pneumatic tires

Abstract

To provide a tire that suppresses noise during acceleration. [Solution] A pattern with a land ratio of 0.70 to 0.85 includes crown, middle, and shoulder ribs on the equator. Each rib has 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. At least one sipe in the crown and middle rib is a varying-depth sipe 50. The varying-depth sipe includes a first portion 51 at a first end 50A, a second portion 52 at a second end 50B, and a third portion 53 therebetween. The first and second portions are shallower than the third portion. A bottom 51B of the first portion includes a first inclined portion 61 extending linearly between the first end and a step 54 so that the depth gradually decreases toward the first end. A bottom 52B of the second portion includes a second inclined portion 62 extending linearly between the second end and the step so that the depth gradually decreases toward the second end.

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, the tread portion having 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 having a land ratio in the range of 0.70 to 0.85, the five ribs including a crown rib including the tire equator, a pair of middle ribs, and a pair of shoulder ribs, each of which 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, the crown rib and the pair of middle ribs each having a plurality of sipes, a plurality of sipes extending from a first end to a second end, at least one of the plurality of sipes being a varying-depth sipe, the varying-depth sipe including a first portion extending from the first end, a second portion extending from the second end, and a third portion between the first portion and the second portion, the bottoms of the first portion and the second portion rising from a bottom of the third portion via a step, such that the first portion and the second portion have a smaller depth than the third portion, the bottom of the first portion including a first inclined portion extending linearly between the first end and the step such that the depth gradually decreases toward the first end, and the bottom of the second portion including a second inclined portion extending linearly between the second end and the step such that the depth gradually decreases toward the second end. [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] 8 is a cross-sectional view taken along line VIII-VIII in FIG. 3, and is a cross-sectional view taken along the length direction of the depth-changing sipe (crown sipe). [Figure 9] FIG. 10 is a cross-sectional view showing another embodiment of a depth-changing sipe. [Figure 10] FIG. 10 is a cross-sectional view showing another embodiment of a depth-changing sipe. [Figure 11] FIG. 10 is a cross-sectional view showing another embodiment of a depth-changing sipe. [Figure 12] FIG. 10 is a cross-sectional view showing another embodiment of a depth-changing sipe. [Figure 13] FIG. 10 is a cross-sectional view showing another embodiment of a depth-changing sipe. [Figure 14] 1 is a graph comparing external vehicle noise between Example 1 and Comparative Example 1. 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 distance between them in the tire axial direction is defined as the tread width TW (see FIG. 2). The pneumatic tire 1 of this embodiment is also designed to be mounted on a vehicle in a specified orientation, with the first tread edge Te1 facing outward from the vehicle and the second tread edge Te2 facing inward from the vehicle when mounted on the vehicle. The orientation of the tire when mounted on a vehicle is indicated, for example, on the sidewall portion 3.

[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 14.

[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 land portion is at least partially continuous in the tire circumferential direction. Therefore, a rib can be said to be a land portion that does not have lateral grooves that completely cross the tire axial direction. Note that a sipe is not considered to interrupt the land portion. Therefore, a rib may be provided with a sipe that completely crosses the land portion in the tire axial direction (so-called full-open sipe).

[0026] In this specification, "sipe" refers to a narrow cut formed in a land portion of the tread portion 2. In the contact area of ​​the pneumatic tire 1 under normal load, at least a portion of a pair of opposing sipe wall surfaces contacts each other, and the continuity of the land portion is substantially maintained. Such a sipe has 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, and more preferably 0.8 mm or less. Most preferably, the sipe has a portion of 0.5 to 1.2 mm.

[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 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 the groove wall is chamfered on the tread contact surface 2a side, 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 2a 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. The first crown circumferential groove 10A and the second crown circumferential groove 10B are located in the tread central region where ground pressure during running is relatively large, so by making these groove widths relatively large, wet performance is improved without impairing dry grip performance. In one aspect, the groove widths of the first crown circumferential groove 10A and the second crown circumferential groove 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 (a collective term for crown sipes 21, first middle sipes 23, and second middle sipes 25, which will be described later) are formed in each of the crown rib 12, the first middle rib 131, and the second middle rib 132. The sipes 20 in this embodiment 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 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. Each crown sipe 21 is inclined with respect to the tire circumferential direction and the tire axial direction. In this embodiment, the crown sipe 21 extends linearly over its entire length.

