阅读说明：本技术 充气轮胎 (Pneumatic tire ) 是由 石坂贵秀 于 2020-04-23 设计创作，主要内容包括：提供一种能够在维持轮胎的耐磨耗性的同时提高雪上性能的充气轮胎。该充气轮胎具备：一对胎肩主槽21、21和两条以上的中央主槽22、22；以及一对胎肩环岸部31、31、一对中间环岸部32、32和一列以上的中央环岸部33,由该主槽21、22划分而成。此外,胎面部中央区域的槽面积比Sc在0.40≤Sc≤0.50的范围。此外,中间环岸部32具备沿轮胎宽度方向延伸并贯通中间环岸部32的多个中间横纹槽321和由中间横纹槽321划分而成的多个中间花纹块322。此外,中间花纹块322具有沿轮胎宽度方向延伸并贯通中间花纹块322的窄浅槽323和由窄浅槽323划分而成的一对小花纹块。(Provided is a pneumatic tire capable of improving on-snow performance while maintaining wear resistance of the tire. The pneumatic tire is provided with: a pair of shoulder main grooves 21, 21 and two or more central main grooves 22, 22; and a pair of shoulder land portions 31, a pair of intermediate land portions 32, and one or more rows of central land portions 33, which are defined by the main grooves 21, 22. The groove area ratio Sc in the center region of the tread portion is in the range of 0.40 to Sc 0.50. The intermediate land portion 32 includes a plurality of intermediate lug grooves 321 extending in the tire width direction and penetrating the intermediate land portion 32, and a plurality of intermediate blocks 322 partitioned by the intermediate lug grooves 321. The intermediate block 322 has a shallow groove 323 extending in the tire width direction and penetrating the intermediate block 322, and a pair of small blocks partitioned by the shallow groove 323.)

1. A pneumatic tire is provided with: a pair of shoulder main grooves and more than two central main grooves; and a pair of shoulder land portions, a pair of intermediate land portions, and one or more rows of central land portions, which are partitioned by the main grooves,

the groove area ratio Sc of the central area of the tread part is in the range of 0.40-Sc 0.50,

the intermediate land portion includes a plurality of intermediate lug grooves extending in the tire width direction and penetrating the intermediate land portion, and a plurality of intermediate blocks partitioned by the intermediate lug grooves,

the intermediate pattern block has a narrow shallow groove extending in the tire width direction and penetrating through the intermediate pattern block, and a pair of small pattern blocks partitioned by the narrow shallow groove.

2. The pneumatic tire of claim 1,

the groove area ratio Sa of the tire ground contact region is in the range of 0.25 to Sa 0.40, and,

the groove area ratio Sc of the tread portion center region and the groove area ratio Ss of the tread portion shoulder region have a relationship of 3.0. ltoreq. Sc/Ss.

3. The pneumatic tire according to claim 1 or 2,

the groove area ratio Ss of the tread shoulder area is within the range of 0.05-Ss 0.15.

4. The pneumatic tire according to any one of claims 1 to 3,

the groove width Wn of the narrow and shallow groove is in the range of 1.2[ mm ] to Wn of 3.0[ mm ], and the ratio of the groove depth Hn of the narrow and shallow groove to the groove depth Hg of the tire shoulder main groove is in the range of 0.05 to Hn/Hg of 0.25.

5. The pneumatic tire according to any one of claims 1 to 4,

the groove depth H2 of the middle cross groove and the groove depth Hg of the shoulder main groove have a relationship of 0.15 ≦ H2/Hg ≦ 0.35.

6. The pneumatic tire according to any one of claims 1 to 5,

the groove width Wn of the narrow and shallow groove and the groove width W2 of the middle cross groove have the relation of Wn/W2 being less than or equal to 0.30.

7. The pneumatic tire according to any one of claims 1 to 6,

the difference between the groove depth H2 of the middle lug groove and the groove depth Hn of the narrow and shallow groove has a relationship of 0.05 ≦ (H2-Hn)/Hg ≦ 0.25 with respect to the groove depth Hg of the shoulder main groove.

8. The pneumatic tire according to any one of claims 1 to 7,

the aspect ratio of the intermediate block is in a range of 1.40 to 1.90.

9. The pneumatic tire according to any one of claims 1 to 8,

the intermediate block has a shape that widens in a central portion in the tire circumferential direction.

10. The pneumatic tire according to any one of claims 1 to 9,

the middle blocks have edge portions of a zigzag shape extending along the middle lug groove.

11. The pneumatic tire of claim 10,

the pitch length Pe of the zigzag shape has a relationship of 0.13. ltoreq. Pe/We. ltoreq.0.33 with the width direction length We of the edge portion, and the amplitude Ae of the zigzag shape is in the range of 1.0[ mm ] to 4.0[ mm ].

12. The pneumatic tire according to any one of claims 1 to 11,

the small block is provided with at least one closed sipe, and,

an extension length Ws of the closed sipe in the tire width direction and a maximum width Wb2 of the intermediate block have a relationship of 0.50 Ws/Wb2 0.80.

