JP2019006371A - Pneumatic tire - Google Patents

Abstract

To provide a pneumatic tire exerting favorable off-road running-through performance, durability performance and steering stability on dry road surface.SOLUTION: In a pneumatic tire 1, the sipes 5 are provided on the blocks 3A and 3B, and a tread part 2 is virtually partitioned into a crown area 7, a middle area 8 and an inner shoulder area 9A. The sipe 5 includes: a crown sipe 10 whose major portion is included in the crown area 7; a middle sipe 11 whose major portion is included in the middle area 8; and a shoulder sipe 12 whose major portion is included in an inner shoulder area 9A. Both depths of the crown sipe 10 and the shoulder sipe 12 are less than that of the middle sipe 11.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a pneumatic tire having a block provided with sipes.

  For example, in a pneumatic tire for four-wheel drive, a tire having a block pattern in which a plurality of blocks are provided in a tread portion is employed. Such a tire is required to have a so-called off-road running performance for running off-road by exhibiting sufficient traction and braking force on an off-road surface such as a rocky road surface and a muddy ground. In order to improve off-road running performance, for example, sipe with the same depth is provided in multiple blocks, reducing the rigidity of the blocks and promoting their deformation, making it easier to grasp rocks and mud in the grooves between the blocks It is known.

  However, in such a pneumatic tire, there is a concern that the steering stability performance on the dry road surface may be deteriorated due to a decrease in the rigidity of the block, and chipping or the like is likely to occur in the block, and the durability performance may be deteriorated.

Japanese Patent Application Laid-Open No. 2015-202776

  The present invention has been devised in view of the above circumstances, and based on improving the sipes provided in the block, while maintaining good off-road running performance, durability performance and dry road surface The main purpose is to provide a pneumatic tire capable of improving the steering stability performance.

  The present invention relates to a pneumatic tire having a block pattern in which a plurality of blocks are provided in a tread portion, wherein the blocks are provided with sipes, and the tread portion is a tread grounding centering on the tire equator. A crown region that is a quarter of the width, a pair of middle regions that are adjacent to both sides of the crown region in the tire axial direction and a region that is 1/8 of the tread contact width, and a tire shaft in each of the middle regions In a state of being virtually divided into a pair of inner shoulder regions that are adjacent to each other on the outer side in the direction and are one-eighth of the tread contact width, the sipe includes a crown sipe that includes a main portion in the crown region, A middle sipe that includes a main part in the middle region, and a shoulder sipe that includes a main part in the inner shoulder region; The depth of less than the depth of the Midorusaipu, the depth of the shoulder sipe is less than the depth of the Midorusaipu.

  In the pneumatic tire according to the present invention, it is preferable that the block includes a crown block disposed across the crown region and the middle region, and the crown sipe and the middle sipe are formed in the crown block. .

  In the pneumatic tire according to the present invention, it is desirable that the depth of the crown sipe and the depth of the shoulder sipe are 60% to 80% of the height in the tire radial direction of the block.

  In the pneumatic tire according to the present invention, it is desirable that the depth of the middle sipe is 65% to 85% of the height of the block in the tire radial direction.

  In the pneumatic tire according to the present invention, when viewed in the tire circumferential direction, the crown sipe and the middle sipe are formed at positions that do not overlap with each other, and the middle sipe and the shoulder sipe are formed at positions that do not overlap with each other. It is desirable that

  In the pneumatic tire according to the present invention, it is desirable that the crown sipe has a crown bent portion that bends at an angle of 95 to 115 degrees in a tread plan view.

  In the pneumatic tire according to the present invention, it is desirable that the crown bent portion has a depth smaller than portions on both sides thereof.

  In the pneumatic tire according to the present invention, one end of the crown sipe terminates inside the block, and a difference in length between sipe perpendiculars extending from the one end to block edges on both sides of the sipe is 10% or less. Is desirable.

  In the pneumatic tire according to the present invention, it is preferable that the middle sipe has a middle bent portion that bends at an obtuse angle in a tread plan view, and the middle bent portion has a depth smaller than portions on both sides thereof.

