Pneumatic tire

Abstract

To provide a pneumatic tire capable of improving traction performance while suppressing the occurrence of uneven wear.SOLUTION: At least one land part 2 which is a block row is provided on a tread surface. A block side 43a included in the block row has a step 8 provided in a range of 70% or more of an edge part of the block side 43a, and a recess 80 recessed inside in the tire radial direction from a bottom surface of the step 8. The recess 80 is formed at a position avoiding a corner C70 where an angle formed by two sides is less than 70 degrees.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to pneumatic tires. [Background technology]

[0002] Traditionally, tires fitted to light trucks, including SUVs and pickup trucks, have adopted a block pattern on the tread surface to ensure excellent traction performance off-road. The blocks that make up such a block pattern can contain areas with low rigidity (resistance to deformation due to external forces), which can cause uneven wear. Therefore, it is desirable to further improve traction performance while suppressing the occurrence of uneven wear.

[0003] Patent Document 1 describes a tire in which blocks formed on the tread surface have recessed portions recessed radially inward. In this document, the recessed portions are positioned as areas that exert shear force on muddy road surfaces, and one form of the recessed portions is disclosed as a step-like recess on the edge of the block. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-195075 Summary of the Invention [Problem to be solved by the invention]

[0005] The present disclosure has been made in consideration of the above-described circumstances, and has an object to provide a pneumatic tire that can improve traction performance while suppressing the occurrence of uneven wear. [Means for solving the problem]

[0006] The pneumatic tire of the present disclosure has at least one land portion that is a block row on the tread surface, and each block included in the block row has a step that is provided over a range of 70% or more of the edge of the block, and a depression that is recessed radially inward from the bottom of the step, and the depression is formed at a position that avoids corners where the angle between two sides is less than 70 degrees. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a plan view of a tread surface of a pneumatic tire according to an embodiment of the present invention; [Figure 2] Enlarged view of the center area [Figure 3] Cross section AA of Figure 2 [Figure 4] Close-up of the center block [Figure 5] A perspective view showing the edge of the center block. [Figure 6] FIG. 10 is a perspective view showing a modified example of the recess; [Figure 7] FIG. 10 is a perspective view showing a modified example of the recess; [Figure 8] Close-up of the center block [Figure 9] Close-up of the center block [Figure 10] Close-up of the shoulder area [Figure 11] Cross section B-B of Figure 10 [Figure 12] CC cross section of Figure 10 DETAILED DESCRIPTION OF THE INVENTION

[0008] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a pneumatic tire according to the present disclosure will be described with reference to the drawings.

[0009] [Tread surface overview] Fig. 1 is a planar development view of a tread surface of a pneumatic tire of this embodiment. The pneumatic tire is an automobile tire having a pair of bead portions (not shown), a pair of sidewall portions (not shown) extending radially outward from each of the pair of bead portions, and a tread portion 10 continuing to the radially outer ends of each of the pair of sidewall portions. The tread surface Tr forms the outer peripheral surface of the tread portion 10. The tire shown in Fig. 1 is new, and the tread surface Tr is in an unworn state. The tire has at least one land portion 2 (multiple in this embodiment) composed of a block row on the tread surface Tr.

[0010] Here, the tire circumferential direction is the direction around the tire's central axis (axis of rotation). The tire radial direction is the direction along the diameter of the tire. The side closer to the tire's central axis is the tire radially inner side, and the side away from the tire's central axis is the tire radially outer side. The tire width direction is the direction parallel to the tire's central axis. The side closer to the tire equator TC is the tire widthwise inner side, and the side away from the tire equator TC is the tire widthwise outer side. The tire equator TC is an imaginary line located at the center of the tire in the tire width direction. In a plan view of the tread surface Tr, the tire equator TC extends in the tire circumferential direction and is perpendicular to the tire's central axis.

[0011] Unless otherwise specified, the dimensions and angles of each tire are determined when the tire is mounted on a standard rim, inflated to the standard internal pressure, and unloaded. The standard rim is the rim specified for each tire by the standard system, including the standard on which the tire is based. For example, it is the standard rim for JATMA, and the "Measuring Rim" for TRA and ETRTO. The standard internal pressure is the air pressure specified for each tire by the standard system, including the standard on which the tire is based. For truck / bus tires and light truck tires, it is the maximum air pressure for JATMA, the value corresponding to the Load Index listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURE" table for TRA, and the "INFLATION PRESSURE" for ETRTO. For passenger car tires, the standard pressure is usually 180 kPa, but for tires labeled "Extra Load" or "Reinforced," it is 220 kPa.

[0012] The land portions 2 are divided in the tire width direction by longitudinal grooves 1 extending in the tire circumferential direction. In this embodiment, the land portions 2 include shoulder land portions 21, 22 and center land portions 23, 24, 25, each of which is a block row in which blocks are arranged in the tire circumferential direction. The center land portions 23, 24, 25 are arranged in an area inward in the tire width direction from the shoulder land portions 21, 22, which include the contact edges CE. The center land portion 25 is arranged on the tire equator TC. The blocks are divided in the tire circumferential direction by lateral grooves 3 extending in a direction intersecting the tire circumferential direction. From the viewpoint of improving traction performance, the angle of the extension direction of the lateral grooves 3 with respect to the tire width direction is preferably 70 degrees or less. The lateral grooves 3 are formed wider than the sipes 5 described below.

