JP2019171941A - Pneumatic tire - Google Patents

Abstract

To provide a pneumatic tire of which wet performance can be improved without reducing wear resistance.SOLUTION: A pneumatic tire in which plural major grooves 10, which extend in a tire circumferential direction, are formed on a tread part 1, and land parts 20, 30 of plural rows are partitioned in the tread part 1 by these major grooves 10. Plural composite grooves 40 are formed on the lad part 30 of at least one row of the tread part 1, and the plural composite grooves have: a narrow groove 41 which extends in a tire width direction; plural blocks 42 which are respectively provided on both sides in a width direction of the narrow groove 41 so as to be adjacent to the narrow groove 41; and a loop-like narrow groove 43 which surrounds each block 42 together with the narrow groove 41. Block elements 44, which comprise the block 42 and the loop-like narrow groove 43, are separated from each other on each side in the width direction of the narrow groove 41 along a lengthwise direction of the narrow groove 41, and the block elements 44 on both sides in the width direction of the narrow groove 41 are so located as to be shifted in the lengthwise direction of the narrow groove 41.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a pneumatic tire in which a plurality of rows of land portions are partitioned in a tread portion, and more particularly, to a pneumatic tire that can improve wet performance without reducing wear resistance.

  In a pneumatic tire, a plurality of main grooves extending in the tire circumferential direction are formed in the tread portion, and a plurality of rows of land portions are defined in the tread portion by the main grooves, and a plurality of lines extending in the tire width direction in each land portion. Lug grooves are formed.

  For example, in a pneumatic tire for a light vehicle, by reducing the groove area of the tread portion, the rigidity of the land portion is increased to improve uneven wear resistance. On the other hand, when the groove area is reduced, there is a concern that the wet performance deteriorates.

  Therefore, in order to avoid the deterioration of the wet performance, a sipe is provided in the land portion partitioned by the tread portion. However, a sipe having a groove width of about 1 mm cannot always sufficiently improve the wet performance. In addition, it has been proposed to improve steering stability when traveling on a wet road surface by dividing a block surrounded by sipes in the land portion of the tread portion (see, for example, Patent Document 1). However, in a structure in which a single block surrounded by a sipe is defined in the land, it is difficult to achieve both wear resistance and wet performance at a higher level.

JP 2000-233612 A

  An object of the present invention is to provide a pneumatic tire capable of improving the wet performance without reducing the wear resistance.

In order to achieve the above object, a pneumatic tire according to the present invention includes a tread portion that extends in the tire circumferential direction and has an annular shape, a pair of sidewall portions disposed on both sides of the tread portion, and the sidewall portions. A plurality of main grooves extending in the tire circumferential direction are formed in the tread portion, and a plurality of rows of land portions are defined in the tread portion by the main grooves. In a pneumatic tire
At least one row of land portions of the tread portion, narrow grooves extending in the tire width direction, and a plurality of blocks respectively disposed on both sides in the width direction of the narrow grooves so as to be adjacent to the narrow grooves; A plurality of composite grooves having loop-shaped fine grooves surrounding each block together with the fine grooves are formed, and a block element composed of the blocks and the loop-shaped fine grooves is formed on each side in the width direction of the fine grooves. Block elements spaced apart from each other along the length direction of the narrow groove and on both sides in the width direction of the narrow groove are arranged so as to be shifted in the length direction of the narrow groove. .

  In the present invention, at least one row of land portions of the tread portion has narrow grooves extending in the tire width direction, and a plurality of grooves arranged on both sides in the width direction of the narrow grooves so as to be adjacent to the narrow grooves. A plurality of composite grooves having a block and a loop-shaped fine groove surrounding each block together with the fine groove are formed, and a block element composed of the block and the loop-shaped fine groove is narrowed on each side in the width direction of the fine groove. The block elements that are spaced apart from each other along the length direction of the groove and are shifted in the width direction of the narrow groove are shifted in the length direction of the narrow groove, thereby increasing the groove area and the edge component. Since the water film removal effect can be enhanced by increasing the amount of water, the wet performance can be effectively improved. In addition, since the block elements are arranged so as to be distributed along the narrow grooves as described above, it is possible to achieve both wet performance and wear resistance, and improve wet performance without reducing wear resistance. it can.

