's rotational axis.

[0019] In this specification, the side closer to the tire rotation axis along the tire radial direction is referred to as the "tire radial inner side," and the side farther from the tire rotation axis along the tire radial direction is referred to as the "tire radial outer side." On the other hand, the side closer to the tire equatorial plane CL along the tire width direction is referred to as the "tire width inner side," and the side farther from the tire equatorial plane CL along the tire width direction is referred to as the "tire width outer side."

[0020] Unless otherwise specified, the positional relationships of tire elements are measured in a standard state. In this specification, the "standard state" refers to a state in which the tire is mounted on the rim of a wheel, which is the applicable rim, inflated to the specified internal pressure, and no load is applied.

[0021] In this specification, "applicable rim" refers to the standard rim (Measuring Rim in the ETRTO Standards Manual, Design Rim in the TRA Year Book) for the applicable size, which is an industry standard valid in the region where the tire is produced and used, and which is set forth in the JATMA Year Book (Japan Automobile Tire Manufacturers Association) in Japan, the Standards Manual (The European Tyre and Rim Technical Organization) in Europe, or the Year Book (The Tire and Rim Association, Inc.) in the United States, or which will be set forth in the future. For sizes not set forth in the above industry standards, "applicable rim" refers to a rim with a width corresponding to the tire bead width. "Applicable rim" includes not only current sizes but also sizes that may be included in the above industry standards in the future. An example of an "applicable size that will be set forth in the future" is the size set forth in the 2013 edition of the ETRTO Standards Manual as "FUTURE DEVELOPMENTS."

[0022] In this specification, "specified internal pressure" refers to the air pressure (maximum air pressure) corresponding to the maximum load capacity of a single wheel for the applicable size and ply rating as specified in the above-mentioned JATMA YEAR BOOK and other industry standards. For sizes not specified in the above-mentioned industry standards, "specified internal pressure" refers to the air pressure (maximum air pressure) corresponding to the maximum load capacity specified for each vehicle on which the tire is to be mounted. Furthermore, in this specification, "specified load" refers to the load corresponding to the maximum load capacity of a single wheel for the applicable size and ply rating as specified in the above-mentioned industry standards. For sizes not specified in the above-mentioned industry standards, "specified load" refers to the load corresponding to the maximum load capacity specified for each vehicle on which the tire is to be mounted.

[0023] In this specification, the term "tread surface" refers to the outer peripheral surface of the tire that comes into contact with the road surface when the tire is mounted on an applicable rim, inflated to a specified internal pressure, and rolled under a specified load. The term "tread edge" refers to the edge of the tread surface in the tire width direction.

[0024] Additionally, "sipe" refers to a sipe whose width is 1 mm or less in an area that is 50% or more of its depth under standard conditions. Here, the sipe depth is measured in a direction perpendicular to the tread surface under standard conditions, and the sipe width is measured in a direction parallel to the tread surface in a cross section perpendicular to the extension direction of the tread surface. Additionally, "length in the extension direction of the sipe" refers to the length of the center line connecting the center points of the sipe width direction on the tread surface under standard conditions. Unless otherwise specified, distances or lengths related to sipes are also measured in the developed view of the tread surface under standard conditions, using the center line as the reference.

[0025] In this embodiment, unless otherwise specified, the internal structure of the tire may be the same as that of a conventional tire. As an example, the tire may have a pair of bead portions, a pair of sidewall portions connected to the pair of bead portions, and a tread portion disposed between the pair of sidewall portions. The tire may also have a carcass toroidally spanning the pair of bead portions, and a belt disposed radially outward of a crown portion of the carcass.

[0026] In the following description, a tire will be described as having an inner cavity filled with air and mounted on a vehicle such as a passenger car, although the inner cavity of the tire may be filled with a fluid other than air, and the tire may be mounted on a vehicle other than a passenger car.

[0027] A tire 1 according to one embodiment of the present invention will be described below with reference to the drawings.

[0028] Fig. 1 is a development view that schematically shows a tread pattern of a tire 1 according to one embodiment of the present invention. In Fig. 1, a part of a tread surface 2 of the tire 1 is shown as a development view (development view of the tread surface 2) that is viewed from the outer side in the tire radial direction.

[0029] 1, a tire 1 has, on a tread surface 2, one or more (four in the illustrated example) circumferential main grooves 3 (3A, 3B, 3C, 3D) extending in the tire circumferential direction, and a plurality of (five in the illustrated example) land portions 4 (4A, 4B, 4C, 4D, 4E) defined between adjacent circumferential main grooves 3 in the tire width direction among the one or more circumferential main grooves 3, or defined by a circumferential main groove 3 (3A or 3D) and a tread edge TE. In this embodiment, the circumferential main grooves 3A and 3B are located in one half in the tire width direction, with the tire equatorial plane CL as the boundary, and the other circumferential main grooves 3C and 3D are located in the other half in the tire width direction, with the tire equatorial plane CL as the boundary. In this embodiment, one land portion 4 (4C) is arranged on the tire equatorial plane CL, and two land portions 4 (4A and 4B, 4D and 4E) are arranged in each half portion in the tire width direction.

[0030] The number of circumferential main grooves 3 that the tire 1 has may be any number other than four. Depending on the number of circumferential main grooves 3, the number of land portions 4 that the tire 1 has may also be any number other than five. Furthermore, the tire 1 may be configured so that the tread surface 2 does not have a circumferential main groove 3. In such a case, the tire 1 may have one land portion 4 that is defined between both tread ends TE in the tire width direction on the tread surface 2.

[0031] In the illustrated example, all circumferential main grooves 3 extend along the tire circumferential direction. In this specification, "the straight line X extends along the Y direction" means that the straight line X extends parallel to the Y direction or that the straight line X extends approximately parallel to the Y direction. "The extension direction of the straight line X is approximately parallel to the Y direction" means, for example, that the angle between the extension direction of the straight line X and the Y direction is within a range of 5 degrees or less. However, at least one circumferential main groove 3 may extend at an angle greater than 5 degrees with respect to the tire circumferential direction. Furthermore, in the illustrated example, all circumferential main grooves 3 extend linearly along the tire circumferential direction, but at least one circumferential main groove 3 may have a shape other than a linear shape, such as a zigzag shape or a curved shape, either entirely or partially.

