pneumatic tires

Abstract

Improve drainage performance and noise performance. [Solution] The tread has a center land portion 30, middle land portions 40, 50, and shoulder land portions 60, 70, the sum of the widths of the pair of center main grooves 21, 22 and the pair of shoulder main grooves 23, 24 is 20% or more and 25% or less of the contact width W of the tread 10, the depth of the pair of center main grooves 21, 22 and the pair of shoulder main grooves 23, 24 is 6.5 mm or more and 7.2 mm or less, and the rectangular ratio of the contact surface of the tread 10 is 0.60 or more and 0.70 or less.

Description

Technical Field

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

Background Art

[0002] Conventionally, a pneumatic tire having a tread with a plurality of main grooves extending along the circumferential direction of the tire and a plurality of land portions defined by the main grooves is known (see, for example, Patent Document 1). Patent Document 1 discloses providing a plurality of sipes in the land portion while making the shape of the ground contact surface of the tread a predetermined shape.

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 of main grooves, lateral grooves, etc. provided in the tread, the noise during running can be reduced. On the other hand, when the volume of the main groove becomes small, it becomes difficult to drain water through the main groove during running, and the drainage performance tends to deteriorate. That is, it is not easy to improve the drainage performance while improving the noise performance.

Means for Solving the Problems

[0005] A pneumatic tire according to one aspect of the present invention is a pneumatic tire equipped with a tread, wherein the tread comprises a pair of center main grooves, a pair of shoulder main grooves positioned axially outward from the center main grooves, a center land area partitioned by the pair of center main grooves, a middle land area partitioned by the center main grooves and the shoulder main grooves, and a shoulder land area positioned axially outward from the shoulder main grooves, wherein the sum of the widths of the pair of center main grooves and the pair of shoulder main grooves is 20% or more and 25% or less of the contact width of the tread, the depth of the pair of center main grooves and the pair of shoulder main grooves is 6.5 mm or more and 7.2 mm or less, and the rectangular ratio of the contact surface of the tread is 0.60 or more and 0.70 or less. [Effects of the Invention]

[0006] According to one aspect of the present invention, a pneumatic tire can improve drainage performance and noise performance. [Brief explanation of the drawing]

[0007] [Figure 1] This is a cross-sectional view of a pneumatic tire, which is an example of an embodiment. [Figure 2] This is a plan view of the tread of a pneumatic tire, which is an example of an embodiment. [Figure 3] This diagram schematically shows the shape of the contact surface of the tread. [Figure 4] This is a plan view of the tread of a pneumatic tire used as a comparative example. [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, and also shows the internal structure of the tire. As shown in Figure 1, the pneumatic tire 1 comprises a tread 10, which is the part 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 ratio of the contact surface of the tread 10 is designed to be 0.6 or more and 0.7 or less.

[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 at a right angle (for example, 80° or more and 90° or less) with respect 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 made of air-permeability-resistant rubber and has a function of maintaining 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​​​​​

[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, the angle (belt angle) of the cords constituting the two belt plies 18A and 18B with respect to the tire circumferential direction is preferably 22° or more and 29° or less, and preferably 23° or more and 28° 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 0.6 or more and 0.7 or less. As a result, the noise performance described later can be improved.

[0026] The tread pattern of the pneumatic tire 1 will be described below 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, 22 and a pair of shoulder main grooves 23, 24 formed further outward in the tire axial direction than the center main grooves 21, 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.

[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] The sum of the widths of the four main grooves is 20% 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 25% or less of the contact width W. In this case, air column resonance noise caused by the main grooves is reduced, improving noise performance. Therefore, by controlling the sum of the widths of the four main grooves to 20% or more and 25% or less of the contact width W, drainage performance and noise performance can be improved. Preferably, the sum of the widths of the four main grooves is 22% or more and 25% or less of the contact width W, and more preferably 23% or more and 25% or less. In this specification, unless otherwise specified, groove width refers to the width of the profile surface along the contact surface of the tread 10.

