pneumatic tires

Abstract

We provide pneumatic tires that improve noise performance while ensuring drainage performance. [Solution] A pneumatic tire equipped with a tread 2, wherein the tread 2 has a pair of shoulder main grooves 12, 13 and shoulder ribs 50, 60 positioned outward in the tire axial direction from the shoulder main grooves 12, 13, the shoulder ribs 50, 60 are provided with slits 51, 61 that extend in a direction intersecting the shoulder main grooves 12, 13 and terminate inside the shoulder ribs 50, 60, the inner ends 51A, 61A of the slits 51, 61 in the tire axial direction are positioned inward in the tire axial direction from the contact edges E1, E2 of the tread 2, and the rectangular ratio A of the contact surface of the tread 2 is 0.6 or more and 0.7 or less.

Description

Technical Field

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

Background Art

[0002] Conventionally, a pneumatic tire having a tread with a pair of shoulder main grooves and a shoulder rib disposed outside the shoulder main grooves in the tire axial direction is known. Patent Document 1 discloses a pneumatic tire in which a slit extending along the tire axial direction is formed in the shoulder rib. By providing the slit, for example, the handling stability can be improved.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As a result of the study by the present inventors, it has been found that when the slit is formed to communicate with the shoulder main groove, the impact sound generated when the shoulder rib contacts the road surface increases and the noise performance deteriorates. On the other hand, when the slit is formed so as not to communicate with the shoulder main groove, the drainage performance tends to deteriorate due to a decrease in the groove volume or the like. Therefore, it is not easy to improve the noise performance while ensuring the drainage performance.

Means for Solving the Problems

[0005] One aspect of the present invention is a pneumatic tire having a tread, wherein the tread has a pair of shoulder main grooves and shoulder ribs positioned outward in the tire axial direction from the shoulder main grooves, the shoulder ribs are provided with slits that extend in a direction intersecting the shoulder main grooves and terminate inside the shoulder ribs, the inner end of the slits in the tire axial direction is positioned inward in the tire axial direction from the contact edge of the tread, and the rectangular ratio A of the contact surface of the tread is 0.6 or more and 0.7 or less. [Effects of the Invention]

[0006] According to the pneumatic tire of the present invention, it is possible to improve noise performance while ensuring drainage performance. [Brief explanation of the drawing]

[0007] [Figure 1] This is a cross-sectional view of a pneumatic tire, which is an example of an embodiment. [Figure 2] This is a plan view of the tread of a pneumatic tire, which is an example of an embodiment. [Figure 3] This diagram schematically shows the shape of the contact surface of the tread. [Modes for carrying out the invention]

[0008] Hereinafter, an example of an embodiment of the 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 embodiments described below. Furthermore, forms obtained by selectively combining the various components of the multiple embodiments and modifications described below are included in the present invention.

[0009] Figure 1 is a schematic diagram showing a cross-section of a pneumatic tire 1 according to this embodiment. As shown in Figure 1, the pneumatic tire 1 comprises a tread 2 which is the part that contacts the road surface, a sidewall 3 which forms the side of the tire, and a bead 4 which is the part that is fixed to the rim of the wheel. The pneumatic tire 1 is suitable for summer tires on electric vehicles (EVs), hybrid vehicles (HVs), and other electric vehicles with high acceleration performance, or on heavy sports utility vehicles (SUVs).

[0010] The pneumatic tire 1 is a tire with a specified mounting direction on the vehicle, meaning that the mounting direction is opposite on the right and left sides of the vehicle. In other words, the tread 2 has different tread patterns on the left and right sides of the tire equator CL. Here, the tire equator CL is a virtual line along the tire circumferential direction passing through the center of the tread 2 in the tire axial direction. Furthermore, for the sake of explanation, the term "left and right" is used in this specification, and this "left and right" refers to the left and right sides in the direction of travel of the vehicle when the pneumatic tire 1 is mounted on the vehicle.

[0011] The tread 2 is provided with a pair of center main grooves 10, 11 and a pair of shoulder main grooves 12, 13 formed further outward in the tire axial direction than the center main grooves 10, 11. The four main grooves are formed straight along the tire circumferential direction without curving in the tire axial direction.

[0012] Further, the tread 2 is provided with a center rib 20 partitioned by center main grooves 10 and 11 and formed on the tire equator CL, a first middle rib 30 partitioned by the center main groove 10 and the shoulder main groove 12, and a second middle rib 40 partitioned by the center main groove 10 and the shoulder main groove 13. Further, the tread 2 is provided with a first shoulder rib 50 disposed opposite to the first middle rib 30 in the tire axial direction across the shoulder main groove 12, and a second shoulder rib 60 disposed opposite to the second middle rib 40 in the tire axial direction across the shoulder main groove 13. The first shoulder rib 50 and the second shoulder rib 60 are formed beyond the grounding ends E1 and E2. Note that a rib is a portion that bulges outward in the tire radial direction from a position corresponding to the bottom of the main groove, and is also called land.

[0013] Here, the grounding ends E1 and E2 of the pneumatic tire 1 are defined as both ends in the tire axial direction of the region (ground contact surface) that contacts the flat road surface when a predetermined load is applied in a state where an unused tire is mounted on a regular rim and filled with air to reach the regular internal pressure. The predetermined load is a load corresponding to 88% of the regular load.