  In the present invention, it is preferable that each composite groove has at least one block group in which a plurality of block elements on both sides in the width direction of the narrow groove overlap each other in the length direction of the narrow groove. By forming such a block group, the groove area and the edge component can be sufficiently secured, and the wet performance can be effectively improved without reducing the wear resistance. In particular, the shift amount of the block element in the block group is preferably in the range of 20% to 90% of the length of the block element. Each block group preferably includes at least three block elements.

The area on the tread surface of each block is preferably in the range of ² mm ^{2 to} 50 mm ² . By optimizing the area on the tread surface of each block, it is possible to effectively improve the wet performance without reducing the wear resistance.

  The depth of the loop-shaped fine groove is preferably in the range of 2 mm to 4 mm. By setting the depth of the loop-shaped fine groove in the above range, both wet performance and wear resistance can be achieved.

  In the pneumatic tire in which the mounting direction with respect to the vehicle is specified, it is preferable that the composite groove block disposed on the vehicle outer side is larger than the composite groove block disposed on the vehicle inner side. By relatively increasing the size of the composite groove block arranged on the outside of the vehicle in this way, the handling stability on the dry road surface is improved, so that both the driving stability on the dry road surface and the wet performance are compatible. Can do. In this case, it is preferable that the area on the tread surface of the composite groove block disposed on the vehicle outer side is in a range of 130% to 250% of the area on the tread surface of the composite groove block disposed on the vehicle inner side.

  Moreover, in the pneumatic tire in which the mounting direction with respect to the vehicle is specified, it is preferable that the loop-shaped fine groove of the composite groove disposed on the vehicle outer side is shallower than the loop-shaped fine groove of the composite groove disposed on the vehicle inner side. By making the loop-shaped narrow groove of the composite groove arranged on the outside of the vehicle relatively shallow in this way, the steering stability on the dry road surface is improved, so the steering stability and wet performance on the dry road surface are improved. It can be compatible. In this case, it is preferable that the depth of the loop-shaped fine groove of the composite groove disposed on the vehicle outer side is in the range of 40% to 80% of the depth of the loop-shaped fine groove of the composite groove disposed on the vehicle inner side.

  Furthermore, in the pneumatic tire in which the rotation direction is designated, it is preferable that the block located on the stepping side with respect to the narrow groove is larger than the block located on the kicking side with respect to the narrow groove. By making the block located closer to the stepping side than the narrow groove in this way, the handling stability on the dry road surface is improved, so that both the driving stability on the dry road surface and the wet performance are compatible. Can do. In this case, it is preferable that the area on the tread surface of the block located on the stepping side from the narrow groove is in a range of 120% to 150% of the area on the tread surface of the block located on the kicking side from the narrow groove.

It is meridian sectional drawing which shows the pneumatic tire which consists of embodiment of this invention. FIG. 2 is a development view showing a tread pattern of the pneumatic tire of FIG. 1. It is a top view which shows a composite groove. It is a top view which shows the modification of a composite groove | channel. It is a top view which shows the other modification of a composite groove | channel. It is a top view which shows the other modification of a composite groove | channel. It is a top view which shows the other modification of a composite groove | channel. It is a top view which shows the other modification of a composite groove | channel. It is a top view which shows the other modification of a composite groove | channel.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings. 1 and 2 show a pneumatic tire according to an embodiment of the present invention, and FIG. 3 shows a composite groove. 1 and 2, CL is the tire equator. 2 and 3, Tc is the tire circumferential direction, and Tw is the tire width direction.

  As shown in FIG. 1, the pneumatic tire of the present embodiment includes a tread portion 1 that extends in the tire circumferential direction and has an annular shape, and a pair of sidewall portions 2, 2 disposed on both sides of the tread portion 1. And a pair of bead portions 3 and 3 disposed inside the sidewall portion 2 in the tire radial direction.

  A two-layer carcass layer 4 is mounted between the pair of bead portions 3 and 3. The carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction, and is folded from the inside of the tire to the outside around the bead core 5 disposed in each bead portion 3. A bead filler 6 made of a rubber composition having a triangular cross-section is disposed on the outer periphery of the bead core 5.

