pneumatic tires

Abstract

To provide a pneumatic tire improved in on-ice gripping performance.SOLUTION: A plurality of minute sipes 7 is disposed on at least one of land parts 4. The minute sipes form connected body sipes 8 connected with each other, and the connected body sipes configure sipe units. The sipe units are repeatedly arranged on the land part. At least one minute sipe terminates in the land part at least one side end in an extending direction of the minute sipe. Assuming tire width direction length of the connected body sipe as w1(mm), and depth of the minute sipe h(mm), w1×h is 150(mm2) or less, and sipe density SD is 0.15(1 / mm) or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a pneumatic tire. [Background technology]

[0002] Traditionally, pneumatic tires, especially studless tires, have had narrow grooves called sipes on the land portion of the tread to improve grip performance on ice. These sipes allow water that seeps out as the ice melts at the tire's contact surface to be discharged outside the contact surface, thereby improving grip performance on ice.

[0003] A technology has been proposed to improve ice grip performance by densely arranging sipes while suppressing a decrease in the rigidity of the land portion (for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2005-186827 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, Patent Document 1 did not adequately balance the rigidity of the land portion with water discharge by sipes, leaving room for improvement in enhancing grip performance on ice.

[0006] Therefore, the present invention aims to provide a pneumatic tire with improved grip performance on ice. [Means for solving the problem]

[0007] The gist of the present invention is as follows: (1) A pneumatic tire having at least one land portion on the tread surface, Multiple micro-sipes are arranged in at least one of the aforementioned land areas. The aforementioned minute sipes form a connected sipe structure, The connected sipes constitute a sipe unit, and the sipe units are arranged repeatedly on the land portion. At least one of the microsipes has at least one end in the direction of extension of the microsipe that terminates within the land area. When the length of the connecting sipe in the tire width direction is w1 (mm) and the depth of the minute sipe is h (mm), then w1 × h = 150 (mm) 2 ) and below, Let n be the number of connecting sipes within the land area, BW be the maximum width of the land area in the tire width direction, and (mm) be the outer contour area of ​​the land area. 2 A pneumatic tire characterized in that, when the equivalent circumferential length of the tire on land is defined as BL (mm) by dividing ) by BW (mm), the equivalent number of sipes N is defined as w1 × n / BW, the average sipe spacing in the circumferential direction of the tire is expressed as BL / (N+1), and the sipe density SD is defined as the reciprocal of the average sipe spacing in the circumferential direction of the tire, then when expressed as SD = (N+1) / BL = ((w1 × n / BW) + 1) / BL, SD is 0.15 (1 / mm) or more.

[0008] Here, "tread surface" refers to the entire circumferential surface of the tread that comes into contact with the road surface when a pneumatic tire is mounted on an applicable rim, filled to the specified internal pressure, and subjected to the maximum load. Furthermore, "sipes" refer to sipes where, when the tire is mounted on the applicable rim, filled to the specified internal pressure, and unloaded, the sipe width is 1 mm or less in an area of ​​50% or more of the sipe depth. Here, the sipe depth is measured in the direction perpendicular to the tread surface in the above condition, and the sipe width is measured in the direction parallel to the tread surface in a cross section perpendicular to the extension direction on the tread surface. The number of interconnected sipes n, the maximum width BW in the tire width direction of the land portion, and the outer contour area of ​​the land portion shall be values ​​measured from a flat view of the tread surface. "Outer contour area" refers to the area enclosed by the outer contour when the tread surface is flat viewed, and therefore, even if non-contact areas such as sipes, small holes, and narrow grooves are located within the land portion, this area does not exclude the area of ​​such sipes, small holes, and narrow grooves.

[0009] In this specification, "applicable rim" refers to the standard rim for the applicable size (Measuring Rim in the ETRTO STANDARDS MANUAL, Design Rim in the TRA YEAR BOOK) which is an industrial standard valid in the region where the tire is produced and used, and which is listed or will be listed in the future in publications such as the JATMA YEAR BOOK of JATMA (Japan Automobile Tire Manufacturers Association) in Japan, the STANDARDS MANUAL of ETRTO (The European Tyre and Rim Technical Organisation) in Europe, and the YEAR BOOK of TRA (The Tire and Rim Association, Inc.) in the United States. (That is, the above "rim" includes not only current sizes but also sizes that may be included in the above industrial standards in the future. An example of a "size to be listed in the future" is the size listed as "FUTURE DEVELOPMENTS" in the ETRTO 2013 edition.) However, in the case of a size not listed in the above industrial standards, it refers to a rim with a width corresponding to the tire bead width. Furthermore, "specified internal pressure" refers to the air pressure (maximum air pressure) corresponding to the maximum load capacity of a single wheel in the applicable size and ply rating as described in JATMA, etc. For sizes not listed in the above industrial 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 mounted. Furthermore, "maximum load capacity" refers to the load corresponding to the above maximum load capacity.

