pneumatic tires

Abstract

To improve handling stability and drainage performance. [Solution] The tread is provided with a center main groove and shoulder main grooves extending along the circumferential direction of the tire, and in at least one of the center main groove and the shoulder main groove, the inclination angle of the groove wall on the outer side in the tire axial direction is smaller than the inclination angle of the groove wall on the inner side in the tire axial direction, and the bead 13 has a bead core 16 and a bead filler 17 extending radially outward from the bead core 16, and a steel reinforcing layer 20 including steel cords is arranged on the outer side in the tire axial direction of the bead filler 17.

Description

Technical Field

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

Background Art

[0002] Conventionally, a pneumatic tire having a tread including a center main groove extending along the tire circumferential direction, a shoulder main groove disposed outside the center main groove in the tire axial direction and extending along the tire circumferential direction, and land portions partitioned by the main grooves is known (see, for example, Patent Document 1). Patent Document 1 discloses a pneumatic tire having a tread in which lug grooves extending in a direction intersecting the main grooves are formed in the land portions for the purpose of improving drainage performance while ensuring noise performance.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, in order to improve the fuel efficiency of automobiles, the demand for reducing the weight of tires has been increasing. As a method for weight reduction, it is conceivable to make the constituent members of the tire (for example, tread, sidewall, etc.) thinner. On the other hand, when the constituent members of the tire are made thinner, the lateral rigidity of the tire decreases, and the handling stability tends to decrease. Further, when the tread is made thinner, the drainage performance tends to decrease as the groove volume of the main groove decreases, and the wet performance deteriorates. Therefore, even when the constituent members of the tire are made thinner to achieve weight reduction, a technique for improving handling stability and drainage performance is required.

Means for Solving the Problems

[0005] A pneumatic tire according to one aspect of the present invention comprises a tread, a pair of sidewalls arranged on both sides of the tread, a pair of beads arranged radially inward of the sidewalls, and a carcass ply spanning between the pair of beads, wherein the tread is provided with a center main groove extending along the circumferential direction of the tire, and a shoulder main groove arranged axially outward of the center main groove and extending along the circumferential direction of the tire, wherein in at least one of the center main groove and the shoulder main groove, the inclination angle of the groove wall axially outward of the tire is smaller than the inclination angle of the groove wall axially inward of the tire is smaller than the inclination angle of the groove wall axially inward of the tire is smaller than the inclination angle of the groove wall axially inward of the tire is smaller than the inclination angle of the groove wall axially inward of the tire is smaller than the inclination angle of the groove wall axially inward of the tire is smaller [Effects of the Invention]

[0006] According to one aspect of the present invention, a pneumatic tire can improve handling stability and drainage performance even when the tire's components are made thinner and lighter. [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 an enlarged view of section A in Figure 1. [Figure 3] This is a plan view 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] Figure 3 is a cross-sectional view along line BB. [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 ply 14 that spans between the pair of beads 13, and an inner liner 15 arranged radially inward of the carcass ply 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] In this embodiment, the contact ends E1 and E2 of the pneumatic tire 1 are defined as the axial ends of the area (contact surface) that contacts a flat road surface when an unused tire is mounted on the rim of a designated vehicle, filled with air to the vehicle's set internal pressure, and then a vehicle axle load is applied.

[0014] 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 ply 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.

[0015] 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.

[0016] 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).

[0017] The bead 13 is the portion of the sidewall 11 located radially inward of the tire and fixed to the wheel rim. The bead 13 has a bead core 16 and a bead filler 17. The bead core 16 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 13. The bead filler 17 is an annular hard rubber member with a tapered tip that extends outward radially in the tire's circumferential direction, extending around the entire circumference. As will be described in more detail later, a steel reinforcing layer 20 containing steel cords is arranged on the axial side of the bead filler 17.