[0014] Note that the "regular rim" is a rim defined by the tire specifications. In the case of JATMA, it is the "standard rim"; in the case of TRA and ETRTO, it is the "Measuring Rim". Also, the "regular internal pressure" is the "maximum air pressure" in the case of JATMA, the maximum value described 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. The regular internal pressure is usually 180 kPa for passenger car tires, but 220 kPa for tires marked as Extra Load or Reinforced. The "regular load" is the "maximum load capacity" in the case of JATMA, the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and the "LOAD CAPACITY" in the case of ETRTO.

[0015] As will be described in more detail later, the contact surface of the tread 2 in this embodiment has a relatively short contact length near the contact edges E1 and E2 compared to the length of the contact surface along the tire circumferential direction (contact length) on the tire equator CL, and the shape of the contact surface of the tread 2 is close to an ellipse shape. Specifically, the rectangularity ratio A of the contact surface of the tread 2 is designed to be 0.6 or more and 0.7 or less.

[0016] The sidewall 3 is positioned on both sides of the tread 2 and is formed in an annular shape along the circumferential direction of the tire. The sidewall 3 is the part of the pneumatic tire 1 that protrudes most outward in the axial direction of the tire and is gently curved so as to be convex outward in the axial direction of the tire. The sidewall 3 has the function of preventing damage to the carcass 5. The sidewall 3 is the part that flexes the most when the pneumatic tire 1 acts as a cushion, and is usually made of a flexible rubber with fatigue resistance.

[0017] The bead 4 is the portion of the sidewall 3 located radially inward and fixed to the wheel rim. The bead 4 has a bead core 4A and a bead filler 4B. The bead core 4A is an annular member made of steel bead wire, extending around the entire circumference in the tire's circumferential direction, and is embedded in the bead 4. The bead filler 4B is an annular hard rubber member with a tapered tip that extends outward radially in the tire's circumferential direction and extends around the entire circumference of the tire.

[0018] The carcass 5 is stretched between a pair of beads 4 and secured by being folded back around the bead core 4A. The carcass 5 is composed of at least one carcass ply. The carcass ply is composed of carcass cords made of organic fibers covered with a coating rubber. The carcass cords are arranged substantially perpendicular to the circumferential direction of the tire (e.g., between 80° and 90°). Examples of organic fibers used in the carcass cords include polyester fibers, rayon fibers, aramid fibers, and nylon fibers.

[0019] The inner liner 6 covers the inner surface of the tire between the pair of beads 4. The inner liner 6 is made of air permeation resistant rubber and has a function of maintaining the air pressure of the pneumatic tire 1.

[0020] Further, the pneumatic tire 1 further includes a belt 7 disposed on the outer side in the tire radial direction of the carcass 5, and a cap ply 8 covering the outer side in the tire radial direction of the belt 7. The cap ply 8 has a function of reinforcing the belt 7. The number of the cap plies 8 may be one or two or more.

[0021] The belt 7 is disposed on the outer side in the tire radial direction at the top of the carcass 5 and is provided so as to overlap the outer peripheral surface of the carcass 5. The belt 7 is formed of a belt ply obtained by rubber coating cords arranged in a direction inclined with respect to the tire circumferential direction. The material of the cords of the belt ply is not particularly limited, and examples thereof include organic fibers such as polyester, rayon, nylon, and aramid, or metals such as steel.

[0022] In the present embodiment, the belt 7 is composed of two belt plies 7A and 7B. The cords constituting the two belt plies 7A and 7B are arranged so as to cross each other between the two belt plies 7A and 7B.

[0023] Here, the angle (belt angle) of the cords constituting the two belt plies 7A and 7B with respect to the tire circumferential direction is preferably 22° or more and 30° or less, and more preferably 24° or more and 28° or less. When the angle of the cords with respect to the tire circumferential direction is within the above range, it becomes easy to control the rectangularity ratio A of the grounding surface of the tread 2 to 0.6 or more and 0.7 or less. As a result, the drainage performance described later can be ensured.

[0024] Next, the tread pattern of the pneumatic tire 1 will be described while referring to FIG. 2. FIG. 2 is a plan view of the tread 2 of the pneumatic tire 1.

[0025] As shown in Figure 2, the tread 2 has an asymmetrical tread pattern with respect to the tire equator CL. The tread pattern of the pneumatic tire 1 exhibits the effects of the present invention most clearly when the tire is mounted on a vehicle such that the contact end E1 is located on the outside of the vehicle and the contact end E2 is located on the inside of the vehicle.

[0026] The tread 2 has a pair of center main grooves 10, 11 and a pair of shoulder main grooves 12, 13 formed further outward in the tire axial direction than the center main grooves 10, 11. The center main groove 10 and shoulder main groove 12 are formed in the region on the contact edge E1 side of the tire equator CL, while the center main groove 11 and shoulder main groove 13 are formed in the region on the contact edge E2 side of the tire equator CL. Note that the number of main grooves is not limited to four, and may be three or fewer, or five or more.

[0027] The center main grooves 10, 11 and the shoulder main grooves 12, 13 are formed straight along the circumferential direction of the tire without curving in the axial direction of the tire. In this case, water from the road surface can easily enter the center main grooves 10, 11 and the shoulder main grooves 12, 13, thereby improving drainage performance. At least one of the center main grooves 10, 11 and the shoulder main grooves 12, 13 may have a zigzag shape.

[0028] In this embodiment, the width of the center main grooves 10 and 11 is larger than the width of the shoulder main grooves 12 and 13. In this case, drainage performance can be further improved. Alternatively, the widths of the center main grooves 10 and 11 are the same, and the widths of the shoulder main grooves 12 and 13 are the same. The width of the center main grooves 10 and 11 is, for example, 6 mm or more and 15 mm or less, and the width of the shoulder main grooves 12 and 13 is, for example, 5 mm or more and 14 mm or less. Note that the width of the shoulder main grooves 12 and 13 may be the same as the width of the center main grooves 10 and 11, or it may be larger than the width of the center main grooves 10 and 11. In this specification, unless otherwise specified, the width of the groove means the width of the profile surface along the contact surface of the tread 2.