[0042] Each crown sipe 21, for example, completely crosses the crown rib 12 in the tire axial direction. That is, each crown sipe 21 extends from the first crown circumferential groove 10A to the second crown circumferential groove 10B, and is a so-called full-open sipe. Each crown sipe 21 has a first end 21A on a first side CD1 in the tire circumferential direction and a second end 21B on a second side CD2 in the tire circumferential direction.

[0043] The first middle rib 131 is provided with a plurality of first middle sipes 23. Each first middle sipe 23 is inclined with respect to the tire circumferential direction and the tire axial direction. In this embodiment, each first middle sipe 23 extends linearly over its entire length.

[0044] Each first middle sipe 23, for example, completely crosses the first middle rib 131 in the tire axial direction. That is, the first middle sipe 23 extends from the first shoulder circumferential groove 10C to the first crown circumferential groove 10A, and is a so-called fully open sipe. The first middle sipe 23 has a first end 23A on a first side CD1 in the tire circumferential direction and a second end 23B on a second side CD2 in the tire circumferential direction.

[0045] The second middle rib 132 is provided with a plurality of second middle sipes 25. Each second middle sipe 25 is inclined with respect to the tire circumferential direction and the tire axial direction. In this embodiment, each second middle sipe 25 extends linearly over its entire length.

[0046] Each second middle sipe 25, for example, completely crosses the second middle rib 132 in the tire axial direction. That is, the second middle sipe 25 extends from the second crown circumferential groove 10B to the second shoulder circumferential groove 10D, and is a so-called fully open sipe. The second middle sipe 25 has a first end 25A on a first side CD1 in the tire circumferential direction and a second end 25B on a second side CD2 in the tire circumferential direction.

[0047] In this embodiment, only sipes 20 are formed on the crown rib 12 and the middle rib 13, and no lateral grooves are provided. The crown rib 12 and the middle rib 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 on these crown ribs 12 and middle ribs 13, it is possible to suppress the generation of noise associated with deformation of the lateral grooves during acceleration. Furthermore, because the sipes 20 are inclined relative to the tire circumferential direction and the tire axial direction, each sipe is prevented from contacting the ground all at once. This helps to further reduce tire noise.

[0048] 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.

[0049] 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 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.

[0050] 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 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.

[0051] 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.

[0052] The first shoulder rib 141 is provided with first shoulder sipes 41. An axially inner end 41B of each first shoulder sipe 41 communicates with the first shoulder circumferential groove 10C, and an axially outer end 41A of each first shoulder sipe 41 is connected to the inner end 28B of the first shoulder lateral groove 28. Therefore, the first shoulder lateral groove 28 communicates indirectly with the first shoulder circumferential groove 10C via the first shoulder sipe 41.

[0053] The second shoulder rib 142 is provided with second shoulder sipes 42. 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 connected to the inner end 29B of the second shoulder lateral groove 29. Therefore, the second shoulder lateral groove 29 communicates indirectly with the second shoulder circumferential groove 10D via the second shoulder sipe 42.

[0054] The shoulder sipes 40 further include a third shoulder sipe 43 and a fourth shoulder sipe 44 .

[0055] Third shoulder sipes 43 are provided on the first shoulder rib 141. One third shoulder sipe 43 is provided between each pair of circumferentially adjacent first shoulder sipes 41. The axially inner end 43B of each third shoulder sipe 43 communicates with the first shoulder circumferential groove 10C, and the axially outer end 43A of each third shoulder sipe 43 is positioned axially outward from the first tread edge Te1.

[0056] Fourth shoulder sipes 44 are provided on the fourth shoulder rib 144. One fourth shoulder sipe 44 is provided between each pair of circumferentially adjacent second shoulder sipes 42. An axially inner end 44B of each fourth shoulder sipe 44 communicates with the second shoulder circumferential groove 10D, and an axially outer end 43A of each fourth shoulder sipe 44 terminates axially outside the second tread edge Te2 without reaching the second tread edge Te2.