[0013] The longitudinal groove 1 has a groove width W1 measured in a direction perpendicular to its extension direction and a groove depth D1 (see FIG. 11) measured in the tire radial direction. The groove width W1 is set to, for example, 4.0 mm or more, preferably 7.0 mm or more. The groove width W1 is measured based on the edge of the longitudinal groove 1 on the surface of the land portion 2. However, when a step-like recess 8 is provided as described below, the groove width W1 is measured based on the intersection of an imaginary line extending the surface of the land portion 2 and an imaginary line extending the groove wall (side wall of the land portion 2) of the longitudinal groove 1. The same applies when measuring the groove width of the lateral groove 3. The groove depth D1 is set to, for example, 5.0 mm or more. The longitudinal groove 1 may be partially provided with a TWI (treadwear indicator) that indicates the limit of use due to wear.

[0014] The groove width W1 is set to, for example, 3% or more of the contact width CW. The contact width CW is the distance between the contact edges CE in the tire width direction. The contact edges CE correspond to the outermost position in the tire width direction of the contact patch when the tire is mounted on a standard rim, inflated to the standard internal pressure, and placed in contact with the ground perpendicular to a plane (i.e., with a camber angle of zero degrees) under a standard load. The standard load is the load determined for each tire by each standard in the standard system that includes the standard on which the tire is based. For JATMA, this is the "maximum load capacity," for TRA, this is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO, this is the "LOAD CAPACITY." For passenger car tires, this is the load equivalent to 88% of the above load.

[0015] In this embodiment, the longitudinal groove 1 includes a pair of shoulder longitudinal grooves 11, 12 and a center longitudinal groove 13, 14 located in a region on the inner side of the pair of shoulder longitudinal grooves 11, 12 in the tire width direction. The shoulder longitudinal grooves 11, 12 and the center longitudinal groove 13, 14 are each formed as zigzag grooves extending while curving left and right along the tire circumferential direction. Such zigzag grooves allow for a large number of edge components along the tire width direction, which is advantageous for improving traction performance. The longitudinal groove 1 may also be formed as a straight groove extending linearly along the tire circumferential direction. The lateral grooves 3 include shoulder lateral grooves 31, 32 and center lateral grooves 33, 34, 35.

[0016] The shoulder land portion 21 is provided adjacent to the shoulder circumferential groove 11 on the outer side in the tire width direction. The shoulder circumferential groove 11 extends continuously along the tire circumferential direction. The shoulder land portion 21 is divided into shoulder blocks 41 by shoulder lateral grooves 31. The shoulder lateral grooves 31 extend from the shoulder circumferential groove 11 outward in the tire width direction and reach the ground contact edge CE. In this embodiment, the shoulder blocks 41 forming the shoulder land portion 21 include two types of blocks, shoulder blocks 41a and shoulder blocks 41b, which are arranged alternately along the tire circumferential direction.

[0017] The shoulder land portion 22 is provided adjacent to the shoulder circumferential groove 12 on the outer side in the tire width direction. The shoulder circumferential groove 12 extends continuously along the tire circumferential direction. The shoulder land portion 22 is divided into shoulder blocks 42 by shoulder lateral grooves 32. The shoulder lateral grooves 32 extend from the shoulder circumferential groove 12 outward in the tire width direction and reach the ground contact edge CE. In this embodiment, the shoulder blocks 42 forming the shoulder land portion 22 include two types of blocks, shoulder blocks 42a and shoulder blocks 42b, which are arranged alternately along the tire circumferential direction.

[0018] In this embodiment, a point-symmetric tread pattern is adopted, which means that when the tread surface Tr is rotated 180 degrees around a point on the tire equator TC, the original shape is restored. Therefore, the shoulder land portion 22, shoulder longitudinal groove 12, shoulder lateral groove 32, shoulder block 42a, and shoulder block 42b have shapes that are substantially point-symmetric with the shoulder land portion 21, shoulder longitudinal groove 11, shoulder lateral groove 31, shoulder block 41a, and shoulder block 41b, respectively.

[0019] The center land portion 23 is provided adjacent to the shoulder longitudinal groove 11 on the inner side in the tire width direction. The center land portion 23 is divided into center blocks 43 by center lateral grooves 33. The center lateral grooves 33 extend from the shoulder longitudinal grooves 11 toward the inner side in the tire width direction and connect to the center lateral groove 13. In this embodiment, the center blocks 43 forming the center land portion 23 include two types of blocks, center blocks 43a and center blocks 43b, which are arranged alternately along the tire circumferential direction.

[0020] The center land portion 24 is provided adjacent to the shoulder longitudinal groove 12 on the inner side in the tire width direction. The center land portion 24 is divided into center blocks 44 by center lateral grooves 34. The center lateral grooves 34 extend from the shoulder longitudinal grooves 12 toward the inner side in the tire width direction and connect to the center lateral groove 14. In this embodiment, the center blocks 44 forming the center land portion 24 include two types of blocks, center blocks 44a and center blocks 44b, which are arranged alternately along the tire circumferential direction.

[0021] Since a point-symmetric tread pattern is employed in this embodiment, the center land portion 24, center lateral groove 34, center block 44a, and center block 44b have shapes that are substantially point-symmetric with the center land portion 23, center lateral groove 33, center block 43a, and center block 43b, respectively. Between the center blocks 43b and 44b, the center longitudinal groove 13 and the center longitudinal groove 14 are connected to each other via a connecting groove 15 so as to form a crank shape. In this way, the center blocks 43b and 44b are separated by the center longitudinal grooves 13 and 14.