[0030] 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 has a significant impact on 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. In addition, the shape of the center main grooves 21 and 22 greatly affects drainage performance, and the wider the center main grooves 21 and 22, the better the drainage performance. The ratio of the width of the shoulder main grooves 23 and 24 to the width of the center main grooves 21 and 22 is, for example, 75% or more and 90% or less.

[0031] 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.

[0032] Furthermore, the depth of the four main grooves is between 6.5 mm and 7.2 mm. When the depth of the four main grooves is within the above range, it is possible to improve drainage performance while reducing air column resonance noise caused by the main grooves. As a result, it is possible to improve noise performance while improving drainage performance. In other words, if the depth of any of the four main grooves is less than 6.5 mm or more than 7.2 mm, it becomes difficult to achieve both drainage performance and noise performance. Preferably, the depth of the four main grooves is between 6.8 mm and 7.2 mm. In this specification, unless otherwise specified, groove depth means 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.

[0033] In this embodiment, the depth of the shoulder main grooves 23 and 24 is formed to be smaller than the depth 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. The ratio of the depth of the shoulder main grooves 23 and 24 to the depth of the center main grooves 21 and 22 is, for example, 50% or more and 97% or less, or it may be 50% or more and 95% or less.

[0034] 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. That is, the cross-sectional area of ​​the center main groove 21 and the center main groove 22 are the same, and the cross-sectional area of ​​the shoulder main groove 23 and the shoulder main groove 24 are the same. The cross-sectional area of ​​each main groove refers to the area of ​​the portion enclosed by the wall surface of the main groove and the profile surface along the contact surface of the tread 10 in the radial cross-section of the tire. Furthermore, the cross-sectional area of ​​each main groove is the value measured in the radial cross-section of the tire when an unused tire is mounted on a standard rim, at standard internal pressure, and under no load.

[0035] The ratio of the groove cross-sectional area of ​​the shoulder main grooves 23 and 24 to the groove cross-sectional area of ​​the center main grooves 21 and 22 is preferably, for example, 0.5 or more and 0.9 or less, and more preferably 0.6 or more and 0.8 or less. In this case, while ensuring the rigidity of the tread 10, the air column resonance noise caused by the shoulder main grooves 23 and 24 can be further reduced, and the noise performance can be further improved.

[0036] In addition, at least one of the center main grooves 21, 22 and the shoulder main grooves 23, 24 is generally provided with a wear indicator (not shown). The wear indicator is a projection located at the bottom of the groove and serves as an indicator for checking the wear level of the tread rubber.

[0037] 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.

[0038] 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".

[0039] [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.

[0040] The center lateral groove 31 is formed in the center land portion 30 at intervals in the tire circumferential direction, communicating with each of the center main grooves 21 and 22. The center lateral groove 31 has, for example, a substantially uniform groove width along its length. The groove width of the center lateral groove 31 is, for example, 2 mm or more and 5 mm or less.

[0041] The center lateral groove 31 has a roughly S-shape in a plan view of the center land area 30. Specifically, the center lateral groove 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 lateral groove 31 in the tire circumferential direction in a plan view of the center land area 30. When the center lateral groove 31 has a bent portion 31A, the strain applied to the center lateral groove 31 during driving is distributed, and the ground pressure on the center land area 30 is distributed. As a result, for example, steering stability is improved. In this embodiment, the bent portion 31A is formed on both sides in the longitudinal direction of the center lateral groove 31.

[0042] Two types of 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. This ensures the rigidity of the center land portion 30, which in turn improves steering stability, for example. In this specification, a sipe refers to a groove with a groove width of 1.5 mm or less.

[0043] The center sipes 32 and 33 are formed one at a time between two adjacent center lateral grooves 31 in the circumferential direction of the tire. In other words, the lateral grooves and sipes are repeatedly formed in the order of center lateral groove 31, center sipe 32, and center sipe 33, toward the Y1 direction in the circumferential direction of the tire.

