pneumatic tires

Abstract

Reduces noise during acceleration. [Solution] A pneumatic tire (1) has a tread portion (2) with a pattern including four circumferential grooves (10) and five ribs. The land ratio of the pattern is 0.70 to 0.85. The ribs include a crown rib (12) including the tire equator, a pair of middle ribs (13), and a pair of shoulder ribs (14). Pitches, which are unit patterns, are repeatedly formed in each rib, and the longitudinal stiffness (Ks) of one pitch of the pair of shoulder ribs (14) is greater than the longitudinal stiffness (Km) of one pitch of the pair of middle ribs (13) and the longitudinal stiffness (Kc) of one pitch of the crown rib (12). The crown rib (12) and the pair of middle ribs (13) each have a plurality of inclined sipes (20) inclined with respect to the tire circumferential direction and the tire axial direction. The inclined sipes (20) do not completely cross each rib in the tire axial direction. The crown rib (12) and the pair of middle ribs (13) each have circumferential sipes (50) extending continuously parallel to the tire circumferential direction. The circumferential sipes (50) are spaced apart from the inclined sipes (20).

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 unit pattern of pitches repeatedly formed therein, and the longitudinal rigidity Ks of one pitch of each shoulder rib is The longitudinal stiffness Km of one pitch of each middle rib is greater than the longitudinal stiffness Kc of one pitch of the crown rib, and a plurality of inclined sipes inclined with respect to the tire circumferential direction and the tire axial direction are formed in each of the crown rib and the pair of middle ribs, and the plurality of inclined sipes do not completely cross each rib in the tire axial direction, and the crown rib and the pair of middle ribs are each provided with circumferential sipes that extend continuously parallel to the tire circumferential direction, and the circumferential sipes are spaced apart from the inclined sipes. [Effects of the Invention]

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

[0008] [Figure 1] 1 is a cross-sectional view of a pneumatic tire according to one embodiment of the present invention. [Figure 2] 1 is a development view of a tread portion of a pneumatic tire showing one embodiment of the present invention. [Figure 3] FIG. 3 is a partially enlarged view of the tread portion of FIG. 2. [Figure 4] FIG. 1 is a diagram showing one pitch of each rib. [Figure 5] FIG. 10 is a perspective view of a schematic block illustrating front-rear rigidity. [Figure 6] FIG. 2 is a plan view showing one pitch of the shoulder rib. [Figure 7A]FIG. 3 is a cross-sectional view of a main part of a tread portion illustrating the boundary of one pitch on the inner side in the tire radial direction. [Figure 7B] FIG. 2 is a side view showing an example of a stiffness measuring device. [Figure 7C] FIG. 10 is a perspective view showing a sample piece of one pitch of the first shoulder rib. [Figure 8] FIG. 8 is a cross-sectional view taken along line VIII-VIII in FIG. 2. [Figure 9] FIG. 9 is a cross-sectional view taken along line IX-IX in FIG. 2. [Figure 10] FIG. 2 is a cross-sectional view of a crown sipe. [Figure 11] 1A is a partially enlarged view of the first shoulder rib, and FIG. 1B is a cross-sectional view taken along line BB in FIG. [Figure 12] FIG. 10 is a development view of a tread portion of another embodiment. [Figure 13] FIG. 2 is a development view of a tread portion of Comparative Example 1. [Figure 14] 1 is a graph comparing external vehicle noise between Comparative Example 1 and Examples 1 to 3. 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 that differ 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 land portion is at least partially continuous in the tire circumferential direction. Therefore, a rib can be said to be a land portion that is not provided with lateral grooves that completely cross the tire axial direction. Note that sipes are not considered to interrupt the land portion. Therefore, a rib may be provided with sipes that completely cross the land portion in the tire axial direction (so-called full-open sipes). Similarly, the term "rib" includes an embodiment in which a lateral groove that is interrupted within the land portion is provided, and a sipe that connects the interrupted end of the lateral groove to the circumferential groove (or the tread edge) is provided.

