JP2020100191A - Pneumatic tire - Google Patents

Abstract

To provide a pneumatic tire improved in traction performance on an ice/snow road surface while optimizing rigidity of blocks and securing steering stability performance on a dry road surface.SOLUTION: The pneumatic tire comprises a tread part 100 including a plurality of blocks. The plurality of blocks include center blocks 4 and 5 provided at positions overlapping with a tire equator CL, and in the center blocks 4 and 5 are formed sipe groups constituted of a plurality of sipes which are smaller in width than grooves partitioning the center blocks 4 and 5. The sipe group formed in the center block 5 has a first sipe 51 and a second sipe 52 which is larger in width than the first sipe 51, where the second sipe 52 is arranged in a center area, being a range corresponding to 50% of a length in a tire circumferential direction of the center block 5 with a center line of the center block 5 in the tire circumferential direction as a center.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a pneumatic tire including a tread portion in which a large number of blocks are arranged.

Conventionally, in a pneumatic tire that has a tread portion with a large number of blocks arranged, by forming a large number of notches called sipes in each block, a pneumatic tire that improves the edge effect and water removal effect and improves tire performance on ice and snow roads Tires are known (see Patent Documents 1 and 2).

In recent years, it has been required to ensure both steering stability performance on a dry road surface and improvement in on-snow performance (see Patent Document 3). Increasing the number of sipes in a block is effective for improving traction performance on ice and snow roads. However, if the number of sipes in the block is increased and the rigidity of the block is excessively reduced, the sipes tend to close, the edge effect and the water removing effect tend to be deteriorated, and the traction performance on the snowy and snowy road surface is deteriorated. Further, an excessive decrease in block rigidity tends to result in a decrease in steering stability performance on a dry road surface. Although increasing the size of the block suppresses the decrease in block rigidity, it locally increases the block rigidity between the central region and the peripheral region of the block.

JP, 2017-190123, A JP, 2014-080112, A JP 2012-180007 A

An object of the present invention is to provide a pneumatic tire in which the block rigidity is optimized and the steering stability performance on a dry road surface is ensured and the traction performance on an ice/snow road surface is improved.

A pneumatic tire having a tread portion including a plurality of blocks,
The plurality of blocks is provided at a position overlapping the tire equator, or provided adjacent to a groove arranged at a position overlapping the tire equator, including a center block,
In the center block, a sipe group including a plurality of sipes having a width smaller than a groove that divides the center block is formed,
The sipe group formed in the center block has a first sipe and a second sipe having a width larger than that of the first sipe,
The second sipe is arranged in a central region within a range of 50% of the tire circumferential direction length of the center block centered on the center line of the center block in the tire circumferential direction.

As a result, the center block is divided into a plurality of small blocks having the second sipe as a boundary. By being divided into small blocks, the block rigidity is reduced, and the road surface followability of the blocks is improved. Further, the width of the second sipe is narrower than the width of the groove that defines the center block. Therefore, the block rigidity does not decrease excessively. The pneumatic tire having such a configuration can improve the traction performance by suppressing the blockage of the first sipe and enhancing the edge effect and the water removal effect on the ice and snow road surface while ensuring the steering stability performance on the dry road surface. ..

Further, since the second sipe is arranged in the central region of the block, it is possible to reduce the block rigidity by aiming at the central region of the block having particularly high block rigidity among the blocks. Therefore, it is possible to reduce local variations in block rigidity between the central region of the block and the peripheral region of the block. Therefore, the block rigidity can be further optimized, and the edge effect and the water removal effect on the snowy and snowy road surface can be further enhanced while ensuring the steering stability performance on the dry road surface.

The width of the second sipe may be 1.5 times or more and 3.0 times or less the width of the first sipe. Thereby, the small blocks on both sides of the second sipe are appropriately interfered with each other, and the block rigidity is appropriately reduced. Further, both ends of the second sipe may be connected to the outer edge of the center block. If the sipes are connected to the outer edge of the block, the rigidity of the block is reduced and it is easy to improve the road surface followability of the block.

In the second sipe, it is preferable that the central part of the sipe has a wavy shape and the end part of the sipe has a straight shape.

