A tread portion includes a crown land portion including first and second longitudinal edges extending in the tire circumferential direction. The crown land portion is provided with first, second and third crown sipes. The first, second and third crown sipes open at the ground contact surface via respective chamfer portions. The first and third crown sipes extend from the first longitudinal edge and have closed ends in the ground contact surface. The second crown sipes extend from the second longitudinal edge and have closed ends in the ground contact surface. Each first crown sipe has a constant opening width in a longitudinal direction of the sipe. Each second crown sipe has a constant opening width in a longitudinal direction of the sipe. Each third crown sipe has an opening width which decreases continuously from the first longitudinal edge toward the closed end thereof.

RELATED APPLICATIONS

This application claims the benefit of foreign priority to Japanese Patent Applications No. JP2022-027772, filed Feb. 25, 2022, and No. JP2022-027771, filed Feb. 25, 2022, which are incorporated by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to a tire.

BACKGROUND OF THE DISCLOSURE

Patent Document 1 below has proposed a tire that includes a crown land portion provided with a plurality of crown sipes. The tire is expected to improve steering stability on dry roads and on-snow performance in a well-balanced manner by improving the plurality of crown sipes.

Patent Document

[Patent document 1] Japanese Unexamined Patent Application Publication 2018-008585

SUMMARY OF THE DISCLOSURE

In recent years, as the performance of vehicles has improved, there has been a demand for further improvements in terms of steering stability on dry roads and on-snow performance.

The present disclosure has been made in view of the above circumstances and has a main object to provide a tire capable of exerting excellent on-snow performance while maintaining steering stability on dry roads.

In one aspect of the present disclosure, a tire includes a tread portion including a first tread edge, a second tread edge, and a crown land portion arranged between the first tread edge and the second tread edge. The crown land portion includes a first longitudinal edge extending in a tire circumferential direction on a first tread edge side, a second longitudinal edge extending in the tire circumferential direction on a second tread edge side, and a ground contact surface between the first longitudinal edge and the second longitudinal edge. The crown land portion is provided with a plurality of first crown sipes, a plurality of second crown sipes, and a plurality of third crown sipes. The first crown sipes, the second crown sipes, and the third crown sipes open at the ground contact surface via chamfer portions. The first crown sipes and the third crown sipes extend from the first longitudinal edge and have closed ends in the ground contact surface. The second crown sipes extend from the second longitudinal edge and have closed ends in the ground contact surface. Each of the first crown sipes has an opening width at the ground contact surface which is constant in a longitudinal direction of the sipe. Each of the second crown sipes has an opening width at the ground contact surface which is constant in a longitudinal direction of the sipe. Each of the third crown sipes has an opening width which decreases continuously from the first longitudinal edge toward the closed end thereof.

DETAILED DESCRIPTION OF THE DISCLOSURE

One or more embodiments of the present disclosure will be described below with reference to the drawings.

FIG.1is a development view of a tread portion2of a tire1showing an embodiment of the present disclosure. The tire1according to the present embodiment, for example, is embodied as a winter tire and may be suitably used as a pneumatic tire for passenger cars. However, the present disclosure is not limited to such an embodiment, and may be applied to heavy-duty pneumatic tires and non-pneumatic tires in which the interior of the tire is not filled with pressurized air.

As illustrated inFIG.1, the tread portion2according to the present disclosure includes a first tread edge T1, a second tread edge T2, a plurality of circumferential grooves3extending continuously in the tire circumferential direction between the first tread edge T1and the second tread edge T2, and a plurality of land portions4divided by the circumferential grooves3. As a preferred embodiment, the tire1according to the present embodiment is configured as a so-called five-rib tire in which the tread portion2is composed of four circumferential grooves3and five land portions4.

In the present embodiment, the tread portion2, for example, has a designated mounting direction on a vehicle. Thus, the first tread edge T1is intended to be positioned outside the vehicle when installed, and the second tread edge T2is intended to be positioned inside the vehicle when installed. The mounting direction on a vehicle is indicated, for example, by letters or symbols on a sidewall portion (not illustrated) of the tire1. However, the tire1according to the present disclosure is not limited to such an embodiment and may be used without specifying the mounting direction on a vehicle.

The first tread edge T1and the second tread edge T2are the axial outermost edges of the ground contacting patch of the tire1which occurs under the condition such that the tire1under a normal state is grounded on a plane by zero camber angles with 70% of a standard tire load.

As used herein, when a tire is a pneumatic tire based on a standard, the “normal state” is such that the tire1is mounted onto a standard wheel rim with a standard pressure but loaded with no tire load. If a tire is not based on the standards, or if a tire is a non-pneumatic tire, the normal state is a standard state of use according to the purpose of use of the tire and means a state of no load. As used herein, unless otherwise noted, the dimensions of portions of the tire are values measured under the normal state.

As used herein, the “standard wheel rim” is a wheel rim officially approved for each tire by standards organizations on which the tire is based, wherein the standard wheel rim is the “standard rim” specified in JATMA, the “Design Rim” in TRA, and the “Measuring Rim” in ETRTO, for example.

As used herein, the “standard pressure” is a standard pressure officially approved for each tire by standards organizations on which the tire is based, wherein the standard pressure is the “maximum air pressure” in JATMA, the maximum pressure given in the “Tire Load Limits at Various Cold Inflation Pressures” table in TRA, and the “Inflation Pressure” in ETRTO, for example.