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

[0027] In this specification, a "groove" has a groove width larger than that of a sipe, and a pair of opposing groove walls do not contact each other in the tread contact 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 inclined sipes 20 inclined with respect to the tire circumferential direction and the tire axial direction. The inclined sipes 20 do not completely cross each rib in the tire axial direction. Such inclined sipes 20 improve the wet grip performance and wear resistance of the pneumatic tire 1. Furthermore, the inclined sipes 20 help improve noise performance during acceleration by optimizing the rigidity distribution of the crown rib 12, the middle ribs 13, etc., 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 as inclined sipes 20. 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 as inclined sipes 20. 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 as the inclined sipes 20. 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 lengths.

[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 pressure and are prone to generating noise during acceleration. However, not providing lateral grooves in these ribs 12 and 13 helps to suppress the generation of noise associated with deformation of the lateral grooves during acceleration.

[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.

[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.

[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] For example, each first shoulder sipe 41 has an axially inner end 41B communicating with the first shoulder circumferential groove 10C, and an axially outer end 41A connected to the inner end 28B of the first shoulder lateral groove 28.

[0056] For example, each second shoulder sipe 42 has an axially inner end 42B communicating with the second shoulder circumferential groove 10D, and an axially outer end 42A connected to the inner end 29B of the second shoulder lateral groove 29.

[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 lower ground contact pressure during straight-ahead driving than the crown rib 12 and the middle rib 13, and tend to slip more on the road surface during acceleration than the 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 of each rib per pitch. Therefore, in this embodiment, assuming a configuration in which each shoulder lateral groove 27 terminates within the shoulder rib 14 without communicating with the shoulder circumferential grooves 10C and 10D, 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. Furthermore, the longitudinal rigidity of each of the crown rib 12, middle rib 13, and shoulder rib 14 per pitch is set to Ks > Km and Ks > Kc. This suppresses the amount of circumferential shear deformation of the shoulder rib 14 during acceleration, and effectively suppresses the amount of slip.

[0064] As shown schematically in FIG. 5, 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. 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] [Circumferential sipes] As shown in FIG. 2 , the crown rib 12 and the middle rib 13 are each provided with circumferential sipes 50 that extend continuously parallel to the tire circumferential direction. In this embodiment, the circumferential sipes 50 extend linearly parallel to the tire circumferential direction. Furthermore, the circumferential sipes 50 are spaced apart from the inclined sipes 20. Compared to the inclined sipes 20, such circumferential sipes 50 are less likely to reduce the longitudinal rigidity of each rib. Rather, the circumferential sipes 50 maintain the longitudinal rigidity of each rib while equalizing the distribution of contact pressure between these ribs when they come into contact with the ground, thereby mitigating input from the tread portion 2 and reducing overall sound pressure during acceleration driving.

[0072] The depth of the circumferential sipes 50 is not particularly limited, but is preferably 1.0 mm or more to effectively improve the ground contact of the rib. On the other hand, to suppress a decrease in the longitudinal rigidity of the rib, the depth of the circumferential sipes 50 is preferably 5.5 mm or less. In particular, the depth of the circumferential sipes 50 is preferably smaller than the depth of the inclined sipes 20 provided on the rib in the tire circumferential direction and the tire axial direction. Furthermore, the depth of the circumferential sipes 50 is preferably 50% or less of the depth of the inclined sipes 20. Similarly, the depth of the circumferential sipes 50 is preferably smaller (for example, 70% or less) than the groove depth of the circumferential grooves 10.

[0073] The circumferential sipes 50 are preferably provided, for example, in the axially central region of each rib. The axially central region of the rib is, for example, an area that is 46% of the maximum axial width of the contact surface of the rib, and its axial center coincides with the axial center of the rib. The circumferential sipes 50 of this embodiment are provided at the axially central position of each rib.