[0018] The carcass ply 14 is stretched between a pair of beads 13 and secured by being folded back around the bead core 16. In this embodiment, the carcass ply 14 consists of two carcass plies 14A and 14B (see Figure 2). The carcass ply 14 includes a carcass ply cord made of organic fibers and a topping rubber. The carcass ply cord is arranged substantially perpendicular to the tire circumferential direction (e.g., 80° or more and 90° or less). Examples of organic fibers used in the carcass ply cord include polyester fibers, rayon fibers, aramid fibers, and nylon fibers.

[0019] The inner liner 15 covers the inner surface of the tire between a pair of beads 13. The inner liner 15 is made of air-permeable rubber and has the function of maintaining the air pressure of the pneumatic tire 1.

[0020] The pneumatic tire 1 further comprises a belt 18 positioned radially outward of the carcass ply 14, and a cap ply 19 covering the radially outward side of the belt 18. The cap ply 19 has the function of reinforcing the belt 18. The number of cap plies 19 may be one or two or more.

[0021] The belt 18 is positioned on the radially outer side of the top of the carcass ply 14 and is provided overlapping the outer circumferential surface of the carcass ply 14. The belt 18 is formed of a belt ply made of cords covered with rubber and arranged in a direction inclined with respect to the circumferential direction of the tire. The material of the cords of the belt ply is not particularly limited and may include, for example, organic fibers such as polyester, rayon, nylon, or aramid, or metals such as steel.

[0022] As shown in Figure 1, the ratio of the tire section height H relative to the maximum tire section width LS (H / LS) is preferably 0.48 or more and 0.60 or less. When a steel reinforcing layer 20 is provided on the outer side of the bead filler 17 in the tire axial direction, the longitudinal stiffness of the tire may increase. On the other hand, by controlling the tire shape so that the ratio (H / LS) is 0.48 or more and 0.60 or less, the increase in the longitudinal stiffness of the tire can be suppressed, making it easier to absorb road surface irregularities and improving ride comfort.

[0023] The maximum tire section width LS refers to the length along the tire axial direction between the two points on the sidewall 11 that protrude furthest outward in the tire axial direction (maximum tire width position P), when the pneumatic tire 1 is mounted on a standard rim and under no load with an internal pressure of 0 kPa. The tire section height H refers to the length along the tire radial direction from the bead baseline BL to the outer surface of the tread 10 at the tire equator CL, when the pneumatic tire 1 is mounted on a standard rim and under no load with an internal pressure of 0 kPa. Here, the bead baseline BL is a virtual straight line in the tire axial direction that defines the rim diameter of the standard rim.

[0024] Next, the steel reinforcement layer 20 will be described with reference to Figure 2. Figure 2 is an enlarged view of section A in Figure 1, and shows the configuration near the steel reinforcement layer 20.

[0025] As shown in Figure 2, a steel reinforcing layer 20 containing steel cords is positioned on the outer side of the bead filler 17 in the tire axial direction. The steel reinforcing layer 20 is sandwiched between the bead filler 17 and the folded carcass ply 14 and is provided in an annular shape along the tire circumferential direction. By providing the steel reinforcing layer 20 on the outer side of the bead filler 17 in the tire axial direction, lateral rigidity can be improved. As a result, the tire becomes less prone to wobbling, for example, when turning, and handling stability can be improved. In particular, when components such as the tread 10 and sidewall 11 are thinned in order to reduce the weight of the tire, the lateral rigidity of the tire tends to decrease, but by providing the steel reinforcing layer 20, the lateral rigidity of the tire can be ensured.

[0026] The steel reinforcement layer 20 is constructed by covering steel cords (not shown) with a coating rubber or the like. The steel cords extend inclined with respect to the tire's radial direction and are arranged at intervals in the tire's circumferential direction while remaining inclined. The inclination angle of the steel cords with respect to the tire's radial direction is not particularly limited, and is, for example, 10° or more and 45° or less. The cord diameter of the steel cords is also not particularly limited, and is, for example, 0.3 mm or more and 1.2 mm or less, or 0.5 mm or more and 0.9 mm or less.

[0027] The number of steel cords embedded in the steel reinforcement layer 20 is preferably 15 cords / inch or more and 25 cords / inch or less, and more preferably 17 cords / inch or more and 23 cords / inch or less. When the number of steel cords embedded is within the above range, it becomes easier to achieve both longitudinal and lateral rigidity of the tire.