[0057] A pattern is formed in the tread portion 2 by the above-mentioned sipes 20, shoulder lateral grooves 27, and shoulder sipes 40. 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] [Depth-varying sipes] In the present invention, in order to reduce acceleration noise, attention is focused on the relationship between a specific range of land ratio of the tread portion 2 and the front-rear rigidity of one pitch of each rib. In order to further reduce the amount of slippage of each rib during acceleration, the sipes 20 include at least one variable depth sipe 50. In a preferred embodiment, at least one, and preferably multiple, variable depth sipes 50 are provided on each of the crown rib 12 and the middle rib 13. In this embodiment, as the most preferred embodiment, all of the sipes 20 formed on the crown rib 12 and the middle rib 13 are variable depth sipes 50.

[0072] 8 shows a cross-sectional view (a cross-sectional view along the sipe length direction of the crown sipe 21) taken along line VIII-VIII in FIG. 3 as a representative example of a varying depth sipe 50. As shown in FIG. 8, the varying depth sipe 50 includes a first portion 51 extending from a first end 50A, a second portion 52 extending from a second end 50B, and a third portion 53 between the first portion 51 and the second portion 52. In this example, the first ends 50A and 50B of the varying depth sipe 50 correspond to the first end 21A and second end 21B of the crown sipe 21, respectively.

[0073] A bottom 51B of the first portion 51 and a bottom 52B of the second portion 52 are configured to locally protrude from a bottom 53B of the third portion 53 via a step 54. As a result, the depth from the tread contact surface 2a to the bottom 51B of the first portion 51 and the depth from the tread contact surface 2a to the bottom 52B of the second portion 52 are configured to be smaller than the depth from the tread contact surface 2a to the bottom 53B of the third portion 53.

[0074] The third portion 53 is, for example, configured as a flat portion having a constant depth and extending in the sipe length direction. The step 54 extends, for example, at an inclination within a range of ±15° with respect to the sipe depth direction line (in this embodiment, it is substantially 0°). Such a third portion 53 can open appropriately while the tire is running, ensuring drainage near the center of the rib in the tire axial direction.

[0075] Furthermore, in the varying-depth sipe 50, the bottom 51B of the first portion 51 includes a first inclined portion 61 extending between the first end 50A and the step 54 so that the depth gradually decreases toward the first end 50A. Furthermore, in the varying-depth sipe 50, the bottom 52B of the second portion 52 includes a second inclined portion 62 extending between the second end 50B and the step 54 so that the depth gradually decreases toward the second end 50B. Generally, the axial ends of the rib facing the circumferential groove 10 have low rigidity. When the sipe end opens or approaches the axial ends, the rigidity of the axial ends further decreases. However, by providing the first inclined portion 61 and the second inclined portion 62, the sipe depth decreases toward the sipe end (rib end), and the change is linear. This configuration can more effectively suppress a decrease in rigidity near the rib end. Therefore, the opening of the sipes at both axial ends of the rib during acceleration and slippage in the vicinity thereof are reduced by the action of the first portion 51 and the second portion 52. Furthermore, such an action helps to reduce noise during acceleration, particularly noise in the high frequency band above 800 Hz.

[0076] In order to effectively exert the above-mentioned effects, the maximum depth of the first portion 51 and the maximum depth of the second portion 52 are preferably in the range of 30% to 70%, and more preferably in the range of 50% to 70%, of the maximum depth of the varying depth sipe 50. Similarly, in the length direction of the sipe, the lengths of the first portion 51 and the second portion 52 are preferably in the range of 20% to 40% of the length of the varying depth sipe 50, and more preferably in the range of 20% to 30%.

[0077] In this embodiment, the bottom 51B of the first portion 51 is formed over its entire range by the first inclined portion 61. Therefore, the depth of the first portion 51 in this embodiment decreases continuously and linearly from the step 54 to the first end 50A. Also, in this embodiment, in order to ensure sufficient rigidity on the first end 50A side of the varying-depth sipe 50 and more effectively suppress slippage during accelerating driving, the depth of the first inclined portion 61 at the first end 50A is set to 1 mm or less.