[0044] In this embodiment, the end of the center sipe 32 on the side of the center main groove 21 and the end of the center sipe 33 on the side of the center main groove 22 are positioned to overlap in the circumferential direction of the tire. The center sipe 32 extends inward in the axial direction of the tire, along a direction inclined toward the Y2 direction relative to the axial direction of the tire, except near the portion communicating with the center main groove 21. The center sipe 33 extends inward in the axial direction of the tire, along a direction inclined toward the Y1 direction relative to the axial direction of the tire, except near the portion communicating with the center main groove 22. The inclination angle of the center sipe 32 with respect to the axial direction is the same as the inclination angle of the center sipe 33 with respect to the axial direction of the tire. The inclination angles of the center sipes 32 and 33 with respect to the axial direction of the tire are, for example, 10° or more and 70° or less, and may be 20° or more and 60° or less.

[0045] 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 land portion 30. In this specification, the axial length of a sipe (including grooves) means the length along the axial direction of the tire between the inner end of the sipe (groove) in the axial direction and the outer end of the sipe (groove) in the axial direction.

[0046] [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 greater than the width of the center land section 30.

[0047] The first middle section 40 has middle lateral grooves 41 formed at intervals in the circumferential direction of the tire. The middle lateral grooves 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 lateral grooves 41 have, for example, a substantially uniform groove width along the length. The groove width of the center lateral groove 31 is, for example, 2 mm or more and 5 mm or less.

[0048] The middle lateral groove 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 lateral groove 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 lateral groove 41 with respect to the tire axis is 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.

[0049] As described above, the middle lateral groove 41 is not connected to the center main groove 21. This improves the rigidity of the first middle land 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 land section 40 is, for example, 50% or more and 90% or less of the width of the first middle land section 40.

[0050] 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 lateral grooves 41 in the circumferential direction of the tire. In other words, lateral grooves and sipes are repeatedly formed in the order of middle lateral groove 41, middle sipe 42, middle sipe 42, toward the Y1 direction in the circumferential direction of the tire. Note that the middle sipes 42 may communicate with only one of the center main groove 21 and the shoulder main groove 23.

[0051] The middle sipe 42, like the center lateral groove 31, has a roughly S-shape in a plan view of the first middle section 40. Specifically, the middle sipe 42 has a bent portion that, in a plan view of the first middle section 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 section 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.

[0052] [Shoulder 1 Track and Field Club 60] 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.

[0053] The first shoulder land portion 60 has shoulder lateral grooves 61 formed at intervals in the tire circumferential direction, extending in a direction intersecting the shoulder main groove 23. The shoulder lateral grooves 61 are formed beyond the contact end E1 and outward in the tire axial direction. The shoulder lateral grooves 61 have, for example, a substantially uniform groove width along the length. The groove width of the shoulder lateral grooves 61 may be larger than that of the center lateral groove 31 and the middle lateral groove 41, for example, 2.5 mm or more and 6 mm or less.

[0054] The shoulder lateral grooves 61 are formed with a slope towards the Y1 direction as they move inward along the tire axial direction. The shoulder lateral grooves 61 are connected to the shoulder main grooves 23 via connecting sipes 62. This improves grip with the road surface when driving on snowy roads and enhances handling stability (snow performance) on snowy roads.

[0055] Furthermore, the shoulder lateral grooves 61 significantly affect the pattern noise generated when the tread 10 makes contact with the road surface. Specifically, the larger the volume of the shoulder lateral grooves 61 that make contact with the road surface, the greater the pattern noise tends to be, and the lower the noise performance tends to be. As described above, by connecting the shoulder lateral grooves 61 to the shoulder main grooves 23 via the connecting sipes 62, the volume of the shoulder lateral grooves 61 that make contact with the road surface is reduced, thereby reducing pattern noise while ensuring drainage performance.

[0056] The axial length of the connecting sipe 62 is, for example, 5% to 30% of the width of the contact surface of the first shoulder land portion 60. The connecting sipe 62 may have a substantially uniform depth along its length, or it may have regions where the depth locally changes.