  On the other hand, a plurality of belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. These belt layers 7 include a plurality of reinforcing cords inclined with respect to the tire circumferential direction, and are arranged so that the reinforcing cords cross each other between the layers. In the belt layer 7, the inclination angle of the reinforcing cord with respect to the tire circumferential direction is set in a range of, for example, 10 ° to 40 °. A steel cord is preferably used as the reinforcing cord of the belt layer 7. For the purpose of improving high-speed durability, at least one belt cover layer 8 in which reinforcing cords are arranged at an angle of, for example, 5 ° or less with respect to the tire circumferential direction is disposed on the outer peripheral side of the belt layer 7. Yes. As the reinforcing cord of the belt cover layer 8, an organic fiber cord such as nylon or aramid is preferably used.

  In addition, although the tire internal structure mentioned above shows the typical example in a pneumatic tire, it is not limited to this.

  As shown in FIG. 2, a plurality of main grooves 10 extending in the tire circumferential direction are formed in the tread portion 1. The main groove 10 includes a center main groove 11 located on the tire equator CL and a pair of shoulder main grooves 12 located on both sides of the center main groove 11. As a result, the tread portion 1 has two rows of center-side land portions 20 defined between the center main groove 11 and each shoulder main groove 12 and two rows defined on the outside of each shoulder main groove 12. The land portion 30 on the shoulder side is formed.

  A plurality of lug grooves 21 extending in the tire width direction are formed in each of the land portions 20 on the center side. One end of each of these lug grooves 21 opens into the shoulder main groove 12, and the other end terminates in the land portion 20. The land portion 20 on the center side is formed with a plurality of sipes 22 extending radially from the vicinity of the closed end of the lug groove 21. On the other hand, each of the land portions 30 on the shoulder side is formed with a plurality of lug grooves 31 extending in the tire width direction and not communicating with the shoulder main groove 12. Also, a plurality of sipes 32 extending radially from the vicinity of the closed end of the lug groove 31 are formed in the land portion 30 on the shoulder side. Further, a composite groove 40 described later is formed between the lug grooves 31 in the land portion 30 on the shoulder side.

  As shown in FIG. 3, the composite groove 40 includes a narrow groove 41 extending in the tire width direction, and a plurality of blocks arranged on both sides in the width direction of the narrow groove 41 so as to be adjacent to the narrow groove 41. 42 and a loop-shaped fine groove 43 surrounding each block 42 together with the fine groove 41. The block elements 44 composed of the blocks 42 and the loop-shaped fine grooves 43 are separated from each other along the length direction of the fine grooves 41 on each side in the width direction of the fine grooves 41 and on both sides of the fine grooves 41 in the width direction. The block elements 44 are arranged so as to be shifted in the length direction of the narrow grooves 41. The fine groove 41 and the loop-like fine groove 43 have a groove width set in a range of 0.8 mm to 2.0 mm, and a groove depth set in a range of 0.5 mm to 5.0 mm. The planar view shape of the block 42 is a rectangle, but the shape is not particularly limited.

  In the pneumatic tire, at least one row of land portions 30 of the tread portion 1 are provided with narrow grooves 41 extending in the tire width direction and on both sides in the width direction of the narrow grooves 41 so as to be adjacent to the narrow grooves 41. A composite groove 40 having a plurality of arranged blocks 42 and a loop-like fine groove 43 surrounding each block 42 together with the fine groove 41 is formed, and a block element 44 composed of the block 42 and the loop-like fine groove 43 is formed. Are spaced apart from each other along the length direction of the narrow groove 41 on each side in the width direction of the narrow groove 41, and the block elements 44 on both sides in the width direction of the narrow groove 41 are displaced in the length direction of the narrow groove 41. Since they are arranged, the narrow grooves 41 and the loop-shaped narrow grooves 43 surrounding the plurality of blocks 42 increase the groove area, and the blocks 42 increase the edge component and increase the water film removing effect. Thereby, wet performance can be improved effectively. Further, since the block elements 44 are arranged so as to be distributed along the narrow grooves 41 as described above, it is possible to achieve both wet performance and wear resistance, and improve the wet performance without reducing the wear resistance. be able to.

  In the pneumatic tire, each composite groove 40 includes at least one block group 45 in which a plurality of block elements 44 on both sides in the width direction of the narrow groove 41 overlap with each other in the length direction of the narrow groove 41. Good. That is, in FIG. 3, three block groups 45 in which the two block elements 44 on both sides in the width direction of the narrow groove 41 overlap each other in the length direction of the narrow groove 41 exist in each composite groove 40. is doing. Each composite groove 40 preferably includes three to five block groups 45. By forming such a block group 45, a sufficient groove area and edge component can be secured, and the wet performance can be effectively improved without deteriorating the wear resistance.