13. The pneumatic tire according to any one of claims 1 to 12,

the narrow shallow grooves are provided with groove bottom sipes.

14. The pneumatic tire according to any one of claims 1 to 13,

the tire shoulder ring land portion is provided with a plurality of tire shoulder cross thread grooves penetrating through the tire shoulder ring land portion in the width direction of a tire, and the groove depth H1 of the tire shoulder cross thread grooves and the groove depth Hg of the tire shoulder main grooves have the relation of 0.15-H1/Hg-0.35.

15. The pneumatic tire according to any one of claims 1 to 14,

the display unit is provided to indicate that the pneumatic tire is a trailer tire.

Technical Field

The present invention relates to a pneumatic tire, and more particularly, to a pneumatic tire capable of improving on-snow performance while maintaining wear resistance of the tire.

Background

In the conventional heavy load tire, there is a problem that the on-snow performance of the tire should be improved. As a conventional pneumatic tire that involves such a problem, a technique described in patent document 1 is known.

Disclosure of Invention

Problems to be solved by the invention

In addition, in recent years, a specified on-snow performance is also required in all season tires attached to trailers. On the other hand, in the heavy load tire, there is also a problem that the wear resistance should be ensured.

The present invention has been made in view of the above problems, and an object thereof is to provide a pneumatic tire capable of improving on-snow performance while maintaining wear resistance of the tire.

Technical scheme

In order to achieve the above object, a pneumatic tire according to the present invention includes: a pair of shoulder main grooves and more than two central main grooves; and a pair of shoulder land portions, a pair of intermediate land portions, and one or more rows of central land portions partitioned by the main groove, wherein a groove area ratio Sc of a tread portion central region is in a range of 0.40 to Sc 0.50, the intermediate land portion includes a plurality of intermediate lug grooves extending in a tire width direction and penetrating the intermediate land portions and a plurality of intermediate blocks partitioned by the intermediate lug grooves, and the intermediate blocks include a narrow shallow groove extending in the tire width direction and penetrating the intermediate blocks and a pair of small blocks partitioned by the narrow shallow groove.

Effects of the invention

In the pneumatic tire of the present invention, (1) the groove area ratio Sc of the tread portion central region is set to the above range, and the intermediate blocks have narrow and shallow grooves opened at the time of tire ground contact instead of through sipes, thereby ensuring the edge component of the tread portion central region. This has an advantage of improving the on-snow performance of the tire, as compared with a configuration in which the blocks have only sipes. Further, (2) the intermediate block has a narrow and shallow groove, and thus has an advantage of ensuring wear resistance of the tire as compared with a configuration in which the block has a through groove having a wide or deep width.

Drawings

Fig. 1 is a cross-sectional view showing a tire meridian direction of a pneumatic tire according to an embodiment of the present invention.

Fig. 2 is a plan view showing a tread surface of the pneumatic tire shown in fig. 1.

Fig. 3 is an enlarged view showing a single-side region of the tread surface shown in fig. 2.

Fig. 4 is a plan view showing a single block shown in fig. 3.

Fig. 5 is a sectional view showing a single block shown in fig. 3.

Fig. 6 is a graph showing the results of a performance test of the pneumatic tire according to the embodiment of the present invention.

Detailed Description

The present invention will be described in detail below with reference to the accompanying drawings. The present invention is not limited to the embodiments. The constituent elements of the present embodiment include those that can be replaced and are clearly replaceable while maintaining the uniformity of the invention. Further, a plurality of modification examples described in the present embodiment can be arbitrarily combined within a range which is obvious to those skilled in the art.

[ pneumatic tires ]

Fig. 1 is a cross-sectional view showing a tire meridian direction of a pneumatic tire according to an embodiment of the present invention. Fig. 1 shows a cross-sectional view of a radial one-sided region of a tire. Further, the figure shows a radial tire for heavy load attached to a trailer as an example of a pneumatic tire.

In the figure, the cross section in the tire meridian direction is defined as a cross section when the tire is cut on a plane including a tire rotation axis (not shown). The tire equatorial plane CL is defined as a plane that passes through the midpoint of the measurement point of the tire cross-sectional width defined by JATMA and is perpendicular to the tire rotation axis. Further, the tire width direction is defined as a direction parallel to the tire rotation axis, and the tire radial direction is defined as a direction perpendicular to the tire rotation axis.

The pneumatic tire 1 has an annular structure centered on a tire rotation axis, and includes: a pair of bead cores 11, 11; a pair of bead cores 12, 12; a carcass layer 13; a belt layer 14; a tread rubber 15; a pair of sidewall rubbers 16, 16; and a pair of rim cushion rubbers 17, 17 (see fig. 1).

The pair of bead cores 11, 11 are formed by annularly and multiply winding one or more bead wires made of steel, and are embedded in the bead portions to constitute cores of the left and right bead portions. The pair of bead fillers 12, 12 include a lower bead filler 121 and an upper bead filler 122, and are respectively disposed on the outer peripheries of the pair of bead cores 11, 11 in the tire radial direction to reinforce the bead portions.