[0010] (2) A pneumatic tire having at least one land area on the tread surface, Multiple micro-sipes are arranged in at least one of the aforementioned land areas. The spaced-apart minute sipes constitute a sipe unit, and these sipe units are arranged repeatedly on the land portion. At least one of the microsipes has at least one end in the direction of extension of the microsipe that terminates within the land area. When the length of the minute sipe in the tire width direction is w2 (mm) and the depth of the minute sipe is h (mm), then w2 × h = 150 (mm) 2 ) and below, Let n be the number of minute sipes within the land area, BW be the maximum width of the land area in the tire width direction, and BW be the outer contour area of ​​the land area (mm²). 2 A pneumatic tire characterized in that, when the equivalent circumferential length of the tire on land is defined as BL (mm) by dividing ) by BW (mm), the equivalent number of sipes N is defined as w² × n / BW, the average sipe spacing in the circumferential direction of the tire is expressed as BL / (N+1), and the sipe density SD is defined as the reciprocal of the average sipe spacing in the circumferential direction of the tire, then when expressed as SD = (N+1) / BL = ((w² × n / BW) + 1) / BL, SD is 0.15 (1 / mm) or more.

[0011] (3) The pneumatic tire according to (1) or (2) above, wherein a plurality of the sipe units are arranged to be spaced apart from each other in the circumferential direction of the tire.

[0012] (4) Multiple rows of the sipe units arranged in the tire width direction are arranged in the tire width direction, A pneumatic tire according to any one of (1) to (3) above, wherein the sipe units in one row and the sipe units in an adjacent row adjacent to the first row are arranged with a phase shift in the circumferential direction of the tire.

[0013] (5) When the pitch distance between adjacent sipe units in the tire circumferential direction within one row is p (mm), and the circumferential distance between a sipe unit in one row and a sipe unit in an adjacent row is q (mm), p / 2 × 0.7 ≤ q ≤ p / 2 × 1.3 A pneumatic tire as described in (4) above, which satisfies the requirements.

[0014] (6) The sipe units are arranged linearly in a row in the tire width direction or at an inclination angle of 30° or less with respect to the tire width direction, When the distance between the connection points in the tire width direction of the adjacent sipe units in one row is b, and the sipe interval, which is the shortest distance in the tire width direction between the adjacent sipe units in the one row, is s, 0.2 ≤ s / (b - s) ≤ 1.0 The pneumatic tire according to (1) above, which satisfies the above condition.

[0015] (7) The pneumatic tire according to (6) above, wherein s is 1.5 (mm) or more.

[0016] (8) The sipe units are arranged in a plurality of rows in the tire width direction, The two adjacent rows are arranged with a phase shift in the tire circumferential direction such that the positions of the sipe units in the tire circumferential direction of one row and the sipe units in the adjacent row adjacent to the one row are staggered from each other, The sipe units are arranged linearly in a row in the tire width direction or at an inclination angle of 30° or less with respect to the tire width direction, When the distance between the connection points in the tire width direction of the adjacent sipe units in one row is b, and the circumferential separation distance between the connection point of the sipe units in the one row and the connection point of the sipe units in the adjacent row is c, 0 ≤ c / b ≤ 1.0 The pneumatic tire according to (1) above, which satisfies the above condition.

Advantages of the Invention

[0017] According to the present invention, it is possible to provide a pneumatic tire with improved ice grip performance.

Brief Description of the Drawings

[0018] [Figure 1] It is a view showing a tread pattern of a pneumatic tire according to an embodiment of the present invention. [Figure 2] Figure 1 is a schematic diagram showing the arrangement of the sipe units. [Figure 3] Figure 1 is a schematic diagram showing the arrangement of the sipe unit when the sipe unit does not include sipe 7C. [Figure 4A] This is a cross-section of the sipe. [Figure 4B] This is a cross-section of the sipe. [Figure 5] This diagram shows a modified sipe unit. [Figure 6] This diagram shows a modified sipe unit. [Figure 7] This diagram shows a modified sipe unit. [Figure 8] This diagram shows the specifications of each tire in the embodiment. [Figure 9] This figure shows the specifications of Comparative Example 1. [Figure 10] This figure shows the specifications of Comparative Example 2. [Figure 11] This figure shows the specifications of Example 1. [Figure 12] This figure shows the specifications of Example 2. [Figure 13] This figure shows the specifications of Example 3. [Figure 14] This figure shows the specifications of Example 4. [Figure 15] This figure shows the simulation results of the block rigidity in the example. [Figure 16] This figure shows the simulation results of the contact area in the example. [Figure 17] This figure shows the results of the friction coefficient on ice in the example (speed: 5 km / h). [Figure 18] This figure shows the results of the friction coefficient on ice in the example (speed: 2 km / h). [Modes for carrying out the invention]

[0019] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0020] First, the internal structure of a pneumatic tire (hereinafter also simply referred to as a tire) can be the same as that of conventional tires. For 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 positioned between the pair of sidewall portions. The tire may also have a carcass that spans the pair of bead portions in a toroidal manner, and a belt positioned on the radially outer side of the crown portion of the carcass. Unless otherwise specified, the dimensions and other specifications refer to those of a tire mounted on the applicable rim, filled to the specified internal pressure, and under no-load conditions.

[0021] Figure 1 shows the tread pattern of a pneumatic tire according to one embodiment of the present invention. As shown in Figure 1, the tire 1 has one or more (four in the illustrated example) circumferential main grooves 3 (3A to 3D) extending in the circumferential direction of the tire on the tread surface 2. The number of circumferential main grooves 3 is not limited to this example and can be changed as appropriate.