[0032] The width of the circumferential main groove 3 is not particularly limited as it depends on the number of circumferential main grooves 3, but may be, for example, 4 to 15 mm. The width of the circumferential main groove 3 is measured as the opening width perpendicular to the extension direction of the groove when viewed in a developed plane from the outer radial direction of the tire in a standard state. Similarly, the depth (maximum depth) of the circumferential main groove 3 is not particularly limited, but may be, for example, 6 to 20 mm. The width of the circumferential main groove 3 does not have to be constant throughout the extension direction of the circumferential main groove 3, and may vary depending on the position on the tread surface 2 where the circumferential main groove 3 is provided.

[0033] In the tire 1, each land portion 4 is divided into a plurality of block land portions 6 by one or more widthwise grooves 5 extending completely across the land portion 4 in the tire width direction.

[0034] In the illustrated example, each widthwise groove 5 extends in the tire width direction, completely crossing the land portion 4. For example, within the illustrated range, a land portion 4C is divided into three block land portions 6A, 6B, and 6C adjacent in the tire circumferential direction by two widthwise grooves 5A and 5B adjacent in the tire circumferential direction. In this specification, "a straight line X extends in the Y direction" means that the straight line X has at least a Y-direction component. In other words, "a straight line X extends in the Y direction" means that the straight line X may extend along the Y direction, or may extend at a predetermined angle with respect to the Y direction. The widthwise grooves 5 may extend linearly in the tire circumferential direction, or may extend in a shape other than a straight line, such as a zigzag or curved shape. The widthwise grooves 5 may extend along the tire width direction, or may extend at an angle greater than 0° and less than 45° with respect to the tire width direction, as in the illustrated example.

[0035] The width (opening width) of the widthwise grooves 5 is not particularly limited because it depends on the number of widthwise grooves 5, but may be, for example, 2 to 10 mm. The width of the widthwise grooves 5 is measured as the opening width perpendicular to the extension direction of the grooves when viewed in a developed plane from the radially outer side of the tire in a standard state. Similarly, the depth (maximum depth) of the widthwise grooves 5 is not particularly limited, but may be, for example, 5 to 20 mm. However, the width of the widthwise grooves 5 is not limited in any way as long as it is equal to or greater than the width that prevents contact between adjacent block land portions 6 in the tire circumferential direction when the tire is in contact with the ground in the standard state. Furthermore, the width of the widthwise grooves 5 does not need to be constant along the extension direction of the widthwise grooves 5, and may vary depending on the position of the land portion 4 on which the widthwise grooves 5 are provided.

[0036] The number of width-direction grooves 5 crossing each land portion 4 may be any number. The number of block land portions 6 included in the land portion 4 may also be any number depending on the number of width-direction grooves 5. Furthermore, the land portion 4 may be configured not to be crossed by width-direction grooves 5, that is, the land portion 4 may be configured as a rib-like land portion that is continuous without interruption in the circumferential direction.

[0037] The land portion 4 has a connecting point P and is provided with a sipe unit 8 composed of three or more sipes 7 extending radially from the connecting point P. Here, "three or more sipes 7 extending radially from the connecting point P in the land portion 4" means that the three or more sipes 7 extend in different directions from the connecting point P. In the illustrated example, a sipe unit 8 composed of three sipes 7A, 7B, and 7C extending radially from the connecting point P is arranged in the block land portion 6 included in the land portion 4. However, the number of sipes 7 constituting one sipe unit 8 may be any number equal to or greater than three. Hereinafter, when there is no particular need to distinguish between the sipes 7A, 7B, and 7C, they will be collectively referred to simply as sipes 7.

[0038] Each of the three or more sipes 7A, 7B, and 7C constituting the sipe unit 8 extends so that both ends in the extension direction of the sipe 7 terminate within the land portion 4. More specifically, each of the three or more sipes 7A, 7B, and 7C extends so that both ends in the extension direction of the sipe 7 terminate within the block land portion 6. In other words, the sipes 7 do not have open ends that open into the circumferential main grooves 3 or widthwise grooves 5 that define the land portion 4. In this way, because the sipes 7 do not have open ends and the block land portions 6 around the sipes 7 are connected, the block land portions 6 are less likely to collapse around the sipes 7, and the rigidity of the block land portions 6 is improved.

[0039] Generally, as shown in FIG. 2 , when an external force such as a frictional force is applied from the road surface to the contact surface of the tread surface 2 that is in contact with the road surface, the block land portions 6 collapse toward the gaps in the sipes 7, causing the block land portions 6 around the sipes 7 to lift up from the road surface. FIG. 2 is a schematic diagram showing the lift up U of the block land portions 6 around the sipes 7. FIG. 2 is a circumferential cross-sectional view of the tire 1 cut along the tire circumferential direction. When an external force is applied to the tire 1 in the direction indicated by the arrow in FIG. 2 , the block land portions 6 on the side to which the external force is applied, rather than the sipe 7, will lift up. In contrast, because the block land portions 6 around the sipes 7 are connected to each other, the block land portions 6 around the sipes 7 are constrained to each other, which can suppress the lift up U of the block land portions 6 around the sipes 7 from the road surface due to the applied external force, thereby increasing the contact area of ​​the tire 1 when an external force is applied. This makes it possible to suppress a decrease in the rigidity of the land portion of the tire 1, which would be caused by arranging the sipes 7 in the block land portion 6, and in turn suppress a decrease in the contact area of ​​the tire 1. As a result, the grip performance of the tire 1 on ice is improved.

[0040] The configuration of the sipe unit 8 will be described below with reference to Fig. 3, Fig. 4, and Fig. 5. Fig. 3 is a schematic diagram showing the arrangement of the sipe unit 8 shown in Fig. 1. Fig. 4 is a schematic diagram showing the arrangement of the sipe unit 8 in the case where the sipe unit 8 shown in Fig. 1 does not include the third sipe 7C. Fig. 5 is a cross-sectional view showing the A-A' cross section (a cross section perpendicular to the extension direction of the sipe 7) shown in Fig. 3.

