Pneumatic tire

Abstract

To provide a pneumatic tire capable of achieving both maintenance or improvement of anti-stone biting performance, and improvement of wet performance and snow performance.SOLUTION: A pneumatic tire includes a block (12, 21) formed on a tread surface Tr. The block (12, 21) has a pair of first sipes 5 separated from each other in a tire circumferential direction CD. Each of the first sipes 5 has a first portion 51 in which a width of a sipe surface is constant, and a second portion 52 in which the width of the sipe surface is larger than in the first portion 51. The second portion 52 of each of the first sipes 5 is not arranged in a central region Ar 3 among five regions Ar 1-Ar 5 defined by five equally dividing lines on both ends in the tire circumferential direction CD of the block (12, 21).SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to pneumatic tires.

Background Art

[0002] Pneumatic tires in which sipes are formed in the blocks on the tread surface are known. For example, Patent Document 1 discloses forming a chamfered portion on the sipe wall surface of the sipe. It is described that the chamfered portion formed in the sipe improves wet performance.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, by providing a chamfered portion on a part of the sipe surface, stone retention is likely to be induced. The occurrence of stone retention is not preferable because it causes cracks in the sipe, vibration, or noise. Also, improvement in snow performance as another performance is required.

[0005] The present disclosure provides a pneumatic tire capable of achieving both improvement in wet performance and snow performance and maintenance or improvement in stone retention resistance performance.

Means for Solving the Problems

[0006] The pneumatic tire of the present disclosure includes blocks formed on a tread surface, and the blocks have a pair of first sipes spaced apart from each other in the tire circumferential direction. Each of the first sipes has a first portion with a constant width of the sipe surface and a second portion with a larger width of the sipe surface than the first portion. The second portion of each of the first sipes is not arranged in the central region among the five regions obtained by the fifth-division lines at both ends of the block in the tire circumferential direction.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0008] [First Embodiment] Hereinafter, a first embodiment of the present disclosure will be described with reference to the drawings.

[0009] FIG. 1 is a developed view at the time of a new tire of a tread surface Tr provided in the pneumatic tire of the first embodiment.

[0010] As shown in Fig. 1, a pneumatic tire (hereinafter sometimes simply referred to as a tire) has a tread surface Tr. A plurality of main grooves (40, 41) that continuously extend in the tire circumferential direction CD are provided on the ground contact surface included in the tread surface Tr. The number of main grooves can be changed. The plurality of main grooves (40, 41) of the first embodiment include a shoulder main groove 40 that is the outermost in the tire axial direction AD on the ground contact surface, and a center main groove 41 that is closest to the tire equator CL. The shoulder main groove 40 of the first embodiment is a zigzag-shaped groove that continuously extends in the tire circumferential direction CD. The center main groove 41 is a groove having a shape including a branching portion and a merging portion, and partitions the center land 2 described later into a plurality of blocks.

[0011] The main groove is not particularly limited, but for example, it may have a groove width of 3% or more of the distance between the ground contact ends (dimension in the tire axial direction AD). Also, the main groove is not particularly limited, but for example, it may have a groove width of 7.0 mm or more. Further, the main groove is not particularly limited, but for example, it may be continuous in the tire circumferential direction CD and have the deepest groove depth within the tread surface Tr. A TWI (tread wear indicator) indicating the service limit due to wear may be partially provided in the groove of the main groove.

[0012] The dimensions and the like of each part of the pneumatic tire are values measured in a non-loaded state in which the pneumatic tire is mounted on a standard rim and filled with a standard internal pressure.

[0013] The ground contact surface means the surface that contacts the road surface when the tire is vertically placed on a flat road surface and a standard load is applied with the tire rim-mounted on a standard rim and filled with a standard internal pressure. The ground contact end is the outermost end in the tire axial direction AD of the ground contact surface.

[0014] The standard rim is the rim defined for each tire in a standard system including the standard on which the tire is based. For example, it is the standard rim in JATMA, and it is the "Measuring Rim" in TRA and ETRTO.

