pneumatic tires

Abstract

Reduces noise during acceleration. [Solution] A pneumatic tire (1) has a tread portion (2) provided with a pattern including four circumferential grooves (10) and five ribs. The land ratio of the pattern is 0.70 to 0.85. The ribs include a crown rib (12) including the tire equator, a pair of middle ribs (13), and a pair of shoulder ribs (14). Pitches, which are unit patterns, are repeatedly formed in each rib, and the longitudinal stiffness Ks of one pitch of each shoulder rib (14) is greater than the longitudinal stiffness Km of one pitch of each middle rib (13) and the longitudinal stiffness Kc of one pitch of the crown rib (12). The crown rib (12) and the pair of middle ribs (13) are each provided with a plurality of sipes (20) inclined relative to the tire circumferential direction and the tire axial direction. The plurality of sipes (20) includes a first sipe group consisting of sipes arranged in a seamless arrangement around one circumference of the tire.

Description

[Technical Field]

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

[0002] In recent years, various efforts have been made to reduce noise generated by tires (see, for example, Patent Document 1 below). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-40966 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0004] Even with tread patterns that have not been problematic in previous noise tests, a new issue has emerged in that noise becomes apparent during acceleration due to the recent increase in vehicle performance and electrification.

[0005] The present invention has been devised in view of the above circumstances, and has as its main object to provide a pneumatic tire that can suppress noise during accelerating driving. [Means for solving the problem]

[0006] The present invention provides a pneumatic tire including a tread portion, a pair of sidewall portions, and a pair of bead portions, wherein the tread portion has a pattern including four circumferential grooves extending continuously and linearly in the tire circumferential direction and five ribs separated by the four circumferential grooves, and the pattern has a land ratio in the range of 0.70 to 0.85, and the five ribs include a crown rib including the tire equator, a pair of middle ribs, and a pair of shoulder ribs, and each rib has a repeated pitch that is a unit pattern, and the longitudinal stiffness Ks of one pitch of each shoulder rib is greater than the longitudinal stiffness Km of one pitch of each middle rib and the longitudinal stiffness Kc of one pitch of the crown rib, and the crown rib and the pair of middle ribs have a plurality of sipes inclined with respect to the tire circumferential direction and the tire axial direction, each of the plurality of sipes having a first end on a first side in the tire circumferential direction and a second end on a second side in the tire circumferential direction, the plurality of sipes including a first sipe group consisting of sipes arranged in a seamless arrangement around one circumference of the tire, the seamless arrangement being such that in each pair of sipes adjacent in the tire circumferential direction, the first end of the sipe located on the second side is located at the same position in the tire circumferential direction as the second end of the sipe located on the first side, and in at least one of the pairs, the sipes constituting the one pair are formed on different ribs. [Effects of the Invention]

[0007] By adopting the above-described configuration, the pneumatic tire of the present invention can suppress noise during acceleration driving. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view of a pneumatic tire according to one embodiment of the present invention. [Figure 2] 1 is a development view of a tread portion of a pneumatic tire showing one embodiment of the present invention. [Figure 3] FIG. 3 is a partially enlarged view of the tread portion of FIG. 2. [Figure 4]FIG. 1 is a diagram showing one pitch of each rib. [Figure 5] FIG. 10 is a perspective view of a schematic block illustrating front-rear rigidity. [Figure 6] FIG. 2 is a plan view showing one pitch of the shoulder rib. [Figure 7A] FIG. 3 is a cross-sectional view of a main part of a tread portion illustrating the boundary of one pitch on the inner side in the tire radial direction. [Figure 7B] FIG. 2 is a side view showing an example of a stiffness measuring device. [Figure 7C] FIG. 10 is a perspective view showing a sample piece of one pitch of the first shoulder rib. [Figure 8] FIG. 8 is a cross-sectional view taken along line VIII-VIII in FIG. 2. [Figure 9] FIG. 9 is a cross-sectional view taken along line IX-IX in FIG. 2. [Figure 10] FIG. 2 is a partially enlarged view of a crown rib. [Figure 11] FIG. 11 is a cross-sectional view taken along line XI-XI in FIG. [Figure 12] FIG. 12 is a cross-sectional view taken along line XII-XII in FIG. 10. [Figure 13] FIG. 4 is a partially enlarged view of a first shoulder rib. [Figure 14] FIG. 4 is a development view of a tread portion showing another embodiment of the present invention. [Figure 15] FIG. 2 is a development view of a tread portion of Comparative Example 1. [Figure 16] FIG. 10 is a development view of the tread portion of Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of the present invention will now be described with reference to the drawings. The drawings may include exaggerated representations or representations different from the dimensional ratios of the actual structures to facilitate understanding of the present invention. Furthermore, when there are multiple embodiments, identical or common elements are designated by the same reference numerals throughout the specification, and redundant explanations are omitted. Furthermore, the specific configurations shown in the embodiments and drawings are intended to aid in understanding the contents of the present invention, and the present invention is not limited to the specific configurations shown in the drawings.

[0010] [Pneumatic tire structure] FIG. 1 shows a cross-sectional view of a pneumatic tire 1 according to one embodiment of the present invention. As shown in FIG. 1, the pneumatic tire 1 includes a tread portion 2, a pair of sidewall portions 3, and a pair of bead portions 4, each having a bead core 5 embedded therein. FIG. 1 shows a pneumatic tire 1 for passenger cars to which the present invention is applied. Pneumatic tires 1 for passenger cars include at least tires of sizes listed in Chapter A, "Passenger Car Tires," of the JATMA YEAR BOOK.

[0011] The tread portion 2 of this embodiment has a first tread edge Te1 and a second tread edge Te2. The axial distance between them is defined as the tread width TW. The pneumatic tire 1 of this embodiment is also designed to be mounted on a vehicle with the first tread edge Te1 facing outward from the vehicle and the second tread edge Te2 facing inward from the vehicle. The mounting orientation is indicated on the sidewall portion 3, for example.

[0012] In this specification, the first tread edge Te1 and the second tread edge Te2 refer to the outermost edges in the tire axial direction of the tread contact surface when a normal pneumatic tire 1 is placed on a flat surface with a normal load and a camber angle of 0°. Here, the definitions of each term are as follows:

[0013] The "normal state" of the pneumatic tire 1 means a state in which the pneumatic tire 1 is mounted on a normal rim with normal internal pressure and no load. The dimensions of each part of the pneumatic tire 1 are intended to be values ​​measured in the normal state unless the state of the tire is particularly specified.

[0014] A "genuine rim" is a rim that is defined for each tire by the standard system that includes the standard on which the tire is based. For example, in the case of JATMA, it is called a "standard rim," in the case of TRA, it is called a "design rim," and in the case of ETRTO, it is called a "measuring rim."

[0015] "Normal internal pressure" is the air pressure specified for each tire by each standard in the standard system, including the standard on which the tire is based. In the case of JATMA, it is the "maximum air pressure," in the case of TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and in the case of ETRTO, it is the "INFLATION PRESSURE."

[0016] "Normal load" refers to the load specified for each tire by a standard system that includes the standards on which the pneumatic tire 1 is based, such as "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. If there is no standard system that includes the standards on which the pneumatic tire 1 is based, the "normal load" refers to the load specified for each tire by the manufacturer or the like as the maximum load that can be applied when using the tire.

[0017] The pneumatic tire 1 also includes a toroidal carcass 6 extending between the pair of bead portions 4, 4, and a belt layer 7 disposed outside the carcass 6 in the tire radial direction and inside the tread portion 2.

[0018] The carcass 6 includes at least one carcass ply 6A. In this embodiment, the carcass 6 is constructed using two carcass plies 6A and 6B. The carcass plies 6A and 6B are formed of a rubber-cord composite in which an arrangement of carcass cords is covered with topping rubber. The carcass cords are made of, for example, organic fiber cords, and polyester cords are particularly preferred. The carcass cords are oriented at an angle of, for example, 75 to 90 degrees, preferably 90 degrees, relative to the tire equator C. Therefore, the carcass 6 in this embodiment is constructed as a radial structure.

[0019] Each carcass ply 6A is a turn-up ply including a main body portion 6a extending in a toroidal shape between a pair of bead cores 5, 5 and a turn-up portion 6b turned up from the axially inner side to the axially outer side at each bead core 5. In this embodiment, the two carcass plies 6A, 6B are turn-up plies. In a preferred embodiment, the turn-up portion 6b of at least one carcass ply has a so-called high turn-up structure located radially outward of a 50% position of the tire cross-sectional height H. Here, the "tire cross-sectional height" refers to the radial distance from the bead base line BL to the radially outermost position of the tire when the pneumatic tire 1 is in a normal state.