[0041] As shown in FIG. 3 , the three or more sipes 7 constituting the sipe unit 8 include, in a developed view of the tread surface 2, a first sipe 7A extending from the connecting point P to one side in the tire width direction (the left side in the drawing) and a second sipe 7B extending from the connecting point P to the other side in the tire width direction (the right side in the drawing). Furthermore, in a developed view of the tread surface 2, the first sipe 7A and the second sipe 7B extend from the connecting point P to the same side in the tire circumferential direction (the lower side in the drawing). As a result, each of the first sipe 7A and the second sipe 7B extends linearly and inclined with respect to the tire width direction. Hereinafter, the first sipe 7A will be simply referred to as sipe 7A, and the second sipe 7B will be simply referred to as sipe 7B.

[0042] More specifically, each of the first sipes 7A and the second sipes 7B extends linearly such that the angle φ formed with the tire width direction satisfies 0°<φ<45°. By inclining the sipes 7A and 7B with respect to the tire width direction in this manner, the sipes 7A and 7B not only contribute to improving the braking force and driving force in the tire circumferential direction of the tire 1, but also contribute to improving the lateral grip performance (turning force) in the tire width direction. In particular, by making φ<45°, the tire width direction components of the sipes 7A and 7B are larger than the tire circumferential components, and the sipes 7A and 7B can contribute to improving the braking force and driving force in the tire circumferential direction, which are most important for safety. In this embodiment, the angle φ (φ1) formed by the first sipe 7A and the tire width direction and the angle φ (φ2) formed by the second sipe 7B and the tire width direction are equal to each other. However, the angle φ1 formed between the first sipe 7A and the tire width direction and the angle φ2 formed between the second sipe 7B and the tire width direction may be different angles.

[0043] In Fig. 3, the first sipe 7A and the second sipe 7B have the same length in the extension direction, indicated by a. The length a in the extension direction of the sipes 7A and 7B is, for example, between 3 and 15 mm. The length a in the extension direction of the sipes 7A and 7B is preferably between 3 and 10 mm, and more preferably between 3 and 5 mm.

[0044] Here, if the length of the sipes 7A and 7B in the tire width direction is d and the length of the sipe unit 8 in the tire width direction is W, then W = 2d = 2a × cosφ. The length W (mm) of the sipe unit 8 in the tire width direction and the depth h (mm) of the sipe 7 are expressed as W × h ≦ 150 mm. 2 The length W of the sipe unit 8 in the tire width direction and the depth h of the sipe 7 constituting the sipe unit 8 may be determined within a range that satisfies the following: W×h≦100 mm 2 It is determined in a range that satisfies W×h≦50mm, and more preferably 2 It is determined within the range that satisfies the above.

[0045] The three or more sipes 7 constituting the sipe unit 8 include a third sipe 7C extending from the connecting point P along the tire circumferential direction. As shown in FIG. 3, the third sipe 7C extends from the connecting point P on the opposite side of the tire width direction from the first sipes 7A and the second sipes 7B (upper side in the drawing) in a developed view of the tread surface 2. Hereinafter, the third sipe 7C will also be simply referred to as the sipe 7C. If the sipe unit 8 does not have the third sipe 7C extending along the tire circumferential direction, as shown in FIG. 4, the sipe unit 8 has a mountain shape (< shape) in which the connecting point P protrudes in the tire circumferential direction. FIG. 4 is a schematic diagram showing the arrangement of the sipe unit 8 when the sipe unit 8 shown in FIG. 1 does not include the third sipe 7C. If the sipe unit 8 is composed only of the first sipes 7A and the second sipes 7B, as shown by the arrows in FIG. 4, when an external force is input along the tire circumferential direction, the external force is likely to be concentrated near the connecting point P. Therefore, in the block land portion 6, the difference in ground pressure applied from the road surface to the block land portion 6 between the portion 6a located forward of the sipe unit 8 with respect to the external force and the portion 6b located rearward of the sipe unit 8 with respect to the external force becomes large, and as described above with reference to FIG. 2, the forward portion 6a is likely to lift up. In contrast, if the sipe unit 8 has a third sipe 7C extending from the connecting point P along the tire circumferential direction in addition to the first sipes 7A and the second sipes 7B, the difference in ground pressure applied to the contact surface of the block land portion 6 between the portion 6a located forward of the sipe unit 8 and the portion 6b located rearward is reduced, making it less likely that the forward portion 6a will lift up. Therefore, it is possible to suppress a decrease in the rigidity of the land portion of the tire 1 caused by arranging the sipe units 8 in the block land portion 6, and in turn suppress a decrease in the contact area of ​​the tire 1. This makes it possible to further improve the grip performance of the tire 1 on ice.

[0046] Furthermore, by arranging the three or more sipes 7 that make up the sipe unit 8 so that they extend in different directions from the connecting point P, the blades that are placed in the mold for the tire 1 to form each sipe 7 during tire manufacturing support each other at the connecting point P, increasing the bending rigidity of the blades and improving the durability of the blades. This improves the durability of the mold for the tire 1, and improves the productivity of the tire 1.

[0047] Referring again to FIG. 3 , the length of the third sipe 7C in the extension direction is indicated by b. The length b of the sipe 7C in the extension direction is, for example, between 1 and 15 mm. The length b of the sipe 7C may be shorter than the length a of the sipes 7A and 7B. By reducing the length b of the sipe 7C without changing the total length of the sipes 7 constituting the sipe unit 8, the proportion of the sipes 7A and 7B, which have tire width direction components, in the sipe unit 8 increases. This makes it easier for the sipe unit 8 to contribute to improving the braking force and driving force in the tire circumferential direction of the tire 1. Furthermore, the depth h of the sipe 7C may be equal to the depth h of the sipes 7A and 7B. The depth h of the sipe 7C is, for example, 3 mm or more. The depth h of the sipe 7C may be, for example, 6.7 mm.

