Pneumatic tires

Abstract

To improve riding comfort performance while suppressing deterioration in braking performance.SOLUTION: A tread portion 2 includes tread rubber having a rubber hardness of less than 60°. The tread portion 2 is provided with a pair of shoulder circumferential grooves 10 extending in a tire circumferential direction, a pair of shoulder land portions 20, and one or more crown land portions 30. The shoulder land portion 20 is divided into shoulder blocks 22 by a shoulder lateral groove 21 having a depth of 50% or more of a depth of the shoulder circumferential grooves 10. At least one (40, 40) of the crown land portions is divided into crown blocks 32 by a crown lateral groove 31 having a depth of 50% or more of the depth of the shoulder circumferential grooves 10. If a value obtained by dividing a ground area of one block by a maximum depth of the lateral groove sectioning off a block is defined as a block area per unit depth, a block area per unit depth of each shoulder block is smaller than a block area per unit groove depth of each crown block.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a pneumatic tire. [Background technology]

[0002] Conventionally, in order to improve the riding comfort of tires, the rigidity of the tread portion has been reduced. Specifically, a method has been proposed in which the block rigidity of the tread portion is reduced and / or the tread rubber is softened (for example, see Patent Document 1 below). This allows the tread portion to absorb input from the road surface, thereby improving the riding comfort of the tire. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-168946 A Summary of the Invention [Problem to be solved by the invention]

[0004] When the above-mentioned method is adopted, there is a tendency for the rigidity of the entire contact surface of the tread to decrease, resulting in a problem of deterioration of braking performance, which is particularly important for pneumatic tires to be mounted on autonomous vehicles.

[0005] The present invention has been devised in consideration of the above-mentioned problems, and has as its main object to provide a pneumatic tire that can improve ride comfort while suppressing deterioration of braking performance. [Means for solving the problem]

[0006] The present invention is a pneumatic tire having a tread portion, the tread portion including a tread rubber having a rubber hardness of less than 60°, the tread portion being provided with a pair of shoulder circumferential grooves extending in the tire circumferential direction, a pair of shoulder land portions separated on the tire axially outer sides of the pair of shoulder circumferential grooves, and one or more crown land portions separated between the pair of shoulder land portions, the shoulder land portions being separated into a plurality of shoulder blocks by a plurality of shoulder lateral groove-like bodies having a depth of 50% or more of the depth of the shoulder circumferential grooves, at least one of the crown land portions being separated into a plurality of crown blocks by a plurality of crown lateral groove-like bodies having a depth of 50% or more of the depth of the shoulder circumferential grooves, and when the block area per unit depth is defined as the value obtained by dividing the ground contact area of ​​one block by the maximum depth of the lateral groove-like bodies separating the block, the block area per unit depth of the shoulder block is smaller than the block area per unit groove depth of the crown block.

[0007] In the present invention, the block area per unit depth of the crown block is 17 to 80 (mm 2 / mm).

[0008] The present invention may be embodied as a non-studless tire.

[0009] In the present invention, the pair of shoulder circumferential grooves may be positioned in an area within 70% of the tread ground contact width centered on the tire equator.

[0010] In the present invention, the shoulder groove may be chamfered.

[0011] In the present invention, the crown lateral groove may be chamfered.

[0012] In the present invention, the shoulder lateral groove-like body may have a depth smaller than that of the shoulder circumferential groove.

[0013] In the present invention, the crown lateral groove may have a depth smaller than that of the shoulder circumferential groove.

[0014] In the present invention, the shoulder lateral groove-like body may have a depth equal to or greater than a depth of the shoulder circumferential groove.

[0015] In the present invention, the crown lateral groove-like body may have a depth equal to or greater than a depth of the shoulder circumferential groove.

[0016] In the present invention, the shoulder lateral groove-like body may be a shoulder sipe, and the crown lateral groove-like body may be a crown lateral groove. Effect of the Invention

[0017] By adopting the above-described configuration, the pneumatic tire of the present invention can improve ride comfort while suppressing deterioration of braking performance. [Brief description of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view of a pneumatic tire showing one embodiment of the present invention. [Diagram 2] 1 is a development view of a tread portion showing one embodiment of the present invention. [Diagram 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a line cross-sectional view showing another example of a shoulder sipe. [Diagram 5] 3 is a cross-sectional view taken along line VV in FIG. 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. It should be noted that throughout the embodiments of this specification, identical or common elements are indicated with the same reference numerals and detailed descriptions thereof will not be repeated.

