pneumatic tires

Abstract

To provide a tire capable of exhibiting excellent uneven wear resistance while retaining wet performance.SOLUTION: A pneumatic tire has a tread part 2 whose direction of mounting on a vehicle is designated. A rigidity KS1 in the tire circumferential direction of a first shoulder land part 13, and a rigidity KS2 in the tire circumferential direction of a second shoulder land part 14 are each 1.05-1.25 times of a rigidity KC in the tire circumferential direction of a crown land part 15. In a tread grounding surface shape 2s when a load of 70% of a normal load is applied to the pneumatic tire in a normal state of being assembled in a normal rim and filled with normal inner pressure, and is grounded on a plane at a camber angle of 0°, a ratio Lc / Ls of a ground contact length Lc in the tire circumferential direction on a tire equator to a maximum ground contact length Ls in the tire circumferential direction in a position separated by 80% of a tread ground contact half-width from the tire equator is 1.22-1.50.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to pneumatic tires. [Background technology]

[0002] Patent Document 1 listed below proposes a tire that is expected to improve uneven wear resistance and wet performance by improving the arrangement of inner shoulder lateral grooves and outer shoulder lateral grooves. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-140745 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, there has been a demand for longer tire life and further improvements in tire wear resistance. However, in the tire of Patent Document 1, further improvement in wear resistance may result in a deterioration in wet performance.

[0005] The present disclosure has been devised in view of the above circumstances, and has as its main object to provide a tire that can exhibit excellent wear resistance while maintaining wet performance. [Means for solving the problem]

[0006] The present disclosure relates to a pneumatic tire having a tread portion whose orientation when mounted on a vehicle is specified, the tread portion including a first tread edge that is on the outer side of the vehicle when mounted on the vehicle, a second tread edge that is on the inner side of the vehicle when mounted on the vehicle, a plurality of circumferential grooves that extend continuously in the tire circumferential direction between the first tread edge and the second tread edge, and a plurality of land portions divided by the plurality of circumferential grooves, the plurality of land portions including a first shoulder land portion that includes the first tread edge, a second shoulder land portion that includes the second tread edge, and a crown land portion provided on the tire equator, The stiffness KS1 of the second shoulder land portion in the tire circumferential direction and the rigidity KS2 of the second shoulder land portion in the tire circumferential direction are each 1.05 to 1.25 times the rigidity KC of the crown land portion in the tire circumferential direction, and the pneumatic tire in a normal state, mounted on a normal rim and inflated to a normal internal pressure, is placed on a flat surface with 70% of a normal load and a camber angle of 0°. In this pneumatic tire, the ratio Lc / Ls of the tire circumferential contact length Lc on the tire equator to the maximum tire circumferential contact length Ls at a position 80% of the tread contact half width from the tire equator is 1.22 to 1.50 in terms of the tread contact patch shape. [Effects of the Invention]

[0007] By adopting the above configuration, the pneumatic tire of the present disclosure can exhibit excellent wear resistance while maintaining wet performance. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a development view of a tread portion of a pneumatic tire according to one embodiment of the present disclosure. [Figure 2] 4 is an explanatory diagram of a method for measuring the rigidity of a land portion in the tire circumferential direction. FIG. [Figure 3] FIG. 2 is an enlarged view of the tread contact surface shape. [Figure 4] 2 is an enlarged view of a first middle land portion, a second middle land portion, and a crown land portion in FIG. 1. [Figure 5] FIG. 5 is an enlarged view of the first middle sipe of FIG. 4. [Figure 6] FIG. 5 is an enlarged view of the second middle sipe of FIG. 4. [Figure 7] FIG. 5 is a cross-sectional view taken along line AA in FIG. 4. [Figure 8] FIG. 5 is a cross-sectional view taken along line BB in FIG. 4. [Figure 9] FIG. 5 is a cross-sectional view taken along line CC in FIG. 4. [Figure 10] FIG. 2 is an enlarged view of the first shoulder land portion of FIG. 1. [Figure 11] FIG. 11 is a cross-sectional view taken along the line DD in FIG. [Figure 12] FIG. 2 is an enlarged view of the second shoulder land portion of FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of the present disclosure will now be described with reference to the drawings. FIG. 1 is a development view of a tread portion 2 of a pneumatic tire 1 (hereinafter, sometimes simply referred to as a "tire") illustrating one embodiment of the present disclosure. The tire 1 of this embodiment is suitable for use as a pneumatic tire for passenger cars, for example. However, the present disclosure is not limited to this embodiment and may also be applied to pneumatic tires for heavy loads.

[0010] 1, the tread portion 2 of the tire 1 of the present disclosure has a specified orientation for mounting on a vehicle, whereby the tread portion 2 includes a first tread edge T1 intended to be on the outer side of the vehicle when mounted on the vehicle, and a second tread edge T2 intended to be on the inner side of the vehicle when mounted on the vehicle.

[0011] The first tread edge T1 and the second tread edge T2 each correspond to the edge of the contact patch when 70% of the normal load is applied to the tire 1 in its normal state and the tread portion 2 is brought into contact with a flat surface at a camber angle of 0°.

[0012] "Normal condition" means, in the case of a pneumatic tire for which various standards are established, that the tire is mounted on a normal rim, inflated to the normal internal pressure, and is in an unloaded state. In the case of a tire for which various standards are not established or a non-pneumatic tire, the normal condition means a standard use state according to the intended use of the tire, in which the tire is not mounted on a vehicle and is unloaded. In this specification, unless otherwise specified, the dimensions of each part of the tire are values ​​measured in the normal condition.