[0029] The sum of the widths of the four main grooves is preferably 5% or more, and 10% or more, of the length W along the tire axis from contact point E1 to contact point E2 (hereinafter referred to as "contact width W"). In this case, drainage performance can be improved. Alternatively, the sum of the widths of the four main grooves is preferably 30% or less, and 25% or less, of the contact width W. In this case, excellent handling stability can be achieved. Therefore, the sum of the widths of the four main grooves is preferably 5% or more, 30% or less, and 10% or more, and 25% or less, of the contact width W.

[0030] The center main grooves 10, 11 and the shoulder main grooves 12, 13 have, for example, the same depth. The depths of the center main grooves 10, 11 and the shoulder main grooves 12, 13 are, for example, 7 mm or more and 15 mm or less. However, the depths of the center main grooves 10, 11 and the shoulder main grooves 12, 13 may be different.

[0031] A wear indicator (not shown) is generally provided in at least one of the center main grooves 10, 11 and the shoulder main grooves 12, 13. The wear indicator is a projection located at the bottom of the groove and serves as an indicator for checking the wear level of the tread rubber.

[0032] The tread 2 is provided with a center rib 20 demarcated by center main grooves 10 and 11, a first middle rib 30 demarcated by the center main groove 10 and shoulder main groove 12, and a second middle rib 40 demarcated by the center main groove 10 and shoulder main groove 13. The tread 2 is also provided with a first shoulder rib 50 positioned opposite the first middle rib 30 in the tire axial direction, straddling the shoulder main groove 12, and a second shoulder rib 60 positioned opposite the second middle rib 40 in the tire axial direction, straddling the shoulder main groove 13. The center rib 20, first middle rib 30, second middle rib 40, first shoulder rib 50, and second shoulder rib 60 are formed continuously in the tire circumferential direction.

[0033] [Center Rib 20] The center rib 20 is formed on the tire equator CL. In this embodiment, the axial center portion of the center rib 20 is positioned closer to the contact end E1 than the tire equator CL. The width of the center rib 20 is, for example, 5% or more and 30% or less of the contact width W.

[0034] Sipes 21 are formed in the center rib 20. The sipes 21 are formed at predetermined intervals in the circumferential direction of the tire. In this specification, a sipe means a groove with a groove width of 1.5 mm or less. The groove width does not include the width of the cut section, which will be described later.

[0035] The sipe 21 is formed from the center main groove 10 toward the tire equator CL and terminates inside the center rib 20. The sipe 21 also has a length that does not reach the tire equator CL from the center main groove 10. However, the sipe 21 may have a length that reaches the tire equator CL from the center main groove 10, or it may be formed from the center main groove 10 to the center main groove 11.

[0036] The axial length of the sipe 21 in the tire is preferably between 10% and 45% of the width of the center rib 20, and more preferably between 20% and 45% of the width of the center rib 20. The width of the sipe 21 is, for example, between 0.5 mm and 1.0 mm. The sipe 21 is generally formed to be shallower than the center main groove 10. The depth of the sipe 21 is, for example, between 60% and 90% of the depth of the center main groove 10.

[0037] The sipes 21 extend along a direction inclined toward one side in the circumferential direction of the tire with respect to the tire axis. The inclination angle of the sipes 21 with respect to the tire axis is, for example, 5° or more and 60° or less, and may be 10° or more and 50° or less. The sipes 21 may have a zigzag shape.

[0038] The center rib 20 has a cut portion 22 formed along the edge of the sipe 21. The cut portion 22 is formed to chamfer and widen the edge of the sipe 21 within a predetermined depth range from the contact surface of the tread 2. The cut portion 22 contributes to improving driving performance by, for example, dispersing the contact pressure acting on the edge of the sipe 21. The cut portion 22 may be formed on both sides in the width direction of the sipe 21, but in this embodiment, it is formed only on one side in the width direction of the sipe 21.

[0039] The slope forming the cut portion 22 is inclined at an angle of 30° or more, 60° or less, or 40° or more, 50° or less with respect to the profile surface along the contact surface of the tread 2, for example, at the widest part. In this case, the function of the cut portion 22 is performed more effectively, and during sudden braking or acceleration, the slope contacts the road surface, suppressing block collapse. The cut portion 22 may be formed along the entire length of the sipe 21, and may widen as it approaches the center main groove 10. The cut portion 22 is formed, for example, within a depth range corresponding to 30% of the depth of the deepest part of the sipe 21 from the contact surface of the tread 2. In this case, driving performance can be improved without impairing the durability of the center rib 20.

[0040] [1st Middle Rib 30] The first middle rib 30 is positioned opposite the center rib 20 in the tire axial direction, with the center main groove 10 in between, and opposite the first shoulder rib 50 in the tire axial direction, with the shoulder main groove 12 in between. The width of the first middle rib 30 is, for example, 5% or more and 30% or less of the contact width W.

[0041] The first middle rib 30 has sipes 31 that extend along the circumferential direction of the tire. The sipes 31 are formed straight along the circumferential direction of the tire without curving in the axial direction of the tire. The sipes 31 are formed around the entire circumference of the tire.