The plurality of blocks further includes a shoulder block provided on the outermost side in the tire width direction, and a quarter block provided between the center block and the shoulder block,
In the quarter block, a sipe group including a plurality of sipes having a width smaller than a groove that divides the quarter block is formed,
The sipe group formed in the quarter block has a third sipe and a fourth sipe having a width larger than the third sipe,
The fourth sipe may be arranged in a central region that is within a range of 50% of a tire circumferential direction length of the quarter block centering on a central line of the quarter block in the tire circumferential direction.

As a result, like the center block, the quarter block is divided into a plurality of small blocks bounded by the fourth sipe. By being divided into small blocks, the block rigidity is reduced, and the road surface followability of the blocks is improved. The width of the fourth sipe is narrower than the width of the groove that divides the quarter block. Therefore, the block rigidity does not decrease excessively. The pneumatic tire having such a configuration can improve the traction performance by suppressing the blockage of the third sipe and enhancing the edge effect and the water removing effect on the ice and snow road surface while ensuring the steering stability performance on the dry road surface. ..

Further, since the fourth sipe is arranged in the central region of the block, the block rigidity can be reduced by aiming at the central region of the block having particularly high block rigidity among the blocks. Therefore, it is possible to reduce local variations in block rigidity between the central region of the block and the peripheral region of the block. Therefore, the block rigidity can be further optimized, and the edge effect and the water removal effect on the snowy and snowy road surface can be further enhanced while ensuring the steering stability performance on the dry road surface.

The width of the fourth sipe may be 1.5 times or more and 3.0 times or less the width of the third sipe. Thereby, the small blocks on both sides of the fourth sipe are appropriately interfered with each other, and the block rigidity is appropriately reduced. Further, both ends of the fourth sipe may be connected to outer edges of the quarter block. If the sipes are connected to the outer edge of the block, the rigidity of the block is reduced and it is easy to improve the road surface followability of the block.

In the fourth sipe, it is preferable that the central part of the sipe has a wavy shape and the end part of the sipe has a straight shape.

The pneumatic tire may be an ice and snow road tire.

Development view showing a tread portion in an embodiment of a pneumatic tire according to the present invention Enlarged view of the center block 5 in FIG. Enlarged view of quarter block 7 in FIG. Enlarged view of the shoulder block 9 in FIG.

Hereinafter, an embodiment of a pneumatic tire according to the present invention will be described with reference to the drawings. In each drawing, the dimensional ratios of the drawings do not necessarily match the actual dimensional ratios, and the dimensional ratios of the drawings do not necessarily match.

FIG. 1 is a development view showing a tread portion in an embodiment of a pneumatic tire according to the present invention. The tread portion 100 includes a plurality of blocks that come into contact with the road surface. The plurality of blocks are partitioned by the first groove and the second groove, or by the first groove, the second groove, and the ground contact end TE which is the tire width direction end where the tread portion 100 contacts the road surface. .. The inclined groove 1 corresponding to the first groove is inclined from the center side toward the shoulder side in the tire width direction and extends in a gentle curve. The intersecting groove 2 corresponding to the second groove intersects the plurality of inclined grooves 1 and connects the two inclined grooves 1. The inclined groove 1 and the intersecting groove 2 are repeatedly arranged at intervals in the tire circumferential direction.

In the present embodiment, an example in which the tread pattern formed on the tread portion 100 is a block pattern based on blocks is shown. However, the block pattern of the tread portion 100 shown in FIG. 1 is an example, and various block patterns can be adopted by changing the shapes, widths, and lengths of the first groove and the second groove. For example, the first groove may extend parallel to the tire width direction, or may extend obliquely to the tire width direction but in a straight line. The first grooves may all have the same length or may have different lengths. The same applies to the second groove.

In the present embodiment, the plurality of blocks include center blocks 4 and 5 provided at positions overlapping the tire equator CL. The centers of gravity of the center blocks 4 and 5 are located on opposite sides of the tire equator CL. The shapes of the center blocks 4 and 5 are different from each other. The center blocks 4 and 5 are repeatedly arranged in the tire circumferential direction.

When the tire equator CL does not overlap with the center block but only overlaps with the groove, the block provided adjacent to the groove arranged at a position overlapping with the tire equator CL is the center block. Further, the center blocks may be arranged so as not to overlap in the tire width direction. The shape of the center block is not limited to two different shapes, but may be three or more different shapes. Further, the center blocks having one type of shape may be arranged at positions overlapping the tire equator CL with a space provided along the tire circumferential direction.