[0020] Fig. 1 is a cross-sectional view of a pneumatic tire (hereinafter, sometimes simply referred to as "tire") 1 showing one embodiment of the present invention. In Fig. 1, the tire 1 is in a normal state.

[0021] In this specification, the normal state means a state in which the tire 1 is mounted on a normal rim (not shown), inflated to normal internal pressure, and no load is applied. Unless otherwise specified, the dimensions of each part of the tire 1 refer to values ​​in the normal state.

[0022] In this specification, a "genuine rim" is a rim that is defined for each tire by a standard system that includes the standard on which tire 1 is based, such as a "standard rim" in the case of JATMA, a "Design Rim" in the case of TRA, or a "Measuring Rim" in the case of ETRTO.

[0023] In this specification, the "normal internal pressure" refers to the air pressure determined for each tire by each standard in a standard system including the standard on which tire 1 is based, and is, for example, the "maximum air pressure" in the case of JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and the "INFLATION PRESSURE" in the case of ETRTO.

[0024] As shown in Fig. 1, the tire 1 includes a tread portion 2, a pair of sidewall portions 3, a pair of bead portions 4 each having a bead core 5 embedded therein, and an air-impermeable inner liner rubber disposed on the tire cavity surface i. The tire 1 of this embodiment can be suitably implemented as a tire for vehicles that are subjected to a relatively large load during traveling, such as a minivan, an SUV, or a commercial vehicle. More specifically, the tire 1 of this embodiment is suitable as a tire for light trucks (LT) or commercial vehicles that comply with the C standard of the ETRTO.

[0025] The tire 1 also includes a carcass 6 extending across the pair of bead cores 5, 5, and a belt layer 7 disposed on the outer side of the carcass 6 in the tire radial direction.

[0026] In this embodiment, the carcass 6 includes, for example, at least one carcass ply 6A in which a plurality of carcass cords are covered with a topping rubber. The carcass cords have a radial structure oriented at an angle of, for example, 80 to 90 degrees with respect to the tire equator C. As the carcass cord, for example, an organic fiber cord is preferably used.

[0027] The carcass ply 6A includes, for example, a main body portion 6a extending between the pair of bead cores 5, and a pair of turn-up portions 6b turned back from the inside to the outside in the tire axial direction around the pair of bead cores 5. In a preferred embodiment, each bead portion 4 has a bead apex 8 made of hard rubber that extends in a tapered shape from the bead core 5 to the outside in the tire radial direction between the main body portion 6a and the turn-up portions 6b.

[0028] The belt layer 7 is composed of a plurality of belt plies 7A, 7B (two layers in this embodiment). Each of the belt plies 7A, 7B includes a steel cord oriented at an angle of, for example, 15 to 40 degrees with respect to the tire equator C. Such a belt layer 7 hoops the carcass 6 and increases the rigidity of the tread portion 2. A band layer 9 may be disposed on the outer side of the belt layer 7 in the tire radial direction. The band layer 9 includes organic fiber cords oriented at an angle of 5 degrees or less with respect to the tire circumferential direction. This is effective in improving the high-speed durability of the tire 1 while suppressing deterioration of the ride comfort.

[0029] In the tread portion 2, a tread rubber 2G is disposed on the outer side of the belt layer 7 in the tire radial direction. The tread rubber 2G in this embodiment forms a contact surface 2a when a normal tire is placed in contact with a flat surface under a normal load. That is, the tread rubber 2G is formed at least from one ground contact end Te to the other ground contact end Te.

[0030] In this specification, the "normal load" refers to the load determined for each tire by each standard in the standard system including the standard on which the tire 1 is based, and is the maximum load capacity in the case of JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and "LOAD CAPACITY" in the case of ETRTO. In addition, in this specification, the "ground contact edge" of the tread portion 2 refers to the outermost edge of the ground contact surface 2a in the tire axial direction.