[0013] 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."

[0014] "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. For JATMA, it is the "maximum air pressure," for TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO, it is the "INFLATION PRESSURE."

[0015] For pneumatic tires for which various standards are established, "normal load" refers to the load specified for each tire in the standard system including the standard on which the tire is based. For JATMA, this is "maximum load capacity," for TRA, this is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO, this is "LOAD CAPACITY." For tires for which various standards are not established, "normal load" refers to the maximum load that can be applied when using the tire in accordance with the above standards.

[0016] The tread portion 2 includes a plurality of circumferential grooves 3 extending continuously in the tire circumferential direction between the first tread edge T1 and the second tread edge T2, and a plurality of land portions 4 divided into the plurality of circumferential grooves 3. The tire 1 of this embodiment is a so-called five-rib tire in which the tread portion 2 is configured with four circumferential grooves 3 and five land portions 4.

[0017] The circumferential grooves 3 include a first shoulder circumferential groove 5 and a second shoulder circumferential groove 6, as well as a first crown circumferential groove 7 and a second crown circumferential groove 8. Of the multiple circumferential grooves 3, the first shoulder circumferential groove 5 is arranged closest to the first tread edge T1. Of the multiple circumferential grooves 3, the second shoulder circumferential groove 6 is arranged closest to the second tread edge T2. The first crown circumferential groove 7 is provided between the first shoulder circumferential groove 5 and the tire equator C. The second crown circumferential groove 8 is provided between the second shoulder circumferential groove 6 and the tire equator C.

[0018] The axial distance L1 from the tire equator C to the groove center line of the first shoulder circumferential groove 5 or the second shoulder circumferential groove 6 is preferably, for example, 25% to 35% of the tread width TW. The axial distance L2 from the tire equator C to the groove center line of the first crown circumferential groove 7 or the second crown circumferential groove 8 is preferably, for example, 5% to 20% of the tread width TW. The tread width TW is the axial distance from the first tread edge T1 to the second tread edge T2 in the normal state.

[0019] Each circumferential groove 3 of this embodiment extends, for example, linearly in parallel to the tire circumferential direction. Each circumferential groove 3 may extend, for example, in a wavy shape.

[0020] The groove width W1 of each circumferential groove 3 is preferably at least 3 mm or more. Furthermore, the groove width W1 of each circumferential groove 3 is preferably 3.0% to 8.0% of the tread width TW. As a more preferable aspect, in this embodiment, among the multiple circumferential grooves 3, the first shoulder circumferential groove 5 has the smallest groove width. However, the present disclosure is not limited to this aspect.

[0021] The multiple land portions 4 include a first shoulder land portion 13, a second shoulder land portion 14, and a crown land portion 15. The first shoulder land portion 13 is located axially outward of the first shoulder circumferential groove 5 and includes a first tread edge T1. The second shoulder land portion 14 is located axially outward of the second shoulder circumferential groove 6 and includes a second tread edge T2. The crown land portion 15 is located between the first crown circumferential groove 7 and the second crown circumferential groove 8 and is disposed on the tire equator C.

[0022] The plurality of land portions 4 in this embodiment further include a first middle land portion 11 and a second middle land portion 12. The first middle land portion 11 in this embodiment is separated between the first shoulder circumferential groove 5 and the first crown circumferential groove 7. The second middle land portion 12 in this embodiment is separated between the second shoulder circumferential groove 6 and the second crown circumferential groove 8.

[0023] In the present disclosure, the circumferential stiffness KS1 of the first shoulder land portion 13 and the circumferential stiffness KS2 of the second shoulder land portion 13 are set to 1.05 to 1.25 times the circumferential stiffness KC of the crown land portion 15, respectively.

[0024] The rigidity of the land portion in the tire circumferential direction is expressed as the load in the tire circumferential direction per unit deformation, and is measured, for example, by the following method. As shown in Fig. 2, a backing plate (not shown) is used that is adhered to the tread surface b of the land portion a at a predetermined adhesive surface, and when a load f is applied in the tire circumferential direction D in a state where the vertical load is zero, the positional deviation t of the tread surface b of the land portion a in the tire circumferential direction D is measured. The rigidity of the land portion a in the tire circumferential direction is specified by the ratio f / t (N / mm) of the load f in the tire circumferential direction to the positional deviation t.

[0025] From the viewpoint of measuring the rigidity of each land portion under the same conditions, it is desirable that the length of the adhesive surface in the tire circumferential direction be the same for each land portion. Also, in order to reflect the influence of lateral grooves or sipes provided on the land portion, it is desirable that the length of the adhesive surface be defined to a length that can include one or more pitches of lateral grooves or sipes.

[0026] However, the method for measuring the circumferential rigidity of the land portions is not limited to the above-described method as long as the measurement can be performed under the same conditions for each land portion. Therefore, the rigidity of the land portions may be calculated by, for example, FEM or the like.

[0027] FIG. 3 shows the tread contact patch shape 2s when the tire 1 in the normal state is placed on a flat surface with 70% of the normal load and a camber angle of 0°. As shown in FIG. 3, in the present disclosure, the ratio Lc / Ls of the tire circumferential contact patch length Lc at the tire equator C to the maximum tire circumferential contact patch length Ls at a position 80% of the half tread contact patch width TWh from the tire equator C is set to 1.22 to 1.50. The half tread contact patch width TWh is the width from the axial center of the contact patch to the axial end of the contact patch in the tread contact patch shape 2s. By adopting the above-described configuration, the present disclosure can exhibit excellent wear resistance while maintaining wet performance. The following mechanism is presumed to be the reason for this.