[0057] The first shoulder land portion 60 has shoulder sipes 63 that communicate with the shoulder main groove 23. Two shoulder sipes 63 are formed between two adjacent shoulder lateral grooves 61 in the circumferential direction of the tire. In other words, grooves and sipes are repeatedly formed in the order of shoulder lateral groove 61, shoulder sipe 63, shoulder sipe 63, toward the Y1 direction in the circumferential direction of the tire.

[0058] The shoulder sipes 63 are formed extending outward in the tire axial direction beyond the contact edge E1 and are shorter than the shoulder lateral grooves 61. Like the shoulder lateral grooves 61, the shoulder sipes 63 are formed with a slope toward the Y1 direction as they move inward in the tire axial direction.

[0059] Next, with further reference to Figure 3, the shape of the contact surface of the tread 10 will be described in detail. Figure 3 is a schematic diagram showing the shape of the contact surface of the tread 10.

[0060] As shown in Figure 3, 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, filled with air to a predetermined internal pressure, and a load equivalent to 88% of the normal load is applied. 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 by the above measurement conditions. The predetermined internal pressure in the above measurement conditions is 200 kPa when the aspect ratio of the tire is 60% or more, and 220 kPa when the aspect ratio is less than 60%. Furthermore, for tires marked "Extra Load," the specified internal pressure under the above measurement conditions is 240 kPa if the aspect ratio is 60% or more, and 260 kPa if the aspect ratio is less than 60%.

[0061] 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.

[0062] 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 lateral grooves 61 that contact 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.

[0063] 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.

[0064] On the other hand, reducing the rectangular ratio can make it difficult for water to enter the main grooves, potentially reducing drainage performance. In this embodiment, as described above, the width and depth of each main groove are controlled within a predetermined range. This allows water to enter the main grooves more easily, even when the rectangular ratio is reduced, thereby improving drainage performance.

[0065] From the viewpoint of improving drainage performance and noise performance, the rectangularity of the contact surface of the tread 10 is preferably 0.60 or more and 0.70 or less, and preferably 0.62 or more and 0.68 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 becomes. Furthermore, 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. [Examples]

[0066] The present invention will be further explained below with reference to experimental examples, but the present invention is not limited to these experimental examples.

[0067] <Example 1> A pneumatic tire 1 (tire size: 235 / 65R17 104H) having the tread pattern shown in Figure 2 was manufactured. In this process, the groove width of the center main grooves 21 and 22 was set to 10.7 mm, the depth of the center main grooves 21 and 22 was set to 7.0 mm, the groove width of the shoulder main grooves 23 and 24 was set to 8.4 mm, the depth of the shoulder main grooves 23 and 24 was set to 6.8 mm, and the groove cross-sectional area of ​​the center main grooves 21 and 22 and the groove cross-sectional area of ​​each shoulder main groove 23 and 24 were manufactured to the values ​​shown in Table 1.

[0068] Furthermore, the belt 18 was constructed from two belt plies 18A and 18B, with each belt having a belt angle of 24°. When the fabricated pneumatic tire 1 was mounted on a standard rim, with an internal tire pressure of 260kPa and a load of 520kg, the rectangularity of the contact surface of the tread 10 was 0.60. Also, the ratio of the sum of the widths of each main groove to the contact width W of the tread 10 (hereinafter sometimes referred to as the "main groove width ratio") was 24%.

[0069] <Examples 2-5> A pneumatic tire was manufactured in the same manner as in Example 1, except that the rectangularity of the contact surface of the tread 10 was set to 0.62, 0.65, 0.67, and 0.70, respectively, by adjusting the belt angle.

[0070] <Comparative Examples 1-4> Based on the tread pattern in Figure 2, the groove width of each main groove was adjusted so that the groove width and groove cross-sectional area would be the values ​​shown in Table 1, while keeping the depth of the center main grooves 21 and 22 and the shoulder main grooves 23 and 24 unchanged. In addition, the belt angle was adjusted so that the rectangular ratio would be the value shown in Table 1.