[0015] The normal internal pressure is the air pressure defined for each tire in the standard system including the standards on which the tire is based. For truck and bus tires and light truck tires, if it is JATMA, it is the maximum air pressure; if it is TRA, it is the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES"; if it is ETRTO, it is "INFLATION PRESSURE". For passenger car tires, it is usually 180 kPa, but for tires marked with Extra Load or Reinforced, it is 220 kPa.

[0016] The normal load is the load defined for each tire in the standard system including the standards on which the tire is based. If it is JATMA, it is the maximum load capacity; if it is TRA, it is the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES"; if it is ETRTO, it is "LOAD CAPACITY". When the tire is for a passenger car, it is the load corresponding to 88% of the above load. When the tire is for a racing cart, the normal load is 392 N.

[0017] In this specification, the slit 30 is a groove that is wider than the sipe described later and extends continuously from one end of the land to the other end. The notch is a groove that is wider than the sipe described later, opens at one end of the land, and terminates within the land away from the other end of the land, and is a groove whose length in the tire axial direction AD is longer than the width in the tire circumferential direction CD. The notch of the first embodiment is shallower than the main groove, but may have the same depth as the main groove. The groove width of the first part (constant width part) of the sipe described later is 0.3 mm or more and 1.5 mm or less. The groove width of the sipe means the width of the first part. The width of the first part is the width along the perpendicular passing through two lines spaced at a constant width on the sipe surface appearing on the tread surface Tr (outer surface of the tire). The two lines include straight lines and curves. The sipe may be a three-dimensional sipe having a bent portion in the depth direction or a two-dimensional sipe extending linearly in the depth direction without bending in the depth direction.

[0018] The pneumatic tire has a shoulder land 1 disposed outside the shoulder main groove 40 in the tire axial direction AD and a center land 2 disposed inside the shoulder main groove 40 in the tire axial direction AD. The shoulder land 1 in the first embodiment has a plurality of shoulder blocks partitioned by the slit 30 and the shoulder main groove 40. The plurality of shoulder blocks include a first type shoulder block 11 and a second type shoulder block 12. The first type shoulder block 11 has a notch 13 opening into the shoulder main groove 40. The second type shoulder block 12 does not have a notch 13 opening into the shoulder main groove 40. Note that a step with a constant width such as 1.0 mm is formed along the ends of each block in the first embodiment, but it is not limited thereto. There may be no step.

[0019] The center land 2 in the first embodiment has a plurality of center blocks partitioned by the slit 30 or the main grooves (40, 41). The plurality of center blocks include a first type center block 21, a second type center block 22, and a third type center block 23. The first type center block 21 is disposed on the tire equator CL and does not face the shoulder main groove 40. The second type center block 22 faces the shoulder main groove 40 and has a notch 24 opening into the shoulder main groove 40. The third type center block 23 faces the shoulder main groove 40 and does not have a notch 24 opening into the shoulder main groove 40.

[0020] <Second type shoulder block 12> Figure 2 is an enlarged plan view showing the second type of shoulder block 12. As shown in Figure 2, both ends of the second type of shoulder block 12 in the tire circumferential direction CD are, in a plan view, the ends of the slit 30 that partitions the second type of shoulder block 12. Both ends of the second type of shoulder block 12 in the tire circumferential direction CD include one or a plurality (two in the example shown in Figure 2) of pairs of straight lines that are spaced apart in the tire circumferential direction CD and parallel to each other. The first pair of straight lines includes a first straight line 12a that is continuous with the shoulder main groove 40 and a second straight line 12b that is parallel to the first straight line 12a. The second pair of straight lines includes a third straight line 12c that is continuous with the first straight line 12a and a fourth straight line 12d that is parallel to the third straight line 12c and continuous with the second straight line 12b.

[0021] When both ends of the shoulder blocks (11, 12) formed on the shoulder land 1 in the tire circumferential direction CD include one or more pairs of straight lines that are parallel to each other, the fifth bisectors of both ends of the shoulder blocks (11, 12) in the tire circumferential direction CD are the fifth bisectors of the straight lines of each pair. On the other hand, when both ends of the shoulder blocks (11, 12) in the tire circumferential direction CD do not include a pair of straight lines that are parallel to each other, the fifth bisectors of both ends of the shoulder blocks (11, 12) in the tire circumferential direction CD are the fifth bisectors of the longest straight lines.