[0022] The center land portion 25 is provided between the center longitudinal groove 13 and the center longitudinal groove 14. The center longitudinal grooves 13, 14 each extend discontinuously along the tire circumferential direction, with one end connected to the lateral groove 3 and the other end connected to the connecting groove 15. The center land portion 25 is divided into center blocks 45 by the center lateral grooves 35. The center lateral groove 35 is connected to both the center longitudinal groove 13 and the center lateral groove 14. In this embodiment, the center blocks 45 forming the center land portion 25 are surrounded by the center longitudinal grooves 13, 14 and the center lateral groove 35. Portions of the center blocks 43b, 44b are arranged between the center blocks 45 arranged along the tire circumferential direction.

[0023] The land portion 2 is provided with sipes 5 extending in a direction intersecting the tire circumferential direction, and dimples 6 formed to widen the opening width of the sipes 5. The sipes 5 have a sipe width measured in a direction perpendicular to the extension direction of the sipes 5, and a sipe depth measured in the tire radial direction. The sipe width is preferably set to 1.5 mm or less, and more preferably 1.0 mm or less. The sipe width is set to, for example, 0.3 mm or more. The sipe depth is set to, for example, 5.0 to 9.0 mm. The sipe depth is set to be equal to or less than the depth D1 of the longitudinal groove 1. The inclination angle of the acute angle side of the sipe 5 with respect to the tire width direction is preferably 45 degrees or less.

[0024] In this embodiment, the sipes 5 are formed as non-wavy sipes, but are not limited to this. The sipes 5 extend in a straight line or in a curved line that is bent halfway, but may also have a gently curved shape, for example. Furthermore, the sipes 5 are formed as two-dimensional sipes in which the sipe shape (excluding the dimples 6) that appear on the tread surface Tr does not change along the depth direction, but may be formed as three-dimensional sipes in which the sipe shape that appears on the tread surface Tr changes along the depth direction (i.e., the sipe 5 has a portion that oscillates in the width direction relative to the depth direction of the sipe 5). The blocks may have a structure in which one or both of the sipes 5 and the dimples 6 are not provided.

[0025] The shoulder region SA is the region located outside the shoulder longitudinal grooves 11, 12, which are located at the outermost positions in the tire width direction among the multiple longitudinal grooves 1 provided on the tread surface Tr, and the center region CA is the region located inside the shoulder longitudinal grooves 11, 12 in the tire width direction. A pair of shoulder regions SA is provided on both sides of the center region CA. For convenience of explanation, one of the pair of shoulder regions SA is referred to as shoulder region SA1, and the other is referred to as shoulder region SA2. Shoulder land portions 21, 22 are arranged in the shoulder regions SA1, SA2, respectively. Center land portions 23, 24, 25 are arranged in the center region CA.

[0026] [Center area] The center region CA will be described in detail. FIG. 2 is an enlarged view of the center region CA. FIG. 3 is a cross-sectional view taken along line AA in FIG. 2. FIG. 4 is an enlarged view of a center block 43a included in the center region CA. The center region CA includes a center lateral groove 33, both ends of which are connected to the longitudinal grooves 1 (specifically, the shoulder longitudinal grooves 11 and the center longitudinal groove 13), and center blocks 43, which are divided in the tire circumferential direction by the center lateral grooves 33. As described above, the center region CA includes a center land portion 23, which is a row of center blocks 43 (center blocks 43a, 43b) arranged in a block row.

[0027] The center block 43a (an example of a block included in a block row) has a step 8 formed over 70% or more of the edge of the center block 43a. This enhances the edge effect of the block edge, improving traction performance on off-road terrain. The length of the step 8 in the center block 43a is 70% or more, and more preferably 80% or more, of the length of the edge of the center block 43a. In this embodiment, the step 8 is formed over the entire edge facing the lateral groove 3 (specifically, the center lateral groove 33), which is advantageous for improving traction performance. The center blocks 43 to 45 have the step 8 formed over the entire edge.

[0028] The center block 43a has a corner C70, where the angle θ43a between two sides is less than 70 degrees. The step 8 is provided in a range of the edge of the center block 43a that includes the corner C70. In FIG. 4, the lengths L1 and L2 of the two sides that make up the corner C70 are shown, and are, for example, 5 mm or more. The corner C70 is positioned as a portion of the center block 43a that has relatively low rigidity. The step 8 is formed by recessing the edge of the block, which is easily deformed by external forces, in a step-like manner. A block without the step 8 is prone to deformation due to the low rigidity of its surface edge. However, in a block with the step 8 of this embodiment, the outer portion of the surface edge (including the bottom surface 8a, described below) acts as a reinforcing portion, increasing rigidity and thereby suppressing deformation. Therefore, by providing the step 8 in the range including the corner C70, the rigidity of the center block 43a having the corner C70 is ensured well, while the edge effect at the edge of the block is increased, thereby improving traction performance.

[0029] The step 8 includes a bottom surface 8a that is substantially parallel to the tread surface Tr and a side surface 8b that extends along the tire radial direction. From the viewpoint of enhancing the edge effect at the edge of the block, the depth D8 of the step 8 is preferably 7.0 mm or less, and more preferably 3.0 mm or less. The depth D8 is preferably 0.5 mm or more. The width W8 of the step 8 is set to, for example, 0.5 to 7.0 mm and is larger than the depth D8 in this embodiment. The depth D8 and the width W8 are each measured based on the intersection of an imaginary line extending the surface of the block and an imaginary line extending the sidewall of the block. The depth D8 and the width W8 are substantially constant along the edge of the block. However, a recess 80, which will be described later, is partially formed in the bottom surface 8a.