[0031] In this embodiment, the tread rubber 2G has a rubber hardness of less than 60°. In this specification, the rubber hardness is measured by cutting out a measurement sample from the tread rubber 2G forming the ground contact surface 2a such that the tire radial direction is the thickness direction, and then pressing a type A durometer against the ground contact surface side of the sample at 23° C. in accordance with JIS K 6253.

[0032] The tread rubber 2G with a rubber hardness of less than 60 degrees can absorb input from the road surface while traveling, reducing the transmission of vibration to the rim and improving the ride comfort of the tire 1. On the other hand, if the rubber hardness of the tread rubber 2G is 60 degrees or more, the rigidity of the tread portion 2 increases, improving braking performance but deteriorating ride comfort. In order to further improve the ride comfort of the tire 1, the rubber hardness of the tread rubber 2G is preferably 58 degrees or less, more preferably 55 degrees or less.

[0033] On the other hand, if the rubber hardness of the tread rubber 2G is too small, the braking performance may be significantly deteriorated. From this viewpoint, the rubber hardness of the tread rubber 2G may be preferably 45 degrees or more, more preferably 50 degrees or more. Note that in the tread portion 2, rubber with a rubber hardness of 60 degrees or more may be used in the portion other than the contact surface 2a.

[0034] Fig. 2 is a development view of the tread portion 2 of the tire 1 of this embodiment. As shown in Fig. 2, the tread portion 2 includes a pair of shoulder circumferential grooves 10 extending in the tire circumferential direction, a pair of shoulder land portions 20 separated on the tire axially outer sides of the pair of shoulder circumferential grooves 10, and one or more crown land portions 30 separated between the pair of shoulder land portions 20.

[0035] The tread portion 2 of this embodiment further has one or more crown circumferential grooves 11 provided between the pair of shoulder circumferential grooves 10. In this embodiment, a pair of crown circumferential grooves 11 are provided. As a result, the crown land portion 30 includes a pair of first crown land portions 40 that are sectioned on the outer sides of the pair of crown circumferential grooves 11, and a second crown land portion 50 formed therebetween. The second crown land portion 50 is provided, for example, on the tire equator C.

[0036] In this specification, the term "groove" refers to a recess having a width large enough to not close (i.e., a pair of groove walls do not contact each other) when the tire 1 is in contact with the ground (flat surface) under a normal load. Therefore, the tire 1 obtains basic drainage performance by the circumferential grooves 10 and 11.

[0037] The groove width of each of the circumferential grooves 10 and 11 is not particularly limited, but is, for example, 3 mm or more, preferably 4 mm or more, and, for example, 12 mm or less, preferably 10 mm or less, in order to ensure a good balance between sufficient drainage performance and ground contact area. The depth D (shown in FIG. 3) of each of the circumferential grooves 10 and 11 is, for example, 5 mm or more, preferably 6 mm or more, and, for example, 12 mm or less. In this embodiment, the circumferential grooves 10 and 11 are both shown as straight grooves whose groove edges extend parallel to the tire circumferential direction. In other embodiments, the circumferential grooves 10 and 11 may be, for example, zigzag or wavy.

[0038] Each of the pair of shoulder land portions 20 is divided into a plurality of shoulder blocks 22 by a plurality of shoulder lateral groove-like bodies 21 having a depth of 50% or more of the depth D of the shoulder circumferential groove 10. In this specification, the "shoulder lateral groove-like body" 21 means any of a groove, a sipe, or a combination of these that extends across the shoulder land portion 20 in the tire axial direction.

[0039] In this specification, a "sipe" refers to a small cut that closes (i.e., a pair of sipe walls come into contact with each other) when the tire 1 is subjected to a normal load and comes into contact with the ground (flat surface). As such, it is desirable for the width of the sipe to be approximately 1 mm or less.

[0040] In this embodiment, the shoulder blocks 22 have an aspect ratio, which is the ratio of the maximum circumferential length of the tire to the maximum axial length (peak-to-peak distance, the same applies below), of 0.60 or less, more preferably 0.40 or less, and are therefore effective in absorbing shocks from the road surface and improving ride comfort, because the shoulder blocks 22 have low circumferential rigidity.

[0041] In this embodiment, at least one of the crown land portions 30, that is, a pair of first crown land portions 40 and 40, is divided into a plurality of crown blocks 32 by a plurality of crown lateral groove-like bodies 31 each having a depth of 50% or more of the depth D of the shoulder circumferential groove 10.