  In the pneumatic tire according to the present invention, it is desirable that both ends of the sipe have a depth of 15% to 25% of the maximum depth of the sipe.

  In the pneumatic tire of the present invention, the main part of the sipe is provided in each of the crown region, the middle region, and the inner shoulder region. Sipes are provided in the block. Thereby, the rigidity of the block in each area | region becomes small, and the deformation | transformation of a block is accelerated | stimulated. For this reason, since a rock, mud, etc. can be grasped effectively in the slot between blocks, off-road running performance is maintained.

  Further, since the depth of the crown sipe is smaller than the depth of the middle sipe, the rigidity of the crown region is maintained higher than the rigidity of the middle region. As a result, damage such as chipping that is likely to occur in the crown region where a large contact pressure acts as compared with the middle region is suppressed, so that the durability performance is improved.

  Further, since the shoulder sipe depth is smaller than the middle sipe depth, the rigidity of the inner shoulder region is maintained higher than the rigidity of the middle region. The inner shoulder region is a region where a lateral force larger than the middle region acts. For this reason, the steering stability performance on a dry road surface improves.

  Therefore, the pneumatic tire of the present invention improves durability performance and driving stability performance on a dry road surface while maintaining excellent off-road running performance.

It is an expanded view of the tread part of the pneumatic tire of one embodiment of the present invention. It is an enlarged view of FIG. (A) is the sectional view on the AA line of FIG. 2, (b) is the sectional view on the BB line of FIG. It is CC sectional view taken on the line of FIG. It is an enlarged view of a crown block. It is an enlarged view of a shoulder block.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a development view of a tread portion 2 of a pneumatic tire 1 (hereinafter sometimes simply referred to as “tire 1”) showing an embodiment of the present invention. In the present embodiment, an all-season tire for a four-wheel drive vehicle is shown as a preferable tire 1.

  As shown in FIG. 1, the tire 1 of the present embodiment is formed as a block pattern in which a plurality of blocks 3 are provided in a tread portion 2. A groove 4 is formed between the blocks 3 and 3.

  The block 3 of the present embodiment includes a crown block 3A and a shoulder block 3B. In the present embodiment, the crown blocks 3A are spaced apart in the tire circumferential direction on both sides of the tire equator C. In the present embodiment, the shoulder block 3B is spaced apart in the tire circumferential direction on the outer side in the tire axial direction than the crown block 3A. In the present embodiment, the crown block 3A and the shoulder block 3B are arranged substantially symmetrically with respect to a point on the tire equator C except for a variable pitch. In addition, the block pattern of the tire 1 is not limited to such an aspect.

  In this embodiment, the block 3 is provided with a sipe 5. In this specification, “sipe 5” is defined as a notch having a width of 1.5 mm or less, and is distinguished from “groove 4” having a larger width.

  In the present embodiment, the tread portion 2 is virtually divided into a crown region 7, a pair of middle regions 8, 8, a pair of inner shoulder regions 9A, 9A, and a pair of outer shoulder regions 9B, 9B. The crown region 7 is a region of ¼ of the tread contact width TW with the tire equator C as the center. The middle region 8 is a region adjacent to both outer sides in the tire axial direction of the crown region 7 and is 1/8 of the tread contact width TW. The inner shoulder region 9A is a region adjacent to the middle region 8 on the outer side in the tire axial direction and １ ／ of the tread contact width TW. The outer shoulder region 9B is a region that is formed between the tread end Te and the inner shoulder region 9A and is １ ／ of the tread ground contact width TW.

  The “tread end” Te is obtained when a normal load is applied to a normal tire 1 that is assembled with a normal rim and filled with a normal internal pressure, and a normal load is applied to the flat tire with a camber angle of 0 degrees. It is determined as the ground contact position on the outermost side in the tire axial direction. In the normal state, the distance in the tire axial direction between the tread ends Te and Te is determined as the tread contact width TW. When there is no notice in particular, the dimension of each part of the tire 1 is a value measured in a normal state.

  The “regular rim” is a rim determined for each tire in the standard system including the standard on which the tire is based. For example, “standard rim” for JATMA, “Design Rim” for TRA, “ETRTO” Then "Measuring Rim".