[0028] To improve wear resistance, it is desirable that the driving forces generated in the crown land portion and the shoulder land portion during tire travel are similar to each other. Meanwhile, the shoulder land portion tends to have a shorter circumferential contact length than the crown land portion. Various experiments have shown that, to approximate the driving forces generated by these land portions, it is desirable to increase the circumferential rigidity of the shoulder land portion relative to the crown land portion. Based on this finding, in the present disclosure, the rigidity KS1 of the first shoulder land portion 13 and the rigidity KS2 of the second shoulder land portion 14 are set to 1.05 to 1.25 times the rigidity KC of the crown land portion 15. This allows these land portions to exert driving forces evenly. This action suppresses localized wear of each land portion, ultimately improving wear resistance.

[0029] In addition to the above-mentioned rigidity specifications, the present disclosure also specifies that the ratio Lc / Ls of the contact patch length of each land portion be 1.22 to 1.50. Therefore, the tire 1 of the present disclosure can ensure sufficient circumferential contact length not only for the crown land portion 15 but also for the first shoulder land portion 13 and the second shoulder land portion 14. This allows each land portion to exert frictional force on wet road surfaces, improving wear resistance while maintaining wet performance. It is believed that this mechanism enables the present disclosure to exhibit excellent wear resistance while maintaining wet performance.

[0030] The rigidity of each land portion can be adjusted as appropriate by, for example, the axial width of the land portion or the grooves provided in the land portion. The contact patch length of each land portion can be adjusted as appropriate by specifying the pattern elements of the tread portion 2, the configuration of the carcass and tread reinforcing layer (not shown), the curvature of the tread portion 2 in the tire cross section, etc.

[0031] The following describes the configuration of this embodiment in more detail. Note that each configuration described below represents a specific aspect of this embodiment. Therefore, it goes without saying that the present disclosure can achieve the above-described effects even if it does not include the configurations described below. Furthermore, even if any one of the configurations described below is applied alone to a tire of the present disclosure having the above-described characteristics, performance improvement corresponding to each configuration can be expected. Furthermore, when several of the configurations described below are applied in combination, combined performance improvement corresponding to each configuration can be expected.

[0032] As shown in Fig. 1, the stiffness KS1 of the first shoulder land portion 13 is preferably 1.10 to 1.20 times the stiffness KC of the crown land portion 15. Similarly, the stiffness KS2 in the tire circumferential direction of the second shoulder land portion 14 is preferably 1.10 to 1.20 times the stiffness KC of the crown land portion 15. In a more preferable embodiment, the stiffness KS2 is 90% to 110% of the stiffness KS1, thereby further improving wear resistance.

[0033] Furthermore, it is desirable that the rigidity of each land portion be determined according to the ratio Lc / Ls. From this perspective, it is desirable that the ratio KS1 / KC of the rigidity KS1 of the first shoulder land portion 13 to the rigidity KC of the crown land portion 15 satisfy the following formula (1). The same applies to the ratio KS2 / KC of the rigidity KS2 of the second shoulder land portion 14 to the rigidity KC of the crown land portion 15. This further improves the wear resistance. KS1 / KC=0.7×Lc / Ls+0.18±0.05…(1)

[0034] In order to improve wet performance and wear resistance in a well-balanced manner, the land ratio of the tread portion 2 of this embodiment is preferably, for example, 60% to 70%. In this specification, the "land ratio" refers to the ratio Sb / Sa of the actual total contact area Sb to the total area Sa of the virtual contact area in which all grooves and sipes are filled.

[0035] The pattern elements of the tread portion 2 of this embodiment will be described below. Note that the tire 1 of the present disclosure is not limited to the configurations described below.

[0036] Fig. 4 shows an enlarged view of the first middle land portion 11, the second middle land portion 12, and the crown land portion 15. As shown in Fig. 2, the first middle land portion 11 is provided with a plurality of first middle sipes 16 that completely traverse the first middle land portion 11 in the tire axial direction. The second middle land portion 12 is provided with a plurality of second middle sipes 17 that completely traverse the second middle land portion 12 in the tire axial direction.

[0037] In this specification, the term "sipe" refers to a small cut in the sipe body, where the width between two sipe walls is 1.5 mm or less. The term "sipe body" also refers to a portion where two sipe walls extend substantially parallel to each other in the tire radial direction. "Substantially parallel" refers to an aspect where the angle between the two sipe walls is 10° or less. As described below, the sipe may include a chamfered portion. The sipe may also have a so-called flask bottom, where the width is expanded at the bottom.

[0038] Fig. 5 shows an enlarged view of the first middle sipe 16. Fig. 6 shows an enlarged view of the second middle sipe 17. Fig. 7 shows a cross-sectional view of the first middle sipe 16 or the second middle sipe 17 taken along line AA in Fig. 4. As shown in Figs. 5 to 7, the first middle sipe 16 and the second middle sipe 17 each include a sipe main body 20 extending in the tire radial direction and a chamfered portion 21 that opens to the tread surface of the tread portion 2 and has a width greater than the width of the sipe main body 20.

[0039] As shown in Fig. 5, in the present disclosure, the chamfered portion 21a of the first middle sipe 16 extends in the tire axial direction with a constant chamfer width W2. Also, as shown in Fig. 6, the chamfered portion 21b of the second middle sipe 17 has a chamfer width that increases from the minimum chamfered width position toward both sides in the tire axial direction. Such first middle sipes 16 and second middle sipes 17 help improve wet performance and noise performance.