[0074] [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 pattern includes a first sipe group G1 in which the inclined sipes 20 are arranged seamlessly around one circumference of the tire. More specifically, the first sipe group G1 of this embodiment includes crown sipes 21 and 22, first middle sipes 23 and 24, and second middle sipes 25 and 26.

[0075] The sipes of the seamlessly arranged first sipe group G1 contact the ground sequentially and substantially continuously as the pneumatic tire 1 rotates. More specifically, in each 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 inclined sipes 20 that separate from the road surface per unit time.

[0076] 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.

[0077] 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 pair satisfies condition a, but does not satisfy condition b because the two sipes are formed on the same rib (first middle rib 131).

[0078] 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.

[0079] 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 21 and 22 (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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] Pitch noise is known as noise generated when a tire is running. For example, an impact force is generated each time a rib on which sipes are formed comes into contact with the road surface. This impact force periodically vibrates the tread portion 2 and the sidewall portion 3, thereby generating pitch noise. Pitch noise also tends to increase as the vehicle accelerates. However, in the first sipe group G1 arranged in a seamless arrangement as in this embodiment, the sipes alternately and continuously contact the ground during running of the tire. This reduces the fluctuation in impact force and reduces pitch noise associated with the ribs touching the ground, thereby further reducing acceleration noise.

[0084] 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.

[0085] In a more preferred embodiment, only the first sipe group G1, 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.

[0086] [Sipe embodiment] The angle β of the crown sipes 21, 22 relative to the tire circumferential direction is not particularly limited, but can be set, for example, in the range of 30 to 85°. On the other hand, sipes with a relatively small angle relative to the tire circumferential direction reduce edge components in the tire axial direction. From this perspective, the angle β of the crown sipes 21, 22 relative to the tire circumferential direction is preferably in the range of 30 to 60°, more preferably 30 to 55°, and even more preferably 30 to 40°.

[0087] The semi-open crown sipes 21, 22 do not completely divide the crown rib 12 in the tire axial direction, thereby maintaining high longitudinal rigidity of the rib and suppressing slippage of each pitch of the crown rib 12 when the rib comes into contact with the ground, even during acceleration. Furthermore, by applying the small angle with respect to the tire circumferential direction to the semi-open crown sipes 21, 22, the lateral edge components of the crown sipes 21, 22 are reduced. Therefore, the amount of opening and slippage of the sipes 21, 22 as they move from the contact patch to the outside of the contact patch are further reduced. This reduces acceleration noise at the crown rib 12. In a particularly preferred embodiment, the axial length Lc of the crown sipes 21, 22 is preferably in the range of 20% to 45% of the axial width Wc of the contact patch of the crown rib 12.

[0088] The angles γ and δ of the first middle sipes 23, 24 and the second middle sipes 25, 26 relative to the tire circumferential direction are not particularly limited, but can be set, for example, in the range of 30 to 85°. As with the crown sipes 21, 22, from the viewpoint of reducing axial edge components and acceleration noise, the angles γ and δ of the first middle sipes 23, 24 and the second middle sipes 25, 26 relative to the tire circumferential direction are preferably in the range of 30 to 60°, more preferably 30 to 55°, and even more preferably 30 to 40°. The axial length Lm1 of the first middle sipes 23, 24 is preferably in the range of 20% to 45% of the axial width Wm1 of the contact patch of the first middle rib 131. Similarly, the axial length Lm2 of the second middle sipes 25, 26 is preferably in the range of 20% to 45% of the axial width Wm2 of the contact patch of the second middle rib 132.

[0089] The difference in angle between the crown sipes 21, 22, the first middle sipes 23, 24, and the second middle sipes 25, 26 and the tire circumferential direction is preferably 50° or less, more preferably 40° or less, and even more preferably 30° or less. Here, the "angle difference" refers to the difference in angle between two sipes and the tire circumferential direction. More specifically, the angle of each sipe with respect to the tire circumferential direction is first determined. Then, among the crown sipes 21, 22, the first middle sipes 23, 24, and the second middle sipes 25, 26, the sipe with the largest angle with respect to the tire circumferential direction and the sipe with the smallest angle with respect to the tire circumferential direction are determined, and the difference in angle between them is calculated. Note that, when each sipe is curved or zigzag, the angles β, γ, and δ of the sipe with respect to the tire circumferential direction are defined as the angle of a straight line connecting both ends of the sipe with respect to the tire circumferential direction.

