pneumatic tires

Abstract

To improve noise performance while maintaining snow performance. [Solution] A pneumatic tire equipped with a tread 10, wherein the tread 10 has a pair of shoulder main grooves 23, 24 and shoulder land portions 60, 70 positioned outward in the tire axial direction from the shoulder main grooves 23, 24, and the shoulder land portions 60, 70 are provided with shoulder sub-grooves 61 extending along the tire circumferential direction and having a width smaller than the shoulder main grooves 23, 24, and shoulder slits 62 extending outward in the tire axial direction from the shoulder sub-grooves 61.

Description

Technical Field

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

Background Art

[0002] Conventionally, a pneumatic tire having a tread including a pair of shoulder main grooves extending along the tire circumferential direction and a shoulder land portion disposed axially outside the tire than the shoulder main grooves is known (see, for example, Patent Document 1). Patent Document 1 discloses a pneumatic tire in which a slit extending inward in the tire axial direction is formed in the shoulder land portion.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, tires with excellent noise performance have been demanded. Generally, by reducing the groove volume such as main grooves and slits provided in the tread, the noise during running can be reduced. On the other hand, when the groove volume becomes small, the snow column shearing force for grasping and compacting snow during running on a snow-covered road surface decreases, and the handling stability on a snow-covered road surface (hereinafter referred to as "snow performance") tends to decrease. That is, it is not easy to improve the noise performance while ensuring the snow 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 a shoulder land portion positioned outward in the tire axial direction from the shoulder main grooves, and the shoulder land portion is provided with shoulder sub-grooves extending along the tire circumferential direction and having a width smaller than the shoulder main grooves, and shoulder slits extending outward in the tire axial direction from the shoulder sub-grooves. [Effects of the Invention]

[0006] According to one aspect of the present invention, a pneumatic tire can improve noise performance while ensuring snow 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 figure shows an enlarged view of the shoulder portion of the tread of a pneumatic tire, which is an example of an embodiment. [Figure 4] This is a cross-sectional view along line AA in Figure 3. [Figure 5] This figure schematically shows the shape of the contact surface of the tread of a pneumatic tire, which is an example of an embodiment. [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 each component of the embodiments described below are included in the present invention.

[0009] Figure 1 is a cross-sectional view of a pneumatic tire 1, which is an example of an embodiment. As shown in Figure 1, the pneumatic tire 1 comprises a tread 10, which is the portion that contacts the road surface, a pair of sidewalls 11 arranged on both sides of the tread 10, and a pair of beads 13 arranged radially inward of the sidewalls 11. The pneumatic tire 1 also comprises a carcass 14 that spans between the pair of beads 13, and an inner liner 15 arranged radially inward of the carcass 14. The pneumatic tire 1 performs well not only on dry roads but also on wet roads and snowy / icy roads, making it suitable as an all-season tire.

[0010] In this embodiment, the pneumatic tire 1 is a point-symmetric tire in which there is no specified mounting direction to the vehicle, and the tread pattern and the shape of the tire sidewall do not change regardless of the direction in which it is mounted on the vehicle. In other words, the tread pattern and the shape of the tire sidewall of the pneumatic tire 1 are the same as the shape rotated 180° on either side of the tire equator CL. Here, the tire equator CL is a virtual line along the tire circumferential direction that passes through the center of the tread 10 in the tire axial direction.

[0011] The tread 10 is provided with a pair of center main grooves 21, 22 extending along the tire circumferential direction, and a pair of shoulder main grooves 23, 24 located axially outward from the center main grooves 21, 22 and extending along the tire circumferential direction. The four main grooves are formed straight along the tire circumferential direction without curving in the tire axial direction.

[0012] Furthermore, the tread 10 is provided with a center land area 30, which is divided by a pair of center main grooves 21 and 22 and formed on the tire equator CL; a first middle land area 40, which is divided by the center main groove 21 and the shoulder main groove 23; and a second middle land area 50, which is divided by the center main groove 22 and the shoulder main groove 24. The tread 10 is also provided with a first shoulder land area 60, which is positioned opposite the first middle land area 40 in the tire axial direction with the shoulder main groove 23 in between; and a second shoulder land area 70, which is positioned opposite the second middle land area 50 in the tire axial direction with the shoulder main groove 24 in between. The first shoulder land area 60 and the second shoulder land area 70 are formed beyond the contact edges E1 and E2. Note that the land area is a portion that rises outward in the tire radial direction from a position corresponding to the bottom of the main groove.