[0020] In each bead portion 4, a bead apex rubber 8 is disposed between the main portion 6a and the turned-up portion 6b of the carcass ply 6A. The bead apex rubber 8 extends, for example, in a tapered shape from the bead core 5 outward in the radial direction of the tire. The bead apex rubber 8 is made of a rubber composition that is harder than the tread rubber and the sidewall rubber. Such a bead apex rubber 8 increases the bending rigidity of the bead portion 4 and helps improve steering stability.

[0021] The belt layer 7 is formed, for example, using two or more belt plies 7A, 7B. Each of the belt plies 7A, 7B is a rubber-cord composite in which an arrangement of belt cords is covered with topping rubber. The belt cords are, for example, steel cords, and are oriented at an angle of, for example, 15 to 35 degrees with respect to the tire equator C. The belt plies 7A, 7B are overlapped so that the steel cords cross each other. Each of the belt plies 7A and 7B has an axial width greater than the tread width TW.

[0022] In the pneumatic tire 1 of this embodiment, a band layer 9 is disposed radially outward of the belt layer 7. The band layer 9 is composed of one or more band plies. The band ply is a rubber-cord composite in which an array of band cords is covered with a topping rubber. The band cords of this embodiment are, for example, organic fiber cords and are oriented at an angle of, for example, 5° or less with respect to the tire equator C. In a particularly preferred embodiment, the band ply is a so-called jointless ply formed by spirally winding a ribbon-shaped ply in which one or more band cords are arranged in parallel along the tire circumferential direction. Such a band layer 9 suppresses lifting of the belt layer 7 and deformation of the tread portion 2 during high-speed driving, and is useful for improving noise characteristics during high-speed driving.

[0023] The band layer 9 of this embodiment includes a full band 9A that covers the entire width of the belt layer 7 in the tire axial direction, and a pair of edge bands 9B that cover only both end portions of the belt layer 7 in the tire axial direction. The full band 9A has a width in the tire axial direction that is larger than that of the belt plies 7A and 7B. The edge bands 9B are overlapped on both end portions of the full band 9A. The inner end of the edge band 9B in the tire axial direction is located within the shoulder rib.

[0024] [Tread pattern] Fig. 2 is a planar development view of a tread portion 2 of one embodiment of the present invention. As shown in Fig. 2, four circumferential grooves 10 extending continuously and linearly in the tire circumferential direction are provided in the tread portion 2. As a result, the tread portion 2 is configured with a pattern (rib pattern) including five ribs 11 separated by the four circumferential grooves 10.

[0025] In this specification, "rib" refers to a land portion of the tread portion 2 that is continuous around the entire circumference of the tire. Here, "continuous" means that the rib is at least partially continuous in the tire circumferential direction. Therefore, the rib may be provided with sipes, lateral grooves, recesses, etc., one end of which terminates within the rib, on one and / or both axial side edges of the tire.

[0026] In this specification, "sipe" refers to a narrow cut formed in a land portion of the tread portion 2. In a sipe, at least a portion of a pair of opposing sipe wall surfaces contacts each other within the contact area of ​​the pneumatic tire 1 under normal load. Such a sipe has, for example, a portion whose width in a direction perpendicular to the sipe length direction (sipe width) is 1.5 mm or less, preferably 1.0 mm or less, or 0.8 mm or less.

[0027] In this specification, a "groove" has a groove width larger than that of a sipe, and a pair of opposing groove walls do not contact each other in the tread contact surface of the pneumatic tire 1 under normal load. A groove usually has a groove width larger than 1.5 mm.

[0028] The four circumferential grooves 10 include a first crown circumferential groove 10A, a second crown circumferential groove 10B, a first shoulder circumferential groove 10C, and a second shoulder circumferential groove 10D.

[0029] The first crown circumferential groove 10A is disposed between the tire equator C and the first tread edge Te1. The second crown circumferential groove 10B is disposed between the tire equator C and the second tread edge Te2. The first shoulder circumferential groove 10C is disposed between the first crown circumferential groove 10A and the first tread edge Te1. The second shoulder circumferential groove 10D is disposed between the second crown circumferential groove 10B and the second tread edge Te2.

[0030] All four circumferential grooves 10 are linear and continuous in the circumferential direction of the tire. This provides effective drainage performance on wet road surfaces. Furthermore, the circumferential grooves 10 of this embodiment extend in the circumferential direction of the tire with a substantially constant groove width. The term "substantially" refers to the tolerances that inevitably occur during the manufacturing of the pneumatic tire 1, a rubber product. Since such circumferential grooves 10 do not have a zigzag or other amplitude, they are less likely to generate periodic noise such as pitch noise during driving. This also helps to suppress noise during acceleration.

[0031] There are no particular limitations on the groove width of the circumferential grooves 10. In the case of a pneumatic tire 1 for a passenger car such as that of the present embodiment, the groove width of the circumferential grooves 10 is preferably, for example, 5 mm or more, and more preferably 6 mm or more, in order to achieve sufficient drainage performance. On the other hand, the groove width of the circumferential grooves 10 is preferably, for example, 20 mm or less in order to achieve sufficient dry grip performance.

[0032] In this specification, "groove width" refers to the distance between a pair of groove edges on the tread contact surface 2a, and is measured in a direction perpendicular to the longitudinal direction of the groove. However, if a chamfer is provided on the tread contact surface side of the groove wall, the groove width is measured excluding the chamfer. More specifically, the groove width is measured by regarding the intersection of an imaginary extension of the groove wall without chamfering and an imaginary extension of the tread contact surface as the groove edge.

[0033] In this embodiment, the groove widths of the first crown circumferential groove 10A and the second crown circumferential groove 10B are larger than the groove widths of the first shoulder circumferential groove 10C and the second shoulder circumferential groove 10D, for example. Since the crown circumferential grooves 10A and 10B are located in the tread central region where ground pressure during running is relatively large, increasing the groove widths of these grooves relatively improves wet performance without impairing dry grip performance. In one aspect, the groove widths of the crown circumferential grooves 10A and 10B are desirably 13% or more, preferably 15% or more, and even more preferably 20% or more larger than the groove width of the first shoulder circumferential groove 10C.

[0034] In this embodiment, the groove width of the first shoulder circumferential groove 10C is smaller than the groove width of the second shoulder circumferential groove 10D. This configuration relatively increases the rigidity of the land portion near the first shoulder circumferential groove 10C located on the outer side of the vehicle, suppresses deformation of the first shoulder rib 141 during cornering, and improves lateral grip. As a result, handling stability during cornering is improved. Furthermore, since passenger cars often have a negative camber angle in their suspensions, the second shoulder circumferential groove 10D located on the inner side of the vehicle and having a relatively larger groove width provides good drainage.

[0035] In this embodiment, the groove depth of the circumferential groove 10 is not particularly limited, but is preferably 5 mm or more, more preferably 6 mm or more, in order to achieve sufficient drainage performance. On the other hand, the groove depth of the circumferential groove 10 is preferably 13 mm or less, in order to maintain the lateral rigidity of each rib.

[0036] The tread portion 2 includes five ribs 11, namely, a crown rib 12, a pair of middle ribs 13, and a pair of shoulder ribs 14.

[0037] The crown rib 12 is located between the first crown circumferential groove 10A and the second crown circumferential groove 10B. Therefore, the crown rib 12 is provided on the tire equator C.

[0038] The middle rib 13 includes a first middle rib 131 located between the first crown circumferential groove 10A and the first shoulder circumferential groove 10C, and a second middle rib 132 located between the second crown circumferential groove 10B and the second shoulder circumferential groove 10D. However, when there is no need to particularly distinguish between the first middle rib 131 and the second middle rib 132, they may be simply referred to as middle ribs 13.

[0039] The shoulder rib 14 includes a first shoulder rib 141 located axially outward of the first shoulder circumferential groove 10C, and a second shoulder rib 142 located axially outward of the second shoulder circumferential groove 10D. However, when there is no need to particularly distinguish between the first shoulder rib 141 and the second shoulder rib 142, they may be simply referred to as shoulder ribs 14.