The carcass layer 13 has a single-layer structure including a single ply or a multilayer structure in which a plurality of plies are laminated, and is annularly arranged between the left and right bead cores 11, 11 to constitute a carcass of the tire. Both ends of the carcass layer 13 are locked by being wound around the outside in the tire width direction so as to wrap the bead core 11 and the bead filler 12. The carcass layer 13 is formed by rolling a plurality of carcass cords made of steel covered with a coating rubber, and has a cord angle (defined as an inclination angle of the longitudinal direction of the carcass cord with respect to the tire circumferential direction) of 80[ deg ] to 90[ deg ] in absolute value.

The belt layer 14 is formed by laminating a plurality of belt layers 141 to 144 and is disposed so as to surround the outer periphery of the carcass layer 13. These belt layers 141 to 144 include: a high angle belt 141, a pair of intersecting belts 142, 143, and a belt cover 144. The high-angle belt 141 is configured by covering a plurality of belt cords made of steel with a coating rubber and performing a rolling process, and has a cord angle (defined as an inclination angle of a longitudinal direction of the belt cord with respect to a tire circumferential direction) having an absolute value of 45[ deg ] to 70[ deg ]. The pair of cross belts 142, 143 are formed by rolling a plurality of belt cords made of steel covered with a coating rubber, and have a cord angle of 10[ deg ] to 55[ deg ] in absolute value. The pair of crossing belts 142, 143 have cord angles of different signs, and are stacked so that the longitudinal directions of the belt cords cross each other (so-called a cross structure). The belt cover layer 144 is formed by covering a plurality of belt cover cords made of steel or an organic fiber material with a coating rubber and performing a rolling process, and has a cord angle of 10[ deg ] to 55[ deg ] in absolute value.

The tread rubber 15 is disposed on the outer periphery of the carcass layer 13 and the belt layer 14 in the tire radial direction, and constitutes a tread portion of the tire. The pair of sidewall rubbers 16, 16 are disposed on the outer sides of the carcass layer 13 in the tire width direction, and constitute left and right sidewall portions. The pair of rim cushion rubbers 17, 17 are disposed on the inner sides in the tire radial direction of the turnback portions of the left and right bead cores 11, 11 and the carcass layer 13, respectively, and constitute rim fitting surfaces of the bead portions.

[ Tread pattern ]

Fig. 2 is a plan view showing a tread surface of the pneumatic tire shown in fig. 1. The figure shows the tread surface of a full season tire with mud and snow marks (mud and snowmark) "M + S". In the figure, the tire circumferential direction refers to a direction around the tire rotation axis. Note that, symbol T is a tire ground contact end, and a size TW is a tire ground contact width.

As shown in fig. 2, the pneumatic tire 1 includes, on a tread surface: four or more circumferential main grooves 21, 22 extending in the tire circumferential direction; and a plurality of land portions 31 to 33 partitioned by the circumferential main grooves 21 and 22.

The main groove has a wear indicator display function defined by JATMA, and has a groove width of 5.0 mm or more and a groove depth of 10 mm or more.

In a no-load state where the tire is mounted on a predetermined rim and a predetermined internal pressure is applied, the distance between the opposing groove walls of the groove opening is measured as the groove width. In the configuration in which the groove opening portion has the notch portion or the chamfered portion, the groove width is measured with an intersection point of an extension line of the tread surface and an extension line of the groove wall as a measurement point in a cross-sectional view in the groove width direction and in parallel with the groove depth direction.

In a no-load state where the tire is attached to a predetermined rim and a predetermined internal pressure is applied, the distance from the tread surface to the maximum groove depth position is measured as the groove depth. In the structure having a partial uneven portion or sipe at the groove bottom, the groove depth was measured except for these.

The predetermined Rim is a "standard Rim" defined by JATMA, a "Design Rim" defined by TRA, or a "Measuring Rim" defined by ETRTO. The predetermined internal pressure is the maximum value of "maximum air pressure" defined by JATMA, "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" defined by TRA, or "INFLATION PRESSURES" defined by ETRTO. The predetermined LOAD is a "maximum LOAD CAPACITY" defined by JATMA, a maximum value of "time LOAD conditions AT variatus COLD stability requirements" defined by TRA, or "LOAD CAPACITY" defined by ETRTO. In JATMA, the internal pressure is defined as 180 kPa in the case of a passenger car tire, and the load is defined as 88 [% ] of the maximum load capacity under the predetermined internal pressure.

In the configuration of fig. 2, two circumferential main grooves 21 and 22 are provided in the left and right regions bounded by the tire equatorial plane CL. The circumferential main grooves 21 and 22 are disposed point-symmetrically about the tire equatorial plane CL. The circumferential main grooves 21, 22 define five rows of land portions 31 to 33. The one-row land portion 33 is disposed on the tire equatorial plane CL.

However, the present invention is not limited to this, and five or more circumferential main grooves may be disposed, and the circumferential main grooves may be disposed asymmetrically about the tire equatorial plane CL (not shown). Further, since the single circumferential main groove is disposed on the tire equatorial plane CL, the land portion can be disposed at a position deviated from the tire equatorial plane CL (not shown).