In this embodiment, an example is shown in which the tire is configured as a directional tire having a designated rotation direction, and the rotation direction is indicated by an arrow RD. The front side (the lower side in FIG. 1) of the rotation direction RD is the stepping side of the block, and the rear side (the upper side of FIG. 1) of the rotation direction RD is the kicking side of the block. The rotation direction is designated by, for example, displaying an arrow or the like indicating the rotation direction on the surface of the sidewall portion of the pneumatic tire.

2A and 2B each show an enlarged view of the center block 5 in FIG. In the center block 5, a sipe group including a plurality of sipes having a width smaller than that of the groove (that is, the inclined groove 1 and the intersecting groove 2) that divides the center block 5 is formed. The grooves defining the blocks have a width of 1.5 mm or more, while the sipes have a width of less than 1.5 mm. The sipe group includes a first sipe 51 and a second sipe 52 having a width larger than that of the first sipe 51. 2A and 2B, the second sipe 52 is shown as a line representing two sipe walls, and the first sipe 51 is simply shown as one line.

As shown in FIG. 2A, the second sipe 52 is arranged in the central region Cr ₅ . The second sipe 52 is not arranged outside the central region Cr ₅ . Central region Cr ₅ is a tire circumferential direction length of the center block 5 and _{L 5,} when the center line of the center blocks 5 in the tire circumferential direction _{C 5,} to within ± 0.25 L ₅ from the center line _{C 5} Represents. That is, the second sipe 52 is arranged in the central region Cr ₅ that is within the range of 50% of the tire circumferential direction length L ₅ of the center block 5 with the center line C ₅ of the center block 5 in the tire circumferential direction as the center. ing. The center line C ₅ is an imaginary line extending in the tire width direction.

According to this structure, the center block 5 is divided into the small blocks 53 and 54 having the appropriate size and having the second sipe 52 as a boundary. As a result, the block rigidity of the center block 5 as a whole is appropriately reduced, and the small blocks 53 and 54 are easily deformed by following the road surface that is in contact with the ground. That is, the road followability of the block is improved. The second sipe 52 is a sipe that is narrower than the groove. Therefore, when the divided small blocks 53 and 54 are deformed, the small blocks 53 and 54 come into contact with each other to support each other, so that the block rigidity can be maintained without being excessively reduced.

Since the center block 5 is closer to the tire equator CL than the other blocks, it contributes particularly to the traction performance. Then, with respect to the center block 5, the pneumatic tire having the above-described configuration suppresses the blockage of the first sipe 51 while ensuring the steering stability performance on the dry road surface, and enhances the edge effect and the water removal effect on the ice and snow road surface. It is effective in improving traction performance.

Further, since the second sipe 52 is arranged in the central region Cr ₅ of the center block 5, the block rigidity can be reduced by aiming at the central region Cr _{5 of the} block having particularly high block rigidity in the center block 5. Therefore, it is possible to reduce the local variation in block rigidity between the central region Cr ₅ of the block and the peripheral region of the block.

It is preferable that only one second sipe 52 is arranged in the central region Cr ₅ of the center block 5 as in the present embodiment. As a result, the center block 5 is divided into two small blocks 53 and 54 having an appropriate size, and the block rigidity does not excessively decrease. However, a plurality of second sipes 52 may be included in the central region Cr ₅ in order to obtain appropriate block rigidity. Further, when a plurality of second sipes 52 are included, the first sipes 51 may be arranged so as to be sandwiched between the second sipes 52.

Width _{T 52} of the second sipe 52 (see FIG. 2 (b)) may is not more than 3.0 times 1.5 times the width _{T 51} of the first sipe 51. If the width _{T 52} of the second sipe 52 is 1.5 times or more the width _{T 51} of the first sipe 51, the small blocks 53 and 54 on both sides sandwiching the second sipes 52, behaves as an integral block It is easy to reduce the block rigidity to an appropriate degree. On the other hand, if the width _{T 52} of the second sipe 52 is 3.0 times or less, when the small blocks 53 and 54 sandwiching the second sipe 52 is deformed, with each other small blocks 53 and 54 are appropriately interference, block It is easy to suppress excessive deformation of. When the width _{T 52} of the second sipe 52 is within the above range with respect to the width _{T 51} of the first sipe 51, easily optimizes the block rigidity.