[0040] In this embodiment, a plurality of sipes 20 inclined with respect to the tire circumferential direction and the tire axial direction are formed on each of the crown rib 12, the first middle rib 131, and the second middle rib 132. The sipes 20 improve the wet grip performance and wear resistance of the pneumatic tire 1. The sipes 20 also optimize the rigidity distribution of the crown rib 12, the middle rib 13, etc., and can improve noise performance during accelerating driving. This will be described later.

[0041] Fig. 3 is a partially enlarged view of the tread portion 2 of Fig. 2. As shown in Fig. 3, the crown rib 12 of this embodiment is provided with a plurality of crown sipes 21, 22. Each of the crown sipes 21, 22 does not completely cross the crown rib 12 in the tire axial direction. Each of the crown sipes 21, 22 is inclined with respect to the tire circumferential direction and the tire axial direction. In this embodiment, the crown sipes 21, 22 extend linearly over their entire lengths.

[0042] The crown sipe 21 is a so-called semi-open sipe that extends from the first crown circumferential groove 10A and terminates within the crown rib 12. The crown sipe 21 has a first end (discontinuous end) 21A on a first side CD1 in the tire circumferential direction and a second end 21B (open end) on a second side CD2 in the tire circumferential direction.

[0043] The crown sipes 22 are so-called semi-open sipes that extend from the second crown circumferential grooves 10B and terminate within the crown rib 12. The crown sipes 22 have a first end (open end) 22A on a first side CD1 in the tire circumferential direction and a second end (disconnected end) 22B on a second side CD2 in the tire circumferential direction.

[0044] The first middle rib 131 is provided with a plurality of first middle sipes 23, 24. Each of the first middle sipes 23, 24 does not completely cross the first middle rib 131 in the tire axial direction. Each of the first middle sipes 23, 24 is inclined with respect to the tire circumferential direction and the tire axial direction. In this embodiment, the first middle sipes 23, 24 extend linearly over their entire length.

[0045] The first middle sipe 23 is a so-called semi-open sipe that extends from the first shoulder circumferential groove 10C and terminates within the first middle rib 131. The first middle sipe 23 has a first end (discontinuous end) 23A on a first side CD1 in the tire circumferential direction and a second end 23B (open end) on a second side CD2 in the tire circumferential direction.

[0046] The first middle sipe 24 is a so-called semi-open sipe that extends from the first crown circumferential groove 10A and terminates within the first middle rib 131. The first middle sipe 24 has a first end (open end) 24A on a first side CD1 in the tire circumferential direction and a second end 24B (discontinuous end) on a second side CD2 in the tire circumferential direction.

[0047] The second middle rib 132 is provided with a plurality of second middle sipes 25, 26. Each of the second middle sipes 25, 26 does not completely cross the second middle rib 132 in the tire axial direction. Each of the second middle sipes 25, 26 is inclined with respect to the tire circumferential direction and the tire axial direction. In this embodiment, the second middle sipes 25, 26 extend linearly over their entire length.

[0048] The second middle sipe 25 is a so-called semi-open sipe that extends from the second crown circumferential groove 10B and terminates within the second middle rib 132. The second middle sipe 25 has a first end (discontinuous end) 25A on a first side CD1 in the tire circumferential direction and a second end 25B (open end) on a second side CD2 in the tire circumferential direction.

[0049] The second middle sipe 26 is a so-called semi-open sipe that extends from the second shoulder circumferential groove 10D and terminates within the second middle rib 132. The second middle sipe 26 has a first end (open end) 26A on a first side CD1 in the tire circumferential direction and a second end 26B (discontinuous end) on a second side CD2 in the tire circumferential direction.

[0050] In this embodiment, only sipes 20 are formed on the crown rib 12 and the middle rib 13, and no lateral grooves are provided. These ribs 12 and 13, located in the central region of the tread, are exposed to high ground pressure and are prone to generating noise during acceleration. However, by not providing lateral grooves on these ribs 12 and 13, it is possible to suppress the generation of noise associated with deformation of the lateral grooves during acceleration.

[0051] 2, a plurality of shoulder lateral grooves 27 are formed in the shoulder rib 14 and spaced apart in the tire circumferential direction. The shoulder lateral grooves 27 include a first shoulder lateral groove 28 and a second shoulder lateral groove 29.

[0052] The first shoulder rib 141 is provided with a plurality of first shoulder lateral grooves 28. The first shoulder lateral grooves 28 intersect with the first tread edge Te1. More specifically, each first shoulder lateral groove 28 has an axially outer end 28A located axially outboard of the first tread edge Te1, and an axially inner end 28B that terminates within the first shoulder rib 141. Therefore, the inner ends 28B of the first shoulder lateral grooves 28 do not communicate with the first shoulder circumferential groove 10C. Furthermore, the inner ends 28B of the first shoulder lateral grooves 28 are not connected to other sipes or the like, and do not communicate with the first shoulder circumferential groove 10C even indirectly.

[0053] The second shoulder rib 142 is provided with a plurality of second shoulder lateral grooves 29. The second shoulder lateral grooves 29 intersect with the second tread edge Te2. More specifically, each second shoulder lateral groove 29 has an axially outer end 29A located axially outboard of the second tread edge Te2, and an axially inner end 29B that terminates within the second shoulder rib 142. Therefore, the inner ends 29B of the second shoulder lateral grooves 29 do not communicate with the second shoulder circumferential groove 10D. Furthermore, the inner ends 29B of the second shoulder lateral grooves 29 are not connected to other sipes or the like, and do not communicate with the second shoulder circumferential groove 10D even indirectly.

[0054] A plurality of shoulder sipes 40 are formed in the shoulder rib 14 and are spaced apart in the tire circumferential direction. The shoulder sipes 40 include first shoulder sipes 41 and second shoulder sipes 42.

[0055] The first shoulder rib 141 is provided with first shoulder sipes 41. Each first shoulder sipe 41 does not completely cross the first shoulder rib 141 in the axial direction. In this embodiment, the axially inner end 41B of each first shoulder sipe 41 communicates with the first shoulder circumferential groove 10C, and the axially outer end 41A of each first shoulder sipe 41 is discontinued within the first shoulder rib 141. Furthermore, each first shoulder sipe 41 does not communicate with the first shoulder lateral groove 28.

[0056] The second shoulder rib 142 is provided with second shoulder sipes 42. Each second shoulder sipe 42 does not completely cross the second shoulder rib 142 in the axial direction. In this embodiment, the axially inner end 42B of each second shoulder sipe 42 communicates with the second shoulder circumferential groove 10D, and the axially outer end 42A of each second shoulder sipe 42 is discontinued within the second shoulder rib 142. Furthermore, each second shoulder sipe 42 does not communicate with the second shoulder lateral groove 29 either.

[0057] The above-mentioned sipes and lateral grooves form a pattern in the tread portion 2. In the pattern, "pitches" which are unit designs are formed repeatedly in the tire circumferential direction.

[0058] Various studies have been conducted on the noise generated by tires when a vehicle accelerates (hereinafter referred to as "acceleration noise"). To date, it is believed that the noise is influenced by the volumetric velocity of tread block slippage per unit time. More specifically, it is believed that the magnitude of acceleration noise has a certain correlation with the product of the volumetric velocity of slippage per block and the number of blocks that break away from the road surface per unit time. Therefore, one method for reducing acceleration noise is to reduce the amount of slippage of the blocks in the tread portion 2 during acceleration. In the case of a rib pattern, the above-mentioned "block" can be read as the "pitch" of each rib.

[0059] Based on this knowledge, the inventors focused on a specific range of land ratio and the longitudinal rigidity of each rib per pitch as follows, in order to reduce the amount of slippage of each rib in order to reduce acceleration noise.

[0060] [Rand ratio] In the pneumatic tire 1 of this embodiment, the land ratio of the pattern of the tread portion 2 is specified within a certain range. Specifically, the land ratio of the pattern is set to a range of 0.70 to 0.85. In this specification, "land ratio" refers to the ratio of the actual contact area Sc to the virtual contact area Sa of the tread portion 2. The virtual contact area Sa of the tread portion 2 is an area specified from the contour shape of the contact area under a normal load condition, in which the pneumatic tire 1 is mounted on a normal rim at a normal internal pressure, subjected to a load of 70% of the load index LI, and brought into contact with a flat surface with a camber angle of 0°. Therefore, the virtual contact area includes not only the actual contact area but also grooves and sipes. On the other hand, the actual contact area Sc of the tread portion 2 is the area of ​​the portion that actually contacts the ground under a normal load condition. By setting this land ratio within the range of 0.70 to 0.85, the basic pattern rigidity of the tread portion 2 can be maintained without impairing drainage performance.