[0078] In this embodiment, the bottom 52B of the second portion 52 is formed over its entire range by the second inclined portion 62. Therefore, the depth of the second portion 52 in this embodiment decreases continuously and linearly from the step 54 to the second end 50B. Also, in this embodiment, in order to ensure sufficient rigidity on the second end 50B side of the varying-depth sipe 50 and more effectively suppress slippage during accelerating driving, the depth of the second inclined portion 62 at the second end 50B is set to 1 mm or less.

[0079] FIG. 9 shows a modified example of a varying depth sipe 50. In the varying depth sipe 50 shown in FIG. 9, the first portion 51 includes a first inclined portion 61 and a flat portion 63 having a constant depth and extending in the sipe length direction. The flat portion 63 extends from the step 54 toward the first end 50A and is connected to the first inclined portion 61. To effectively utilize the function of the first inclined portion 61, it is desirable that the first inclined portion 61 be longer in the sipe length direction than the flat portion 63. Similarly, the second portion 52 includes a second inclined portion 62 and a flat portion 64 having a constant depth and extending in the sipe length direction. The flat portion 64 extends from the step 54 toward the second end 50B and is connected to the second inclined portion 62. To effectively utilize the function of the second inclined portion 62, it is desirable that the second inclined portion 62 be longer in the sipe length direction than the flat portion 64.

[0080] [Planar view shape of sipe] 3, in this embodiment, the sipes 20 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 20 is inclined upward to the right in the drawing.

[0081] The angle β1 of the crown sipe 21 with respect to the tire circumferential direction is not particularly limited, but can be set, for example, in the range of 30 to 85°, and more preferably in the range of 30 to 55°. Note that hereinafter, the angle of the sipe 20 with respect to the tire circumferential direction is expressed as an acute angle.

[0082] The angles β2 and β3 of the first middle sipe 23 and the second middle sipe 25 relative to the tire circumferential direction are not particularly limited, but can be set, for example, in the range of 30 to 85°, and more preferably in the range of 30 to 55°.

[0083] The difference in angle between the crown sipes 21, the first middle sipes 23, and the second middle sipes 25 relative to 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 relative to the tire circumferential direction. More specifically, the angle of each sipe relative to the tire circumferential direction is first determined. Then, among the crown sipes 21, the first middle sipes 23, and the second middle sipes 25, the sipe with the largest angle relative to the tire circumferential direction and the sipe with the smallest angle relative 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 β1, β2, and β3 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 circumferential direction.

[0084] In this embodiment, the angle β1 of the crown sipe 21 relative to the tire circumferential direction is approximately 74°. The angles β2 and β3 of the first middle sipe 23 and the second middle sipe 25 relative to the tire circumferential direction are also approximately 74°. Therefore, the crown sipe 21, the first middle sipe 23, and the second middle sipe 25 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 further reduce acceleration noise.

[0085] As shown in FIG. 3, in this embodiment, the crown sipes 21, the first middle sipes 23 and the second middle sipes 25 are chamfered at the sipe edges between the tread ground contact surface 2a and the sipe wall surfaces.

[0086] Each crown sipe 21 has a pair of sipe edges each provided with a chamfer 70. The chamfer 70 is formed, for example, over the entire area of ​​the crown sipe 21. The width of these chamfers 70 (chamfer width measured in a direction perpendicular to the sipe length direction in a plan view of the tread) is substantially constant. Each first middle sipe 23 has a pair of sipe edges each provided with a chamfer 71. The chamfer 71 is formed, for example, over the entire area of ​​the first middle sipe 23. The width of these chamfers 71 continuously increases toward the tire equator. Each second middle sipe 25 has a pair of sipe edges each provided with a chamfer 72. The chamfer 72 is formed, for example, over the entire area of ​​the second middle sipe 25. The width of these chamfers 72 continuously increases toward the tire equator. Therefore, these sipes 20 can effectively drain water from the road surface by guiding it to the first crown circumferential groove 10A and the second crown circumferential groove 10B, which have larger groove widths, in the tread central region. The widths of the chamfers 70, 71, and 72 are preferably about 1 to 3 mm, for example.