[0013] Here, the contact points E1 and E2 of the pneumatic tire 1 are defined as the axial ends of the area (contact surface) that touches a flat road surface when a predetermined load is applied to an unused tire mounted on a standard rim and inflated to the standard internal pressure. The predetermined load is equivalent to 88% of the standard load.

[0014] Note that "standard rim" refers to the rim defined by the tire standard, which is "standard rim" for JATMA and "Measuring Rim" for TRA and ETRTO. Also, "standard internal pressure" is "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. The standard internal pressure is usually 180kPa for passenger car tires, but it is 220kPa for tires marked Extra Load or Reinforced. "Standard load" is "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.

[0015] As will be described in more detail later, the contact surface of the tread 10 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 10 is close to an ellipse shape. Specifically, the rectangularity of the contact surface of the tread 10 is designed to be between 0.55 and 0.65.

[0016] The sidewalls 11 are positioned on both sides of the tread 10 and are provided in an annular shape along the circumferential direction of the tire. The sidewalls 11 are the parts of the pneumatic tire 1 that protrude most outward in the axial direction of the tire and are gently curved so as to be convex outward in the axial direction of the tire. The sidewalls 11 have the function of preventing damage to the carcass 14. The sidewalls 11 are the parts that flex the most when the pneumatic tire 1 acts as a cushion, and are usually made of flexible rubber with fatigue resistance.

[0017] The pneumatic tire 1 may have side ribs 12 between the contact edges E1, E2 of the tread 10 and the part of the sidewall 11 that protrudes most outward in the tire axial direction. The side ribs 12 protrude outward in the tire axial direction and are arranged in an annular shape along the tire circumferential direction. The portion of the pneumatic tire 1 from the contact edges E1, E2 or their vicinity to the left and right side ribs 12 is also called the buttress region.

[0018] Additionally, the sidewall 11 typically features letters, numbers, and symbols known as serial numbers. These serial numbers may include information such as the size code, manufacturing date (year and week), and manufacturing location (factory code).

[0019] The bead 13 is disposed on the inner side in the tire radial direction of the sidewall 11 and is a portion fixed to the rim of the wheel. The bead 13 has a bead core 16 and a bead filler 17. The bead core 16 is composed of a steel bead wire and is an annular member extending over the entire circumference in the tire circumferential direction, and is embedded in the bead 13. The bead filler 17 has a tip-tapering shape extending outward in the tire radial direction and is an annular rigid rubber member extending over the entire circumference in the tire circumferential direction.

[0020] The carcass 14 is spanned between a pair of beads 13 and is locked by being folded around the bead core 16. The carcass 14 includes a carcass cord made of organic fiber and topping rubber. The carcass cord is disposed substantially perpendicular (for example, 80° or more and 90° or less) to the tire circumferential direction. Examples of the organic fiber used for the carcass cord include polyester fiber, rayon fiber, aramid fiber, and nylon fiber.

[0021] The inner liner 15 covers the inner surface of the tire between a pair of beads 13. The inner liner 15 is composed of air permeation resistant rubber and has a function of holding the air pressure of the pneumatic tire 1.

[0022] Further, the pneumatic tire 1 further includes a belt 18 disposed on the outer side in the tire radial direction of the carcass 14 and a cap ply 19 covering the outer side in the tire radial direction of the belt 18. The cap ply 19 has a function of reinforcing the belt 18. The number of the cap plies 19 may be one or two or more.

[0023] The belt 18 is disposed on the outer side in the tire radial direction at the top of the carcass 14 and is provided so as to overlap the outer peripheral surface of the carcass 14. The belt 18 is formed of a belt ply in which cords arranged in a direction inclined with respect to the tire circumferential direction are rubber-coated. 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.

[0024] In this embodiment, the belt 18 is composed of two belt plies 18A and 18B. The cords constituting the two belt plies 18A and 18B are arranged to cross each other between the two belt plies 18A and 18B.

[0025] Here, it is preferable that the angle (belt angle) of the cords constituting the two belt plies 18A and 18B with respect to the tire circumferential direction is 22° or more and 26° or less. When the angle of the cords with respect to the tire circumferential direction is within the above range, the restraining force acting on the belt 18 outward in the tire axial direction increases, the shape of the contact surface of the tread 10 becomes curved, and it becomes easier to control the rectangular ratio of the contact surface of the tread 10 to 0.55 or more and 0.65 or less.