[0061] [Front-rear rigidity of one rib pitch] Next, the inventors focused on the longitudinal rigidity of one pitch of the crown rib 12, the middle rib 13, and the shoulder ribs 14. FIG. 4 illustrates one pitch of each rib constituting the pattern of the tread portion 2. FIG. 4 shows one pitch Pc of the crown rib 12, one pitch Pm1 of the first middle rib 131, one pitch Pm2 of the second middle rib 132, one pitch Ps1 of the first shoulder rib 141, and one pitch Ps2 of the second shoulder rib 142. One pitch of each rib is intended for the tread rubber portion, and as shown in FIG. 7A, the radially inner boundary of one pitch is a profile plane TP that passes through the groove bottom of the circumferential groove 10 and is parallel to the tread contact surface 2a. Therefore, the hatched areas in FIG. 7A indicate a cross section of one pitch of each of the ribs 12, 13, and 14. The outer boundary of one pitch of the shoulder rib 14 in the tire axial direction is defined as the outer contact edge 14e when the pneumatic tire 1 is mounted on a regular rim, the internal pressure is adjusted to 240 kPa, and a vertical load of 6.16 kN is applied and pressed against a horizontal surface. One pitch of the shoulder rib 14 is defined by a tread normal erected at this outer contact edge 14e.

[0062] In the pneumatic tire 1 of this embodiment, assuming the above-mentioned land ratio, the front-to-rear stiffness Ks of each pitch of the first shoulder rib 141 and the second shoulder rib 142 is configured to be greater than the front-to-rear stiffness Km of each pitch of the first middle rib 131 and the second middle rib 132 and the front-to-rear stiffness Kc of each pitch of the crown rib 12.

[0063] The shoulder ribs 14 have a relatively lower ground contact pressure during straight-ahead driving than the crown rib 12 and middle rib 13, and tend to slip more on the road surface during acceleration than other ribs. It has also been found that the amount of slip of each rib during acceleration correlates with the amount of circumferential shear deformation per pitch of each rib. Therefore, in this embodiment, the land ratio of the pattern in the tread portion 2 is limited to a range of 0.70 to 0.85 to ensure sufficient basic pattern rigidity, and the longitudinal rigidity per pitch of the crown rib 12, middle rib 13, and shoulder ribs 14 is set to Ks > Km and Ks > Kc. This suppresses the amount of circumferential shear deformation of the shoulder ribs 14 during acceleration, and effectively suppresses the amount of slip.

[0064] The longitudinal stiffness K of one pitch of each rib is expressed as the force that generates a unit deflection when a load P in the longitudinal direction (tire circumferential direction X) acts on one pitch, as shown schematically in FIG. 5. In this specification, the longitudinal stiffness of one pitch of each rib can be measured using a stiffness measuring device 100 as shown in FIG. 7B. The stiffness measuring device 100 includes a first fixed table 101, a movable table 102 that can move smoothly in the X direction on the first fixed table 101, a distance measuring device 103 for measuring the movement distance of the movable table 102 in the X direction, a lateral load measuring device 104 for measuring a lateral load f applied to the movable table 102, a second fixed table 105 that is located above the movable table 102 and can move up and down, a vertical load loader 106 that applies a vertically downward vertical load to the second fixed table 105, and a lateral load loader 107 that applies a horizontal lateral load f to the movable table 102.

[0065] Between the movable stage 102 and the second fixed stage 105 of the stiffness measuring device 100, a sample piece 200 corresponding to one pitch of each rib cut out from the tread portion 2 of the pneumatic tire 1 is placed. As shown in FIG. 7A, the sample piece 200 is a one-pitch portion of the tread rubber defined by a profile plane TP that passes through the groove bottom of the circumferential groove 10 and is parallel to the tread contact surface 2a. FIG. 7C shows the sample piece 200 corresponding to one pitch (Ps1) of the first shoulder rib. The upper surface of the sample piece 200 (the side facing the tread contact surface 2a) is fixed to the lower surface of the second fixed stage 105 by a fixing means such as an adhesive or double-sided tape. The lower surface of the sample piece 200 is fixed to the upper surface of the movable stage 102 by the fixing means. Furthermore, the tire circumferential direction of the sample piece 200 is aligned with the X direction of the stiffness measuring device 100.

[0066] First, a vertical load F0 is applied to the sample piece 200 by the vertical load loader 106, and then a lateral load f is applied by the lateral load loader. As a result, the sample piece 200 undergoes shear deformation in the X direction as shown by the imaginary line in Fig. 7A, and the X-direction shear displacement t at that time is measured by the distance measuring device 103. The longitudinal stiffness of one pitch of each rib is expressed by the following equation using the lateral load f and the X-direction displacement t. Front-rear stiffness of one pitch = f / t (unit: N / mm) Here, the vertical load F0 is the area of ​​the tread contact surface of the sample piece 200 (unit: cm 2 ) is A, it is specified as F0 = 25 × A (unit: N). The lateral load f can be determined arbitrarily.

[0067] The longitudinal stiffness of each pitch can be adjusted to a desired value by adjusting the rib width, sipe length, and / or sipe depth. In some examples, a wide rib width, a small sipe length, and a small sipe depth can increase the longitudinal stiffness of the rib.

[0068] In a preferred embodiment, the longitudinal stiffness Ks of the shoulder ribs 14 is 1.10 to 1.20 times the longitudinal stiffness Kc of the crown rib 12. Similarly, in a preferred embodiment, the longitudinal stiffness Ks of the shoulder ribs 14 is 1.10 to 1.20 times the longitudinal stiffness Km of the middle ribs 13. It is desirable that the longitudinal stiffness Kc of the crown rib 12 and the longitudinal stiffness Km of each middle rib 13 are the same or similar. More specifically, the longitudinal stiffness Kc of the crown rib 12 is desirably 0.97 to 1.03 times, and more desirably 0.99 to 1.02 times, the longitudinal stiffness Km of each middle rib 13. The pneumatic tire 1 of this embodiment can also suppress relative slippage between the crown rib 12 and the middle rib 13 during acceleration, which is caused by the difference in stiffness between the crown rib 12 and the middle rib 13, in the tread central region where ground pressure is high. As a result, the pneumatic tire 1 of this embodiment can further reduce acceleration noise.

[0069] [Circumferential length of one pitch] As shown in FIG. 4, it is also effective to specify the circumferential length LP of one pitch in the pattern of the tread portion 2. In a preferred embodiment, one pitch has a circumferential length LP of 25 to 35 mm. By specifying the pitch length LP, the longitudinal rigidity of each pitch is further optimized, and the amount of slip during accelerated running is effectively suppressed. The circumferential length LP of one pitch may be constant around the tire or may be variable. The latter embodiment is called a variable pitch. A variable pitch is desirable in that it further reduces pitch noise during accelerated running. In addition, in a pattern employing a variable pitch, the longitudinal rigidity of one pitch differs within each rib. In such a case, the greatest longitudinal rigidity is adopted as the longitudinal rigidity of one pitch of each rib.

[0070] As shown in FIG. 2 , in a preferred embodiment of the present invention, the profile lengths L of the contact surfaces of the crown rib 12, the first middle rib 131, and the second middle rib 132 are substantially the same. The profile length L of the contact surface is the length along the contact surface between the side edges of the ribs. The side edges of the ribs are synonymous with the “groove edges” described with respect to the circumferential grooves 10. By making the profile lengths L of the contact surfaces of the crown rib 12, the first middle rib 131, and the second middle rib 132 substantially the same and making their contact widths equal to each other, the rigidity of each rib can be made even more similar. Therefore, the pneumatic tire 1 of the present embodiment can suppress slippage of the individual ribs 12 and 13 and can also suppress relative slippage between the ribs 12 and 13 due to differences in rigidity in the tread central region where ground pressure is high. As a result, the pneumatic tire 1 of the present embodiment can further reduce acceleration noise.

[0071] [Seamless sipe placement] As described above, acceleration noise is related to the number of blocks that break away from the road surface per unit time, and reducing this number is effective. In this regard, the pattern of this embodiment includes a first sipe group G1 in which multiple sipes are arranged seamlessly around one circumference of the tire, as shown in FIG.