[0071] <Comparative Example 5> Instead of the tread pattern shown in Figure 2, the tread pattern shown in Figure 4 was used. The configuration of the tread 110 shown in Figure 4 will be described below.

[0072] As shown in Figure 4, the tread 110 of Comparative Example 5 has a pair of center main grooves 121, 122 and a pair of shoulder main grooves 123, 124, similar to the tread 10 in Figure 2. In this case, the groove width of the center main grooves 121, 122 was set to 8.8 mm, the depth of the center main grooves 121, 122 was set to 7.3 mm, the groove width of the shoulder main grooves 123, 124 was set to 8.6 mm, and the depth of the shoulder main grooves 123, 124 was set to 7.1 mm. The groove cross-sectional areas of the center main grooves 121, 122 and the groove cross-sectional area per shoulder main groove 123, 124 were manufactured to the values ​​shown in Table 1. As a result, as shown in Table 1, in the tread 110 shown in Figure 4, the groove cross-sectional areas of the center main grooves 121, 122 and the groove cross-sectional areas of the shoulder main grooves 123, 124 are approximately the same.

[0073] Furthermore, the tread 110, like the tread 10 in Figure 2, has a center tread 130, a first middle tread 140, a second middle tread 150, a first shoulder tread 160, and a second shoulder tread 170. The center tread 130, first middle tread 140, second middle tread 150, first shoulder tread 160, and second shoulder tread 170 extend in the circumferential direction of the tire. Also, in the tread 110 shown in Figure 4, similar to the tread 10 shown in Figure 2, the shape of the second middle tread 150 is the same as the shape of the first middle tread 140 when it is inverted relative to the tire equator CL, and the shape of the second shoulder tread 170 is the same as the shape of the first shoulder tread 160 when it is inverted relative to the tire equator CL.

[0074] The center land portion 130 has a center lateral groove 131 and a center sipe 132 that communicate with the center main groove 121, and a center lateral groove 133 and a center sipe 134 that communicate with the center main groove 122.

[0075] The first middle section 140 has a middle lateral groove 141 that communicates with the shoulder main groove 123, a middle sipe 142 that communicates with the center main groove 121, a middle sipe 143 that communicates with the shoulder main groove 123, and a middle sipe 144 that is formed to span the middle sipes 142 and 143, respectively.

[0076] The first shoulder land portion 160 has a shoulder longitudinal groove 161 extending along the circumferential direction of the tire, and shoulder transverse grooves 162 and 163 extending inward from the shoulder longitudinal groove 161 in the tire axial direction. Neither of the shoulder transverse grooves 162 and 163 communicates with the shoulder main groove 123, and the shoulder transverse groove 162 is longer than the shoulder transverse groove 163. In addition, the first shoulder land portion 160 has a shoulder sipe 164 that communicates with the shoulder main groove 123 and extends outward in the tire axial direction.

[0077] Furthermore, the belt angle of the pneumatic tire 101 in Comparative Example 5 was set to 22°. When the fabricated pneumatic tire was mounted on a standard rim, with an internal tire pressure of 260kPa and a load of 520kg, the rectangularity of the contact surface of the tread 10 was 0.77.

[0078] [Evaluation of noise performance] Each of the fabricated pneumatic tires was mounted on a test vehicle, and a microphone was placed at ear level in the driver's seat inside the vehicle. The sound pressure was measured while driving on a dry, flat asphalt road at 80 km / h. The evaluation results are relative values ​​with the evaluation result of Comparative Example 5 set to 100. A higher value indicates a greater noise reduction effect and superior noise performance.

[0079] [Evaluation of drainage performance] For each pneumatic tire that was fabricated, the test tire was rotated on a wet road surface with a water depth of 10 mm, and the speed at which hydroplaning occurred was measured. The evaluation results are relative values ​​with the speed measurement result of Comparative Example 5 set to 100, and a larger value indicates better drainage performance.

