Pneumatic tire

Abstract

To provide a pneumatic tire with an improved brake performance on a snow road surface.SOLUTION: A pneumatic tire includes at least one land part 2 being a block row or a rib on a treat surface. The land part 2 is provided with a sipe 5 extending in a direction crossing with a tire peripheral direction and a dimple 6 formed so as to increase an open width of the sipe 5. At least a part of the dimple 6 is arranged in a width center region of the land part 2. The dimple 6 has a bottom surface 61 extending in substantially parallel to the tread surface and along the sipe 5. A ratio of a length of the bottom surface 61 in a length of the sipe 5 is equal to or less than 50%. The sipe 5 includes a protrusion 7 protrudes from a sipe bottom and is formed with a region DA in which the dimple 6 and the protrusion 7 overlap in a tire radial direction.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] Winter tires and all-season tires have cut-like sipes in the land portions of the tread surface. This creates a so-called edge effect, whereby the edges of the sipes scratch the road surface, increasing grip and improving braking performance on snowy roads. However, on road surfaces with a low coefficient of friction, such as snowy roads, the contact pressure tends to be higher in the center region of the land portion in the tire width direction. If this causes the sipes to close in this center region, the edge effect will not be properly exerted, and braking performance on snowy roads will not be sufficiently improved.

[0003] Patent Document 1 describes a pneumatic tire that includes sipes that penetrate land portions in the tire width direction and chamfered portions provided in the sipes, with the length of the chamfered portions set to less than 70% of the length of the sipes. However, the chamfered portions are formed as flat surfaces (C-chamfers) or curved surfaces (R-chamfers) that connect the edge portions of the sipes, and are thought to close in the central regions of the land portions where ground pressure tends to be high. Of course, this document does not suggest any solutions to the phenomenon of the edge effect not being properly exerted as described above. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-163939 Summary of the Invention [Problem to be solved by the invention]

[0005] The present disclosure has been made in consideration of the above circumstances, and an object of the present disclosure is to provide a pneumatic tire that can improve braking performance on snowy road surfaces. [Means for solving the problem]

[0006] The pneumatic tire of the present disclosure has at least one land portion which is a block row or a rib on the tread surface, and the land portion is provided with a sipe extending in a direction intersecting the tire circumferential direction and a dimple formed to widen the opening width of the sipe, at least a portion of the dimple is arranged in the central region of the width of the land portion, the dimple has a bottom surface which is substantially parallel to the tread surface and extends along the sipe, the length of the bottom surface accounts for 50% or less of the length of the sipe, the sipe includes a raised portion which is raised from the bottom of the sipe, and an area is formed where the dimple and the raised portion overlap in the tire radial direction. [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] Close-up of shoulder block [Figure 3] XX cross section of Figure 2 [Figure 4] YY cross section of Figure 2 [Figure 5] ZZ cross section of Figure 2 [Figure 6] Close-up of shoulder block [Figure 7] Close-up of the center block [Figure 8] Close-up of the center block [Figure 9] Close-up of the center block 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 that is a block row or a rib 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 4 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 4 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 braking performance, the angle of the extension direction of the lateral grooves 3 relative 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. 5) 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 (see FIG. 5) 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 braking performance on snowy roads. 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 in the tire circumferential direction. The shoulder land portion 21 is divided into blocks 4 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 blocks 4 forming the shoulder land portion 21 include two types of blocks: shoulder blocks 41a and shoulder blocks 41b, which are arranged alternately in 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 blocks 4 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 blocks 4 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 blocks 4 by center lateral grooves 33. The center lateral grooves 33 extend from the shoulder longitudinal grooves 11 to the inner side in the tire width direction and connect to the center lateral groove 13. In this embodiment, the blocks 4 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 blocks 4 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 blocks 4 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 blocks 4 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 block 4 forming the center land portion 25 is a center block 45 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 width W5 measured in a direction perpendicular to the extension direction of the sipes 5, and a depth D5 measured in the tire radial direction (see FIGS. 3 and 5). The width W5 is preferably set to 1.5 mm or less, and more preferably 1.0 mm or less. The width W5 is set to, for example, 0.3 mm or more. The depth D5 is set to, for example, 5.0 to 9.0 mm. The depth D5 is set to be equal to or less than the depth D1 of the longitudinal groove 1. The inclination angle of the acute side of the sipes 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. The sipes 5 extend in a straight line or in a curved line that is bent partway along, 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 that appears on the tread surface Tr (however, dimples 6 are not taken into consideration) does not change along the depth direction, but may also 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., has a portion that oscillates in the width direction of the sipe 5 relative to the depth direction of the sipe 5).