[0022] As shown in Figure 2, five regions (Ar1 to Ar5) can be obtained by the fifth bisectors (shown by dotted lines) of both ends of the second type of shoulder block 12 in the tire circumferential direction CD. The five regions include a pair of end regions Ar1, Ar5 located on the outermost side in the tire circumferential direction CD, a central region Ar3 disposed at the center in the tire circumferential direction CD, and a pair of middle regions Ar2, Ar4 disposed between the pair of end regions Ar1, Ar5 and the central region Ar3.

[0023] FIG. 3A is a cross-sectional view of the II-II portion in FIGS. 2 and 4. As shown in FIG. 2, the second type shoulder block 12 has a pair of first sipes 5 spaced apart from each other in the tire circumferential direction CD. As shown in FIGS. 2 and 3A, the first sipe 5 has a first portion 51 and a second portion 52. The width D1 of the sipe surface of the first portion 51 is constant. The width D2 of the sipe surface of the second portion 52 is larger than the width D1 of the first portion 51. Since the first sipe 5 has not only the first portion 51 but also the second portion 52, the groove width increases compared to the case where the first sipe 5 has only the first portion 51, so the wet performance can be improved. In addition, by having the second portion 52, the tire is more likely to deform due to grounding and air is more likely to enter. When leaving the road surface, the discharge of snow in the first sipe 11 is promoted. As a result, it is possible to step in a fresh state where no snow has entered the first sipe 11, and the edge effect is more likely to be exerted, so the snow performance can be improved.

[0024] As shown in FIG. 3A, the second portion 52 includes a sipe portion 52a having the same width D1 as the sipe width of the first portion 51, and a pair of recesses 52b formed on both sides of the sipe portion 52a in the sipe width direction WD. The pair of recesses 52b open to the tread surface Tr and have a flat bottom surface 53 extending parallel to the direction (sipe width direction WD) orthogonal to the sipe depth direction ND of the first sipe 5, and a vertical wall surface 56 extending in the sipe depth direction from the tread surface Tr. The sipe depth direction ND is the normal direction of the tread surface Tr. Since the second portion 52 has the vertical wall surface 56, the edge effect is improved compared to the case where the second portion 52 has an inclined surface inclined in the depth direction instead of the vertical wall surface 56, so the snow performance can be improved.

[0025] Preferably, the width D3 of each recess 52b is larger than the width D1. Also, in order to achieve balance, it is preferable that the widths D3 of the pair of recesses 52b are equal. In the first embodiment, the width D1 is 0.8 mm, the width D2 is 3.0 mm, and the width D3 is 1.1 mm. In the first embodiment, the depth D4 of the second part 52 is 1.0 mm, but it is not limited thereto. The minimum value of the depth D4 of the second part 52 is 0.5 mm. If the depth D4 of the second part 52 is less than 0.5 mm, it becomes difficult to obtain the effect of improving the wet performance and the snow performance by the second part 52. The maximum value of the depth D4 of the second part 52 is 30% of the depth of the first sipe 5. If the second part 52 is too deep, it becomes difficult to eliminate stone biting.

[0026] Figure 3B is a cross-sectional view of the III-III part in Figures 2 and 4. As shown in Figures 2 and 3B, the second part 52 has an inclined surface 54. The inclined surface 54 is disposed between the end 53a of the bottom surface 53 in the sipe length direction LD and the tread surface Tr in a cross-section along the sipe length direction LD. The inclined surface 54 is inclined with respect to the sipe length direction LD and the tire diameter direction RD. Thus, since the second part 52 has the inclined surface 54, it becomes easier to guide water in the second part 52 to the outside in the sipe length direction LD, promoting drainage and making it possible to improve the wet performance.

