JP7750060B2 - pneumatic tires - Google Patents

Description

This disclosure relates to pneumatic tires.

Patent Document 1 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.

Japanese Patent Application Laid-Open No. 2018-140745

In recent years, there has been a demand for longer tire life, and further improvements in tire wear resistance are also required. However, further improving the wear resistance of the tire described in Patent Document 1 above may result in a decrease in wet performance.

This disclosure was devised in light of the above-mentioned circumstances, and its primary objective is to provide a tire that can exhibit excellent wear resistance while maintaining wet performance.

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, and the circumferential rigidity of the first shoulder land portion The stiffness KS1 and circumferential stiffness KS2 of the second shoulder land portion are each 1.05 to 1.25 times the circumferential stiffness KC of the crown land portion, and the pneumatic tire is in a normal state, mounted on a normal rim, inflated to a normal internal pressure, and placed on a flat surface with a camber angle of 0° and subjected to 70% of the normal load. In this pneumatic tire, the ratio Lc/Ls of the circumferential contact length Lc at the tire equator to the maximum 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.

By adopting the above configuration, the pneumatic tire of the present disclosure is able to exhibit excellent wear resistance while maintaining wet performance.

1 is a development view of a tread portion of a pneumatic tire according to one embodiment of the present disclosure. 4 is an explanatory diagram of a method for measuring the rigidity of a land portion in the tire circumferential direction. FIG. FIG. 2 is an enlarged view of the tread contact surface shape. 2 is an enlarged view of a first middle land portion, a second middle land portion, and a crown land portion of FIG. 1 . FIG. 5 is an enlarged view of the first middle sipe of FIG. 4 . FIG. 5 is an enlarged view of the second middle sipe of FIG. 4 . 5 is a cross-sectional view taken along line AA in FIG. 4. 5 is a cross-sectional view taken along line BB in FIG. 4. 5 is a cross-sectional view taken along line CC in FIG. 4. FIG. 2 is an enlarged view of a first shoulder land portion of FIG. 1 . 11 is a cross-sectional view taken along line DD in FIG. 10. FIG. 2 is an enlarged view of a second shoulder land portion of FIG. 1 .

An embodiment of the present disclosure will now be described with reference to the drawings. FIG. 1 is a developed view of the 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, for example, as a pneumatic tire for passenger vehicles. However, the present disclosure is not limited to this embodiment and may also be applied to pneumatic tires for heavy loads.

As shown in FIG. 1, the tread portion 2 of the tire 1 of the present disclosure has a specified orientation for mounting on a vehicle. As a result, 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.

The first tread edge T1 and the second tread edge T2 each correspond to the edges of the contact patch when the tire 1 is in a normal state and is subjected to 70% of the normal load, with the tread portion 2 in contact with the ground at a flat surface with a camber angle of 0°.

In the case of pneumatic tires for which various standards are established, "normal condition" refers to a state in which the tire is mounted on a normal rim, inflated to the normal internal pressure, and unloaded. In the case of tires for which various standards are not established or non-pneumatic tires, the normal condition refers to a standard use state according to the tire's intended use, in which the tire is not mounted on a vehicle and is unloaded. Unless otherwise specified, the dimensions of each part of the tire in this specification are values measured in the normal condition.

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."

"Normal internal pressure" is the air pressure specified for each tire by each standard, including the standards 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."

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 standards 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.

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 separated by 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 composed of four circumferential grooves 3 and five land portions 4.

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 located closest to the first tread edge T1. Of the multiple circumferential grooves 3, the second shoulder circumferential groove 6 is located closest to the second tread edge T2. The first crown circumferential groove 7 is located between the first shoulder circumferential groove 5 and the tire equator C. The second crown circumferential groove 8 is located between the second shoulder circumferential groove 6 and the tire equator C.

The axial distance L1 from the tire equator C to the groove centerline 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 centerline 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.

In this embodiment, each circumferential groove 3 extends, for example, linearly parallel to the tire circumferential direction. For example, each circumferential groove 3 may extend in a wavy pattern.

It is desirable that the groove width W1 of each circumferential groove 3 be at least 3 mm. Furthermore, it is desirable that the groove width W1 of each circumferential groove 3 be 3.0% to 8.0% of the tread width TW. In a more desirable aspect, in this embodiment, of 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.

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 the first tread edge T1. The second shoulder land portion 14 is located axially outward of the second shoulder circumferential groove 6 and includes the 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.

The multiple 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.

In this 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 each set to 1.05 to 1.25 times the circumferential stiffness KC of the crown land portion 15.

The circumferential stiffness of the land portion mentioned above is expressed as the circumferential load per unit deformation, and is measured, for example, by the following method. As shown in Figure 2, a backing plate (not shown) is attached to the tread surface b of land portion a at a specified adhesive surface. When a load f is applied in the circumferential direction D of the tire under zero longitudinal load, the circumferential displacement t of the tread surface b of land portion a in the circumferential direction D of the tire is measured. The circumferential stiffness of land portion a is determined by the ratio f/t (N/mm) of the circumferential load f to the displacement t.