[0048] With reference to FIG. 5, the cross-sectional shape of the sipe 7 on the tread surface 2, which is perpendicular to the extension direction of the sipe 7, will be described. In this embodiment, as shown in FIG. 5(a), the cross-section perpendicular to the extension direction of the sipe 7 is substantially rectangular. In the sipe 7 shown in FIG. 5(a), the width w of the sipe 7 is set to 1 mm or less as described above, and may be set to, for example, 0.4 mm. However, the cross-section perpendicular to the extension direction of the sipe 7 may have a shape other than rectangular. For example, as shown in FIG. 5(b), the sipe 7 may have a bulging shape at the groove bottom in the cross-section perpendicular to the extension direction of the sipe 7. Furthermore, for example, the sipe 7 may have a rounded shape at the groove bottom in the cross-section perpendicular to the extension direction of the sipe 7. For example, in the cross-section perpendicular to the extension direction of the sipe 7 shown in FIG. 5(a), the sipe 7 may have a shape in which both ends of the groove bottom in the width direction of the sipe 7 are rounded, or the groove bottom may be semicircular. In the sipe 7 shown in FIG. 5(b), the width w of the sipe 7 may be set to, for example, 0.4 mm in a region that is 50% or more of the depth of the sipe 7.

[0049] 1 again, in the land portion 4, a plurality of sipe units 8 are spaced apart from one another and repeatedly arranged in the tire circumferential direction to form a sipe unit row 9. In the illustrated example, in each block land portion 6, four sipe units 8 are repeatedly arranged in the tire circumferential direction to form the sipe unit row 9. However, the number of sipe units 8 that form one sipe unit row 9 may be any number equal to or greater than two.

[0050] In Figure 3, the multiple sipe units 8 that make up the sipe unit row 9 are repeatedly arranged at a pitch p in the tire circumferential direction. This makes it possible to uniform the sipe density in the block land portion 6. This allows the tread surface 2 to come into contact with the road surface more uniformly, making it possible to uniformly distribute the ground pressure applied to the contact surface of the tread surface 2 and increasing the contact area of ​​the tire 1. This further improves the grip performance of the tire 1 on ice.

[0051] The multiple sipe units 8 constituting the sipe unit row 9 are arranged so that the respective third sipes 7C are aligned in a straight line extending along the tire circumferential direction. As a result, water trapped in the gaps between the sipes 7 constituting the sipe unit 8 is drained in the tire circumferential direction along the multiple third sipes 7C arranged in a straight line, thereby improving grip performance on ice in the land portion 4. Hereinafter, the line connecting the third sipes 7C extending along the tire circumferential direction of the multiple sipe units 8 constituting the sipe unit row 9 is also referred to as the center line L of the sipe unit row 9. However, the multiple sipe units 8 constituting the sipe unit row 9 do not have to be arranged so that the respective third sipes 7C are aligned in a straight line extending along the tire circumferential direction.

[0052] 1 again, the land portion 4 includes a plurality of sipe unit rows 9 arranged side by side in the tire width direction. In the illustrated example, two sipe unit rows 9 are arranged side by side in the tire width direction in each of the block land portions 6 of land portions 4A and 4E. Furthermore, six sipe unit rows 9 are arranged side by side in the tire width direction in each of the block land portions 6 of land portions 4B, 4C, and 4D. However, the number of sipe unit rows 9 arranged in one block land portion 6 may be any number.

[0053] The arrangement of the multiple sipe unit rows 9 will be described below with reference to Fig. 3. In Fig. 3, two sipe unit rows 9A and 9B are arranged side by side in the tire width direction in a developed view of the tread surface 2. In this embodiment, the shapes of the multiple sipe units 8 arranged in the block land portion 6 are line-symmetrical with respect to each third sipe 7C.

[0054] Two sipe unit rows 9A and 9B adjacent to each other in the tire width direction are arranged such that the third sipes 7C of the sipe units 8 constituting each row extend in different directions in the tire circumferential direction from the connecting point P. Specifically, in Fig. 3, the plurality of sipe units 8 constituting a first sipe unit row 9A of the plurality of sipe unit rows 9A and 9B are arranged such that the respective third sipes 7C extend from the connecting point P to one side in the tire circumferential direction (upper side in the drawing). On the other hand, the plurality of sipe units 8 constituting a second sipe unit row 9B adjacent to the first sipe unit row 9A are arranged such that the respective third sipes 7C extend from the connecting point P to the other side in the tire circumferential direction (lower side in the drawing).

[0055] By arranging the sipe unit rows 9 in this manner, in the region of the block land portion 6 sandwiched in the tire width direction between the third sipes 7C of the plurality of sipe units 8 constituting the adjacent sipe unit rows 9A and 9B (between the center lines L of the adjacent sipe unit rows 9A and 9B), the plurality of sipes 7 extend inclined in the same direction with respect to the tire width direction. Specifically, in FIG. 3 , the second sipe 7B of the sipe unit 8A included in the sipe unit row 9A and the second sipe 7B of the sipe unit 8B included in the sipe unit row 9B extend approximately parallel to each other. As a result, in the region of the block land portion 6 sandwiched between the center lines L of the sipe unit rows 9A and 9B adjacent to each other in the tire width direction, the sipes 7 are periodically arranged, and the shape and size of the block land portions 6 sandwiched between the sipes 7 in the tire circumferential direction can be made uniform. This allows the sipe density in the block land portion 6 to be made uniform. This allows the tread surface 2 to come into contact with the road surface more evenly, making it possible to more evenly distribute the contact pressure applied to the contact surface of the tread surface 2 and increasing the contact area of ​​the tire 1. This therefore further improves the grip performance of the tire 1 on ice.

