Pneumatic tire

Abstract

To provide a pneumatic tire making both wet performance and dry performance compatible at a high degree.SOLUTION: A pneumatic tire 1 comprises a tread 10 whose direction of mounting on a vehicle is specified. The tread 10 has: four main grooves 11, 12, 13 and 14 extending in a tire circumferential direction; and a plurality of blocks partitioned by the main grooves respectively. The plurality of blocks include a center block 20 arranged on an equator CL, and a sub groove 15 is formed on the center block 20. Respective widths W1, W2, W3 and W4 of the main grooves 11, 12, 13 and 14 gradually become narrower from a first direction side in which the main grooves are arranged inside a vehicle toward a second direction side in which the main grooves are arranged outside the vehicle.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a pneumatic tire, and more particularly to a tire that is provided with main grooves extending in the tire circumferential direction and has a specified mounting direction on a vehicle. [Background technology]

[0002] Conventionally, there is known a pneumatic tire having a plurality of main grooves extending in the tire circumferential direction and rib-shaped blocks partitioned by the main grooves (see, for example, Patent Document 1). The tire of Patent Document 1 has lateral grooves and sipes formed in the blocks, and is characterized in that the total groove width of the lateral grooves and sipes communicating with the second circumferential groove having a larger groove width is smaller than the total groove width of the lateral grooves and sipes communicating with the first circumferential groove having a smaller groove width. Patent Document 1 describes the effect of improving wet performance, performance on snow, and noise performance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2022-37668 A Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, tires with a specified mounting direction on a vehicle have higher performance than tires with no specified mounting direction, but the required performance level is also higher. In particular, achieving both wet and dry performance is an important issue. The tire of Patent Document 1 still has a lot of room for improvement in terms of achieving both wet and dry performance. [Means for solving the problem]

[0005] The pneumatic tire of the present invention is a pneumatic tire having a tread and a specified mounting direction relative to a vehicle, the tread having four main grooves extending in a circumferential direction of the tire and a plurality of blocks separated by each of the main grooves, the plurality of blocks including a center block positioned on the tire equator, in which secondary grooves that are shallower and narrower than the main grooves are formed along the circumferential direction of the tire, the width of each main groove gradually narrowing from a first direction side positioned on the inside of the vehicle toward a second direction side positioned on the outside of the vehicle. Effect of the Invention

[0006] The pneumatic tire according to the present invention can achieve both wet performance and dry performance. The pneumatic tire according to the present invention also has excellent snow performance, for example, and is suitable as an all-season tire. [Brief description of the drawings]

[0007] [Figure 1] 1 is a plan view of a pneumatic tire as an example of an embodiment. [Diagram 2] FIG. 2 is a diagram showing a part of a cross section taken along line AA in FIG. [Diagram 3] 1 is a plan view of a pneumatic tire as an example of an embodiment, showing an enlarged view of a portion of a tread. [Figure 4] FIG. 2 is an enlarged perspective view of a portion of the tread. [Diagram 5] FIG. 2 is an enlarged perspective view of a portion of the tread. [Figure 6] 4 is an enlarged perspective view showing a slit in a second shoulder block and its vicinity. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an example of an embodiment of a pneumatic tire according to the present invention will be described in detail with reference to the drawings. The embodiment described below is merely an example, and the present invention is not limited to the following embodiment. In addition, the present invention includes embodiments obtained by selectively combining the respective components of the embodiment described below.

[0009] FIG. 1 is a plan view of a pneumatic tire 1 according to an embodiment. The pneumatic tire 1 is a tire that includes a tread 10 that is a portion that comes into contact with the road surface, and is a tire that is specified for installation on a vehicle. That is, the pneumatic tire 1 is installed on the vehicle in opposite directions on the right and left sides of the vehicle. The tread 10 has different tread patterns on the left and right sides of a tire equator CL. The equator CL is an imaginary line that passes through the center of the tread 10 in the axial direction of the tire and extends in the tire circumferential direction. In this embodiment, the direction indicated by the arrow α in FIG. 1 is the main rotation direction of the pneumatic tire 1 (the direction in which the tire rotates when the vehicle moves forward).

[0010] The tread 10 has four main grooves extending in the tire circumferential direction and a plurality of blocks partitioned by each main groove. The four main grooves include, in order from the first direction side arranged on the vehicle inner side, a first main groove 11, a second main groove 12, a third main groove 13, and a fourth main groove 14. The main grooves are circumferential grooves extending parallel to each other along the tire circumferential direction and formed with different widths. As will be described in detail later, the width of each main groove gradually narrows from the first direction side arranged on the vehicle inner side toward the second direction side arranged on the vehicle outer side. By adopting this configuration, wet performance and dry performance are highly compatible.

[0011] The blocks include a center block 20 arranged on the equator CL, a first shoulder block 30 arranged on the vehicle inner side of the equator CL, and a second shoulder block 40 arranged on the vehicle outer side of the equator CL. The center block 20 has a sub-groove 15 formed along the tire circumferential direction, the sub-groove 15 being shallower and narrower than the main groove. The blocks further include a first mediate block 50 arranged between the center block 20 and the shoulder block 30, and a second mediate block 60 arranged between the center block 20 and the shoulder block 40. Each block is a rib-shaped block extending in the tire circumferential direction. The block is a protrusion protruding toward the tire radially outward, and may be called a land in the tire industry.

[0012] The center block 20 and the shoulder blocks 30 and 40 are formed with slits 21, 31, 41, and 42 each having a width of 1.5 mm or more, and sipes 22, 23, 24, 32, and 43 each having a width of less than 1.5 mm, as lateral grooves extending in a direction intersecting with the main grooves. Similarly, the mediate block 50 is formed with a slit 51 and a sipe 52 as lateral grooves. The mediate block 60 is formed with only sipes 61 and 62 as lateral grooves, and no slits having a width of 1.5 mm or more are formed.

[0013] The lateral grooves of each block are grooves extending in the tire axial direction that are narrower than the main grooves, extend in a direction intersecting the main grooves, and are formed in different patterns for each block. In this specification, a lateral groove having a width of 1.5 mm or more is defined as a slit, and a lateral groove having a width of less than 1.5 mm is defined as a sipe. The width of the slit is preferably 2.0 mm or more and 4.0 mm or less. The width of the sipe is preferably 0.3 mm or more and 1.0 mm or less.

[0014] As will be described in more detail later, the pneumatic tire 1 has many lateral grooves and has excellent snow performance. For this reason, the pneumatic tire 1 is suitable as an all-season tire. Properly arranged lateral grooves effectively distribute the tire's ground pressure and increase the edge effect, improving braking performance, cornering power characteristics (hereinafter referred to as "CP characteristics"), and snow performance.