[0090] In this embodiment, the angle β of the crown sipes 21, 22 relative to the tire circumferential direction is approximately 55°. The angles γ and δ of the first middle sipes 23, 24 and the second middle sipes 25, 26 relative to the tire circumferential direction are also approximately 55°. Therefore, the crown sipes 21, 22, the first middle sipes 23, 24, and the second middle sipes 25, 26 extend parallel to one another, and the difference in the angles of these sipes relative to the tire circumferential direction is substantially zero. This configuration helps to further reduce acceleration noise.

[0091] FIG. 8 shows a cross-sectional view taken along line VIII-VIII in FIG. 2. As shown in FIG. 8, the crown sipe 21 of this embodiment includes a base portion 21m having a substantially constant depth D1 and a sub-portion 21s whose depth gradually decreases toward the first end 21A. The depth D1 of the base portion 21m is, for example, 70% to 90% of the depth D of the first crown circumferential groove 10A, and is approximately 85% in this embodiment. The sub-portion 21s has an end portion inclined at an angle θ1 with respect to a tread normal extending from the first end 21A of the crown sipe 21. The angle θ1 is preferably larger than the angle θ2 of the rib wall of the crown rib 12, for example. This minimizes the change in rigidity of the crown rib 12, which is desirable from the perspective of reducing acceleration noise. More specifically, the angle θ1 is preferably 15° or greater, more preferably 18° to 25°.

[0092] The crown sipe 22 of this embodiment also includes a base 22m having a substantially constant depth D1 and a sub-portion 22s whose depth gradually decreases toward the second end 22B. The configurations of the base 22m and the sub-portion 22s are identical to those of the base 21m and the sub-portion 21s of the crown sipe 21 (which have a substantially symmetrical structure with respect to the tire equator C).

[0093] FIG. 9 shows a cross-sectional view taken along line IX-IX in FIG. 2. As shown in FIG. 9, the first middle sipe 23 of this embodiment also includes a base portion 23m having a substantially constant depth D1 and a secondary portion 23s whose depth gradually decreases toward the first end 23A. The depth D1 of the base portion 23m is, for example, 70% to 90% of the depth D of the first shoulder circumferential groove 10C, and in this embodiment, it is approximately 85%. The secondary portion 23s has an end bottom portion inclined at an angle θ1 with respect to the tread normal at the first end 23A of the first middle sipe 23. The angle θ1 is preferably greater than the angle θ2 of the rib wall of the first middle rib 131, for example. This minimizes the change in rigidity of the first middle rib 131, which is desirable from the perspective of reducing acceleration noise. More specifically, the angle θ1 is preferably 15° or greater, more preferably 18° to 25°.

[0094] 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.

[0095] FIG. 10 shows a cross-sectional view of a crown sipe 21 as a representative example of the inclined sipe 20. The other inclined sipes, the crown sipe 22, the first middle sipes 23 and 24, and the second middle sipes 25 and 26, also have similar cross-sectional shapes. As shown in FIG. 10 , the inclined sipe 20 of this embodiment has a substantially constant width and extends radially inward from the tread contact surface 2a. Furthermore, the inclined 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 inclined sipe 20 at the tread contact surface 2a are formed with sharp corners. Specifically, the radius of curvature of the corners of the inclined 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.