[0042] The sipe 31 is formed on the side of the tire axial center of the first middle rib 30 that is closer to the contact end E1. In other words, the width of the region of the first middle rib 30 that is closer to the contact end E1 than the sipe 31 is smaller than the width of the region of the first middle rib 30 that is closer to the tire equator CL than the sipe 31. The width of the region of the first middle rib 30 that is closer to the contact end E1 than the sipe 31 is, for example, 20% or more and less than 50% of the width of the first middle rib 30. The sipe 31 may also be formed on the tire axial center of the first middle rib 30.

[0043] The width of the sipe 31 is, for example, 0.5 mm or more and 1.0 mm or less. The sipe 31 is generally formed to be shallower than the center main groove 10 and the shoulder main groove 12. The depth of the sipe 31 is, for example, 60% or more and 90% or less of the depth of the center main groove 10.

[0044] The first middle rib 30 has sipes 31 that extend along the circumferential direction of the tire, as well as sipes 32 that cross the first middle rib 30. In other words, the sipes 32 are formed from the shoulder main groove 12 to the center main groove 10. The sipes 32 are formed at predetermined intervals in the circumferential direction of the tire.

[0045] The sipe 32 extends along a direction inclined toward one side in the circumferential direction of the tire with respect to the tire axis. The inclination angle of the sipe 32 with respect to the tire axis is, for example, 5° or more and 60° or less, and may be 10° or more and 50° or less. In this embodiment, the inclination angle of the sipe 32 with respect to the tire axis is substantially the same as the inclination angle of the sipe 21 with respect to the tire axis.

[0046] The width of the sipe 32 is, for example, 0.5 mm or more and 1.0 mm or less. The width of the sipe 32 is, for example, approximately the same as the width of the sipe 31. The depth of the sipe 32 is, for example, 60% or more and 90% or less of the depth of the center main groove 10. The sipe 32 may be formed to be shallower than the sipe 31.

[0047] It is preferable that the number of sipes 32 is greater than the number of sipes 21 formed on the center rib 20. In other words, it is preferable that the spacing of the sipes 32 in the tire circumferential direction is smaller than the spacing of the sipes 21 in the tire circumferential direction.

[0048] The first middle rib 30 has a cut portion 33 formed along the edge of the sipe 32. Similar to the cut portion 22 described above, the cut portion 33 is formed to chamfer and widen the edge of the sipe 32 within a predetermined depth range from the contact surface of the tread 2. The cut portion 33 may be formed on both sides in the width direction of the sipe 32, but in this embodiment, it is formed only on one side in the width direction of the sipe 32. The cut portion 33 contributes to improving driving performance by, for example, distributing the contact pressure acting on the edge of the sipe 32.

[0049] The incision portion 33 is formed in the region of the sipe 32 between the shoulder main groove 12 and the sipe 31. In other words, the incision portion 33 is not formed in the region of the sipe 32 between the center main groove 10 and the sipe 31. This makes it easier to ensure the durability of the first middle rib 30.

[0050] The slope forming the incision 33 is inclined at an angle of 30° or more, 60° or less, or 40° or more, 50° or less with respect to the profile surface along the contact surface of the tread 2, for example, at the point where the width is maximum. In this case, the function of the incision 33 is performed more effectively. The incision 33 may widen as it approaches the shoulder main groove 12. The incision 33 is formed, for example, within a depth range corresponding to 30% of the depth of the deepest part of the sipe 32 from the contact surface of the tread 2. In this case, running performance can be improved without impairing the durability of the first middle rib 30.

[0051] [2nd Middle Rib 40] The second middle rib 40 is positioned opposite the center rib 20 in the tire axial direction, with the center main groove 11 in between, and opposite the second shoulder rib 60 in the tire axial direction, with the shoulder main groove 13 in between. The width of the second middle rib 40 is, for example, 5% or more and 30% or less of the contact width W. In this embodiment, the width of the second middle rib 40 is formed to be greater than the width of the first middle rib 30.

[0052] The second middle rib 40 has sipes 41 that extend along the circumferential direction of the tire. The sipes 41 are formed straight along the circumferential direction of the tire without curving in the axial direction of the tire. The sipes 41 are formed around the entire circumference of the tire.

[0053] The sipe 41 is formed on the side of the contact end E2 that is closer to the tire axial center of the second middle rib 40. In other words, the width of the region of the second middle rib 40 that is closer to the contact end E2 than the sipe 41 is smaller than the width of the region of the second middle rib 40 that is closer to the tire equator CL than the sipe 41. The width of the region of the second middle rib 40 that is closer to the contact end E1 than the sipe 41 is, for example, 20% or more and less than 50% of the width of the second middle rib 40. The sipe 41 may also be formed in the tire axial center of the second middle rib 40.

[0054] The width of the sipe 41 is, for example, 0.5 mm or more and 1.0 mm or less. The sipe 41 is generally formed to be shallower than the center main groove 11 and the shoulder main groove 13. The depth of the sipe 41 is, for example, 60% or more and 90% or less of the depth of the center main groove 11.

[0055] The second middle rib 40 has sipes 41 that extend along the circumferential direction of the tire, as well as sipes 42 that cross the second middle rib 40. In other words, the sipes 42 are formed from the center main groove 11 to the shoulder main groove 13. The sipes 42 are formed at predetermined intervals in the circumferential direction of the tire.

[0056] The sipe 42 extends along a direction inclined toward one side in the circumferential direction of the tire with respect to the tire axis. The inclination angle of the sipe 42 with respect to the tire axis is, for example, 5° or more and 60° or less, and may be 10° or more and 50° or less. In this embodiment, the inclination angle of the sipe 42 with respect to the tire axis is substantially the same as the inclination angle of the sipe 21 with respect to the tire axis.

