pneumatic tires

Abstract

To provide a tire that suppresses noise during acceleration. [Solution] The ribs in the pattern with a land ratio of 0.70 to 0.85 include a crown rib 12, a middle rib 13, and shoulder ribs 14 on the equator. Each rib is formed with a unit pattern pitch, and the longitudinal stiffness Ks of one pitch of the shoulder rib is greater than the longitudinal stiffness Km and Kc of one pitch of the middle rib and crown rib. The crown and middle ribs are provided with sipes 20 inclined with respect to the axial direction. The sipes do not completely cross each rib in the axial direction. Each shoulder rib is provided with a shoulder lateral groove 27 and a shoulder sipe 40, and the axial inner ends of the shoulder sipes communicate with the circumferential groove, but each shoulder sipe does not communicate with the shoulder lateral groove. Each shoulder sipe is provided between shoulder lateral grooves adjacent in the tire circumferential direction, and the shoulder sipe has a tie bar portion with a locally raised sipe bottom.

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 a longitudinal stiffness Ks of one pitch of each shoulder rib is greater than a longitudinal stiffness Km of one pitch of each middle rib and a longitudinal stiffness Kc of one pitch of the crown rib, and the crown rib and the pair of middle ribs each have a longitudinal stiffness Ks of one pitch of the shoulder rib that is greater than a longitudinal stiffness Km of one pitch of the middle rib and a longitudinal stiffness Kc of one pitch of the crown rib, a plurality of sipes inclined with respect to the tire circumferential direction and the tire axial direction, none of which completely crosses each shoulder rib in the tire axial direction; a plurality of shoulder lateral grooves arranged at intervals in the tire circumferential direction and a plurality of shoulder sipes arranged at intervals in the tire circumferential direction are provided in each shoulder rib; the inner end of each shoulder sipe in the tire axial direction communicates with one of the four circumferential grooves, and each shoulder sipe does not communicate with the shoulder lateral groove; each shoulder sipe is provided between two shoulder lateral grooves adjacent to each other in the tire circumferential direction; and at least one of the shoulder sipes has a tie bar portion formed by locally raising the sipe bottom. [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. 6. [Figure 9] FIG. 9 is a cross-sectional view taken along line IX-IX in FIG. 2. [Figure 10] FIG. 3 is a cross-sectional view taken along line XX in FIG. 2. [Figure 11] FIG. 2 is a cross-sectional view of a sipe. [Figure 12] FIG. 2 is a development view of a tread portion of a comparative example. [Figure 13] FIG. 10 is a development view of a tread portion of another comparative example. [Figure 14] FIG. 10 is a development view of a tread portion of another comparative example. [Figure 15] FIG. 10 is a development view of a tread portion of another comparative example. 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 2a 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 contact area under normal load of the pneumatic tire 1. 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] [Inclined sipes on crown rib and middle rib] In this embodiment, the crown rib 12, the first middle rib 131, and the second middle rib 132 each have a plurality of sipes 20 formed therein that are inclined with respect to the tire circumferential direction and the tire axial direction. 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 ribs 13, etc., and are useful for improving noise performance during acceleration, as 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 one circumferential groove 10 (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 sipe 22 is a so-called semi-open sipe that extends from one circumferential groove 10 (second crown circumferential groove 10B) and terminates within the crown rib 12. The crown sipe 22 has 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 one circumferential groove 10 (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 one circumferential groove 10 (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 (disconnected 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 one circumferential groove 10 (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 one circumferential groove 10 (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 (disconnected end) on a second side CD2 in the tire circumferential direction.

[0050] In this embodiment, no lateral grooves are provided in the crown rib 12 and the middle rib 13. These ribs 12 and 13, located in the central region of the tread, are exposed to high ground contact pressure and are prone to generating noise during acceleration. However, by not providing lateral grooves in these ribs 12 and 13, the generation of noise due to deformation of the lateral grooves during acceleration is suppressed.

[0051] [Shoulder rib] 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 formed in the first shoulder rib 141 and a second shoulder lateral groove 29 formed in the second shoulder rib 142.