  In particular, the shift amount S of the block element 44 in the block group 45 is preferably in the range of 20% to 90% of the length L of the block element 44 (see FIG. 3). By setting such a deviation amount S of the block element 44, it is possible to sufficiently secure the groove area and the edge component, and to effectively improve the wet performance without reducing the wear resistance. Here, if the shift amount S of the block element 44 in the block group 45 is smaller than 20% of the length L of the block element 44, the edge component does not function effectively, so the effect of improving the wet performance is reduced, and conversely 90% If it is larger than that, the integrity as the block group 45 becomes insufficient, and the effect of improving the wet performance is lowered.

  In the pneumatic tire, a chamfer 46 is formed around each block 42. When the chamfered portion 46 is provided around each block 42, wet performance can be effectively improved while suppressing uneven wear of the block 42.

In the pneumatic tire, the area of each block 42 on the tread surface is preferably in the range of ² mm ^{2 to} 50 mm ² . By optimizing the area on the tread surface of each block 42, the wet performance can be effectively improved without reducing the wear resistance. Here, if the area on the tread surface of each block 42 is smaller than 2 mm ² , the effect of improving the wear resistance is lowered, and conversely if it is larger than 50 mm ^{2, the} effect of improving the wet performance is lowered.

  In the pneumatic tire, the depth of the loop-shaped fine groove 43 is preferably in the range of 2 mm to 4 mm. By setting the depth of the loop-shaped narrow groove 43 within the above range, both wet performance and wear resistance can be achieved. Here, when the depth of the loop-shaped fine groove 43 is smaller than 2 mm, the effect of improving the wet performance is lowered. Conversely, when the depth is larger than 4 mm, the effect of improving the wear resistance is lowered and uneven wear is easily caused. In addition, the depth of the narrow groove 41 and the depth of the loop-shaped thin groove 43 may be the same, or may be different from each other.

  4 to 7 each show a modification of the composite groove. 4 to 7, the composite groove 40 includes a narrow groove 41 extending in the tire width direction and a plurality of blocks arranged on both sides in the width direction of the narrow groove 41 so as to be adjacent to the narrow groove 41. 42 and a loop-shaped fine groove 43 surrounding each block 42 together with the fine groove 41, and a block element 44 composed of the block 42 and the loop-shaped fine groove 43 is arranged on each side in the width direction of the fine groove 41. The block elements 44 that are spaced apart from each other along the length direction of the narrow groove 41 and that are on both sides in the width direction of the narrow groove 41 are shifted in the length direction of the narrow groove 41.

  In FIG. 4, two block groups 45 are formed in which three block elements 44 on both sides in the width direction of the narrow groove 41 overlap each other in the length direction of the narrow groove 41. As described above, each block group 45 preferably includes at least three block elements 44. Thereby, the groove area and the edge component can be sufficiently secured, and the wet performance can be effectively improved without deteriorating the wear resistance. In FIG. 5, one block group 45 is formed in which the eight block elements 44 on both sides in the width direction of the narrow groove 41 are overlapped with each other in the length direction of the narrow groove 41. 6 and 7, one block group 45 is formed in which the four block elements 44 on both sides in the width direction of the narrow groove 41 are overlapped with each other in the length direction of the narrow groove 41. 6 and 7, the aspect ratio of the length to the width of the composite groove 40 is different.

  FIG. 8 shows still another modification of the composite groove. In FIG. 8, IN is the inside of the vehicle when the vehicle is mounted, and OUT is the outside of the vehicle when the vehicle is mounted. In the pneumatic tire in which the mounting direction with respect to the vehicle is designated, an asymmetric structure in which the block 42A of the composite groove 40A disposed on the vehicle outer side is larger than the block 42B of the composite groove 40B disposed on the vehicle inner side may be employed. it can. By relatively increasing the size of the block 42A of the composite groove 40A arranged outside the vehicle in this manner, the steering stability on the dry road surface is improved, so that both the steering stability on the dry road surface and the wet performance are compatible. can do.