[0015] The pneumatic tire 1 includes a pair of sidewalls 2 that bulge outward in the tire axial direction, and a pair of beads. The sidewalls 2 extend radially inward from both left and right ends of the tread 10, forming the side surfaces of the pneumatic tire 1. In this embodiment, a side rib 3 that protrudes slightly outward is formed in an annular shape along the tire circumferential direction at the upper portion of the tire side surface, and this side rib 3 is the boundary position between the tread 10 and the sidewalls 2. The beads are the parts that are fixed to the rim of the wheel.

[0016] The ground contact ends E1, E2 of the pneumatic tire 1 or the portions from the vicinity thereof to the left and right side ribs 3 are also called shoulder or buttress regions. The ground contact end E1 is a first ground contact end located on the inside of the vehicle when the pneumatic tire 1 is mounted on a vehicle, and the ground contact end E2 is a second ground contact end located on the outside of the vehicle, and they are located in the shoulder blocks 40, 50, respectively. In the following, the region between the ground contact end E1 and the equator CL is defined as a first region R1, and the region between the ground contact end E2 and the equator CL is defined as a second region R2.

[0017] In this specification, the ground contact ends E1 and E2 are defined as both axial ends of the area (ground contact surface) that comes into contact with a flat road surface when a predetermined load is applied to an unused pneumatic tire 1 mounted on a standard rim and filled with air to a standard internal pressure. In the case of passenger car tires, the predetermined load is a load equivalent to 88% of the standard load.

[0018] Here, "regular rim" refers to a rim determined by tire standards, and is "standard rim" for JATMA, and "measuring rim" for TRA and ETRTO. "Regular internal pressure" refers to "maximum air pressure" for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and "INFLATION PRESSURE" for ETRTO. Regular internal pressure is usually 180 kPa for passenger tires, but 220 kPa for tires labeled "Extra Load" or "Reinforced." "Regular load" refers to "maximum load capacity" for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and "LOAD CAPACITY" for ETRTO.

[0019] The pneumatic tire 1 includes, for example, a carcass, a belt, and a cap ply. The carcass is a cord layer covered with rubber, and serves as the skeleton of the tire that can withstand loads, impacts, air pressure, and the like. The carcass is made up of two carcass plies, and has a radial structure in which carcass cords are arranged in a direction perpendicular to the tire circumferential direction. An inner liner, which is a rubber layer for retaining air pressure, is generally provided on the inside of the carcass. The belt is a reinforcing band that is disposed between the rubber that constitutes the tread 10 and the carcass.

[0020] Since the pneumatic tire 1 is used as a tire with a specified mounting direction relative to the vehicle, it is preferable that the tire has a marking for indicating the mounting direction relative to the vehicle. The marking for indicating the mounting direction may be a letter, symbol, illustration, or the like indicating the inside or outside of the vehicle, and the configuration is not particularly limited. Generally, a symbol called a serial number is provided on the sidewall 2, but the serial number may be used as a marking for indicating the mounting direction.

[0021] The serial number includes information such as a size code, a manufacturing time (manufacturing year and week), and a manufacturing location (manufacturing factory code). The mounting direction of the pneumatic tire 1 on the vehicle may be specified by providing a serial number only on the sidewall 2 facing the outside of the vehicle, or by providing different serial numbers on the sidewall 2 facing the outside of the vehicle and the sidewall 2 facing the inside of the vehicle. A specific example is to provide a manufacturing factory code and a size code on both sidewalls 2, and provide the manufacturing year and week only on the sidewall 2 facing the outside of the vehicle.

[0022] The configuration of the four main grooves and the sub grooves 15 will be described in detail below with reference to FIG.

[0023] 2 is a diagram showing a part of the cross section taken along line AA in FIG. 1. As described above, the four main grooves have different widths. The widths of the four main grooves are gradually narrowed from the tread edge E1 on the vehicle inner side toward the tread edge E2 on the vehicle outer side. That is, of the four main grooves, the width W1 of the main groove 11 located closest to the tread edge E1 is the largest, and the width W4 of the main groove 14 located closest to the tread edge E2 is the smallest. The widths of the four main grooves satisfy the following condition: width W1 of main groove 11>width W2 of main groove 12>width W3 of main groove 13>width W4 of main groove 14.

[0024] According to the pneumatic tire 1, by providing the above-mentioned four main grooves, good drainage performance is exhibited in the first region R1 on the vehicle inner side, and excellent braking performance on wet road surfaces is obtained. In addition, in the second region R2 on the vehicle outer side, the contact area with the road surface is increased, and excellent CP characteristics are obtained on dry road surfaces. Therefore, the pneumatic tire 1 is a high-performance tire that achieves a high level of both wet and dry performance. Furthermore, the center block 20 is formed with a sub-groove 15. By introducing the sub-groove 15, it is possible to effectively distribute the ground pressure of the wide center block 20 while increasing the width of the center block 20 and improving initial response performance.

[0025] In this specification, the width of the main groove means the groove width along the profile surface of the tread 10, in other words, the groove width at the opening of the groove. The profile surface is a surface along the surface of the tread 10. The same applies to the sub groove and the lateral groove, but the width of the cut portion of the lateral groove described later is not included in the groove width. The total width of the pneumatic tire 1 is not particularly limited, but is, for example, 265 mm or more and 325 mm or less. In addition, the ground contact width of the pneumatic tire 1 is, for example, 210 mm or more and 270 mm or less.

[0026] The first main groove 11 is a circumferential groove that separates the first shoulder block 30 and the first mediate block 50. The main groove 11 extends straight in the tire circumferential direction and is formed in an annular shape with a substantially constant width over its entire length. The depth of the main groove 11 is substantially constant over its entire length, except for a portion where a wear indicator is formed. The width W1 of the main groove 11 is the largest among the four main grooves, and is preferably 1.02 to 1.10 times, or 1.03 to 1.07 times, the width W2 of the second largest main groove 12.

[0027] The second main groove 12 is a circumferential groove that divides the center block 20 and the first mediate block 50. The main groove 12 extends straight in the tire circumferential direction and is formed in an annular shape with a substantially constant width over the entire length. The width W2 of the main groove 12 is the second largest among the four main grooves, and in this embodiment, is closer to the width W1 of the largest main groove 11 than the width W3 of the third largest main groove 13. The width W2 of the main groove 12 is, for example, 1.15 to 1.35 times the width W3 of the main groove 13, or 1.20 to 1.30 times the width W3 of the main groove 13.