[0030] FIG. 5 is a perspective view showing the edge of the center block 43a. The center block 43a has a recess 80 recessed radially inward from the bottom surface 8a of the step 8. The recess 80 is formed partially relative to the step 8, and in FIG. 4 (and FIGS. 8 to 10 described below), the area where the recess 80 is formed is depicted in color to facilitate distinction on the drawings. The recess 80 is formed at a position that avoids a corner C70 where the angle between two sides is less than 70 degrees. Note that "avoiding the corner" may be a position that avoids the tip of the corner, but preferably a position that avoids a range of 3 mm from the tip of the corner along the edge.

[0031] Although the step 8 improves the rigidity of the edge of the block, if the block includes a portion with relatively low rigidity, such as a corner C70, that portion is likely to wear out first. In contrast, in this embodiment, the recess 80 is formed at a position that avoids the corner C70, and the rigidity of the portion where the recess 80 is formed is lower than that of the portion where the recess 80 is not formed, which makes it possible to equalize the block rigidity and thereby suppress the occurrence of uneven wear. Furthermore, when the step 8 disappears as the wear of the tread surface Tr progresses, the recess 80 that appears on the surface of the block provides an edge effect, thereby improving traction performance.

[0032] In this embodiment, the center block 43a has a corner C90, where the angle between two sides is less than 90 degrees. The length of the two sides that make up the corner C90 is, for example, 5 mm or more. The aforementioned corner C70 is one aspect of this corner C90. The step 8 is provided in a range that includes the corner C90 on the edge of the center block 43a. The corner C90 is also positioned as a portion of the center block 43a that has relatively low rigidity. As shown in FIG. 4, the recess 80 is formed at a position that avoids the corner C90. This configuration is advantageous for improving traction performance while suppressing uneven wear.

[0033] In a single center block 43a (an example of a block), the ratio of the length L80s of the recess 80 formed in the step 8 to the length L8 of the step 8 is preferably 30 to 70%. If this ratio is 30% or more, the recess 80 is formed within an appropriate range, making it easier to uniformize the block rigidity. Furthermore, if this ratio is 70% or less, the recess 80 is not excessive, making it easier to maintain the block rigidity. The length L8 is the length of the step 8 along the edge of the block, and if the step 8 is formed around the entire periphery of the block, it corresponds to the length of the edge of the block. The length L80s of the recess 80 is calculated by adding up the individual lengths L80 of the multiple recesses 80 included in the block. The lengths L8 and L80 are determined by the groove depth position on the bottom surface 8a.

[0034] From the viewpoint of appropriately reducing the rigidity of the portion where the recess 80 is formed, the depth D80 of the recess 80 is preferably 0.3 mm or more, and more preferably 0.8 mm or more. Furthermore, the step 8 extends along the edge of the block, and in order to maintain the continuity of the step 8, the depth D80 of the recess 80 is preferably 2.0 mm or less. Therefore, the depth D80 of the recess 80 is preferably 0.3 to 2.0 mm. The depth D80 is preferably the same as or smaller than the depth D8 of the step 8. The depth D80 is defined as the depth (maximum depth) of the recess 8 at the position that is recessed furthest inward in the tire radial direction, with the bottom surface 8a of the step 8 as the reference.

[0035] It is preferable that the ratio of the length of the recesses 80 included in one side of the center block 43a (an example of a block) to the length of that side is 60% or less. This prevents the recesses 80 from becoming excessive, making it easier to maintain block rigidity. The ratio is, for example, 10% or more, but may be less. When one side of a block includes multiple recesses 80, the length of the recesses 80 included in that side is calculated by adding up the individual lengths of the multiple recesses 80. One side of a block is one side that forms the outline of the surface of the block, and is shown, for example, in Figure 4 as a section having length L1 (or length L2).

[0036] The length of the recesses 80 formed in the steps 8 extending along the lateral grooves 3 that divide the center block 43a (an example of a block) in the tire circumferential direction may be longer than the length of the recesses 80 formed in the steps 8 extending along the longitudinal grooves 1 that divide the block in the tire width direction. With this configuration, the length of the recesses 80 in the tire width direction becomes relatively longer, thereby improving traction performance. The length of the recesses 80 formed in the steps 8 extending along the lateral grooves 3 and the length of the recesses 80 formed in the steps 8 extending along the longitudinal grooves 1 can be calculated by adding up the individual lengths of the corresponding recesses 80.

[0037] As described above, in this embodiment, a sipe 5 is provided in the center block 43a (an example of a block). As shown in FIG. 4, the sipe 5 has an open end 52 that opens on the side wall of the block and is set at the position where the depression 80 is formed. The open end 52 faces the depression 80 on the side wall of the block. This configuration can further reduce the rigidity of the area where the depression 80 is formed, which can be useful for achieving uniform block rigidity. The sipe 5 is a so-called one-sided open sipe that has an open end 52 and a closed end 53 that terminates within the block. This reduces the reduction in block rigidity compared to a double-sided open sipe that has open ends, which is advantageous for improving traction performance.