Of the circumferential main grooves 21, 22 arranged in one region of the tire equatorial plane CL, the outermost circumferential main grooves 21, 21 in the tire width direction are defined as shoulder main grooves, and the other circumferential main grooves 22 are defined as center main grooves.

For example, in the configuration of fig. 2, the distance Dg1 from the tire equatorial plane CL to the groove center lines of the left and right shoulder main grooves 21, 21 is in the range of 26 [% ] to 32 [% ] of the tire ground contact width TW. The distance Dg2 from the tire equatorial plane CL to the groove center lines of the left and right center main grooves 22, 22 is in the range of 8 [% ] to 12 [% ] of the tire ground contact width TW.

The slot centerline is defined as an imaginary line connecting the midpoints of the distances between the left and right slot walls. When the groove center line of the main groove has a zigzag shape or a wavy shape, a straight line passing through the midpoint of the left and right maximum amplitude positions of the groove center line and parallel to the tire circumferential direction is defined as a measurement point as a distance to the groove center line.

When a tire is attached to a predetermined rim and a predetermined internal pressure is applied and a load corresponding to a predetermined load is applied while being placed perpendicularly to a flat plate in a stationary state, the maximum linear distance in the tire axial direction of the contact surface between the tire and the flat plate is measured as a tire ground contact width TW.

The tire contact end T is defined as the maximum width position in the tire axial direction of the contact surface of the tire and the flat plate when the tire is attached to a prescribed rim and a prescribed internal pressure is applied, and is placed vertically with respect to the flat plate in a stationary state, and a load corresponding to a prescribed load is applied.

Further, a region located on the tire equatorial plane CL side with the left and right shoulder main grooves 21, 21 as a boundary is defined as a center region, and a region located on the left and right of the tire ground contact edge T side is defined as a shoulder region.

The land portions 31, 31 on the outer side in the tire width direction defined by the shoulder main grooves 21, 21 are defined as shoulder land portions. The shoulder land portion 31 is an outermost land portion in the tire width direction and is located on the tire ground contact edge T. The land portions 32, 32 on the inner side in the tire width direction defined by the shoulder main grooves 21, 21 are defined as intermediate land portions. The intermediate land portions 32, 32 are adjacent to the shoulder land portion 31 with the shoulder main groove 21 therebetween. Further, a land portion 33 located closer to the tire equatorial plane CL than the intermediate land portion 32 is defined as a central land portion. The central land portion 33 may be disposed on the tire equatorial plane CL (see fig. 2), or may be disposed at a position deviated from the tire equatorial plane CL (not shown).

In the configuration including the four circumferential main grooves 21 and 22 as shown in fig. 2, a pair of shoulder land portions 31 and 31, a pair of intermediate land portions 32 and 32, and a single center land portion 33 are defined. For example, in a configuration including five or more circumferential main grooves, two or more rows of central land portions (not shown) are defined.

For example, in the configuration of fig. 2, all the circumferential main grooves 21, 22 have a zigzag shape having an amplitude in the tire width direction. Further, the adjacent circumferential main grooves 21 and 22, 22 and 22, and 22 and 21 are arranged so as to shift the phase of the zigzag shape, respectively. However, the present invention is not limited to this, and some or all of the circumferential main grooves 21 and 22 may have a linear shape (not shown).

In the configuration of FIG. 2, the groove area ratio Sa of the tire contact patch is in the range of 0.25 to Sa to 0.40. Moreover, the groove area ratio Ss of the tread shoulder area is within the range of 0.05 to Ss of 0.15, and the groove area ratio Sc of the tread central area is within the range of 0.40 to Sc of 0.50. Further, the groove area ratio Sc in the tread portion center region and the groove area ratio Ss in the tread portion shoulder region have a relationship of 3.0. ltoreq. Sc/Ss. Therefore, the groove area ratio Sc in the tread portion center region is set relatively large. Thereby, the snow performance of the tire can be improved.

The groove area ratio is defined as the ratio of the groove area of a predetermined region to the area of that region. The groove area is an opening area of a groove of the tread surface, and is measured on a contact surface of the tire and the flat plate when the tire is attached to a prescribed rim and a prescribed internal pressure is applied, and is vertically placed with respect to the flat plate in a stationary state and a load corresponding to a prescribed load is applied. The groove is a groove that is open when the tire contacts the ground and contributes to drainage, and does not include a sipe, a cut, or the like that is closed when the tire contacts the ground.

The tread portion shoulder region is defined as a region from the tire ground contact end T to the groove center line of the shoulder main groove 21. The tread portion center region is defined as a region between the groove center lines of the left and right shoulder main grooves 21, 21.

[ shoulder land portion ]

Fig. 3 is an enlarged view showing a single-side region of the tread surface shown in fig. 2. The configuration of fig. 2 has a tread pattern that is point-symmetric about a point on the tire equatorial plane CL, and therefore, the other region will not be described.

In fig. 3, the shoulder land portion 31 includes a plurality of shoulder lug grooves 311 and a plurality of shoulder blocks 312.

