JP7779107B2 - tire - Google Patents

Description

This disclosure relates to tires.

Patent Document 1 below proposes a tire with sipes that completely cross the middle land area in the tire axial direction. The tire is expected to improve handling stability and noise performance through the sipes.

Japanese Patent Application Laid-Open No. 2015-137015

In recent years, vehicles have become quieter, and there is a demand for tires to have even better noise performance. At the same time, there is also a demand for improved wet performance for tires.

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

The present disclosure relates to a 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 middle land portion disposed between the first tread edge and the tire equator and a second middle land portion disposed between the second tread edge and the tire equator, the first middle land portion including at least one groove that completely crosses the first middle land portion in the tire axial direction. Each of the first and second middle sipes has one first middle sipe, and the second middle land portion has at least one second middle sipe that completely traverses the second middle land portion in the tire axial direction. The first and second middle sipes each include a sipe main body extending in the tire radial direction and a chamfered portion that opens to the tread surface of the tread portion with a width greater than the width of the sipe main body. The chamfered portion of the first middle sipe extends in the tire axial direction with a constant chamfer width, and the chamfered portion of the second middle sipe has a chamfer width that increases from the position where the chamfer width is smallest toward both sides in the tire axial direction.

By adopting the above-described configuration, the tire disclosed herein is able to exhibit excellent wet performance and noise performance.

1 is a development view of a tread portion of a tire according to one embodiment of the present disclosure. 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. 3 is an enlarged view of a first middle sipe of FIG. 2 . FIG. 3 is an enlarged view of the second middle sipe of FIG. 2 . 3 is a cross-sectional view taken along line AA in FIG. 2. 3 is a cross-sectional view taken along line BB in FIG. 2. 3 is a cross-sectional view taken along line CC in FIG. 2. FIG. 2 is an enlarged view of a first shoulder land portion of FIG. 1 . 9 is a cross-sectional view taken along line DD in FIG. 8. FIG. 2 is an enlarged view of a second shoulder land portion of FIG. 1 . FIG. 2 is a development view of a tread portion of a reference tire. FIG. 2 is a development view of a tread portion of a comparative example.

An embodiment of the present disclosure will now be described with reference to the drawings. FIG. 1 is a developed view of a tread portion 2 of a tire 1 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 and non-pneumatic tires that do not contain pressurized air inside the tire.

As shown in Figure 1, the tread portion 2 of the tire 1 has a specified orientation for installation on a vehicle. As a result, the tread portion 2 includes a first tread edge T1 that is intended to be on the outer side of the vehicle when installed on the vehicle, and a second tread edge T2 that is intended to be on the inner side of the vehicle when installed 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. However, the present disclosure is not limited to this configuration. In other embodiments of the tire 1 of this disclosure, for example, the tread portion 2 may be a so-called four-rib tire in which the tread portion 2 is composed of three circumferential grooves 3 and four 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 middle land portion 11 and a second middle land portion 12. The first middle land portion 11 is disposed between the first tread edge T1 and the tire equator C. In this embodiment, the first middle land portion 11 is separated between the first shoulder circumferential groove 5 and the first crown circumferential groove 7. The second middle land portion 12 is disposed between the second tread edge T2 and the tire equator C. In this embodiment, the second middle land portion 12 is separated between the second shoulder circumferential groove 6 and the second crown circumferential groove 8.

The multiple land portions 4 in this embodiment 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.

Figure 2 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 at least one first middle sipe 16 that completely traverses the first middle land portion 11 in the tire axial direction. In this embodiment, the first middle land portion 11 is provided with multiple first middle sipes 16. The second middle land portion 12 is provided with at least one second middle sipe 17 that completely traverses the second middle land portion 12 in the tire axial direction. In this embodiment, the second middle land portion 12 is provided with multiple second middle sipes 17.

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 3 shows an enlarged view of the first middle sipe 16. Figure 4 shows an enlarged view of the second middle sipe 17. Figure 5 shows a cross-sectional view of the first middle sipe 16 or the second middle sipe 17 taken along line A-A in Figure 2. As shown in Figures 3 to 5, 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 3, in the present disclosure, the chamfered portion 21a of the first middle sipe 16 extends axially with a constant chamfer width W2. Furthermore, as shown in Figure 4, the chamfered portion 21b of the second middle sipe 17 has a chamfer width that increases axially from the minimum chamfer width toward both sides. By adopting the above configuration, the tire 1 of the present disclosure is able to exhibit excellent wet and noise performance. The following mechanism is believed to be the reason for this.

In the tire 1 disclosed herein, the first middle sipes 16 and second middle sipes 17, which completely cross the land areas, provide frictional force during wet driving and improve wet performance. In particular, because the first middle sipes 16 and second middle sipes 17 include chamfered portions 21, they are able to more easily guide the water film toward the circumferential grooves 3 when the sipes contact the ground, which is expected to improve wet performance.