[0057] The width of the sipe 42 is, for example, 0.5 mm or more and 1.0 mm or less. The width of the sipe 42 is, for example, approximately the same as the width of the sipe 41. The depth of the sipe 42 is, for example, 60% or more and 90% or less of the depth of the center main groove 11. The sipe 42 may be formed to be shallower than the sipe 41.

[0058] It is preferable that the number of sipes 42 is greater than the number of sipes 21 formed on the center rib 20. In other words, it is preferable that the spacing of the sipes 42 in the tire circumferential direction is smaller than the spacing of the sipes 21 in the tire circumferential direction.

[0059] The second middle rib 40 has an incision 43 formed along the edge of the sipe 42. Similar to the incision 22 described above, the incision 43 is formed to chamfer and widen the edge of the sipe 42 within a predetermined depth range from the contact surface of the tread 2. The incision 43 may be formed on both sides in the width direction of the sipe 42, but in this embodiment, it is formed only on one side in the width direction of the sipe 42. The incision 43 contributes to improving driving performance by, for example, dispersing the contact pressure acting on the edge of the sipe 42.

[0060] The incision 43 is formed on the edge of the sipe 42 in the region between the shoulder main groove 13 and the sipe 41. In other words, the incision 43 is not formed on the edge of the sipe 42 in the region between the center main groove 11 and the sipe 41. This makes it easier to ensure the durability of the second middle rib 40.

[0061] The slope forming the incision 43 is inclined at an angle of 30° or more, 60° or less, or 40° or more, 50° or less with respect to the profile surface along the contact surface of the tread 2, for example, at the point where the width is maximum. In this case, the function of the incision 43 is performed more effectively. The incision 43 may widen as it approaches the shoulder main groove 13. The incision 43 is formed, for example, within a depth range corresponding to 30% of the depth of the deepest part of the sipe 42 from the contact surface of the tread 2. In this case, running performance can be improved without impairing the durability of the second middle rib 40.

[0062] [First shoulder rib 50] The first shoulder rib 50 is positioned opposite the first middle rib 30 in the tire axial direction, with the shoulder main groove 12 in between. The width of the contact surface of the first shoulder rib 50 is, for example, 10% or more and 30% or less of the contact width W.

[0063] The first shoulder rib 50 has multiple slits 51 formed therein, spaced apart in the circumferential direction of the tire, and extending in a direction intersecting the shoulder main groove 12. In this specification, a slit means a groove with a groove width of 2.0 mm or more, and is a groove wider than the sipes described above.

[0064] The slit 51 does not communicate with the shoulder main groove 12, but terminates inside the first shoulder rib 50. Therefore, the area of ​​the contact surface of the first shoulder rib 50 near the shoulder main groove 12 is continuous in the circumferential direction of the tire. This significantly reduces the impact noise when the first shoulder rib 50 makes contact with the road surface. As a result, noise performance can be improved. In other words, if the slit 51 communicates with the shoulder main groove 12, the contact surface of the first shoulder rib 50 becomes discontinuous in the circumferential direction of the tire, increasing the impact noise when the first shoulder rib 50 makes contact with the road surface and worsening noise performance.

[0065] The inner end 51A of the slit 51 in the tire axial direction is positioned further inward in the tire axial direction than the contact end E1. The outer end 51B of the slit 51 in the tire axial direction is positioned further outward in the tire axial direction than the contact end E1. In other words, the slit 51 is formed to straddle the contact end E1.

[0066] The number of slits 51 is, for example, the same as the number of sipes 32 formed on the first middle rib 30. In this embodiment, the slits 51 are formed with a substantially constant width over the entire length of the slit 51. The maximum width of the slit 51 is preferably 2.0 mm or more and 6.0 mm or less, and more preferably 2.5 mm or more and 5.5 mm or less. In this case, drainage performance can be improved while ensuring the durability of the first shoulder rib 50. The slits 51 may narrow inward toward the inner side in the tire axial direction, or widen outward toward the outer side in the tire axial direction. The depth of the slits 51 at its deepest point may be substantially the same as the depth of the shoulder main groove 12, or it may be 60% or more and 95% or less of the depth of the shoulder main groove 12.

[0067] The length of the slit 51 along the tire axial direction from the inner end 51A in the tire axial direction to the outer end 51B in the tire axial direction is preferably, for example, 30% or more and 80% or less of the width of the first shoulder rib 50, and preferably 40% or more and 70% or less.

[0068] Let X1 [mm] be the length along the tire axial direction from the outer end of the shoulder main groove 12 in the tire axial direction to the inner end 51A of the slit 51 in the tire axial direction. Let Y1 [mm] be the length along the tire axial direction from the contact end E1 to the inner end 51A of the slit 51 in the tire axial direction. In this case, the ratio of Y1 [mm] to X1 [mm] (Y1 / X1) is preferably 0.3 or more, more preferably 0.4 or more, and even more preferably 0.5 or more. When the ratio (Y1 / X1) is 0.3 or more, the groove volume of the slit 51 increases, and thus the drainage performance can be improved.