[0038] As shown in FIG. 5, the recess 80 has a width W80 that is the same as the width W8 of the step 8. The width W80 may be smaller than the width W8, but is preferably 50% or more of the width W8 in order to reduce the rigidity of the area where the recess 80 is formed. The recess 80 is formed by cutting out the corner between the bottom surface 8a and the side wall of the block (the groove wall of the longitudinal groove 1 or the lateral groove 3). This configuration is advantageous in terms of reducing the rigidity of the area where the recess 80 is formed. In FIG. 5, the recess 80 is recessed in a trapezoidal shape, and the length L80 of the recess 80 along the edge of the block is greater than the width W80, but this is not limited to this. Various shapes are applicable to the recess 80, including, for example, modified examples shown in FIGS. 6 and 7.

[0039] In FIG. 6(A), the depression 80 is curved, while in FIG. 6(B), the depression 80 is triangular. In FIG. 6(C), the depression 80 is trapezoidal, but the depth of the depression 80 increases with distance from the side surface 8b. In FIG. 6(D), the width and depth of the depression 80 vary along the length. The depression 80 shown in FIG. 6(D) has its maximum width and depth at the center of the length along the edge of the block, and the width and depth decrease with distance from the center. In FIG. 7, multiple small depressions 80 are arranged. The depression 80 shown in FIG. 7(A) has a shape similar to that shown in FIG. 5, while the depression 80 shown in FIG. 7(B) has a shape similar to that shown in FIG. 6(D). In FIGS. 7(C) and (D), the depressions 80 are spherical, with the corners between adjacent depressions 80 in FIG. 7(D) being chamfered.

[0040] Providing the step 8 to improve traction performance increases strain on the groove bottoms of the center lateral grooves 33 (especially the groove corners 33c where the groove bottoms and groove walls connect), raising concerns about reduced durability due to the occurrence of groove bottom cracks. In particular, the center lateral grooves 33 that divide the center blocks 43a are connected at both ends to the longitudinal grooves 1. Therefore, compared with lateral grooves that are closed within the blocks, they are more likely to move significantly in the longitudinal direction when exerting traction performance, which makes them more susceptible to groove bottom cracks. Therefore, in this embodiment, in order to maintain durability, the center lateral grooves 33 are provided with reinforcing portions (center reinforcing portions 9) that protrude from the groove corners 33c and extend along the extension direction of the center lateral grooves 33. The groove width W3 of the lateral grooves 3 where the center reinforcing portions 9 are provided is, for example, 6.0 mm or more.

[0041] As shown in FIG. 3 , in this embodiment, center reinforcing portions 9 are provided on both sides of the groove width center C33 of the center lateral groove 33, and a recess 9d is formed in the groove width center C33 of the center lateral groove 33. This shape is advantageous for suppressing a decrease in drainage performance in the center lateral groove 33. The recess 9d is recessed radially inward in the tire direction and extends along the extension direction of the center lateral groove 33, similar to the center reinforcing portion 9. In this embodiment, the recess 9d is formed in a cross-sectional arc shape with a single radius of curvature. From the perspective of appropriately suppressing a decrease in drainage performance while ensuring the reinforcing effect of the center reinforcing portion 9, it is preferable that the width W9d of the recess 9d at the groove depth position of the top surface 9t (described later) be 95 to 105% of the width W9 of the center reinforcing portion 9.

[0042] The center reinforcing portion 9 has a top surface 9t that is substantially parallel to the tread surface Tr. At the groove depth position of the top surface 9t, the width W9 of the center reinforcing portion 9 is half or less of the groove width (W9+W9d+W9) of the center lateral groove 33, preferably 10 to 40% of the groove width. The width W9 is determined based on (an extension of) the groove wall of the center lateral groove 33. From the viewpoint of maintaining good durability, the width W9 is preferably 0.5 mm or more. To avoid excessively reducing the drainage performance of the center lateral groove 33, the width W9 is preferably 3.0 mm or less. The center reinforcing portion 9 is provided adjacent to (the side forming) the corner C90 of the center block 43a in the tire circumferential direction.

[0043] From the viewpoint of maintaining good durability, the groove depth D9 from the tread surface Tr at the top surface 9t is preferably 95% or less of the groove depth D33 of the center lateral groove 33. Furthermore, in order to avoid excessively reducing the drainage performance of the center lateral groove 33, the groove depth D9 is preferably 70% or more of the groove depth D33. In order to maintain good durability, the protrusion height 9h of the center reinforcing portion 9 based on the groove bottom of the center lateral groove 33 is preferably 0.5 mm or more. In order to avoid excessively reducing the drainage performance of the center lateral groove 33, the protrusion height 9h is preferably 3.0 mm or less. In this embodiment, the protrusion height 9h is smaller than the protrusion height 7h described below.

[0044] FIG. 3 shows a cross section (cross section AA in FIG. 2) of the center lateral groove 33 adjacent to the center block 43a on the upper side in FIG. 2, but the cross sections of the center lateral groove 33 adjacent to the center block 43a on the lower side in FIG. 2 and the other center lateral grooves 34, 35 also have the same or similar shapes.

[0045] 8 is an enlarged view of the center block 43b. The center block 43b has a step 8 formed over 70% or more of the edge of the center block 43b and a recess 80 recessed radially inward from the bottom of the step 8. The center block 43b does not have any corners where two sides form an angle of less than 70 degrees. Therefore, the recess 80 is formed at a position that avoids any corners where two sides form an angle of less than 70 degrees. However, the center block 43b does have a corner C90 where two sides form an angle of less than 90 degrees, and the recess 80 is formed at a position that avoids the corner C90. The matters described for the center block 43a can also be applied to the center block 43b.