[0026] Next, the tread pattern of the pneumatic tire 1 will be described with reference to Figure 2. Figure 2 is a plan view of the pneumatic tire 1 (tread 10).

[0027] The tread 10 has a pair of center main grooves 21 and 22, and a pair of shoulder main grooves 23 and 24 formed further outward in the tire axial direction than the center main grooves 21 and 22. The center main groove 21 and shoulder main groove 23 are formed in a region on the contact edge E1 side of the tire equator CL, while the center main groove 22 and shoulder main groove 24 are formed in a region on the contact edge E2 side of the tire equator CL. In this embodiment, the center main grooves 21 and 22 have the same shape, and the shoulder main grooves 23 and 24 have the same shape. Note that the number of main grooves is not limited to four, and may be three or fewer, or five or more.

[0028] The center main grooves 21, 22 and the shoulder main grooves 23, 24 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 21, 22 and the shoulder main grooves 23, 24, improving drainage performance.

[0029] In this embodiment, the width of the shoulder main grooves 23 and 24 is smaller than the width of the center main grooves 21 and 22. Since the shoulder main grooves 23 and 24 are located outward in the tire axial direction compared to the center main grooves 21 and 22, the shape of the shoulder main grooves 23 and 24 greatly affects noise during driving. Therefore, by making the width of the shoulder main grooves 23 and 24 smaller than the width of the center main grooves 21 and 22, the volume of the shoulder main grooves 23 and 24 is reduced, and the air column resonance noise caused by the shoulder main grooves 23 and 24 is reduced. As a result, noise performance can be improved.

[0030] The width of each of the shoulder main grooves 23 and 24 is preferably 6% or less, and more preferably 5% or less, of the length W along the tire axial direction from the contact end E1 to the contact end E2 (hereinafter referred to as "contact width W"). When the width of the shoulder main grooves 23 and 24 is 6% or less of the contact width W, the air column resonance noise caused by the shoulder main grooves 23 and 24 is further reduced, and the noise performance can be further improved. The lower limit of the width of the shoulder main grooves 23 and 24 is, for example, 3% of the contact width W. When the width of the shoulder main grooves 23 and 24 is 3% or more of the contact width W, snow or water can easily enter the shoulder main grooves 23 and 24, and the snow performance and drainage performance can be improved. 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 10.

[0031] The sum of the widths of the four main grooves is preferably, for example, 12% or more of the ground width W, and preferably 15% or more. In this case, for example, snow performance and drainage performance can be improved. Alternatively, the sum of the widths of the four main grooves is preferably, for example, 25% or less of the ground width W, and preferably 22% or less. In this case, air column resonance noise caused by the main grooves is reduced, and noise performance can be improved. Therefore, the sum of the widths of the four main grooves is preferably, for example, 12% or more and 25% or less of the ground width W, and preferably 15% or more and 22% or less.

[0032] Furthermore, in this embodiment, the depth of the shoulder main grooves 23 and 24 is smaller than the depth of the center main grooves 21 and 22. Therefore, the cross-sectional area of ​​the shoulder main grooves 23 and 24 is smaller than the cross-sectional area of ​​the center main grooves 21 and 22. As described above, the shape of the shoulder main grooves 23 and 24 has a significant impact on noise during driving. Therefore, by making the depth of the shoulder main grooves 23 and 24 smaller than the depth of the center main grooves 21 and 22, the volume of the shoulder main grooves 23 and 24 is reduced, and the air column resonance noise caused by the shoulder main grooves 23 and 24 is reduced. As a result, noise performance can be improved.

[0033] The depth of the center main grooves 21 and 22 is, for example, 7 mm or more and 10 mm or less, and the depth of the shoulder main grooves 23 and 24 is, for example, 6 mm or more and 9 mm or less. In this specification, unless otherwise specified, groove depth refers to the length along the tire radial direction from the profile surface along the contact surface of the tread 10 to the deepest part of the groove.

[0034] The tread 10 is provided with a center land area 30 defined by center main grooves 21 and 22, a first middle land area 40 defined by the center main groove 21 and shoulder main groove 23, and a second middle land area 50 defined by the center main groove 22 and shoulder main groove 24. The tread 10 is also provided with a first shoulder land area 60 positioned opposite the first middle land area 40 in the tire axial direction, with the shoulder main groove 23 in between, and a second shoulder land area 70 positioned opposite the second middle land area 50 in the tire axial direction, with the shoulder main groove 24 in between. The center land area 30, the first middle land area 40, the second middle land area 50, the first shoulder land area 60, and the second shoulder land area 70 are formed continuously in the tire circumferential direction.