[0025] At least a portion of the dimple 6 is located in the widthwise center region of the land portion 2, has a bottom surface 61 that is substantially parallel to the tread surface Tr and extends along the sipe 5, the length of the bottom surface 61 accounts for 50% or less of the length of the sipe 5, the sipe 5 includes a raised portion 7 that protrudes from the sipe bottom, and a region is formed where the dimple 6 and the raised portion 7 overlap in the tire radial direction (see FIGS. 3 to 5 ). While such a characteristic structure may be applied to at least one land portion 2, in this embodiment it is applied to each of the shoulder land portions 21, 22 and the center land portions 23, 24, 25. It is preferable that such a characteristic structure be formed in at least 40% or 60% of the dimples 6 provided on the tread surface Tr.

[0026] [Shoulder land area] The shoulder land portions 21, 22 will now be described in detail. FIG. 2 is an enlarged view of a shoulder block 41a. FIGS. 3 to 5 are cross-sectional views taken along lines XX, YY, and ZZ in FIG. 2, respectively. The shoulder block 41a is provided with a plurality of sipes 5 (two in this embodiment), each of which has a dimple 6 formed therein. The sipes 5 provided in the shoulder block 41a are arranged over an area that is 50% or more of the width W41a of the shoulder block 41a. This configuration is advantageous for ensuring the edge effect of the sipes 5 and improving braking performance on snowy roads.

[0027] The widthwise central region C41a is a range that is 50% of the width W41a, centered on the center of the width W41a of the shoulder block 41a serving as the land portion 2, and may alternatively be a range that is 30% of the width W41a. At least a portion of the dimple 6 is disposed in the widthwise central region C41a of the shoulder land portion 21 (land portion 2). As shown in FIGS. 2 to 5, the dimple 6 has a bottom surface 61 that is substantially parallel to the tread surface Tr and extends along the extension direction of the sipe 5. It is preferable that the central portion 61c of the bottom surface 61 of the dimple 6 be disposed in the widthwise central region C41a. When disposing (at least a portion of) the dimple 6 in the widthwise central region C41a, it is preferable that the dimple 6 be away from the sidewall of the land portion 2.

[0028] In each sipe 5, the ratio of the length L61 of the bottom surface 61 to the length L5 of the sipe 5 is set to 50% or less. The length L5 is the actual length measured along the extension direction of the sipe 5. Therefore, the length L5 of a sipe 5 extending in a curved line is calculated as the sum of the lengths of each straight line element. In the example of FIG. 2, multiple dimples 6 (two in this embodiment) are formed in one sipe 5. In such a case, the ratio is calculated by dividing the sum of the lengths L61 of the bottom surfaces 61 of the dimples 6 by the length L5. As shown in FIG. 5, the sipe 5 includes a raised portion 7 that protrudes from the sipe bottom 51, and a region DA (hereinafter referred to as overlap region DA) is formed where the dimple 6 and the raised portion 7 overlap in the tire radial direction.