[0056] In the illustrated example, at least one of the plurality of sipe units 8 constituting a first sipe unit row 9A among the plurality of sipe unit rows 9 and at least one of the plurality of sipe units 8 constituting a second sipe unit row 9B adjacent to the first sipe unit row 9A are opposed to each other in the tire width direction in the tire circumferential direction. Specifically, in FIG. 3, the second sipe 7B of the sipe unit 8A constituting the sipe unit row 9A and the second sipe 7B of the sipe unit 8B constituting the sipe unit row 9B are opposed to each other in the tire width direction in the tire circumferential direction only in the tire width direction. Here, "the line segment X and the line segment Y are opposed to each other in the Z direction" means that the line segment X and the line segment Y are spaced from each other in the Z direction, and both ends of the line segment Y are located on two straight lines extending from both ends of the line segment X along the Z direction, respectively. However, the phrase "the second sipes 7B of the sipe unit 8A constituting the sipe unit row 9A and the second sipes 7B of the sipe unit row 8B constituting the sipe unit row 9B face each other in the tire circumferential direction only at portions in the tire width direction" also includes a case where only the end points of the second sipes 7B of the sipe unit 8A and the second sipes 7B of the sipe unit 8B are located on a straight line extending along the tire circumferential direction. In FIG. 3, a portion 7a of the second sipes 7B of the sipe unit 8A in the tire width direction faces a portion 7b of the second sipes 7B of the sipe unit 8B in the tire width direction. In this case, the length W (W = 2a × cos φ) of each of the sipe unit rows 9A and 9B in the tire width direction and the distance D between the center lines L of adjacent sipe unit rows 9A and 9B in the tire width direction satisfy WD≧0. As a result, as shown by the diagonal shading in Figure 3, when the sipe unit 8A that constitutes the sipe unit row 9A and the sipe unit 8B that constitutes the sipe unit row 9B are projected along the tire circumferential direction, at least one of the sipe units 8A and 8B extends seamlessly across the tire width direction of the sipe unit 8.Therefore, by increasing the length of the sipe unit rows 9 in the tire width direction within a range that satisfies WD≧0 without changing the shape of each of the sipe units 8 that make up the first sipe unit row 9A and the second sipe unit row 9B, it is possible to widen the range in which the sipe units 8 can exert their edge effect and water removal effect while maintaining the sipe density in the block land portion 6. This makes it possible to improve the grip performance of the tire 1 on ice.

[0057] In addition, in FIG. 3 , if the distance in the tire circumferential direction between the second sipes 7B of the sipe units 8A and 8B, in which the second sipes 7B partially oppose each other in the tire circumferential direction, is q, the block land portion 6 surrounded by the sipe unit 8A (the sipes 7B and 7C of the sipe unit 8A) and the sipe unit 8B (the sipes 7B and 7C of the sipe unit 8B) is a rectangle (a parallelogram in the illustrated example) with a tire circumferential length q and a tire widthwise length D. In this case, it is preferable that q≦3D. This ensures a sufficient density in the tire width direction of the multiple sipe units 8 arranged in the block land portion 6. Here, if the distance in the tire circumferential direction between the connecting points P of the sipe units 8A and 8B is c, q is expressed as q=D×tanφ+c. When φ≦45°, tanφ≦1, and q≦D+c. Therefore, in order to satisfy q≦3D, it is preferable that the distance c in the tire circumferential direction between the connection points P of the sipe units 8A and 8B satisfies c≦2D.

[0058] Among the multiple sipe unit rows 9, between the sipe unit rows 9 in which the third sipes 7C of the sipe units 8 constituting each sipe unit row 9 are arranged to extend in the same direction in the tire circumferential direction from the connecting point P, the positions of the multiple sipe units 8 constituting each sipe unit row 9 in the tire circumferential direction may be equal to each other. Specifically, the third sipes 7C of the sipe units 8 constituting the sipe unit row 9A and the sipe units 8 constituting the sipe unit row 9C arranged to sandwich the sipe unit rows 9A and 9B in the tire width direction extend in the same direction in the tire circumferential direction from the connecting point P. In FIG. 3 , the sipe units 8A included in the sipe unit row 9A and the sipe units 8C included in the sipe unit row 9C are arranged to be equal to each other in the tire circumferential direction. This allows the sipe density in the block land portion 6 to be further uniform. This allows the tread surface 2 to contact the road surface more uniformly, uniforming the distribution of ground pressure applied to the contact surface of the tread surface 2 and increasing the contact area of ​​the tire 1. Therefore, the grip performance of the tire 1 on ice can be further improved.

[0059] 1, eight sipe units 8 are arranged in each of the block land portions 6 of the land portions 4A and 4E, and 24 sipe units 8 are arranged in each of the block land portions 6 of the land portions 4B, 4C, and 4D. However, the number of sipe units 8 arranged in one block land portion 6 may be any number.

[0060] For example, the number of sipe units 8 arranged in the block land portion 6 may be determined based on the circumferential sipe density SD of the tire. The circumferential sipe density SD is an index that indicates the density at which transverse sipes, which are provided so as to completely cross the block land portion 6, are arranged in the circumferential direction of the tire. The outer contour area (mm 2If the equivalent circumferential length of the block land portion 6, calculated by dividing the block land portion 6 length (length) by the maximum width (BW), is BL (mm), and the number of transverse sipes provided so as to completely cross the block land portion 6 is N', the average circumferential sipe spacing is expressed as BL / (N'+1). The circumferential sipe density SD is expressed as the reciprocal of the average sipe spacing by the following equation (1). SD=(N'+1) / BL (1)

[0061] The "outer contour area" of the block land portion 6 refers to the area surrounded by the outer contour of the block land portion 6 in a developed view of the tread surface 2. Therefore, even if non-contacting portions such as sipes, small holes, narrow grooves, etc. are arranged within the block land portion 6, the "outer contour area" does not exclude the areas of the sipes, small holes, narrow grooves, etc.

[0062] A method for calculating the sipe density SD in this embodiment will be described below. For example, as shown in the sipe shape diagram of FIG. 9 , assume that a rectangular block land portion 6 is provided with a plurality of sipe units 8. First, let us assume that the number of sipe units 8 in the block land portion 6 is n, the total length in the tire width direction of the sipes 7 constituting the sipe unit 8 is T (mm), and the maximum width in the tire width direction of the block land portion 6 is BW (mm). The equivalent number of sipes N is expressed as T × n / BW. In this embodiment, T is the total length in the tire width direction of the sipes 7A, 7B, and 7C, and is expressed as 2d (= 2a × cos φ). Here, the equivalent number of sipes N is the number of sipes 7 in this embodiment converted into transverse sipes (equivalent sipes) that are provided so as to completely cross the block land portion 6. Furthermore, let us assume that the equivalent circumferential length of the block land portion 6 is BL (mm), and the average circumferential sipe spacing in the tire width direction is expressed as BL / (N + 1). Here, the average sipe spacing in the tire circumferential direction is the spacing in the tire circumferential direction of the equivalent sipes in the block land portion 6 when the sipes 7 of this embodiment are converted to equivalent sipes. The sipe density SD in the tire circumferential direction is expressed as the reciprocal of the average sipe spacing by the following equation (2). SD=(N+1) / BL=((T×n / BW)+1) / BL (2)

[0063] The number n of sipe units 8 in the block land portion 6, the total length T of the sipes 7 constituting the sipe unit 8 in the tire width direction, the maximum width BW of the block land portion 6 in the tire width direction, and the outer contour area of ​​the block land portion 6 are values ​​measured in a developed view of the tread surface 2.