  “Regular internal pressure” is the air pressure that each standard defines for each tire in the standard system including the standard on which the tire is based. “JATIMA” is the “maximum air pressure”, TRA is the table “TIRE LOAD LIMITS” The maximum value described in “AT VARIOUS COLD INFLATION PRESSURES”, “INFLATION PRESSURE” in the case of ETRTO.

  “Regular load” is the load that each standard defines for each tire in the standard system including the standard on which the tire is based. It is “Maximum load capacity” for JATMA and “TIRE LOAD” for TRA. The maximum value described in “LIMITS AT VARIOUS COLD INFLATION PRESSURES”, or “LOAD CAPACITY” in ETRTO.

  FIG. 2 is an enlarged view of FIG. As shown in FIG. 2, the sipe 5 includes a crown sipe 10, a middle sipe 11, and a shoulder sipe 12 in the present embodiment. The main part of the crown sipe 10 of this embodiment is arranged in the crown region 7. The middle sipe 11 of the present embodiment is arranged in the middle region 8 in the main part. The main part of the shoulder sipe 12 of this embodiment is arranged in the inner shoulder region 9A. Thereby, as for the block 3, the rigidity of each area | region 7, 8 and 9A becomes small, and a deformation | transformation of the block 3 is accelerated | stimulated. Therefore, since rocks, mud, and the like can be effectively grasped in the groove 4 between the blocks 3, 3, the off-road running performance is improved. The main part refers to a part of 70% or more of the actual length of each sipe 5.

  3A is a cross-sectional view taken along the line AA in FIG. 2, and FIG. 3B is a cross-sectional view taken along the line BB in FIG. As shown in FIGS. 3A and 3B, the depth d1 (maximum depth) of the crown sipe 10 is smaller than the depth d2 (maximum depth) of the middle sipe 11. Thereby, the rigidity of the crown region 7 is maintained higher than the rigidity of the middle region 8. For this reason, damage such as chipping that is likely to occur in the crown region 7 where a large contact pressure acts as compared with the middle region 8 is suppressed, and thus durability performance is improved.

  When the depth d1 of the crown sipe 10 is excessively smaller than the depth d2 of the middle sipe 11, deformation of the crown block 3A is suppressed, and rocks and mud cannot be effectively grasped in the groove 4 between the blocks. Off-road performance may be reduced. For this reason, the depth d1 of the crown sipe 10 is desirably 75% or more of the depth d2 of the middle sipe 11, and is desirably 95% or less of the depth d2 of the middle sipe 11.

  4 is a cross-sectional view taken along the line CC of FIG. As shown in FIG. 4, the depth d3 (maximum depth) of the shoulder sipe 12 is smaller than the depth d2 of the middle sipe 11. Thereby, the rigidity of the inner shoulder region 9 </ b> A is maintained higher than the rigidity of the middle region 8. The inner shoulder region 9 </ b> A is a region where a greater lateral force acts than the middle region 8. For this reason, the steering stability performance on a dry road improves.

  When the depth d3 of the shoulder sipe 12 is excessively smaller than the depth d2 of the middle sipe 11, the off-road running performance may not be improved. For this reason, the depth d3 of the shoulder sipe 12 is desirably 75% or more of the depth d2 of the middle sipe 11, and is desirably 95% or less of the depth d2 of the middle sipe 11.

  Although not particularly limited, it is desirable that the depth d1 of the crown sipe 10 is 60% to 80% of the height H1 of the crown block 3A in the tire radial direction. Similarly, it is desirable that the depth d3 of the shoulder sipe 12 is 60% to 80% of the height H2 of the shoulder block 3B in the tire radial direction. The depth d2 of the middle sipe 11 is desirably 65% to 85% of the height H1 of the crown block 3A in the tire radial direction.

  As shown in FIG. 2, when viewed in the tire circumferential direction, the crown sipe 10 and the middle sipe 11 are formed at positions that do not overlap each other in the present embodiment. Further, when viewed in the tire circumferential direction, the middle sipe 11 and the shoulder sipe 12 are formed at positions that do not overlap each other in the present embodiment. Thereby, the block 3 is suppressed in the areas 7, 8 and 9 from significant reduction in rigidity. Accordingly, the steering stability performance on the dry road surface is further improved, and damage such as chipping is suppressed, and the durability performance is further improved.