[0029] On road surfaces with a low coefficient of friction, such as snowy road surfaces, the ground pressure tends to be high in the central region of the land portion 2 in the tire width direction. This makes it easier for the sipes 5 to close in this region, especially when the land portion 2 is new and has low rigidity. However, with the configuration of this embodiment, even if the sipes 5 are closed, gaps are formed by the dimples 6 having bottom surfaces 61, as shown in FIG. 3(B), thereby producing an edge effect. Furthermore, by keeping the above ratio at 50% or less, uneven wear (heel-and-toe wear) due to reduced rigidity around the sipes 5 can be suppressed. Furthermore, the formation of the overlapping region DA reinforces the radially inner portion of the dimples 6, enhancing the edge effect of the dimples 6. Therefore, braking performance on snowy road surfaces can be improved.

[0030] The sipes 5 are preferably so-called one-sided open sipes, having an open end 52 that opens on the side wall of the land portion 2 and a closed end 53 that terminates within the land portion 2. This reduces the decrease in rigidity of the land portion 2 compared to a double-sided open sipe that is open on both ends, which is advantageous for improving braking performance on snowy roads. Furthermore, since the sipes 5 are open on the side wall of the land portion 2, the generation of noises such as pumping sounds caused by air trapped in the sipes 5 when the tire touches the ground is suppressed. Note that dimples 6 do not have to be formed in all sipes 5 within a block 4, but it is preferable that dimples 6 be formed in more than half of the sipes 5 included in a block 4.

[0031] From the viewpoint of ensuring an appropriate edge effect of the dimples 6, it is preferable that the ratio of the length L61 of the bottom surface 61 to the length L5 of the sipe 5 be 20% or more. Also, from the viewpoint of ensuring an appropriate edge effect of the dimples 6, it is preferable that the length L61 of the bottom surface 61 of a single dimple 6 be 20% or more of the length L5. Furthermore, from the viewpoint of suppressing uneven wear (heel-and-toe wear) due to a decrease in rigidity around the sipe 5, it is preferable that the length L61 of the bottom surface 61 of a single dimple 6 be 45% or less of the length L5. It is preferable that the dimples 6 be formed in one or two locations per sipe 5 in the extension direction of the sipe 5.

[0032] As shown in FIG. 3, the dimples 6 are formed by depressing the surface of the land portion 2 radially inward. In this embodiment, the dimples 6 are formed in a rectangular shape in plan view (see FIG. 2). The dimples 6 widen the opening width of the sipe 5 on both of a pair of opposing sipe wall surfaces 54, but may also widen the opening width of the sipe 5 on only one of the pair of sipe wall surfaces 54. The overall width W6t of the dimple 6 is set to, for example, 1.5 to 6.0 times the width W5 of the sipe 5. The width W6p of the dimple 6, measured from the sipe wall surface 54, is preferably equal to or larger than the width W5 of the sipe 5. Furthermore, the width W6p is preferably equal to each other on both sides of the sipe 5 in the width direction. The depth D6 of the dimple 6 is set to, for example, 10 to 30% of the depth D5 of the sipe 5. The depth D6 is preferably 0.5 mm or greater.

[0033] Each dimple 6 has a wall surface 62 (see FIG. 3 ) that faces the width direction of the sipe 5 and extends radially outward from the bottom surface 61, and a wall surface 63 (see FIG. 4 ) that faces the extension direction of the sipe 5 and extends radially outward from the bottom surface 61. From the viewpoint of enhancing the edge effect of the dimple 6, the angle θ62 formed between the surface of the land portion 2 and the wall surface 62 is preferably 90 to 120 degrees. From the same viewpoint, the angle θ63 formed between the surface of the land portion 2 and the wall surface 63 is preferably 90 to 150 degrees. From the viewpoint of suppressing the occurrence of cracks on the bottom surface 61, the bottom surface 61 and the wall surface 62, and the bottom surface 61 and the wall surface 63 are preferably connected via arc-shaped surfaces, and the radius of curvature of the arc-shaped surfaces is preferably 0.1 mm or more. In this case, the length L61 is determined based on the intersection of an imaginary line extending the bottom surface 61 and an imaginary line extending the wall surface 63.