[0040] 7, in the first middle sipe 16 and the second middle sipe 17, the sipe main body 20 extends along the tire radial direction with a constant width, and in a preferred embodiment, extends parallel to the tire radial direction. The width W3 of the sipe main body 20 is, for example, 0.2 to 1.2 mm, and preferably 0.4 to 0.8 mm. The sipe main body 20 may extend in the tire radial direction while oscillating.

[0041] The chamfered portion 21 includes an inclined surface 25 that is inclined between the sipe main body 20 and the tread surface of the tread portion 2. In this embodiment, the chamfered portion 21 includes a pair of inclined surfaces 25 formed on both sipe edges, but the inclined surface 25 may be formed on only one of the sipe edges. The angle θ1 of the inclined surface 25 with respect to the tire normal is, for example, 55 to 80°, and preferably 65 to 75°. In this specification, the chamfer width refers to the opening width of the sipe on the tread surface of the tread portion 2, where the chamfered portion 21 is provided, and corresponds to the sum of the width of the inclined surface 25 and the width of the sipe main body 20 in a plan view of the tread.

[0042] As shown in Fig. 4, the first middle sipes 16 and the second middle sipes 17 are inclined in the same direction relative to the tire axial direction. The angle of the first middle sipes 16 and the second middle sipes 17 relative to the tire axial direction is, for example, 5 to 15 degrees. In a desirable embodiment, the first middle sipes 16 and the second middle sipes 17 are inclined at the same angle relative to the tire axial direction. Such first middle sipes 16 and second middle sipes 17 can improve wet performance while maintaining wear resistance.

[0043] As shown in FIG. 5, the chamfered portion 21a of the first middle sipe 16 is disposed over the entire length of the first middle sipe 16. The chamfered portion 21a of the first middle sipe 16 includes a first inclined surface 26a that connects to one sipe wall of the sipe main body 20a and a second inclined surface 27a that connects to the other sipe wall of the sipe main body 20a. In this embodiment, the first inclined surface 26a and the second inclined surface 27a of the first middle sipe 16 have the same size. The chamfered width W2 of the chamfered portion 21a of the first middle sipe 16 is, for example, 1.0 to 2.0 mm.

[0044] 6, the chamfered portion 21b of the second middle sipe 17 is disposed over the entire length of the second middle sipe 17. The chamfered width of the second middle sipe 17 changes continuously. Such second middle sipes 17 are useful for suppressing uneven wear of the land portion.

[0045] The position where the chamfer width of the second middle sipe 17 is smallest is preferably located in the central region when the second middle land portion 12 is divided into three equal parts in the axial direction of the tire. Such second middle sipes 17 can guide the water film toward the second shoulder circumferential groove 6 and the second crown circumferential groove 8 in a balanced manner during wet driving.

[0046] The minimum chamfer width W4a of the chamfered portion 21b of the second middle sipe 17 is, for example, 1.0 to 2.0 mm. In this embodiment, the chamfer width W4a is the same as the chamfer width W2 of the first middle sipe 16. The maximum chamfer width W4b of the chamfered portion 21b of the second middle sipe 17 is preferably 1.5 times or more, more preferably 2.0 times or more, and preferably 3.0 times or less, more preferably 2.5 times or less, of the chamfer width W4a. This improves wet performance and noise performance in a balanced manner.

[0047] The chamfered portion 21b of the second middle sipe 17 includes a first inclined surface 26b that connects to one sipe wall of the sipe main body 20b and a second inclined surface 27b that connects to the other sipe wall of the sipe main body 20b. In this embodiment, at an end 17b of the chamfered portion 21b of the second middle sipe 17 on the second tread edge T2 side, the width of the first inclined surface 26b is smaller than the width of the second inclined surface 27b. Furthermore, at an end 17a of the chamfered portion 21b of the second middle sipe 17 on the tire equator C side, the width of the first inclined surface 26b is larger than the width of the second inclined surface 27b. In a more preferable embodiment, the width of the inclined surface at a location where the groove wall of the circumferential groove 3 and the sipe wall of the second middle sipe 17 join to form an obtuse-angled corner is larger than the width of the inclined surface at a location where the groove wall and the sipe wall join to form an acute-angled corner. As a result, uneven wear at the end of the second middle sipe 17 is suppressed.

[0048] The first middle sipes 16 and the second middle sipes 17 each extend in the tire axial direction at a constant depth. In this embodiment, the first middle sipes 16 and the second middle sipes 17 have the same depth. Furthermore, the depth of these sipes is preferably, for example, 60% to 80% of the depth of the circumferential grooves 3. This improves wet performance and noise performance in a balanced manner.

[0049] As shown in FIG. 4, it is desirable that the first middle land portion 11 be provided with, for example, a plurality of middle shallow grooves 30. In this embodiment, the first middle sipes 16 and the middle shallow grooves 30 are provided alternately in the circumferential direction of the tire. The middle shallow grooves 30 extend, for example, from the first shoulder circumferential grooves 5 and terminate within the first middle land portion 11. The middle shallow grooves 30 terminate closer to the first tread edge T1 than the axial center of the first middle land portion 11. The axial length L3 of the middle shallow grooves 30 is, for example, 35% to 50% of the axial width W5 of the first middle land portion 11. Such middle shallow grooves 30 improve wet performance and steering stability on dry roads (hereinafter sometimes simply referred to as "steering stability") in a well-balanced manner.