[0069] Furthermore, the ratio of Y1 [mm] to X1 [mm] (Y1 / X1) is preferably 5.0 or less, more preferably 3.0 or less, and even more preferably 2.0 or less. When the ratio (Y1 / X1) is 5.0 or less, a region in which the contact surface of the first shoulder rib 50 is continuous in the tire circumferential direction can be more easily formed near the shoulder main groove 12. This can further improve noise performance. Therefore, the ratio of Y1 [mm] to X1 [mm] (Y1 / X1) is preferably 0.3 or more and 5.0 or less, more preferably 0.4 or more and 3.0 or less, and even more preferably 0.5 or more and 2.0 or less. Furthermore, the ratio of Y1 [mm] to X1 [mm] (Y1 / X1) may be 0.3 or more and 3.0 or less, 0.3 or more and 2.0 or less, 0.4 or more and 5.0 or less, 0.4 or more and 2.0 or less, 0.5 or more and 5.0 or less, or 0.5 or more and 3.0 or less.

[0070] The length X1 [mm] along the tire axial direction from the outer end of the shoulder main groove 13 in the tire axial direction to the inner end 51A of the slit 51 in the tire axial direction is preferably 10 or more and 25 or less, and more preferably 12 or more and 20 or less. In this case, noise performance can be further improved while ensuring drainage performance.

[0071] Furthermore, the length Y1 [mm] along the tire axial direction from the contact end E1 to the inner end 51A of the slit 51 is preferably 15 or more and 30 or less, and more preferably 15 or more and 25 or less. In this case, noise performance can be further improved while ensuring drainage performance.

[0072] The slit 51 extends along a direction inclined with respect to the tire axis. The inclination angle of the slit 51 with respect to the tire axis is, for example, 5° or more and 60° or less, and may be 10° or more and 50° or less. In this embodiment, the inclination angle of the slit 51 with respect to the tire axis is approximately the same as the inclination angle of the sipes 21, 32, and 42 with respect to the tire axis. The slit 51 is inclined in the opposite direction to the sipes 21, 32, and 42 with respect to the tire axis.

[0073] [2nd shoulder rib 60] The second shoulder rib 60 is positioned opposite the second middle rib 40 in the tire axial direction, with the shoulder main groove 13 in between. The width of the contact surface of the second shoulder rib 60 is, for example, 10% or more and 30% or less of the contact width W.

[0074] The second shoulder rib 60 has multiple slits 61 that are spaced apart in the circumferential direction of the tire and extend in a direction intersecting the shoulder main groove 13. The slits 61 have the same shape as the slits 51 formed on the first shoulder rib 50. The number of slits 61 is the same as, for example, the number of sipes 42 formed on the second middle rib 40.

[0075] Like the slit 51, the slit 61 does not communicate with the shoulder main groove 13, but terminates inside the second shoulder rib 60. Therefore, the area of ​​the contact surface of the second shoulder rib 60 near the shoulder main groove 13 is continuous in the circumferential direction of the tire. This significantly reduces the impact noise when the second shoulder rib 60 contacts the road surface. As a result, noise performance can be improved.

[0076] The inner end 61A of the slit 61 in the tire axial direction is positioned further inward in the tire axial direction than the contact end E2. The outer end 61B of the slit 61 in the tire axial direction is positioned further outward in the tire axial direction than the contact end E2. In other words, the slit 61 is formed to straddle the contact end E2.

[0077] The length of the slit 61 along the tire axial direction from the inner end 61A in the tire axial direction to the outer end 61B in the tire axial direction is preferably, for example, 30% or more and 80% or less of the width of the second shoulder rib 60, and preferably 40% or more and 70% or less.

[0078] Let X2 [mm] be the length along the tire axial direction from the outer end of the shoulder main groove 13 in the tire axial direction to the inner end 61A of the slit 61 in the tire axial direction. Also, let Y2 [mm] be the length along the tire axial direction from the contact end E2 to the inner end 61A of the slit 61 in the tire axial direction. In this case, the ratio of Y2 [mm] to X2 [mm] (Y2 / X2) is preferably 0.3 or more, more preferably 0.4 or more, and even more preferably 0.5 or more, similar to the slit 51. When the ratio (Y2 / X2) is 0.3 or more, the groove volume of the slit 61 increases, and thus the drainage performance can be improved.

[0079] Furthermore, the ratio of Y2 [mm] to X2 [mm] (Y2 / X2) is preferably 5.0 or less, more preferably 3.0 or less, and even more preferably 2.0 or less, similar to the slit 51. When the ratio (Y2 / X2) is 5.0 or less, a region in which the contact surface of the second shoulder rib 60 is continuous in the tire circumferential direction can be more easily formed near the shoulder main groove 13. This can further improve noise performance. Therefore, the ratio of Y2 [mm] to X2 [mm] (Y2 / X2) is preferably 0.3 or more and 5.0 or less, more preferably 0.4 or more and 3.0 or less, and even more preferably 0.5 or more and 2.0 or less. Furthermore, the ratio of Y2 [mm] to X2 [mm] (Y2 / X2) may be 0.3 or more and 3.0 or less, 0.3 or more and 2.0 or less, 0.4 or more and 5.0 or less, 0.4 or more and 2.0 or less, 0.5 or more and 5.0 or less, or 0.5 or more and 3.0 or less.

[0080] The length X2 [mm] along the tire axial direction from the outer end of the shoulder main groove 13 in the tire axial direction to the inner end 61A of the slit 61 in the tire axial direction is preferably 10 or more and 25 or less, and more preferably 12 or more and 20 or less, similar to the slit 51. In this case, noise performance can be further improved while ensuring drainage performance.

[0081] Furthermore, the length Y2 [mm] along the tire axial direction from the contact end E2 to the inner end 61A of the slit 61 is preferably 15 or more and 30 or less, and more preferably 15 or more and 25 or less, similar to the slit 51. In this case, noise performance can be further improved while ensuring drainage performance.