[0022] The groove width (opening width) of the circumferential main groove 3 is not particularly limited, but can be, for example, 4 to 15 mm, and the depth (maximum depth) of the circumferential main groove 3 is not particularly limited, but can be, for example, 6 to 20 mm. In the illustrated example, the circumferential main groove 3 extends straight in the circumferential direction of the tire, but it may extend in a zigzag pattern or while bending. The circumferential main groove 3 may be inclined at an angle of 5° or less with respect to the circumferential direction of the tire.

[0023] As shown in Figure 1, the circumferential main groove 3 and the tread edge TE divide the tire into multiple (five in the illustrated example) land areas 4 (4A to 4E). Specifically, land area 4A is divided between the tread edge TE and the circumferential main groove 3A, land area 4B is divided between the circumferential main grooves 3A and 3B, land area 4C is divided between the circumferential main grooves 3B and 3C, land area 4D is divided between the circumferential main grooves 3C and 3D, and land area 4E is divided between the tread edge TE and the circumferential main groove 3D. Thus, the tire has at least one land area 4.

[0024] Each of the land sections 4A to 4E has multiple widthwise grooves 5 (5A, 5B) extending in the tire width direction, spaced apart in the tire circumferential direction. In land sections 4A, 4C, 4D, and 4E, the widthwise grooves 5 are connected to two adjacent circumferential main grooves 3, and land sections 4A, 4C, 4D, and 4E are divided into block 6 (6A, 6B, 6C). On the other hand, in land section 4B, one end of the widthwise groove 5 is connected to the circumferential main groove 3B, and the other end terminates within land section 4B, making land section 4B a rib-shaped land section (land section that is not completely separated in the circumferential direction depending on the widthwise groove 5). A widthwise sipe extending in the tire width direction is connected to the other end of the widthwise groove 5, and the widthwise sipe extends from the other end of the widthwise groove 5 and communicates with the circumferential main groove 3A.

[0025] The groove width (opening width, or maximum width if the groove width changes) of the widthwise groove 5 is not particularly limited, but can be, for example, 2 to 10 mm, and the depth (maximum depth) of the widthwise groove 5 is not particularly limited, but can be, for example, 5 to 20 mm. Furthermore, it is preferable that the widthwise groove 5 extends in the tire width direction or is inclined at an angle of more than 0° and 45° or less with respect to the tire width direction. The widthwise groove 5 can be arranged at equal intervals in the tire circumferential direction, or the pitch interval may be changed to reduce pattern noise. The sipe width (opening width) of the lateral sipe is not particularly limited, but can be 0.3 to 1 mm, and the sipe depth (maximum depth) of the lateral sipe is not particularly limited, but can be, for example, 3 to 10 mm. Furthermore, it is preferable that the lateral sipe extends in the tire width direction or is inclined at an angle of more than 0° and 45° or less with respect to the tire width direction. Furthermore, the land sections 4A and 4E are equipped with multiple widthwise sipes 10 that extend from the tread edge and terminate within the land section.

[0026] In this tire 1, multiple micro-sipes 7 (7A, 7B, 7C) are arranged on at least one of the land sections 4 (all of the land sections 4 in the illustrated example). In the illustrated example, multiple micro-sipes 7 are arranged on each block (or each section of the land section 4B that is partitioned by the widthwise grooves 5 and widthwise sipes). The micro-sipes 7A, 7B, and 7C are connected to each other to form a connected sipe 8. The connected sipe 8 constitutes a sipe unit, and the sipe units are arranged repeatedly on the land section 4 (in the circumferential direction of the tire in the illustrated example).

[0027] As shown in Figure 1, at least one microsipe (in the illustrated example, each microsipe 7A, 7B, and 7C) terminates within the land area 4 at at least one end in the direction of extension of the microsipe. In the illustrated example, one end of each microsipe 7A, 7B, and 7C terminates within the land area 4 without communicating with the circumferential main groove or the widthwise groove, while the other end terminates within the land area 4, connected to each other at a single connection point P. As shown in the illustration, the microsipes 7A, 7B, and 7C extend radially from the connection point P. It is also possible to have a configuration in which two or more microsipes extend radially from a single connection point.

[0028] The configuration of the sipe unit will be described below with reference to Figures 2, 3, and 4. Figure 2 is a schematic diagram showing the arrangement of the sipe unit shown in Figure 1. Figure 3 is a schematic diagram showing the arrangement of the sipe unit when the sipe unit shown in Figure 1 does not include the third sipe 7C. Figures 4A and 4B are cross-sectional views of the sipe.

[0029] As shown in Figures 1 and 2, the sipe 7 constituting the sipe unit includes a first sipe 7A extending from the connection point P to one side in the tire width direction (left side in the drawing) and a second sipe 7B extending from the connection point P to the other side in the tire width direction (right side in the drawing), when viewed in an unfolded view of the tread surface 2. Furthermore, the first sipe 7A and the second sipe 7B extend from the connection point P to the same side in the tire circumferential direction (downward side in the drawing) when viewed in an unfolded view of the tread surface 2. 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 also be simply referred to as sipe 7A, and the second sipe 7B will also be simply referred to as sipe 7B.