[0028] The third main groove 13 is a circumferential groove that divides the center block 20 and the second mediate block 60. The main groove 13 extends straight in the tire circumferential direction and is formed in an annular shape with a substantially constant width over the entire length. The width W3 of the main groove 13 is the third largest among the four main grooves, and in this embodiment, is closer to the width W2 of the second largest main groove 12 than the width W4 of the smallest main groove 14. The width W3 of the main groove 13 is, for example, 1.55 to 1.75 times the width W4 of the main groove 14, or 1.60 to 1.70 times the width W4 of the main groove 14.

[0029] The fourth main groove 14 is a circumferential groove that divides the second shoulder block 40 and the second mediate block 60. The main groove 14 extends straight in the tire circumferential direction and is formed in an annular shape with a substantially constant width over the entire length. As described above, the width W4 of the main groove 14 is the smallest among the four main grooves. In this embodiment, the difference in width between the main grooves is the largest between the width W3 of the main groove 13 and the width W4 of the main groove 14. The width W4 of the main groove 14 is, for example, 0.35 to 0.55 times, or 0.40 to 0.50 times, the width W1 of the main groove 11.

[0030] The sub groove 15 is shallower and narrower than the main grooves, and is formed in parallel to each main groove. The sub groove 15 extends straight in the tire circumferential direction and is formed in an annular shape with a substantially constant width over the entire length. The width W5 of the sub groove 15 is smaller than the width W4 of the main groove 14, which is the narrowest of the main grooves, and in this embodiment, for example, is 0.60 times or more and 0.80 times or less, or 0.65 times or more and 0.75 times or less, of the width W4 of the main groove 14. The depth of the sub groove 15 is shallower than the depth of the shallowest main groove, and is preferably 50% to 90% of the depth of the main groove, and more preferably 80% to 90%.

[0031] When the total width of the pneumatic tire 1 is 265 mm or more and 305 mm or less, a suitable example of the width of each of the main grooves and the sub grooves 15 is as follows. W1: 18.6mm ±0.5mm W2: 17.7mm ±0.5mm W3: 14.0mm±0.5mm W4: 8.5mm±0.3mm W5: 6.1mm ±0.3mm

[0032] The four main grooves are formed parallel to each other with the above-mentioned widths. As described above, by making the width W1 of the main groove 11 and the width W2 of the main groove 12 similar to each other and increasing the difference between the width W3 of the main groove 13 and the width W3 of the main groove 14, the drainage performance in the first region R1 of the tread 10 is stabilized, and good wet braking performance is obtained. In addition, by increasing the difference (W3-W4) between the width W3 of the main groove 13 and the width W4 of the main groove 14, the contact area of ​​the second region R2, particularly the shoulder block 40, can be increased, and the improvement effect of the CP characteristic becomes more remarkable.

[0033] The four main grooves may have the same depth or different depths. In this embodiment, the main grooves 12 and 13 have substantially the same depth, and the main groove 11 is slightly shallower than the main grooves 12 and 13. The depth of the main groove 14 is, for example, substantially the same as the depth of the main groove 11. The wear indicators may be formed in all the main grooves, or may be formed in only some of the main grooves. In this embodiment, the depth of each main groove is substantially constant over its entire length (except for the portion where the wear indicator is present, if any).

[0034] An example of the depth of the main grooves 12, 13 is 1.01 to 1.15 times the depth of the main groove 11, i.e., 7.7 mm±9.0 mm. The walls of each main groove are inclined so that the groove volume gradually decreases toward the groove bottom. The walls of the main groove form the side walls of the blocks, in other words, the side walls of the blocks are inclined so that the block width increases the farther away from the ground contact surface. In this specification, the depth of the groove means the length from the profile surface to the bottom of the deepest part of the groove.

[0035] In this embodiment, the center block 20 and the intermediate blocks 50 and 60 have slopes 27, 55, and 65 formed at the ends on the ground contact edge E1 side along the main grooves 11, 12, and 13, respectively. The slopes 27, 55, and 65 are inclined at an angle of 20° to 50° with respect to the profile surface, for example, in a depth range within 20% of the depth of the main grooves 11, 12, and 13 from the ground contact surface of each block, and are formed with a constant width along the tire circumferential direction. The slopes cause the main grooves 11, 12, and 13 to have a large degree of widening near the openings.

[0036] The overall configuration of the tread pattern will now be described with reference to FIG.

[0037] 3 is an enlarged view (plan view) of a portion of the tread 10. As described above, the tread 10 has, in order from the ground contact edge E1 side, the first shoulder block 30, the first mediate block 50, the center block 20, the second shoulder block 40, and the second mediate block 60. The center block 20 is disposed on the equator CL, and for example, the width direction center of the block is located on the ground contact edge E2 side from the equator CL. In this embodiment, the main groove 12 and the sub groove 15 are formed so that the tire equator CL is located between the two grooves.

[0038] The void ratio of the first region R1 arranged on the vehicle inner side of the tread 10 is preferably larger than the void ratio of the second region R2 arranged on the vehicle outer side. Here, the void ratio means the ratio of the area corresponding to the voids to the area of ​​the profile surface of each region (ground contact area + area corresponding to the voids). The void ratio when the areas of the main grooves, slits, and sipes are counted is referred to as "void ratio A," and the void ratio when the area of ​​the sipes is not counted is referred to as "void ratio B."

[0039] The first region R1 has the widest main groove 11 and the second widest main groove 12, and also has more slits than the second region R2. Therefore, the void ratio of the first region R1 is greater than the void ratio of the second region R2. By making the void ratio of the tread 10 in the first region R1 > the second region R2, it becomes easier to achieve both wet performance and dry performance.

[0040] The void ratio of the first region R1 is preferably 1.15 to 1.30 times the void ratio of the second region R2, and more preferably 1.20 to 1.30 times. In the first region R1, the void ratio A is preferably 39% to 44%, and the void ratio B is preferably 37% to 42%. In the second region R2, the void ratio A is preferably 31% to 36%, and the void ratio B is preferably 28% to 33%.

[0041] The center block 20 and the mediate blocks 50, 60 may have the same width, but in this embodiment, the center block 20 is formed wider than the mediate blocks 50, 60. The mediate block 50 is formed slightly wider than the mediate block 60. The width of the center block 20 is, for example, 1.30 to 1.50 times, or 1.35 to 1.40 times, the width of the mediate block 50. When the total width of the pneumatic tire 1 is 265 mm to 325 mm, an example of the width of the center block 20 is 39 mm to 48 mm.

[0042] The width of the ground contact surface of the second shoulder block 40 is larger than the width of the ground contact surface of the first shoulder block 30. In this case, it is easy to achieve both wet performance and dry performance. The width of the ground contact surface of the shoulder block 40 is preferably 1.01 to 1.10 times the width of the ground contact surface of the shoulder block 30.