[0052] The first shoulder lateral groove 28 intersects with the first tread edge Te1. More specifically, the first shoulder lateral groove 28 has an axially outer end 28A located axially outer than the first tread edge Te1, and an axially inner end 28B that terminates within the first shoulder rib 141. Therefore, the inner end 28B of the first shoulder lateral groove 28 does not directly communicate with the first shoulder circumferential groove 10C. Such a first shoulder lateral groove 28 can maintain high longitudinal rigidity of the first shoulder rib 141 while maintaining drainage performance. In this embodiment, the first shoulder lateral groove 28 extends linearly throughout its entire length.

[0053] The second shoulder lateral groove 29 intersects with the second tread edge Te2. More specifically, the second shoulder lateral groove 29 has an axially outer end 29A located axially outer than the second tread edge Te2, and an axially inner end 29B that terminates within the second shoulder rib 142. Therefore, the inner end 29B of the second shoulder lateral groove 29 does not directly communicate with the second shoulder circumferential groove 10D. Such a second shoulder lateral groove 29 can maintain high longitudinal rigidity of the second shoulder rib 142 while maintaining drainage performance. In this embodiment, the second shoulder lateral groove 29 extends linearly throughout its entire length.

[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 provided in the first shoulder rib 141 and second shoulder sipes 42 provided in the second shoulder rib 142.

[0055] Each first shoulder sipe 41 does not completely cross the first shoulder rib 141 in the tire 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. In this embodiment, one first shoulder sipe 41 is provided between two circumferentially adjacent first shoulder lateral grooves 28. This allows the longitudinal rigidity of the first shoulder rib 141 to be adjusted in a well-balanced manner in the tire circumferential direction. The first shoulder sipe 41 extends, for example, linearly. In a preferred embodiment, the first shoulder sipe 41 extends linearly over its entire length.

[0056] Each second shoulder sipe 42 does not completely cross the second shoulder rib 142 in the tire 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. In addition, each second shoulder sipe 42 does not communicate with the second shoulder lateral groove 29. In this embodiment, one second shoulder sipe 42 is provided between two circumferentially adjacent second shoulder lateral grooves 29. This allows the front-to-rear rigidity of the second shoulder rib 142 to be adjusted in a balanced manner in the tire circumferential direction. The second shoulder sipe 42 extends linearly, for example. In a preferred embodiment, the second shoulder sipe 42 extends linearly throughout its entire length.

[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 for one pitch as follows 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] [Tie bar part of shoulder sipe] Figure 8 is a cross-sectional view taken along line VIII-VIII in Figure 6. Figure 8 shows a first shoulder sipe 41 as a representative example of one shoulder sipe 40, but it should be noted that the second shoulder sipe 42 also includes a sipe having a similar configuration. As shown in Figure 8, at least one shoulder sipe 40 includes a sipe main body portion 401 and a tie bar portion 402.

[0072] The tie bar portion 402 is a locally raised portion of the sipe bottom. In this embodiment, the tie bar portion 402 is provided at an end portion of the shoulder sipe 40, including the axially inner end 41B, so as to communicate with the first shoulder circumferential groove 10C. The tie bar portion 402 has a sipe bottom that is substantially parallel to the tread contact surface 2a of the shoulder rib 14. The shoulder sipe 40 including the tie bar portion 402 suppresses a decrease in the longitudinal rigidity of the shoulder rib 14 while maintaining drainage performance and wear performance, and as a result, can effectively suppress the amount of slippage of the shoulder rib 14 during acceleration.

[0073] In order to fully achieve the above-described effects, the tie bar portion 402 preferably has a depth in the range of 20% to 30% of the groove depth of the circumferential groove (the first shoulder circumferential groove 10C to which the first shoulder sipe 41 communicates), and more preferably has a depth of 10 to 25%. In this embodiment, the groove depth of the first shoulder circumferential groove 10C is 7.0 mm, and the depth of the tie bar portion 402 is 1.4 mm (20% of the groove depth of the first shoulder circumferential groove 10C). In addition, the length of the tie bar portion 402 is preferably, for example, 5% to 20% of the length of the shoulder sipe 40. In this embodiment, the length of the shoulder sipe 40 is 28.7 mm, and the length of the tie bar portion 402 is 2.0 mm (approximately 7% of the total length of the shoulder sipe), which is within the range of the inner straight portion 413 described above. Here, the "length" of the tie bar portion 402 or the sipe means the periphery length measured along the sipe in a plan view of the sipe.