In addition, the first middle sipes 16 and second middle sipes 17 that cross the land areas allow air to flow in and out of the circumferential grooves 3 by opening and closing the sipes during dry driving, suppressing the generation of standing waves within the circumferential grooves 3. This action is expected to reduce the air column resonance noise generated by the circumferential grooves 3. Furthermore, because the chamfered portions 21a of the first middle sipes 16 and the chamfered portions 21b of the second middle sipes 17 have different shapes, the pitch noise when they come into contact with the ground tends to become white noise, which is expected to improve noise performance.

Furthermore, because the second middle sipes 17 are positioned closer to the second tread edge T2 than the tire equator C, they tend to receive greater ground contact pressure than the first middle sipes 16, making a significant contribution to wet performance. In the present disclosure, the width of the chamfered portion 21b of the second middle sipes 17 increases toward both sides in the tire axial direction, allowing the second middle sipes 17 to significantly contribute to improved wet performance. Therefore, the tire 1 of the present disclosure significantly improves wet performance compared to a tire in which the chamfer width of the chamfered portion of the second middle sipe is constant and the chamfer width of the chamfered portion of the first middle sipe is varied. It is believed that this mechanism enables the present disclosure to exhibit excellent wet performance and noise performance.

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 5, 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 2, 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. 3, 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 of 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 4, 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. 2, 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 6 shows a cross-sectional view taken along line B-B in Figure 2. As shown in Figure 6, 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. 2, 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 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. In a more desirable embodiment, the length L6 of the second crown sipes 37 is longer 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 for the pitch noise of the first crown sipes 36 and the second crown sipes 37 to be converted into white noise.

Figure 7 shows a cross-sectional view taken along line CC in Figure 2. As shown in Figure 7, 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 2, 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 8 shows an enlarged view of the first shoulder land portion 13. As shown in Figure 8, the first shoulder land portion 13 is provided with, for example, multiple first shoulder lateral grooves 41 and multiple shoulder shallow grooves 45.

The first shoulder lateral grooves 41, for example, 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 desirably increases axially inward. The axial distance L7 from the terminated 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. Such first shoulder lateral grooves 41 help to improve handling stability and wet performance in a well-balanced manner.

Figure 9 shows a cross-sectional view taken along line D-D in Figure 8. As shown in Figure 9, 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, respectively. A first shoulder lateral groove 41 having such a chamfered portion 42 can exhibit excellent wear resistance.

As shown in FIG. 8, it is desirable that the width W10 (shown in FIG. 9) 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 desirably shorter than the axial length L3 (shown in FIG. 2) 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 10 shows an enlarged view of the second shoulder land portion 14. As shown in Figure 10, 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 8) 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 2) described above have the same depth. Such shoulder sipes 52 can provide friction on wet roads while maintaining steering stability and wear resistance.

To achieve a good balance between noise performance and wet performance, the land ratio of the tread portion 2 of this embodiment is preferably, for example, 60% to 70%, as shown in Figure 1. 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.

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.

A pneumatic tire of size 245/45R18 having the basic pattern of Figure 1 was prototyped based on the specifications in Table 1. Additionally, a tire having the pattern shown in Figure 11 was prototyped as a reference tire (reference tire) for comparing noise performance. As shown in Figure 11, this reference tire, compared to the pattern shown in Figure 1, has first shoulder lateral grooves a and second shoulder lateral grooves b that communicate with circumferential grooves, does not have middle shallow grooves or shoulder shallow grooves, and does not have chamfered sipes.

Additionally, as a comparative example, a tire having the pattern shown in Fig. 12 was prototyped. As shown in Fig. 12, the comparative tire has chamfered portions extending at a constant width in the first middle sipe c and the second middle sipe d. Except for the above-mentioned features, the comparative tire is substantially the same as the example tire. Furthermore, these test tires were tested for wet performance and noise performance. 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 the comparative example being 100, and the higher the score, the better the wet performance.

<Noise performance>
The test vehicle was driven on a dry road at a speed of 40 to 100 km/h, and the maximum sound pressure inside the vehicle was measured. The results are expressed as an index where the reduction in sound pressure, which is the difference from the sound pressure of the reference tire, is set to 100 for the reduction in sound pressure of the comparative tire. The larger this index, the smaller the maximum sound pressure of the noise, indicating excellent noise performance.
The test results are shown in Table 1.

The test results confirmed that the tires of the example exhibited excellent wet performance and noise performance.

[Note]
The present disclosure includes the following aspects.