  The crown block 3 </ b> A of the present embodiment is disposed across the crown region 7 and the middle region 8. Specifically, the crown block 3A is disposed across the crown region 7, the middle region 8, and the inner shoulder region 9A. In the present embodiment, the shoulder block 3B is disposed across the middle region 8, the inner shoulder region 9A, and the outer shoulder region 9B. In this embodiment, the crown block 3A is not formed in the outer shoulder region 9B. The shoulder block 3B is not formed in the crown region 7 in this embodiment.

  FIG. 5 is an enlarged view of the crown block 3A. As shown in FIG. 5, the crown block 3 </ b> A includes a first inclined portion 15 and a second inclined portion 16 in the present embodiment, and the tread surface 3 a is formed in an L shape. The first inclined portion 15 is inclined from the tire equator C to one side in the tire circumferential direction. The second inclined portion 16 is inclined in a direction opposite to the first inclined portion 15 and at a larger angle than the first inclined portion 15 with respect to the tire circumferential direction.

  In the present embodiment, the first inclined portion 15 is formed including the first block edge 17, the second block edge 18, and the third block edge 19. The first block edge 17 of the present embodiment continuously extends from the inner end 3i in the tire axial direction of the crown block 3A in the same inclination direction as the first inclined portion 15 and the tire circumferential direction. The second block edge 18 of the present embodiment continuously extends from the outer end 17e of the first block edge 17 in the tire axial direction in the opposite direction to the tire circumferential direction. The third block edge 19 of the present embodiment extends continuously from the outer end 18e in the tire axial direction of the second block edge 18 in the same inclination direction as the first block edge 17 and the tire circumferential direction. In the present specification, each block edge is an outer peripheral edge where the tread surface of the block and the groove wall intersect, and does not include a sipe in the block or an edge of the chamfered portion.

  In the present embodiment, the second inclined portion 16 includes a fourth block edge 20, a fifth block edge 21, and a sixth block edge 22. The fourth block edge 20 of the present embodiment extends continuously from the inner end 3i of the crown block 3A to the second inclined portion 16 in the same inclination direction with respect to the tire circumferential direction. The fifth block edge 21 of the present embodiment continuously extends from the outer end 20e in the tire axial direction of the fourth block edge 20 in the opposite direction to the tire circumferential direction. The sixth block edge 22 of the present embodiment continuously extends from the outer end 21e of the fifth block edge 21 in the tire axial direction in the same inclination direction as the fourth block edge 20 and the tire circumferential direction.

  FIG. 6 is an enlarged view of the shoulder block 3B. As shown in FIG. 6, the shoulder block 3 </ b> B includes an inclined portion 24 and an axial direction portion 25 in the present embodiment, and the tread surface 3 b is formed in a bent shape. The inclined portion 24 is inclined in the same direction as the first inclined portion 15 outward from the tire equator C side in the tire axial direction. The axial portion 25 is connected to the inclined portion 24 and extends in the tire axial direction to the outside of the tread end Te.

  In the present embodiment, the inclined portion 24 includes a seventh block edge 27, an eighth block edge 28, and a ninth block edge 29. The seventh block edge 27 of the present embodiment continuously extends from the inner end 3e closest to the tire equator C of the shoulder block 3B in the same inclination direction as the inclined portion 24 and the tire circumferential direction. The eighth block edge 28 of the present embodiment continuously extends from the inner end 3e in the direction opposite to the inclined portion 24 in the tire circumferential direction. The ninth block edge 29 of the present embodiment continuously extends from the outer end 28e in the tire axial direction of the eighth block edge 28 toward the tread end Te in the same inclination direction as the seventh block edge 27.

  The angle θ of the seventh block edge 27 and the ninth block edge 29 of the inclined portion 24 with respect to the tire axial direction is preferably 45 to 55 degrees. When the angle θ is less than 45 degrees, the lateral rigidity of the inclined portion 24 becomes excessively large, the deformation of the inclined portion 24 is not promoted, and the off-road running performance may be deteriorated. When the angle θ exceeds 55 degrees, the lateral rigidity of the inclined portion 24 is reduced, and the steering stability performance on the dry road surface may be deteriorated.