[0074] The sipe main body 401 constitutes the outer portion of the tie bar portion 402 in the tire axial direction. The sipe main body 401 has a greater depth than the tie bar portion 402. Such a sipe main body 401 not only equalizes the ground contact pressure of the shoulder rib 14 and improves its wear performance, but also serves to further suppress slippage during accelerating driving.

[0075] The sipe main body 401 of this embodiment includes a bottom portion 405 extending along the contact patch of the shoulder rib 14, an outer inclined surface portion 403 connecting the bottom portion 405 to the outer end of the shoulder sipe 40 (in this example, the outer end 41A of the first shoulder sipe 41), and an inner inclined surface portion 404 connecting the bottom portion 405 to the tie bar portion 402. The outer inclined surface portion 403 and the inner inclined surface portion 404 are bent relative to the bottom portion 405. The outer inclined surface portion 403 is inclined at an angle λo with respect to a normal to the contact patch that is erected at the axially outer end of the shoulder sipe 40. The inclination is inward in the tire radial direction, and inward in the tire axial direction. The inner inclined surface portion 404 is inclined at an angle λi with respect to a normal to the contact patch that passes through the connection between the tie bar portion 402 and the inner inclined surface portion 404. The inclination is toward the inside in the tire radial direction and toward the outside in the tire axial direction.

[0076] In this embodiment, as a preferred aspect of the shoulder sipe 40, the angle λi of the inner inclined surface portion 404 is configured to be larger than the angle λo of the outer inclined surface portion 403. The axially inner side of the shoulder rib 14 is adjacent to the circumferential groove 10, and therefore has lower rigidity than the tread edge side of the shoulder rib 14. Therefore, by making the angle relationship λi > λo as described above, the front and rear rigidity of the shoulder rib 14 can be made uniform in the tire axial direction. This makes the contact pressure of the shoulder rib 14 uniform and further suppresses slippage during acceleration. Preferably, the angle λi is in the range of 25 to 35°, and the angle λo is in the range of 15 to 25°. The difference between the angle λi and the angle λo is 5° or more, more preferably 8° or more.

[0077] 6, the shoulder sipes 40 have an angle α2 of, for example, 0 to 30°, more preferably 0 to 20°, relative to the tire axial direction. That is, the shoulder sipes 40 of this embodiment extend at an angle closer to the tire axial direction. Such shoulder sipes 40 are less likely to match the contour of the contact patch of the shoulder rib 14, which prevents the air compressed within the sipes from being suddenly expelled outward from the contact patch. This helps reduce pitch noise.

[0078] Although there are no particular restrictions on the axial length of the shoulder sipes 40, it is preferable that they do not overlap with the shoulder lateral grooves 27 in the axial direction. For example, it is desirable that the axial outer end 41A of the first shoulder sipe 41 be located axially more inward than the inner end 28B of the first shoulder lateral groove 28. This prevents the axial center of the shoulder rib 14 from being created with low front-to-rear rigidity due to the overlap between the shoulder sipes 40 and the shoulder lateral grooves 27. Therefore, in this embodiment, slippage of the shoulder rib 14 during acceleration is more effectively suppressed.

[0079] [Shoulder groove] Similarly, the shoulder lateral grooves 27 also have an angle α1 of, for example, 0 to 30°, more preferably 0 to 20°, relative to the tire axial direction. That is, the shoulder lateral grooves 27 of this embodiment also extend at an angle closer to the tire axial direction. Such shoulder lateral grooves 27 are less likely to match the contour of the contact patch of the shoulder rib 14, which prevents the compressed air in the grooves from being suddenly discharged outward from the contact patch. This helps reduce pitch noise. In this embodiment, the shoulder lateral grooves 27 extend parallel to the shoulder sipes 40. This allows the front-to-rear rigidity of the shoulder rib 14 to be well-balanced in the tire circumferential direction.