[0027] As shown in Figure 2, the second parts 52 of the pair of first sipes 5 are not arranged in the central region Ar3, but are arranged in the pair of middle regions Ar2, Ar4. Since the amount of change in the block in the central region Ar3 is relatively small, once stone biting occurs, it is difficult to eliminate the stone biting even when centrifugal force or the like acting with the rolling of the tire is applied. Since the second part 52 where stone biting is likely to occur is not arranged in the central region Ar3, it is possible to maintain or improve the stone biting resistance performance. Also, the first sipe 5 including the first part 51 and the second part 52 is not arranged in the pair of end regions Ar1, Ar5. If a sipe is arranged in the pair of end regions Ar1, Ar5, the block will be deformed too much, causing uneven wear. By not arranging a sipe in the pair of end regions Ar1, Ar5, it is possible to suppress uneven wear. As shown in the same figure, the second part 52 is preferably away from the block end. This is to promote drainage inside the block.

[0028] As shown in Fig. 2, at least one of the pair of first sipes 5 opens into the shoulder main groove 40 facing the second type of shoulder block 12. This makes the second type of shoulder block 12 more likely to deform, so it is easier to eliminate stone biting and the wet and snow performance can be improved. In the first embodiment, both of the pair of first sipes 5 open into the shoulder main groove 40. In the shoulder block (12), neither of the pair of first sipes 5 opens at the outer end in the tire axial direction AD of the shoulder block (12). The outer ends in the tire axial direction AD of the first part 51 of the first sipes 5 and the outer ends in the tire axial direction AD of the second part 52 are made to coincide. This makes it possible to improve the wet performance by promoting drainage while avoiding a decrease in the rigidity of the block.

[0029] As shown in Fig. 2, the second type of shoulder block 12 has a second sipes 6 between the pair of first sipes 5. The second sipes 6 has only the first part 51 with a constant width of the sipes surface and does not have a second part with a width of the sipes surface larger than that of the first part 51. This arranges the second part where stone biting is likely to occur in the central region Ar3, so stone biting in the central region Ar3 can be suppressed. Furthermore, since it has the second sipes 6, it is possible to improve the wet performance by increasing the grooves and improve the snow performance by increasing the edge effect. In the second type of shoulder block 12 of the first embodiment, the maximum number of sipes spaced apart in the tire circumferential direction CD is three.

[0030] In the above, the second type of shoulder block 12 has been described as an example of the shoulder block, but it is not limited to this. The same can be said for the first type of shoulder block 11.

[0031] <The first type of center block 21> Figure 4 is an enlarged plan view showing the first type of center block 21. As shown in Figure 4, both ends of the center block 21 of the first type in the tire circumferential direction CD include one or more (two in the example of Figure 4) pairs of straight lines that are spaced apart in the tire circumferential direction CD and parallel to each other in plan view. The first pair of straight lines includes a first straight line 21a and a second straight line 21b parallel to the first straight line 21a. The second pair of straight lines includes a third straight line 21c and a fourth straight line 21d parallel to the third straight line 21c.

[0032] When both ends of the center block formed on the center land 2 in the tire circumferential direction CD include one or more pairs of straight lines that are parallel to each other, the fifth bisectors of both ends of the center block in the tire circumferential direction CD are the fifth bisectors of the outermost and longest straight lines among the one or more pairs of straight lines. In the example of Figure 4, the fifth bisectors based on the third straight line 21c and the fourth straight line 21d can be mentioned. On the other hand, when both ends of the center block in the tire circumferential direction CD do not include a pair of straight lines that are parallel to each other, the fifth bisectors of both ends of the center block in the tire circumferential direction CD are the fifth bisectors of the outermost and longest straight lines.

[0033] Five regions (Ar1 to Ar5) can be obtained by the fifth bisectors (shown by dotted lines and the fifth bisectors based on the third straight line 21c and the fourth straight line 21d) of both ends of the first type of center block 21 in the tire circumferential direction CD. The five regions include a pair of end regions Ar1 and Ar5 located on the outermost side in the tire circumferential direction CD, a central region Ar3 arranged at the center in the tire circumferential direction CD, and a pair of middle regions Ar2 and Ar4 arranged between the pair of end regions Ar1 and Ar5 and the central region Ar3.

[0034] As shown in Figure 4, the first type of center block 21 has a pair of first sipes 5 spaced apart from each other in the tire circumferential direction CD. The first sipes 5 have a first part 51 and a second part 52. The width D1 of the sipe surface of the first part 51 is constant. The width D2 of the sipe surface of the second part 52 is larger than the width D1 of the first part 51. Details of the first part 51 and the second part 52 are the same as those of the first sipe 5 in the second type of shoulder block 12, so they are omitted.