[0072] In this embodiment, the first sipe group G1 is formed between the tire equator C and the first tread edge Te1. Specifically, the first sipe group G1 is formed across a portion of the crown rib 12 closer to the first tread edge Te1 than the tire equator C and the first middle rib 131. More specifically, the first sipe group G1 in this embodiment includes the crown sipe 21 and the first middle sipes 23, 24.

[0073] The sipes of the seamlessly arranged first sipe group G1 contact the ground sequentially and substantially continuously as the pneumatic tire 1 rotates. More specifically, in each of the pairs of sipes SP1, SP2, and SP3 adjacent to each other in the tire circumferential direction, the first end of the sipe located on the second side CD2 in the tire circumferential direction is located at the same position in the tire circumferential direction as the second end of the sipe located on the first side CD1 (condition a). Furthermore, in the seamless arrangement of this embodiment, the sipes constituting at least one pair of the pairs SP1, SP2, and SP3 are formed on different ribs (condition b). Such a seamless arrangement of sipes can prevent overlapping contact between sipes, thereby reducing the number of sipes 20 that separate from the road surface per unit time.

[0074] In the example of FIG. 3 , for example, a sipe pair SP1 is identified. The pair SP1 consists of sipes 23 and 24. In the pair SP1, the first end 23A of the sipe 23 located on the second circumferential side CD2 of the tire is at the same circumferential position as the second end 24B of the sipe 24 located on the second circumferential side CD2 of the tire. Here, whether the first and second ends of two sipes are at the same circumferential position in the tire is determined using their sipe centerlines. That is, the first and second ends of the two sipes constituting a pair are identified by the ends of the sipe centerlines. The sipe centerline is the centerline between a pair of sipe edges. If a chamfered portion is provided on the sipe edge, the sipe edge is identified excluding the chamfered portion. More specifically, the intersection of an imaginary extension line of the sipe wall assuming no chamfer and an imaginary extension line of the tread contact patch is considered to be the sipe edge.

[0075] However, taking into account the characteristics of a tire, a vulcanized rubber product, and allowing for manufacturing tolerances, the "same position" also includes situations in which the two ends are offset by a very small distance in the tire circumferential direction. In this case, the distance is 5% or less of the sum of the circumferential lengths of the center lines of the two sipes in the sipe pair, preferably 3% or less, and more preferably 1% or less. Most preferably, the two ends are not offset in the tire circumferential direction. In summary, pair SP1 satisfies condition a, but does not satisfy condition b because the two sipes are formed on the same rib (first middle rib 131).

[0076] Next, sipe pair SP2 is identified. Pair SP2 is a pair of sipes adjacent to pair SP1 on the second side CD2. Pair SP2 consists of a sipe 23 located on the second side CD2 of pair SP1 and a sipe 21 provided on the crown rib 12. In pair SP2, the first end 21A of the sipe 21 located on the second side CD2 in the tire circumferential direction is at the same position in the tire circumferential direction as the second end 23B of the sipe 23 located on the first side CD1 in the tire circumferential direction. Therefore, pair SP2 satisfies condition a. Furthermore, in pair SP2, the sipe 23 is formed on the first middle rib 131, while the sipe 21 is formed on the crown rib 12. Therefore, the two sipes 23 and 21 of pair SP2 are formed on different ribs, and condition b is also satisfied.

[0077] Next, sipe pair SP3 is identified. Pair SP3 consists of sipes 21 and 24. That is, pair SP3 includes the sipe 21 adjacent to the second side CD2 of pair SP2 and the sipe 24 located on the first side CD1 of pair SP1. In pair SP3, the first end 24A of the sipe 24 located on the second side CD2 in the tire circumferential direction is also located at the same position in the tire circumferential direction as the second end 21B of the sipe 21 located on the first side CD1 in the tire circumferential direction. Therefore, pair SP3 satisfies condition a. Furthermore, in pair SP3, the sipe 21 is formed in the crown rib 12, while the sipe 24 is formed in the first middle rib 131. Therefore, the two sipes 21 and 24 of pair SP3 are formed in different ribs, and condition b is also satisfied.

[0078] Pitch noise is known as noise generated when a tire is running. For example, an impact force is generated each time a rib on which sipes are formed comes into contact with the road surface. This impact force periodically vibrates the tread portion 2 and the sidewall portion 3, thereby generating pitch noise. Pitch noise also tends to increase as the vehicle accelerates. However, in the first sipe group G1 arranged in a seamless arrangement as in this embodiment, the sipes alternately and continuously contact the ground during running of the tire. This reduces the fluctuation in impact force and reduces pitch noise associated with the ribs touching the ground, thereby reducing acceleration noise.

[0079] The pneumatic tire 1 of this embodiment also includes a second sipe group G2 in which a plurality of sipes are arranged seamlessly around one circumference of the tire.

[0080] In this embodiment, the second sipe group G2 is formed between the tire equator C and the second tread edge Te2. More specifically, the second sipe group G2 is formed between the tire equator C and the second shoulder circumferential groove 10D, that is, from a portion of the crown rib 12 closer to the second tread edge Te2 than the tire equator C to the second middle rib 132. The second sipe group G2 in this embodiment is made up of the crown sipe 22 and the second middle sipes 25, 26.

[0081] The second sipe group G2 includes sipe pairs SP4, SP5, and SP6, which correspond to the sipe pairs SP1, SP2, and SP3 of the first sipe group G1, respectively, and therefore will not be described in detail. The second sipe group G2 also has sipes that alternately and continuously contact the ground during tire operation, thereby reducing fluctuations in impact force and reducing pitch noise associated with the ribs contacting the ground, thereby reducing acceleration noise.

[0082] In a more preferred embodiment, only the first sipe group G1 and the second sipe group G2 are formed seamlessly as sipes in the crown rib 12 and the middle rib 13. Such a tread portion 2 is useful for reducing acceleration noise generated in the central region of the tread where ground pressure is high.

[0083] In this embodiment, when the sipes belonging to the first sipe group G1 are rotated 180° around any point on the tire equator C, they substantially overlap with the sipes belonging to the second sipe group G2. That is, the second sipe group G2 is arranged point-symmetrically with the first sipe group G1. As a result, the circumferentially adjacent sipes 26, 25, 22, 21, 24, and 23 contact the ground seamlessly in this order from the first side CD1 to the second side CD2 in the tire circumferential direction. This sipe arrangement further reduces acceleration noise.

[0084] The sipes formed on the crown rib 12 and the middle rib 13 are inclined in the same direction relative to the tire circumferential direction. In this embodiment, each sipe is inclined upward to the right in the drawing.

[0085] The angle β of the crown sipes 21, 22 relative to the tire circumferential direction is not particularly limited, but can be set, for example, in the range of 30 to 85°. On the other hand, sipes with a relatively small angle relative to the tire circumferential direction reduce edge components in the tire axial direction. From this perspective, the angle β of the crown sipes 21, 22 relative to the tire circumferential direction is preferably in the range of 30 to 60°, more preferably 30 to 55°, and even more preferably 30 to 40°.

[0086] The semi-open crown sipes 21, 22 do not completely divide the crown rib 12 in the tire axial direction, thereby maintaining high longitudinal rigidity of the rib and suppressing slippage of each pitch of the crown rib 12 when the rib comes into contact with the ground, even during acceleration. Furthermore, by applying the small angle with respect to the tire circumferential direction to the semi-open crown sipes 21, 22, the lateral edge components of the crown sipes 21, 22 are reduced. Therefore, the amount of opening and slippage of the sipes 21, 22 as they move from the contact patch to the outside of the contact patch are further reduced. This reduces acceleration noise at the crown rib 12. In a particularly preferred embodiment, the axial length Lc of the crown sipes 21, 22 is preferably in the range of 20% to 45% of the axial width Wc of the contact patch of the crown rib 12.

[0087] The angles γ and δ of the first middle sipes 23, 24 and the second middle sipes 25, 26 relative to the tire circumferential direction are not particularly limited, but can be set, for example, in the range of 30 to 85°. As with the crown sipes 21, 22, from the viewpoint of reducing axial edge components and acceleration noise, the angles γ and δ of the first middle sipes 23, 24 and the second middle sipes 25, 26 relative to the tire circumferential direction are preferably in the range of 30 to 60°, more preferably 30 to 55°, and even more preferably 30 to 40°. The axial length Lm1 of the first middle sipes 23, 24 is preferably in the range of 20% to 45% of the axial width Wm1 of the contact patch of the first middle rib 131. Similarly, the axial length Lm2 of the second middle sipes 25, 26 is preferably in the range of 20% to 45% of the axial width Wm2 of the contact patch of the second middle rib 132.