[0082] The slit 61 extends along a direction inclined with respect to the tire axis. The inclination angle of the slit 61 with respect to the tire axis is, for example, 5° or more and 60° or less, and may be 10° or more and 50° or less. In this embodiment, the inclination angle of the slit 61 with respect to the tire axis is approximately the same as the inclination angle of the sipes 21, 32, and 42 with respect to the tire axis. In other words, the slit 61 is inclined in the same direction as the sipes 21, 32, and 42 with respect to the tire axis.

[0083] Next, we will explain in detail the shape of the contact surface of the tread 2, referring to Figure 3. Figure 3 is a schematic diagram showing the shape of the contact surface of the tread 2.

[0084] As shown in Figure 3, the contact surface of the tread 2 in this embodiment has a shape close to an ellipse, with the contact length (L2) near the contact edge being relatively shorter than the contact length (L1) on the tire equator CL. Here, the contact length (L1) is the length of the contact surface along the tire circumferential direction on the tire equator CL when an unused pneumatic tire 1 is mounted on a regular rim, with an internal tire pressure of 260 kPa and a load of 520 kg. The contact length (L2) is the length of the contact surface along the tire circumferential direction at a position 10 mm inward from both ends of the contact surface in the tire axial direction, as determined under the above measurement conditions.

[0085] Here, the ratio of L2 to L1 (L2 / L1), which is the rectangularity A of the contact surface of the tread 2, is 0.6 or more and 0.7 or less. In this embodiment, as described above, the slits 51 and 61 do not communicate with the shoulder main grooves 12 and 13, respectively. This improves noise performance. On the other hand, if the slits 51 and 61 do not communicate with the shoulder main grooves 12 and 13, respectively, water on the road surface is less likely to be drained through the slits 51 and 61, and drainage performance tends to decrease. In other words, if the slits 51 and 61 do not communicate with the shoulder main grooves 12 and 13, respectively, it is not possible to improve noise performance while ensuring drainage performance.

[0086] Therefore, the inventors conducted further studies and found that in a tread pattern in which the slits 51 and 61 do not communicate with the shoulder main grooves 12 and 13, respectively, noise performance can be improved while ensuring drainage performance by controlling the rectangularity A of the contact surface of the tread 2 to 0.6 or more and 0.7 or less. By controlling the rectangularity A of the contact surface of the tread 2 to 0.6 or more and 0.7 or less, water on the road surface is effectively diverted to the left and right along the contour of the contact surface of the tread 2, thereby improving drainage performance.

[0087] Here, the rectangularity ratio A of the contact surface of the tread 2 should be between 0.6 and 0.7, but preferably between 0.62 and 0.68. In this case, a higher level of balance between drainage performance and noise performance can be achieved. Note that if the rectangularity ratio A is less than 0.6, handling stability may decrease.

[0088] Furthermore, it is preferable that the length X1 along the tire axial direction from the outer end of the shoulder main groove 12 in the tire axial direction to the inner end 51A of the slit 51 in the tire axial direction, the length X2 along the tire axial direction from the outer end of the shoulder main groove 13 in the tire axial direction to the inner end 61A of the slit 61 in the tire axial direction, and the rectangular ratio A satisfy the following equations (I) and (II). When X1, X2, and A satisfy the following equations (I) and (II), a higher level of balance between drainage performance and noise performance can be achieved. Equation (I) X 1 / (1 - A) ≤ 60 Equation (II) X 2 / (1 - A) ≤ 60

[0089] One method for controlling the rectangularity A of the contact surface of the tread 2 is to adjust the angle (belt angle) of the cords constituting the belt plies 7A and 7B with respect to the tire circumferential direction. Specifically, by setting the angle (belt angle) of the cords constituting the belt plies 7A and 7B with respect to the tire circumferential direction to 22° or more and 30° or less, it becomes easy to control the rectangularity A of the contact surface of the tread 2 to 0.6 or more and 0.7 or less.

[0090] Another method for controlling the rectangularity ratio A of the contact surface of the tread 2 is to adjust the axial length of the belt 7. By increasing the axial length of the belt 7 and thereby increasing the restraining force acting on the outer side of the belt 7 in the axial direction, the rectangularity ratio A can be reduced. Alternatively, the restraining force acting on the outer side of the belt 7 in the axial direction can be increased by providing a reinforcing layer (e.g., an edge ply) on the outer side of the belt 7 in the axial direction to reinforce the strength of the belt 7. [Examples]

[0091] The present invention will be further explained below with reference to experimental examples, but the present invention is not limited to these experimental examples.

[0092] <Example 1> A pneumatic tire (tire size: 235 / 50R20 104V) with the tread pattern shown in Figure 2 was manufactured. The lengths X1, X2, Y1, Y2, and belt angle were manufactured to the values ​​shown in Table 1. When the manufactured pneumatic tire was mounted on a standard rim, with an internal tire pressure of 260 kPa and a load of 520 kg, the rectangularity A of the contact surface of tread 2 was 0.675. The shape of the tread pattern is as follows.

[0093] Ground contact width W: 180mm Total length of slits 51 and 61: 31 mm Groove width for slits 51 and 61: 3.3-5.4 mm

[0094] <Examples 2-4, Comparative Examples 1-5> The tires were manufactured in the same manner as the pneumatic tire in Example 1, except that the lengths X1, X2, Y1, Y2, and belt angle were made to the values ​​shown in Table 1. The values ​​of the rectangle ratio A for each pneumatic tire are as shown in Table 1.