[0035] As shown in FIG. 4, the second portions 52 of the pair of first sipes 5 are not disposed in the central region Ar3, but are disposed in the pair of middle regions Ar2 and Ar4. Further, the second portions 52 of the first sipes 5 are not disposed in the pair of end regions Ar1 and Ar5.

[0036] As shown in FIG. 4, at least one of the pair of first sipes 5 opens into the center main groove 41 that partitions the first type center block 21. Thereby, the second type shoulder block 12 is more likely to be deformed, so that stone biting can be suppressed and wet and snow performance can be improved. In the first embodiment, both of the pair of first sipes 5 open into the center main groove 41.

[0037] The first type center block 21 has a second sipe 6 between the pair of first sipes 5. The second sipe 6 has only the first portion 51 with a constant width on the sipe surface and does not have a second portion with a width of the sipe surface larger than that of the first portion 51. In the first type center block 21 of the first embodiment, the maximum number of sipes separated in the tire circumferential direction CD is three.

[0038] [Second Embodiment] Hereinafter, a second embodiment of the present disclosure will be described with reference to the drawings. The same members and parts as those in the first embodiment are denoted by the same reference numerals and the description thereof will be omitted. FIG. 5 is an enlarged plan view showing the second type shoulder block 12 of the second embodiment.

[0039] While the second type shoulder block 12 of the first embodiment shown in FIG. 2 has the second sipe 6, the second type shoulder block 12 of the second embodiment shown in FIG. 5 does not have the second sipe 6. As shown in FIG. 5, the second type shoulder block 12 of the second embodiment has a pair of first sip es 5 spaced apart from each other in the tire circumferential direction CD. The first sipe 5 has a first part 51 and a second part 52. The width of the sipe surface of the first part 51 is constant. The width D2 of the sipe surface of the second part 52 is larger than the width of the first part 51. The shapes of the first part 51 and the second part 52 are the same as those of the first embodiment. The second parts 52 of the pair of first sip es 5 are not arranged in the central region Ar3, but are arranged in the pair of middle regions Ar2, Ar4. Also, the first sipe 5 including the first part 51 and the second part 52 is not arranged in the pair of end regions Ar1, Ar5. At least one of the pair of first sip es 5 opens into the shoulder main groove 40 facing the second type shoulder block 12. In the second embodiment, both of the pair of first sip es 5 open into the shoulder main groove 40. The maximum number of sip es spaced apart in the tire circumferential direction CD in the second type shoulder block 12 of the second embodiment is two.

[0040] [Examples and Comparative Examples] Examples are shown below, but the present disclosure is not limited to these examples. FIG. 6 is a plan view schematically showing the shoulder blocks of Comparative Examples 1 to 4 and Examples 1 to 4.

[0041] Comparative Example 1 The second type shoulder block 12 of Comparative Example 1 has a pair of first sip es 5 spaced apart from each other in the tire circumferential direction CD. Each first sipe 5 has only the first part 51 with a constant width of the sipe surface and does not have the second part 52. The pair of first sip es 5 are respectively arranged in the pair of middle regions Ar2, Ar4. The pair of first sip es 5 terminate within the block without opening at the block ends. No sipe or depression is formed other than the pair of first sip es 5. The maximum number of sip es spaced apart in the tire circumferential direction CD in the block is two.

[0042] Example 1 For a pair of first sipes 5 in Comparative Example 1, a second part 52 is provided. The pair of first sipes 5 are arranged in a pair of middle regions Ar2, Ar4 including the first part 51 and the second part 52, and the first part 51 and the second part 52 are not arranged in the central region Ar3. Otherwise, it is the same as Comparative Example 1.

[0043] Comparative Example 2 For the central region Ar3 of Example 1, a depression 55 corresponding to the second part 52 of the first sipes 5 is provided. Otherwise, it is the same as Example 1.

[0044] Example 2 Both of the pair of first sipes 5 in Example 1 open at the block ends. Otherwise, it is the same as Example 1.