As used herein, when a tire is a pneumatic tire based on a standard, the “standard tire load” is a tire load officially approved for each tire by the standards organization in which the tire is based, wherein the standard tire load is the “maximum load capacity” in JATMA, the maximum value given in the above-mentioned table in TRA, and the “Load Capacity” in ETRTO, for example. Also, in the case of tires for which various standards are not specified, “standard tire load” refers to the maximum load that can be applied when using the tire according to the above-mentioned standards.

The circumferential grooves3include a first shoulder circumferential groove5and a second shoulder circumferential groove6. Further, the circumferential grooves3include a first crown circumferential groove7and a second crown circumferential groove8, which are arranged between the first and second shoulder circumferential grooves5and6. The first shoulder circumferential groove5is located nearest to the first tread edge T1among the circumferential grooves3. The second shoulder circumferential groove6is located nearest to the second tread edge T2among the circumferential grooves3. The first crown circumferential groove7is located between the first shoulder circumferential groove5and the tire equator C. The second crown circumferential groove8is located between the second shoulder circumferential groove6and the tire equator C.

Preferably, a distance L1in the tire axial direction from the tire equator C to the groove centerline of the first shoulder circumferential groove5or the second shoulder circumferential groove6is, for example, in a range from 25% to 35% of the tread width TW. Preferably, a distance L2in the tire axial direction from the tire equator C to the groove centerline of the first crown circumferential groove7or the second crown circumferential groove8is, for example, in a range from 5% to 15% of the tread width TW. Note that the tread width TW is the distance from the first tread edge T1to the second tread edge T2in the tire axial direction under the normal state.

In the present embodiment, the second shoulder circumferential groove6, the first crown circumferential groove7, and the second crown circumferential groove8each extend in a straight manner in parallel with the tire circumferential direction. On the other hand, the first shoulder circumferential groove5has a zigzag groove edge on the tire equator C side. However, each of the circumferential grooves3is not limited to such a shape.

The circumferential grooves3have a groove width W1which is preferably equal to or more than 3 mm. In addition, the groove width W1of the circumferential grooves3, for example, is preferably in a range from 3.0% to 7.0% of the tread width TW. A groove depth of the circumferential grooves3is in a range from 5 to 10 mm for passenger car tires, for example.

The five land portions4according to the present embodiment include a crown land portion15located between the first tread edge T1and the second tread edge T2. The crown land portion15is sectioned between the first crown circumferential groove7and the second crown circumferential groove8and thus is located on the tire equator C. Further, the land portions4according to the present embodiment include a first middle land portion13, a second middle land portion14, a first shoulder land portion11and a second shoulder land portion12. The first middle land portion13is sectioned between the first shoulder circumferential groove5and the first crown circumferential groove7. The second middle land portion14is sectioned between the second shoulder circumferential groove6and the second crown circumferential groove8. The first shoulder land portion11includes the first tread edge T1and is located outwardly in the tire axial direction of the first shoulder circumferential groove5. The second shoulder land portion12includes the second tread edge T2and is located outwardly in the tire axial direction of the second shoulder circumferential groove6.

FIG.2illustrates an enlarged view of the crown land portion15ofFIG.1. As illustrated inFIG.2, the crown land portion15includes a first longitudinal edge15aextending in the tire circumferential direction on a first tread edge T1side, a second longitudinal edge15bextending in the tire circumferential direction on a second tread edge T2side, and a ground contact surface15sbetween the first longitudinal edge15aand the second longitudinal edge15b. In addition, the crown land portion15is provided with a plurality of first crown sipes41, a plurality of second crown sipes42and a plurality of third crown sipes43. Further, the crown land portion15according to the present embodiment is provided with a plurality of fourth crown sipes44.

As used herein, “sipe” means an incision having a small width and includes a main body portion thereof having a width between two opposite inner walls being 1.5 mm or less. Further, the main body portion means a portion in which two opposite inner walls extend substantially parallel to each other in the tire radial direction. Here, “substantially parallel” means that the angle between two opposite inner walls is 10 degrees or less. As will be described later, the sipe may be provided with one or more chamfered portions. Further, the sipe may have a so-called flask bottom with an increased width at the bottom.

FIG.3illustrates an enlarged view of one of the first crown sipes41, one of the second crown sipes42, one of the third crown sipes43, and one of the fourth crown sipes44. As illustrated inFIG.3, in the present disclosure, the first crown sipes41extend from the first longitudinal edge15aand have closed end41ain the ground contact surface15s. The second crown sipes42extend from the second longitudinal edge15band have closed end42ain the ground contact surface15s. The third crown sipes43extend from the first longitudinal edge15aand have closed end43ain the ground contact surface15s.

FIG.4illustrates a cross-sectional view taken along the line E-E ofFIG.2, as an example of a sipe cross-sectional view. As illustrated inFIG.4, the first crown sipes41, the second crown sipes42, and the third crown sipes43open at the ground contact surface15svia chamfer portions45. Each chamfer portion45includes an inclined surface45sbetween the ground contact surface15sand one of the sipe walls18. In the present embodiment, each of the sipes has two chamfer portions45which are inclined surfaces45sconnected to the respective sipe walls18. Each inclined surface45shas a width Wb in a direction orthogonal to the longitudinal direction of the sipe. In the present embodiment, each inclined surface45sis slightly curved in a direction convex outward in the tire radial direction. The inclined surface45smay, for example, be planar. In addition, each sipe has an opening width Wa at the ground contact surface15s. The opening width Wa corresponds to the distance in the direction orthogonal to the longitudinal direction of the sipe from an end of one of the inclined surfaces45son the ground contact surface15sside to an end of the other one of the inclined surfaces45son the ground contact surface15sside.