  In this case, the area of the tread surface of the block 42A of the composite groove 40A arranged on the vehicle outer side is preferably in the range of 130% to 250% of the area of the tread surface of the block 42B of the composite groove 40B arranged on the vehicle inner side. . Here, when the area of the tread of the block 42A of the composite groove 40A arranged on the vehicle outer side is smaller than 130% of the area of the tread of the block 42B of the composite groove 40B arranged on the inner side of the vehicle, The effect of improving the steering stability is lowered, and conversely, if it is larger than 250%, the effect of improving the wet performance is lowered.

  Further, in the pneumatic tire in which the mounting direction with respect to the vehicle is designated as shown in FIG. 8, the loop-shaped narrow groove 43A of the composite groove 40A disposed on the vehicle outer side is the loop-shaped thin groove of the composite groove 40B disposed on the vehicle inner side. An asymmetric structure that is shallower than the groove 43B can be employed. By making the loop-shaped narrow groove 43A of the composite groove 40A arranged on the vehicle outer side relatively shallow in this way, the steering stability on the dry road surface is improved, so the steering stability and wet performance on the dry road surface are improved. And both.

  In this case, the depth of the loop-shaped fine groove 43A of the composite groove 40A arranged on the vehicle outer side is in the range of 40% to 80% of the depth of the loop-shaped fine groove 43B of the composite groove 40B arranged on the vehicle inner side. And good. Here, when the depth of the loop-shaped fine groove 43A of the composite groove 40A disposed on the vehicle outer side is smaller than 40% of the depth of the loop-shaped fine groove 43B of the composite groove 40B disposed on the vehicle inner side, the wet performance is achieved. On the other hand, if it is greater than 80%, the effect of improving the steering stability on the dry road surface is reduced.

  FIG. 9 shows still another modification of the composite groove. In FIG. 9, R is the designated rotation direction. In the pneumatic tire in which the rotation direction R is specified, an asymmetric structure is adopted in which the block 42C positioned on the step-in side of the narrow groove 41 in the composite groove 40 is larger than the block 42D positioned on the kick-out side of the narrow groove 41. can do. In this way, the relative stability of the block 42C located on the step-down side of the narrow groove 41 in the composite groove 40 improves the driving stability on the dry road surface, so that the driving stability and wet on the dry road surface are improved. Both performance and performance can be achieved.

  In this case, the area on the tread surface of the block 42C located on the stepping side of the narrow groove 41 in the composite groove 40 is in the range of 120% to 150% of the area on the tread surface of the block 42D located on the kicking side of the fine groove 41. Good to have. Here, if the area on the tread surface of the block 42C located on the stepping side of the narrow groove 41 in the composite groove 40 is smaller than 120% of the area on the tread surface of the block 42D located on the kicking side of the fine groove 41, dry The effect of improving the steering stability on the road surface decreases, and conversely if it exceeds 150%, the effect of improving the wet performance decreases.

  In the embodiment described above, the case where the three main grooves 10 are formed in the tread portion 1 has been described. However, the number of the main grooves 10 is not particularly limited, and may be four or five, for example. . In any case, by providing the composite groove 40 having a predetermined structure with respect to at least one row of land portions of the tread portion, an excellent effect as described above can be obtained.

  The tire size is 155 / 65R14 75S, and extends in the tire circumferential direction to form an annular tread portion, a pair of sidewall portions disposed on both sides of the tread portion, and the tire radial inner sides of these sidewall portions A pneumatic tire in which three main grooves extending in the tire circumferential direction are formed in the tread portion, and four rows of land portions are partitioned in the tread portion by the main grooves. A narrow groove extending in the tire width direction on the shoulder portion of the shoulder side, a plurality of blocks respectively arranged on both sides in the width direction of the narrow groove so as to be adjacent to the narrow groove, and each block being a narrow groove A plurality of composite grooves having a loop-shaped fine groove surrounding the block, and a block element composed of the block and the loop-shaped fine groove is mutually connected along the length direction of the fine groove on each side in the width direction of the fine groove. The block elements on both sides in the width direction of the narrow groove are arranged apart from each other in the width direction of the narrow groove, and the length of the composite groove, the number of blocks included in the composite groove, and the blocks in the block group Deviation amount of elements, number of block elements in block group, groove width of narrow groove, groove depth of narrow groove, area on tread of each block, groove width of loop narrow groove, groove depth of loop narrow groove The tires of Examples 1 to 5 having various variations as shown in Table 1 were produced.