[0096] Generally, when a vehicle accelerates, the pneumatic tire 1 exhibits a greater tendency to kick off the road surface while sliding. Acceleration noise therefore varies depending on the edge shape of the sipes formed in the tread portion 2. For example, chamfered edges of sipes reduce friction between the sipes and the road surface, making them more likely to slip on the road surface than sipes without chamfers. Furthermore, such slippage tends to cause the sipes to open wider when they leave the ground contact patch. Therefore, by not providing chamfered edges to the sipes of the crown rib 12 and the middle rib 13, which experience relatively high ground contact pressure, slippage near the sipes of the crown rib 12 and the middle rib 13 and the resulting large opening of the sipes during acceleration are suppressed. In other words, the pneumatic tire 1 of the present invention suppresses sipe displacement during acceleration, effectively suppressing acceleration noise.

[0097] [First and second shoulder grooves] FIG. 11(a) shows a partial plan view of a first shoulder rib 141 as a representative example of the shoulder rib 14. FIG. 11(b) is a cross-sectional view taken along line BB. The configuration of the first shoulder rib 141 will be described in detail below, but it should be noted that the second shoulder rib 142 also has a similar configuration. Examples of similar configurations include a symmetrical structure with respect to the tire equator C and a rotationally symmetrical structure with respect to a point on the tire equator C. As shown in FIGS. 11(a) and 11(b), the first shoulder lateral grooves 28 extend linearly. In a preferred embodiment, the first shoulder lateral grooves 28 extend linearly throughout their entire length. The first shoulder lateral grooves 28 also have an angle α1 of, for example, 60 to 90°, more preferably 70 to 90°, and even more preferably 75 to 90° relative to the tire circumferential direction. In other words, the first shoulder lateral grooves 28 of this embodiment extend at an angle closer to the tire axial direction. Such first shoulder lateral grooves 28 are less likely to match the contour of the contact patch of the first shoulder rib 141, which prevents the compressed air in the grooves from being suddenly expelled outward from the contact patch, which helps reduce pitch noise.

[0098] 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.

[0099] [Shoulder sipes] The first shoulder sipes 41 extend linearly, for example. In a preferred embodiment, the first shoulder sipes 41 extend linearly throughout their entire length. The first shoulder sipes 41 have an angle α2 of, for example, 60 to 90°, more preferably 70 to 90°, and even more preferably 75 to 90° with respect to the tire circumferential direction. That is, the first shoulder sipes 41 of this embodiment extend at an angle closer to the tire axial direction. Since such first shoulder sipes 41 are less likely to match the contour of the contact patch of the first shoulder rib 141, the air compressed within the sipes is prevented from suddenly being 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.

[0100] [Shoulder circumferential sipes] Each shoulder rib 14 is provided with a shoulder circumferential sipe 60. The shoulder circumferential sipes 60 extend parallel to the tire circumferential direction. In this embodiment, the shoulder circumferential sipes 60 extend linearly along the tire circumferential direction. There is little concern that the shoulder circumferential sipes 60 will reduce the front-to-rear rigidity of the shoulder ribs 14. Rather, the shoulder circumferential sipes 60 maintain the front-to-rear rigidity of each shoulder rib 14 while equalizing the distribution of contact pressure when these ribs come into contact with the tire, thereby mitigating input from the tread portion 2 and reducing overall sound pressure during accelerating driving.

[0101] The depth of the shoulder circumferential sipes 60 is not particularly limited, but is preferably 1.0 mm or more to effectively improve the ground contact of the shoulder rib 14. On the other hand, to prevent a decrease in the longitudinal rigidity of the shoulder rib 14, the depth of the shoulder circumferential sipes 60 is preferably 5.5 mm or less. In particular, the depth of the shoulder circumferential sipes 60 is preferably smaller than the groove depth of the first shoulder circumferential groove 10C, and is set to a range of, for example, 18% to 69%.

[0102] The shoulder circumferential sipes 60 are preferably positioned axially outward from the axially inner edge 14i of the contact patch of the shoulder rib 14, and more preferably 10 mm or more. This prevents an excessive decrease in longitudinal rigidity near the axially inner edge 14i of the shoulder rib 14. On the other hand, the shoulder circumferential sipes 60 are preferably positioned axially inward from the axially outer end 7e of the belt layer 7. A rigidity step is likely to occur near the axially outer end 7e of the belt layer 7, but by positioning the shoulder circumferential sipes 60 away from this area, an excessive decrease in longitudinal rigidity can be prevented, and slippage of the shoulder rib 14 during acceleration can be effectively prevented.