[0030] More specifically, the first sipe 7A and the second sipe 7B each extend linearly such that the angle θ they make with the tire width direction satisfies 0° < θ < 45° in this example. Because the sipes 7A and 7B are inclined with respect to the tire width direction, they contribute not only to improving the braking and driving force in the circumferential direction of the tire 1, but also to improving the lateral grip performance. In particular, by setting θ < 45°, the tire width direction component of the sipes 7A and 7B becomes larger than the tire circumferential component, allowing the sipes 7 to contribute to improving the braking and driving force in the circumferential direction, which is the most important aspect for safety. In this embodiment, the angle θ(θ1) between the first sipe 7A and the tire width direction and the angle θ(θ2) between the second sipe 7B and the tire width direction are equal. However, the angle θ1 between the first sipe 7A and the tire width direction, and the angle θ2 between the second sipe 7B and the tire width direction, may be different angles from each other. It is more preferable that θ1 and θ2 are 35° or less.

[0031] In Figure 2, the lengths of the first sipe 7A and the second sipe 7B in the extending direction are the same. The lengths of the sipes 7A and 7B in the extending direction are preferably 3 to 15 mm, more preferably 3 to 10 mm, and even more preferably 3 to 5 mm.

[0032] In this embodiment, when the length of the connecting sipe 8 in the tire width direction (length when projected in the tire width direction) is w1 (mm) and the depth (maximum depth) of the minute sipe 7 is h (mm), then w1 × h = 150 (mm) 2 ) or less. Preferably, w1 × h is 100 (mm 2 ) or less, and more preferably 50(mm 2 ) are as follows:

[0033] The sipe 7 constituting the sipe unit includes a third sipe 7C that extends from the connection point P along the circumferential direction of the tire. As shown in Figure 2, the third sipe 7C, in an unfolded view of the tread surface 2, extends from the connection point P to the first sipe 7A and the second sipe 7B of the tire. Zhou It extends in the opposite direction (upward in the drawing). Hereinafter, the third sipe 7C will also be simply referred to as sipe 7C. Figure 3 is a schematic diagram showing the arrangement of the sipe unit when the sipe unit shown in Figure 1 does not include the third sipe 7C. When the sipe unit does not have the third sipe 7C that extends along the tire circumferential direction, the sipe unit becomes a mountain shape (< shape) with the connection point P protruding in the tire circumferential direction, as shown in Figure 3. Thus, the sipe unit may be composed only of the first sipe 7A and the second sipe 7B.

[0034] Referring again to Figure 2, the length of the third sipe 7C in the extending direction can be, for example, 1 to 15 mm. The length of sipe 7C may be shorter than the lengths of sipes 7A and 7B. This reduces the length of sipe 7C without changing the total length of the sipes 7 that make up the sipe unit 8, thereby increasing the proportion of sipes 7A and 7B that have a tire width component in the sipe unit 8. As a result, the sipe unit is more likely to contribute to improving the braking force and driving force in the circumferential direction of the tire 1. The depth h of sipe 7C may also be equal to the depth h of sipes 7A and 7B. The depth h of sipe 7C is, for example, 3 mm or more. The depth h of sipe 7C may be, for example, 6.7 mm.

[0035] Referring to Figures 4A and 4B, the cross-sectional shape perpendicular to the extension direction of the sipe 7 on the tread surface 2 will be described. In this embodiment, as shown in Figure 4A, the cross-section perpendicular to the extension direction of the sipe 7 is approximately rectangular. In the sipe 7 shown in Figure 4A, the width w of the sipe 7 may be, for example, 0.4 mm. However, the cross-section perpendicular to the extension direction of the sipe 7 may be a shape other than rectangular. For example, as shown in Figure 4B, the sipe 7 may have a shape in which the groove bottom portion is bulging in the cross-section perpendicular to the extension direction of the sipe 7. Alternatively, for example, the sipe 7 may have a shape in which the groove bottom portion is rounded 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 Figure 4A, both ends of the groove bottom portion in the width direction of the sipe 7 may be rounded, or the groove bottom portion may be semicircular. In the sipe 7 shown in Figure 4B, the width w of the sipe 7 may be, for example, 0.4 mm in a region of 50% or more of the depth of the sipe 7.

[0036] As shown in Figure 1, the connected sipes 8 constitute a sipe unit, and the sipe units are arranged repeatedly on the land portion 4. In the illustrated example, the sipe units are arranged spaced apart from each other in the circumferential direction of the tire. In the illustrated example, multiple rows of sipe units arranged in the circumferential direction of the tire are arranged in the width direction of the tire, and the sipe units of one row and the sipe units of the adjacent row adjacent to the first row are arranged with a phase shift in the circumferential direction of the tire (shifted by half a pitch in the illustrated example).

[0037] Furthermore, let n be the number of connecting sipes 8 within the land section, BW be the maximum width of the land section in the tire width direction (mm), and the outer contour area of ​​the land section (mm) 2 By dividing the length of the tire's circumferential length on land by BW (mm), we define BL (mm) as the equivalent length of the tire's circumferential length on land, and the equivalent number of sipes N (which is the number of sipes converted to transverse sipes that completely cross the land area) as w1 × n / BW, expressing the average sipe spacing in the circumferential direction of the tire as BL / (N+1), and defining the sipe density SD as the reciprocal of the average sipe spacing in the circumferential direction of the tire, When expressed as SD = (N + 1) / BL = ((w1 × n / BW) + 1) / BL, In the present embodiment, SD is 0.15 (1 / mm) or more. Hereinafter, the effects of the pneumatic tire of the present embodiment will be described.