[0043] The center block 20 and the first mediate block 50 have slits 21, 51 formed from the end on the ground contact end E1 side, i.e., the first end in the width direction of each block arranged on the vehicle inner side. The slit 21 is connected to the main groove 12 and terminates inside the center block 20. The slit 51 is connected to the main groove 11 and terminates inside the block. The number of slits 51 is greater than the number of slits 21, and is twice the number of slits 21 in this embodiment.

[0044] Sipes 22, 23 are formed in the center block 20 from the secondary groove 15. The sipes 22, 23 are connected to the secondary groove 15 and terminate within the center block 20. A sipe 52 is formed in the first mediate block 50 from the end on the ground contact edge E2 side, i.e., the second end in the width direction of the block arranged on the outer side of the vehicle. The sipe 52 is connected to the main groove 12 and terminates within the mediate block 50. The center block 20 further has a sipe 24 formed across the block to connect the secondary groove 15 to the two main grooves 12, 13.

[0045] In this embodiment, the slits 51 and sipes 52 of the first mediate block 50 are each formed with a length of 50% or more of the width of the block, are arranged alternately in the tire circumferential direction, and terminate within each block. Note that it is also possible to form the slits 51 from the end of the block on the ground contact end E2 side and the sipes 52 from the end of the block on the ground contact end E1 side, but the configuration of this embodiment has a more significant effect on improving the CP characteristics.

[0046] The slits and sipes formed in the center block 20 and the first mediate block 50 distribute ground pressure and provide an edge effect to the blocks, which contributes to improving wet and snow performance in particular. The slits and sipes are arranged, for example, parallel to each other.

[0047] In the second mediate block 60, first sipes 61 extending from the end on the ground contact end E1 side, i.e., the first end in the width direction of the block located on the vehicle inner side, and second sipes 62 extending from the end on the ground contact end E2 side, i.e., the second end in the width direction of the block located on the vehicle outer side, are alternately formed in the tire circumferential direction. On the other hand, no slits with a width of 1.5 mm or more are formed in the mediate block 60. Furthermore, the number of lateral grooves in the mediate block 60 is smaller than the number of lateral grooves in the mediate block 50. By forming the sipes 61 and 62, the ground contact pressure of the mediate block 60 is dispersed, while high rigidity of the block can be ensured by not forming slits.

[0048] The first shoulder block 30 is formed with one type of slit 31 and two types of sipes 32, 33. The slits 31 are connected to the main groove 11 via the narrow grooves 33. The sipes 32 are disposed between two adjacent slits 31. All of the slits in the shoulder block 30 are connected to the main groove 11 via the narrow grooves 33, and none of them are directly connected to the main groove 11. In this case, it is possible to ensure high rigidity of the shoulder block 30 while ensuring good drainage performance, and excellent braking performance can be obtained on both wet and dry road surfaces.

[0049] The second shoulder block 40 is formed with two types of slits 41, 42 and two types of sipes 43, 44. The first slit 41 is directly connected to the main groove 14, and the second slit 42 is connected to the main groove 14 via the sipe 44. The slits 41, 42 are arranged alternately in the tire circumferential direction, and the sipe 43 is arranged between adjacent slits 41, 42. By arranging the slits 41, 42 alternately, it is possible to ensure high rigidity of the shoulder block 40 while ensuring good drainage performance, and excellent CP characteristics are obtained.

[0050] As described above, the shoulder blocks 30 and 40 are provided with a plurality of slits connected to the main groove, and sipes are provided between each slit. The number of slits 31 in the shoulder block 30 is equal to the total number of slits 41 and 42 in the shoulder block 40 and the number of slits 51 in the intermediate block 50. The number of sipes provided between each slit relative to the circumferential length of the block is greater in the first shoulder block 30 than in the second shoulder block 40. The number of sipes 32 in the shoulder block 30 is greater than the number of sipes 43 in the shoulder block 40, and is preferably twice the number of sipes 43. The sipes 32 and 43 are both sipes that extend from the main groove to the ground contact edge.

[0051] Since most general vehicles have a camber angle, the first region R1 of the tread 10 has a higher ground pressure and a longer ground contact length than the second region R2. Therefore, by forming many sipes in the first region R1, the ground pressure is dispersed and the edge effect and snow column shear force are increased, thereby improving the traction and braking performance on ice and snowy roads with low friction coefficients. By forming sipes in the center block 20 and the first mediate block 50 from the opposite direction to the slits while forming sipes in the opposite direction to the slits, the traction and braking performance can be improved while suppressing a decrease in block rigidity.

[0052] The configuration of each block will be described in detail below with reference to FIGS. 4 to 6 as appropriate.

[0053] [Center block] As shown in Figures 4 and 5, in the center block 20, slits 21 are formed from the main grooves 12, sipes 22 and 23 are formed from the sub-grooves 15, and further, a sipe 24 is formed across the block. The width of the sipe 24 is less than 1.5 mm, and preferably 0.3 mm to 1.0 mm. The center block 20 is not divided by lateral grooves (slits) having a width of 1.5 mm or more, and is a land that is substantially continuous around the entire circumference of the tire. In the tire industry, such land is sometimes conventionally called a rib, and the center block 20 can be said to be a rib.

[0054] Each of the slits 21, sipes 22, 23, and sipes 24 is formed, for example, at a variable pitch that slightly changes the interval in a predetermined number units in the tire circumferential direction. The configuration of the center block 20 has a large effect on the braking performance and initial response performance, especially when driving straight ahead, but in this embodiment, the effects of the sub grooves 15 and lateral grooves are designed to effectively distribute the ground pressure of the block, and the edge effect is also exhibited, sufficiently contributing to improving the CP characteristics and snow performance.

[0055] The sub groove 15 is formed in the center of the center block 20 in the width direction, and is disposed slightly toward the ground edge E2 side from the tire equator CL. The sub groove 15 is formed, for example, with a width of 5% to 30% or 10% to 20% of the width of the center block 20. The center block 20 is divided by the sub groove 15 into a first region on the ground edge E1 side and a second region on the ground edge E2 side. The slits 31 are formed only in the first region, and no lateral grooves with a width of 1.5 mm or more are formed in the second region. In this case, it is easy to achieve both wet performance and dry performance.

[0056] The slit 21 and the three sipes 22, 23, 24 extend linearly in a direction intersecting the tire circumferential direction and the axial direction, and are inclined to the tire axial direction at an angle of 10° to 30°. All the lateral grooves are formed parallel to each other, and are inclined at the above angle to the tire axial direction so that the first end in the length direction on the ground contact edge E1 side is located rearward in the tire main rotation direction from the second end in the length direction on the ground contact edge E2 side. Since the sipe 24 is divided by the sub groove 15, it can be said that the two sipes extending from the sub groove 15 to the main grooves 12, 13 are formed on the same straight line.