[0035] As described above, the pneumatic tire 1 is a point-symmetric tire in which there is no specified mounting direction on the vehicle, and the tread pattern and the shape of the tire sidewall do not change regardless of the direction in which it is mounted on the vehicle. Therefore, the shape of the second middle section 50 is the same as the shape obtained by rotating the first middle section 40 around any point on the tire equator CL, and the shape of the second shoulder section 70 is the same as the shape obtained by rotating the first shoulder section 60 around any point on the tire equator CL. For this reason, the center section 30, the first middle section 40, and the first shoulder section 60 will be described below, and the descriptions of the second middle section 50 and the second shoulder section 70 will be omitted. Also, as shown in Figure 2 below, the first direction in the circumferential direction of the tire may be referred to as the "Y1 direction" and the second direction as the "Y2 direction".

[0036] [Center Track and Field Club 30] The center land portion 30 is formed on the tire equator CL. In this embodiment, the axial center of the center land portion 30 is positioned on the tire equator CL. The width of the center land portion 30 is, for example, 5% or more and 30% or less of the contact width W.

[0037] The center land portion 30 has center slits 31 formed at intervals in the tire circumferential direction, each communicating with the respective center main grooves 21 and 22. The center slits 31 have, for example, a substantially uniform width along their length. In this specification, a slit means a groove with a width of 1.5 mm or more. The width of the center slits 31 is, for example, 2 mm or more and 5 mm or less.

[0038] The center slit 31 has a roughly S-shape in a plan view of the center land portion 30. Specifically, the center slit 31 has a bent portion 31A that protrudes to one side in the tire circumferential direction from the positions of both ends of the center slit 31 in the tire circumferential direction in a plan view of the center land portion 30. When the center slit 31 has a bent portion 31A, it becomes easier to secure groove volume and improve snow performance. In this embodiment, the bent portions 31A are formed on both sides in the longitudinal direction of the center slit 31.

[0039] The end of the center slit 31 on the side of the center main groove 21 overlaps in the circumferential direction of the tire with the position of the middle slit 41, which will be described later and formed in the first middle land portion 40, when extended to the center main groove 21. In this case, pattern noise can be reduced and noise performance can be improved.

[0040] Center sipes 32 and 33 are formed in the center land portion 30. Center sipe 32 communicates with the center main groove 21 and is formed toward the inside of the center land portion 30, but does not communicate with the center main groove 22. On the other hand, center sipe 33 communicates with the center main groove 22 and is formed toward the inside of the center land portion 30, but does not communicate with the center main groove 21. By having center sipes 32 and 33 communicate with only one of the main grooves, the rigidity of the center land portion 30 is ensured, which, for example, makes it easier to improve steering stability. In this specification, a sipe means a groove with a width of less than 1.5 mm.

[0041] The center sipes 32 and 33 are formed one by one between two adjacent center slits 31 in the circumferential direction of the tire. In other words, slits and sipes are repeatedly formed in the order of center slit 31, center sipe 32, and center sipe 33, toward the Y1 direction in the circumferential direction of the tire.

[0042] In this embodiment, the center sipe 32 extends in a direction inclined toward one side of the tire circumferential direction (Y1 direction in Figure 2) relative to the tire axial direction, except for the vicinity of the portion communicating with the center main groove 21. The center sipe 33 extends in a direction inclined toward the other side of the tire circumferential direction (Y2 direction in Figure 2) relative to the tire axial direction, except for the vicinity of the portion communicating with the center main groove 22. The end of the center sipe 32 on the center main groove 22 side and the end of the center sipe 33 on the center main groove 21 side are positioned to overlap in the tire circumferential direction.

[0043] The inclination angle of the center sipe 32 with respect to the tire axis is the same as the inclination angle of the center sipe 33 with respect to the tire axis. The inclination angles of the center sipes 32 and 33 with respect to the tire axis are, for example, 10° or more and 70° or less, and may also be 20° or more and 60° or less.

[0044] The axial lengths of the center sipes 32 and 33 are the same. The axial lengths of the center sipes 32 and 33 are, for example, 50% or more and 90% or less of the width of the center foot section 30. In this specification, the axial length of a sipe (including grooves) means the length along the axial direction of the tire between the axial ends of the sipe (groove).