As illustrated inFIG.2, an opening width W6at the ground contact surface15sof each of the first crown sipes41is constant in the longitudinal direction of the sipe, and an opening width W7at the ground contact surface15sof each of the second crown sipes42is constant in the longitudinal direction of the sipe. On the other hand, an opening width at the ground contact surface15sof each of the third crown sipes43decreases continuously from the first longitudinal edge15atoward the closed end43a. By adopting the above configuration, the tire according to the present disclosure can exert excellent on-snow performance, while maintaining steering stability on dry roads (hereinafter simply referred to as “steering stability”). The mechanism can be as follows.

The tire according to the present disclosure include the crown land portion15being provided with the plurality of crown sipes having the closed ends. These sipes can improve on-snow performance while maintaining the rigidity of the crown land portion15. In addition, since these sipes open via the chamfer portions45, the ground pressure acting on the crown land portion15can be equalized by the chamfer portions45, which can be expected to improve the steering stability and on-snow performance.

Further, since the opening width at the ground contact surface15sof each of the third crown sipes43decreases toward the closed end, an axial middle region of the crown land portion15has sufficient ground contact area, which can ensure the steering stability. By such a mechanism, the tire1according to the present disclosure can exert excellent on-snow performance while maintaining the steering stability.

Hereinafter, a more detailed configuration of the present embodiment will be described. Note that each configuration described below shows a specific aspect of the present embodiment. Thus, the present disclosure can exert the above-mentioned effects even if the tire does not include the configuration described below. Further, if any one of the configurations described below is applied independently to the tire of the present disclosure having the above-mentioned characteristics, the performance improvement according to each additional configuration can be expected. Furthermore, when some of the configurations described below are applied in combination, it is expected that the performance of the additional configurations will be improved.

The first crown sipes41and the second crown sipes42are inclined with respect to the tire axial direction in the same direction with each other. An angle of these sipes, for example, ranges from 25 to 35 degrees with respect to the tire axial direction.

Preferably, the opening width W7at the ground contact surface15sof each of the second crown sipes42ranges from 80% to 120% of the opening width W6at the ground contact surface15sof each of the first crown sipes41, and in this embodiment, they are substantially the same with each other. Thus, uneven wear around the sipes can be suppressed.

The maximum opening width W8at the ground contact surface15sof each of the third crown sipes43is smaller than the opening width W6at the ground contact surface15sof each of the first crown sipes41. Specifically, the maximum opening width W8of each of the third crown sipes43ranges from 75% to 90% of the opening width W6of each of the first crown sipes41. In the third crown sipes43of the present embodiment, each chamfer portion is substantially eliminated at the closed end43a, but each chamfer portion45is not limited to such an aspect, and one or more chamfer portions may have a chamfer width at the closed ends43a. The same is true for the fourth crown sipes44.

The fourth crown sipes44extend from the second longitudinal edge15band have closed end44ain the ground contact surface15s. In a tread plan view, the fourth crown sipes44have a shape different from the first crown sipes41and the second crown sipes42. In the present embodiment, the fourth crown sipes44also open at the ground contact surface15svia chamfer portions45. In addition, it is preferable that an opening width at the ground contact surface15sof each of the fourth crown sipes44decreases continuously from the second longitudinal edge15btoward the closed end44a. This ensures sufficient ground contact area in a middle region of the crown land portion15, and thus the steering stability can be maintained.

An opening width W9at the ground contact surface15sof each of the fourth crown sipes44is smaller than the opening width W7of each of the second crown sipes42. Specifically, the opening width W9of the fourth crown sipes44ranges from 75% to 90% of the opening width W7of the second crown sipes42. The fourth crown sipes44can help to enhance the balance between steering stability and on-snow performance.

As illustrated inFIG.3, in the present embodiment, a minimum distance L4in the tire circumferential direction between outer ends41bon the first longitudinal edge15aside of the first crown sipes41and outer ends42bon the second longitudinal edge15bside of the second crown sipes42is preferably equal to or less than 10% of a circumferential arrangement pitch P1(shown inFIG.2) of the first crown sipes41. This makes it easier for water pushed away by a middle region of the crown land portion to be guided to the outer edges of these sipes when driving on wet roads, thus improving wet performance.

A length L6in the tire axial direction of the first crown sipes41, for example, ranges from 40% to 60% of a width W5(shown inFIG.2) in the tire axial direction of the ground contact surface15sof the crown land portion15. Note that in this document, a length of a sipe is measured by the center line of the sipe.

Preferably, the second crown sipes42extend beyond the axial center in the tire axial direction of the ground contact surface15sof the crown land portion15. The second crown sipes42have closed ends42awhich are located on the first longitudinal edge15aside with respect to the closed ends41aof the first crown sipes41. Preferably, a length L7in the tire axial direction of the second crown sipes42is greater than a length L6in the tire axial direction of the first crown sipes41. Specifically, the length L7of the second crown sipes42preferably ranges from 65% to 85% of the width W5in the tire axial direction of the ground contact surface15sof the crown land portion15. The second crown sipes42as such can improve on-snow performance and wet performance while maintaining steering stability.

The third crown sipes43and the fourth crown sipes44are inclined with respect to the tire axial direction in the same direction as the first crown sipes41and the second crown sipes42, and angles of these sipes range from 25 to 35 degrees with respect to the tire axial direction, for example.

Preferably, a minimum distance L5in the tire circumferential direction between outer ends43bon the first longitudinal edge15aside of the third crown sipes43and outer ends44bthe second longitudinal edge15bside of the fourth crown sipes44is equal to or less than 10% of a circumferential arrangement pitch P2(shown inFIG.2) of the third crown sipes43. This can improve wet performance further.