  For comparison, the tire of Conventional Example 1 having the same structure as that of Example 1 except that a linear narrow groove extending in the tire width direction is provided instead of the composite groove, and the number of blocks included in the composite groove is 1. A tire of Conventional Example 2 having the same structure as Example 1 was prepared except that the tires were separated. In Table 1, for the sake of convenience, the length of the narrow groove is described in the column “Composite groove length L” of Conventional Example 1.

  These test tires were evaluated for wear resistance, uneven wear resistance, and steering stability on wet road surfaces by the following evaluation methods, and the results are also shown in Table 1.

Abrasion resistance:
Each test tire was mounted on a wheel with a rim size of 14 × 4.5 J, and the front / rear air pressure was set to 240 kPa / 240 kPa and mounted on a test vehicle (light vehicle), and the depth of the shoulder main groove after running 8000 km was measured. . The evaluation results are shown as index values with the conventional example 1 as 100. A larger index value means better wear resistance.

Uneven wear resistance:
Each test tire was assembled to a wheel with a rim size of 14 × 4.5 J, and the front / rear wheel air pressure was set to 240 kPa / 240 kPa and mounted on a test vehicle (light vehicle), and the tire appearance after running 8000 km was evaluated. The evaluation results are shown as index values with the conventional example 1 as 100. The larger the index value, the better the uneven wear resistance.

Steering stability on wet surfaces:
Each test tire is mounted on a wheel with a rim size of 14 x 4.5 J and the front / rear air pressure is set to 240 kPa / 240 kPa and mounted on a test vehicle (light vehicle), and a sensory evaluation is performed by a test driver on a test course consisting of a wet road surface. Carried out. The evaluation results are shown as index values with the conventional example 1 as 100. The larger the index value, the better the steering stability on the wet road surface.

  As is clear from Table 1, the tires of Examples 1 to 5 can improve steering stability on a wet road surface while maintaining good wear resistance in comparison with Conventional Example 1. did it. On the other hand, in the tire of Conventional Example 2, although the effect of improving the steering stability on the wet road surface was recognized, the wear resistance and uneven wear resistance were deteriorated.

  Next, the tire size is 155 / 65R14 75S, the tread portion extends in the tire circumferential direction to form an annular shape, the pair of sidewall portions disposed on both sides of the tread portion, and the tires of these sidewall portions A pair of bead portions disposed on the radially inner side, three main grooves extending in the tire circumferential direction are formed in the tread portion, and four rows of land portions are partitioned in the tread portion by these main grooves, In a pneumatic tire in which a mounting direction and a rotation direction with respect to a vehicle are specified, a narrow groove extending in the tire width direction on a shoulder side land portion, and both sides in the width direction of the narrow groove so as to be adjacent to the narrow groove A plurality of composite grooves each having a plurality of blocks arranged in each and a loop-like fine groove surrounding each block together with the fine grooves, and a block comprising the blocks and the loop-like fine grooves A structure in which the elements are separated from each other along the length direction of the narrow groove on each side in the width direction of the narrow groove, and the block elements on both sides of the width direction of the narrow groove are shifted in the length direction of the narrow groove The length of the composite groove, the number of blocks included in the composite groove, the shift amount of the block element in the block group, the number of block elements in the block group, the groove width of the fine groove, the groove depth of the fine groove, Area on tread (vehicle inside, vehicle outside and kicking side, vehicle outside and stepping side), groove width of loop narrow groove, groove depth of loop narrow groove (vehicle inside, vehicle outside and kicking side, vehicle Tires of Examples 11 to 15 having different outer and stepping sides) as shown in Table 2 were produced.

  For comparison, a tire of Conventional Example 11 having the same structure as Example 11 was prepared except that a linear narrow groove extending in the tire width direction was provided instead of the composite groove. In Table 1, for the sake of convenience, the length of the narrow groove is described in the column “Composite groove length L” of Conventional Example 11.

  About these test tires, while evaluating the wear resistance, uneven wear resistance, and handling stability on a wet road surface by the above-described evaluation methods, the steering stability on a dry road surface is evaluated by the following evaluation method. The results are also shown in Table 2. However, the evaluation results of wear resistance, uneven wear resistance, and steering stability on a wet road surface are shown as index values with the conventional example 11 as 100.