The shoulder lug groove 311 extends in the tire width direction, penetrates the shoulder land portion 31, and opens at the tire ground contact edge T and the shoulder main groove 21. The shoulder lug grooves 311 are arranged at predetermined intervals in the tire circumferential direction. In addition, the groove width W1 of the shoulder cross groove 311 is in the range of 8.0[ mm ] W1 [ mm ] to 20.0[ mm ]. The inclination angle theta 1 of the shoulder lug grooves 311 with respect to the tire circumferential direction is in the range of 60 deg.C to 85 deg.C.

The angle formed by the tire circumferential direction and an imaginary straight line passing through the left and right openings of the lug groove is measured as the inclination angle of the lug groove.

The groove depth H1 (not shown) of the shoulder lug grooves 311 and the groove depth Hg of the shoulder main grooves 21 (see FIG. 5 described later) preferably have a relationship of 0.15. ltoreq.H 1/Hg. ltoreq.0.35, and more preferably have a relationship of 0.20. ltoreq.H 1/Hg. ltoreq.0.30. In the above configuration, the shoulder lug grooves 311 are shallow grooves, thereby improving the on-snow performance of the tire at the initial stage of wear and ensuring the wear resistance of the tire after the middle stage of wear.

The shoulder blocks 312 are partitioned by the shoulder lug grooves 311, 311 adjacent to each other. Further, the maximum width Wb1 of the shoulder block 312 has a relationship of 0.13. ltoreq. Wb 1/TW. ltoreq.0.23 with the tire ground contact width TW.

For example, in the configuration of fig. 3, as described above, the shoulder main groove 21 has a zigzag shape having an amplitude in the tire width direction. The shoulder lug groove 311 has a gently curved shape and is open at the maximum amplitude position of the zigzag shape of the shoulder main groove 21. Further, the shoulder block 312 has an edge portion protruding toward the shoulder main groove 21 side. The shoulder blocks 312 have flat treads that do not have narrow grooves, sipes, or notches and have continuous edge portions. This increases the rigidity of the shoulder block 312.

[ intermediate land portion and Central land portion ]

Fig. 4 and 5 are a plan view (fig. 4) and a sectional view (fig. 5) showing a single block shown in fig. 3. In these drawings, fig. 5 shows a cross-sectional view of a middle block 322 cut in the tire width direction.

In fig. 3, the intermediate land portion 32 includes a plurality of intermediate lug grooves 321, a plurality of intermediate blocks 322, and narrow and shallow grooves 323. Similarly, the center land portion 33 includes a plurality of center lug grooves 331, a plurality of center blocks 332, and a plurality of shallow and narrow grooves 333.

In the configuration of fig. 3, the central land portion 33 has a symmetrical structure with respect to the intermediate land portion 32 and has the same internal structure, and therefore, as an example, the configuration of the intermediate land portion 32 will be described in detail, and the description of the configuration of the central land portion 33 will be omitted.

The intermediate lug groove 321 extends in the tire width direction, penetrates the intermediate land portion 32, and opens in the circumferential main grooves 21, 22 that divide the intermediate land portion 32 on the left and right. The intermediate lug grooves 321 are arranged at predetermined intervals in the tire circumferential direction. Further, the groove width W2 of the middle lug groove 321 is in the range of 8.0[ mm ] W2 [ mm ] to 20.0[ mm ]. Further, the groove width W2 of the middle lug groove 321 and the pitch length P2 (refer to FIG. 2) of the middle lug groove 321 have a relationship of 0.13. ltoreq.W 2/P2. ltoreq.0.23. Further, the shoulder lug groove 311 has a groove width W1 narrower than the groove width W2 of the middle lug groove 321. This improves the passing noise performance of the tire.

Further, the inclination angle theta 2 of the intermediate lug groove 321 with respect to the tire circumferential direction is in the range of 60[ deg ] ≦ theta 2 ≦ 85[ deg ]. Further, the intermediate lug groove 321 is inclined in the opposite direction to the shoulder lug groove 311. The shoulder lug groove 311 and the intermediate lug groove 321 are arranged offset from each other in the tire circumferential direction with respect to the opening of the shoulder main groove 21. This improves the passing noise performance of the tire.

Further, the groove depth H2 (see FIG. 5) of the intermediate lug groove 321 and the groove depth Hg of the shoulder main groove 21 preferably have a relationship of 0.15. ltoreq.H 2/Hg. ltoreq.0.35, and more preferably have a relationship of 0.20. ltoreq.H 2/Hg. ltoreq.0.30. In the above-described configuration, the intermediate lug grooves 321 are shallow grooves, thereby improving the on-snow performance of the tire at the initial stage of wear and ensuring the wear resistance of the tire after the middle stage of wear.