[0050] The middle shallow grooves 30 are inclined, for example, in the same direction as the first middle sipes 16 relative to the tire axial direction. The angle of the middle shallow grooves 30 relative to the tire axial direction is, for example, 5 to 15 degrees. In a more desirable embodiment, the difference in angle between the first middle sipes 16 and the middle shallow grooves 30 is 5 degrees or less. This improves wet performance and noise performance while maintaining wear resistance.

[0051] FIG. 8 shows a cross section taken along line BB in FIG. 4. As shown in FIG. 8, the groove depth d1 of the middle shallow groove 30 is, for example, 0.5 to 1.5 mm. The groove width W6 of the middle shallow groove 30 is, for example, 1.5 to 2.5 mm. In a more desirable embodiment, the middle shallow groove 30 has a V-shaped cross section formed by two groove walls 30a that are inclined relative to the tire radial direction. The angle of the groove wall 30a relative to the tire normal is, for example, 30 to 50°. When cornering on a wet road, for example, the groove wall 30a comes into contact with the ground as the land portion deforms due to increased ground pressure, thereby improving wet performance.

[0052] 4, for example, at least one semi-open middle sipe 33 is provided in the second middle land portion 12. One end of the semi-open middle sipe 33 is connected to the second shoulder circumferential groove 6, and the other end is terminated within the second middle land portion 12. In this embodiment, the second middle land portion 12 is provided with a plurality of semi-open middle sipes 33, and specifically, the second middle sipes 17 and the semi-open middle sipes 33 are provided alternately in the tire circumferential direction.

[0053] The semi-open middle sipes 33 desirably terminate closer to the second tread edge T2 than the axial center of the second middle sipes 17. The axial length L4 of the semi-open middle sipes 33 is, for example, 35% to 45% of the axial width W7 of the second middle land portion 12. Such semi-open middle sipes 33 can improve wet performance while maintaining steering stability.

[0054] The semi-open middle sipes 33 are inclined, for example, in the same direction as the second middle sipes 17 relative to the tire axial direction. The angle of the semi-open middle sipes 33 relative to the tire axial direction is, for example, 5 to 15 degrees. In a more desirable embodiment, the difference in angle between the second middle sipes 17 and the semi-open middle sipes 33 is 5 degrees or less. This improves wet performance and noise performance while maintaining wear resistance.

[0055] The semi-open middle sipes 33 extend, for example, with a constant width from the tread surface to the bottom of the tread portion 2. The depth of the semi-open middle sipes 33 is desirably smaller than the depth of the second middle sipes 17. The depth of the semi-open middle sipes 33 is 20% or less of the maximum depth of the second middle sipes 17, and specifically, is 0.5 to 1.5 mm. Such semi-open middle sipes 33 can provide friction on wet road surfaces while maintaining wear resistance and steering stability.

[0056] The crown land portion 15 is provided with, for example, a plurality of first crown sipes 36 and second crown sipes 37. The first crown sipes 36 extend from the first crown circumferential grooves 7 and terminate within the crown land portion 15. The second crown sipes 37 extend from the second crown circumferential grooves 8 and terminate within the crown land portion 15. In the crown land portion 15 of this embodiment, the first crown sipes 36 and the second crown sipes 37 are provided alternately in the tire circumferential direction. Such first crown sipes 36 and second crown sipes 37 are useful for improving wet performance and noise performance in a well-balanced manner.

[0057] The first crown sipes 36 and the second crown sipes 37 are inclined in the same direction relative to the tire axial direction, and in a desirable embodiment, are inclined in the same direction as the first middle sipes 16 and the second middle sipes 17. The angle of the first crown sipes 36 and the second crown sipes 37 relative to the tire axial direction is, for example, 10 to 20 degrees.

[0058] The first crown sipes 36 and the second crown sipes 37 each cross the axial center of the crown land portion 15. The axial length L5 of the first crown sipes 36 and the axial length L6 of the second crown sipes 37 are each 55% to 70% of the axial width W8 of the crown land portion 15. As a result, the discontinuous ends 36a of the first crown sipes 36 are located closer to the second tread edge T2 than the discontinuous ends 37a of the second crown sipes 37. This appropriately reduces the rigidity of the crown land portion 15, improving wet performance and wear resistance.

[0059] In a more desirable embodiment, the length L6 of the second crown sipes 37 is greater than the length L5 of the first crown sipes 36. The length L6 is desirably 103% to 130% of the length L5, and more desirably 103% to 115%. This improves wet performance and makes it easier for the pitch noise of the first crown sipes 36 and the second crown sipes 37 to become white noise.

[0060] Fig. 9 shows a cross-sectional view taken along line CC in Fig. 4. As shown in Fig. 9, the first crown sipe 36 includes a first sipe wall 23 and a second sipe wall 24. The first sipe wall 23 is a sipe wall that is continuous with the groove wall of the first crown circumferential groove 7 and forms an obtuse corner portion in a tread plan view. The second sipe wall 24 is a sipe wall that is continuous with the groove wall of the first crown circumferential groove 7 and forms an acute corner portion in a tread plan view.

[0061] The first sipe wall 23 includes a main body surface 23a that constitutes the sipe main body portion 20c and an inclined surface 23b that constitutes the chamfered portion 21c. The angle θ3 of the inclined surface 23b with respect to the tire normal is, for example, 55 to 65°. The second sipe wall 24 is connected to the tread surface of the crown land portion 15 without being chamfered. The first crown sipe 36 having such a chamfered portion 21c can improve wet performance and wear resistance in a well-balanced manner.