[0057] The number of slits 21 and sipes 22, 23, 24 may be the same, but in this embodiment, they are different, with the number of sipes 22 being the largest. The number of slits 21 and sipes 23, 24 is the same. These three types of lateral grooves are arranged in the first region of the center block 20 in the tire circumferential direction in the order of sipes 22, slits 21, sipes 22, and sipes 24. That is, the sipes 22 are arranged between the slits 21 and sipes 24. The sipes 23 are located on the same straight line as the slits 21 in the second region of the center block 20. In the second region of the center block 20, the sipes 23 and sipes 24 are arranged alternately in the tire circumferential direction.

[0058] The depth of the slit 21 and the sipes 22, 23, 24 is, for example, 50% to 90% or 60% to 80% of the depth of the main grooves 12, 13 at the deepest part. In this embodiment, the sipes 22, 23 are shallower at the part adjacent to the sub-groove 15 than the other parts of the sipes 22, 23. The sipes 24 are shallower at the part adjacent to the sub-groove 15 than the other parts of the sipes 22, 23 in the first region, and shallower at the part adjacent to the main groove 13 in the second region. This configuration improves the rigidity of the block on the main groove 13 side, and contributes to improving the CP characteristics and braking performance. The width of the sipes 22, 23, 24 is substantially constant over the entire length, and is preferably 0.3 mm to 1.0 mm.

[0059] The slit 21 is formed with a length from the main groove 12 beyond the equator CL to the sub-groove 15. The sipe 22 is formed with a length from the sub-groove 15 beyond the equator CL to the main groove 12. The slit 23 is formed with a length from the sub-groove 15 to the main groove 13. The length of the sipe 21 and the sipes 22, 23 along the tire axial direction is, for example, 50% to 90% or 55% to 80% of the width of the center block 20. The length of the sipe 21 and the sipes 22, 23 may be the same, but in this embodiment, the slit 21 is formed longer than the sipes 22, 23. The length of the sipes 22, 23 along the tire axial direction is substantially the same.

[0060] The slit 21 has a tapered shape with the groove width gradually decreasing toward the tip (the end on the ground contact edge E2 side). However, the portion where the groove width gradually decreases is only near the tip of the slit 21, and the other portions are formed with substantially the same width. The width of the slit 21 is preferably 2.0 mm or more and 4.0 mm or less at the widest portion. The depth of the slit 21 may be constant over the entire length, or may be shallower near the tip. The slit 21 narrows to the same width as the sipes 22, 23 within a predetermined length range from the tip. For this reason, it can be said that a short sipe extends from the tip of the slit 21.

[0061] At the edge of the slit 21, cutouts 25, 26 are formed along the length of the slit 21. The cutouts 25, 26 are formed by chamfering both widthwise edges of the opening of the slit 21 and cutting them open. The cutouts 25, 26 have the function of dispersing ground pressure while ensuring a large contact area, and contribute to improving braking performance. The cutouts 25, 26 are preferably formed within a range of up to a depth of 2 mm from the contact surface of the center block 20. At the edge of the slit 21, a cutout may be formed only on one widthwise side, but by forming the cutouts 25, 26 on both widthwise sides, the above effect becomes more pronounced.

[0062] The cutouts 25, 26 are formed, for example, from a first end in the length direction of the slit 21 to the vicinity of the tip (second end in the length direction), and gradually narrow toward the tip of the slit 21. The width of the cutouts 24, 25 is preferably smaller than the width of the slit 21, and as an example, is 1.0 mm or more and 2.0 mm or less at the portion where the width is maximum. The cutouts 25, 26 form slopes on both edges in the width direction of the slit 21. An example of the inclination angle of the slope with respect to the profile surface of the tread 10 is 15° or more and 60° or less.

[0063] [First shoulder block] As shown in FIG. 4, the first shoulder block 30 is formed with slits 31 connected to the main groove 11 via a narrow groove 33. By connecting the slits 31 to the main groove 11 via the narrow groove 33, it is possible to ensure high rigidity of the shoulder block 30 while ensuring good drainage performance. Furthermore, two sipes 32 are formed between two adjacent slits 31 in the shoulder block 30. That is, the number of sipes 32 is twice the number of slits 31. Each of the slits 31 and sipes 32 is formed, for example, at a variable pitch in which the intervals are slightly changed by a predetermined number in the circumferential direction of the tire.

[0064] The narrow grooves 33 are lateral grooves narrower than the slits 31 and may be either slits having a width of 1.5 mm or sipes having a width of less than 1.5 mm. The shoulder blocks 30 may be ribs that are substantially continuous around the entire circumference of the tire without being separated by slits having a width of 1.5 mm or more. Alternatively, the shoulder blocks 30 may be separated by slits having a width of 1.5 mm or more, but in this case too, the width of the narrow grooves 33 is preferably 2.0 mm or less.

[0065] The slit 31 is formed from the vicinity of the main groove 11, past the ground edge E1, to the side rib 3. The slit 31 may be formed along the tire axial direction, or may be gently inclined with respect to the tire axial direction so that a first end in the length direction on the side rib 3 side is located forward in the tire main rotation direction than a second end in the length direction on the main groove 11 side. The slit 31 is formed, for example, in a substantially linear shape in a plan view, and is inclined at an angle of 15° or less with respect to the tire axial direction. The slit 31 is narrowed near the second end in the length direction, and has a substantially constant width in other parts. The width of the slit 31 is preferably 3.1 mm or more and 5.1 mm or less at its widest part.

[0066] The sipes 32 may be formed straight along the tire axial direction, or may be gently curved. In this embodiment, the sipes 32 are formed substantially parallel to the slits 31 with a length that extends from the main groove 11 beyond the ground contact edge E1 and does not reach the side rib 3. The sipes 32 are bent so that the inclination with respect to the tire axial direction becomes large near the main groove 11. A bent portion 37 where the bending of the sipes 32 is maximum is formed so as to be aligned with the intersection of the slits 31 and the narrow grooves 33 in the tire circumferential direction.

[0067] The depth of the slits 31 and the sipes 32 is, for example, 50% to 90% or 60% to 80% of the depth of the main groove 11 at the deepest part. Also, the second end of the sipe 32 in the length direction connected to the main groove 11, specifically at least a part of the range from the main groove 11 to the bent part 37, may be shallower than the part from the bent part 37 of the sipe 32 to the ground contact edge E1. This configuration improves the rigidity of the shoulder block 30 and contributes to improving the braking performance and CP characteristics. The width of the sipe 32 is substantially constant over the entire length, and is preferably 0.3 mm to 1.0 mm.