[0042] The crown blocks 32 of this embodiment are formed with an aspect ratio, which is the ratio of the maximum circumferential length of the tire to the maximum axial length of the tire, larger than that of the shoulder blocks 22. In a preferred embodiment, the aspect ratio of the crown blocks 32 is 0.8 or more, more preferably 1.0 or more. Such shoulder blocks 22 are preferred in that they have a higher circumferential rigidity than the shoulder blocks, and therefore can compensate for the reduction in braking performance caused by the rubber hardness of the tread rubber 2G.

[0043] In this specification, the crown lateral groove 31 includes any of a groove extending across the crown land portion 30 in the tire axial direction, a sipe, or a combination of these, similar to the shoulder lateral groove.

[0044] The vibration inside the vehicle while the tire is running is caused by the vibration of the tire generated by contact with the road surface and transmitted to the inside of the vehicle via the rim. Therefore, the vibration of the shoulder land portion 20 close to the rim contributes greatly to the vibration inside the vehicle. On the other hand, at the contact surface 2a of the tread portion 2, the crown land portion 30 has a larger contact area and contact pressure than the shoulder land portion 20. Therefore, the crown land portion 30 contributes greatly to the braking force of the tire 1.

[0045] The present invention, on the premise that the hardness of the tread rubber 2G is less than 60 degrees, suppresses the transmission of vibrations to the vehicle interior to ensure a comfortable ride, and also suppresses deterioration of braking performance by improving the block rigidity distribution of the shoulder land portion 20 and the crown land portion 30. Specifically, when the block area per unit depth is defined as the value obtained by dividing the ground contact area of ​​one block by the maximum depth of the lateral groove-like body that divides the block, the block area per unit depth of the shoulder block 22 is configured to be smaller than the block area per unit groove depth of the crown block 32.

[0046] The block area per unit depth is correlated with block rigidity, and the larger this value, the higher the braking performance of each block, but the lower the shock absorbing ability. In this embodiment, focusing on the respective functions of the shoulder blocks 22 and the crown blocks 32, the block area per unit depth of the shoulder blocks 22 is configured to be smaller than the block area per unit groove depth of the crown blocks 32, thereby making it possible to improve ride comfort by taking advantage of the flexibility of the tread rubber 2G while suppressing deterioration of braking performance.

[0047] The block area per unit depth of the shoulder blocks 22 and the crown blocks 32 can be adjusted by appropriately changing the ground contact area of ​​each block and / or the depth of the lateral grooves.

[0048] In a preferred embodiment, the block area per unit depth of the crown block 32 is, for example, 17 (mm 2 / mm) or more, more preferably 30 (mm 2 / mm) or more, and more preferably 40 (mm 2 / mm) or more. This increases the block rigidity of the crown block 32, and further suppresses deterioration of braking performance.

[0049] On the other hand, if the block area per unit depth of the crown block 32 becomes excessively large, the improvement in ride comfort due to the regulation of the rubber hardness of the tread rubber 2G cannot be expected to be sufficient. From this point of view, the block area per unit depth of the crown block 32 is preferably 80 (mm 2 / mm) or less, more preferably 75 (mm 2 / mm) or less, and more preferably 70 (mm 2 / mm) or less.

[0050] In a preferred embodiment, the block area per unit depth of the shoulder block 22 is, for example, 60 (mm 2 / mm) or less, more preferably 55 (mm 2 / mm) or less, and more preferably 50 (mm 2 / mm) or less. This optimizes the block rigidity of the shoulder block 22, thereby further improving the vibration damping and absorbing capacity, and thus further improving the ride comfort.

[0051] On the other hand, if the block area per unit depth of the shoulder block 22 is excessively small, the braking performance may deteriorate, even though the contribution rate is small. From this point of view, the block area per unit depth of the shoulder block 22 is preferably 20 (mm 2 / mm) or more, more preferably 25 (mm 2 / mm) or more, and more preferably 30 (mm 2 / mm) or more.

[0052] In a more preferred embodiment, the ratio (As / Ac) of the block area per unit depth As (mm2 / mm) of the shoulder block 22 to the block area per unit groove depth Ac (mm2 / mm) of the crown block may be in the range of 0.21 to 0.88.