A length L8in the tire axial direction of the third crown sipes43is smaller than the length L7of the second crown sipes42and the length L6of the first crown sipes41. In addition, the closed ends43aof the third crown sipes43are located on the first longitudinal edge15aside with respect to the closed ends44aof the fourth crown sipes44. In some more preferred embodiments, the closed ends43aof the third crown sipes43are located on the second longitudinal edge15bside with respect to the closed ends42aof the second crown sipes42. The length L8of the third crown sipes43ranges from 25% to 45% of the width W5of the ground contact surface15sof the crown land portion15. Such third crown sipes43can help to improve steering stability, on-snow performance, and wet performance in a well-balanced manner.

From a similar point of view, a length L9in the tire axial direction of the fourth crown sipes44, for example, is smaller than the length L7of the second crown sipes42and the length L6of the first crown sipes41. Specifically, the length L9of the fourth crown sipes44preferably range from 25% to 45% of the width W5of the ground contact surface15sof the crown land portion15.

FIG.5illustrates an enlarged view of the first middle land portion13. As illustrated inFIG.5, the first middle land portion13includes a first longitudinal edge13aextending in the tire circumferential direction on the first tread edge T1side, a second longitudinal edge13bextending in the tire circumferential direction on the second tread edge T2side, and a ground contact surface13sbetween the first longitudinal edge13aand the second longitudinal edge13b. In addition, the first middle land portion13is provided with a plurality of middle lateral grooves20. The middle lateral grooves20, for example, are inclined with respect to the tire axial direction in the same direction as with the first crown sipes41(shown inFIG.2).

FIG.6illustrates an enlarged view of two middle lateral grooves20. Note thatFIG.6is an enlarged view of a first middle lateral groove21and a second middle lateral groove22, which will be described later. As illustrated inFIG.6, at least one of the middle lateral grooves20includes a first groove portion26and a second groove portion27. The first groove portion26extends in the tire axial direction from the first longitudinal edge13a. The second groove portion27extends in the tire axial direction from the second longitudinal edge13b.

In the present embodiment, the first groove portion26and the second groove portion27are displaced in the tire circumferential direction to form a pair of circumferential groove edges28eextending in the tire circumferential direction between groove edges26eof the first groove portion26and groove edges27eof the second groove portion27. In addition, the maximum groove depth of the first groove portion26is different from the maximum groove depth of the second groove portion27. When driving on snow, the middle lateral grooves20can provide a large reaction force by shearing the snow that is strongly pressed inside (hereinafter, such reaction force is sometimes called “snow-column shear force”). Further, since the respective maximum depths of the first groove portion26and the second groove portion27are different, the shallower groove portion can maintain the rigidity of the first middle land portion13to maintain the steering stability, and the deeper groove portion can provide a larger snow-column shear force, which improves on-snow performance.

Furthermore, the circumferential groove edges28edescribed above can provides frictional force in the tire axial direction and help to improve cornering performance on snow. Furthermore, the combination of the circumferential groove edges28e, the first groove portions26and the second groove portions27allows snow entering the deeper groove portions to be pushed more strongly in the tire axial direction and exerts greater snow-column shear force.

As illustrated inFIG.5andFIG.6, in the present embodiment, each of the middle lateral grooves20has the above-mentioned structure. In a tread plan view. the first groove portions26and the second groove portions27extend in the tire axial direction with a constant groove width W3(shown inFIG.5). The groove width W3of the first groove portions26and the second groove portions27, for example, ranges from 15% to 25% of a width W2(shown inFIG.5) in the tire axial direction of the ground contact surface13sof the first middle land portion13. An angle of the first groove portions26and the second groove portions27ranges from 25 to 35 degrees with respect to the tire axial direction, for example.

The middle lateral grooves20, for example, include a plurality of the first middle lateral grooves21and a plurality of the second middle lateral grooves22which have different distribution of groove depths from one another. The first middle lateral grooves21and the second middle lateral grooves22are arranged alternately in the tire circumferential direction.

FIG.7illustrates a cross-sectional view taken along the line A-A ofFIG.5.FIG.7is a cross-sectional view of one of the first middle lateral grooves21along a groove longitudinal direction thereof.FIG.8illustrates a cross-sectional view taken along the line B-B ofFIG.5.FIG.8is a cross-sectional view of one of the second middle lateral grooves22along a groove longitudinal direction thereof. As illustrated inFIG.7andFIG.8, in the present embodiment, the first groove portions26and the second groove portions27of the first middle lateral grooves21and the first groove portions26and the second groove portions27of the second middle lateral grooves22extend in the groove longitudinal direction with respective constant groove depths.

As illustrated inFIG.7, in each first middle lateral groove21, the maximum groove depth d1of the first groove portion26is smaller than the maximum groove depth d2of the second groove portion27. In each of the first middle lateral grooves21, the groove depth d2of the second groove portion27, for example, ranges from 60% to 80% of a groove depth dc of the first crown circumferential groove7. Further, in each of the first middle lateral grooves21, the groove depth d1of the first groove portion26ranges from 40% to 60% of the groove depth dc of the first crown circumferential groove7. Preferably, the groove depth d1of the first groove portion26ranges from 60% to 70% of the groove depth d2of the second groove portion27.