[0038] In the pneumatic tire of the present embodiment, the above-described sipe units are repeatedly arranged on the land portion, and w1 × h is 150 (mm 2 ) or less, and the sipe density SD is 0.15 (1 / mm) or more. Thereby, the sipes can be arranged at a high density, and the effect of removing the water film can be improved. Furthermore, since at least one end of the minute sipe in the extending direction terminates within the land portion 4, (compared with the case where both ends communicate with the circumferential main groove and the width direction groove, for example), a decrease in the rigidity of the land portion can be suppressed. Thereby, while arranging the sipes at a high density, a decrease in the block rigidity can be suppressed, so that the grip performance on ice can be improved. In particular, when a plurality of sipe units are arranged so as to be separated from each other in the tire circumferential direction as in the present embodiment, the land portions continuously reinforce each other, so that a decrease in the rigidity of the land portion can be further suppressed. In addition, columns in which the sipe units are arranged in the tire circumferential direction are arranged in a plurality of rows in the tire width direction, and the sipe units in one row and the sipe units in an adjacent row adjacent to the one row are arranged with a phase shift in the tire circumferential direction. As a result, the sipe units can be arranged in a balanced manner, so that a portion where the rigidity of the land portion locally decreases greatly does not occur, and the edge components are arranged in a balanced manner to improve the efficiency of the effect of removing the water film, and the grip performance on ice can be further improved. In particular, it is preferable that w1 × h is 100 (mm 2 ) or less, and more preferably, w1 × h is 50 (mm 2 ) or less. This is because by making the sipes minute, the sipes can be arranged at a higher density, and the effect of removing the water film can be further improved. Furthermore, a sipe density SD of 0.20 (1 / mm) or higher is preferable, and a sipe density of 0.30 (1 / mm) or higher is more preferable. This is because a higher density of sipes can further improve the effect of removing the water film.

[0039] Furthermore, by having the micro-sipes 7 connect to each other to form a connected sipe 8, the micro-sipes 7 can be arranged at a high density. Also, by having the micro-sipes 7 extend radially from the connection point P, edge components can be secured in various directions. In addition, the blades placed in the mold of the tire 1 to form each micro-sipe 7 during tire manufacturing support each other at the connection point P, increasing the bending rigidity of the blades and improving the durability of the blades. As a result, the durability of the mold of the tire 1 is improved, and the productivity of the tire 1 is improved. Moreover, since the sipe unit has a third sipe 7C that extends along the circumferential direction of the tire from the connection point P, in addition to the first sipe 7A and the second sipe 7B, the difference in ground pressure applied to the contact surface of the land portion 4 between the front and rear portions of the sipe unit is reduced, making it less likely for the front portion to lift up and suppressing a decrease in the contact area.

[0040] In Figure 2, in an unfolded view of the tread surface 2, two rows of sipe units 9A and 9B are arranged side by side in the tire width direction. In this embodiment, the shapes of the multiple sipe units arranged on the land portion 4 are symmetrical with respect to their respective third sipes 7C.

[0041] In the tire width direction, two adjacent rows of sipe units are arranged such that the third sipe 7C of each sipe unit extends in different directions in the tire circumferential direction from the connection point P. Specifically, in Figure 2, of the multiple rows of sipe units 9A and 9B, the multiple sipe units constituting the first row of sipe units 9A are arranged such that the third sipe 7C of each extends from the connection point P to one side (upper side in the drawing) in the tire circumferential direction. On the other hand, the multiple sipe units constituting the second row of sipe units 9B, which is adjacent to the first row of sipe units 9A, are arranged such that the third sipe 7C of each extends from the connection point P to the other side (lower side in the drawing) in the tire circumferential direction.

[0042] Due to the arrangement of the sipe unit rows in this manner, in the land area sandwiched between the third sipes 7C of multiple sipe units constituting adjacent sipe unit rows 9A and 9B (between the centerlines of adjacent sipe unit rows 9A and 9B) in the tire width direction, multiple minute sipes 7 extend inclined in the same direction with respect to the tire width direction. Specifically, in Figure 3, the second sipe 7B of sipe unit 8A included in sipe unit row 9A and the second sipe 7B of sipe unit 8B included in sipe unit row 9B extend approximately parallel to each other. As a result, minute sipes 7 are periodically arranged in the land area sandwiched between the centerlines of adjacent sipe unit rows 9A and 9B in the tire width direction, and the shape and size of the land area sandwiched by minute sipes 7 in the tire circumferential direction can be made uniform. This makes it possible to make the sipe density in the land area uniform. Therefore, the tread surface 2 can be made to contact the road surface more uniformly, and the distribution of contact pressure applied to the contact surface of the tread surface 2 can be made uniform, thereby increasing the contact area of ​​the tire 1. Consequently, the ice grip performance of the tire 1 can be further improved.