From the perspective 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. Furthermore, in order to reflect the effects of lateral grooves or sipes provided in the land portion, it is desirable that the length of the adhesive surface be specified to a length that can include one or more pitches of lateral grooves or sipes.

However, the method for measuring the circumferential rigidity of land portions is not limited to the above method, as long as it can be measured under equal conditions for each land portion. Therefore, the rigidity of the land portions may also be calculated using, for example, FEM.

Figure 3 shows the tread contact patch shape 2s when the tire 1 in the normal state is placed on a flat surface with a load of 70% of the normal load and a camber angle of 0°. As shown in Figure 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 away from the tire equator C is set to be 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 edge of the contact patch in the tread contact patch shape 2s. By adopting the above configuration, the present disclosure can exhibit excellent wear resistance while maintaining wet performance. The following mechanism is believed to be the reason for this.

To improve wear resistance, it is desirable for the driving forces generated in the crown land portion and the shoulder land portion during tire operation to be similar. Meanwhile, the shoulder land portion tends to have a shorter circumferential contact length than the crown land portion. As a result of various experiments, it was determined that in order 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 that of the crown land portion. Based on this knowledge, in this 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 on each land portion, ultimately improving wear resistance.

In addition to the rigidity specifications above, the present disclosure also specifies that the ratio Lc/Ls for the contact patch length of each land portion is 1.22 to 1.50. Therefore, 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 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.

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

The configuration of this embodiment will be described in more detail below. 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, improved performance can be expected according to each configuration. Furthermore, when several of the configurations described below are applied in combination, improved composite performance according to each configuration can be expected.

As shown in Figure 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 circumferential stiffness KS2 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 an even more desirable embodiment, the stiffness KS2 is 90% to 110% of the stiffness KS1. This further improves wear resistance.

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 wear resistance.
KS1/KC=0.7×Lc/Ls+0.18±0.05…(1)

To achieve a good balance between wet performance and wear resistance, the land ratio of the tread portion 2 of this embodiment is preferably 60% to 70%, for example. In this specification, "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.

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

Figure 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 Figure 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.

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

Figure 5 shows an enlarged view of the first middle sipe 16. Figure 6 shows an enlarged view of the second middle sipe 17. Figure 7 shows a cross-sectional view of the first middle sipe 16 or the second middle sipe 17, taken along line A-A in Figure 4. As shown in Figures 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.

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

As shown in Figure 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.

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°. Note that 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.

As shown in Figure 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.

As shown in FIG. 5, the chamfered portion 21a of the first middle sipe 16 is disposed along 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 in the first middle sipe 16 have the same size. Furthermore, the chamfer width W2 of the chamfered portion 21a of the first middle sipe 16 is, for example, 1.0 to 2.0 mm.

As shown in Figure 6, the chamfered portion 21b of the second middle sipe 17 is arranged over the entire length of the second middle sipe 17. Furthermore, the chamfer width of the second middle sipe 17 changes continuously. Such second middle sipes 17 help to suppress uneven wear of the land portion.

The position where the chamfer width of the second middle sipe 17 is smallest is preferably located, for example, 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 when driving on wet roads.

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.

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 the 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 the 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 desirable embodiment, the width of the inclined surface at the 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 the location where the groove wall and the sipe wall join to form an acute-angled corner. This reduces uneven wear at the ends of the second middle sipes 17.

The first middle sipes 16 and the second middle sipes 17 each extend axially to 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.

As shown in FIG. 4, it is desirable to provide, for example, multiple middle shallow grooves 30 in the first middle land portion 11. In this embodiment, the first middle sipes 16 and the middle shallow grooves 30 are arranged alternately in the circumferential direction of the tire. The middle shallow grooves 30 extend, for example, from the first shoulder circumferential groove 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 handling stability on dry roads (hereinafter sometimes simply referred to as "handling stability") in a balanced manner.

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.

Figure 8 shows a cross-sectional view taken along line B-B in Figure 4. As shown in Figure 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 degrees. When cornering on wet roads, for example, the groove wall 30a comes into contact with the ground as the land portion deforms due to increased ground pressure, improving wet performance.

As shown in FIG. 4 , the second middle land portion 12 is provided with, for example, at least one semi-open middle sipe 33. 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 multiple semi-open middle sipes 33; specifically, the second middle sipes 17 and the semi-open middle sipes 33 are arranged alternately in the tire circumferential direction.

It is desirable that the semi-open middle sipes 33 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.

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.

The semi-open middle sipes 33 extend, for example, from the tread surface to the bottom of the tread portion 2 at a constant width. The depth of the semi-open middle sipes 33 is preferably 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, specifically 0.5 to 1.5 mm. Such semi-open middle sipes 33 can provide friction on wet roads while maintaining wear resistance and handling stability.

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 this embodiment, the crown land portion 15 is provided with the first crown sipes 36 and second crown sipes 37 alternately arranged in the tire circumferential direction. Such first crown sipes 36 and second crown sipes 37 help to improve wet performance and noise performance in a well-balanced manner.

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 preferred 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.

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

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 preferably 103% to 130% of the length L5, and more preferably 103% to 115%. This improves wet performance and makes it easier to convert the pitch noise of the first crown sipes 36 and second crown sipes 37 into white noise.