[0053] As a preferred embodiment, the tire 1 of the present embodiment is configured as a non-studless tire (i.e., a summer tire). Studless tires have the word "STUDLESS" written on the sidewall, but the non-studless tire of the present embodiment does not have such a marking. Studless tires are intended for use in winter, and a large number of sipes are formed in the tread portion 2 from the viewpoint of ensuring driving performance on frozen roads. In such studless tires, the block rigidity of both the crown and shoulder is reduced, and braking performance is reduced. On the other hand, in the present embodiment, the number of sipes in the tread portion 2 is reduced to configure the tire as a non-studless tire, and sufficient braking performance can be ensured.

[0054] In order to further improve the ride comfort while suppressing deterioration of the braking performance, the pair of shoulder circumferential grooves 10, 10 are desirably positioned in an area within 70% of the tread contact width TW centered on the tire equator C.

[0055] In this specification, the "tread width" TW is the distance between the ground contact ends Te, Te of the tread portion 2 in the tire axial direction.

[0056] When the shoulder circumferential groove 10 is located outside 70% of the tread contact width TW, the area of ​​the crown land portion 30 increases, improving the braking performance. However, this increases the likelihood of input from the road surface being transmitted to the tread portion 2, which may result in a deterioration in ride comfort.

[0057] Fig. 3 is a cross-sectional view taken along line III-III in Fig. 2. As shown in Fig. 3, the shoulder lateral groove-like body 21 of this embodiment is configured with shoulder sipes 21A. Compared with lateral grooves, such shoulder sipes 21A are superior in the uniformity of the rigidity of the shoulder land portion 20 in the tire circumferential direction, and are therefore useful in suppressing periodic vibrations occurring in the shoulder land portion 20 during driving.

[0058] In this embodiment, each shoulder block 22 is divided by a shoulder sipe 21A. Therefore, in this embodiment, the maximum depth of the lateral groove-like body dividing the shoulder block 22 is the maximum depth Ds of the shoulder sipe 21A. The shoulder sipe 21A in this embodiment has a constant depth Ds.

[0059] 3, the shoulder sipes 21A of the present embodiment have a depth Ds smaller than the depth D of the shoulder circumferential groove 10. This makes it possible to ensure braking performance while reducing the rigidity of the shoulder land portion 20, which contributes greatly to ride comfort. In another embodiment, the shoulder sipes 21A may have a depth D or greater than that of the shoulder circumferential groove 10.

[0060] In the present embodiment, the shoulder sipes 21A are preferably provided with chamfers 21B on the ground contact surface 2a. In the present embodiment, the chamfers 21B are provided on both sides of the opening of each shoulder sipe 21A in the tire circumferential direction. In another embodiment, the chamfers 21B may be provided only on one side of the opening of each shoulder sipe 21A.

[0061] The width w and depth d of the chamfer 21B are not particularly limited, but are preferably 1.5 mm or more, more preferably in the range of 2 to 5 mm. When a shear force acts on the shoulder block 22 in the circumferential direction of the tire during braking, such chamfer 21B comes into contact with the road surface, thereby increasing the contact area of ​​the shoulder block 22 and thereby enabling a stable braking force to be exerted.

[0062] 2, the shoulder sipes 21A as the shoulder lateral grooves 21 in this embodiment extend in an arc shape in a plan view of the tread. Such shoulder sipes 21A are useful for reducing vibrations generated in the shoulder blocks 22 because the entire area of ​​the sipe edge does not contact the ground at the same time while the tire is running.

[0063] The shoulder sipes 21A in FIG. 3 extend straight toward the inside in the tire radial direction. In another embodiment, as shown in FIG. 4, the shoulder sipes 21A may extend while bending in a zigzag or wavy manner toward the inside in the tire radial direction. Such three-dimensional shoulder sipes 21A can engage the adjacent shoulder blocks 22 with each other and suppress their collapse when a braking force acts on the shoulder land portion 20. Therefore, the braking ability can be improved without increasing the rigidity of the shoulder blocks 22, and the ride comfort performance and the braking performance can be improved in a well-balanced manner.