[0043] In the illustrated example, at least one of the multiple sipe units constituting the first sipe unit row 9A and at least one of the multiple sipe units 8 constituting the second sipe unit row 9B adjacent to the first sipe unit row 9A have portions of each other facing each other in the tire width direction in the tire circumferential direction. Specifically, in Figure 2, the second sipe 7B of the sipe unit constituting sipe unit row 9A and the second sipe 7B of the sipe unit constituting sipe unit row 9B face each other in the tire width direction only in the tire circumferential direction. Here, "line segments X and Y face each other in the Z direction" means that line segments X and Y are separated from each other in the Z direction, and that the ends of line segment Y are located on two straight lines extending from both ends of line segment X along the Z direction. However, the statement that "only a portion of the second sipe 7B of the sipe unit constituting sipe unit row 9A and the second sipe 7B of the sipe unit constituting sipe unit row 9B are opposite each other in the tire circumferential direction" includes the case where only the endpoints of the second sipe 7B of the sipe unit and the second sipe 7B of the sipe unit are located on a straight line extending along the tire circumferential direction. In Figure 2, a portion of the second sipe 7B of sipe unit row 9A in the tire circumferential direction and a portion of the second sipe 7B of sipe unit row 9B in the tire circumferential direction are opposite each other in the tire circumferential direction. In this case, the length w1 (w1=2L×cosθ) of each sipe unit row 9A and 9B in the tire circumferential direction and the distance b between the centerlines of adjacent sipe unit rows 9A and 9B in the tire circumferential direction satisfy b-w1≧0. As a result, as shown by the shaded area in Figure 3, when the sipe units constituting sipe unit row 9A and the sipe units constituting sipe unit row 9B are projected along the tire circumferential direction, at least one of them extends seamlessly across the tire width direction of the sipe unit.Therefore, by widening the length of the sipe unit row 9 in the tire width direction within the range where b-w1≧0 is satisfied, without changing the shape of each sipe unit constituting 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 can exert edge effect and water removal effect while maintaining the sipe density on land. This makes it possible to improve the ice grip performance of the tire 1.

[0044] Furthermore, in the illustrated example, at least one third sipe 7C of the multiple sipe units constituting the first sipe unit row 9A among the multiple sipe unit rows 9, and at least one third sipe 7C of the multiple sipe units constituting the second sipe unit row 9B adjacent to the first sipe unit row 9A, are opposed to each other in the tire width direction, at least a portion of each in the tire circumferential direction. Specifically, in Figure 2, the third sipe 7C of the sipe unit constituting the sipe unit row 9A and the third sipe 7C of the sipe unit constituting the sipe unit row 9B are opposed to each other in the tire width direction, at least a portion of each in the tire circumferential direction. In this case, if c is the distance in the tire circumferential direction between the connection point P of the sipe units where the third sipes 7Cs are opposed to each other in the tire width direction, it is preferable that c ≤ d. Here, d is the length of the third sipe in the extending direction.

[0045] In a plurality of rows of sipe units 9, the positions of the multiple sipe units constituting each row of sipe units in the tire circumferential direction may be equal to each other, provided that the third sipe 7C of each sipe unit constituting each row of sipe units extends in the same direction from the connection point P in the tire circumferential direction. Specifically, the third sipe 7C of the sipe units constituting row 9A and the sipe units constituting row 9C, which is arranged to sandwich row 9A and row 9B in the tire width direction, extends in the same direction from the connection point P in the tire circumferential direction. In Figure 2, the positions of the sipe units included in row 9A and the sipe units included in row 9C are equal in the tire circumferential direction. This makes it possible to further equalize the sipe density in the block land portion 6. As a result, the tread surface 2 can be made to contact the road surface more uniformly, the distribution of ground pressure applied to the contact surface of the tread surface 2 can be made uniform, and the contact area of ​​the tire 1 can be increased. Therefore, the ice grip performance of tire 1 can be further improved.

[0046] As shown in Figure 2, when the pitch spacing between adjacent sipe units in the tire circumferential direction within a row is p (mm), and the circumferential separation distance between a sipe unit in one row and a sipe unit in an adjacent row is q (mm), p / 2 × 0.7 ≤ q ≤ p / 2 × 1.3 It is preferable that the following conditions be met. This is because the above range allows for a balanced arrangement of the sipe units.

[0047] Furthermore, as shown in Figure 1, the sipe units are arranged in rows in a linear fashion, either in the tire width direction or at an inclination angle of 30° or less relative to the tire width direction. As shown in Figure 2, when b is the distance between the connection points in the tire width direction of adjacent sipe units in one row, and s is the sipe interval, which is the shortest distance in the tire width direction between adjacent sipe units in one row, 0.2 ≤ s / (bs) ≤ 1.0 It is preferable that the following conditions be met. By setting s / (bs)=s / w1 to 0.2 or greater, the spatial region width s between sipes, i.e., the connecting region width of the land area, can be sufficiently secured, thereby improving the rigidity of the land area. On the other hand, by setting s / (bs)=s / w1 to 1.0 or less, s>w1 can be ensured so that the widthwise components of adjacent sipes in the circumferential direction overlap, preventing the occurrence of sipe gaps.

[0048] The spacing s is preferably 1.5 mm or more. This is because the width of the spatial area s between the sipes, i.e., the width of the connecting area of ​​the land section, is made sufficiently wide, thereby ensuring sufficient rigidity of the land section.