As illustrated inFIG.8, the second middle lateral groove22has substantially the inverted shape of the first middle lateral groove21. That is, in each of the second middle lateral grooves22, the maximum groove depth d1of the first groove portion26is greater than the maximum groove depth d2of the second groove portion27. In each of the second middle lateral grooves22, the groove depth d1of the first groove portion26, for example, ranges from 60% to 80% of the groove depth dc of the first crown circumferential groove7. Further, in each of the second middle lateral grooves22, the groove depth d2of the second groove portion27ranges from 40% to 60% of the groove depth dc of the first crown circumferential groove7. Preferably, the groove depth d2of the second groove portion27ranges from 60% to 70% of the groove depth d1of the first groove portion26.

In the present embodiment, since the first middle lateral grooves21and the second middle lateral grooves22are provided alternately in the tire circumferential direction, the steering stability and on-snow performance can be improved in a well-balanced manner.

FIG.9illustrates a cross-sectional view taken along the line C-C ofFIG.5.FIG.9is a cross-sectional view of the second groove portion27of each of the first middle lateral grooves21, or the first groove portion26of each of the second middle lateral grooves22(hereinafter, sometimes referred to collectively as deep groove portion37).FIG.10illustrates a cross-sectional view take along the line D-D ofFIG.5.FIG.10is a cross-sectional view of the first groove portion26of each of the first middle lateral grooves21, or the second groove portion27of each of the second middle lateral grooves22(hereinafter, sometimes referred to collectively as shallow groove portion36).

As illustrated inFIG.9andFIG.10, the deep groove portion37and the shallow groove portion36preferably open at the ground contact surface via chamfer portions25. Each chamfer portion25includes an inclined surface25sbetween the ground contact surface and one of the groove walls. In the present embodiment, each inclined surface25sis slightly curved in a direction convex outward in the tire radial direction. The inclined surface25smay, for example, be planar. Such a chamfer portion25can help to equalize the ground pressure acting on the ground contact surface13sto improve uneven wear resistance.

As illustrated inFIG.9, the deep groove portion37, for example, is configured to include a flat groove bottom37d. On the other hand, as illustrated inFIG.10, the shallow groove portion36includes a groove bottom36dwhich is provided with a groove bottom sipe38extending inwardly in the tire radial direction. Such a groove bottom sipe38can facilitate the opening of the shallow groove portion36appropriately and help to improve on-snow performance. Note that the above-mentioned depths d1and d2of the first groove portion26of the first middle lateral grooves21and the second groove portion27of the second middle lateral grooves22, respectively, mean a depth without including the groove bottom sipe38. In addition, inFIG.7andFIG.8, the groove bottom sipes38are not illustrated. In some preferred embodiments, a total depth from the ground contact surface to a bottom of the groove bottom sipe38is smaller than a depth of the deep groove portion37. This can improve the balance between steering stability and on-snow performance.

In the present embodiment as illustrated inFIG.6, each of the pair of groove edges of each middle lateral groove20includes a circumferential groove edge28e. Each circumferential groove edge28e, for example, is located in the central area when the ground contact surface13sof the first middle land portion13is divided into three equal portions in the tire axial direction. In the present embodiment, a pair of circumferential groove edges28eare positioned such that the axial center position of the ground contact surface13sof the first middle land portion13is located therebetween. In addition, the pair of circumferential groove edges28eextends along the tire circumferential direction, preferably extending in parallel with the tire circumferential direction. For example, an angle of the pair of circumferential groove edges28eis preferably equal to or less than 10 degrees, more preferably equal to or less than 5 degrees with respect to the tire circumferential direction. Preferably, a length L3in the tire circumferential direction of the pair of circumferential groove edges28eis smaller than the maximum width of the first groove portion26and the second groove portion27. Specifically, the length L3ranges from 75% to 95% of the maximum groove width. Such a pair of circumferential groove edges28ecan improve cornering performance when driving on snow, while suppressing uneven wear of the land portion.

Each of the middle lateral grooves20includes a circumferential groove portion28arranged between the first groove portion26and the second groove portion27. In the present embodiment, the area between one of the pair of circumferential groove edges28eand its imaginary extension line extending in the longitudinal direction and the other one of the pair of circumferential groove edges28eand its imaginary extension line extending in the longitudinal direction is configured as the circumferential groove portion28, for example.

As illustrated inFIG.7andFIG.8, the maximum groove depth d3of the circumferential groove portions28is smaller than the maximum groove depth d1of the first groove portions26and the maximum groove depth d2of the second groove portions27. Specifically, the maximum groove depth d3of the circumferential groove portions28ranges from 20% to 30% of the groove depth dc of the first crown circumferential groove7. The circumferential groove portions28can increase the rigidity of a middle region of the first middle land portion13and improve uneven wear resistance.

As illustrated inFIG.5, it is preferable that the first middle land portion13is provided with at least one circumferential sipe30extending in the tire circumferential direction. In the present embodiment, the first middle land portion13is provided with a plurality of circumferential sipes30spaced in the tire circumferential direction. In addition, each circumferential sipe30according to the present embodiment extends from the ground contact surface13sof the first middle land portion13to a bottom thereof with a constant sipe width. The circumferential sipes30can provide a large frictional force in the tire axial direction when driving on wet or snow.

Preferably, each circumferential sipe30, for example, is located in the central area when the ground contact surface13sof the first middle land portion13is divided into three equal portions in the tire axial direction. An angle of each circumferential sipe30with respect to the tire circumferential direction is, for example, equal to or less than 10 degrees, preferably equal to or less than 5 degrees. Such a circumferential sipe30can provide a large frictional force in the tire axial direction when driving on snow.