[0064] Returning to FIG. 2, in this embodiment, each shoulder block 22 is formed with one shoulder longitudinal sipe 23 that divides the shoulder block 22 into two in the tire axial direction. The shoulder longitudinal sipe 23 extends, for example, at an angle of 10 degrees or less with respect to the tire circumferential direction. The shoulder longitudinal sipe 23 serves to reduce the rigidity of the shoulder block 22 and to increase the vibration absorption capacity of the shoulder block 22. In this embodiment, the depth of the shoulder longitudinal sipe 23 is less than 50% of the depth of the shoulder circumferential groove, and is preferably 30 to 50%.

[0065] Fig. 5 is a cross-sectional view taken along line VV in Fig. 2. As shown in Fig. 5, the crown lateral groove-like body 31 of this embodiment is configured with a crown lateral groove 31A. Compared to sipes, such crown lateral grooves 31A promote a reduction in the rigidity of the first crown land portion 40, thereby contributing to an improvement in ride comfort.

[0066] The crown lateral grooves 31A as the crown lateral groove-like bodies 31 in this embodiment are arranged at a larger circumferential pitch than the shoulder sipes 21A as the shoulder lateral groove-like bodies 21. In this embodiment, the pitch of the crown lateral grooves 31A is twice the pitch of the shoulder sipes 21A. As a result, in this embodiment, the ground contact area of ​​the crown blocks 32 is formed to be larger than the ground contact area of ​​the shoulder blocks 22.

[0067] In this embodiment, the maximum depth of the crown lateral groove-like body 31 dividing the crown block 32 is the depth Dc of the crown lateral groove 31A. The depth Dc of the crown lateral groove 31A in this embodiment is set to be equal to or greater than the depth D of the shoulder circumferential groove 10 (FIG. 4 shows the state of Dc-D). As a result, the pair of first crown land portions 40 can contribute not only to the braking performance but also to improving the ride comfort. The crown lateral groove 31A in this embodiment has a constant depth Dc.

[0068] In the present embodiment, the crown lateral groove 31A is preferably formed with a chamfer 31B on the ground contact surface 2a. In the present embodiment, the chamfer 31B is formed on both sides of the opening of the crown lateral groove 31A in the tire circumferential direction, but may be formed on one side. The width w and depth d of the chamfer 31B are not particularly limited, but are preferably 1.5 mm or more, more preferably in the range of 2 to 5 mm. When a shear force in the tire circumferential direction acts on the crown block 32 during braking, such chamfer 31B comes into contact with the road surface to increase the contact area of ​​the crown block 32, which in turn can provide a stable braking force.

[0069] 2, the crown lateral groove 31A of the present embodiment also extends in an arc shape in a plan view of the tread. Such a crown lateral groove 31A is useful for reducing vibrations generated in the crown block 32 because the entire area of ​​the lateral groove edge does not contact the ground at the same time while the tire is running.

[0070] In this embodiment, each crown block 32 is formed with one longitudinal crown sipe 33 that divides the crown block 32 in the tire axial direction. The longitudinal crown sipe 33 extends at an angle of 10 degrees or less with respect to the tire circumferential direction, for example. The longitudinal crown sipe 33 serves to reduce the rigidity of the crown block 32 and to increase the vibration absorbing ability of the crown block 32.

[0071] In this embodiment, the second crown land portion 50 is configured as a rib. That is, the second crown land portion 50 is not completely divided in the tire circumferential direction. The second crown land portion 50 of this embodiment is provided with second crown sipes 51 and second crown longitudinal sipes 52.

[0072] The second crown longitudinal sipes 52 extend, for example, continuously in the tire circumferential direction. In a preferred embodiment, the second crown longitudinal sipes 52 are disposed at the center position of the second crown land portion 50 in the tire axial direction.

[0073] The second crown sipes 51 extend axially inward from each of the pair of crown circumferential grooves 11 and terminate within the second crown land portion 50. In this embodiment, the second crown sipes 51 are arranged in a staggered manner in the tire circumferential direction. The inner ends of the second crown sipes 51 in the tire axial direction communicate with and terminate in the second crown longitudinal sipes 52.

[0074] 3, the cross-sectional shape of the second crown sipes 51 is similar to that of the shoulder sipes 21A, and is formed with chamfers 51B. Such second crown sipes 51 reduce the rigidity of the second crown land portion 50. During braking, the chamfers 51B of the second crown sipes 51 come into contact with the road surface, thereby increasing the contact area of ​​the second crown land portion 50, which in turn helps to increase the braking force.