[0049] As shown in Figure 2, the sipe units are arranged in multiple rows in the tire width direction, and the sipe units of one row and the sipe units of an adjacent row are arranged with a phase shift in the tire circumferential direction such that their positions in the tire circumferential direction are staggered, and the sipe units form rows arranged linearly in the tire width direction or at an inclination angle of 30° or less with respect to the tire width direction, and when the distance between the connecting points of adjacent sipe units in one row in the tire width direction is b, and the distance between the connecting point of a sipe unit in one row and the connecting point of a sipe unit in an adjacent row in the tire circumferential direction is c, 0 ≤ c / b ≤ 1.0 It is preferable that the following conditions be met. Since the circumferential separation distance q between adjacent sipe rows is (w1+s) / 2×α+c, by setting c to 0 or greater, sufficient distance q can be ensured, thereby ensuring sufficient rigidity of the land portion. On the other hand, by ensuring that the circumferential distance c at the connection point does not exceed the widthwise distance b, the distance between sipes q does not become excessive, and sipe density can be ensured.

[0050] Furthermore, as shown in Figure 2, when the extension length of the first sipe 7A and the second sipe 7B is L (mm), and the extension length of the third sipe 7C is d (mm), d ≤ L, and d ≤ q - α × s / 2 It is preferable that the following conditions be met, where α = tanθ. If the length d of sipe 7C exceeds q-αs / 2, the end of sipe 7C will protrude circumferentially beyond the end of the adjacent sipe 7A or sipe 7B. This means that it will protrude into the spatial region between sipes 7A and 7B, i.e., the connecting region of the land, and will reduce the rigidity of the land in that connecting region. Therefore, the rigidity of the land can be ensured by limiting d to the above range.

[0051] Furthermore, as another example of minute sipes forming a connected sipe, as shown in Figure 5, the connected sipe 41 has a main portion 41a extending in a first predetermined direction, and side portions 41b1 and 41b2 extending from the main portion 41a to the side of the main portion 41a at an inclination with respect to the first predetermined direction and terminating in the land portion. The side portions can also be configured such that a first side portion 41b1 is located on one side of the main portion, and a second side portion 41b2 is located on the other side of the main portion, arranged alternately in the circumferential direction of the tire. This configuration is effective in promoting drainage in the circumferential direction of the tire and improving grip performance.

[0052] In another embodiment of the present invention, spaced-apart microsipes constitute sipe units (for example, as paired sipes consisting of a pair of microsipes), and these sipe units are arranged repeatedly on the land portion. In another embodiment, when the length of the micro-sipe in the tire width direction is w2 (mm) and the depth of the micro-sipe is h (mm), then w2 × h = 150 (mm) 2 ) are as follows: Furthermore, the number of minute sipes within the land area is n, the maximum width of the land area in the tire width direction is BW (mm), and the outer contour area of ​​the land area is (mm 2 By dividing the length of the tire's circumferential length by BW (mm), we define BL (mm) as the equivalent length of the tire's circumferential portion, the equivalent number of sipes N as w² × n / BW, the average sipe spacing in the tire's circumferential direction as BL / (N+1), and defining the sipe density SD as the reciprocal of the average sipe spacing in the tire's circumferential direction, When expressed as SD=(N+1) / BL=((w2×n / BW)+1) / BL, The SD is 0.15 (1 / mm) or greater. Other embodiments can also improve ice grip performance, similar to the embodiment using connected sipes shown in Figure 1. In this case as well, especially if w2 x h is 100 (mm 2 Preferably, w2 × h is 50 (mm 2 It is more preferable that the sipes are smaller than the specified size. This is because by making the sipes smaller, it is possible to arrange them at a higher density and further improve the effect of removing the water film. In this case as well, it is preferable that the sipe density SD be 0.20 (1 / mm) or higher, and more preferably 0.30 (1 / mm) or higher. This is because a higher density of sipes can further improve the effect of removing the water film.

[0053] This section describes a specific example of how spaced-apart minute sipes can constitute a sipe unit. As shown in Figure 6, the sipes are composed of a pair of sipes 8, where each of the pair of sipes 7A and 7B extends such that both ends in the direction of extension of the sipe terminate within the land portion, and the pair of sipes can be configured such that only a portion of each other in the tire width direction faces each other in the tire circumferential direction.

[0054] Alternatively, as shown in Figure 7, the tire can be configured as a pair of sipes, where one sipe 7D and the other sipe 7E are arranged facing each other in the circumferential direction of the tire, and each has a long side extending in the width direction of the tire. One sipe 7D has a short side extending from one end of the long side in the width direction of the tire towards the other sipe 7E, and the other sipe 7E has a short side extending from the other end of the long side in the width direction of the tire towards the one sipe 7D. In addition, in the adjacent row to the row where sipes 7D and 7E are located, one sipe 7F and the other sipe 7G form a sipe unit consisting of a pair of sipes, and are arranged symmetrically with respect to an axis parallel to the tire width direction with respect to the first row, and with a phase shift in the tire circumferential direction between the first row and the adjacent row. Note that in Figure 7, the first row and the adjacent row are arranged without offsetting each other in the tire width direction, but they can also be arranged with an offset. [Examples]