  The axial portion 25 includes a tenth block edge 30 and an eleventh block edge 31. The tenth block edge 30 of the present embodiment is smoothly connected to the seventh block edge 27 and extends in the tire axial direction. The eleventh block edge 31 of the present embodiment is smoothly connected to the ninth block edge 29 and extends in the tire axial direction. The shoulder block 3B and the crown block 3A are not limited to such an aspect.

  As shown in FIGS. 3 and 4, although not particularly limited, the heights H1 and H2 in the tire radial direction of the crown block 3A and the shoulder block 3B are preferably 12 to 18 mm.

  As shown in FIG. 5, the crown sipe 10 and the middle sipe 11 are provided in the crown block 3A in this embodiment. Thereby, the rigidity of the crown block 3A is effectively reduced, and rocks, mud, and the like are more effectively grasped in the groove 4 adjacent to the crown block 3A.

  The crown sipe 10 of the present embodiment is a semi-open type in which one end 10i is terminated inside the crown block 3A and the other end 10e is terminated at the second block edge 18 of the crown block 3A. Such a crown sipe 10 can suppress an excessive decrease in rigidity of the crown region 7 on which a large ground pressure acts.

  In the present embodiment, the crown sipe 10 has a crown bent portion 10c that bends at an angle α1 of 95 to 115 degrees in a plan view of the tread. Such a crown bent portion 10c locally reduces the rigidity of the crown block 3A and promotes deformation of the crown block 3A. When the angle α1 is less than 95 degrees, the rigidity of the crown bent portion 10c is excessively lowered, and the occurrence of chipping or the like may not be suppressed. When the angle α1 exceeds 115 degrees, the deformation of the crown block 3A may not be promoted.

  The crown sipe 10 of the present embodiment includes a first crown straight portion 10a that linearly connects between the crown bent portion 10c and the one end 10i, and a first shape that linearly connects between the crown bent portion 10c and the other end 10e. It is formed in an L shape that further includes two crown straight portions 10b. Such a crown sipe 10 can suppress an excessive decrease in rigidity of the crown block 3A. Each straight line portion (including a middle straight line portion described later) is not limited to a straight line in a strict sense, and may be formed in an arc shape having a curvature radius R of 80 mm or more, for example.

  In the present embodiment, the first crown straight portion 10a extends along the fourth block edge 20. The second crown straight portion 10 b extends along the first block edge 17. Such a crown sipe 10 maintains a small rigidity step of the first inclined portion 15 of the crown block 3A.

  The difference (La-Lb) between the lengths La and Lb of the sipe perpendiculars extending from one end 10i of the crown sipe 10 to the block edges 3s and 3t on both sides of the crown sipe 10 is 10% of the lengths La and Lb of each sipe perpendicular. The following is desirable. Thereby, the rigidity of the crown block 3A in the vicinity of the one end 10i of the crown sipe 10 is maintained high, and chipping or the like starting from the one end 10i is suppressed. In this specification, “both block edges 3s, 3t” mean block edges on both sides in the tire axial direction. The block edge 3s on the tire equator C side is formed by the first block edge 17 and the fourth block edge 20 in the present embodiment. The block edge 3t on the tread end Te side is formed of the third block edge 19 and the sixth block edge 22 in the present embodiment.

  As shown in FIG. 3 (a), the crown bent portion 10c has a smaller depth than portions on both sides thereof, in this embodiment, the first crown straight portion 10a and the second crown straight portion 10b. . As a result, a decrease in rigidity in the vicinity of the crown bent portion 10c is suppressed, and chipping and the like are more effectively reduced. In order to improve off-road running performance and durability performance in a well-balanced manner, the depth d4 at the crown bent portion 10c is desirably 30% to 50% of the height H1 in the tire radial direction of the crown block 3A.

  The first crown straight portion 10a and the second crown straight portion 10b have the maximum depth of the crown sipe 10 in the present embodiment.