[0064] For example, a plurality of sipe units 8 may be arranged in the block land portion 6 so that the sipe density SD is 0.15 (1 / mm) or more, thereby improving the grip performance of the tire 1 on ice.

[0065] In a block land portion 6, multiple sipes 7 may be connected by shallow grooves 10. FIG. 6 is a schematic diagram showing the arrangement of sipe units 8 in which sipes 7 are connected by shallow grooves 10 in one embodiment of the present invention. The block land portion 6 shown in FIG. 6 corresponds to, for example, the block land portion 6B shown in FIG. 1. In FIG. 6, six sipe unit rows 9 are arranged side by side in the tire width direction in the block land portion 6. In the sipe unit row 9, four sipe units 8 are arranged repeatedly in the tire circumferential direction. In FIG. 6, the sipe units 8 included in the sipe unit rows 9 arranged every other row in the tire width direction are connected by shallow grooves 10 crossing the block land portion 6. Specifically, the shallow groove 10 is composed of a straight line 10A extending from the connecting point P of any one of the sipe units 8 along the first sipe 7A to the center line L' of the adjacent sipe unit row 9, and a straight line 10B extending from the connecting point P of any one of the sipe units 8 along the second sipe 7B to the center line L'' of the adjacent sipe unit row 9. That is, in the block land portion 6, multiple sipe units 8 are connected by a zigzag shallow groove 10 that crosses the block land portion 6 in the tire width direction. In FIG. 6, a cross section (B-B' cross section) of the tire 1 cut along the extension direction of the shallow groove 10 is shown in FIG. 7. In FIG. 7, the depth (maximum depth) H of the shallow groove 10 may be determined depending on the depth h of the sipe 7. For example, the depth H of the shallow groove 10 may be determined in a range of 5 to 60% of the depth h of the sipe 7, and preferably in a range of 5 to 20%. For example, the depth h of the sipes 7 may be 6.7 mm, and the depth H of the shallow grooves 10 may be 0.7 mm. With this configuration, water trapped in the gaps of the sipes 7 is drained in the tire width direction through the shallow grooves 10, improving the grip performance on ice in the block land portion 6.

[0066] 1, the block land portion 6 of the tire 1 may be provided with sipes other than the above-described sipe units 8. For example, in the illustrated example, the land portions 4A and 4E are provided with a plurality of zigzag sipes 11 extending in the tire width direction toward the tread edge TE. This improves drainage in the tread surface 2 and improves the grip performance of the tire 1 on ice.

[0067] Referring to FIG. 8, a modified example of the sipe unit 8 according to one embodiment of the present invention will be described. FIG. 8 is a schematic diagram showing the arrangement of a modified example of the sipe unit 8 according to one embodiment of the present invention. In FIG. 8, the modified example of the sipe unit 8 is shown in a developed view of the tread surface 2. In FIG. 8, the vertical direction in the drawing is the tire circumferential direction, and the horizontal direction in the drawing is the tire width direction. Hereinafter, the modified example of the sipe unit 8 will be described, focusing on differences from the above-described sipe unit 8. Portions not described below, such as the modified example of the sipe unit 8, the size of the sipes 7 constituting the modified example of the sipe unit 8, and their arrangement in the block land portion 6, may be the same as the above-described sipe unit 8. For example, FIG. 8(a) shows a sipe unit 8D, which is a first modified example of the sipe unit 8. The sipe unit 8D differs from the sipe unit 8A shown in FIG. 3 in that the widths of the three or more sipes 7 constituting the sipe unit 8D are wider near the connecting point P of the sipe unit 8D. In the illustrated example, the widths of the three sipes 7A, 7B, and 7C that make up the sipe unit 8D are increased near the connecting point P of the sipe unit 8D, forming a circular sipe centered on the connecting point P. The shape of this sipe unit 8D is realized by providing a blade reinforcing core at the position of the connecting point P of the blades that are placed in the mold for the tire 1 to form each sipe 7 during tire manufacturing. In this way, by providing a blade reinforcing core in the portion of the mold for the tire 1 that corresponds to the connecting point P of the sipe unit 8D, the durability of the blade is improved. Therefore, the durability of the mold for the tire 1 is improved, and the productivity of the tire 1 is improved.

[0068] Also, for example, (b) of FIG. 8 shows a sipe unit 8E that is a second modified example of the sipe unit 8. The sipe unit 8E differs from the sipe unit 8A shown in FIG. 3 in that the three or more sipes in the sipe unit 8E include a plurality of sipes 7 extending in the tire circumferential direction from the junction point P, instead of the third sipe 7C extending in the tire circumferential direction from the junction point P. In the illustrated example, the sipe unit 8E is composed of four sipes 7A, 7B, 7D, and 7E, including two sipes 7D and 7E extending in the tire circumferential direction from the junction point P. In a developed view of the tread surface 2, the sipes 7D and 7E extend from the junction point P on the opposite side in the tire width direction from the first sipe 7A and the second sipe 7B (upper side in the drawing). The sipe 7D extends at an angle toward one side in the tire width direction (left side in the drawing) from the connecting point P in the tire circumferential direction (upper side in the drawing). On the other hand, the sipe 7E extends at an angle toward the other side in the tire width direction (right side in the drawing) from the connecting point P in the tire circumferential direction (upper side in the drawing). [Example]

[0069] Examples of tire 1 according to one embodiment of the present invention will be described below with reference to Figs. 9, 10, and 11. Fig. 9 is a table showing examples and comparative examples. Fig. 10 is a diagram showing block rigidity and sipe density in the examples and comparative examples shown in Fig. 9. Fig. 11 is a diagram showing contact area and sipe density in the examples and comparative examples shown in Fig. 9. In Example 1 and Comparative Examples 1 and 2, evaluations were performed assuming that sipes shown in the sipe shape diagram in Fig. 9 were arranged on rectangular block land portions measuring 30 mm in the tire circumferential direction and 27 mm in the tire width direction.