[0045] [1st Middle Track and Field Club 40] The first middle land section 40 is positioned opposite the center land section 30 in the tire axial direction, with the center main groove 21 in between, and opposite the first shoulder land section 60 in the tire axial direction, with the shoulder main groove 23 in between. The width of the first middle land section 40 is, for example, 5% or more and 30% or less of the contact width W. In this embodiment, the width of the first middle land section 40 is smaller than the width of the center land section 30.

[0046] Middle slits 41 are formed in the first middle section 40 at intervals in the circumferential direction of the tire. The middle slits 41 communicate with the shoulder main groove 23, are formed toward the inside of the first middle section 40, and do not communicate with the center main groove 21. The middle slits 41 have, for example, a substantially uniform width along their length. The width of the center slit 31 is, for example, 2 mm or more and 5 mm or less.

[0047] The middle slit 41 extends along a direction inclined toward the Y2 direction with respect to the tire axis, except in the vicinity of the portion communicating with the shoulder main groove 23. The inclination angle of the middle slit 41 with respect to the tire axis is, for example, 10° or more and 70° or less, and may be 20° or more and 60° or less. In this embodiment, the inclination angle of the middle slit 41 with respect to the tire axis is substantially the same as the inclination angle of the center sipes 32 and 33 formed on the center land portion 30 with respect to the tire axis.

[0048] As described above, the middle slit 41 is not in communication with the center main groove 21. This improves the rigidity of the first middle section 40 on the inner side in the tire axial direction. As a result, for example, handling stability is improved. The axial length of the first middle section 40 is, for example, 50% or more and 90% or less of the width of the first middle section 40.

[0049] The end of the middle slit 41 on the shoulder main groove 23 side (outer side in the tire axial direction) faces the communicating sipe 63, which will be described later, via the shoulder main groove 23. In this case, pattern noise can be reduced and noise performance can be improved.

[0050] The middle slit 41 has a bent portion 41A that, in a plan view of the first middle land portion 40, protrudes to one side in the tire circumferential direction from the positions of both ends of the middle slit 41 in the tire circumferential direction. When the middle slit 41 has a bent portion 41A, it becomes easier to secure groove volume and snow performance is improved.

[0051] The first middle section 40 has middle sipes 42 that communicate with the center main groove 21 and the shoulder main groove 23, respectively. Two middle sipes 42 are formed between two adjacent middle slits 41 in the circumferential direction of the tire. In other words, slits and sipes are repeatedly formed in the order of middle slit 41, middle sipe 42, middle sipe 42, toward the Y1 direction in the circumferential direction of the tire.

[0052] The middle sipe 42, like the center slit 31, has a roughly S-shape in a plan view of the first middle ground portion 40. Specifically, the middle sipe 42 has a bent portion that, in a plan view of the first middle ground portion 40, protrudes to one side in the tire circumferential direction from the positions of both ends of the middle sipe 42 in the tire circumferential direction. When the middle sipe 42 has the above shape, the strain applied to the middle sipe 42 during driving is distributed, and the ground pressure of the first middle ground portion 40 is distributed. As a result, for example, steering stability is improved. In this embodiment, the bent portion is formed on both sides in the longitudinal direction of the middle sipe 42.

[0053] [Shoulder 1 Track and Field Club 60] Next, the first shoulder land portion 60 will be described with further reference to Figure 3. Figure 3 is a magnified view of the vicinity of the first shoulder land portion 60 in Figure 2.

[0054] As shown in Figures 2 and 3, the first shoulder land portion 60 is positioned opposite the first middle land portion 40 in the tire axial direction, with the shoulder main groove 23 in between. The width of the contact surface of the first shoulder land portion 60 is, for example, 10% or more and 30% or less of the contact width W.

[0055] The first shoulder land portion 60 has a shoulder sub-groove 61 that extends along the circumferential direction of the tire and is narrower than the shoulder main groove 23, and a shoulder slit 62 that extends from the shoulder sub-groove 61 outward in the tire axial direction. In addition, the first shoulder land portion 60 has a communicating sipe 63 that faces the shoulder slit 62 via the shoulder sub-groove 61 and communicates with the shoulder main groove 23.