Width _{T 51} of the first sipe 51 is preferable to be 0.3mm or more, and more preferably 0.4mm or more. Furthermore, the width T ₅₁ of the first sipe 51 is preferably less than 0.8 mm, more preferably less than 0.6 mm. Width _{T 52} of the second sipe 52 is preferable to be 0.5mm or more, and more preferably 0.6mm or more. Width _{T 52} of the second sipe 52 is preferably to be less than 1.5 mm, more preferably less than 1.3 mm. The depth of each sipe is preferably shallower than the depth of the groove that defines the block, and may be the same depth.

As the sipes constituting the sipe group of the center block 5, it is preferable to use a composite sipe that includes both the corrugated shape and the straight shape in a plan view of the tread portion 100. When the sipes are straight sipes, uneven wear in the block, particularly heel and toe wear that occurs in the tire circumferential direction, tends to increase. By making at least a part of the first sipe 51 and the second sipe 52 have a wavy shape, it is possible to suppress the collapse when the tire is subjected to a lateral force and improve the uneven wear resistance performance.

It is preferable to use a composite sipe in which the central part of the sipe has a wavy shape and the sipe ends have a straight shape. If the shape of the sipe is corrugated to the sipe end, the sharp angle of the corner formed by the extending direction of the sipe and the block outer edge at the sipe end increases, and the rigidity at the corner locally decreases, Uneven wear that occurs in the tire width direction tends to increase. When both ends of the sipe are straight, uneven wear occurring in the tire width direction can be suppressed.

As shown in FIG. 2 (b), the extending direction D ₅₁ of the first sipe 51 and the extending direction D ₅₂ of the second sipe 52, either, a straight line passing through the center of the sipe width at both ends of the sipe Shown. Extending direction _{D 51} of the first sipe 51 at an angle of _{A 51} with respect to the tire width direction WL, the extending direction _{D 52} of the second sipe 52, the angle of _{A 52} with respect to the tire width direction WL Eggplant In FIG. 2B, the extending direction D ₅₁ and the extending direction D ₅₂ are upward to the tire width direction WL, but the extending direction D ₅₁ and the extending direction D ₅₂ are in the tire width direction WL. On the other hand, the direction may be downward to the right. Both the angle A ₅₁ and the angle A ₅₂ are preferably within 5 degrees. That is, the first sipe 51 and the second sipe 52 may extend within ±5 degrees with respect to the tire width direction. As a result, the edge effect of the sipe group formed on the center block 5 contributes to the improvement of the traction (driving/braking) performance particularly on an ice/snowy road surface. Further, the extending direction D ₅₁ and the extending direction D ₅₂ may be the same direction as the tire width direction WL (that is, the angle A ₅₁ and the angle A ₅₂ are each 0 degrees). When the extending directions D ₅₁ and D ₅₂ of the first sipe 51 and the second sipe 52 in the center block 5 are downward rightward, the sipe of the center block 4 located on the opposite side with the tire equator CL interposed therebetween. The extending direction may be a right upward direction. At that time, the absolute values of the angles of the center blocks 4 and 5 with respect to the tire width direction may be set to be equal. The angle A ₅₁ and the angle A ₅₂ may have the same value or different values.

The center block 5 has been described above, but the same applies to the center block 4 and other center blocks arranged at intervals in the tire circumferential direction.

Returning to FIG. 1, in the present embodiment, the plurality of blocks include shoulder blocks 8 and 9 provided on the outermost side in the tire width direction. The shoulder blocks 8 and 9 are defined by the inclined groove 1, the intersecting groove 2, and the ground contact TE.

The ground contact end TE is an outermost position in the tire width direction when the tire, which is assembled to the regular rim and is loaded with the regular internal pressure and the regular load, is grounded on a flat road surface. A regular rim is a rim that is defined for each tire in the standard system including the standard on which the tire is based. For example, a standard rim defined by JATMA, “Design Rim” defined by TRA, or ETRTO. It is a defined "Measuring Rim". The normal internal pressure is the air pressure that each standard defines for each tire in a standard system including the standard on which the tire is based. It is the maximum value described in “INFLATION PRESSSURES” or “INFLATION PRES SURE” specified in ETRTO. The normal load is a load that each standard defines for each tire in a standard system including standards on which the tire is based. For example, the maximum load capacity specified in JATMA and the maximum value described in the above table of TRA. , Or "LOAD CAPACITY" defined in ETRTO.