[0028] As shown in Figure 2, the outer end 20X of the steel reinforcement layer 20 in the tire radial direction is positioned radially inward from the tire's maximum width position P. This suppresses an excessive increase in the tire's longitudinal rigidity, making it easier to absorb road surface irregularities and improving ride comfort. The length L1 along the tire radial direction from the outer end 20X of the steel reinforcement layer 20 to the tire's maximum width position P is, for example, 3 mm or more and 15 mm or less, or 5 mm or more and 10 mm or less.

[0029] Furthermore, the outer end 20X of the steel reinforcement layer 20 in the tire radial direction is positioned radially outward from the outer end 17X of the bead filler 17. This increases the strength of the tire sidewall and improves lateral rigidity. In addition, by offsetting the outer end 20X of the steel reinforcement layer 20 and the outer end 17X of the bead filler 17, stress concentration around the outer end 17X of the bead filler 17 can be suppressed, improving durability. From the viewpoint of further improving lateral rigidity, the length L2 along the tire radial direction from the outer end 20X of the steel reinforcement layer 20 to the outer end 17X of the bead filler 17 is preferably 5 mm or more, and more preferably 6 mm or more.

[0030] Furthermore, if the length L2 along the tire radial direction from the outer end 20X of the steel reinforcement layer 20 to the outer end 17X of the bead filler 17 becomes too large, the longitudinal rigidity may increase excessively. For this reason, the length L2 along the tire radial direction from the outer end 20X of the steel reinforcement layer 20 to the outer end 17X of the bead filler 17 is preferably 10 mm or less, and more preferably 9 mm or less. Thus, the length L2 along the tire radial direction from the outer end 20X of the steel reinforcement layer 20 to the outer end 17X of the bead filler 17 is preferably 5 mm or more and 10 mm or less, and more preferably 6 mm or more and 9 mm or less.

[0031] In the example shown in Figure 2, the inner end 20Y of the steel reinforcement layer 20 in the tire radial direction and the inner end 17Y of the bead filler 17 in the tire radial direction are positioned to substantially overlap in the tire radial direction. This increases the strength of the tire sidewall and improves lateral rigidity. The inner end 20Y of the steel reinforcement layer 20 in the tire radial direction may be positioned radially outward from the inner end 17Y of the bead filler 17. In that case, the length along the tire radial direction from the inner end 20Y of the steel reinforcement layer 20 to the inner end 17Y of the bead filler 17 is preferably 5 mm or less, and more preferably 3 mm or less.

[0032] Next, the tread pattern of the pneumatic tire 1 will be described with reference to Figures 3 to 5. Figure 3 is a plan view of the pneumatic tire 1 (tread 10), Figure 4 is a cross-sectional view of Figure 3 along line AA, and Figure 5 is a cross-sectional view of Figure 3 along line BB.

[0033] As shown in Figure 3, 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 the 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 the region on the contact edge E2 side of the tire equator CL. In this embodiment, the center main groove 22 has a shape obtained by rotating the center main groove 21 180° to the left and right of the tire equator CL, and the shoulder main groove 24 has a shape obtained by rotating the shoulder main groove 23 180° to the left and right of the tire equator CL.

[0034] 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, thereby improving drainage performance.

[0035] The sum of the widths of the four main grooves is, for example, 15% or more of the length W along the tire axial direction from contact edge E1 to contact edge E2 (hereinafter referred to as "contact width W"). In this case, water from the road surface can easily enter each main groove, improving drainage performance. Alternatively, the sum of the widths of the four main grooves is, for example, 30% or less of the contact width W. In this case, block rigidity is improved, making it easier to ensure handling stability. Therefore, the sum of the widths of the four main grooves is, for example, 15% or more and 30% or less of the contact width W. In this specification, unless otherwise specified, groove width refers to the width on the profile surface α (see Figures 4 and 5) along the contact surface of the tread 10.