[0087] [Shoulder groove] As shown in Figure 2, 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 also have an angle α of 70 to 90° with respect to the tire circumferential direction. Because these first shoulder lateral grooves 28 and second shoulder lateral grooves 29 are less likely to match the contour of the contact patch of the shoulder rib 14, the compressed air in the grooves is prevented from suddenly being expelled outward from the contact patch. This helps reduce pitch noise.

[0088] 1 and 2, 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 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 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, thereby 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.

[0089] [Shoulder sipes] As shown in Figure 2, the first shoulder sipes 41 have an angle θ1 of, for example, 70 to 90 degrees with respect to the tire circumferential direction. Such first shoulder sipes 41 are unlikely to match the contour of the contact patch of the shoulder rib 14, which prevents compressed air from being suddenly discharged outward from the contact patch. This helps reduce pitch noise. In this embodiment, the first shoulder sipes 41 extend parallel to the first shoulder lateral grooves 28.

[0090] The third shoulder sipes 43 have an angle θ2 of, for example, 70 to 90° with respect to the tire circumferential direction. Such third shoulder sipes 43 also have difficulty matching 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 third shoulder sipes 43 extend parallel to the first shoulder sipes 41.

[0091] The first shoulder sipes 41 and the second shoulder sipes 42 have substantially the same configuration. The fourth shoulder sipes 44 have substantially the same configuration as the third shoulder sipes 43, except that they are semi-open sipes.

[0092] 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]

[0093] More specific, non-limiting examples of the present invention will now be described. Pneumatic tires (tire size: 235 / 55R19) having the basic structure of FIG. 1 and the basic pattern of FIG. 2 were prototyped based on the specifications in Table 1, and their performance was tested. In Comparative Example 1, the sipes in the crown rib and middle rib both had a constant depth of 4.9 mm and a length of 21 mm, and no variable-depth sipes were provided. Cross-sectional views of the variable-depth sipes in Examples 1 to 5 are shown in FIGS. 10 to 13. The front-to-rear rigidity of one pitch of the first middle rib and the front-to-rear rigidity of one pitch of the second middle rib are substantially the same. The test method is as follows:

[0094] [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.

[0095] [Acceleration noise test] An acceleration test was conducted based on the test method (R51-03) for vehicle exterior noise regulations established by the United Nations Economic Commission for Europe (UNECE). Specifically, a hybrid SUV vehicle equipped with the test tire entered the test road at a low speed of 20 km / h or less. The vehicle then appropriately selected a gear and fully opened the accelerator just before the measurement area, accelerating until it reached a speed of 50 km / h (0.2 G condition). The maximum noise level (dB(A)) was 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 tire was 240 kPa, and the longitudinal load per tire was 6.16 kN. The results were expressed as an index, with a higher value indicating better performance, with the acceleration noise of Comparative Example 1 being assigned a value of 100.

[0096] [Steering stability test] The handling stability of a test vehicle fitted with the test tires was evaluated by the driver's senses. The results are expressed as a rating based on the handling stability of Comparative Example 1 being 100, with a higher rating indicating better performance. The test results are shown in Table 1.

[0097] [Table 1]

[0098] It was confirmed that the maximum displacement amount (corresponding to the amount of slippage) in the contact patch of the pneumatic tires of Examples 1 to 5 was kept small, and more specifically, the average value of the ribs was kept to 0.42 mm or less. In addition, it was confirmed that the pneumatic tires of Examples 1 to 5 were provided with depth-varying sipes, thereby suppressing acceleration noise. Furthermore, it was confirmed that some Examples showed improvements in both acceleration noise and driving stability.

[0099] Fig. 14 shows the results of frequency analysis of external noise for Example 1 and Comparative Example 1. As is clear from Fig. 14, it was confirmed that Example 1 significantly reduced noise in the high frequency band of approximately 800 Hz or higher.

[0100] [Note] The present invention includes the following aspects.