Quarter blocks 6 and 7 are arranged between center blocks 4 and 5 and shoulder blocks 8 and 9, respectively. The quarter blocks 6 and 7 are not essential blocks, and the blocks included in the tread portion 100 may be composed of the center blocks 4 and 5 and the shoulder blocks 8 and 9.

3A and 3B each show an enlarged view of the quarter block 7 in FIG. The quarter block 7 is formed with a sipe group including a plurality of sipes each having a width smaller than that of the groove (that is, the inclined groove 1 and the intersecting groove 2) that divides the quarter block 7. The grooves defining the blocks have a width of 1.5 mm or more, while the sipes have a width of less than 1.5 mm. The sipe group includes a third sipe 71 and a fourth sipe 72 having a width larger than that of the third sipe 71. In FIGS. 3A and 3B, the fourth sipe 72 is shown as a line representing two sipe walls, and the third sipe 71 is simply shown as one line.

As shown in FIG. 3A, the fourth sipe 72 is arranged in the central region Cr ₇ . The fourth sipe 72 is not arranged outside the central region Cr ₇ . Central region Cr ₇ is a tire circumferential direction length of the quota block 7 and _{L 7,} when the center line of the quota blocks 7 in the tire circumferential direction and _{C 7,} a range within ± 0.25 L ₇ from the centerline _{C 7} Represent That is, the fourth sipe 72 is arranged in the central region Cr ₇ that is within a range of 50% of the tire circumferential direction length of the quarter block 7 around the central line C ₇ of the quarter block 7 in the tire circumferential direction. .. With this configuration, like the center block 5 described above, the road followability of the quarter block 7 is improved, and the block rigidity of the quarter block 7 can be maintained without being excessively reduced.

Since the quarter block 7 is located away from the tire equator CL, it particularly contributes greatly to turning. Then, with respect to the quarter block 7, the pneumatic tire having the above configuration is effective in improving the steering stability performance.

Although only one fourth sipe 72 is arranged in the central region Cr ₇ of the quarter block 7, the fourth sipe 72 is not limited to this, and a plurality of fourth sipe 72 may be included in the central region Cr ₇ in order to obtain appropriate block rigidity. I do not care. Further, when a plurality of fourth sipes 72 are included, the third sipes 71 may be arranged so as to be sandwiched between the fourth sipes 72.

Width _{T 72} of the fourth sipe 72, as well as the first sipes 51 and second sipes 52, may not more than 3.0 times 1.5 times the width _{T 71} of the third sipes 71. When the width T ₇₂ of the fourth sipe 72 is in the above range, easily optimizes the block rigidity. The preferable size of the width T ₇₁ of the third sipe 71 conforms to the width T ₅₁ of the first sipe 51. The preferred size of the width T ₇₂ of the fourth sipe 72 conforms to the width T ₅₂ of the second sipe 52. The depths of the third sipe 71 and the fourth sipe 72 are preferably shallower than the depths of the grooves that partition the block, and may be the same depth.

As the sipes constituting the sipe group of the quarter block 7, it is preferable to use a composite sipe including both a wave shape and a straight shape in a plan view of the tread portion 100. This makes it possible to obtain the same effect as that of the center block described above. Further, it is preferable to use a composite sipe in which the central part of the sipe has a wavy shape and the sipe end has a straight shape. As a result, if both ends of the sipe are straight, uneven wear that occurs in the tire width direction can be suppressed.