  As shown in FIG. 5, the middle sipe 11 of the present embodiment is a full open type in which both ends 11e and 11i end at the fourth block edge 20 and the fifth block edge 21 of the crown block 3A. Such a middle sipe 11 reduces the rigidity of the crown block 3A in the middle region 8 where a contact pressure smaller than that of the crown region 7 and a lateral force smaller than that of the inner shoulder region 9A acts, thereby improving off-road running performance. It helps to further improve.

  In the present embodiment, the middle sipe 11 has a middle bent portion 13 that is bent at an obtuse angle in plan view of the tread. The middle bent portion 13 includes a first middle bent portion 13a and a second middle bent portion 13b having a smaller bending angle than the first middle bent portion 13a. Such a middle bent portion 13 locally reduces the rigidity of the crown block 3A in the middle region 8 and promotes deformation of the crown block 3A.

  The angle α2 of the first middle bent portion 13a is preferably 130 to 160 degrees. The angle α3 of the second middle bent portion 13b is preferably more than 90 degrees and 120 degrees or less.

  In the present embodiment, the middle sipe 11 includes a first middle straight line portion 11a, a second middle straight line portion 11b, and a third middle straight line portion 11c. The first middle straight portion 11a of the present embodiment has a straight line between the one end 11i and the first middle bent portion 13a. The second middle straight portion 11b of the present embodiment has a straight line between the first middle bent portion 13a and the second middle bent portion 13b. The third middle straight portion 11c of the present embodiment has a straight line between the second middle bent portion 13b and the other end 11e.

  The first middle straight line portion 11 a and the second middle straight line portion 11 b extend along the sixth block edge 22. The third middle straight line portion 11 c extends along the fifth block edge 21 in the present embodiment. Such a middle sipe 11 suppresses an excessive decrease in the rigidity of the crown block 3 </ b> A in the middle region 8.

  As shown in FIG. 3 (b), the first middle bent portion 13a has a depth smaller than the portions on both sides thereof, in the present embodiment, the first middle straight portion 11a and the second middle straight portion 11b. ing. This effectively reduces chipping and the like starting from the first middle bent portion 13a.

  Desirably, the depth d5 of the first middle bent portion 13a is greater than the depth d4 of the crown bent portion 10c. As a result, the rigidity of the crown block 3A in the middle region 8 where a small ground pressure acts as compared with the crown region 7 is relatively lowered, so that off-road running performance is improved. In order to improve off-road running performance and durability performance in a well-balanced manner, it is desirable that the depth d5 of the first middle bent portion 13a is 40% to 60% of the height H1 of the crown block 3A in the tire radial direction.

  Since the second middle bent portion 13b has a smaller bending angle than the first middle bent portion 13a, the rigidity in the vicinity of the second middle bent portion 13b of the crown block 3A is smaller than the rigidity in the vicinity of the first middle bent portion 13a. Become. For this reason, in order to effectively suppress chipping at the second middle bent portion 13b, the depth d6 of the second middle bent portion 13b is desirably smaller than the depth d5 of the first middle bent portion 13a, for example. . The depth d6 of the second middle bent portion 13b is desirably 50% to 80% of the depth d5 of the first middle bent portion 13a.

  The 1st middle straight part 11a and the 2nd middle straight part 11b have the maximum depth of middle sipe 11 in this embodiment. The third middle straight portion 11 c has the minimum depth of the middle sipe 11 in the present embodiment.

  As shown in FIG. 6, the shoulder sipe 12 is provided on the shoulder block 3B in this embodiment. Thereby, since the rigidity of the shoulder block 3B becomes small, rocks, mud, and the like are effectively gripped by the grooves 4 sandwiched between the shoulder blocks 3B.

  The shoulder sipe 12 is inclined to one side with respect to the tire circumferential direction in the tread plan view. In this embodiment, the shoulder sipe 12 is inclined in the same direction as the inclined portion 24 of the shoulder block 3B. Such a shoulder sipe 12 suppresses an excessive decrease in rigidity of the shoulder block 3B on which a large lateral force acts.