[0046] The center region CA includes a center lateral groove 34, both ends of which are connected to the longitudinal grooves 1 (specifically, the shoulder longitudinal grooves 12 and the center longitudinal groove 14), and center blocks 44, which are divided in the tire circumferential direction by the center lateral groove 34. As described above, the center region CA includes a center land portion 24, which is a row of center blocks 44 (center blocks 44a, 44b). The center blocks 44a, 44b and the center lateral groove 34 correspond to the center blocks 43a, 43b and the center lateral groove 33 rotated 180 degrees, and the steps and recesses provided therein also have the same configuration, so redundant explanations will be omitted.

[0047] The center region CA includes center lateral grooves 35 connected at both ends to the longitudinal grooves 1 (specifically, the center longitudinal grooves 13 and 14), and center blocks 45 divided in the tire circumferential direction by the center lateral grooves 35. As described above, the center region CA includes a center land portion 25, which is a block row in which the center blocks 45 are arranged.

[0048] 9 is an enlarged view of the center block 45. The center block 45 has a step 8 that occupies 70% or more of the edge of the center block 45, and a recess 80 that is recessed radially inward from the bottom of the step 8. The center block 45 also has a corner C70 where the angle θ45 between two sides is less than 70 degrees, and the step 8 is located in a range of the edge of the center block 43a that includes the corner C70. The recess 80 is formed at a position that avoids the corner C70. Because the corner C70 is included in one aspect of the corner C90, it can also be said that the recess 80 is formed at a position that avoids the corner C90.

[0049] Like the center lateral groove 33, the center lateral groove 35 that divides the center block 45 also has a center reinforcing portion 9. The center reinforcing portion 9 protrudes from the groove corner of the center lateral groove 35 and extends along the extension direction of the center lateral groove 35. The shape and dimensions of this center reinforcing portion 9 are as described above, and the specific cross-sectional shape is shown in FIG. 3. The matters already described for the center block 43a are also applicable to the center block 45.

[0050] Of the center blocks 43a and 45 aligned in the tire width direction on either side of the center longitudinal groove 13, the center reinforcing portion 9 provided at the groove corner of the center lateral groove 35 that separates the center block 45 closest to the tire equator TC preferably has a larger volume and / or a longer top surface 9t than the center reinforcing portion 9 provided at the groove corner 33c of the center lateral groove 33 that separates the center block 43a. This makes it possible to suppress the occurrence of groove bottom cracks near the tire equator TC and maintain good durability. The same applies to the center blocks 44a and 45 aligned on either side of the center longitudinal groove 14.

[0051] As shown in Figures 1 and 2, the center lateral groove 33 adjacent to the center block 43a above in Figure 2 and the center lateral groove 34, which is point-symmetrical thereto, are inclined with respect to the tire width direction. The center lateral groove 33 adjacent to the center block 43a below in Figure 2 and the center lateral groove 34 and center lateral groove 35, which are point-symmetrical thereto, are inclined in the opposite direction with respect to the tire width direction. Thus, the center region CA is provided with a center lateral groove having a portion inclined toward one side with respect to the tire width direction and a center lateral groove having a portion inclined toward the other side with respect to the tire width direction. This configuration improves traction performance while suppressing skidding in both directions.

[0052] [Shoulder area] The shoulder region SA will now be described in detail. FIG. 10 is an enlarged view of the shoulder region SA1. FIG. 11 is a cross-sectional view taken along line BB in FIG. 10. FIG. 12 is a cross-sectional view taken along line CC in FIG. 11. The shoulder region SA1 includes shoulder lateral grooves 31 extending outward in the tire width direction from the axial grooves 1 (specifically, shoulder axial grooves 11) and reaching the tread edge CE, and shoulder blocks 41 divided in the tire circumferential direction by the shoulder lateral grooves 31. As described above, the shoulder region SA1 includes shoulder land portions 21 each consisting of a row of shoulder blocks 41 (shoulder blocks 41a, 41b). The matters already described for the center region CA can also be applied to the shoulder region SA within the spirit thereof.

[0053] Each shoulder block 41a has a step 8 extending over at least 70% of the edge of the shoulder block 41a, and a recess 80 recessed radially inward from the bottom of the step 8. The length of the step 8 in the shoulder block 41a is at least 70% of the edge length of the shoulder block 41a, and more preferably at least 80%. In this embodiment, the step 8 is provided over the entire edge facing the shoulder lateral groove 31, which is advantageous for improving traction performance. The shoulder block 41a does not have any corners where the angle between two sides is less than 70 degrees. Therefore, the recess 80 is formed at a position that avoids corners where the angle between two sides is less than 70 degrees. The shapes and dimensions of the step 8 and the recess 80 are as described above for the center region CA.

[0054] The shoulder block 41a has a corner C100, where two sides form an angle of 100 degrees or less, and a recess 80 is formed at a position that avoids the corner C100. The lengths L3 and L4 of the two sides that make up the corner C100 are, for example, 5 mm or more. The corner C100 is positioned as a portion of the shoulder block 41a that has relatively low rigidity. While the center block described above focuses on corners C90 with angles of less than 90 degrees, the shoulder block focuses on corners C100 with angles of 100 degrees or less because larger loads are more likely to act on the shoulder region SA than on the center region CA.