[0062] 4, it is desirable that the inclined surface 23b of the chamfered portion 21c of the first crown sipe 36 has a width that narrows toward the tire equator C. This allows the water film to be actively guided into the first crown circumferential groove 7 when the first crown sipe 36 comes into contact with a wet road surface.

[0063] The second crown sipes 37 have substantially the same configuration as the first crown sipes 36. Therefore, the configuration of the first crown sipes 36 described above can be applied to the second crown sipes 37, and a description thereof will be omitted here.

[0064] Fig. 10 shows an enlarged view of the first shoulder land portion 13. As shown in Fig. 10, the first shoulder land portion 13 is provided with, for example, a plurality of first shoulder lateral grooves 41 and a plurality of shoulder shallow grooves 45.

[0065] For example, the first shoulder lateral grooves 41 extend axially inward from at least the first tread edge T1 and terminate within the first shoulder land portion 13. In this embodiment, the first shoulder lateral grooves 41 extend across the first tread edge T1. The angle of the first shoulder lateral grooves 41 relative to the tire axial direction preferably increases axially inward. The axial distance L7 from the end 41a of the first shoulder lateral groove 41 to the first shoulder circumferential groove 5 is 3% to 10% of the tread width W9 of the first shoulder land portion 13. The groove width of the first shoulder lateral grooves 41 is preferably 33% to 40% of the maximum depth of the first shoulder lateral grooves 41. Such first shoulder lateral grooves 41 not only improve wear resistance but also contribute to a well-balanced improvement in handling stability and wet performance.

[0066] FIG. 11 shows a cross section taken along line DD in FIG. 10. As shown in FIG. 11, the first shoulder lateral groove 41 is provided with a chamfered portion 42. The chamfered portion 42 includes an inclined surface 43 between the tread surface of the first shoulder land portion 13 and the groove wall 41w of the first shoulder lateral groove 41. The angle θ4 of the inclined surface 43 with respect to the tire normal is, for example, 35 to 55°. The width W10 and depth d2 of the inclined surface 43 are preferably 0.2 to 0.7 mm. The first shoulder lateral groove 41 having such a chamfered portion 42 can exhibit excellent wear resistance.

[0067] As shown in Fig. 10, it is desirable that the width W10 (shown in Fig. 11) of the inclined surface 43 of the chamfered portion 42 of the first shoulder lateral groove 41 increases axially outward around the first tread edge T1. Specifically, at the first tread edge T1, the width W10 of the inclined surface 43 is 20% to 30% of the width of the region excluding the inclined surface 43 of the first shoulder lateral groove 41. Furthermore, at the axially outer end 41b of the first shoulder lateral groove 41, the width W10 of the inclined surface 43 is 45% to 55% of the width of the region excluding the inclined surface 43 of the first shoulder lateral groove 41. As a result, when a large load is applied to the tire during cornering, the inclined surface 43 comes into contact with the ground, providing strong grip.

[0068] The shoulder shallow groove 45 extends, for example, from the first shoulder circumferential groove 5 and terminates within the first shoulder land portion 13. In this embodiment, the shoulder shallow groove 45 extends, for example, further toward the first tread edge T1 than the terminated end 41a of the first shoulder lateral groove 41. The axial length L8 of the shoulder shallow groove 45 is preferably shorter than the axial length L3 (shown in FIG. 4 ) of the middle shallow groove 30. Specifically, the length L8 of the shoulder shallow groove 45 is 50% to 80% of the length L3 of the middle shallow groove 30. Such a shoulder shallow groove 45 helps to improve noise performance and wet performance in a well-balanced manner.

[0069] At the end of the shoulder shallow groove 45 on the side of the first shoulder circumferential groove 5, the shoulder shallow groove 45 has substantially the same cross-sectional shape as the above-described middle shallow groove 30. Therefore, the cross-sectional configuration of the above-described middle shallow groove 30 can be applied to the shoulder shallow groove 45. Furthermore, the width and depth of the shoulder shallow groove 45 become smaller toward the first tread edge T1. This improves wear resistance and steering stability.

[0070] Fig. 12 shows an enlarged view of the second shoulder land portion 14. As shown in Fig. 12, the second shoulder land portion 14 is provided with, for example, a plurality of second shoulder lateral grooves 51 and a plurality of shoulder sipes 52.

[0071] The second shoulder lateral grooves 51 extend axially inward from at least the second tread edge T2 and terminate within the second shoulder land portion 14. In this embodiment, the second shoulder lateral grooves 51 extend across the second tread edge T2. The axial distance L9 from the end 51a of the second shoulder lateral grooves 51 to the second shoulder circumferential groove 6 is, for example, 10% to 20% of the tread width W11 of the second shoulder land portion 14. In a more preferred embodiment, the distance L9 is greater than the axial distance L7 (shown in FIG. 10 ) from the end 41a of the first shoulder lateral groove 41 to the first shoulder circumferential groove 5. This achieves a balanced improvement in handling stability and wet performance, while also converting pitch noise from the first shoulder lateral grooves 41 and second shoulder lateral grooves 51 into white noise, which is expected to improve noise performance.

[0072] The second shoulder lateral grooves 51 have chamfered portions similar to those of the first shoulder lateral grooves 41. Therefore, the configuration of the chamfered portions 42 of the first shoulder lateral grooves 41 described above can be applied to the second shoulder lateral grooves 51, and therefore a description thereof will be omitted here.