The circumferential sipes30, for example, extend across some middle lateral grooves20in the tire circumferential direction. In some preferred embodiments, the circumferential sipes30are arranged to extend across the respective first middle lateral grooves21but not to be communicated with the second middle lateral grooves22. More specifically, the circumferential sipes30extend across the respective circumferential groove portions28of the first middle lateral grooves21. Thus, at the groove bottoms of the circumferential groove portions28, the circumferential sipes30are formed as the groove bottom sipes. On the other hand, the second middle lateral grooves22do not have such a structure. As a result, the steering stability, on-snow performance, and uneven wear are resistance can be improved in a well-balanced manner.

As illustrated inFIG.5, the first middle land portion13is further provided with a plurality of the first middle sipes31and a plurality of second middle sipes32. The first middle sipes31extend from the first longitudinal edge13a, have a length L10in the tire axial direction, and are in communication with the respective circumferential sipes30. The second middle sipes32extend from the second longitudinal edge13band are in communication with the respective circumferential sipes30. In some preferred embodiments, ends of the first middle sipes31in the ground contact surface13sare connected to ends31aon a first side in the tire circumferential direction of the respective circumferential sipes30. Ends32aof the second middle sipes32in the ground contact surface13sare connected to ends on a second side in the tire circumferential direction of the respective circumferential sipes30. The first middle sipes31and the second middle sipes32work together with the circumferential sipe30to provide multi-directional frictional force, further improving on-snow performance.

The first middle sipes31and the second middle sipes32, for example, are inclined with respect to the tire axial direction in the same direction as the middle lateral grooves20. An angle of these sipes with respect to the tire axial direction, for example, ranges from 25 to 35 degrees. In some preferred embodiments, an angle between the first middle sipes31and the circumferential sipes30is an acute angle. Similarly, an angle between the second middle sipes32and the circumferential sipes30is an acute angle. This makes it easier for the corners between the middle sipes and the circumferential sipes to bite into a road surface when driving on snow, thereby exhibiting excellent performance on snow.

The first middle sipes31and the second middle sipes32open at the ground contact surface13svia chamfer portions35. The configuration of the chamfer portions45of crown sipes (shown inFIG.4) can be applied to the chamfer portions35of these sipes, and thus the details of the chamfer portions35will not be described here. The chamfer portions35can help to equalize the ground pressure acting on the ground contact surface13sand to improve the steering and uneven wear resistance.

As illustrated inFIG.5, it is preferable that each of the first middle sipes31has an opening width at the ground contact surface13s, and the opening width decreases toward the circumferential sipe30. Similarly, it is preferable that each of the second middle sipes32has an opening width at the ground contact surface13s, and the opening width decrease toward the circumferential sipe30. This ensures the ground contact area in a middle region of the first middle land portion13and maintains the steering stability.

FIG.11illustrates an enlarged view of the second middle land portion14. As illustrated inFIG.11, the second middle land portion14is provided with third middle lateral grooves23and fourth middle lateral grooves24which are arranged alternately in the tire circumferential direction. The third middle lateral grooves23and the fourth middle lateral grooves24have the same shape in a tread plan view, and extend across the second middle land portion14entirely in the tire axial direction. In addition, the third middle lateral grooves23and the fourth middle lateral grooves24are inclined with respect to the tire axial direction in the same direction as the middle lateral grooves20(shown inFIG.5). An angle of the third middle lateral grooves23and the fourth middle lateral grooves24with respect to the tire axial direction is smaller than an angle of the middle lateral grooves20(shown inFIG.5) with respect to the tire axial direction and an angle of the sipes provided on the crown land portion15(shown inFIG.2) with respect to the tire axial direction. Specifically, an angle of the third middle lateral grooves23and the fourth middle lateral grooves24with respect to the tire axial direction, for example, ranges from 10 to 20 degrees. On the other hand, the third middle lateral grooves23and the fourth middle lateral grooves24differ in their internal configuration.

FIG.12illustrates a cross-sectional view taken along the line F-F ofFIG.11. As illustrated inFIG.12, the third middle lateral grooves23each have a shallow groove portion46on the second crown circumferential groove8side and a deep groove portion47on the second shoulder circumferential groove6side.FIG.13illustrates a cross-sectional view taken along the line G-G ofFIG.11. As illustrated inFIG.13, the fourth middle lateral groove24have substantially the inverted shape of the third middle lateral grooves23. That is, the fourth middle lateral grooves24each have a deep groove portion47on the second crown circumferential groove8side and a shallow groove portion46on the second shoulder circumferential groove6side. In this embodiment, the third middle lateral grooves23and the fourth middle lateral grooves24are provided alternately in the tire circumferential direction, which improve the uneven wear resistance and the steering stability.

For the shallow groove portions46of the third middle lateral grooves23and the fourth middle lateral grooves24, the shallow groove portions36of the middle lateral grooves20(shown inFIG.10) of the middle lateral grooves20described above can be applied to the shallow groove portions46of the third middle lateral grooves23and the fourth middle lateral grooves24. Similarly, for the deep groove portions47of the third middle lateral grooves23and the fourth middle lateral grooves24, the deep groove portions37of the middle lateral grooves20(shown inFIG.9) of the middle lateral grooves20described above can be applied to the deep groove portions47of the third middle lateral grooves23and the fourth middle lateral grooves24.