[0036] In this embodiment, the width of the center main grooves 21 and 22 is larger than the width of the shoulder main grooves 23 and 24. The shape of the center main grooves 21 and 22, which are formed on the inner side of the tire axial direction, greatly affects the drainage performance, and the wider the center main grooves 21 and 22, the better the drainage performance. Therefore, by making the width of the center main grooves 21 and 22 larger than the width of the shoulder main grooves 23 and 24, the drainage performance can be further improved. The width of the center main grooves 21 and 22 is, for example, 6 mm or more and 15 mm or less, and the width of the shoulder main grooves 23 and 24 is, for example, 5 mm or more and 12 mm or less. Note that the width of the center main grooves 21 and 22 may be approximately the same as the width of the shoulder main grooves 23 and 24, or it may be smaller than the width of the shoulder main grooves 23 and 24.

[0037] Figure 4 shows a cross-sectional view of the center main groove 21. As shown in Figure 4, in an axial cross-sectional view of the tread 10, the center main groove 21 has groove walls 21A and 21B that extend inclined with respect to a normal perpendicular to the profile surface α of the tread 10. Groove wall 21A forms the groove wall on the outer side of the center main groove 21 in the tire axial direction, and groove wall 21B forms the groove wall on the inner side of the center main groove 21 in the tire axial direction. Groove walls 21A and 21B are formed from the profile surface α of the tread 10 to near the bottom of the center main groove 21.

[0038] Here, the inclination angle θ of the groove wall 21A, which is the groove wall on the outer side of the tire axial direction, with respect to the normal perpendicular to the profile surface α of the tread 10.21A , 21B is the inclination angle θ with respect to the normal perpendicular to the profile surface α of the tread 10 of the groove wall 21B which is the groove wall on the inner side in the tire axial direction 21B is smaller than. Thereby, even when, for example, the tread 10 is made thinner and the depth of the center main groove 21 becomes smaller, the groove volume of the outer portion in the tire axial direction of the center main groove 21 can be increased. As a result, the amount of water entering the center main groove 21 during running increases, and the drainage performance can be improved. Also, the inclination angle θ 21B is made larger than the inclination angle θ 21A to improve the rigidity of the center land portion 30. As a result, the handling stability can be improved.

[0039] The inclination angle θ 21A is preferably 5° or more and 15° or less, more preferably 7° or more and 13° or less, and even more preferably 9° or more and 11° or less from the viewpoint of increasing the groove volume of the center main groove 21 while ensuring the rigidity of the first middle land portion 40. Also, the inclination angle θ 21B is preferably 15° or more and 25° or less, more preferably 17° or more and 23° or less, and even more preferably 19° or more and 21° or less from the viewpoint of increasing the rigidity of the center land portion 30 while ensuring the groove volume of the center main groove 21. Also, the difference (θ 21B -θ 21A ) between θ 21B and θ 21A is preferably 5° or more, more preferably 7° or more, and even more preferably 10° or more. The upper limit of the difference (θ 21B -θ 21A ) between θ 21B and θ 21A ) is, for example, 20°.

[0040] The depth D of the center main groove 21 21 is, for example, 5 mm or more and 10 mm or less, and may be 6 mm or more and 9 mm or less. Generally, the depth D of the center main groove 21 21When the size decreases, the groove volume of the center main groove 21 decreases, and the drainage performance tends to deteriorate. However, in this embodiment, as described above, the inclination angle θ of the groove wall 21A 21A The inclination angle θ of the groove wall 21B 21B It is made smaller than this. This reduces the depth D of the center main groove 21. 21 Even when the depth D of the center main groove 21 is small, the groove volume of the center main groove 21 is secured, and the drainage performance can be improved. In other words, the effect of the present invention is that by thinning the tread 10, the depth D of the center main groove 21 can be increased. 21 This is more pronounced when the value is small. Unless otherwise specified, groove depth refers to the length along the tire's radial direction from the profile surface α along the contact surface of the tread 10 to the deepest part of the groove.