[0080] Table 1 shows the dimensions of the tread pattern for each pneumatic tire, and Table 2 shows the evaluation results for the drainage performance and noise performance of each pneumatic tire.

[0081] [Table 1]

[0082] [Table 2]

[0083] As shown in Tables 1 and 2, the tires of the examples show improved drainage performance and noise performance compared to the tire of Comparative Example 5. On the other hand, the tires of Comparative Examples 1 to 4, which have a rectangularity ratio exceeding 0.7, show improved drainage performance compared to the tire of Comparative Example 5, but no improvement in noise performance. [Explanation of symbols]

[0084] 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 lateral groove, 31A flex section, 32, 33 center sipe, 40 first middle land section, 41 middle lateral groove, 42 middle sipe, 50 second middle land section, 60 first shoulder land section, 61 shoulder lateral groove, 62 connecting sipe, 63 shoulder sipe, 70 second shoulder land section, 101 pneumatic tire, 121, 122 center main groove, 123, 124 shoulder main groove, 130 center land section, 131, 133 Center lateral groove, 132, 134 Center sipe, 140 First middle section, 141 Middle lateral groove, 142, 143, 144 Middle sipe, 150 Second middle section, 160 First shoulder section, 161 Shoulder longitudinal groove, 162, 163 Shoulder lateral groove, 164 Shoulder sipe, 170 Second shoulder section, CL Tire equator, E1, E2 Contact point

Claims

1. A pneumatic tire with a tread, The aforementioned tread is A pair of center main grooves, A pair of shoulder main grooves are positioned outward in the tire axial direction from the aforementioned center main groove, The central land area is partitioned by the pair of central main grooves, The middle land area is partitioned by the aforementioned center main groove and the aforementioned shoulder main groove, A shoulder land portion positioned outward in the tire axial direction from the shoulder main groove, It has, The sum of the widths of the pair of center main grooves and the pair of shoulder main grooves is 20% or more and 25% or less of the contact width of the tread. The depth of the pair of center main grooves and the pair of shoulder main grooves is 6.5 mm or more and 7.2 mm or less. A pneumatic tire in which the rectangularity of the contact surface of the tread is 0.60 or more and 0.70 or less.

2. The pneumatic tire according to claim 1, wherein the ratio of the groove width of the shoulder main groove to the groove width of the center main groove is 75% or more and 90% or less.

3. The pneumatic tire according to claim 1, wherein the ratio of the groove cross-sectional area of ​​the shoulder main groove to the groove cross-sectional area of ​​the center main groove is 0.6 or more and 0.8 or less.

4. Multiple sipes are provided in the aforementioned center land area and the aforementioned middle land area. The sipe provided on the land portion of the center communicates with one of the pair of main center grooves, The pneumatic tire according to claim 1, wherein the sipe provided in the middle land portion communicates with at least one of the center main groove and the shoulder main groove.

5. The aforementioned land portion of the center is provided with a center lateral groove that communicates with each of the pair of center main grooves, The pneumatic tire according to claim 1, wherein the center lateral groove has a bent portion that, in a plan view of the center land portion, protrudes to one side in the tire circumferential direction from the positions of both ends of the center lateral groove in the tire circumferential direction.

6. The pneumatic tire according to claim 1, wherein the middle land portion is provided with a middle lateral groove that communicates with the shoulder main groove but does not communicate with the center main groove.

7. The pneumatic tire according to claim 1, wherein the groove depth of the shoulder main groove is smaller than the groove depth of the center main groove.

8. The aforementioned shoulder land portion is provided with a shoulder lateral groove extending outward in the axial direction of the tire, The pneumatic tire according to claim 1, wherein the shoulder lateral groove is connected to the shoulder main groove via the sipe.

9. Carcass and, A belt having at least one belt ply arranged on the radially outer side of the carcass, with the cords arranged inclined with respect to the circumferential direction of the tire, Furthermore, The pneumatic tire according to claim 1, wherein the angle of the cord with respect to the circumferential direction of the tire is 22° or more and 29° or less.

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