[0080] The axial length Ls of the shoulder lateral grooves 27 from the first tread edge Te1 is, for example, 40% to 60%, preferably 45% to 55%, of the axial length Ws of the contact patch of the first shoulder rib 141. In a preferred embodiment, as shown in FIG. 1, the first shoulder lateral grooves 28 and second shoulder lateral grooves 29 are provided so as to cover the areas where the respective edge bands 9B are disposed. More specifically, the axially inner ends 28B and 29B of the first shoulder lateral grooves 28 and second shoulder lateral grooves 29 are both located at substantially the same axial position 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 second shoulder lateral grooves 29 are located axially outward beyond the axially outer ends of the pair of edge bands 9B. The area where the edge band 9B of the shoulder rib 14 is located overlaps with the full band 9A, providing locally high rigidity, but by arranging the first shoulder lateral grooves 28 and second shoulder lateral grooves 29 to cover the area where the edge band 9B is located, the front-to-rear rigidity of the shoulder rib 14 is made uniform in the tire axial direction, and the ground contact pressure distribution of the shoulder rib 14 during acceleration is made uniform, thereby suppressing the amount of slippage of the shoulder rib 14. This further reduces acceleration noise.

[0081] [Sipe embodiment] Returning to Figure 3, the angle β1 of the crown sipes 21, 22 relative to the tire axial direction is not particularly limited, but can be set, for example, in the range of 15 to 50 degrees. In particular, sipes with a relatively small angle β1 relative to the tire axial direction reduce edge components in the tire circumferential direction. From this perspective, the angle β1 of the crown sipes 21, 22 relative to the tire axial direction is preferably in the range of 30 to 60 degrees, more preferably 30 to 55 degrees, and even more preferably 30 to 40 degrees.

[0082] 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 accelerated driving. Applying the small angle β1 with respect to the tire axial direction to the semi-open crown sipes 21, 22 is also desirable because it makes it less likely for these sipes to coincide with the contour edge of the contact surface of 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 surface of the crown rib 12.

[0083] The axial angles β2 and β3 of the first middle sipes 23, 24 and the second middle sipes 25, 26 are not particularly limited, but can be set, for example, in the range of 15 to 50°. In particular, sipes with relatively small axial angles β2 and β3 reduce circumferential edge components. From this perspective, the axial angles β2 and β3 of the first middle sipes 23, 24 and the second middle sipes 25, 26 are preferably in the range of 15 to 40°, and more preferably 15 to 30°. 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.

[0084] The difference in angle between the crown sipes 21, 22, the first middle sipes 23, 24, and the second middle sipes 25, 26 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 relative to the tire axial direction. More specifically, the angle of each sipe relative to the tire axial 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 relative to the tire axial direction and the sipe with the smallest angle relative to the tire axial direction are determined, and the difference between these angles is calculated. Note that, when each sipe is curved or zigzag, the angles β1, β2, and β3δ of the sipe relative to the tire circumferential direction are defined as the angle of a straight line connecting both ends of the sipe relative to the tire axial direction.

[0085] In this embodiment, the angle β1 of the crown sipes 21, 22 relative to the tire axial direction is approximately 16°. The angles β2 and β3 of the first middle sipes 23, 24 and the second middle sipes 25, 26 relative to the tire axial direction are also approximately 16°. 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 is substantially zero. This configuration helps to further reduce acceleration noise.

[0086] FIG. 9 shows a cross-sectional view taken along line IX-IX in FIG. 2. As shown in FIG. 9, 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 circumferential groove (first crown circumferential groove 10A), and in this embodiment, it is approximately 85%. 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°.

[0087] The crown sipe 22 of this embodiment also includes a base portion 22m having a substantially constant depth D1 and a sub-portion 22s whose depth gradually decreases toward the second end 22B. The configurations of the base portion 22m and the sub-portion 22s are identical to those of the base portion 21m and the sub-portion 21s of the crown sipe 21 (which have a substantially symmetrical structure with respect to the tire equator C).

[0088] FIG. 10 shows a cross-sectional view taken along line XX in FIG. 2. As shown in FIG. 10, 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°.

[0089] 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.