[0041] Figure 5 shows a cross-sectional view of the shoulder main groove 23. As shown in Figure 5, in an axial cross-sectional view of the tread 10, the shoulder main groove 23 has groove walls 23A and 23B that extend inclined with respect to a normal perpendicular to the profile surface α of the tread 10. Groove wall 23A forms the groove wall on the outer side of the shoulder main groove 23 in the tire axial direction, and groove wall 23B forms the groove wall on the inner side of the shoulder main groove 23 in the tire axial direction. Groove walls 23A and 23B are formed from the profile surface α of the tread 10 to near the bottom of the shoulder main groove 23.

[0042] In this embodiment, similar to the case of the center main groove 21, the inclination angle θ of the groove wall 23A, which is the groove wall on the outer side in the tire axial direction, with respect to the normal perpendicular to the profile surface α of the tread 10. 23A The inclination angle θ of the groove wall 23B, which is the groove wall on the inner side of the tire axial direction, with respect to the normal perpendicular to the profile surface α of the tread 10. 23B It is formed to be smaller than the original. This makes it possible to increase the groove volume of the outer axial portion of the shoulder main groove 23, even if, for example, the tread 10 is made thinner and the depth of the shoulder main groove 23 is reduced. As a result, the amount of water that enters the shoulder main groove 23 during driving increases, improving drainage performance.

[0043] Furthermore, as described above, the inclination angle θ of the groove wall 21A, which is the groove wall on the outer side of the tire axial direction of the center main groove 21. 21A Because it is small, there is a risk that the rigidity of the first middle section 40 will decrease. Therefore, the inclination angle θ 23B The inclination angle θ 23A By making it larger, the rigidity of the first middle section 40 can be ensured, and handling stability can be improved.

[0044] Incline angle θ 23A From the viewpoint of ensuring the rigidity of the first shoulder land portion 60 while increasing the groove volume of the shoulder main groove 23, the inclination angle is preferably 5° or more and 15° or less, more preferably 7° or more and 13° or less, and even more preferably 9° or more and 11° or less. 23B From the viewpoint of ensuring the groove volume of the shoulder main groove 23 while increasing the rigidity of the first middle land section 40, it is preferable that the angle is 15° or more and 25° or less, more preferably 17° or more and 23° or less, and even more preferably 19° or more and 23° or less. 23B and θ 23A The difference (θ) 23B -θ 23A ) is preferably 5° or more, more preferably 7° or more, and even more preferably 10° or more. 23B and θ 23A The difference (θ) 23B -θ 23A The upper limit of ) is, for example, 20°.

[0045] Note that the angle of the gold θ 23A The inclination angle θ of the groove wall 21A, which is the groove wall on the outer side of the tire axial direction of the center main groove 21. 21A It may be the same as, or it may be different. Similarly, the inclination angle θ 23B The inclination angle θ of the groove wall 21B, which is the groove wall on the inner side of the center main groove 21 in the tire axial direction. 21B It may be the same as, or it may be different. In this embodiment, the inclination angle θ 23A and the inclination angle θ 21A This is essentially the same, and the inclination angle θ 23B and the inclination angle θ 21B This is essentially the same thing.

[0046] Depth D of the main shoulder groove 23 23 For example, it may be 5 mm or more and 10 mm or less, or 6 mm or more and 9 mm or less. Similar to the case of the center main groove 21, the inclination angle θ of the groove wall 23A 23A The inclination angle θ of the groove wall 23B 23B Because it is smaller than the depth D of the shoulder main groove 23 23 Even when the depth D of the shoulder main groove 23 is small, the groove volume of the shoulder main groove 23 can be secured, and the drainage performance can be improved. In other words, the effect of the present invention is that by thinning the tread 10, the depth D of the shoulder main groove 23 can be increased. 23 This is more pronounced when the value is small.

[0047] Depth D of the main shoulder groove 23 23 The depth D of the center main groove 21 21 It may be the same, but in this embodiment, the depth D of the center main groove 21 21 It is formed to be smaller than that. In other words, the depth D of the center main groove 21 21 The depth D of the shoulder main groove 23 23 It is formed to be larger than the above. As described above, the shape of the center main groove 21 formed on the inner side of the tire axis greatly affects the drainage performance. Therefore, the depth D of the center main groove 21 21 The depth D of the shoulder main groove 23 23 By making it larger, drainage performance can be further improved.