As shown in FIG. 3 (b), the extending direction D ₇₁ of the third sipes 71 and the extending direction D ₇₂ of the fourth sipe 72, either, a straight line passing through the center of the sipe width at both ends of the sipe Shown. Extending direction _{D 71} of the third sipe 71 at an angle of _{A 71} with respect to the tire width direction WL, the extending direction _{D 72} of the fourth sipe 72, the angle of _{A 72} with respect to the tire width direction WL Eggplant In FIG. 3B, the extending direction D ₇₁ and the extending direction D ₇₂ are downward rightward with respect to the tire width direction WL, but the extending direction D ₇₁ and the extending direction D ₇₂ are the tire width direction WL. On the other hand, you may take the direction of rising to the right. The angle A ₇₁ and the angle A ₇₂ are each preferably 10 degrees or more and 30 degrees or less. Thereby, the edge effect of the sipe group particularly contributes to turning traveling. When the extending direction of the third sipe 71 and the fourth sipe 72 in the quarter block 7 is downward right, the extending direction of the sipe of the quarter block 6 located on the opposite side of the tire equator CL is right. You may take the upward direction. At this time, the absolute values of the angles of the quarter blocks 6 and 7 with respect to the tire width direction may be set to be equal. The angle A ₇₁ and the angle A ₇₂ may have the same value or different values.

Although the quarter block 7 has been described above, the same applies to the quarter block 6 and other quarter blocks arranged at intervals in the tire circumferential direction.

FIG. 4 shows an enlarged view of the shoulder block 9 in FIG. The shoulder block 9 has a plurality of sipes 91. The width of the sipe 91 is smaller than the width of the groove that defines the shoulder block. The width of the sipe 91 is preferably 0.3 mm or more and 0.8 mm or less. The representation of the width is the same as that of the center blocks 4 and 5 and the quarter blocks 6 and 7. Regarding the sipe shape, like the first to fourth sipes, a complex sipe that includes both a wavy shape and a straight shape in a plan view of the tread portion 100 is preferable, and the sipe center portion has a wavy shape and the sipe end portion has a straight shape. Is more preferable. The same applies to the shoulder block 8 and other shoulder blocks arranged at intervals in the tire circumferential direction.

Common to the center blocks 4, 5, quarter blocks 6, 7 and shoulder blocks 8, 9, the sipe group is a double-sided open type in which both ends of the sipe are connected to the outer edge of the block, and one end of the sipe is attached to the outer edge of the block. It may be either a one-side open type in which one end is connected and the other end is not connected to the outer edge of the block, or a both-side closed type in which both ends of the sipes are not connected to the outer edge of the block. As the number of open-sided sipes increases, the effect of lowering the block rigidity increases.

The pneumatic tire may be a so-called all-season tire that is used on both an ice-snow road in the winter and a dry road in the summer, but an ice-snow road tire that is mainly used in the ice-snow road and the dry road in the winter (so-called Winter tires). The tire for ice and snow roads has a rubber hardness in the tread portion in the range of 60 to 75 degrees, and has a lower rubber hardness in the tread portion as compared with a normal tire including an all-season tire. The rubber hardness is a value (durometer hardness) measured using a type A durometer in an atmosphere of 23° C. according to JIS K6253.

The pneumatic tire according to the present invention can be configured in the same manner as a normal pneumatic tire except that the tread portion is configured as described above, and any conventionally known material, shape, structure, manufacturing method, etc. can be adopted. Although illustration is omitted, the pneumatic tire of the present embodiment has a pair of bead portions, a sidewall portion extending from each of the bead portions to a tire radial direction outer side, and a tire radial direction outer end of each of the sidewall portions. And a tread portion continuous with.

The present invention is not limited to the above-described embodiments, and various improvements and modifications can be made without departing from the spirit of the present invention.

Has a block pattern shown in FIG. 1, the width _{T 51} of the first sipe 51, the width _{T 52} of the second sipe 52, the width _{T 71} of the third sipe 71, the width _{T 72} of the fourth sipe 72, the third The pneumatic tire having a tread portion satisfying the conditions shown in Examples 1 to 6 and Comparative Examples 1 to 3 in Table 1 is evaluated as the angle A ₇₁ formed by the sipe 71 with respect to the tire width direction WL and the sipe shape. did. In Table 1, the unit of each width is mm (millimeter). The angle A ₇₁ is an absolute value. Regarding the sipe shape, "composite" indicates that the central part of the sipe is corrugated and the end of the sipe is straight, and "corrugated" indicates a corrugated sipe in which all of the sipes have a corrugated shape. "Indicates a straight sipe that does not include a wave shape and extends in a substantially straight line shape. Other conditions such as the position of each sipe and the number of sipes are unified in the example and the comparative example.

<Evaluation>
The pneumatic tires having the tread portion of each of the examples and the comparative examples were attached to a test vehicle, and the on-snow driving performance, which is an index of traction performance, and the dry steering stability performance, which is the steering stability performance on a dry road surface, were evaluated. In addition, the uneven wear resistance performance was also evaluated. The evaluation conditions and evaluation items are shown below.