As illustrated inFIG.11, the second middle land portion14is provided with a plurality of middle sipe groups55each of which includes a plurality of bent sipes56arranged in the tire axial direction. The middle sipe groups55are spaced in the tire circumferential direction. In the present embodiment, each middle sipe group55is configured such that the plurality of bent sipes56is arranged so as to overlap partially in the tire axial direction with each other. The bent sipes56each include a convex part on one side or the other in the tire circumferential direction. The middle sipe groups55are difficult to open during braking and driving, so that snow and ice are less likely to clog the inside of the sipes, and thus excellent on-snow performance can be maintained.

In the present disclosure, it is not limited to the second middle land portion14shown inFIG.11.FIG.14illustrates an enlarged view of the second middle land portion14in accordance with another embodiment of the present disclosure. As illustrated inFIG.14, the second middle land portion14is provided with a plurality of third middle sipes33and a plurality of fourth middle sipes34in addition to the above-mentioned third middle lateral grooves23and the fourth middle lateral grooves24. The third middle sipes33extend from the second crown circumferential groove8and have closed ends in the ground contact surface of the second middle land portion14. The fourth middle sipes34extend from the second shoulder circumferential grooves6and have closed end in the ground contact surface. The third middle sipes33and the fourth middle sipes34, for example, are inclined with respect to the tire axial direction in the same direction as the third middle lateral grooves23and the fourth middle lateral grooves24. An angle of these sipes, for example, ranges from 10 to 20 degrees with respect to the tire axial direction. The structure of the above-mentioned first middle sipes31and second middle sipes32can be applied to the third middle sipes33and the fourth middle sipes34.

In yet another embodiment of the second middle land portion14, for example, in a region between the third middle lateral groove23and the fourth middle lateral groove24which are adjacent to each other in the circumferential direction of the tire, at least one middle sipe group55described above (shown inFIG.11), at least one third middle sipe33and at least one fourth middle sipe34shown inFIG.14may be arranged (not illustrated). Such a sipe arrangement can help to further enhance on-snow performance.

As illustrated inFIG.1, the first shoulder land portion11is provided with a plurality of first shoulder lateral grooves51and a plurality of first shoulder sipes52. The first shoulder lateral grooves51and the first shoulder sipes52extend, for example, from the first shoulder circumferential groove5to at least the first tread edge T1. In addition, the second shoulder land portion12is provided with a plurality of second shoulder lateral grooves53and a plurality of shoulder sipe groups60each of which includes a plurality of bent sipes61arranged in the tire axial direction. The shoulder sipe groups60have substantially the same configuration as the middle sipe groups55described above. These grooves and sipes can help to further improve on-snow performance.

Although the tire according to one or more embodiments of the present disclosure has been described in detail above, the present disclosure is not limited to the specific embodiments described above, and can be embodied in various ways.

Example

As Example, pneumatic tires of size 245/40ZR18 with the basic pattern ofFIG.1were prepared. As Comparative Example 1, tires each having the crown land portion “a” shown inFIG.15were also prepared. The crown land portion “a” is provided with the third crown sipes “b” and the fourth crown sipes “c” extending with a constant opening width. The tires of Comparative Example 1 have substantially the same configuration as the tires of Example, except for the above-mentioned items.

Then, the steering stability on a dry road and on-snow performance were tested for Comparative Example 1 and Example. The common specifications and test methods of each test tire are as follows.Rim: 18×8.5JTire pressure: 240 kPa on all wheelsTest vehicle: 2000 cc displacement, rear-wheel drive vehicleTire position: All wheels
Steering Stability on Dry Road Test:

The steering stability of the above test vehicle on a dry road was evaluated by the driver's sensory evaluation. The test results are indicated using a score of 100, where the steering stability of Comparative Example 1 is set to 100, and the higher the score, the better the steering stability.

The on-snow performance of the above test vehicle on a snowy road was evaluated by the driver's sensory evaluation. The test results are indicated using a score of 100, where the on-snow performance of Comparative Example 1 is set to 100, and the higher the score, the better the on-snow performance.

Table 1 shows the test results.

TABLE 1ComparativeExample 1ExampleSteering stability on dry road (score)100105On-snow performance (score)100105

The test results show that the tires of Example exhibit excellent on-snow performance while maintaining better steering stability on a dry road.

Pneumatic tires of size 245/40ZR18 were prepared as Comparative Example 2, Reference Example and Example. Reference Example has a crown land portion15shown inFIG.16. The crown land portion15shown inFIG.16includes features of the embodiment shown inFIG.1, and the minimum distance L4in the tire circumferential direction between the outer ends41bof the first crown sipes41and the outer ends42bof the second crown sipes42is about 4% of the circumferential arrangement pitch of the first crown sipes. Each tire of Example has the crown land portion15shown inFIG.2, and the distance is about 4% of the circumferential arrangement pitch P1.

On the other hand, the tires of Comparative Example 2 each has the crown land portion “d” shown inFIG.17. The crown land portion “d” is such that the minimum distance L4in the tire circumferential direction between the outer ends of the first crown sipes “e” and the outer ends of the second crown sipes “f” is about 27% of the circumferential arrangement pitch P1. The crown land portion of Comparative Example 2 is substantially the same as the crown land portion15of Reference Example and Example, except for the items mentioned above. In addition, Comparative Example 2, Reference Example and Example have the basic pattern shown inFIG.1, except for the configuration of the crown land portion described above, and have substantially the same configuration.

Comparative Example 2, Reference Example and Example were tested for the steering stability on a dry road and wet performance as described above. The common specifications of each test tire are described above.

Steering Stability on Dry Road Test:

As above, the steering stability on dry road was evaluated. The test results are indicated using a score with 100 for the steering stability of Comparative Example 2.