[0090] FIG. 11 shows a cross-sectional view of a crown sipe 21 as a representative example of a sipe 20. The other sipes, namely, the crown sipe 22, first middle sipes 23 and 24, and second middle sipes 25 and 26, also have similar cross-sectional shapes. As shown in FIG. 11 , the sipe 20 of this embodiment has a substantially constant width and extends radially inward from the tread contact surface 2a. Furthermore, the sipe 20 of this embodiment does not have chamfered corners between the sipe wall surface and the tread contact surface 2a. That is, the edges of the sipe 20 at the tread contact surface 2a are formed with sharp corners. Specifically, the radius of curvature of the corners of the sipe 20 is preferably 1.0 mm or less, more preferably 0.5 mm or less. The sipe 20 without chamfered corners has a smaller sipe volume than the sipe with chamfered corners. This suppresses air displacement within the sipe during contact with the tire during acceleration, thereby reducing pattern noise. Therefore, the acceleration noise can be further suppressed in the pneumatic tire 1 having such sipes. In addition, the sipes 20 that are not provided with chamfers reduce the contact pressure when they enter the ground contact patch during tire running, and also reduce impact noise.

[0091] [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, in a more preferred embodiment of the pattern of this embodiment, as shown in Fig. 3, the sipes 20 include a first sipe group in which the sipes are arranged seamlessly around the entire circumference of the tire. More specifically, the first sipe group of this embodiment includes crown sipes 21 and 22, first middle sipes 23 and 24, and second middle sipes 25 and 26.

[0092] The sipes of the seamlessly arranged first sipe group contact the ground sequentially and substantially continuously as the pneumatic tire 1 rotates. More specifically, in each pair of sipes 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 are formed on different ribs (condition b). Such a seamless arrangement can prevent sipes from contacting the ground twice, thereby reducing the number of sipes 20 that separate from the road surface per unit time and further reducing acceleration noise.

[0093] In the example of FIG. 3 , for example, a first pair is identified among the pairs of sipes. The first pair consists of a first middle sipe 24 and a first middle sipe 23 adjacent to it on the second side CD2 in the tire circumferential direction (these sipes are connected by an imaginary line in the tire axial direction in FIG. 3 ). In this first pair, the first end 23A of the first middle sipe 23 located on the second side CD2 in the tire circumferential direction is in the same position in the tire circumferential direction as the second end 24B of the first middle sipe 24 located on the first side CD1 in the tire circumferential direction. Here, whether the first and second ends of two sipes are in the same position in the tire circumferential direction is determined using the sipe center lines. That is, the first and second ends of the two sipes that make up a pair are identified by the ends of the sipe center lines, respectively. The sipe center line is the center line between a pair of edges of a sipe. If the sipe edge has a chamfer, the sipe edge is determined excluding the chamfer. More specifically, the intersection of an imaginary extension of the sipe wall without the chamfer and an imaginary extension of the tread contact surface is considered to be the sipe edge.

[0094] 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, the first pair satisfies condition a, but does not satisfy condition b because the two sipes are formed on the same rib (first middle rib 131).

[0095] Next, a second pair is identified from among the sipe pairs. The second pair is a pair of sipes adjacent to the second side CD2 of the first pair. Specifically, the second pair consists of a first middle sipe 23 and a crown sipe 22 provided on the crown rib 12 (these sipes are connected by an imaginary line in the tire axial direction in FIG. 3 ). In the second pair, the first end 22A of the crown sipe 22 located on the second side CD2 in the tire circumferential direction is in the same position in the tire circumferential direction as the second end 23B of the first middle sipe 23 located on the first side CD1 in the tire circumferential direction. Therefore, the second pair satisfies condition a. Furthermore, in the second pair, the first middle sipe 23 is formed on the first middle rib 131, while the crown sipe 22 is formed on the crown rib 12. Therefore, the two sipes in the second pair are formed on different ribs, and condition b is also satisfied.

[0096] Next, a third pair is identified from among the pairs of sipes. The third pair is a pair of sipes adjacent to the second side CD2 of the second pair. Specifically, the third pair consists of crown sipes 22 and 21 (these sipes are connected by an imaginary line in the tire axial direction in FIG. 3). In the third pair, the first end 21A of the crown 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 22B of the crown sipe 22 located on the first side CD1 in the tire circumferential direction, but they are on the same rib. Therefore, the third pair satisfies condition a but not condition b.

[0097] Next, a fourth pair is identified from among the sipe pairs. The fourth pair is a pair of sipes adjacent to the second side CD2 of the third pair. Specifically, the fourth pair consists of a crown sipe 21 and a second middle sipe 26 (these sipes are connected by an imaginary line in the tire axial direction in FIG. 3). In the fourth pair, the first end 26A of the second middle sipe 26 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 21B of the crown sipe 21 located on the first side CD1 in the tire circumferential direction. Therefore, the fourth pair satisfies both conditions a and b.