[0045] Comparative Example 3 The second type of shoulder block 12 in Comparative Example 3 has a pair of first sipes 5 spaced apart from each other in the tire circumferential direction CD. Each first sipe 5 has only a first part 51 with a constant width of the sipe surface and does not have a second part 52. The pair of first sipes 5 are respectively arranged in a pair of middle regions Ar2, Ar4. The pair of first sipes 5 terminate within the block without opening at the block ends. A second sipe 6 is arranged between the pair of first sipes 5. The second sipe 6 has only a first part 51 with a constant width of the sipe surface and does not have a second part 52. The second sipe 6 is arranged in the central region Ar3. The maximum number of sipes spaced apart in the tire circumferential direction CD in the block is three.

[0046] Example 3 For the pair of first sipes 5 in Comparative Example 3, a second part 52 is provided. The pair of first sipes 5 are arranged in a pair of middle regions Ar2, Ar4 including the first part 51 and the second part 52, and the first part 51 and the second part 52 are not arranged in the central region Ar3. Otherwise, it is the same as Comparative Example 3.

[0047] Comparative Example 4 A second part 52 is provided for the second sipe 6 of Example 3. The second sipe 6 is arranged in the central region Ar3 including the first part 51 and the second part 52. Otherwise, it is the same as Example 3.

[0048] Example 4 Both of the pair of first sipess 5 in Example 3 open at the block ends. Otherwise, it is the same as Example 3.

[0049] Tires having the blocks of the above Examples 1 to 4 and Comparative Examples 1 to 4 were manufactured and evaluated for wet performance, snow performance, and chipping resistance performance. Each evaluation method is as follows.

[0050] <Wet performance> Each test tire was mounted on a FF vehicle with a displacement of 2000 cc, and on a wet road surface, the braking distance was measured while operating the ABS at a speed of 90 km / h until decelerating to 20 km / h (average value of n = 10), and shown as an index with Comparative Example 1 as 100. The larger the value, the shorter the braking distance, indicating better wet performance.

[0051] <Snow performance> Each test tire was mounted on a FF vehicle with a displacement of 2000 cc, and on a snow-packed road, the braking distance was measured while operating the ABS at a speed of 40 km / h (average value of n = 10), and shown as an index with Comparative Example 1 as 100. The larger the value, the shorter the braking distance, indicating better snow performance.

[0052] <Chipping resistance performance> Each test tire was mounted on a FF vehicle with a displacement of 2000 cc, and after driving 20,000 km, the number of small stones that invaded the sipe of the tire was counted, and the reciprocal was used as an index. The larger the index, the fewer the chippings and the better the chipping resistance performance.

[0053] The evaluation results are shown in Table 1.

Table 1

[0054] Comparing Comparative Examples 1 to 2 with Example 1, it can be understood that when the number of sipes in the block is two, the anti-chip performance can be maintained without arranging the recess 55 (including the second part 52) in the central region Ar3. By arranging the second part 52 provided in the first sipe 5 to avoid the central region Ar3, it can be understood that the wet performance and snow performance can be improved while ensuring the anti-chip performance. Comparing Comparative Examples 3 to 4 with Example 3, it can be understood that when the number of sipes in the block is three, the anti-chip performance can be maintained without arranging the recess 55 (including the second part 52) in the central region Ar3. By arranging the second part 52 provided in the first sipe 5 to avoid the central region Ar3, it can be understood that the wet performance and snow performance can be improved while ensuring the anti-chip performance. Comparing Example 1 with Example 2 and Example 3 with Example 4, it can be understood that when a pair of first sipes 5 open at the block ends, the anti-chip performance, wet performance, and snow performance are improved.

[0055] [Modification Example] (A) In the above embodiment, the center land 2 is the land passing through the tire equator CL, but it is not limited thereto. For example, when the main groove is arranged on the tire equator CL, the land closest to the tire equator CL may be used as the center land 2. Also, the center block (21) is the block passing through the tire equator CL, but it is not limited thereto. For example, the block arranged between a pair of shoulder main grooves 40 may be used as the center block.