  As shown in FIG. 4, the shoulder sipe 12 has a central portion 12 c in the longitudinal direction having a depth smaller than portions on both sides thereof. Thereby, the excessive rigidity fall of the shoulder block 3B is suppressed. The depth d7 of the central portion 12c of the shoulder sipe 12 is desirably 50% to 70% of the depth d3 of the shoulder sipe 12.

  As shown in FIG. 6, in the present embodiment, the shoulder sipe 12 has a shoulder lug groove 14 that extends outward in the tire axial direction beyond the tread end Te and communicates with the other outer end 12 e in the tire axial direction. . The shoulder lug groove 14 extends along the inclined portion 24 and the axial direction portion 25. Such a shoulder lug groove 14 can promote deformation of the shoulder block 3B while suppressing an excessive decrease in rigidity of the shoulder block 3B.

  As shown in FIG. 3A, it is desirable that both end portions 5 a and 5 b in the longitudinal direction of the sipe 5 have a depth Db that is 15% to 25% of the maximum depth Da of the sipe 5. When the depth Db of both ends 5a and 5b is less than 15% of the maximum depth Da, the off-road running performance may be reduced. When the depth Db of the both end portions 5a and 5b exceeds 25% of the maximum depth Da, the rigidity of the block 3 is reduced, and there is a concern that durability performance and steering stability performance on a dry road surface may be deteriorated. Both ends 5a and 5b have a length of 5 mm from one end 5i and the other end 5e of the sipe 5.

  As shown in FIG. 2, a crown sipe 10 and a middle sipe 11 are provided in the crown region 7 of the present embodiment. In the present embodiment, the entire crown sipe 10 is provided in the crown region 7. On the other hand, with respect to the middle sipe 11, an end portion having the other end 11e is provided in the crown region 7. The sum (L1 × 2 + L2 × 2) of the tire axial direction length L1 of the crown sipe 10 provided in the crown region 7 and the tire axial direction length L2 of the end of the middle sipe 11 is the tire axial direction of the crown region 7 It is desirable that it is 60% or more of the width Wc. When the sum of the lengths of the crown sipe 10 and the middle sipe 11 (L1 × 2 + L2 × 2) is less than 60% of the width Wc of the crown region 7, a decrease in rigidity of the crown region 7 of the crown block 3A is suppressed, and the groove 4 There is a risk that the force to grab mud and rocks will be reduced. If the sum (L1 × 2 + L2 × 2) of the lengths of the crown sipe 10 and the middle sipe 11 is too large, the rigidity of the crown region 7 of the crown block 3A on which a large contact pressure acts is greatly reduced, and the steering on the dry road surface is performed. There is a risk that stability and durability will deteriorate. For this reason, the crown region sipe ratio, which is the ratio of the sum of the lengths of the crown sipe 10 and the middle sipe 11 to the width Wc of the crown region 7 (L1 × 2 + L2 × 2), is preferably 80% or less.

  A middle sipe 11 and a shoulder sipe 12 are provided in the middle region 8 of the present embodiment. In the present embodiment, the main part of the middle sipe 11 is provided in the middle region 8. As for the shoulder sipe 12, only the end including the one end 12 i is provided in the middle region 8 in the present embodiment. The sum (L3 + L4) of the length in the tire axial direction of the sipe 5 provided in one crown block 3A and one shoulder block 3B included in each middle region 8 with respect to the width Wm in the tire axial direction of the middle region 8 The middle region sipe ratio, which is the ratio, is preferably larger than the crown region sipe ratio, for example. Thereby, since the rigidity of the middle region 8 is relatively smaller than the rigidity of the crown region 7, the off-road running performance, the durability performance, and the steering stability performance on the dry road surface are improved in a well-balanced manner. From such a viewpoint, the middle region sipe ratio is preferably 75% or more and 95% or less.

  The sipe is not provided in the inner shoulder region 9A of the crown block 3A. Thereby, since the excessive fall of the rigidity of crown block 3A is controlled, durability performance and steering stability performance on a dry road surface are maintained high.

  As mentioned above, although embodiment of this invention was explained in full detail, it cannot be overemphasized that this invention is not limited to exemplary embodiment, and can be deform | transformed and implemented in a various aspect.