Steering stability on dry roads:
Each test tire is mounted on a wheel with a rim size of 14 x 4.5 J and the front / rear wheel pressure is set to 240 kPa / 240 kPa and mounted on a test vehicle (light vehicle). Carried out. The evaluation results are shown as index values with the conventional example 11 as 100. The larger the index value, the better the steering stability on the dry road surface.

  As is clear from Table 2, the tires of Examples 11 to 15 can improve steering stability on wet road surfaces while maintaining good wear resistance in comparison with Conventional Example 11. did it. In particular, in the tires of Examples 12 to 15, since the asymmetric structure is adopted in the composite groove according to the mounting direction and the rotation direction with respect to the vehicle, the effect of achieving both the steering stability on the dry road surface and the wet performance is obtained. It was.

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 10 Main groove 11 Center main groove 12 Shoulder main groove 20, 30 Land part 21, 31 Lug groove 22, 32 Sipe 40, 40A, 40B Composite groove 41, 41A, 41B Narrow groove 42 , 42A, 42B, 42C, 42D Block 43, 43A, 43B Loop-shaped narrow groove 44 Block element 45 Block group 46 Chamfer

Claims (12)

An annular tread portion extending in the tire circumferential direction, a pair of sidewall portions disposed on both sides of the tread portion, and a pair of bead portions disposed on the inner side in the tire radial direction of the sidewall portions. In the pneumatic tire in which a plurality of main grooves extending in the tire circumferential direction are formed in the tread portion, and a plurality of rows of land portions are defined in the tread portion by the main grooves,
At least one row of land portions of the tread portion, narrow grooves extending in the tire width direction, and a plurality of blocks respectively disposed on both sides in the width direction of the narrow grooves so as to be adjacent to the narrow grooves; A plurality of composite grooves having loop-shaped fine grooves surrounding each block together with the fine grooves are formed, and a block element composed of the blocks and the loop-shaped fine grooves is formed on each side in the width direction of the fine grooves. A pneumatic tire characterized in that block elements that are spaced apart from each other along the length direction of the narrow groove and that are located on both sides in the width direction of the narrow groove are shifted in the length direction of the narrow groove. .   The at least one block group in which a plurality of block elements on both sides in the width direction of the narrow groove overlap with each other in the length direction of the narrow groove exists in each composite groove. Pneumatic tire described in 2.   3. The pneumatic tire according to claim 2, wherein a shift amount of the block element in the block group is in a range of 20% to 90% of a length of the block element.   The pneumatic tire according to claim 2 or 3, wherein each block group includes at least three block elements. The pneumatic tire according to any one of claims 1 to 4, wherein an area of each block on the tread surface is in a range of ² mm ^{2 to} 50 mm ² .   The pneumatic tire according to any one of claims 1 to 5, wherein a depth of the loop-shaped narrow groove is in a range of 2 mm to 4 mm.   In the pneumatic tire in which the mounting direction with respect to the vehicle is specified, the composite groove block disposed on the vehicle outer side is larger than the composite groove block disposed on the vehicle inner side. Pneumatic tire described in 2.   8. The area of the tread of the composite groove block arranged outside the vehicle is in the range of 130% to 250% of the area of the tread of the block of composite groove arranged inside the vehicle. The described pneumatic tire.   The pneumatic tire in which the mounting direction with respect to the vehicle is specified, wherein the loop-shaped narrow groove of the composite groove disposed on the vehicle outer side is shallower than the loop-shaped narrow groove of the composite groove disposed on the vehicle inner side. The pneumatic tire according to any one of 1 to 8.   The depth of the loop-shaped narrow groove of the composite groove disposed outside the vehicle is in the range of 40% to 80% of the depth of the loop-shaped narrow groove of the composite groove disposed inside the vehicle. 9. The pneumatic tire according to 9.   11. A pneumatic tire having a designated rotational direction, wherein the block located on the stepping side from the narrow groove is larger than the block located on the kicking side from the narrow groove. The pneumatic tire according to Crab.   The area on the tread surface of the block located on the stepping side from the narrow groove is in a range of 120% to 150% of the area on the tread surface of the block located on the kicking side from the narrow groove. Item 12. The pneumatic tire according to Item 11.

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