[0056] (B) In the above embodiment, both of the pair of first sipes 5 in each block open to the main groove facing the block, but it is not limited thereto. Either one of the pair of first sipes 5 may open to the main groove facing the block. Also, at least one of the pair of first sipes 5 may open to the main groove facing the block.

[0057] (C) In the above-described embodiment, the second portion 52 of the first sipe 5 has recesses 52b on both sides in the sipe width direction WD of the sipe portion 52a, but is not limited thereto. For example, the second portion 52 may have a recess 52b only on one side in the sipe width direction WD of the sipe portion 52a.

[0058] (D) In the above-described embodiment, as shown in FIG. 3A, the shape of the cross section along the sipe width direction WD of the second portion 52 is a bottom surface 53, a vertical wall surface extending from the tread surface Tr in the sipe depth direction ND, and one curved surface connecting the vertical wall surface and the bottom surface 53, but is not limited thereto. For example, as shown in FIG. 7A, the bottom surface 53 and the tread surface Tr may be connected by a flat tapered surface. As another example, as shown in FIG. 7B, the vertical wall surface of the sipe and the tread surface Tr may be connected by a flat tapered surface. FIG. 7A is a cross-sectional view of the II-II portion according to a modified example. FIG. 7B is a cross-sectional view of the II-II portion according to a modified example.

[0059] (E) In the above-described embodiment, as shown in FIG. 3B, the second portion 52 has an inclined surface 54, but it may not have the inclined surface 54. For example, instead of the inclined surface 54, a vertical wall surface may be formed from the tread surface Tr toward the inside in the tire diameter direction RD, and the vertical wall surface and the bottom surface 53 may be connected via a curved surface or without a curved surface.

[0060] [1] As described above, like the above-described embodiment, the pneumatic tire includes blocks (12, 21) formed on the tread surface Tr, the blocks (12, 21) have a pair of first sipes 5 spaced apart from each other in the tire circumferential direction CD, each first sipe 5 has a first portion 51 with a constant width of the sipe surface and a second portion 52 with a larger width of the sipe surface than the first portion 51, and the second portion 52 of each first sipe 5 may not be arranged in the central region Ar3 of the five regions (Ar1 to Ar5) obtained by the fifth-division lines at both ends in the tire circumferential direction CD of the blocks (12, 21). In the central region Ar3 of the block (12, 21) in the tire circumferential direction CD, the deformation amount of the block is relatively small, and it is difficult to eliminate stone retention. On the other hand, if it is closer to the end of the block (12, 21) in the tire circumferential direction CD, the deformation amount of the block is relatively large, and it is easy to eliminate stone retention. If the second portion 52 that is prone to stone retention is arranged in the central region Ar3 of the block (12, 21), stone retention is likely to be caused, but it is difficult to eliminate stone retention, and the stone retention resistance performance deteriorates. On the other hand, by arranging the second portion 52 that is prone to stone retention while avoiding the central region Ar3, although stone retention is caused by the second portion 52, it is easy to eliminate stone retention, so it is possible to maintain or improve the stone retention resistance performance. Nevertheless, since the groove width increases due to the second portion 52, the wet performance is improved. In addition, due to the second portion 52, the tire is more likely to deform when in contact with the ground and air is more likely to enter, and when leaving the road surface, the discharge of snow in the first sipe 11 is promoted. As a result, it is possible to step in a fresh state where no snow has entered the first sipe 11, and the edge effect is more likely to be exerted, so the snow performance is improved. Therefore, it is possible to achieve both an improvement in wet performance and snow performance and the maintenance or improvement of stone retention resistance performance.

[0061] [2] The pneumatic tire according to the above [1], wherein the block (12, 21) has a second sipe 6 arranged between a pair of first sipes 5, the second sipe 6 is arranged in the central region Ar3, the second sipe 6 has a first portion 51 and does not have a second portion 52, which is also possible. While maintaining or improving the stone retention resistance performance, it is further possible to improve the wet performance and snow performance.

[0062] [3] The pneumatic tire according to the above [1] or [2], wherein the block (12, 21) faces main grooves (40, 41) extending in the tire circumferential direction CD, and at least one of the pair of first sipes 5 opens into the main grooves (40, 41), which is also possible. It is possible to further improve wet performance and snow performance while maintaining or improving the stone chipping resistance performance.