[0098] Next, a fifth pair is identified among the sipe pairs. The fifth pair is a pair of sipes adjacent to the second side CD2 of the fourth pair. Specifically, the fifth pair consists of second middle sipes 26 and 25 (these sipes are connected by an imaginary line in the tire axial direction in FIG. 3). In the fifth pair, the first end 25A of the second middle sipe 25 located on the second side CD2 in the tire circumferential direction is in the same position in the tire circumferential direction as the second end 26B of the second middle sipe 26 located on the first side CD1 in the tire circumferential direction, but they are on the same rib. Therefore, the fifth pair satisfies condition a but not condition b.

[0099] Next, a sixth pair is identified from among the sipe pairs. The sixth pair is a pair of sipes adjacent to the fifth pair on the second side CD2. Specifically, the sixth pair consists of a second middle sipe 25 and a first middle sipe 24 (these sipes are connected by an imaginary line in the tire axial direction in FIG. 3). In the sixth pair, the first end 24A of the first middle sipe 24 located on the second side CD2 in the tire circumferential direction is in the same position in the tire circumferential direction as the second end 25B of the second middle sipe 25 located on the first side CD1 in the tire circumferential direction. Therefore, the fourth pair satisfies both conditions a and b.

[0100] 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 arranged in a seamless arrangement as in this embodiment, the sipes alternately and continuously contact the ground while the tire is running. This reduces the fluctuation in impact force and reduces the pitch noise associated with the ribs touching the ground, thereby further reducing acceleration noise.

[0101] In addition, the first sipe group of this embodiment is configured so that the first to sixth pairs appear repeatedly in the tire circumferential direction. Here, the first, third, and fifth pairs all satisfy only condition a, while the second, fourth, and sixth pairs all satisfy both conditions a and b. Therefore, the above-mentioned pitch noise is dispersed over an even wider frequency band, further reducing acceleration noise.

[0102] In a more preferred embodiment, only the first sipe group, which is seamlessly arranged, is formed 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.

[0103] 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]

[0104] 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. Example 1 has the pattern shown in Figure 2. Comparative Examples 1 to 5 have the patterns shown in Figures 13, 14, and 15. 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:

[0105] [Exterior noise (coasting) test] A coasting test was 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 was driven onto the test track, accelerated to 50 km / h, and then the accelerator was released completely at a designated point, allowing the vehicle to coast. 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). The internal pressure of the test tires was 240 kPa, and the longitudinal load per tire was 6.16 kN.

[0106] [Exterior noise (acceleration) 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.

[0107] [Wear energy 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 the larger the index, the smaller the wear energy and the better the wear resistance.

[0108] [Wear life test] Each tire was mounted on a rim at 240 kPa, and the wear energy was calculated using a wear energy measuring tester under running conditions of a load of 6.16 kN and a driving force of 0.2 G. The results were evaluated as the reciprocal of the wear energy, and are expressed as an index with the reciprocal of the wear energy of Comparative Example 1 set to 100. A larger value indicates a longer wear life. The test results are shown in Table 1.

[0109] [Table 1]

[0110] It was confirmed that the pneumatic tires of the Examples were superior in terms of external vehicle noise (acceleration and coasting) compared to Comparative Examples 1 to 5. In addition, it was also confirmed that the pneumatic tires of the Examples were superior in terms of wear energy and wear life compared to Comparative Examples 1 to 5.

[0111] [Note] The present invention includes the following aspects.