[0055] Providing the step 8 to improve traction performance increases strain on the groove bottoms of the shoulder lateral grooves 31 (particularly the groove corners 31c where the groove bottoms and groove walls connect), raising concerns about reduced durability due to the occurrence of groove bottom cracks. In particular, the shoulder lateral grooves 31 that separate the shoulder blocks 41 extend from the longitudinal groove 1 to the tread edge CE. Therefore, compared with lateral grooves that are closed within the block, they are more likely to move significantly in the longitudinal direction when exerting traction performance, making them more susceptible to groove bottom cracks. Therefore, in this embodiment, the shoulder lateral grooves 31 have shoulder reinforcement portions 7 to maintain durability. The shoulder reinforcement portions 7 protrude from the groove bottoms and connect the shoulder blocks 41 together. This shape is also advantageous for suppressing heel-and-toe wear that tends to occur in the shoulder region SA.

[0056] As shown in Figures 11 and 12, the shoulder reinforcement portion 7 is formed by raising the groove bottom of the shoulder lateral groove 31 radially outward. From the viewpoint of maintaining good durability, the groove depth D7 at the formation location of the shoulder reinforcement portion 7 is preferably 80% or less of the groove depth D31 of the shoulder lateral groove 31. Furthermore, to avoid excessively reducing the drainage performance of the shoulder lateral groove 31, the groove depth D7 is preferably 30% or more of the groove depth D31. From the viewpoint of maintaining good durability, the raised height 7h of the shoulder reinforcement portion 7 relative to the groove bottom of the shoulder lateral groove 31 is preferably 0.5 mm or more. To avoid excessively reducing the drainage performance of the shoulder lateral groove 31, the raised height 7h is preferably 3.0 mm or less.

[0057] The shoulder reinforcement 7 has a top surface 7t that is substantially parallel to the tread surface Tr. The length L7t of the top surface 7t in the extension direction of the shoulder lateral groove 31 is, for example, 3 to 10 mm. The top surface 7t is formed with a depression 7d that has a depth smaller than the protrusion height 7h, but is not limited to this. The top surface 7t is connected to the groove wall of the shoulder lateral groove 31 via an arc-shaped surface (see FIG. 12). The shoulder reinforcement 7 is provided circumferentially adjacent to (the side that forms) the corner C100 of the shoulder block 41a. The shoulder reinforcement 7 is offset in the tire circumferential direction so as not to intersect with an imaginary line extending from the center lateral groove 33 that divides the center block 43 (see FIG. 1).

[0058] The shoulder blocks 41b have substantially the same structure as the shoulder blocks 41a, although the block shape and the configuration of the sipes 5 are partially different. The shoulder blocks 41b have steps 8 that cover 70% or more of the edge of the shoulder blocks 41b and recesses 80 that are recessed radially inward from the bottoms of the steps 8. The shoulder blocks 41b do not have corners where two sides form an angle of less than 70 degrees. Therefore, the recesses 80 are formed in positions that avoid corners where two sides form an angle of less than 70 degrees. However, the shoulder blocks 41b do have corners C100 where two sides form an angle of 100 degrees or less, and the recesses 80 are formed in positions that avoid the corners C100. The matters already described for the shoulder blocks 41a are also applicable to the shoulder blocks 41b.

[0059] The shoulder region SA2 includes shoulder lateral grooves 32 that extend outward in the tire width direction from the longitudinal groove 1 (specifically, the shoulder lateral groove 12) and reach the ground contact edge CE, and shoulder blocks 42 that are divided in the tire circumferential direction by the shoulder lateral grooves 32. As described above, the shoulder region SA2 includes a shoulder land portion 22 that is a row of shoulder blocks 42 (shoulder blocks 42a, 42b). The shoulder blocks 42a, 42b and the shoulder lateral groove 32 correspond to the shoulder blocks 41a, 41b and the shoulder lateral groove 31 rotated 180 degrees, and the steps and recesses provided therein also have similar configurations, so redundant explanations will be omitted.

[0060] The shoulder lateral grooves 31 extend at an angle relative to the tire width direction, and lug grooves 36 are provided that are smoothly connected to the shoulder lateral grooves 31 via longitudinal grooves 1 (specifically, shoulder lateral grooves 11) and have closed ends on the inner side in the tire width direction. The center lateral groove 33 and center lateral groove 35 are smoothly connected via longitudinal grooves 1 (specifically, center lateral groove 13), and extend at an angle relative to the tire width direction in the opposite direction to the shoulder lateral grooves 31. Here, "two lateral grooves 3 smoothly connected via longitudinal grooves 1" refers to a state in which an imaginary line extending from the groove width center of one lateral groove 3 in the extension direction overlaps within the longitudinal groove 1 or is close enough that the distance between them in the tire circumferential direction is 5.0 mm or less.

[0061] In this manner, in the tread surface Tr of this embodiment, the shoulder lateral grooves 31 extend at an inclination to one side with respect to the tire width direction, and the lug grooves 36 are provided, smoothly continuing with the shoulder lateral grooves 31 via the longitudinal grooves 1 and having closed ends on the inner side in the tire width direction. Furthermore, in the center region CA, multiple center lateral grooves 33, 35 are smoothly continuing via the longitudinal grooves 1 and extend at an inclination to the other side with respect to the tire width direction. Therefore, long edge components along the shoulder lateral grooves 31 and lug grooves 36 are formed from the shoulder regions SA to the center region CA, and long edge components along the center lateral grooves 33 and 35 are formed in the center region CA, resulting in a structure in which these are inclined in opposite directions with respect to the tire width direction. This configuration improves traction performance while suppressing skidding in both the left and right directions.