[0034] As shown in FIG. 5, the raised portion 7 is formed by raising the sipe bottom 51 radially outward in the tire. When multiple dimples 6 are formed in one sipe 5, it is sufficient that an overlapping region DL is formed for at least one dimple 6. The depth D7 of the sipe 5 where the raised portion 7 is formed is smaller than the maximum depth (depth D5) of the sipe 5. From the viewpoint of enhancing the reinforcing effect of the raised portion 7, the depth D7 is preferably 60% or less of the depth D5. From the viewpoint of improving traction performance on snowy roads, the depth D7 is preferably 10% or more of the depth D5. It is preferable that at least a portion of the peak of the raised portion 7, where the depth D7 is smallest, is located radially inward of the bottom surface 61. It is also preferable that the peak of the raised portion 7 is located radially inward of the center portion 61c of the bottom surface 61 (see FIG. 4).

[0035] As shown in Figures 2 and 5, in this embodiment, the step 8 is provided over 70% or more of the edge of the block 4. This configuration enhances the edge effect at the edge of the block 4, which is advantageous for improving traction performance on off-road roads. The length of the step 8 is 70% or more of the length of the edge of the block 4, and more preferably 80% or more (it is also preferable for the center block to be 100% (i.e., the entire circumference)). In this embodiment, the step 8 is provided over the entire edge facing the lateral groove 3, which is advantageous for improving braking performance.

[0036] The step 8 is formed by a surface 8a that is substantially parallel to the tread surface Tr and a surface 8b that extends along the tire radial direction. From the viewpoint of enhancing the edge effect at the edge of the block 4, 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 land portion 2 and an imaginary line extending the groove wall (side wall of the land portion 2) of the longitudinal groove 1. The depth D8 and the width W8 are substantially constant along the edge of the block 4.

[0037] FIG. 6 is an enlarged view of a shoulder block 41b. The shoulder block 41b has a structure substantially similar to that of the shoulder block 41a, although the block shape and the configuration of the sipes 5 are partially different. At least some of the dimples 6 are arranged in the widthwise center region C41b. The widthwise center region C41b is defined in the same manner as the widthwise center region C41a described above. For the cross-sectional shapes of the sipes 5 and the dimples 6, see FIGS. 3 to 5. The shoulder block 41b has the characteristic structure described above, and the matters already described for the shoulder block 41a are also applicable to the shoulder block 41b. The shoulder blocks 42a and 42b are equivalent to the shoulder blocks 41a and 41b rotated 180 degrees, so redundant description will be omitted.

[0038] Position MP shown in Figure 6 is 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 under a load of 60% of the standard load. In the region from the outermost position MP to the contact edge CE, the load during braking is relatively large, making it easier for the sipes 5 to close. In this embodiment, by arranging the dimples 6 at the outermost position MP, the edge effect of the dimples 6 can be exerted even when the sipes 5 are closed. However, because uneven wear may occur if the dimples 6 are positioned too close to the contact edge CE, it is preferable that the dimples 6 positioned at the outermost position MP include an outer portion 6o located outward in the tire width direction from the outermost position MP and an inner portion 6i located inward in the tire width direction from the outermost position MP and having a greater length in the tire width direction than the outer portion 6o.

[0039] [Center Land Area] The center land portions 23, 24, and 25 will now be described. The characteristic structures of the sipes 5 and dimples 6 can be configured in the same manner as the shoulder land portions 21 and 22, so a description of the commonalities will be omitted where appropriate. The matters already described for the shoulder land portions 21 and 22 can also be applied to the center land portions 23, 24, and 25 within the scope of the spirit thereof.