[0048] Depth D of the main shoulder groove 23 23 The depth D of the center main groove 21 21 The ratio (D 21 / D 23 For example, the value may be 1.01 or higher, and may also be 1.02 or higher. In this case, drainage performance can be further improved.

[0049] As shown in Figure 3, 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.

[0050] 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".

[0051] [Center Track and Field Club 30] As shown in Figure 3, 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.

[0052] The center land portion 30 has center sipes 31 formed at intervals in the circumferential direction of the tire, communicating with each of the center main grooves 21 and 22. The center sipes 31 have, for example, a substantially uniform width along their length. In this specification, a sipe refers to a groove with a width of less than 1.5 mm. The width of the center sipes 31 is, for example, 0.5 mm or more and 1.0 mm or less.

[0053] The center sipe 31 has a roughly S-shape in a plan view of the center ground portion 30. Specifically, the center sipe 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 sipe 31 in the tire circumferential direction in a plan view of the center ground portion 30. When the center sipe 31 has a bent portion 31A, the strain applied to the center sipe 31 during driving is distributed, and the ground pressure on the center ground portion 30 is distributed. As a result, for example, steering stability is improved. In this embodiment, the bent portions 31A are formed on both sides in the longitudinal direction of the center sipe 31.

[0054] In this embodiment, only a center sipe 31 is formed on the center land portion 30, and no grooves with a width of 1.5 mm or more are formed. This improves the contact area of ​​the tread 10 and enhances grip performance on dry surfaces. As a result, even if the lateral rigidity of the tire is reduced by thinning components such as the tread 10 and sidewall 11, it is possible to improve handling stability on dry surfaces.

[0055] [1st Middle Track and Field Club 40] As shown in Figure 3, 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.

[0056] 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. In this specification, a slit means a groove with a width of 1.5 mm or more. The width of the middle slits 41 is, for example, 2 mm or more and 5 mm or less.

[0057] The middle slit 41 extends inward along the tire axis 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.

[0058] As described above, the middle slit 41 does not communicate 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. In addition, because the middle slit 41 does not communicate with the center main groove 21, the contact area of ​​the tread 10 is improved, which can improve grip performance on dry surfaces. The tire 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. Note that the tire axial length of a slit (similar to a sipe) refers to the length along the tire axial direction between the tire axial ends of the slit (sipe).

[0059] 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 for example, snow on the road surface can enter the middle slit 41 more easily, thereby improving snow performance.

[0060] 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.

[0061] The middle sipe 42, like the center sipe 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.

[0062] [Shoulder 1 Track and Field Club 60] As shown in Figure 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.

[0063] 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.

[0064] As described above, when components such as the tread 10 and sidewall 11 are thinned in order to reduce the weight of the tire, the lateral rigidity of the tire tends to decrease, and handling stability tends to decrease. In the pattern of this embodiment, the void ratio, which means the ratio of grooves to the surface area of ​​the tread 10, is reduced by not forming slits in the center land portion 30, thereby improving the contact area of ​​the tread 10. As a result, grip performance is improved mainly on dry roads, and handling stability is ensured. On the other hand, when the void ratio of the tread 10 is reduced, the amount of snow that enters the grooves on snowy roads decreases, the shear force of the snow columns that grips and compacts the snow decreases, and snow performance tends to deteriorate.

[0065] Therefore, as in this embodiment, by providing a shoulder sub-groove 61 extending along the circumferential direction of the tire 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. In other words, by providing a shoulder sub-groove 61 in a pattern with a reduced void ratio of the tread 10, it is possible to achieve both handling stability on dry roads and snow performance.

[0066] The shoulder sub-grooves 61 extend in the circumferential direction of the tire and have a uniform width around 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, an excessive increase in the void ratio can be suppressed, making it easier to ensure handling stability on dry surfaces. 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.