As shown in fig. 3, the middle block 322 is partitioned by adjacent middle lug grooves 321, 321. Further, the maximum width Wb2 of the middle block 322 has a relationship of 0.10. ltoreq. Wb 2/TW. ltoreq.0.20 with the tire ground contact width TW (refer to FIG. 2). Further, the maximum width Wb1 of the shoulder block 312 and the maximum width Wb2 of the middle block 322 preferably have a relationship of 1.00. ltoreq. Wb1/Wb 2. ltoreq.1.30, and more preferably have a relationship of 1.10. ltoreq. Wb1/Wb 2. ltoreq.1.20. Further, the maximum width Wb2 of the middle block 322 and the maximum width Wb3 of the center block 332 preferably have a relationship of 0.90. ltoreq. Wb2/Wb 3. ltoreq.1.10, and more preferably have a relationship of 0.95. ltoreq. Wb2/Wb 3. ltoreq.1.05.

Further, in FIG. 4, the circumferential length Lb of the middle block 322 has a relationship of 0.98. ltoreq. Lb/P2. ltoreq.1.08 with the pitch length P2 (refer to FIG. 2) of the middle lug 321. The aspect ratio Lb/Wb2 of the intermediate block 322 is in the range of 1.40 to 1.90. Thus, the aspect ratio Lb/Wb2 of the middle block 322 is optimized to suppress the heel and toe wear.

For example, in the configuration of fig. 3, as described above, the shoulder main grooves 21 and the center main groove 22 have a zigzag shape having an amplitude in the tire width direction. The intermediate lug groove 321 extends at a predetermined inclination angle θ 2 with respect to the tire circumferential direction, and opens at the maximum amplitude position of the zigzag shape of the shoulder main groove 21 and the center main groove 22. The intermediate block 322 has left and right edge portions projecting toward the shoulder main groove 21 and the center main groove 22. Further, the intermediate block 322 has a shape that widens in the center portion in the tire circumferential direction. Further, the width of the middle block 322 gradually decreases from the maximum width position toward the front and rear edge portions in the tire circumferential direction. This increases the rigidity of the middle block 322.

Further, the tire circumferential direction distance Lb 'of the intermediate block 322 from one end to the maximum width position and the circumferential direction length Lb of the intermediate block 322 preferably have a relationship of 0.35. ltoreq. Lb'/Lb. ltoreq.0.65. Further, the width-direction length We of the edge portion on the intermediate lug 321 side of the intermediate block 322 and the maximum width Wb2 of the intermediate block 322 preferably have a relationship of 0.80. ltoreq. We/Wb 2. ltoreq.0.98.

Further, as shown in fig. 4, the middle block 322 has an edge portion of a zigzag shape extending along the middle lug groove 321. For example, in the configuration of fig. 4, the wall surface of the intermediate lug groove 321 is not a chamfered portion formed only at the edge portion, but a notched portion having a uniform saw-tooth-shaped cross section in the groove depth direction. The maximum depth (not shown) of the saw-tooth-shaped notch portion is preferably 60 [% ] or more with respect to the groove depth H2 (see fig. 5) of the intermediate lug groove 321. This increases the edge component of the middle block 322, and improves the on-snow performance of the tire.

For example, in the configuration of fig. 4, the edge portion of the intermediate block 322 has a zigzag shape formed by alternately connecting long strip portions and short strip portions. Further, the pitch length Pe of the sawtooth shape and the width direction length We of the edge portion preferably have a relationship of 0.13. ltoreq. Pe/We. ltoreq.0.33, more preferably have a relationship of 0.18. ltoreq. Pe/We. ltoreq.0.28. The amplitude Ae of the saw-tooth shape is preferably in the range of 1.0[ mm ] to Ae to 4.0[ mm ].

The shallow narrow grooves 323 extend in the tire width direction, penetrate the intermediate blocks 322, and open to the left and right circumferential main grooves 21, 22 that define the intermediate land portion 32. The narrow and shallow grooves 323 are different from sipes closed at the time of tire contact, in that they are open at the time of tire contact and function as grooves. Further, a single shallow and narrow groove 323 is disposed in each of the intermediate blocks 322. The shallow and narrow grooves 323 divide the intermediate block 322 into a pair of small blocks (symbols in the figure are omitted).

In addition, the groove width Wn of the narrow and shallow grooves 323 is in the range of 1.2[ mm ] to Wn of 3.0[ mm ]. The groove width Wn of the shallow and narrow grooves 323 and the groove width W2 of the intermediate latitudinal grooves 321 are set sufficiently narrow in the relationship of Wn/W2 ≦ 0.30.

In the above configuration, (1) the groove area ratio Sc in the tread portion center region is set to the above range, and the intermediate block 322 has the narrow and shallow groove 323 opened at the time of tire contact, instead of the through sipe, thereby securing the edge component in the tread portion center region. This improves the on-snow performance of the tire, as compared with a configuration in which the blocks have only sipes (not shown). Further, (2) the intermediate blocks 322 have the narrow and shallow grooves 323, thereby ensuring the wear resistance of the tire as compared with a configuration in which the blocks have through grooves having a wide or deep width.

For example, in the configuration of fig. 4, the shallow and narrow grooves 323 have a straight line shape, extend substantially parallel to the intermediate lug grooves 321, and open at the maximum width positions on the left and right of the intermediate blocks 322. The narrow shallow groove 323 bisects the middle block 322, thereby forming a trapezoidal small block. Thereby, the rigidity of the middle block 322 is maintained.