[0040] FIG. 7 is an enlarged view of a center block 43a. The center block 43a is provided with three sipes 5, and dimples 6 are formed in two of the sipes 5. At least a portion of the dimples 6 is located in the widthwise center region C43a of the center land portion 23. The widthwise center region C43a is defined in the same manner as the widthwise center region C41a described above. For the cross-sectional shapes of the sipes 5 and dimples 6, see FIGS. 3 to 5. Thus, the dimples 6 have bottom surfaces 61 that are substantially parallel to the tread surface Tr and extend along the sipes 5, the length of the bottom surfaces 61 accounting for 50% or less of the length of the sipes 5, the sipes 5 include raised portions 7 that protrude from the sipe bottoms, and there is a region where the dimples 6 and the raised portions 7 overlap in the tire radial direction (see FIGS. 3 to 5).

[0041] The center land portions 23, 24, and 25 contribute more to traction performance on snowy roads than the shoulder land portions 21 and 22. In this embodiment, in the region on the inner side of the shoulder land portions 21 and 22 in the tire width direction, the dimples 6 that are adjacent to each other in the tire circumferential direction are arranged offset in the tire width direction (see FIGS. 7 to 9). With this configuration, the arrangement area of ​​the dimples 6 expands in the tire width direction, increasing the range in which the edge effect is exerted, thereby improving traction performance on snowy roads. The dimples 6 that are adjacent to each other in the tire circumferential direction have an offset width OW in which their centers are offset in the tire width direction. The offset width OW is preferably 1 mm or more, and more preferably 3 mm or more.

[0042] FIG. 8 is an enlarged view of the center block 43b. The center block 43b has a structure substantially similar to that of the center block 43a, although the block shape and the configuration of the sipes 5 are different. At least a portion of the dimples 6 are arranged in the widthwise central region C43b. The widthwise central region C43b is defined in the same manner as the widthwise central region C41a described above. For the cross-sectional shapes of the sipes 5 and the dimples 6, see FIGS. 3 to 5. The center block 43b has the characteristic structure described above, and the matters already described for the center block 43a are also applicable to the center block 43b. The center blocks 44a and 44b are equivalent to the center blocks 43a and 43b rotated 180 degrees, so redundant description will be omitted.

[0043] FIG. 9 is an enlarged view of a center block 45. The center block 45 is provided with three sipes 5, and dimples 6 are formed in two of the sipes 5. At least a portion of the dimples 6 is located in the widthwise center region C45 of the center land portion 25. The widthwise center region C45 is defined in the same manner as the widthwise center region C41a described above. For the cross-sectional shapes of the sipes 5 and dimples 6, see FIGS. 3 to 5. Thus, the dimples 6 have bottom surfaces 61 that are substantially parallel to the tread surface Tr and extend along the sipes 5, the length of the bottom surfaces 61 accounting for 50% or less of the length of the sipes 5, the sipes 5 include raised portions 7 that protrude from the sipe bottoms, and there is a region where the dimples 6 and the raised portions 7 overlap in the tire radial direction (see FIGS. 3 to 5).

[0044] In the above-described embodiment, an example was shown in which the sipes 5 and dimples 6 as described above are provided in the land portion 2 which is a block row, but this is not limited to this, and they may also be provided in the land portion which is a rib extending continuously in the tire circumferential direction.

[0045] [1] A pneumatic tire according to the present disclosure has at least one land portion that is a block row or a rib on the tread surface, and the land portion is provided with sipes extending in a direction intersecting the tire circumferential direction and dimples formed to widen the opening width of the sipes, at least a portion of the dimples being located in a widthwise central region of the land portion, the dimples having bottom surfaces that are substantially parallel to the tread surface and extend along the sipes, the length of the bottom surfaces accounting for 50% or less of the length of the sipes, the sipes including raised portions that protrude from the sipe bottoms, and an area where the dimples and the raised portions overlap in the tire radial direction. This configuration can improve braking performance on snowy roads.