[0055] Finite element method (FEM) simulations were performed on the tires of Examples 1-4 and Comparative Examples 1 and 2 shown in Figure 8 to evaluate block stiffness and contact area. Figure 9 shows the dimensions of Comparative Example 1, Figure 10 shows the dimensions of Comparative Example 2, Figure 11 shows the dimensions of Example 1, Figure 12 shows the dimensions of Example 2, Figure 13 shows the dimensions of Example 3, and Figure 14 shows the dimensions of Example 4. Although omitted in these figures, the units are (mm). For block stiffness, the lateral input at a displacement of 1 mm was determined by simulation, and for actual contact area, the contact area at a contact pressure of 230 kPa and a lateral input of 0.3 G was determined by simulation. As shown in Figures 15 and 16, Examples 1-4 all showed improved block stiffness and increased contact area compared to Comparative Examples 1 and 2.

[0056] Next, block samples of Comparative Examples 1 and 2 and Examples 2 to 4 were fabricated, and their ice surface friction coefficients (μ) were measured using an indoor testing machine at speeds of 5 km / h and 2 km / h. The evaluation results are shown in Figures 17 and 18. The ice temperature was set to -2°C, and the ground pressure to 250 kPa. As shown in Figures 17 and 18, the ice surface friction coefficients of Invention Examples 2 to 4 were improved compared to Comparative Examples 1 and 2. [Explanation of Symbols]

[0057] 1: Pneumatic tire, 2: Tread surface, 3: Circumferential main grooves, 4: Land area, 5: Width-direction trench, 6: Block, 7: Micro-sipes, 8: Connecting sipe, 9: Sipe unit row, 10: Width direction sipe

Claims

1. A pneumatic tire having at least one land portion on the tread surface, On the aforementioned land area, sipe units consisting of three linear micro-sipes are arranged in a repeating pattern. The three minute sipes constituting the sipe unit are connected to each other to form a connected sipe. The three minute sipes constituting the sipe unit are connected at a single connection point when viewed in an unfolded view of the tread surface, and each extends radially from the connection point. Of the three micro-sipes constituting the sipe unit, the first and second micro-sipes are located on one side in the tire circumferential direction when viewed from the connection point, and the remaining third micro-sipe is located on the other side in the tire circumferential direction when viewed from the connection point. The length of the third microsipe is shorter than the lengths of the first and second microsipes. The three minute sipes constituting the sipe unit all terminate within the land area at the end opposite to the side with the connection point. When the length of the sipe unit in the tire width direction is w1 (mm) and the depth of the minute sipe is h (mm), then w1 × h = 150 (mm) ２ ) and below, n is the number of sipe units within the land area, BW is the maximum width of the land area in the tire width direction (mm), and (mm) is the outer contour area of ​​the land area. ２ A pneumatic tire characterized in that, when the equivalent circumferential length of the tire on land is defined as BL (mm) by dividing ) by BW (mm), the equivalent number of sipes N is defined as w1 × n / BW, the average sipe spacing in the circumferential direction of the tire is expressed as BL / (N+1), and the sipe density SD is defined as the reciprocal of the average sipe spacing in the circumferential direction of the tire, then when expressed as SD = (N+1) / BL = ((w1 × n / BW) + 1) / BL, SD is 0.15 (1 / mm) or more.

2. The pneumatic tire according to claim 1, wherein a plurality of the sipe units are arranged so as to be spaced apart from each other in the circumferential direction of the tire.

3. Multiple rows of the aforementioned sipe units, arranged in the circumferential direction of the tire, are arranged in the width direction of the tire. The pneumatic tire according to claim 1 or 2, wherein the sipe units in one row and the sipe units in an adjacent row adjacent to the first row are arranged with a phase shift in the circumferential direction of the tire.

4. When the pitch interval between adjacent sipe units in the tire circumferential direction within the aforementioned row is p (mm), and the circumferential distance between a sipe unit in the aforementioned row and a sipe unit in the adjacent row is q (mm), p / 2×0.7≦q≦p / 2×1.3 A pneumatic tire according to claim 3, satisfying the requirements.

5. The sipe units are arranged in rows in a linear fashion, either in the tire width direction or at an inclination angle of 30° or less relative to the tire width direction. When b is the distance between the connection points in the tire width direction of adjacent sipe units in one row, and s is the sipe interval which is the shortest distance in the tire width direction between adjacent sipe units in one row, 0.2≦s / (b−s)≦1.0 A pneumatic tire according to claim 1, satisfying the requirements.

6. The pneumatic tire according to claim 5, wherein s is 1.5 (mm) or more.

7. The sipe units are arranged in multiple rows in the tire width direction, The sipe units in one row and the sipe units in the adjacent row adjacent to the first row are arranged such that their positions in the circumferential direction of the tire are staggered, with the two adjacent rows being arranged with a phase shift in the circumferential direction of the tire. The sipe units are arranged in a linear fashion in the tire width direction or at an inclination angle of 30° or less relative to the tire width direction, forming rows. Let b be the distance between the connection points in the tire width direction of adjacent sipe units in one row, and let c be the distance in the tire circumferential direction between the connection point of the sipe unit in the first column and the connection point of the sipe unit in the adjacent column. 0 ≤ c / b ≤ 1.0 A pneumatic tire according to claim 1, satisfying the requirements.

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