[0056] The shape of the shoulder slit 62 greatly affects the pattern noise generated when the tread 10 makes contact with the road surface. Specifically, the larger the volume of the shoulder slit 62 that makes contact with the road surface, the greater the pattern noise tends to be, and the lower the noise performance tends to be. By not connecting the shoulder slit 62 to the shoulder main groove 23, as in this embodiment, the axial length of the shoulder slit 62 in the tire is reduced. As a result, the volume of the shoulder slit 62 that makes contact with the road surface is reduced, and pattern noise can be reduced.

[0057] On the other hand, if the axial length of the shoulder slit 62 in the tire becomes smaller and the volume of the shoulder slit 62 decreases, snow will have difficulty entering the shoulder slit 62 when driving on snowy roads, reducing the snow column shear force that grips and compacts the snow, and tending to worsen snow performance.

[0058] Therefore, as in this embodiment, by providing a shoulder sub-groove 61 extending along the tire circumferential direction on the first shoulder land portion 60, the shoulder sub-groove 61 grips and compacts the snow when driving on a snowy road surface. This increases the snow column shear force and improves snow performance.

[0059] The shoulder sub-grooves 61 extend in the circumferential direction of the tire and have a uniform width over the entire circumference. The width of the shoulder sub-grooves 61 is preferably 0.7% or more of the contact width W of the tread 10, and more preferably 0.8% or more. By setting the width of the shoulder sub-grooves 61 to 0.7% or more of the contact width W of the tread 10, the snow column shear force can be increased, and snow performance can be further improved. Furthermore, the width of the shoulder sub-grooves 61 is preferably 2.0% or less of the contact width W of the tread 10, and more preferably 1.8% or less. By setting the width of the shoulder sub-grooves 61 to 2.0% or less of the contact width W of the tread 10, pattern noise caused by the shoulder sub-grooves 61 can be reduced, and noise performance can be ensured. Therefore, the width of the shoulder sub-grooves 61 is preferably 0.7% or more and 2.0% or less and more and more preferably 0.8% or more and 1.8% or less of the contact width W of the tread 10.

[0060] The shoulder sub-groove 61 is formed at a position a predetermined length away from the inner end of the first shoulder land portion 60 in the tire axial direction, and further outward in the tire axial direction. Specifically, the width (L, see Figure 3) of the area of ​​the first shoulder land portion 60 demarcated by the shoulder main groove 23 and the shoulder sub-groove 61 is preferably 4% or more and 8% or less of the contact width W of the tread 10, and more preferably 5% or more and 7% or less of the contact width W of the tread 10. By setting the width (L) of this area within the above range, the axial length of the shoulder slit 62 can be controlled within a predetermined range, thereby further improving noise performance and snow performance. In other words, if the width (L) of this area is less than 4% of the contact width W of the tread 10, the axial length of the shoulder slit 62 becomes larger, and pattern noise is more likely to occur. Furthermore, if the width (L) of the area in question exceeds 8% of the contact width W of the tread 10, the axial length of the shoulder slit 62 becomes excessively short, which can reduce the snow column shear force generated in the shoulder slit 62 and degrade snow performance.

[0061] The depth of the shoulder sub-groove 61 is smaller than the depth of the shoulder main groove 23, for example, between 2 mm and 6 mm. When the depth of the shoulder sub-groove 61 is within the above range, snow performance can be further improved while ensuring noise performance.

[0062] The shoulder slits 62 extend outward in the tire axial direction from the shoulder sub-groove 61 and are formed in multiple locations spaced apart in the tire circumferential direction. The shoulder slits 62 extend outward in the tire axial direction beyond the contact end E1. The shoulder slits 62 have, for example, a substantially uniform groove width along their length. The width of the shoulder slits 62 may be greater than that of the center slit 31 and the middle slit 41, for example, between 2.5 mm and 6 mm.

[0063] The depth of the shoulder slit 62 is preferably greater than the depth of the shoulder sub-groove 61, except for the raised portion 62A described later. The depth of the shoulder slit 62 is, for example, 4 mm or more and 9 mm or less. When the depth of the shoulder slit 62 is within the above range, noise performance and snow performance can be further improved.

[0064] Furthermore, the shoulder slit 62 communicates with the shoulder sub-groove 61, which allows air within the groove to flow more easily outward in the axial direction of the tire. As a result, pattern noise is reduced, and noise performance is further improved.