[0062] In the tread surface Tr of this embodiment, a groove element including a connecting groove 15 is provided between the center block 43b and the center block 44b. This groove element extends through the center longitudinal groove 13 and the center longitudinal groove 14 and forms an edge component that extends at an angle with respect to the tire width direction. This edge component is inclined in the same direction as the long edge component along the center lateral groove 33 and the center lateral groove 35. Therefore, the traction performance is improved in cooperation with the long edge component along the center lateral groove 33 and the center lateral groove 35, while the above-mentioned effect of suppressing skidding in both the left and right directions is obtained in cooperation with the long edge component along the shoulder lateral grooves 31 and the lug grooves 36.

[0063] [1] A pneumatic tire according to the present disclosure has at least one land portion that is a block row on the tread surface, and each block included in the block row has a step that is provided over 70% or more of the edge of the block and a depression that is recessed radially inward from the bottom of the step, and the depression is formed at a position that avoids corners where the angle between two sides is less than 70 degrees. This configuration can improve traction performance while suppressing uneven wear.

[0064] [2] In the pneumatic tire of [1] above, the block may have a corner where the angle between two sides is less than 70 degrees, and the step may be provided in a range of the edge of the block that includes the corner where the angle between two sides is less than 70 degrees.

[0065] [3] In the pneumatic tire of the above [1] or [2], the ratio of the length of the recess formed in the step to the length of the step may be 30 to 70%.

[0066] [4] In the pneumatic tire of any one of the above items [1] to [3], the depth of the recess may be 0.3 to 2.0 mm.

[0067] [5] In the pneumatic tire of any one of the above [1] to [4], the ratio of the length of the recess included in one side to the length of the one side of the block may be 60% or less.

[0068] [6] In any one of the pneumatic tires [1] to [5] above, the length of the recess formed in the step extending along the lateral groove that divides the block in the tire circumferential direction may be greater than the length of the recess formed in the step extending along the longitudinal groove that divides the block in the tire width direction.

[0069] [7] In the pneumatic tire of any one of the above [1] to [6], a sipe may be provided in the block, and the sipe may have an opening end that opens in a side wall of the block and is set at a position where the depression is formed.

[0070] [8] In the pneumatic tire of any one of the above [1] to [7], a lateral groove that divides the blocks in the tire circumferential direction may be provided with a reinforcing portion that protrudes from a groove corner and extends along the extension direction of the lateral groove.

[0071] The pneumatic tire of the present disclosure is equivalent to a normal pneumatic tire except that the land portions of the tread surface are provided with the blocks as described above, and any conventionally known material, shape, structure, etc. can be used. The tread pattern formed on the tread surface is not particularly limited. The pneumatic tire of the present disclosure is useful as a tire to be mounted on light trucks including SUVs and pickup trucks.

[0072] Although the embodiments of the present disclosure have been described, the specific configurations are not limited to these embodiments. The present disclosure is not limited to the above-described embodiments, and various improvements and modifications are possible within the scope of the present disclosure. The configurations employed in the above-described embodiments may be employed in any combination. [Explanation of symbols]

[0073] 1 longitudinal groove, 2 land portion, 3 lateral groove, 5 sipe, 8 step, 8a bottom surface, 9 reinforcement portion, 33c groove corner portion, 41, 41a, 41b, 42, 42a, 42b shoulder block, 43, 43a, 43b, 44, 44a, 44b, 45 center block, 52 opening edge, 80 depression, C70 corner portion, Tr tread surface

Claims

1. At least one land portion is provided on the tread surface, the land portion being a block row. Each block included in the block row has a step provided in a range of 70% or more of an edge of the block, and a depression recessed from a bottom surface of the step toward an inner side in the tire radial direction, The depression is formed at a position that avoids a corner where the angle between two sides is less than 70 degrees.

2. The block has a corner portion where the angle between two sides is less than 70 degrees, The pneumatic tire according to claim 1 , wherein the step is provided in a range including the corner portion of the edge of the block, the corner portion having two sides that form an angle of less than 70 degrees.

3. 2. The pneumatic tire according to claim 1, wherein a ratio of the length of the recess formed in the step to the length of the step is 30 to 70%.

4. 2. The pneumatic tire according to claim 1, wherein the depth of the recess is 0.3 to 2.0 mm.

5. The pneumatic tire according to claim 1 , wherein a ratio of the length of the depression included in one side to the length of the one side of the block is 60% or less.

6. 2. The pneumatic tire according to claim 1, wherein a length of the recess formed in the step extending along a lateral groove that divides the block in the tire circumferential direction is greater than a length of the recess formed in the step extending along a longitudinal groove that divides the block in the tire width direction.

7. The blocks are provided with sipes, The pneumatic tire according to claim 1 , wherein the sipe has an open end that opens at a side wall of the block and is set at a position where the depression is formed.

8. The pneumatic tire according to any one of claims 1 to 7, wherein a reinforcing portion is provided in a lateral groove that divides the blocks in the tire circumferential direction, the reinforcing portion protruding from a groove corner and extending along the extension direction of the lateral groove.

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