[0067] 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 away in the tire axial direction. Specifically, the length along the tire axial direction between the inner end of the shoulder sub-groove 61 in the tire axial direction and the outer end of the shoulder main groove 23 in the tire axial direction is preferably 5 mm or more, and more preferably 6 mm or more. In this case, the rigidity of the region of the first shoulder land portion 60 that is inward in the tire axial direction from the shoulder sub-groove 61 can be ensured, and damage to that region can be suppressed. Furthermore, the length along the tire axial direction between the inner end of the shoulder sub-groove 61 in the tire axial direction and the outer end of the shoulder main groove 23 in the tire axial direction is preferably 10 mm or less, and more preferably 9 mm or less. In this case, snow can easily enter the shoulder sub-groove 61, further improving snow performance. Therefore, the length along the tire axial direction between the inner end of the shoulder sub-groove 61 in the tire axial direction and the outer end of the shoulder main groove 23 in the tire axial direction is preferably 5 mm or more, 10 mm or less, and more preferably 6 mm or more, 9 mm or less.

[0068] 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 handling stability.

[0069] 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 the width of the middle slits 41 provided in the first middle ground portion 40, for example, 2.5 mm or more and 6 mm or less.

[0070] The depth of the deepest part of the shoulder slit 62 is preferably greater than the depth of the shoulder sub-groove 61. For example, the depth of the deepest part of the shoulder slit 62 is between 4 mm and 9 mm. When the depth of the shoulder slit 62 is within the above range, snow performance can be further improved.

[0071] In this embodiment, the shoulder slit 62 has a raised portion 62A, where the groove bottom is raised outward in the tire radial direction, near the portion that communicates with the shoulder sub-groove 61. In other words, the depth of the region of the shoulder slit 62 on the inner side in the tire axial direction is formed to be smaller than other parts. 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 depth of the shoulder slit 62 in the region where the raised portion 62A is formed may be, for example, 10% to 80% of the depth of the deepest part of the shoulder slit 62, or 20% to 70%.

[0072] Furthermore, the axial length of the raised portion 62A in the tire axis direction may be, for example, 3% or more and 20% or less of the width of the contact surface of the first shoulder land portion 60, or 5% or more and 10% or less. Note that the shoulder slit 62 does not necessarily have to have a raised portion 62A.

[0073] As described above, the shoulder slit 62 is connected to the shoulder sub-groove 61. This makes it easier for water in the shoulder sub-groove 61 to flow outward in the axial direction of the tire. As a result, drainage performance can be further improved.

[0074] 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. The communicating sipe 63 has, for example, a substantially uniform width along its length. The width of the communicating sipe 63 is, for example, 0.5 mm or more and 1.0 mm or less. The depth of the communicating sipe 63 is, for example, 2 mm or more and 8 mm or less. In this embodiment, the communicating sipe 63 is provided in a position that faces all of the shoulder slits 62 via the shoulder sub-groove 61.

[0075] Furthermore, in addition to the shoulder sub-grooves 61, shoulder slits 62, and connecting sipes 63, the first shoulder land portion 60 also has shoulder sipes 64 extending outward from the shoulder sub-grooves 61 in the axial direction of the tire. Two shoulder sipes 64 are formed between two adjacent shoulder slits 62 in the circumferential direction of the tire. 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 circumferential direction of the tire. The shoulder sipes 64 are formed beyond the contact end E1 and outward in the axial direction of the tire, 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.