[0112] [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. a longitudinal stiffness Ks of one pitch of the pair of shoulder ribs is greater than a longitudinal stiffness Km of one pitch of the pair of middle ribs and a longitudinal stiffness Kc of one pitch of the crown rib; 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, None of the plurality of sipes completely crosses each rib in the tire axial direction, Each shoulder rib is provided with a plurality of shoulder lateral grooves spaced apart in the tire circumferential direction and a plurality of shoulder sipes spaced apart in the tire circumferential direction, The inner end of each shoulder sipe in the tire axial direction communicates with one of the four circumferential grooves, Each shoulder sipe does not communicate with the shoulder lateral groove, Each shoulder sipe is provided between the shoulder lateral grooves adjacent in the tire circumferential direction, At least one of the shoulder sipes has a tie bar portion that locally raises the bottom of the sipe. Pneumatic tires. [Invention 2] The pneumatic tire according to invention 1, wherein the tie bar portion has a depth that is 20% to 30% of the groove depth of the circumferential groove. [Invention 3] 3. The pneumatic tire according to claim 1 or 2, wherein the tie bar portion has a length that is 5% to 20% of the length of the shoulder sipe. [Invention 4] The pneumatic tire according to any one of claims 1 to 3, wherein the tie bar portion is provided at an end portion including the inner end of the shoulder sipe. [Invention 5] 5. The pneumatic tire according to any one of claims 1 to 4, wherein the plurality of sipes are all semi-open sipes. [Invention 6] 6. The pneumatic tire according to any one of claims 1 to 5, wherein the angle of the plurality of sipes with respect to the tire axial direction is 15 to 50 degrees. [Invention 7] 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 are 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, The pneumatic tire according to any one of the first to sixth aspects of the present invention, wherein in at least one of the pairs, the sipes constituting the pair are formed in different ribs. [Invention 8] 8. The pneumatic tire according to any one of claims 1 to 7, 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 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 Km of the middle rib. [Invention 10] 10. The pneumatic tire according to any one of claims 1 to 9, 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]

[0113] 1 pneumatic tire 2 Tread section 3 Sidewall 4 Bead section 10 Circumferential groove 11 Ribs 12 Crown Rib 13 Middle Rib 14 Shoulder Rib 21, 22 Crown sipes 23, 24 1st middle sipe 25, 26 Second middle sipe 27 Shoulder groove 40 Shoulder sipes 402 Tie bar section

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, None of the plurality of sipes completely crosses each rib in the tire axial direction, Each shoulder rib is provided with a plurality of shoulder lateral grooves spaced apart in the tire circumferential direction and a plurality of shoulder sipes spaced apart in the tire circumferential direction, An inner end of each shoulder sipe in the tire axial direction communicates with one of the four circumferential grooves, Each shoulder sipe does not communicate with the shoulder lateral groove, Each shoulder sipe is provided between the shoulder lateral grooves adjacent in the tire circumferential direction, At least one of the shoulder sipes includes a tie bar portion having a locally raised sipe bottom, and a sipe main body portion that constitutes an axially outer portion of the tie bar portion, the sipe main body portion includes a bottom portion extending along the contact surface of the shoulder rib, an outer inclined surface portion connecting the bottom portion to an outer end of the shoulder sipe in the tire axial direction, and an inner inclined surface portion connecting the bottom portion to the tie bar portion, the outer inclined surface portion is inclined at an angle λo toward the inside in the tire radial direction with respect to a normal to the contact surface that is erected at an outer end of the shoulder sipe in the tire axial direction, the inner inclined surface portion is inclined at an angle λi toward the inside in the tire radial direction and toward the outside in the tire axial direction with respect to a normal to the ground contact patch that passes through a connection portion between the tie bar portion and the inner inclined surface portion, the angle λi of the inner inclined surface portion is greater than the angle λo of the outer inclined surface portion; Pneumatic tires.

2. The pneumatic tire according to claim 1, wherein the tie bar portion has a depth that is 20% to 30% of the groove depth of the circumferential groove.

3. The pneumatic tire according to claim 2, wherein the tie bar portion has a length that is 5% to 20% of a length of the shoulder sipe.

4. The pneumatic tire according to claim 1 , wherein the tie bar portion is provided at an end portion including the inner end of the shoulder sipe.

5. The pneumatic tire according to claim 1 , wherein all of the plurality of sipes are semi-open sipes.

6. The pneumatic tire according to claim 1, wherein the angle of the plurality of sipes with respect to the tire axial direction is 15 to 50 degrees.

7. 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 are 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, The pneumatic tire according to claim 1 , wherein the sipes constituting at least one of the pairs are formed on different ribs.

8. 7. 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. 7. The pneumatic tire according to claim 1, wherein the longitudinal stiffness Kc of the crown rib is 0.97 to 1.03 times the longitudinal stiffness Km of each middle rib.

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