[0046] [2] In the pneumatic tire of the above item [1], the length of the bottom surface of a single dimple may be 45% or less of the length of the sipe.

[0047] [3] In the pneumatic tire of the above [1] or [2], the sipe may have an open end that opens to a side wall of the land portion and a closed end that terminates within the land portion.

[0048] [4] In the pneumatic tire of any one of the above [1] to [3], the land portion may be a block row in which blocks are arranged along the tire circumferential direction, and steps may be provided over a range of 70% or more of the edge of the block.

[0049] [5] In the pneumatic tire of any one of [1] to [4] above, the dimples that are adjacently arranged in the tire circumferential direction may be arranged offset in the tire width direction in a region that is more inward in the tire width direction than a shoulder land portion that includes a ground contact edge.

[0050] [6] In the pneumatic tire of any one of [1] to [5] above, the dimples may be arranged at the outermost position in the tire width direction of the contact patch when the tire is mounted on a normal rim, inflated to a normal internal pressure, and placed in contact with a flat surface perpendicularly under a load of 60% of a normal load.

[0051] [7] In the pneumatic tire of [6] above, the dimple located at the outermost position may include an outer portion located outward in the tire width direction from the outermost position, and an inner portion located inward in the tire width direction from the outermost position and having a greater length in the tire width direction than the outer portion.

[0052] 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 sipes and dimples as described above, and any conventionally known materials, shapes, structures, 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 winter tire or an all-season tire.

[0053] 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]

[0054] 1 longitudinal groove, 2 land portion, 4 block, 5 sipe, 6 dimple, 6i inner portion, 6o outer portion, 7 raised portion, 8 step, 11 shoulder longitudinal groove, 12 shoulder longitudinal groove, 13 center longitudinal groove, 14 center longitudinal groove, 21, 22 shoulder land portion, 23, 24, 25 center land portion, 41a, 41b, 42a, 42b shoulder block, 43a, 43b, 44a, 44b, 45 center block, 51 sipe bottom, 52 open end, 53 closed end, 61 bottom surface, C41a, C41b, C43a, C45 width center region, DA overlap region

Claims

1. The tread surface has at least one land portion which is a block row or a rib, The land portion is provided with sipes extending in a direction intersecting the tire circumferential direction and dimples formed to widen the opening width of the sipes, At least a portion of the dimples is disposed in a widthwise central region of the land portion, the dimple has a bottom surface that is substantially parallel to the tread surface and extends along the sipe, and the ratio of the length of the bottom surface to the length of the sipe is 50% or less, The sipe includes a raised portion that protrudes from the bottom of the sipe, and a region is formed in which the dimple and the raised portion overlap in the tire radial direction.

2. 2. The pneumatic tire according to claim 1, wherein the length of the bottom surface of a single dimple is 45% or less of the length of the sipe.

3. The pneumatic tire according to claim 1 , wherein the sipe has an open end that opens to a side wall of the land portion and a closed end that terminates within the land portion.

4. the land portion is the block row in which blocks are arranged along the tire circumferential direction, The pneumatic tire according to claim 1 , wherein the step is provided over 70% or more of the edge of the block.

5. 2. The pneumatic tire according to claim 1, wherein the dimples arranged adjacent to each other in the tire circumferential direction are arranged offset in the tire width direction in a region inward in the tire width direction from a shoulder land portion including a ground contact edge.

6. 6. The pneumatic tire according to claim 1, wherein the dimples are arranged at the outermost positions in the tire width direction of the contact patch when the pneumatic tire is mounted on a normal rim, inflated to a normal internal pressure, and brought into contact with a flat surface perpendicularly under a load of 60% of a normal load.

7. 7. The pneumatic tire according to claim 6, wherein the dimples arranged at the outermost positions include an outer portion located outward in the tire width direction from the outermost positions, and an inner portion located inward in the tire width direction from the outermost positions and having a greater length in the tire width direction than the outer portion.

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