[0068] At the edge of the slit 31, cutouts 34, 35 are formed along the length of the slit 31. The width of the cutouts 34, 35 is preferably smaller than the width of the slit 31, and as an example, is 1.0 mm or more and 1.5 mm or less at the portion where the width is maximum. Also, at the edge of the portion of the sipe 32 from the main groove 11 to the bend portion 37, a cutout 36 is formed on one side in the width direction of the sipe 32. The cutout 36 gradually widens as it approaches the main groove 11, and is formed wider than the width of the sipe 32 at the portion where the width is maximum.

[0069] The cutouts 34, 35, and 36 are preferably formed within a range of 2 mm deep from the ground contact surface of the shoulder block 30. The cutouts 34, 35, and 36 are formed by chamfering the opening edges of the lateral grooves and have the function of dispersing ground pressure while securing a large ground contact area. The cutouts form slopes on the edges of the slits 31 and the sipes 32. An example of the inclination angle of the slope with respect to the profile surface is 15° or more and 60° or less.

[0070] The narrow groove 33 is a short sipe connecting the main groove 11 and the slit 31, and is formed substantially parallel to the portion of the sipe 32 from the main groove 11 to the bend 37. The width of the narrow groove 33 is larger than that of the sipe 32 and smaller than that of the slit 31 from the viewpoint of drainage and the like. It is preferably 1.3 mm or more and 1.7 mm or less. The depth of the narrow groove 33 is preferably shallower than the deepest part of the slit 31 from the viewpoint of ensuring block rigidity and the like. Note that no cut portion is formed on the edge of the narrow groove 33.

[0071] [First mediate block] As shown in Fig. 4, the first mediate block 50 has slits 51 formed from the end on the ground contact edge E1 side and sipes 52 formed from the end on the equator CL side. Each of the slits 51 and sipes 52 is formed, for example, at a variable pitch in which the intervals are slightly changed in units of a predetermined number in the tire circumferential direction. The slits 51 and sipes 52 are formed in the same number in parallel to each other and are alternately arranged in a staggered pattern in the tire circumferential direction.

[0072] The slits 51 and the sipes 52 extend linearly in a direction intersecting the tire circumferential direction and the axial direction, and are inclined at an angle of 10° to 30° with respect to the tire axial direction. The slits 51 and the sipes 52 are arranged such that the slits 51 are aligned on the same line as the slits 31 or narrow grooves 33 of the shoulder blocks 30, and the sipes 52 are aligned on the same line as the sipes 32. In this case, the balance of block rigidity in the vicinity of the equator CL of the first region R1 is improved, and the effect of dispersing ground pressure is improved.

[0073] The depth of the slits 51 and the sipes 52 is, for example, 50% to 90%, or 60% to 80% of the depth of the main groove 12 at the deepest portion. In this embodiment, the second end portion of the sipe 52 in the longitudinal direction connected to the main groove 12 is shallower than other portions of the sipe 52. This configuration improves the rigidity of the block on the main groove 12 side, contributing to improvement of the CP characteristics. The width of the sipe 52 is substantially constant over the entire length, and is preferably 0.3 mm to 1.0 mm.

[0074] The slits 51 are formed with a length that extends from the main groove 11 beyond the widthwise center of the mediate block 50, but does not reach the main groove 12. The sipes 52 are formed with a length that extends from the main groove 12 beyond the widthwise center of the block, but does not reach the main groove 11. The length of the slits 51 and the sipes 52 along the tire axial direction is, for example, 50% or more and 90% or less, or 55% or more and 80% or less, of the width of the mediate block 50. The slits 51 and the sipes 52 may be substantially the same length.

[0075] The slits 51 and the sipes 52 do not intersect with each other and terminate within the mediate block 50. The mediate block 50 does not have any slits or sipes that cross the width direction, and the mediate block 50 is continuous around the entire circumference of the tire. Conventionally, the mediate block 50 can be called a rib.

[0076] The slit 51 has a shape similar to that of the slit 31 of the shoulder block 30, and has a tapered shape in which the groove width gradually decreases near the tip (the end on the ground contact end E2 side) toward the tip. The width and depth of the slit 51 are similar to those of the slit 31. Cutouts 53, 54 are formed on the edges of the slit 51 along the length direction of the slit 51. The cutouts 53, 54 are preferably formed with a width smaller than that of the slit 51 in the range from the ground contact surface of the block to a depth of 2 mm, similar to the cutouts 24, 25 of the center block 20. The inclination angle of the slope formed by the cutouts 53, 54 with respect to the profile surface is, for example, 15° or more and 60° or less.

[0077] [Second shoulder block] As shown in Fig. 5, the second shoulder block 40 is formed with a slit 41 that is directly connected to the main groove 14, and a slit 42 that is connected to the main groove 14 via a sipe 44. By connecting the slit 42 to the main groove 14 via the sipe 44, it is possible to ensure high rigidity of the shoulder block 40 while maintaining good drainage performance. Also, in the shoulder block 40, one sipe 43 is formed between adjacent slits 41, 42. Each of the slits 41, 42 and the sipe 43 is formed, for example, at a variable pitch in which the intervals are slightly changed by a predetermined number of units in the tire circumferential direction.

[0078] The slit 41 is formed from the main groove 14, past the ground edge E2, to the side rib 3. The slit 42 is formed with a length from the vicinity of the main groove 14 past the ground edge E2, but not reaching the side rib 3. The slits 41, 42 may be formed along the tire axial direction, or may be gently inclined with respect to the tire axial direction so that the first end in the length direction on the main groove 14 side is located forward in the tire main rotation direction than the second end in the length direction on the side rib 3 side. The slits 41, 42 are formed, for example, in a substantially linear shape in a plan view, and are inclined with respect to the tire axial direction by 15° or less. The slits 41, 42 are narrowed in the vicinity of the main groove 14, and have a substantially constant width in other portions. The width of the slits 41, 42 is preferably 0.3 mm or more and 1.0 mm or less at the widest portion.

[0079] The sipes 43 may be formed straight along the tire axial direction, or may be gently curved. In this embodiment, the sipes 43 are formed substantially parallel to the slits 41 and 42 with a length from the main groove 14 beyond the ground contact edge E2 and not reaching the side rib 3. The sipes 43 are bent in the opposite direction to the sipes 32 of the shoulder blocks 30 in the vicinity of the main groove 14 so that the inclination with respect to the tire axial direction becomes large. A bent portion 48 where the bending of the sipes 43 is maximum is formed to be aligned with the intersection of the slits 41 and the sipes 44 in the tire circumferential direction.