Further, in FIG. 5, the groove depth Hn of the shallow and narrow grooves 323 and the groove depth Hg of the shoulder main grooves 21 preferably have a relationship of 0.05. ltoreq. Hn/Hg. ltoreq.0.25, more preferably 0.10. ltoreq. Hn/Hg. ltoreq.0.20. The shallow narrow grooves 323 are shallower than the middle lug grooves 321. Specifically, the difference between the groove depth H2 of the middle lug groove 321 and the groove depth Hn of the narrow and shallow grooves 323 and the groove depth Hg of the shoulder main grooves 21 preferably have a relationship of 0.05 ≦ (H2-Hn)/Hg ≦ 0.25.

Further, as shown in fig. 4 and 5, the shallow and narrow grooves 323 have groove bottom sipes 3231.

The groove bottom sipe 3231 is a groove formed in the groove bottom of the shallow and narrow groove 323, and has a sipe width of less than 1.5[ mm ] and a sipe depth of 2.0[ mm ] or more, thereby being closed when the tire is grounded. Further, the groove-bottom sipe 3231 extends along the shallow groove 323 and penetrates the intermediate land portion 32 in the tire width direction. Further, the ratio of the depth Hbs of the groove bottom sipe 3231 to the groove depth Hg of the shoulder main groove 21 is preferably in the range of 0.45 Hbs/Hg to 0.65, and more preferably in the range of 0.50 Hbs/Hg to 0.60. The on-snow performance of the tire is improved by the groove bottom sipe 3231.

In a no-load state where a tire is attached to a predetermined rim and a predetermined internal pressure is applied, the maximum opening width of the sipe in the tread surface is measured as a sipe width.

In a no-load state where a tire is attached to a predetermined rim and a predetermined internal pressure is applied, the distance from the tread surface to the maximum depth position of the sipe is measured as the sipe depth.

Further, as shown in fig. 4 and 5, the intermediate block 322 has a plurality of closed sipes 324.

The closed sipe 324 is a cut groove formed on the tread surface of the intermediate block 322, has a sipe width of less than 1.5[ mm ] and a sipe depth of 2.0[ mm ] or more, and is thus closed when the tire is grounded. Further, the closed sipe 324 has a closed configuration having both end portions in the middle block 322. Further, the extended length Ws of the closed sipe 324 in the tire width direction has a relationship of 0.50. ltoreq. Ws/Wb 2. ltoreq.0.80 with the maximum width Wb2 of the intermediate block 322. Further, in FIG. 5, the depth Hs of the closed sipes 324 and the groove depth Hg of the shoulder main grooves 21 preferably have a relationship of 0.45. ltoreq. Hs/Hg. ltoreq.0.65, and more preferably have a relationship of 0.50. ltoreq. Hs/Hg. ltoreq.0.60.

For example, in the configuration of fig. 4, a single closed sipe 324 is formed in each of a pair of small blocks defined by the shallow narrow grooves 323. However, the present invention is not limited to this, and a plurality of closed sipes 324 (not shown) may be formed in one small block. Further, in the configuration of fig. 4, the closed sipe 324 has a zigzag shape. However, the closed sipes 324 are not limited thereto, and may have a W-shape or a straight shape (not shown). In the configuration of fig. 5, the closed sipe 324 has a raised bottom portion (reference numeral in the figure is omitted) at the left and right terminal end portions, and thus the occurrence of a crack starting from the sipe end portion can be suppressed.

[ Effect ]

As described above, the pneumatic tire 1 includes: a pair of shoulder main grooves 21, 21; two or more central main grooves 22, 22; and a pair of shoulder land portions 31, a pair of intermediate land portions 32, and one or more rows of central land portions 33, which are defined by the main grooves 21, 22 (see fig. 2). The groove area ratio Sc in the center region of the tread portion is in the range of 0.40 to Sc 0.50. The intermediate land portion 32 includes a plurality of intermediate lug grooves 321 extending in the tire width direction and penetrating the intermediate land portion 32, and a plurality of intermediate blocks 322 partitioned by the intermediate lug grooves 321. The intermediate block 322 has a shallow groove 323 extending in the tire width direction and penetrating the intermediate block 322, and a pair of small blocks (symbols in the figure are omitted) partitioned by the shallow groove 323.

In the above-described configuration, (1) the groove area ratio Sc in the tread portion central region is set to the above range, and the intermediate blocks 322 have the narrow and shallow grooves 323 opened at the time of tire contact without the through sipes, thereby securing the edge component in the tread portion central region. This has an advantage of improving the on-snow performance of the tire, as compared with a configuration in which the blocks have only sipes (not shown). Further, (2) the intermediate block 322 has the narrow and shallow groove 323, and thus has an advantage of ensuring wear resistance of the tire as compared with a configuration in which the block has a through groove having a wide or deep width.