[0075] In this embodiment, the depth of the second crown sipes 51 and the second crown longitudinal sipes 52 is set to less than 50% of the depth of the shoulder circumferential groove 10, and preferably to 30 to 50%.

[0076] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above specific disclosure, and can be implemented in various modified forms within the scope of the technical ideas described in the claims. EXAMPLES

[0077] More specific, non-limiting examples of the present invention will now be described. Pneumatic tires (non-studless tires) with the basic structure shown in Figure 1 were prototyped based on the specifications in Table 1, and the ride comfort and braking performance of each tire were tested. The common specifications and test methods for each prototype tire are as follows: Tire size (front and rear): 235 / 60R17C Rim: 17×6.0J Internal pressure (front and rear): 525kPa

[0078] <Ride comfort performance test> A professional test driver drove a minivan with each test tire mounted on the front and rear on a dry paved road, and the ride comfort was evaluated by the driver's senses. The results were indexed, with the higher the value, the better.

[0079] <Braking performance test> A professional test driver suddenly braked a minivan equipped with each test tire on a dry paved road from a speed of 50 km / h, and the braking distance was measured. The results were indexed, with the higher the value, the better. The test results are shown in Table 1. [Table 1]

[0080] As a result of the test, it was confirmed that the Example tires suppressed deterioration of braking performance and improved ride comfort performance compared to the Comparative Example tires. [Explanation of symbols]

[0081] 1 Tire 2 Tread section 2G Tread rubber 2a Ground plane 10 Shoulder circumferential groove 20 Shoulder Land Section 21 Shoulder groove 21A Shoulder sipes 22 Shoulder Block 30 Crown Land Division 31 Crown groove 31A Crown lateral groove 31B Chamfering 32 Crown Block

Claims

1. A pneumatic tire having a tread portion, The tread portion includes a tread rubber having a rubber hardness of less than 60°, The tread portion is provided with a pair of shoulder circumferential grooves extending in a tire circumferential direction, a pair of shoulder land portions separated on tire axially outer sides of the pair of shoulder circumferential grooves, and one or more crown land portions separated between the pair of shoulder land portions, the shoulder land portion is divided into a plurality of shoulder blocks by a plurality of shoulder lateral groove-like bodies each having a depth that is 50% or more of the depth of the shoulder circumferential groove, At least one of the crown land portions is divided into a plurality of crown blocks by a plurality of crown lateral grooves each having a depth that is 50% or more of a depth of the shoulder circumferential groove, When the block area per unit depth is calculated by dividing the ground contact area of ​​one block by the maximum depth of a lateral groove that divides the block, the block area per unit depth of the shoulder block is smaller than the block area per unit groove depth of the crown block, The shoulder lateral groove is a shoulder sipe, The crown lateral groove-like structure is a crown lateral groove in which a pair of groove walls do not contact each other when the tire is in contact with a flat surface under a normal load. Pneumatic tires.

2. The block area per unit depth of the crown block is 17 to 80 (mm 2 2. The pneumatic tire according to claim 1, wherein the axial length of the tire is in the range of 1 / mm.

3. The pneumatic tire according to claim 1 or 2, which is a non-studless tire.

4. The pneumatic tire according to claim 1 , wherein the pair of shoulder circumferential grooves are positioned in an area within 70% of the tread ground contact width centered on the tire equator.

5. The pneumatic tire according to claim 1 , wherein the shoulder lateral grooves are chamfered.

6. The pneumatic tire according to claim 1 , wherein the crown lateral groove is chamfered.

7. The pneumatic tire according to claim 1 , wherein the shoulder lateral grooves have a depth smaller than that of the shoulder circumferential grooves.

8. The pneumatic tire according to claim 1 , wherein the crown lateral groove has a depth smaller than that of the shoulder circumferential groove.

9. The pneumatic tire according to claim 1 , wherein the shoulder lateral groove-like body has a depth equal to or greater than a depth of the shoulder circumferential groove.

10. The pneumatic tire according to claim 1 , wherein the crown lateral groove-like body has a depth equal to or greater than a depth of the shoulder circumferential groove.

Images