[0080] The depth of the slits 41, 42 and the sipes 43 is, for example, 50% to 90% or 60% to 80% of the depth of the main groove 14 at the deepest part. In this embodiment, the groove bottom is raised and shallowed at the first end of the slit 41 on the main groove 14 side in the longitudinal direction. In addition, the portion of the sipe 43 from the main groove 14 to the bent portion 48 may be shallower than the portion from the bent portion 48 to the ground edge E2. This configuration improves the rigidity of the shoulder block 40, and particularly contributes to improving the CP characteristics. The width of the sipe 43 is substantially constant over the entire length, and is preferably 0.3 mm to 1.0 mm.

[0081] At the edges of the slits 41 and 42, cutouts 45 and 46 are formed along the length direction of each slit. The width of the cutouts 45 and 46 is preferably smaller than the width of the slit, and as an example, the width is 1.0 mm or more and 1.5 mm or less at the maximum width. The maximum width of the cutouts 45 and 46 formed at the edges of the slits 41 and the maximum width of the cutouts 45 and 46 formed at the edges of the slits 42 may be the same. In addition, at the edges of the portion of the sipe 43 from the main groove 14 to the bent portion 48, a cutout 47 is formed on one side in the width direction of the sipe 43. The cutout 47 gradually widens as it approaches the main groove 14, and is formed wider than the width of the sipe 43 at the maximum width.

[0082] The cutouts 45, 46, 47 are preferably formed within a range of 2 mm deep from the ground contact surface of the shoulder block 40. The cutouts 45, 46, 47 are formed by chamfering the opening edges of the lateral grooves and have the function of dispersing ground pressure while securing a large ground contact area. The cutouts form slopes on the edges of the slits 41, 42 and the sipes 43. An example of the inclination angle of the slope with respect to the profile surface is 15° or more and 60° or less.

[0083] The sipe 44 is a short sipe that connects the main groove 14 and the slit 42, and is formed substantially parallel to the portion of the sipe 43 from the main groove 14 to the bent portion 48. From the viewpoint of drainage, etc., the width of the sipe 44 is larger than the width of the sipe 43, and is preferably 0.8 mm or more and less than 1.5 mm. From the viewpoint of ensuring block rigidity, etc., the depth of the sipe 44 is preferably shallower than the deepest portion of the slit 41. Note that no cut portion is formed on the edge of the sipe 44.

[0084] Fig. 6 is an enlarged perspective view of the slit 41 and its vicinity. As shown in Fig. 6, a cutout 45 is formed on the edge of the slit 41 that is directly connected to the main groove 14, from a start position 45a away from the main groove 14 to a position beyond the ground contact edge E2. The start position 45a is the end of the cutout 45 on the main groove 14 side, and the cutout 45 continues uninterrupted from the start position 45a to a position beyond the ground contact edge E2. Similarly, the cutout 46 is formed from a start position 46a away from the main groove 14 to a position beyond the ground contact edge E2. The start positions 45a, 46a are, for example, aligned in the tire circumferential direction.

[0085] From the viewpoint of improving the CP characteristic, the shoulder block 40 preferably has a high block rigidity. On the other hand, it is necessary to effectively distribute the ground pressure while securing a large ground contact area. As a result of the study by the inventor, it was found that the reduction in rigidity of the block can be suppressed by separating the cutouts 45, 46 by a predetermined length from the main groove 14, and uneven wear can be effectively suppressed. Since the rigidity of the block is low in the vicinity of the main groove 14, it is considered that if the cutout is formed continuously with the main groove 14, the block rigidity is significantly reduced and uneven wear is likely to occur. By providing a portion without a cutout within a predetermined length range from the main groove 14, uneven wear is specifically suppressed, and the ride comfort performance, durability, CP characteristic, etc. of the tire are improved.

[0086] The length L along the tire axial direction from the main groove 14 to the starting position 45a is, for example, shorter than the width of the slit 41, longer than the maximum width of the cutout 45, or substantially the same as the maximum width of the cutout 45. Specifically, the lower limit of the length L is preferably 0.5 mm, more preferably 0.8 mm, and particularly preferably 1.0 mm. The upper limit of the length L is preferably 3.0 mm, more preferably 2.5 mm, and particularly preferably 2.0 mm. If the length L is within this range, the effect of introducing the cutout 45 can be sufficiently obtained while effectively suppressing uneven wear of the shoulder block 40. An example of a suitable range of the length L is 0.5 mm to 3.0 mm, 0.8 mm to 2.0 mm, or 1.0 mm to 2.0 mm.

[0087] The slit 41 has a raised portion 41a formed in an area adjacent to the main groove 14, the groove bottom being raised. The depth of the slit 41 where the raised portion 41a is formed is, for example, 40% to 70% of the depth of the deepest portion of the slit 41. By providing the raised portion 41a, it becomes easy to achieve both good drainage performance and CP characteristics. The raised portion 41a has a substantially constant height up to a position P1 that is a predetermined distance away from the main groove 14, and is formed so as to gradually decrease from the position P1. The length along the tire axial direction from the main groove 14 to the position P1 is, for example, 5 mm to 15 mm.

[0088] The cutout 45 includes a first region 45b whose width changes and a second region 45c whose width is substantially constant. The first region 45b gradually widens as it moves away from the starting position 45a, and a slope that is triangular in plan view is formed in the first region 45b. The first region 45b is formed, for example, from the starting position 45a to a position P1. By providing the first region 45b, the effect of suppressing uneven wear becomes more pronounced. The second region 45c is formed from the position P1 to a position beyond the ground edge E2. Similarly, the cutout 46 includes a first region 46b whose width changes and a second region 46c whose width is substantially constant.

[0089] [Second Mediate Block] As shown in Fig. 5, the second mediate block 60 has a sipe 61 formed from the end on the equator CL side and a sipe 62 formed from the end on the ground contact edge E2 side. Each of the sipes 61, 62 is formed, for example, at a variable pitch in which the intervals are slightly changed in units of a predetermined number in the tire circumferential direction. The sipes 61, 62 are formed in the same number in parallel to each other and are alternately arranged in a staggered pattern in the tire circumferential direction.

[0090] The sipes 61, 62 extend linearly in a direction intersecting the tire circumferential direction and the axial direction, and are inclined at an angle of 25° to 55° with respect to the tire axial direction. The sipes 61, 62 are inclined at the above angle with respect to the tire axial direction so that a first end in the length direction on the main groove 13 side is located forward in the tire main rotation direction than a second end in the length direction on the main groove 14 side. That is, the sipes 61, 62 extend in a direction intersecting the extension direction of the lateral grooves of the center block 20 and the first mediate block 50.