[0070] Simulations were performed using the finite element method (FEM) for the tires of Example 1 and Comparative Examples 1 and 2 shown in FIG. 9, and block rigidity and contact area relative to sipe density were evaluated under the condition that a vertical load calculated by multiplying the outer contour area of ​​the block land portion by the standard contact pressure of 230 kPa for passenger car tires was applied.

[0071] As a result, as shown in Figs. 10 and 11, in the example, the block rigidity Kx (N / mm) and the actual contact area Ar (mm) during shear were significantly lower than in the comparative example, where the sipe density was set to the same level. 2 Here, block stiffness Kx (N / mm) is the shear input value in the same direction when the lateral displacement in the tire circumferential direction is 1 mm, and the actual contact area Ar (mm 2 ) is the remaining contact area in a state where partial lift occurs when the shear input in the tire circumferential direction is 0.3 times the vertical load. In this way, in the examples, compared to the comparative examples, it is possible to improve the land portion rigidity while maintaining the sipe density, or to increase the sipe density while maintaining the land portion rigidity. Therefore, in tire 1 according to one embodiment of the present invention, by achieving both sipe density and land portion rigidity, it is possible to improve grip performance on ice.

[0072] From the above, it has become clear that the tire 1 according to one embodiment of the present invention improves the grip performance of the tire 1 on ice.

[0073] As described above, a tire 1 according to one embodiment of the present invention is a tire 1 having land portions 4 (block land portions 6) on a tread surface 2, in which a sipe unit 8 is disposed in the land portion 4 (block land portion 6), the sipe unit 8 having a connecting point P and composed of three or more sipes 7 extending radially from the connecting point P, each of the three or more sipes 7 in the sipe unit 8 extending such that both ends in the extension direction of the sipe 7 terminate within the land portion 4 (block land portion 6), and the three or more sipes 7 in the sipe unit 8 include a first sipe 7A extending from the connecting point P to one side in the tire width direction and a second sipe 7B extending from the connecting point P to the other side in the tire width direction. With this configuration, a decrease in the rigidity of the land portion 4 (block land portion 6) due to the arrangement of the sipe unit 8 in the land portion 4 (block land portion 6) is suppressed, and ultimately a decrease in the contact area of ​​the tire 1 can be suppressed. This makes it possible to improve the grip performance of the tire 1 on ice.

[0074] In tire 1 according to one embodiment of the present invention, each of first sipes 7A and second sipes 7B preferably extends linearly so that the angle φ formed with the tire width direction satisfies 0°<φ<45°. With this configuration, sipe unit 8 not only contributes to improving the braking force and driving force in the tire circumferential direction of tire 1, but also contributes to improving lateral grip performance (cornering force) in the tire width direction.

[0075] In a tire 1 according to one embodiment of the present invention, the three or more sipes 7 in a sipe unit 8 preferably include a third sipe 7C extending from the connecting point P along the tire circumferential direction, and the third sipe 7C extends from the connecting point P on the opposite side of the tire width direction from the first sipe 7A and the second sipe 7B. With this configuration, it is possible to suppress a decrease in the rigidity of the land portion 4 (block land portion 6) caused by arranging the sipe unit 8 in the land portion 4 (block land portion 6), and thus to suppress a decrease in the contact area of ​​the tire 1. This makes it possible to further improve the grip performance of the tire 1 on ice.

[0076] In the tire 1 according to one embodiment of the present invention, the length of the third sipe 7C is preferably shorter than the first sipe 7A and the second sipe 7B. With this configuration, the proportion of the tire width direction components of the sipes 7 constituting the sipe unit 8 increases, and the sipe unit 8 is more likely to contribute to improving the braking force and driving force of the tire 1 in the tire circumferential direction.

[0077] In a tire 1 according to one embodiment of the present invention, in a land portion 4 (block land portion 6), a plurality of sipe units 8 are repeatedly arranged in the tire circumferential direction to form a sipe unit row 9, and the plurality of sipe units 8 that form the sipe unit row 9 are preferably arranged so that each of the third sipes 7C is aligned in a straight line extending along the tire circumferential direction. With this configuration, water trapped in the gaps of the sipes 7 that form the sipe unit 8 is drained in the tire circumferential direction along the plurality of third sipes 7C that are aligned in a straight line, thereby further improving the grip performance of the tire 1 on ice.

[0078] In a tire 1 according to one embodiment of the present invention, the land portion 4 (block land portion 6) includes a plurality of sipe unit rows 9 arranged side by side in the tire width direction. The plurality of sipe units 8 constituting a first sipe unit row 9A among the plurality of sipe unit rows 9 are preferably arranged such that each of the third sipes 7C extends from the connecting point P to one side in the tire circumferential direction, and the plurality of sipe units 8 constituting a second sipe unit row 9B adjacent to the first sipe unit row 9A are preferably arranged such that each of the third sipes 7C extends from the connecting point P to the other side in the tire circumferential direction. With this configuration, when an external force is applied to the tire 1, the land portions 4 (block land portions 6) in the range where adjacent sipe unit rows 9 are arranged support each other, making them less likely to collapse. This increases the rigidity of the land portions 4 (block land portions 6). This further improves the grip performance of the tire 1 on ice.

[0079] In the tire 1 according to one embodiment of the present invention, it is preferable that at least one of the sipe units 8 constituting the first sipe unit row 9A and at least one of the sipe units 8 constituting the second sipe unit row 9B are arranged such that a portion of each of the sipe units 8 in the tire width direction faces the other in the tire circumferential direction. With this configuration, the sipe density in the land portion 4 (block land portion 6) can be maintained while the range in which the sipe units 8 can exert the edge effect and water removal effect can be widened.