[0073] The shoulder sipes 52 extend, for example, from the second shoulder circumferential groove 6 to a position beyond the second tread edge T2. The shoulder sipes 52 extend, for example, with a constant width from the tread surface to the bottom of the tread portion 2. The depth of the shoulder sipes 52 is, for example, 0.5 to 1.5 mm. In a more desirable embodiment, the shoulder sipes 52 and the semi-open middle sipes 33 (shown in FIG. 4) have the same depth. Such shoulder sipes 52 can provide friction on wet roads while maintaining steering stability and wear resistance.

[0074] Although a tire according to one embodiment of the present disclosure has been described in detail above, the present disclosure is not limited to the above-described specific embodiment and can be modified and implemented in various aspects. [Example]

[0075] Pneumatic tires of size 245 / 45R18 having the basic pattern of FIG. 1 were prototyped based on the specifications in Tables 1 and 2. Comparative Examples 1 to 5 were prototyped pneumatic tires having the basic pattern of FIG. 1 but with the rigidity ratio of each land portion and / or the ratio Lc / Ls outside the range of the present disclosure. In the tires of Comparative Examples 1 to 5, the rigidity ratio was adjusted by changing the depth of the grooves or sipes provided in each land portion. In addition, in the tires of Comparative Examples 1 to 5, the ratio Lc / Ls was adjusted by changing the curvature of the tread portion. Except for the above-mentioned points, the tires of Comparative Examples 1 to 5 were substantially the same as the tires of the Examples. Furthermore, wet performance and wear resistance were tested for these test tires. The common specifications and test methods for each test tire are as follows: Rim: 18 x 8.0J Tire pressure: 230kPa on all wheels Test vehicle: 2000cc, rear-wheel drive Tire mounting position: All wheels

[0076] <Wet performance> The wet performance of the test vehicle when driven on a wet road surface was evaluated by the driver. The results are rated based on the wet performance of Comparative Example 1 being 100, with a higher value indicating better wet performance.

[0077] <Wear resistance> After the test vehicle was driven a certain distance on a public road, the average remaining land height of the first shoulder land portion and the second shoulder land portion was measured. The results are expressed as an index, with the average remaining land height of Comparative Example 1 being 100, and a larger index indicates better wear resistance. The test results are shown in Tables 1-2.

[0078] [Table 1]

[0079] [Table 2]

[0080] As shown in Tables 1 and 2, the wet performance of the tires of each example was 101 to 104 points, which indicates that the wet performance was maintained. On the other hand, the wear resistance of the tires of each example was 121 to 132 points, which indicates that the tires exhibited excellent wear resistance.

[0081] In contrast, it is believed that Comparative Examples 1 and 2 had poor wear resistance due to the low rigidity of each shoulder land portion. In Comparative Example 3, the excessively high rigidity of each shoulder land portion increased the amount of slippage of the contact patch of the shoulder land portion, which is thought to have reduced wear resistance. In Comparative Examples 4 and 5, the contact length ratio Lc / Ls was outside the preferred range, which increased the contact pressure acting on each shoulder land portion or increased the amount of slippage of the contact patch of the shoulder land portion, which is thought to have reduced wear resistance.

[0082] As described above, the test results confirmed that the tires of the examples exhibited excellent wear resistance while maintaining wet performance.

[0083] [Note] The present disclosure includes the following aspects.

[0084] [Disclosure 1] A pneumatic tire having a tread portion whose mounting direction on a vehicle is specified, the tread portion includes a first tread edge that is on the outer side of the vehicle when mounted on the vehicle, a second tread edge that is on the inner side of the vehicle when mounted on the vehicle, a plurality of circumferential grooves that extend continuously in the tire circumferential direction between the first tread edge and the second tread edge, and a plurality of land portions that are divided by the plurality of circumferential grooves, the plurality of land portions include a first shoulder land portion including the first tread edge, a second shoulder land portion including the second tread edge, and a crown land portion provided on the tire equator, a stiffness KS1 of the first shoulder land portion in the tire circumferential direction and a stiffness KS2 of the second shoulder land portion in the tire circumferential direction are each 1.05 to 1.25 times a stiffness KC of the crown land portion in the tire circumferential direction, The tread contact surface shape when the pneumatic tire is mounted on a regular rim, inflated to a regular internal pressure, and placed on a flat surface with a camber angle of 0° and subjected to a load of 70% of the regular load, is as follows: The ratio Lc / Ls of the tire circumferential contact length Lc on the tire equator to the maximum tire circumferential contact length Ls at a position 80% of the tread contact half width away from the tire equator is 1.22 to 1.50. Pneumatic tires. [Disclosure 2] The pneumatic tire according to Disclosure 1, wherein the land ratio of the tread portion is 60% to 70%. [Disclosure 3] The first shoulder land portion is provided with a plurality of first shoulder lateral grooves that extend axially inward from at least the first tread edge and have discontinued ends within the first shoulder land portion, The pneumatic tire according to Disclosure 1 or 2, wherein the groove width of the first shoulder lateral groove is 33% to 40% of the maximum depth of the first shoulder lateral groove. [Disclosure 4] the plurality of land portions include a first middle land portion provided between the first shoulder land portion and the crown land portion, The pneumatic tire according to any one of Disclosures 1 to 3, wherein the first middle land portion is provided with a plurality of first middle sipes that completely cross the first middle land portion in the tire axial direction. [Disclosure 5] the plurality of land portions include a second middle land portion provided between the second shoulder land portion and the crown land portion, The pneumatic tire according to any one of Disclosures 1 to 4, wherein the second middle land portion is provided with a plurality of second middle sipes that completely cross the second middle land portion in the tire axial direction. [Disclosure 6] the plurality of circumferential grooves include a first crown circumferential groove adjacent to the first tread end side of the crown land portion and a second crown circumferential groove adjacent to the second tread end side of the crown land portion, A pneumatic tire as described in any one of Disclosures 1 to 5, wherein the crown land portion is provided with a plurality of first crown sipes extending from the first crown circumferential groove and having discontinued ends within the crown land portion, and a plurality of second crown sipes extending from the second crown circumferential groove and having discontinued ends within the crown land portion. [Disclosure 7] The pneumatic tire according to any one of Disclosures 1 to 6, wherein the discontinued end of the first crown sipe is located closer to the second tread edge than the discontinued end of the second crown sipe. [Disclosure 8] The pneumatic tire according to any one of Disclosures 1 to 7, wherein a ratio KS1 / KC of the stiffness KS1 of the first shoulder land portion to the stiffness KC of the crown land portion satisfies the following formula (1). KS1 / KC=0.7×Lc / Ls+0.18±0.05…(1) [Explanation of symbols]