[0088] The difference in angle between the crown sipes 21, 22, the first middle sipes 23, 24, and the second middle sipes 25, 26 and the tire circumferential direction is preferably 50° or less, more preferably 40° or less, and even more preferably 30° or less. Here, the "angle difference" refers to the difference in angle between two sipes and the tire circumferential direction. More specifically, the angle of each sipe with respect to the tire circumferential direction is first determined. Then, among the crown sipes 21, 22, the first middle sipes 23, 24, and the second middle sipes 25, 26, the sipe with the largest angle with respect to the tire circumferential direction and the sipe with the smallest angle with respect to the tire circumferential direction are determined, and the difference in angle between them is calculated. Note that, when each sipe is curved or zigzag, the angles β, γ, and δ of the sipe with respect to the tire circumferential direction are defined as the angle of a straight line connecting both ends of the sipe with respect to the tire circumferential direction.

[0089] In this embodiment, the angle β of the crown sipes 21, 22 relative to the tire circumferential direction is approximately 35°. The angles γ and δ of the first middle sipes 23, 24 and the second middle sipes 25, 26 relative to the tire circumferential direction are also approximately 35°. Therefore, the crown sipes 21, 22, the first middle sipes 23, 24, and the second middle sipes 25, 26 extend parallel to one another, and the difference in the angles of these sipes relative to the tire circumferential direction is substantially zero. This configuration helps to further reduce acceleration noise.

[0090] FIG. 8 shows a cross-sectional view taken along line VIII-VIII in FIG. 2. As shown in FIG. 8, the crown sipe 21 of this embodiment includes a base portion 21m having a substantially constant depth D1 and a sub-portion 21s whose depth gradually decreases toward the first end 21A. The depth D1 of the base portion 21m is, for example, 70% to 90% of the depth D of the first crown circumferential groove 10A, and is approximately 85% in this embodiment. The sub-portion 21s has an end portion inclined at an angle θ1 with respect to a tread normal extending from the first end 21A of the crown sipe 21. The angle θ1 is preferably larger than the angle θ2 of the rib wall of the crown rib 12, for example. This minimizes the change in rigidity of the crown rib 12, which is desirable from the perspective of reducing acceleration noise. More specifically, the angle θ1 is preferably 15° or greater, more preferably 18° to 25°.

[0091] The crown sipe 22 of this embodiment also includes a base 22m having a substantially constant depth D1 and a sub-portion 22s whose depth gradually decreases toward the discontinuous end 22B. The configurations of the base 22m and the sub-portion 22s are the same as those of the base 21m and the sub-portion 21s of the crown sipe 21 (which have a substantially symmetrical structure with respect to the tire equator C).

[0092] FIG. 9 shows a cross-sectional view taken along line IX-IX in FIG. 2. As shown in FIG. 9, the first middle sipe 23 of this embodiment also includes a base portion 23m having a substantially constant depth D1 and a secondary portion 23s whose depth gradually decreases toward the first end 23A. The depth D1 of the base portion 23m is, for example, 70% to 90% of the depth D of the first shoulder circumferential groove 10C, and in this embodiment, it is approximately 85%. The secondary portion 23s has an end bottom portion inclined at an angle θ1 with respect to the tread normal at the first end 23A of the first middle sipe 23. The angle θ1 is preferably greater than the angle θ2 of the rib wall of the first middle rib 131, for example. This minimizes the change in rigidity of the first middle rib 131, which is desirable from the perspective of reducing acceleration noise. More specifically, the angle θ1 is preferably 15° or greater, more preferably 18° to 25°.

[0093] The first middle sipe 24 of this embodiment also has a base 24m having a substantially constant depth D1 and a secondary portion 24s whose depth gradually decreases toward the second end 24B. The configurations of the base 24m and secondary portion 24s are the same as those of the base 23m and secondary portion 23s of the first middle sipe 23 (they have a substantially symmetrical structure with respect to the center line of the rib). The second middle sipes 25 and 26 also have the same structure as the first middle sipes 23 and 24.

[0094] [Sipe chamfering] Some of the sipes 20 may be provided with chamfered portions 30. The chamfered portions 30 improve the ground contact near the edges of the sipes 20 during driving and braking, and are useful for enhancing traction and braking performance. In this embodiment, each of the sipes 20 (i.e., the crown sipes 21, 22, the first middle sipes 23, 24, and the second middle sipes 25, 26) is provided with a chamfered portion 30. On the other hand, providing chamfered portions on the sipes 20 may increase the sound pressure level of the primary frequency band (approximately 550 to 650 Hz) of pitch noise. From this perspective, it is desirable to arrange the chamfered portions 30 of the sipes 20 more specifically as follows.

[0095] FIG. 10 is a partially enlarged view of the crown rib 12. As shown in FIG. 10, the crown sipes 21 and 22 each have a chamfered portion 30. In the crown sipe 21, the chamfered portion 30 is formed only on the sipe edge on the first side CD1 of the crown sipe 21. Therefore, the chamfered portion 30 is formed only on the sipe edge on the side where an acute angle is formed between the crown sipe 21 and the edge 12e of the crown rib 12, and no chamfered portion 30 is formed on the opposite edge. In addition, in the crown sipe 22, the chamfered portion 30 is formed only on the sipe edge on the second side CD2 of the crown sipe 22. Therefore, the chamfered portion 30 is formed only on the sipe edge on the side where an acute angle is formed between the crown sipe 22 and the edge 12e of the crown rib 12, and no chamfered portion 30 is formed on the opposite edge.

[0096] FIG. 11 shows a cross-sectional view taken along line XI-XI in FIG. 10 , and FIG. 12 shows a cross-sectional view taken along line XII-XII in FIG. 10 . The chamfered portion 30 has a continuously changing chamfer width W. The chamfer width W is the width of the chamfered portion 30 in a direction perpendicular to the sipe longitudinal direction and is measured in a plan view of the tread. In this embodiment, the chamfer width W of the chamfered portion 30 gradually decreases from the open ends of the sipes 21, 22 to their discontinuous ends, and is set to zero at the discontinuous ends. Similarly, the chamfered portion 30 has a continuously changing chamfer depth dc. The chamfer depth dc is the depth of the chamfered portion 30 in the tire radial direction. In this embodiment, the chamfered depth dc of the chamfered portion 30 gradually decreases from the open ends of the sipes 21, 22 to their discontinuous ends, and is set to zero at the discontinuous ends. Similar chamfered portions 30 are also provided on the first middle sipes 23, 24 and the second middle sipes 25, 26.

[0097] The chamfered portion 30 on only one side as in this embodiment can improve wet performance while suppressing an increase in the sound pressure level of the first frequency band of pitch noise during acceleration. In addition, the chamfered portion 30 is expected to have the effect of improving the wear resistance around the sipes of each rib.

[0098] [Circumferential sipes] As shown in Fig. 2, at least one of the crown rib 12, the first middle rib 131, and the second middle rib 132 is provided with a circumferential sipe 50 extending in the tire circumferential direction. In this embodiment, the crown rib 12 and the middle rib 13 are provided with the circumferential sipes 50. Compared to the inclined sipes 20, the circumferential sipes 50 are less likely to reduce the front-to-rear rigidity of each rib. Rather, the circumferential sipes 50 are preferable in that they equalize the distribution of contact pressure when the rib comes into contact with the ground, alleviate input from the tread portion 2, and reduce overall sound pressure during acceleration driving.

[0099] The circumferential sipes 50 are provided, for example, in the axially central region of each rib. The axially central region of the rib is an area that is 30% of the maximum axial width of the contact surface of the rib, and its axial center coincides with the axial center of the rib. The circumferential sipes 50 of this embodiment are provided at the axially central position of each rib, and are separated from the sipes 20 that are inclined in the circumferential and axial directions of the tire. Furthermore, the circumferential sipes 50 of this embodiment extend linearly along the circumferential direction of the tire and are continuous in the circumferential direction of the tire.