[Disclosure 1]
A 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 middle land portion disposed between the first tread edge and the tire equator, and a second middle land portion disposed between the second tread edge and the tire equator,
The first middle land portion is provided with at least one first middle sipe that completely crosses the first middle land portion in the tire axial direction,
The second middle land portion is provided with at least one second middle sipe that completely crosses the second middle land portion in the tire axial direction,
the first middle sipe and the second middle sipe each include a sipe main body portion extending in the tire radial direction and a chamfered portion having a width greater than a width of the sipe main body portion and opening to the tread surface of the tread portion,
The chamfered portion of the first middle sipe extends in the tire axial direction with a constant chamfer width,
The chamfered portion of the second middle sipe has a chamfer width that increases from a position where the chamfer width is minimum toward both sides in the tire axial direction.
tire.
[Disclosure 2]
The tire according to Disclosure 1, wherein the chamfer width of the second middle sipe changes continuously.
[Disclosure 3]
The tire according to Disclosure 1 or 2, wherein the chamfered portion of the first middle sipe is disposed over the entire length of the first middle sipe.
[Disclosure 4]
The tire according to any one of Disclosures 1 to 3, wherein the chamfered portion of the second middle sipe is disposed over the entire second middle sipe in the length direction.
[Disclosure 5]
The tire according to any one of Disclosures 1 to 4, wherein a maximum chamfer width of the chamfered portion of the second middle sipe is larger than the chamfer width of the chamfered portion of the first middle sipe.
[Disclosure 6]
The tire according to any one of Disclosures 1 to 5, wherein the first middle sipes and the second middle sipes are inclined in the same direction with respect to the tire axial direction.
[Disclosure 7]
The tire according to Disclosure 6, wherein the first middle sipe and the second middle sipe are inclined at the same angle relative to the tire axial direction.
[Disclosure 8]
the chamfered portion of the first middle sipe and the chamfered portion of the second middle sipe each include a first inclined surface connected to one sipe wall of the sipe main body portion and a second inclined surface connected to the other sipe wall of the sipe main body portion,
The tire according to any one of the first to sixth disclosures, wherein at an end portion of the chamfered portion of the second middle sipe on the second tread edge side, the width of the first inclined surface is smaller than the width of the second inclined surface.
[Disclosure 9]
The tire described in present disclosure 8, wherein the width of the first inclined surface is greater than the width of the second inclined surface at the end of the chamfered portion of the second middle sipe on the tire equator side.
[Disclosure 10]
The tire according to any one of Disclosures 1 to 9, wherein the second middle land portion is provided with at least one semi-open middle sipe, one end of which is connected to the circumferential groove and the other end of which is terminated within the second middle land portion.
[Disclosure 11]
The tire of disclosure 10, wherein the semi-open middle sipe extends with a constant width from the tread surface to the bottom of the tread portion.

2 Tread portion 3 Circumferential groove 4 Land portion 11 First middle land portion 12 Second middle land portion 16 First middle sipe 17 Second middle sipe 20 Sipe main body portion 21 Chamfered portion T1 First tread edge T2 Second tread edge

Claims (10)

A 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 middle land portion disposed between the first tread edge and the tire equator, and a second middle land portion disposed between the second tread edge and the tire equator,
The first middle land portion is provided with at least one first middle sipe that completely crosses the first middle land portion in the tire axial direction,
The second middle land portion is provided with at least one second middle sipe that completely crosses the second middle land portion in the tire axial direction,
the first middle sipe and the second middle sipe each include a sipe main body portion extending in the tire radial direction and a chamfered portion having a width greater than a width of the sipe main body portion and opening to the tread surface of the tread portion,
The chamfered portion of the first middle sipe extends in the tire axial direction with a constant chamfer width,
The chamfered portion of the second middle sipe has a chamfer width that increases from a position where the chamfer width is minimum toward both sides in the tire axial direction,
The second middle land portion is provided with at least one semi-open middle sipe, one end of which is connected to the circumferential groove and the other end of which is terminated within the second middle land portion,
The depth of the semi-open middle sipe is smaller than the depth of the second middle sipe .
tire. The tire of claim 1, wherein the chamfer width of the second middle sipe varies continuously. The tire described in claim 1 or 2, wherein the chamfered portion of the first middle sipe is arranged over the entire length of the first middle sipe. The tire described in any one of claims 1 to 3, wherein the chamfered portion of the second middle sipe is arranged over the entire length of the second middle sipe. The tire described in any one of claims 1 to 4, wherein the maximum chamfer width of the chamfered portion of the second middle sipe is greater than the chamfer width of the chamfered portion of the first middle sipe. The tire described in any one of claims 1 to 5, wherein the first middle sipe and the second middle sipe are inclined in the same direction relative to the tire axial direction. The tire described in claim 6, wherein the first middle sipe and the second middle sipe are inclined at the same angle relative to the tire axial direction. the chamfered portion of the first middle sipe and the chamfered portion of the second middle sipe each include a first inclined surface connected to one sipe wall of the sipe main body portion and a second inclined surface connected to the other sipe wall of the sipe main body portion,
The tire according to claim 1 , wherein a width of the first inclined surface is smaller than a width of the second inclined surface at an end portion of the chamfered portion of the second middle sipe on the second tread edge side. The tire described in claim 8, wherein the width of the first inclined surface is greater than the width of the second inclined surface at the end of the chamfered portion of the second middle sipe on the tire equator side. 10. The tire according to claim 1 , wherein the semi-open middle sipe extends with a constant width from the tread surface to the bottom of the tread portion.