[0076] The above embodiments can be modified as appropriate without altering the objective of the present invention. For example, in the above embodiments, both the center main groove 21 and the shoulder main groove 23 have an inclination angle θ of the groove walls 21A and 23A on the outer side of the tire axial direction. 21A ,θ 23A However, the inclination angle θ of the groove walls 21B and 23B on the inner side of the tire axial direction 21B ,θ 23B It is smaller than, but not limited to. Specifically, only the center main groove 21 has an inclination angle θ of the groove wall 21A on the outer side of the tire axial direction. 21A However, the inclination angle θ of the groove wall 21B on the inner side of the tire axial direction 21B It may be smaller than that, and only the shoulder main groove 23 has an inclination angle θ of the groove wall 23A on the outer side of the tire axial direction. 23A However, the inclination angle θ of the groove wall 23B on the inner side of the tire axial direction 23B It may be smaller than this. Note that both the center main groove 21 and the shoulder main groove 23 have an inclination angle θ of the groove walls 21A and 23A on the outer side of the tire axial direction. 21A ,θ 23A However, the inclination angle θ of the groove walls 21B and 23B on the inner side of the tire axial direction 21B ,θ 23B When the value is smaller than this, the effects of the present invention are more pronounced.

[0077] Furthermore, in the above embodiment, 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 embodiment is not limited to this. In other words, the tread 10 may have different tread patterns on the left and right sides of the tire equator CL.

[0078] Furthermore, in the above embodiment, the steel reinforcement layer 20 is positioned only on the tire axial side of the bead filler, but it may also be positioned on the tire axial side of the bead filler in addition to the tire axial side. In this case, the lateral rigidity of the tire can be further improved. [Explanation of symbols]

[0079] 1 Pneumatic tire, 10 Tread, 11 Sidewall, 12 Side rib, 13 Bead, 14,14A,14B Carcass ply, 15 Inner liner, 16 Bead core, 17 Bead filler, 18 Belt, 19 Cap ply, 20 Steel reinforcement layer, 21,22 Center main groove, 21A,21B Groove wall, 23,24 Shoulder main groove, 23A,24B Groove wall, 30 Center land section, 31 Center sipe, 31A Bent section, 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. Tread and A pair of sidewalls positioned on both sides of the tread, A pair of beads positioned radially inward of the sidewall of the tire, A carcass ply is stretched between the pair of beads, A pneumatic tire equipped with, The tread is provided with a center main groove extending along the circumferential direction of the tire, and shoulder main grooves positioned outward from the center main groove in the axial direction of the tire and extending along the circumferential direction of the tire. In at least one of the center main groove and the shoulder main groove, the angle of inclination of the groove wall on the outer side in the tire axial direction with respect to the normal perpendicular to the profile surface of the tread is smaller than the angle of inclination of the groove wall on the inner side in the tire axial direction with respect to the normal perpendicular to the profile surface of the tread. The bead comprises a bead core and a bead filler extending radially outward from the bead core. A pneumatic tire in which a steel reinforcing layer, including steel cords, is positioned on the axial side of the bead filler.

2. The tread has a shoulder land portion that is positioned outward in the tire axial direction from the shoulder main groove, The pneumatic tire according to claim 1, wherein the shoulder land portion is provided with a shoulder sub-groove that extends along the circumferential direction of the tire and has a groove width smaller than that of the shoulder main groove.

3. The pneumatic tire according to claim 2, wherein the length along the tire axial direction between the inner end of the shoulder sub-groove in the tire axial direction and the outer end of the shoulder main groove in the tire axial direction is 5 mm or more and 10 mm or less.

4. The pneumatic tire according to claim 1, wherein the outer end of the steel reinforcement layer in the tire radial direction is positioned inward from the tire's maximum width position and is positioned at a distance of 5 mm or more and 10 mm or less in the tire radial direction from the outer end of the bead filler in the tire radial direction.

5. In at least one of the center main groove and the shoulder main groove, The angle of inclination of the groove wall on the outer side of the tire axial direction with respect to the normal perpendicular to the profile surface of the tread is 5° or more and 15° or less. The pneumatic tire according to claim 1, wherein the angle of inclination of the groove wall on the inner side of the tire axial direction with respect to the normal perpendicular to the profile surface of the tread is 15° or more and 25° or less.

6. The pneumatic tire according to claim 1, wherein the ratio of the tire section height H, based on the bead baseline BL, to the maximum tire section width LS (H / LS) is 0.48 or more and 0.60 or less.

7. The pneumatic tire according to claim 1, wherein the number of steel cords driven into the steel reinforcement layer is 15 [cords / inch] or more and 25 [cords / inch] or less.

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