Further, in this pneumatic tire 1, the groove area ratio Sa in the tire contact patch region is in the range of 0.25. ltoreq. Sa. ltoreq.0.40, and the groove area ratio Sc in the tread portion center region and the groove area ratio Ss in the tread portion shoulder region have a relationship of 3.0. ltoreq. Sc/Ss (refer to FIG. 2). This has the advantage of optimizing the groove area ratios Sa, Sc, Ss in the tire contact patch.

In the pneumatic tire 1, the groove area ratio Ss in the tread shoulder region is in the range of 0.05 Ss 0.15 (see fig. 2). This provides an advantage of ensuring the rigidity of the shoulder land portion 31 and improving the cut resistance of the tire.

In the pneumatic tire 1, the groove width Wn (see FIG. 4) of the shallow and narrow grooves 323 is in the range of 1.2[ mm ] Wn to 3.0[ mm ], and the ratio of the groove depth Hn (see FIG. 5) of the shallow and narrow grooves to the groove depth Hg of the shoulder main grooves 21 is in the range of 0.05 Hn/Hg to 0.25. Therefore, the method has the following advantages: the shallow narrow groove 323 is appropriately opened at the time of tire contact, and the function of the shallow narrow groove 323 as a groove is appropriately secured.

In the pneumatic tire 1, the groove depth H2 (see FIG. 5) of the intermediate lug groove 321 and the groove depth Hg of the shoulder main groove 21 have a relationship of 0.15. ltoreq.H 2/Hg. ltoreq.0.35. This has the advantage of optimizing the groove depth H2 of the intermediate lug groove 321.

In addition, in this pneumatic tire 1, the groove width Wn of the shallow-narrow grooves 323 and the groove width W2 of the intermediate lug grooves 321 have a relationship Wn/W2 ≦ 0.30. This has the advantage that the groove width Wn of the shallow and narrow grooves 323 is sufficiently narrow to ensure the wear resistance of the intermediate block 322.

In addition, in this pneumatic tire 1, the difference between the groove depth H2 (see FIG. 5) of the middle lug grooves 321 and the groove depth Hn of the narrow and shallow grooves 323 has a relationship of 0.05 ≦ (H2-Hn)/Hg ≦ 0.25 with respect to the groove depth Hg of the shoulder main grooves 21. This has the advantage of optimizing the groove depth Hn of the shallow and narrow grooves 323.

In the pneumatic tire 1, the aspect ratio Lb/Wb2 (see fig. 4) of the intermediate block 322 is in the range of 1.40 to 1.90. This has the advantage of suppressing heel and toe wear by optimizing the aspect ratio Lb/Wb2 of the intermediate block 322.

In the pneumatic tire 1, the intermediate block 322 has a shape that is widened in the center portion in the tire circumferential direction (see fig. 4). This has the advantage of optimizing the shape of the middle block 322.

Further, in this pneumatic tire 1, the intermediate block 322 has an edge portion of a zigzag shape extending along the intermediate lug groove 321 (see fig. 4). This has the advantage of increasing the edge component of the middle block 322 and improving the on-snow performance of the tire.

Further, in this pneumatic tire 1, the pitch length Pe of the zigzag shape and the width direction length We of the edge portion have a relationship of 0.13. ltoreq. Pe/We. ltoreq.0.33, and the amplitude Ae of the zigzag shape is in the range of 1.0[ mm ] Ae.ltoreq.4.0 [ mm ] (refer to FIG. 4).

In addition, in the pneumatic tire 1, the small block (symbol in the figure is omitted) includes at least one closed sipe 324 (see fig. 4). Further, the extended length Ws of the closed sipe 324 in the tire width direction has a relationship of 0.50. ltoreq. Ws/Wb 2. ltoreq.0.80 with the maximum width Wb2 of the intermediate block 322. Thus, there is an advantage in that the extended length Ws of the closed sipe 324 is optimized.

In addition, in the pneumatic tire 1, the shallow and narrow grooves 323 have groove bottom sipes 3231 (see fig. 4 and 5). This has the advantage of improving the on-snow performance of the tire.

In the pneumatic tire 1, the shoulder land portion 31 has a plurality of shoulder lug grooves 311 (see fig. 2) penetrating the shoulder land portion 31 in the tire width direction. The groove depth H1 (not shown) of the shoulder lug grooves 311 and the groove depth Hg of the shoulder main grooves 21 are in a relationship of 0.15. ltoreq.H 1/Hg. ltoreq.0.35. This provides the advantage of optimizing the groove depth H1 of the shoulder lug grooves 311 and of achieving both the on-snow performance and the cut resistance of the tire.

[ application object ]

The pneumatic tire 1 further includes a display unit (not shown) for indicating that the pneumatic tire 1 is a trailer tire. The display unit is constituted by, for example, a mark or a projection/recess attached to a sidewall of the tire. For example, ECR54 (article 54 of the european economic commission regulations) specifies that a display unit for use as a trailer must be provided.

Further, the pneumatic tire 1 is particularly preferably an all season tire having a mud and snow Mark "M + S" and having a Three Peak Mountain Snowflake Mark (Three Peak Mountain Snowflake Mark) "3 PMSF". These markings are for example engraved in the tyre sidewall. In the all-season tire, a prescribed snow performance is required when the tire is new.