[0091] The depth of the sipes 61, 62 is, for example, 50% to 90% or 60% to 80% of the depth of the main groove 13 at the deepest part. The width of the sipes 61, 62 is substantially constant over the entire length, and is preferably 0.3 mm to 1.0 mm. The sipe 61 is formed with a length from the main groove 13 beyond the widthwise center of the mediate block 60 to not reach the main groove 14. Similarly, the sipe 62 is formed with a length from the main groove 14 beyond the widthwise center of the mediate block 60 to not reach the main groove 13. The length of the sipes 61, 62 along the tire axial direction is, for example, substantially the same, and is 60% to 90% or 70% to 85% of the width of the mediate block 50.

[0092] The sipes 61, 62 do not intersect with each other and terminate within the mediate block 60. The mediate block 60 does not have any slits or sipes that cross the width direction, and the mediate block 60 is continuous around the entire circumference of the tire. Conventionally, the mediate block 60 can be called a rib.

[0093] At the edges of the sipes 61, 62, cutouts 63, 64 are formed along the length of the sipes 61, 62, respectively. The cutouts 63, 64 are preferably formed within a range of 2 mm from the ground contact surface of the mediate block 60, like the cutouts of the other lateral grooves, but differ from the other cutouts in that the surface formed by the cutouts 63, 64 is substantially parallel to the profile surface. The cutouts 63, 64 are formed, for example, with a length of 50% to 90% of the length of the sipes 61, 62 and a width wider than the width of the sipes 61, 62, and gradually widen as they approach the main grooves 13, 14.

[0094] In this embodiment, cutouts are formed on the edges of all the slits in each block. Also, cutouts are formed on the edges of the sipes in the shoulder blocks 30 and 40 and the mediate block 60. This allows the tread 10 to have a large contact area over its entirety while distributing ground pressure effectively in a well-balanced manner.

[0095] As described above, the pneumatic tire 1 having the above-mentioned configuration can achieve both wet and dry performance at a high level. By providing the four main grooves 11, 12, 13, and 14 whose groove width gradually narrows from the first region R1 on the vehicle inner side toward the second region R2 on the vehicle outer side, the first region R1 exhibits good drainage performance and provides excellent braking performance on wet road surfaces, and the second region R2 has a large contact area with the road surface and provides excellent CP characteristics on dry road surfaces.

[0096] Furthermore, the pneumatic tire 1 has many appropriately arranged slits and sipes that effectively distribute ground pressure and provide a good edge effect. In addition, the width of the center block 20 is increased to improve initial response performance, while the secondary grooves 15 are formed to distribute the ground pressure of the blocks. As a result, the pneumatic tire 1 has a high level of both wet and dry performance, and also has excellent snow performance. The pneumatic tire 1 is suitable as an all-season tire.

[0097] The above embodiment can be appropriately modified in design without impairing the object of the present invention. The configuration of the slits and sipes formed in each block of the tread 10 is suitable for improving the wet performance, dry performance, and snow performance of the tire in a well-balanced manner, but it is possible to omit some of the slits or sipes, or to change the shape, length, width, depth, etc. [Explanation of symbols]

[0098] 1 pneumatic tire, 2 sidewall, 3 side rib, 10 tread, 11 first main groove, 12 second main groove, 13 third main groove, 14 fourth main groove, 15 secondary groove, 20 center block, 21 slit, 22, 23, 24 sipe, 25, 26 cutout, 27 slope, 30 first shoulder block, 31 slit, 32 sipe, 33 narrow groove, 34, 35, 36 cutout, 37 bend, 40 second shoulder block, 41, 42 slit, 41a raised portion, 43, 44 sipe, 45, 46, 47 cutout, 45a, 46a starting position, 45b, 46b first region, 45c, 46c second region, 48 bend, 50 first mediate block, 51 slit, 52 Sipe, 53, 54 Cutout, 55 Slope, 60 Second mediate block, 61, 62 Sipe, 63, 64 Cutout, 65 Slope, CL Equator, E1, E2 Ground contact edge

Claims

1. A pneumatic tire having a tread and a specified mounting direction on a vehicle, The tread is Four main grooves extending in a tire circumferential direction; A plurality of blocks defined by the main grooves; having The plurality of blocks includes a center block disposed on the tire equator, A sub-groove that is shallower and narrower than the main groove is formed in the center block along the tire circumferential direction, The width of each of the main grooves gradually narrows from a first direction side disposed on an inner side of the vehicle toward a second direction side disposed on an outer side of the vehicle.

2. the plurality of blocks further includes a first shoulder block disposed on a vehicle inner side of a tire equator and a second shoulder block disposed on a vehicle outer side of the tire equator, 2. The pneumatic tire according to claim 1, wherein the center block, the first shoulder block, and the second shoulder block have, as lateral grooves, slits having a width of 1.5 mm or more and sipes having a width of less than 1.5 mm.

3. The pneumatic tire according to claim 2 , wherein the number of the sipes disposed between the slits relative to a circumferential length of the block is greater in the first shoulder block than in the second shoulder block.

4. The plurality of blocks further includes a first mediate block disposed between the center block and the first shoulder block, and a second mediate block disposed between the center block and the second shoulder block, The center block is formed with the slit having a length not reaching the sub-groove from the end on the first direction side, and the sipe having a length not reaching the main groove from the sub-groove, The pneumatic tire according to claim 2 , wherein the slit is formed in the first mediate block from an end on the first direction side, and the slit terminates within the block.

5. In the second mediate block, as the sipes, first sipes extending from an end on the first direction side and second sipes extending from an end on the second direction side are alternately formed in the tire circumferential direction, The pneumatic tire according to claim 4 , wherein the number of lateral grooves in the second mediate block is smaller than the number of lateral grooves in the first mediate block.

6. 5. The pneumatic tire according to claim 4, wherein the number of the slits in the first mediate block is the same as the number of the slits in the first shoulder block and is twice the number of the slits in the center block.

7. The pneumatic tire according to claim 2 , wherein a width of a ground contact surface of the second shoulder block is greater than a width of a ground contact surface of the first shoulder block.

8. In the second shoulder block, as the slits, first slits directly connected to the main groove and second slits connected to the main groove via the sipes are alternately formed in the tire circumferential direction, The pneumatic tire according to claim 2 , wherein all of the slits of the first shoulder block are connected to the main groove via a third slit having a width narrower than the first slits or the sipes.

9. The pneumatic tire according to claim 2 , wherein an incision is formed on an edge of each of the slits.

10. The pneumatic tire according to claim 2 , wherein the sipes are formed in the center block so as to cross the block and connect the auxiliary groove to the two main grooves.

11. When the region between the first ground contact edge located on the vehicle inner side and the tire equator is defined as a first region, and the region between the second ground contact edge located on the vehicle outer side and the tire equator is defined as a second region, The pneumatic tire according to claim 2 , wherein a void ratio of the first region is greater than a void ratio of the second region.

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