<Evaluation conditions>
Tire size: 225/50R17
Rim: 17X7.5J
Tire pressure: 220kPa
Test vehicle: Passenger car with displacement of 1984cc

<Evaluation of snow driving performance>
The tire was attached to the vehicle, an acceleration test was performed on a snowy road, and the time from the stopped state to running for 20 m was measured. The evaluation result is shown by an index with Comparative Example 1 being 100, using the reciprocal of the measured value. The larger the index value, the better the snow driving performance.

<Evaluation of dry steering stability>
The tires were mounted on the vehicle, and the vehicle was driven on the asphalt-paved dry road surface for acceleration, braking, turning, and lane change. A professional driver relatively evaluated the result and indicated it as an index with Comparative Example 1 being 100. The larger the index value, the better the steering stability performance on a dry road surface.

<Evaluation of uneven wear resistance performance>
Tires were attached to the vehicle, a load equivalent to four passengers (driver + 55 kg weight x 3) was loaded, and the vehicle was run for 12000 km. After running, the difference in wear between the stepping side and the kicking side of the center block was measured for the two pneumatic tires. Then, the average value of the wear difference between the two pneumatic tires was obtained, and the reciprocal of the average value was indexed. The index is shown as an index with Comparative Example 1 being 100. The larger this index, the smaller the difference in wear and the better the uneven wear resistance.

Table 2 shows the evaluation results. From this, it was shown that the example in which the sipe having a large width is in the central region improves the driving performance on snow while ensuring the steering stability performance on a dry road surface, as compared with the comparative example.
Further, among the examples in which there is a wide sipe in the central region, an example having a composite sipe in which the central part of the sipe has a corrugated shape and the sipe ends have a straight shape, an implementation of a corrugated sipe with all corrugated shapes It was shown that the uneven wear resistance is higher than that of the example and the example of the straight sipe extending substantially linearly without including the wave shape.

1... Inclined groove 2... Intersection groove 4, 5... Center block 6, 7... Quarter block 8, 9... Shoulder block 51... 1st sipe 52... 2nd sipe 53, 54, 73, 74... Small block 71... 3rd Sipe 72... Fourth Sipe 91... Sipe 100... Tread part

Claims (7)

A pneumatic tire having a tread portion including a plurality of blocks,
The plurality of blocks is provided at a position overlapping the tire equator, or provided adjacent to a groove arranged at a position overlapping the tire equator, including a center block,
In the center block, a sipe group including a plurality of sipes having a width smaller than a groove that divides the center block is formed,
The sipe group formed in the center block has a first sipe and a second sipe having a width larger than that of the first sipe,
The second sipe is arranged in a central region within a range of 50% of a tire circumferential direction length of the center block centered on a center line of the center block in the tire circumferential direction, Included tires. The width of the second sipe is 1.5 times or more and 3.0 times or less the width of the first sipe, and both ends of the second sipe are connected to the outer edge of the center block. Pneumatic tire described. The pneumatic tire according to claim 1 or 2, wherein in the second sipe, the central part of the sipe has a wavy shape and the end part of the sipe has a straight shape. The plurality of blocks further includes a shoulder block provided on the outermost side in the tire width direction, and a quarter block provided between the center block and the shoulder block,
In the quarter block, a sipe group including a plurality of sipes having a width smaller than a groove that divides the quarter block is formed,
The sipe group formed in the quarter block has a third sipe and a fourth sipe having a width wider than the third sipe,
The said 4th sipe is arrange|positioned in the center area|region which becomes the range of 50% of the tire circumferential direction length of the said quarter block centering on the center line of the said quarter block in a tire circumferential direction. The pneumatic tire according to any one of items. The width of the fourth sipe is not less than 1.5 times and not more than 3.0 times the width of the third sipe, and both ends of the fourth sipe are connected to the outer edge of the quarter block. Pneumatic tire described. The pneumatic tire according to claim 4 or 5, wherein in the fourth sipe, the sipe central portion has a wavy shape and the sipe end portion has a straight shape. The pneumatic tire according to any one of claims 1 to 6, wherein the pneumatic tire is an ice and snow road tire.

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