[0065] Figure 4 is a cross-sectional view of line AA in Figure 3, showing the shape of the groove bottom of the shoulder slit 62. As shown in Figure 4, the shoulder slit 62 may have a raised portion 62A in the groove bottom that rises outward in the radial direction of the tire, near the portion that communicates with the shoulder sub-groove 61. By providing the raised portion 62A, the rigidity of the first shoulder land portion 60 is improved. As a result, for example, steering stability can be improved. The axial length of the raised portion 62A in the tire axis direction is, for example, 3% or more and 20% or less of the width of the contact surface of the first shoulder land portion 60, and may be 5% or more and 10% or less. Also, the depth of the shoulder slit 62 in the raised portion 62A is, for example, 2 mm or more and 6 mm or less. Note that the shoulder slit 62 does not have to have a raised portion 62A.

[0066] As shown in Figure 3, the communicating sipe 63 faces the shoulder slit 62 via the shoulder sub-groove 61 and communicates with the shoulder sub-groove 61 and the shoulder main groove 23. As a result of our investigation, it has become clear that by providing the communicating sipe 63 at a position facing the shoulder slit 62 via the shoulder sub-groove 61, pattern noise can be reduced and noise performance can be improved.

[0067] The connecting sipe 63 has, for example, a substantially uniform width along its length. The width of the connecting sipe 63 is, for example, 0.5 mm or more and 1.0 mm or less. The depth of the connecting sipe 63 is, for example, 2 mm or more and 8 mm or less. In this embodiment, the connecting sipe 63 is provided in a position facing all of the shoulder slits 62 via the shoulder sub-grooves 61.

[0068] Furthermore, shoulder sipes 64 are formed on the first shoulder land portion 60, extending outward in the tire axial direction from the shoulder sub-grooves 61. Two shoulder sipes 64 are formed between two adjacent shoulder slits 62 in the tire circumferential direction. In other words, slits and sipes are repeatedly formed in the order of shoulder slits 62, shoulder sipes 64, and shoulder sipes 64 toward the Y1 direction in the tire circumferential direction. The shoulder sipes 64 are formed beyond the contact end E1 toward the tire axial direction and are shorter than the shoulder slits 62. By providing shoulder sipes 64, grip with the road surface is improved when driving on snowy roads, and snow performance is improved.

[0069] Next, the shape of the contact surface of the tread 10 will be explained in detail with reference to Figure 5. Figure 5 is a schematic diagram showing the shape of the contact surface of the tread 10.

[0070] As shown in Figure 5, the contact surface of the tread 10 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 is mounted on a regular rim, with an internal tire pressure of 240 kPa and a load of 510 kgf. 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.

[0071] In this specification, L2 / L1 is defined as the ratio of the rectangularity of the contact surface of the tread 10. In this embodiment, the contact length (L2) is substantially the same on both the left and right sides of the tread 10. As described above, the smaller the ratio of rectangularity, the closer the shape of the contact surface of the tread 10 becomes to an elliptical shape. Therefore, the smaller the ratio of rectangularity, the more the frequencies of the air column resonance sound generated in the center main grooves 21, 22 and the shoulder main grooves 23, 24 are dispersed. As a result, noise caused by air column resonance sound is reduced, and noise performance is improved.

[0072] Furthermore, as the squareness ratio decreases, the contact area on the outer side of the tire's axial direction decreases, thus reducing the volume of the shoulder slit 62 that contacts the road surface when the tread 10 makes contact with the road surface. As a result, pattern noise can be reduced. In addition, a smaller squareness ratio tends to distribute the contact pressure more evenly. Therefore, the impact noise when the tread 10 hits the road surface is reduced, improving noise performance.

[0073] Furthermore, during driving, water on the road surface tends to be pushed to the left and right along the contour of the contact patch of the tread 10. Therefore, the smaller the rectangular aspect ratio, the easier it is for water on the road surface to be pushed to the left and right, improving drainage performance.

[0074] On the other hand, reducing the rectangularity ratio makes it more difficult for snow to enter the main grooves and slits, which tends to reduce snow performance. However, in this embodiment, as described above, shoulder sub-grooves 61 are formed on the shoulder land portion. As a result, even when the rectangularity ratio is reduced, the shoulder sub-grooves 61 grip the snow, ensuring snow performance.