[0103] In a preferred embodiment, the shoulder circumferential sipes 60 are desirably arranged so as to connect circumferentially adjacent shoulder lateral grooves 27. This improves the road contact of the shoulder rib 14, which has a relatively high front-rear rigidity, and is expected to reduce impact noise.

[0104] [Shoulder circumferential narrow groove] FIG. 12 shows a developed view of the tread portion 2 of another embodiment of the pneumatic tire 1 of the present invention. In the embodiment of FIG. 2, shoulder circumferential sipes 60 are provided in the shoulder ribs 14. However, instead of such shoulder circumferential sipes 60, shoulder circumferential narrow grooves 70 as shown in FIG. 12 may be provided. The groove width of the shoulder circumferential narrow grooves 70 is, for example, greater than 1.5 mm and smaller than the groove width of the circumferential grooves 10. Such shoulder circumferential narrow grooves 70 also have a narrow groove width, which is limited to a small width. This allows the front-rear rigidity of each shoulder rib 14 to be maintained while the contact pressure distribution of these ribs when they come into contact with the tire to be uniform, which reduces input from the tread portion 2 and reduces overall sound pressure during acceleration. In a preferred embodiment, the groove width of the shoulder circumferential narrow grooves 70 is, for example, 3.0 mm or less.

[0105] In this embodiment, the shoulder circumferential narrow groove 70 is arranged to communicate between the shoulder lateral grooves 27 adjacent in the tire circumferential direction. The axially inner groove edge of the shoulder circumferential narrow groove 70 may be substantially aligned with or close to the axially inner ends (28B, 29B) of the shoulder lateral grooves 27. Note that the preferred arrangement positions described for the shoulder circumferential sipes 60 can be applied to the arrangement position of the shoulder circumferential narrow groove 70.

[0106] 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]

[0107] 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. Comparative Example 1 has the tread pattern shown in FIG. 13. Examples 1 to 5 are based on the patterns shown in FIG. 2 or FIG. 12. 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:

[0108] [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.

[0109] [Acceleration noise test] Acceleration tests were conducted based on the United Nations Economic Commission for Europe (UNECE) vehicle exterior noise regulation test method (R51-03 conditions). Specifically, a hybrid SUV fitted with test tires entered the test track at a low speed of less than 20 km / h, 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.

[0110] [Ride comfort test] The ride comfort of a test vehicle fitted with the test tires was evaluated by the driver's senses. The results are rated based on the ride comfort of Comparative Example 1 being 100, with a higher score indicating better ride comfort.

[0111] [Rolling resistance test] Using a rolling resistance tester, the rolling resistance of each test tire was measured in accordance with ISO 28580. The results are expressed as an index with Comparative Example 1 being 100, with a larger index indicating a lower and more favorable rolling resistance. The test results are shown in Table 1.

[0112] [Table 1]

[0113] It was confirmed that the maximum displacement (corresponding to the amount of slippage) within the contact patch of the pneumatic tires of Examples 1 to 5 was kept small, more specifically, the average value of the ribs was kept to 0.32 mm or less. In addition, it was confirmed that the pneumatic tires of Examples 1 to 5 also had excellent ride comfort and rolling resistance performance.

[0114] Fig. 14 shows the relationship between the frequency and sound pressure level of external noise during acceleration for Examples 1 to 3 and Comparative Example 1. As is clear from Fig. 14, it is presumed that Examples 1 to 3 had a significantly reduced sound pressure level in the high frequency range of 1000 Hz or higher compared to Comparative Example 1, which resulted in an improvement in acceleration noise.

[0115] [Note] The present invention includes the following aspects.