[0080] In the tire 1 according to one embodiment of the present invention, when the length of the sipe unit 8 in the tire width direction is W (mm) and the depth of the sipe 7 constituting the sipe unit 8 is h (mm), W×h is 150 (mm 2 ) or less, where n is the number of sipe units 8 in the land portion 4 (block land portion 6), T (mm) is the total length of the sipes 7 constituting the sipe unit 8 in the tire width direction, BW (mm) is the maximum width of the land portion 4 (block land portion 6) in the tire width direction, and BW (mm) is the outer contour area (mm 2When the equivalent circumferential length of the land portion 4 (block land portion 6) is expressed as BL (mm), where BL is the equivalent number of sipes N, T×n / BW, the average circumferential sipe spacing is expressed as BL / (N+1), and the circumferential sipe density SD is expressed as the reciprocal of the average sipe spacing, SD = (N+1) / BL = ((T×n / BW)+1) / BL, it is preferable that SD be 0.15 (1 / mm) or more. With this configuration, it is possible to increase the sipe density while suppressing a decrease in the rigidity of the land portion 4 (block land portion 6) due to the placement of sipes 7 in the land portion 4 (block land portion 6). This allows for improved grip performance on ice of the tire 1.

[0081] Although the present invention has been described based on the drawings and embodiments, it should be noted that those skilled in the art can make various modifications and alterations based on the present invention. Therefore, it should be noted that these modifications and alterations are within the scope of the present invention. For example, the configurations or functions included in each embodiment can be rearranged so as not to cause logical inconsistencies. Furthermore, the configurations or functions included in each embodiment can be combined with other embodiments, and multiple configurations or functions can be combined, divided, or partially omitted. [Explanation of symbols]

[0082] 1: tire, 2: tread surface, 3 (3A, 3B, 3C, 3D): circumferential main groove, 4 (4A, 4B, 4C, 4D, 4E): land portion, 5 (5A, 5B): widthwise groove, 6 (6A, 6B, 6C): block land portion, 6a, 6b: portion of block land portion, 7: sipe, 7A: first sipe, 7B: second sipe, 7C: third sipe, 7D, 7E: other sipe, 7a, 7b: portion of sipe, P: connection point, 8 (8A, 8B, 8C, 8D, 8E): sipe unit, 9 (9A, 9B, 9C): sipe unit row, 10: shallow groove, 10A, 10B: straight line constituting shallow groove, a, b: sipe length, w: sipe width, h: sipe depth, φ (φ1, φ2): angle between the sipe and the tire width direction, d: length of the first sipe or the second sipe in the tire width direction, p: pitch of the sipe unit in the tire circumferential direction, q: distance in the tire circumferential direction between second sipes of sipe units in which the second sipes are partially opposed to each other in the tire circumferential direction, L (L', L''): center line of the sipe unit row, W: length of the sipe unit row in the tire width direction, D: distance between the center lines in the tire width direction between adjacent sipe unit rows in the tire width direction, SD: sipe density, N: number of equivalent sipes, BW: maximum width in the tire width direction of the block land portion, BL: equivalent length in the tire circumferential direction of the block land portion, A-A', B-B': cross section, TE: tread edge, CL: tire equatorial plane, Ar: actual contact area during shear, Kx: block rigidity, H: depth of shallow groove, U: lift

Claims

1. A tire having a land portion on the tread surface, A sipe unit having a connecting point and configured with three sipes extending radially from the connecting point is disposed in the land portion, each of the three sipes in the sipe unit extends such that both ends in an extension direction of the sipe terminate within the land portion; the three sipes in the sipe unit include a first sipe extending from the connecting point to one side in the tire width direction and a second sipe extending from the connecting point to the other side in the tire width direction, the three sipes in the sipe unit include a third sipe extending from the connecting point along the tire circumferential direction, the third sipe extends from the connecting point to a side opposite to the first sipe and the second sipe in the tire circumferential direction, The tire, wherein the third sipes have a length shorter than the first sipes and the second sipes.

2. The tire according to claim 1 , wherein each of the first sipes and the second sipes extends linearly such that an angle φ formed with the tire width direction satisfies 0°<φ<45°.

3. In the land portion, a plurality of the sipe units are repeatedly arranged in the tire circumferential direction to form a sipe unit row, The tire according to claim 1 , wherein the plurality of sipe units constituting the sipe unit row are arranged such that the third sipes are aligned on a straight line extending along the tire circumferential direction.

4. The land portion includes a plurality of sipe unit rows arranged side by side in the tire width direction, a plurality of sipe units constituting a first sipe unit row among the plurality of sipe unit rows are arranged such that each of the third sipes extends from the connecting point to one side in the tire circumferential direction, 4. The tire according to claim 3, wherein the plurality of sipe units constituting the second sipe unit row adjacent to the first sipe unit row are arranged such that the third sipes of each extend from the connecting point to the other side in the tire circumferential direction.

5. 5. The tire according to claim 4, wherein at least one of the plurality of sipe units constituting the first sipe unit row and at least one of the plurality of sipe units constituting the second sipe unit row have portions in the tire width direction that face each other in the tire circumferential direction.

6. When the length of the sipe unit in the tire width direction is W (mm) and the depth of the sipe is h (mm), W x h is 150 (mm ２ ) or less, The number of sipe units in the land portion is defined as n, the total length of the sipes constituting the sipe unit in the tire width direction is defined as T (mm), the maximum width of the land portion in the tire width direction is defined as BW (mm), and the outer contour area of ​​the land portion (mm ２ 6. The tire according to claim 1, wherein, when an equivalent circumferential length of the land portion is defined as BL (mm) obtained by dividing the maximum width BW by the maximum width BW, the equivalent number of sipes N is expressed as T×n / BW, the average circumferential spacing of the sipes is expressed as BL / (N+1), and the circumferential sipe density SD is expressed as the reciprocal of the average sipe spacing, SD = (N+1) / BL = ((T×n / BW)+1) / BL, SD is 0.15 (1 / mm) or more.

Images