[0075] From the viewpoint of improving noise performance while ensuring snow performance, the rectangularity of the contact surface of the tread 10 is preferably 0.55 or more and 0.65 or less, and more preferably 0.57 or more and 0.63 or less. The rectangularity of the contact surface of the tread 10 can be controlled, for example, by the angle (belt angle) of the cords of the belt plies 18A and 18B that constitute the belt 18 with respect to the tire circumferential direction. The larger the belt angle, the greater the restraining force acting outward in the tire axial direction, and the smaller the rectangularity. Note that the method of controlling the rectangularity of the contact surface of the tread 10 is not limited to changing the belt angle, and may also be controlled by changing, for example, the arrangement of cap plies 19 and edge plies (not shown) that reinforce the belt 18.

[0076] The above embodiments can be modified as appropriate without altering the objective of the present invention. For example, in the above embodiments, the shape of the second middle land portion 50 is the same as the shape obtained when the first middle land portion 40 is rotated with respect to any point on the tire equator CL, and the shape of the second shoulder land portion 70 is the same as the shape obtained when the first shoulder land portion 60 is rotated with respect to any point on the tire equator CL, but the invention is not limited thereto. In other words, the tread 10 may have different tread patterns on the left and right sides of the tire equator CL.

[0077] Furthermore, grooves other than the shoulder sub-groove 61, shoulder slit 62, connecting sipe 63, and shoulder sipe 64 may be formed in the first shoulder land portion 60 and the second shoulder land portion 70. [Explanation of symbols]

[0078] 1 Pneumatic tire, 10 Tread, 11 Sidewall, 12 Side rib, 13 Bead, 14 Carcass, 15 Inner liner, 16 Bead core, 17 Bead filler, 18 Belt, 18A, 18B Belt ply, 19 Cap ply, 21, 22 Center main groove, 23, 24 Shoulder main groove, 30 Center land section, 31 Center slit, 31A Bent section, 32, 33 Center sipe, 40 First middle land section, 41 Middle slit, 41A Bent section, 42 Middle sipe, 50 Second middle land section, 60 First shoulder land section, 61 Shoulder secondary groove, 62 Shoulder slit, 62A Raised section, 63 Connecting sipe, 64 Shoulder sipe, 70 Second shoulder land section, CL Tire equator, E1, E2 Contact edge

Claims

1. A pneumatic tire with a tread, The aforementioned tread is A pair of shoulder main grooves, A shoulder land portion positioned outward in the tire axial direction from the shoulder main groove, It has, The aforementioned shoulder land portion is A shoulder sub-groove extends along the circumferential direction of the tire and is narrower in width than the shoulder main groove, A shoulder slit extending outward in the tire axial direction from the shoulder sub-groove, A pneumatic tire equipped with a ventilator.

2. The pneumatic tire according to claim 1, wherein the shoulder land portion is provided with sipes that face the shoulder slit via the shoulder sub-groove and communicate with the shoulder main groove.

3. The pneumatic tire according to claim 1, wherein the width of the shoulder sub-groove is 0.7% or more and 2% or less of the contact width of the tread.

4. The pneumatic tire according to claim 1, wherein the width of the area of ​​the shoulder land portion that is partitioned by the shoulder main groove and the shoulder sub-groove is 4% or more and 8% or less of the contact width of the tread.

5. The pneumatic tire according to claim 1, wherein the shoulder slit has a raised portion at the bottom of the groove that protrudes outward in the radial direction of the tire, near the portion that communicates with the shoulder sub-groove.

6. The pneumatic tire according to claim 1, wherein the width of the shoulder main groove is 6% or less of the contact width of the tread.

7. The aforementioned tread is A pair of center main grooves are positioned inward from the shoulder main groove in the tire axial direction, The central land area is partitioned by the pair of central main grooves, A pair of middle land areas are separated by the center main groove and the shoulder main groove, The pneumatic tire according to claim 1, further comprising the above.

8. The shoulder land portion is provided with sipes that face the shoulder slit via the shoulder sub-groove and communicate with the shoulder main groove, The pneumatic tire according to claim 7, wherein the middle land portion is provided with a middle slit that faces the sipe via the shoulder main groove and extends inward in the tire axial direction.

9. The pneumatic tire according to claim 8, wherein the middle slit has a bent portion that, in a plan view of the middle land portion, protrudes to one side in the tire circumferential direction from the positions of both ends of the middle slit in the tire circumferential direction.

10. Carcass and, A belt having at least one belt ply positioned on the radially outer side of the carcass, with the cords arranged in an inclination 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 26° or less.

11. The pneumatic tire according to claim 1, wherein the rectangular ratio of the contact surface of the tread is 0.55 or more and 0.65 or less.

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