[0116] [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, a plurality of inclined sipes inclined with respect to the tire circumferential direction and the tire axial direction are formed in each of the crown rib and the pair of middle ribs, The plurality of inclined sipes do not completely cross each rib in the tire axial direction, The crown rib and the pair of middle ribs are each provided with a circumferential sipe extending continuously in parallel to the tire circumferential direction, The circumferential sipes are spaced apart from the inclined sipes. Pneumatic tires. [Invention 2] The pneumatic tire according to invention 1, wherein the circumferential sipes have a depth of 1.0 to 5.5 mm. [Invention 3] The circumferential sipes are provided in the central region of each rib in the tire axial direction, 3. The pneumatic tire according to claim 1 or 2, wherein the central region of each rib is 46% of the maximum width of the contact surface of the rib in the axial direction of the tire. [Invention 4] A belt layer is disposed inside the tread portion, Each shoulder rib is provided with a shoulder circumferential sipe extending parallel to the tire circumferential direction, The pneumatic tire according to any one of claims 1 to 3, wherein the shoulder circumferential sipe is located axially outward from an axially inner edge of the contact surface of the shoulder rib and axially inward from an axially outer end of the belt layer. [Invention 5] A belt layer is disposed inside the tread portion, Each shoulder rib is provided with a shoulder circumferential narrow groove extending parallel to the tire circumferential direction, The groove width of the shoulder circumferential narrow groove is greater than 1.5 mm and smaller than the groove width of the circumferential groove, The pneumatic tire according to any one of claims 1 to 4, wherein the shoulder circumferential narrow groove is located axially outward from the axially inner edge of the contact surface of the shoulder rib and axially inward from the axially outer end of the belt layer. [Invention 6] 6. The pneumatic tire according to any one of claims 1 to 5, 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 7] 7. The pneumatic tire according to any one of claims 1 to 6, 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 8] 8. The pneumatic tire according to any one of claims 1 to 7, 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]

[0117] 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 Inclined sipes 50 circumferential sipes 60 Shoulder circumferential sipes 70 Narrow grooves in the circumferential direction of the shoulder

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 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, a plurality of inclined sipes inclined with respect to the tire circumferential direction and the tire axial direction are formed in each of the crown rib and the pair of middle ribs, The plurality of inclined sipes do not completely cross each rib in the tire axial direction, The crown rib and the pair of middle ribs are each provided with a circumferential sipe extending continuously in parallel to the tire circumferential direction, The circumferential sipes are spaced apart from the inclined sipes. Pneumatic tires.

2. The pneumatic tire according to claim 1, wherein the circumferential sipes have a depth of 1.0 to 5.5 mm.

3. The circumferential sipes are provided in the central region of each rib in the tire axial direction, The pneumatic tire according to claim 1 , wherein the central region of each rib is 46% of the maximum axial width of the rib's contact surface.

4. A belt layer is disposed inside the tread portion, Each shoulder rib is provided with a shoulder circumferential sipe extending parallel to the tire circumferential direction, 4. The pneumatic tire according to claim 1, wherein the shoulder circumferential sipe is located axially outward from an axially inner edge of the contact surface of the shoulder rib by 5 mm or more and axially inward from an axially outer end of the belt layer by 9 mm or more.

5. A belt layer is disposed inside the tread portion, Each shoulder rib is provided with a shoulder circumferential narrow groove extending parallel to the tire circumferential direction, a groove width of the shoulder circumferential narrow groove is greater than 1.5 mm and smaller than a groove width of the circumferential groove; 4. The pneumatic tire according to claim 1, wherein the shoulder circumferential narrow groove is located axially outward from an axially inner edge of the contact surface of the shoulder rib by 5 mm or more and axially inward from an axially outer end of the belt layer by 9 mm or more.

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

7. The pneumatic tire according to claim 6, wherein the longitudinal stiffness Ks of the shoulder ribs is 1.10 to 1.20 times the longitudinal stiffness Km of the middle rib.

8. 4. 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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