[0095] [Evaluation of noise performance] Each of the fabricated pneumatic tires was mounted on a test vehicle, and a microphone was placed at ear level in the driver's seat inside the vehicle. The sound pressure was measured while driving on a dry, flat asphalt road at 80 km / h. The evaluation results are relative values ​​with the evaluation result of Comparative Example 1 set to 100. A higher value indicates a greater pattern noise reduction effect and superior noise performance.

[0096] [Evaluation of drainage performance] Each pneumatic tire was rotated on a wet road surface with a water depth of 8 mm, and the speed at which hydroplaning occurred was measured. The evaluation results are relative values ​​with the evaluation result of Comparative Example 1 set to 100. A larger value indicates a higher speed at which hydroplaning occurs and superior drainage performance. Tire mounting conditions: Air pressure: 260kPa, Load: 520kgf (single wheel)

[0097] Furthermore, if pneumatic tires have poor drainage, they may not be able to remove water from the contact area with the road surface in time while driving. The remaining water forms a water film between the road surface and the tire tread, causing the tire to lose contact with the road surface and leading to hydroplaning. Therefore, the speed at which hydroplaning occurs was measured as an indicator of drainage performance.

[0098] Table 1 shows the evaluation results for the noise performance and drainage performance of each pneumatic tire. Table 1 also shows the lengths X1, X2, Y1, Y2, belt angle, and rectangle ratio A for each pneumatic tire.

[0099] [Table 1]

[0100] As shown in Table 1, the pneumatic tires of the embodiments improve noise performance while maintaining drainage performance. Furthermore, the pneumatic tires of embodiments 1, 3, and 4, which satisfy X1 / (1-A)≦60 and X2 / (1-A)≦60, have improved drainage performance compared to the pneumatic tire of embodiment 2, which does not satisfy X1 / (1-A)≦60 and X2 / (1-A)≦60.

[0101] On the other hand, even when the slits 51 and 61 do not communicate with the shoulder main grooves 12 and 13 respectively, the pneumatic tires of Comparative Examples 2 and 3, where the rectangular ratio A is not 0.6 or greater and 0.7 or less, show reduced drainage performance. Furthermore, even when the rectangular ratio A is 0.6 or greater and 0.7 or less, the pneumatic tires of Comparative Examples 4 and 5, where the slits 51 and 61 communicate with the shoulder main grooves 12 and 13 respectively, do not show improved noise performance.

[0102] Based on the above results, it can be said that in a tread pattern where the slits 51 and 61 do not communicate with the shoulder main grooves 12 and 13, respectively, noise performance can be improved while ensuring drainage performance by controlling the rectangularity A of the contact surface of the tread 2 to 0.6 or more and 0.7 or less. [Explanation of symbols]

[0103] 1 pneumatic tire, 2 tread, 3 sidewall, 4 bead, 4A bead core, 4B bead filler, 5 carcass, 6 inner liner, 7 belt, 7A, 7B belt ply, 8 cap ply, 10, 11 center main groove, 12, 13 shoulder main groove, 20 center rib, 21 sipe, 22 cut section, 30 first middle rib, 31, 32 sipe, 33 cut section, 40 second middle rib, 41, 42 sipe, 43 cut section, 50 first shoulder rib (shoulder rib), 51, 61 slit, 51A, 61A inner end of tire axial direction, 51B, 61B outer end of tire axial direction, 60 second shoulder rib (shoulder rib), A rectangular ratio, CL tire equator, W contact width, E1, E2 contact edge.

Claims

1. A pneumatic tire with a tread, The tread has a pair of shoulder main grooves and shoulder ribs positioned outward from the shoulder main grooves in the tire axial direction, The shoulder rib is provided with a slit that extends in a direction intersecting the shoulder main groove and terminates inside the shoulder rib. The inner end of the slit in the tire axial direction is positioned inward in the tire axial direction from the contact edge of the tread. A pneumatic tire in which the rectangularity A of the contact surface of the tread is 0.6 or more and 0.7 or less.

2. The pneumatic tire according to claim 1, wherein the length along the tire axis from the outer end of the shoulder main groove in the tire axis direction to the inner end of the slit in the tire axis direction is X [mm], and the length along the tire axis direction from the contact end of the tread to the inner end of the slit in the tire axis direction is Y [mm], and the ratio of Y [mm] to X [mm] (Y / X) is 0.3 or more and 5.0 or less.

3. The pneumatic tire according to claim 2, wherein the ratio of Y [mm] to X [mm] (Y / X) is 0.3 or more and 2.0 or less.

4. The pneumatic tire according to claim 1, wherein the length X [mm] and the rectangle ratio A satisfy the relationship expressed by the following formula. Formula: X / (1-A)≦60

5. The pneumatic tire according to claim 1, wherein the length X [mm] along the tire axis from the outer end of the shoulder main groove in the tire axis direction to the inner end of the slit in the tire axis direction is 10 or more and 25 or less.

6. The pneumatic tire according to claim 1, wherein the length Y [mm] along the tire axis from the contact end of the tread to the inner end of the slit in the tire axis direction is 15 or more and 30 or less.

7. The pneumatic tire according to claim 1, wherein the maximum width of the slit is 2.0 mm or more and 6.0 mm or less.

8. Carcass and, A belt having at least one belt ply arranged on the radially outer side of the carcass, with the cords arranged inclined with respect to the circumferential direction of the tire, Furthermore, The pneumatic tire according to claim 1, wherein the angle of the cord with respect to the circumferential direction of the tire is 22° or more and 30° or less.

9. The pneumatic tire according to claim 8, wherein the angle of the cord with respect to the circumferential direction of the tire is 24° or more and 28° or less.

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