[0100] The depth of the circumferential sipes 50 is not particularly limited, but is preferably 1.0 mm or more to effectively improve the ground contact of the rib. On the other hand, to prevent a decrease in the longitudinal rigidity of the rib, the depth of the circumferential sipes 50 is preferably 5.5 mm or less. In particular, the depth of the circumferential sipes 50 is preferably smaller than the depth of the sipes 20 inclined with respect to the tire circumferential direction and tire axial direction provided on the rib, and further, the depth of the circumferential sipes 50 is preferably 50% or less of the depth of the inclined sipes 20.

[0101] [First and second shoulder grooves] In this embodiment, the first shoulder lateral grooves 28 and second shoulder lateral grooves 29 extend linearly, and in a preferred embodiment, they extend linearly over their entire length. The first shoulder lateral grooves 28 and second shoulder lateral grooves 29 form an angle α of 90° with respect to the tire circumferential direction. That is, in this embodiment, the first shoulder lateral grooves 28 and second shoulder lateral grooves 29 extend parallel to the tire axial direction. Because these first shoulder lateral grooves 28 and second shoulder lateral grooves 29 are unlikely to match the contour of the contact patch of the shoulder rib 14, the compressed air in the grooves is prevented from suddenly escaping outward from the contact patch. This helps reduce pitch noise.

[0102] As shown in FIG. 1 , the first shoulder lateral grooves 28 and the second shoulder lateral grooves 29 are arranged to cover the area where the edge bands 9B are located. More specifically, the axially inner ends 28B and 29B of the first shoulder lateral grooves 28 and the second shoulder lateral grooves 29 are both axially positioned substantially at the same positions as the axially inner ends of the pair of edge bands 9B. The axially outer ends 28A and 29A of the first shoulder lateral grooves 28 and the second shoulder lateral grooves 29 are positioned axially outward beyond the axially outer ends of the pair of edge bands 9B. The area where the edge bands 9B of the shoulder rib 14 are located overlaps with the full band 9A, providing locally high rigidity. However, by arranging the first shoulder lateral grooves 28 and the second shoulder lateral grooves 29 to cover the area where the edge bands 9B are located, the front-rear rigidity of the shoulder rib 14 is made uniform in the axial direction, and the contact pressure distribution of the shoulder rib 14 during acceleration is made uniform, thereby suppressing the amount of slippage of the shoulder rib 14. Therefore, the acceleration noise is further reduced.

[0103] [Shoulder sipes, shoulder grooves] The first shoulder sipes 41 and the second shoulder sipes 42 have substantially the same configuration. In this embodiment, the second shoulder sipes 42 have a point-symmetrical structure to the first shoulder sipes 41. Similarly, the second shoulder lateral grooves 29 also have a point-symmetrical structure to the first shoulder lateral grooves 28. The configurations of the first shoulder sipes 41 and the first shoulder lateral grooves 28 will be described below using the first shoulder sipes 41 and the first shoulder lateral grooves 28 as examples.

[0104] One first shoulder sipe 41 is provided between two circumferentially adjacent first shoulder lateral grooves 28. FIG. 13 shows an enlarged plan view of the first shoulder sipe. As shown in FIG. 13, the first shoulder sipe 41 includes a curved portion 411. A first shoulder sipe 41 having such a curved portion 411 is less likely to match the contour of the contact patch of the shoulder rib 14, which prevents the air compressed within the sipe from being suddenly discharged outward from the contact patch. This helps reduce pitch noise. To achieve this effect, the curved portion 411 preferably has a curvature radius R of, for example, 15 to 25 mm.

[0105] The first shoulder sipe 41 of this embodiment includes a curved portion 411, an outer straight portion 412 located axially outward of the curved portion 411, and an inner straight portion 413 located axially inward of the curved portion 411. The outer straight portion 412 is longer than the inner straight portion 413. The outer straight portion 412 extends, for example, parallel to the first shoulder lateral groove 28. The outer straight portion 412 constitutes the axially outer end 41A of the first shoulder sipe 41, and this outer end 41A is axially aligned with or axially inward of the axially inner end 28B of the first shoulder lateral groove. This embodiment illustrates the former configuration. This arrangement eliminates localized reductions in the rigidity of the shoulder rib 14 due to axial overlap between the first shoulder sipe 41 and the first shoulder lateral groove 28. This helps to uniform the contact pressure distribution of the shoulder rib 14 during acceleration and further suppress slippage during acceleration.

[0106] Fig. 14 shows a pattern according to another embodiment of the present invention. The pattern in Fig. 14 differs from the pattern in Fig. 2 in the configuration of the crown rib 12, but the other configurations are the same as those in Fig. 2. As shown in Fig. 14, the crown rib 12 is provided with a first crown sipe 61 and a second crown sipe 62.

[0107] In this embodiment, the angle β1 of the first crown sipes 61 relative to the tire circumferential direction is larger than the angle β2 of the second crown sipes relative to the tire circumferential direction. For example, the angle β1 of the first crown sipes 61 is larger than the angles γ and δ of the first middle sipes 23, 24 and the second middle sipes 25, 26 relative to the tire circumferential direction, respectively. On the other hand, the angle β2 of the second crown sipe 62 is smaller than the angles γ and δ of the first middle sipes 23, 24 and the second middle sipes 25, 26 relative to the tire circumferential direction, respectively. The difference in angle between the first crown sipes 61 and the second crown sipes 62 (β1 - β2) is set to 40° or less.

[0108] 14, the crown rib 12, the first middle rib 131, and the second middle rib 132 are provided with a seamlessly arranged first sipe group G1 and a seamlessly arranged second sipe group G2. In this embodiment, the crown rib 12 and the middle rib 13 are also provided with only the seamlessly arranged first sipe group G1 and the seamlessly arranged second sipe group G2.

[0109] In the first sipe group G1, the second middle sipes 26, 25, the crown sipes 22, 21, and the first middle sipes 24, 23 contact the ground in succession from the first side CD1 to the second side CD2 in the tire circumferential direction (see the thick dashed line). Similarly, in the second sipe group G2, the second middle sipes 26, 25, the crown sipes 22, 21, and the first middle sipes 24, 23 contact the ground in succession from the first side CD1 to the second side CD2 in the tire circumferential direction (see the thin dashed line). These first sipe group G1 and second sipe group G2 are arranged alternately. Even in this embodiment, acceleration noise can be suppressed by specifying the longitudinal rigidity of the rib.

[0110] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above specific disclosure, and can be implemented in various modified forms within the scope of the technical idea described in the claims. [Example]

[0111] More specific, non-limiting examples of the present invention will now be described. Based on the specifications in Table 1, pneumatic tires (tire size: 235 / 55R19) were prototyped and their performance was tested. Examples 1 to 3 have the pattern shown in FIG. 2, and Example 4 has the pattern shown in FIG. 14. Comparative Examples 1 and 2 have the patterns shown in FIGS. 15 and 16, respectively. In the patterns of Comparative Examples 1 and 2, the crown rib and middle rib do not have seamlessly arranged sipes. The front-to-rear rigidity of one pitch of the first middle rib is substantially the same as that of one pitch of the second middle rib. The front-to-rear rigidity of one pitch of the first shoulder rib is substantially the same as that of one pitch of the second shoulder rib. The test method is as follows:

[0112] [Maximum displacement within the contact patch] Each test tire was mounted on a standard rim and the internal pressure was adjusted to 240 kPa. Then, a single-point measurement marker was applied to the surface of each rib. Then, under conditions of camber angle 0°, slip angle 0°, vertical load 5.01 kN, and driving force 1 kN, the tire was rolled on a multi-point bench wear energy evaluation tester, and the maximum displacement (amount of slip) of each marker from the start of contact to the end of contact was measured. The smaller the displacement, the smaller the amount of slip of each rib during contact, indicating a better result.

[0113] [Acceleration noise test] Acceleration tests were conducted based on the United Nations Economic Commission for Europe (UNECE) vehicle exterior noise regulation test method (R51-03 conditions). Specifically, a hybrid SUV fitted with test tires entered the test track at a low speed of 20 km / h or less, then selected the appropriate gear and fully opened the accelerator just before the measurement area, accelerating until it reached a speed of 50 km / h. The maximum noise level (dB(A)) was then measured as the test vehicle passed a measurement microphone (installed 7.5 m to the side of the vehicle) during acceleration. The internal pressure of the test tires was 240 kPa, and the longitudinal load per tire was 6.16 kN.