[0101] [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, The plurality of sipes extend from a first end to a second end; At least one of the plurality of sipes is a varying depth sipe, The varying depth sipe includes a first portion extending from the first end, a second portion extending from the second end, and a third portion between the first portion and the second portion, a bottom of the first portion and a bottom of the second portion are raised from a bottom of the third portion via a step, so that the first portion and the second portion have a smaller depth than the third portion; the bottom of the first portion includes a first inclined portion extending linearly between the first end and the step so that the depth gradually decreases toward the first end; the bottom of the second portion includes a second inclined portion extending linearly between the second end and the step so that the depth gradually decreases toward the second end; Pneumatic tires. [Invention 2] The pneumatic tire according to invention 1, wherein the maximum depth of the first portion and the maximum depth of the second portion are 30% to 70% of the maximum depth of the depth-varying sipe. [Invention 3] 3. The pneumatic tire according to claim 1 or 2, wherein the length of each of the first portion and the second portion is 20% to 40% of the length of the varying-depth sipe. [Invention 4] 4. The pneumatic tire according to any one of claims 1 to 3, wherein the varying-depth sipe has a portion having a width of 0.5 to 1.2 mm in a direction perpendicular to the length direction of the sipe. [Invention 5] the third portion includes a flat portion having a constant depth and extending in the sipe length direction, the bottom of the first portion is formed by the first inclined portion over the entire range, The pneumatic tire according to any one of the first to fourth aspects of the present invention, wherein the bottom of the second portion is formed by the second inclined portion over the entire range. [Invention 6] A pneumatic tire according to any one of claims 1 to 5, wherein the first inclined portion has a depth of 1 mm or less at the first end, and / or the second inclined portion has a depth of 1 mm or less at the second end. [Invention 7] 7. The pneumatic tire according to any one of claims 1 to 6, wherein the varying depth sipes are full-open sipes. [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]

[0102] 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 Crown sipes 23 First Middle Sipe 25 Second middle sipe 50 Depth-varying sipes 50A 1st terminal 50B 2nd end 51 Part 1 51B Bottom of first part 52 Part 2 52B Bottom of second part 53 Part 3 54 steps 61 1st slope 62 2nd slope

Claims

1. A pneumatic tire for a passenger vehicle, 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, Each rib is not provided with a lateral groove having a groove width greater than 1.5 mm that completely crosses each rib in the tire axial direction, 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, The plurality of sipes extend from a first end to a second end, At least one of the plurality of sipes is a varying depth sipe, The depth-changing sipe is a full-open sipe, the varying depth sipe includes a first portion extending from the first end, a second portion extending from the second end, and a third portion between the first portion and the second portion, a bottom portion of the first portion and a bottom portion of the second portion are raised from a bottom portion of the third portion via a step, so that the first portion and the second portion have a smaller depth than the third portion; the bottom of the first portion includes a first inclined portion extending linearly between the first end and the step so that the depth gradually decreases toward the first end; the bottom of the second portion includes a second inclined portion extending linearly between the second end and the step such that the depth gradually decreases toward the second end; The maximum depth of the first portion is equal to the maximum depth of the second portion. Pneumatic tires.

2. The pneumatic tire according to claim 1, wherein the maximum depth of the first portion and the maximum depth of the second portion are 30% to 70% of the maximum depth of the varying-depth sipe.

3. The pneumatic tire according to claim 1, wherein the length of each of the first portion and the second portion is 20% to 40% of the length of the varying-depth sipe.

4. 2. The pneumatic tire according to claim 1, wherein the varying-depth sipe has a portion having a width of 0.5 to 1.2 mm in a direction perpendicular to the sipe length direction.

5. the third portion includes a flat portion having a constant depth and extending in the sipe length direction, the bottom of the first portion is formed by the first inclined portion over the entire range, The pneumatic tire according to claim 1 , wherein the bottom of the second portion is formed by the second inclined portion over an entire range.

6. 6. The pneumatic tire according to claim 1, wherein the first inclined portion has a depth of 1 mm or less at the first end, and / or the second inclined portion has a depth of 1 mm or less at the second end.

7. A pneumatic tire as described in any one of claims 1 to 5, wherein the front-to-rear stiffness Ks of the shoulder rib is 1.10 to 1.20 times the front-to-rear stiffness Kc of the crown rib.

8. A pneumatic tire as described in claim 7, wherein the front-rear stiffness Ks of the shoulder rib is 1.10 to 1.20 times the front-rear stiffness Km of the middle rib.

9. A pneumatic tire as described in any one of claims 1 to 5, 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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