[0063] [4] The pneumatic tire according to any one of [1] to [3] above, wherein the block (12, 21) is a center block (21) passing through the tire equator CL, or a shoulder block (12) disposed on the outermost side in the tire axial direction AD on the tread surface Tr, may be used.

[0064] [5] The pneumatic tire according to any one of [1] to [4] above, wherein no sipe is formed in a pair of end regions Ar1 and Ar5 among the five regions (Ar1 to Ar5), may be used. According to this configuration, it is possible to suppress excessive deformation of the block (12, 21) and suppress the occurrence of uneven wear.

[0065] [6] The pneumatic tire according to any one of [1] to [5] above, wherein the second part 52 may have a vertical wall surface 56 extending in the sipe depth direction ND from the tread surface Tr in a cross section along the sipe width direction WD. Since the second part 52 has the vertical wall surface 56, the edge effect is improved compared to the case where the second part 52 has an inclined surface inclined in the depth direction instead of the vertical wall surface 56, so that the snow performance can be improved.

[0066] [7] The pneumatic tire according to any one of [1] to [6] above, wherein the second part 52 has a flat bottom surface 53 extending in a direction orthogonal to the sipe depth direction in a cross section along the sipe width direction WD, and the second part 52 has an inclined surface 54 disposed between the end 53a of the bottom surface 53 in the sipe length direction and the tread surface Tr in a cross section along the sipe length direction LD, and the inclined surface 54 is inclined with respect to the sipe length direction LD and the tire radial direction RD, may be used. According to this configuration, it is possible to promote drainage and improve wet performance.

[0067] As described above, the embodiments of the present disclosure have been described with reference to the drawings. However, the specific configuration should not be considered limited to these embodiments. The scope of the present disclosure is indicated not only by the description of the above-described embodiments but also by the claims, and further includes all modifications within the meaning and scope equivalent to the claims.

[0068] It is possible to adopt the structure employed in each of the above embodiments in any other embodiment. The specific configuration of each part is not limited to only the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure.

Description of Reference Numerals

[0069] 12: Second type shoulder block (shoulder block) 21: First type center block (center block) 5: First sipe 6: Second sipe 51: First part 52: Second part 53: Bottom surface 54: Inclined surface AD: Tire axial direction Ar1, Ar5: End region Ar3: Central region CD: Tire circumferential direction CL: Tire equator LD: Sipe length direction ND: Sipe depth direction RD: Tire radial direction Tr: Tread surface WD: Sipe width direction

Claims

1. A pneumatic tire comprising blocks formed on a tread surface, wherein the blocks have a pair of first sipes spaced apart from each other in the tire circumferential direction, each of the first sipes having a first portion with a constant width of the sipe surface and a second portion with a width of the sipe surface larger than that of the first portion, wherein the second portion of each of the first sipes is not disposed in a central region among five regions obtained by fifth division lines at both ends in the tire circumferential direction of the block.

2. The block has a second sipe disposed between the pair of first sipes, wherein the second sipe is disposed in the central region, and the second sipe has the first portion and does not have the second portion, the pneumatic tire according to claim 1.

3. The block faces a main groove extending in the tire circumferential direction, wherein at least one of the pair of first sipes opens into the main groove, the pneumatic tire according to claim 1 or 2.

4. The block is a center block passing through the tire equator or a shoulder block disposed at the outermost side in the tire axial direction on the tread surface, the pneumatic tire according to claim 1 or 2.

5. No sipe is formed in a pair of end regions among the five regions, the pneumatic tire according to claim 1 or 2.

6. The second portion has a vertical wall surface extending in the sipe depth direction from the tread surface in a cross section along the sipe width direction, the pneumatic tire according to claim 1 or 2.

7. The second portion has a flat bottom surface extending in a direction orthogonal to the sipe depth direction in a cross section along the sipe width direction, and the second portion has an inclined surface disposed between an end of the bottom surface in the sipe length direction and the tread surface in a cross section along the sipe length direction, wherein the inclined surface is inclined with respect to the sipe length direction and the tire diameter direction, the pneumatic tire according to claim 1 or 2.

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