Tires for four-wheel drive vehicles of size 285 / 70R17 having the basic pattern shown in FIG. 1 were prototyped based on the specifications shown in Table 1. Tested. The main common specifications and test methods for each sample tire are as follows.
Crown block height H1: 15.0mm
Shoulder block height H2: 15.0mm
d4 / H1: 40%
d5 / H1: 45%
Angle θ: 50 degrees

<Off-road running performance / Stable driving performance on dry road>
Each sample tire was mounted on all wheels of a 3600cc four-wheel drive vehicle under the following conditions. The test driver then drove off-road test courses on soft and rocky roads made of mud and test courses on dry asphalt roads. The test driver evaluated the running characteristics related to the traction, the gripping force of mud and rocks, and the running stability at this time. The results are displayed with a score of Comparative Example 1 being 100. The larger the value, the better.
Rim: 17 × 7.5J
Internal pressure: 255kPa
Load: 54% of normal load

<Durability (Chipping occurrence)>
After the test of the off-road running performance and the driving stability performance on the dry road surface, the chipping generated in the crown block and the shoulder block was confirmed by visual inspection with a tester. The result is displayed with a score of Comparative Example 1 being 100 based on the number and state of chipping. The larger the value, the more the chipping is suppressed and the durability performance is excellent.
Table 1 shows the test results.

  As a result of the test, it was confirmed that the tire of the example had improved durability performance and driving stability performance on a dry road surface while maintaining off-road running performance as compared with the tire of the comparative example.

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Tread part 3 Block 5 Sipe 7 Crown area | region 8 Middle area | region 9A Inner shoulder area | region 10 Crown sipe 11 Middle sipe 12 Shoulder sipe Te Tread edge

Claims (10)

A pneumatic tire of a block pattern in which a plurality of blocks are provided in the tread portion,
The block is provided with sipes,
The tread portion is a crown region that is a quarter of the tread contact width centered on the tire equator, and a pair that is adjacent to both sides in the tire axial direction of the crown region and is a 1/8 region of the tread contact width. In the state of being virtually divided into a middle region and a pair of inner shoulder regions that are adjacent to each other in the tire axial direction of the middle region and are 1/8 of the tread contact width,
The sipe includes a crown sipe in which a main portion is included in the crown region, a middle sipe in which a main portion is included in the middle region, and a shoulder sipe in which a main portion is included in the inner shoulder region,
The depth of the crown sipe is smaller than the depth of the middle sipe,
The depth of the shoulder sipe is smaller than the depth of the middle sipe,
Pneumatic tire.   2. The pneumatic tire according to claim 1, wherein the block includes a crown block disposed across the crown region and the middle region, and the crown sipe and the middle sipe are formed in the crown block.   The pneumatic tire according to claim 1 or 2, wherein a depth of the crown sipe and a depth of the shoulder sipe are 60% to 80% of a height in a tire radial direction of the block.   The pneumatic tire according to any one of claims 1 to 3, wherein a depth of the middle sipe is 65% to 85% of a height in a tire radial direction of the block.   The crown sipe and the middle sipe are formed at positions that do not overlap each other when viewed in the tire circumferential direction, and the middle sipe and the shoulder sipe are formed at positions that do not overlap each other. The pneumatic tire according to any one of the above.   The pneumatic tire according to any one of claims 1 to 5, wherein the crown sipe has a crown bent portion that bends at an angle of 95 to 115 degrees in a tread plan view.   The pneumatic tire according to claim 6, wherein the crown bent portion has a depth smaller than portions on both sides thereof. One end of the crown sipe terminates inside the block;
The pneumatic tire according to any one of claims 1 to 7, wherein a difference in length of sipe perpendiculars extending from the one end to block edges on both sides of the sipe is 10% or less. The middle sipe has a middle bent portion that bends at an obtuse angle in a tread plan view,
The pneumatic tire according to any one of claims 1 to 8, wherein the middle bent portion has a depth smaller than portions on both sides thereof.   The pneumatic tire according to any one of claims 1 to 9, wherein both ends of the sipe have a depth of 15% to 25% of a maximum depth of the sipe.

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