Figure 9 shows a cross-sectional view taken along line CC in Figure 4. As shown in Figure 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 continues to 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 continues to the groove wall of the first crown circumferential groove 7 and forms an acute corner portion in a tread plan view.

The first sipe wall 23 includes a main surface 23a that forms the sipe main body portion 20c and an inclined surface 23b that forms 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. A first crown sipe 36 with such a chamfered portion 21c can improve wet performance and wear resistance in a well-balanced manner.

As shown in Figure 4, it is desirable that the inclined surface 23b of the chamfered portion 21c of the first crown sipe 36 narrows in width, for example, 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.

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 further explanation will be omitted here.

Figure 10 shows an enlarged view of the first shoulder land portion 13. As shown in Figure 10, the first shoulder land portion 13 is provided with, for example, multiple first shoulder lateral grooves 41 and multiple shoulder shallow grooves 45.

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 width W9 of the tread surface of the first shoulder land portion 13. Furthermore, 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. In addition to improving wear resistance, such first shoulder lateral grooves 41 also contribute to a well-balanced improvement in handling stability and wet performance.

Figure 11 shows a cross section taken along line D-D in Figure 10. As shown in Figure 11, the first shoulder lateral groove 41 has 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 degrees. The width W10 and depth d2 of the inclined surface 43 are preferably 0.2 to 0.7 mm. A first shoulder lateral groove 41 having such a chamfered portion 42 can exhibit excellent wear resistance.

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 area 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 area excluding the inclined surface 43 of the first shoulder lateral groove 41. As a result, when a large load acts on the tire, such as during cornering, the inclined surface 43 comes into contact with the ground, providing strong grip.

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, beyond the terminated end 41a of the first shoulder lateral groove 41 toward the first tread edge T1. Furthermore, 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 shoulder shallow grooves 45 help to improve noise performance and wet performance in a well-balanced manner.

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 decrease toward the first tread edge T1. This improves wear resistance and handling stability.

Figure 12 shows an enlarged view of the second shoulder land portion 14. As shown in Figure 12, the second shoulder land portion 14 is provided with, for example, multiple second shoulder lateral grooves 51 and multiple shoulder sipes 52.

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 groove 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 desirable configuration, the distance L9 is greater than the axial distance L7 (shown in Figure 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 reducing pitch noise from the first shoulder lateral grooves 41 and second shoulder lateral grooves 51 to white noise, which is expected to improve noise performance.

The second shoulder lateral groove 51 has a chamfered portion similar to that of the first shoulder lateral groove 41. Therefore, the configuration of the chamfered portion 42 of the first shoulder lateral groove 41 described above can be applied to the second shoulder lateral groove 51, and further description here will be omitted.

The shoulder sipes 52 extend, for example, from the second shoulder circumferential groove 6 to a position beyond the second tread edge T2. For example, the shoulder sipes 52 extend at 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 Figure 4) described above have the same depth. Such shoulder sipes 52 can provide friction on wet roads while maintaining steering stability and wear resistance.

A tire according to one embodiment of the present disclosure has been described in detail above, but the present disclosure is not limited to the specific embodiment described above and can be modified and implemented in various ways.

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 and/or the Lc/Ls ratio of each land portion 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 and sipes provided in each land portion. Furthermore, in the tires of Comparative Examples 1 to 5, the Lc/Ls ratio was adjusted by changing the curvature of the tread portion. Except for the above-mentioned features, 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: 18x8.0J
Tire pressure: 230kPa on all wheels
Test vehicle: 2000cc displacement, rear-wheel drive Tire mounting position: all wheels

<Wet performance>
The wet performance of the test vehicle when driven on a wet road surface was evaluated by the driver. The results are expressed as a score, with the wet performance of Comparative Example 1 being 100, and the higher the score, the better the wet performance.

<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 were expressed as an index, with the average remaining land height of Comparative Example 1 being 100, and a larger index value indicates better wear resistance.
The test results are shown in Tables 1-2.

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

In contrast, it is believed that Comparative Examples 1 and 2 had poor wear resistance due to the low rigidity of each shoulder land area. In Comparative Example 3, the excessively high rigidity of each shoulder land area increased the amount of slippage of the shoulder land area's contact surface, resulting in poor wear resistance. In Comparative Examples 4 and 5, the contact length ratio Lc/Ls was outside the preferred range, resulting in increased contact pressure acting on each shoulder land area or increased slippage of the shoulder land area's contact surface, resulting in poor wear resistance.

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

[Note]
The present disclosure includes the following aspects.

[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 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;
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 extending axially inward from at least the first tread edge and having 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 interrupted end of the first crown sipe is located closer to the second tread edge than the interrupted 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)

2 Tread portion 2s Tread contact surface shape 3 Circumferential groove 4 Land portion 13 First shoulder land portion 14 Second shoulder land portion 15 Crown land portion T1 First tread edge T2 Second tread edge KS1 Rigidity of first shoulder land portion in the tire circumferential direction KS2 Rigidity of second shoulder land portion in the tire circumferential direction KC Rigidity of crown land portion in the tire circumferential direction

Claims (8)

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