[0114] [Ride comfort test] The ride comfort of a test vehicle fitted with the test tires was evaluated by the driver's senses. The results are rated based on the ride comfort of Comparative Example 1 being 100, with a higher score indicating better ride comfort.

[0115] [Pitch noise test] The tire pattern noise was measured when a test vehicle fitted with each sample tire was traveling at a speed of 50 km / h, and the sound pressure was calculated by analyzing the waveform. The results are given as a score, with the sound pressure level of Comparative Example 1 being 100, with a higher score indicating better pitch noise.

[0116] [Wear resistance test] The wear energy of each prototype tire was measured using a bench wear energy evaluation tester. The results are expressed as an index, with Comparative Example 1 being 100, and a larger index value indicates smaller wear energy and better wear resistance. The test results are shown in Table 1.

[0117] [Table 1]

[0118] It was confirmed that the maximum displacement (corresponding to the amount of slip) of each rib in the contact patch of the pneumatic tires of Examples 1 to 4 was kept small, and more specifically, the average displacement of each rib was kept to 0.35 mm or less. In addition, it was confirmed that the pneumatic tires of Examples 1 to 4, which employ a seamless sipe arrangement, also suppressed the deterioration of pitch noise. Thus, it was confirmed that the acceleration noise of the pneumatic tires of Examples 1 to 4 was significantly suppressed compared to Comparative Examples 1 and 2 due to the synergistic effect of suppressing the amount of slip of the ribs during acceleration and reducing pitch noise.

[0119] It was also confirmed that the ride comfort of the pneumatic tires of Examples 1, 2 and 4 was superior to that of Comparative Example 1.

[0120] Furthermore, it was confirmed that the wear resistance of the pneumatic tire of Example 1 was superior to that of Comparative Example 1.

[0121] [Note] The present invention includes the following aspects.

[0122] [Invention 1] A pneumatic tire, A tread portion; A pair of sidewall portions; a pair of bead portions; The tread portion has a pattern including four circumferential grooves extending continuously and linearly in the tire circumferential direction and five ribs separated by the four circumferential grooves, The pattern has a land ratio in the range of 0.70 to 0.85, The five ribs include a crown rib including the tire equator, a pair of middle ribs, and a pair of shoulder ribs, Each rib has a repeating unit pattern called a pitch. The longitudinal stiffness Ks of each shoulder rib per pitch is greater than the longitudinal stiffness Km of each middle rib per pitch and the longitudinal stiffness Kc of each crown rib per pitch, The crown rib and the pair of middle ribs are each provided with a plurality of sipes inclined with respect to the tire circumferential direction and the tire axial direction, Each of the plurality of sipes has a first end on a first side in the tire circumferential direction and a second end on a second side in the tire circumferential direction, The plurality of sipes includes a first sipe group consisting of sipes arranged in a seamless arrangement around one circumference of the tire, The seamless arrangement is such that, in each of a pair of sipes adjacent to each other in the tire circumferential direction, the first end of the sipe located on the second side is provided at the same position in the tire circumferential direction as the second end of the sipe located on the first side, In at least one of the pairs, the sipes constituting the pair are formed on different ribs. Pneumatic tires. [Invention 2] The pneumatic tire according to Invention 1, wherein the plurality of sipes includes a second sipe group consisting of sipes arranged in the seamless arrangement around one circumference of the tire. [Invention 3] the first sipe group is formed between the tire equator and a first tread edge, A pneumatic tire according to invention 2, wherein the second sipe group is formed between the tire equator and a second tread edge. [Invention 4] The pneumatic tire according to invention 2 or 3, wherein each sipe of the second sipe group is arranged point-symmetrically with respect to each sipe of the first sipe group, with respect to an arbitrary point on the tire equator. [Invention 5] The pneumatic tire according to any one of claims 2 to 4, wherein the sipes provided on the crown rib and the pair of middle ribs are only sipes belonging to the first sipe group and the second sipe group. [Invention 6] 6. The pneumatic tire according to any one of claims 1 to 5, wherein the plurality of sipes have angles that differ from each other in the circumferential direction of the tire by 50° or less. [Invention 7] 7. The pneumatic tire according to any one of claims 1 to 6, wherein the plurality of sipes extend parallel to one another. [Invention 8] 8. The pneumatic tire according to any one of claims 1 to 7, wherein one pitch has a length of 25 to 35 mm in the tire circumferential direction. [Invention 9] 9. The pneumatic tire according to any one of inventions 1 to 8, wherein the longitudinal stiffness Ks of the shoulder ribs is 1.10 to 1.20 times the longitudinal stiffness Kc of the crown rib. [Invention 10] 10. The pneumatic tire according to any one of claims 1 to 9, wherein the longitudinal stiffness Ks of the shoulder ribs is 1.10 to 1.20 times the longitudinal stiffness Km of the middle rib. [Invention 11] 11. The pneumatic tire according to any one of claims 1 to 10, wherein the longitudinal stiffness Kc of the crown rib is 0.97 to 1.03 times the longitudinal stiffness Km of each middle rib. [Explanation of symbols]

[0123] 1 pneumatic tire 2 Tread section 3 Sidewall 4 Bead section 10 Circumferential groove 11 Ribs 12 Crown Rib 13 Middle Rib 131 1st Middle Rib 132 Second Middle Rib 14 Shoulder Rib 141 First Shoulder Rib 142 Second Shoulder Rib 20 sipes 21, 22 Crown sipes 23, 24 1st middle sipe 25, 26 Second middle sipe G1 First Sipe Group G2 Second Sipe Group Te1 First tread edge Te2 Second tread edge

Claims

1. A pneumatic tire, A tread portion; A pair of sidewall portions; a pair of bead portions; the tread portion has a pattern including four circumferential grooves extending continuously and linearly in the tire circumferential direction and five ribs separated by the four circumferential grooves, the pattern has a land ratio in the range of 0.70 to 0.85; The five ribs include a crown rib including the tire equator, a pair of middle ribs, and a pair of shoulder ribs, Each rib has a repeating unit pattern called a pitch. The longitudinal stiffness Ks of each shoulder rib pitch is greater than the longitudinal stiffness Km of each middle rib pitch and the longitudinal stiffness Kc of each crown rib pitch, The crown rib and the pair of middle ribs are each provided with a plurality of sipes inclined with respect to the tire circumferential direction and the tire axial direction, Each of the plurality of sipes has a first end on a first side in the tire circumferential direction and a second end on a second side in the tire circumferential direction, The plurality of sipes includes a first sipe group consisting of sipes arranged in a seamless arrangement around one circumference of the tire, The seamless arrangement is such that, in each of a pair of sipes adjacent to each other in the tire circumferential direction, the first end of the sipe located on the second side is provided at the same position in the tire circumferential direction as the second end of the sipe located on the first side, At least one of the pairs has the sipes constituting the pair formed on different ribs, The plurality of sipes further includes a second sipe group consisting of sipes arranged in the seamless arrangement around one circumference of the tire. Pneumatic tires.

2. The first sipe group is formed between the tire equator and a first tread edge, The pneumatic tire according to claim 1 , wherein the second sipe group is formed between the tire equator and a second tread edge.

3. An air-filled tire as described in claim 2, wherein each sipe in the second sipe group is arranged point-symmetrically with respect to each sipe in the first sipe group, with respect to any point on the tire equator.

4. A pneumatic tire described in any one of claims 1 to 3, wherein the sipes provided on the crown rib and the pair of middle ribs are only sipes belonging to the first sipe group and the second sipe group.

5. A pneumatic tire as described in any one of claims 1 to 3, wherein the difference in angle between the plurality of sipes relative to the tire circumferential direction is 50° or less.

6. A pneumatic tire as described in any one of claims 1 to 3, wherein the multiple sipes extend parallel to each other.

7. A pneumatic tire described in any one of claims 1 to 3, wherein one pitch has a circumferential length of 25 to 35 mm.

8. 4. The pneumatic tire according to claim 1, wherein the longitudinal stiffness Ks of the shoulder ribs is 1.10 to 1.20 times the longitudinal stiffness Kc of the crown rib.

9. The pneumatic tire according to claim 8, wherein the longitudinal stiffness Ks of the shoulder ribs is 1.10 to 1.20 times the longitudinal stiffness Km of the middle rib.

10. A pneumatic tire as described in any one of claims 1 to 3, wherein the front-to-rear stiffness Kc of the crown rib is 0.97 to 1.03 times the front-to-rear stiffness Km of each middle rib.

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