[0085] 2 Tread section 2s Tread contact surface shape 3 Circumferential groove 4 Land 13 First Shoulder Land Section 14 Second Shoulder Land Section 15 Crown Land Division T1 First tread edge T2 Second tread edge KS1 Circumferential stiffness of the first shoulder land area KS2 Circumferential stiffness of the second shoulder land area KC Circumferential stiffness of the crown land area

Claims

1. A pneumatic tire having a tread portion whose mounting direction on a vehicle is specified, the tread portion includes a first tread edge that is on the outer side of the vehicle when mounted on the vehicle, a second tread edge that is on the inner side of the vehicle when mounted on the vehicle, a plurality of circumferential grooves that extend continuously in the tire circumferential direction between the first tread edge and the second tread edge, and a plurality of land portions that are divided by the plurality of circumferential grooves, the plurality of land portions include a first shoulder land portion including the first tread edge, a second shoulder land portion including the second tread edge, and a crown land portion provided on the tire equator, a circumferential stiffness KS1 of the first shoulder land portion and a circumferential stiffness KS2 of the second shoulder land portion are each 1.05 to 1.25 times a circumferential stiffness KC of the crown land portion, The tread contact surface shape when the pneumatic tire in a normal state, mounted on a normal rim and inflated to a normal internal pressure, is placed on a flat surface with a camber angle of 0° and subjected to a load of 70% of the normal load, is: a ratio Lc / Ls of a tire circumferential contact length Lc on the tire equator to a maximum tire circumferential contact length Ls at a position 80% of the tread contact half width away from the tire equator is 1.22 to 1.50, the plurality of circumferential grooves include a first crown circumferential groove adjacent to the first tread end side of the crown land portion, the crown land portion includes a plurality of first crown sipes extending from the first crown circumferential groove and having discontinued ends within the crown land portion, the first crown sipe includes a first sipe wall that is continuous with a groove wall of the first crown circumferential groove and that forms an obtuse corner portion in a tread plan view, and a second sipe wall that is continuous with the groove wall of the first crown circumferential groove and that forms an acute corner portion in a tread plan view, The first sipe wall includes a main body surface constituting a sipe main body portion and an inclined surface constituting a chamfered portion, The second sipe wall is connected to the tread surface of the crown land portion without being chamfered. Pneumatic tires.

2. The pneumatic tire according to claim 1, wherein the land ratio of the tread portion is 60% to 70%.

3. The first shoulder land portion is provided with a plurality of first shoulder lateral grooves extending axially inward from at least the first tread edge and having discontinued ends within the first shoulder land portion, 3. The pneumatic tire according to claim 1, wherein the groove width of the first shoulder lateral groove is 33% to 40% of the maximum depth of the first shoulder lateral groove.

4. the plurality of land portions include a first middle land portion provided between the first shoulder land portion and the crown land portion, The pneumatic tire according to claim 1 , wherein the first middle land portion is provided with a plurality of first middle sipes that completely cross the first middle land portion in the tire axial direction.

5. the plurality of land portions include a second middle land portion provided between the second shoulder land portion and the crown land portion, The pneumatic tire according to claim 1 , wherein the second middle land portion is provided with a plurality of second middle sipes that completely cross the second middle land portion in the tire axial direction.

6. the plurality of circumferential grooves include a first crown circumferential groove adjacent to the first tread end side of the crown land portion and a second crown circumferential groove adjacent to the second tread end side of the crown land portion, 6. The pneumatic tire according to claim 1, wherein the crown land portion is provided with a plurality of first crown sipes extending from the first crown circumferential groove and having discontinuous ends within the crown land portion, and a plurality of second crown sipes extending from the second crown circumferential groove and having discontinuous ends within the crown land portion.

7. The pneumatic tire according to claim 6 , wherein the discontinued end of the first crown sipe is located closer to the second tread edge than the discontinued end of the second crown sipe.

8. The pneumatic tire according to claim 1 , wherein a ratio KS1 / KC of the stiffness KS1 of the first shoulder land portion to the stiffness KC of the crown land portion satisfies the following formula (1): KS1 / KC=0.7×Lc / Ls+0.18±0.05…(1)

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