Wet Performance Test:

Wet performance was evaluated by the driver's sensory evaluation when the test vehicle was driven on wet roads. The test results are indicated using a score with the wet performance of Comparative Example 2 being 100, and the larger the number, the better the wet performance.

Table 2 shows the test results.

As a result of the test, it was confirmed that the Reference Example exhibited excellent wet performance while maintaining steering stability on a dry road. It was also confirmed that Example obtained a further improvement in performance compared to Reference Example.

The present disclosure includes the following aspects.

A tire comprising:a tread portion comprising a first tread edge, a second tread edge, and a crown land portion arranged between the first tread edge and the second tread edge, whereinthe crown land portion comprises a first longitudinal edge extending in a tire circumferential direction on a first tread edge side, a second longitudinal edge extending in the tire circumferential direction on a second tread edge side, and a ground contact surface between the first longitudinal edge and the second longitudinal edge,the crown land portion is provided with a plurality of first crown sipes, a plurality of second crown sipes, and a plurality of third crown sipes,the first crown sipes, the second crown sipes, and the third crown sipes open at the ground contact surface via chamfer portions,the first crown sipes and the third crown sipes extend from the first longitudinal edge and have closed ends in the ground contact surface,the second crown sipes extend from the second longitudinal edge and have closed ends in the ground contact surface,each of the first crown sipes has an opening width at the ground contact surface which is constant in a longitudinal direction of the sipe,each of the second crown sipes has an opening width at the ground contact surface which is constant in a longitudinal direction of the sipe, andeach of the third crown sipes has an opening width which decreases continuously from the first longitudinal edge toward the closed end thereof.

The tire according to note 1, whereinthe first crown sipes, the second crown sipes and the third crown sipes are inclined in a same direction with each other with respect to a tire axial direction.

The tire according to note 1 or 2, whereinthe opening width of each of the second crown sipes ranges from 80% to 120% of the opening width of each of the first crown sipes.

The tire according to any one of notes 1 to 3, whereina maximum opening width of each of the third crown sipes is smaller than the opening width of each of the first crown sipe.

The tire according to any one of notes 1 to 4, whereina length in a tire axial direction of the third crown sipes is smaller than a length in the tire axial direction of the first crown sipes.

The tire according to any one of notes 1 to 5, whereinthe closed ends of the third crown sipes are located on a second longitudinal edge side with respect to the closed ends of the second crown sipes.

The tire according to any one of notes 1 to 6, whereinthe crown land portion is further provided with a plurality of fourth crown sipes extending from the second longitudinal edge and having closed ends in the ground contact surface,the plurality of fourth crown sipes opens at the ground contact surface via chamfer portions, andeach of the fourth crown sipes has an opening width at the ground contact surface which decreases continuously from the second longitudinal edge toward the closed end thereof.

The tire according to note 7, whereina maximum opening width of each of the fourth crown sipes is smaller than the opening width of each of the second crown sipes.

The tire according to note 7 or 8, whereina length in a tire axial direction of the fourth crown sipes is smaller than a length in the tire axial direction of the second crown sipes.

The tire according to any one of notes 1 to 9, whereinthe tread portion has a designated mounting direction on a vehicle, and the first tread edge is located outside the vehicle when mounted on the vehicle.

The tire according to any one of notes 1 to 10, whereinthe first crown sipes have outer ends on a first longitudinal edge side,the second crown sipes have outer ends on a second longitudinal edge side, anda minimum distance in the tire circumferential direction between the outer ends of the first crown sipes and the outer ends of the second crown sipes is equal to or less than 10% of a circumferential arrangement pitch of the first crown sipes.

The tire according to any one of notes 1 to 11, whereinthe closed ends of the second crown sipes are located on a first longitudinal edge side with respect to the closed ends of the first crown sipes.

The tire according to any one of notes 1 to 12, whereina length in the tire axial direction of the second crown sipes is greater than a length in the tire axial direction of the first crown sipes.

The tire according to any one of notes 1 to 13, whereinthe crown land portion is further provided with a plurality of fourth crown sipes extending from the second longitudinal edge and having closed ends in the ground contact surface,in a tread plan view, the fourth crown sipes have a shape different from the first crown sipes and the second crown sipes,the third crown sipes have outer ends on a first longitudinal edge side,the fourth crown sipes have outer ends on a second longitudinal edge side, anda minimum distance in the tire circumferential direction between the outer ends of the third crown sipes and the outer ends of the fourth crown sipes is equal to or less than 10% of a circumferential arrangement pitch of the third crown sipes.

The tire according to note 14, whereinthe third crown sipes and the fourth crown sipes are inclined with respect to a tire axial direction in a same direction as with the first crown sipes and the second crown sipes.

The tire according to note 14 or 15, whereinthe closed ends of the third crown sipes are located on a first longitudinal edge side with respect to the closed ends of the fourth crown sipes.

The tire according to any one of notes 1 to 16, whereina length in a tire axial direction of the first crown sipes ranges from 40% to 60% of a width in the tire axial direction of the ground contact surface of the crown land portion.

The tire according to any one of notes 1 to 17, whereina length in the tire axial direction of the second crown sipes ranges from 65% to 85% of a width in the tire axial direction of the ground contact surface of the crown land portion.

The tire according to any one of notes 1 to 18, whereina length in the tire axial direction of the third crown sipes ranges from 25% to 45% of a width in the tire axial direction of the ground contact surface of the crown land portion.

The tire according to any one of notes 1 to 19, whereinangles of the first crown sipes, the second crown sipes and the third crown sipes range from 25 to 35 degrees with respect to a tire axial direction.