A tire has a tread having a first tread edge, a second tread edge on the opposite side, and multiple inclined main grooves formed such that each inclined main groove is obliquely extending from one of the first and second tread edges toward a tire equator and is terminated without reaching the other one of the first and second tread edges. The inclined main grooves are formed such that each of the inclined main grooves includes a tire axial direction outer side portion obliquely extending in an inclined direction, a tire axial direction inner side portion inclining in the inclined direction, and a middle portion formed between the tire axial direction outer side portion and the tire axial direction inner side portion and inclining in the opposite inclined direction with respect to the inclined direction of the tire axial direction outer side portion and tire axial direction inner side portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is based upon and claims the benefit of priority to Japanese Patent Application No. 2016-126864, filed Jun. 27, 2016, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a tire having excellent on-snow performance.

Description of Background Art

Japanese Patent Laid-Open Publication No. 2016-016694 describes a tire in which inclined main grooves are provided. The entire contents of this publication are incorporated herein by reference.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a tire has a tread having a first tread edge, a second tread edge on the opposite side with respect to the first tread edge, and multiple inclined main grooves formed such that each of the inclined main grooves is obliquely extending from one of the first tread edge and the second tread edge toward a tire equator and terminated without reaching the other one of the first tread edge and the second tread edge. The inclined main grooves are formed such that each of the inclined main grooves includes a tire axial direction outer side portion obliquely extending in an inclined direction, a tire axial direction inner side portion inclining in the inclined direction, and a middle portion formed between the tire axial direction outer side portion and the tire axial direction inner side portion and inclining in the opposite inclined direction with respect to the inclined direction of the tire axial direction outer side portion and tire axial direction inner side portion.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1is a developed view of a tread part2of a tire1illustrating an embodiment of the present invention. The tire1of the present embodiment can be used, for example, for various tires such as a pneumatic tire for a passenger car or a vehicle for a heavy load, and for a non-pneumatic tire that is not filled with pressurized air. The tire1of the present embodiment is, for example, a pneumatic tire, and is suitably used as a winter tire for a passenger car.

As illustrated inFIG. 1, the tire1has the tread part2demarcated by a first tread edge (Te1) and a second tread edge (Te2). InFIG. 1, a left side is the first tread edge (Te1), and a right side is the second tread edge (Te2).

In the case of a pneumatic tire, the tread edges (Te1, Te2) are respectively tire axial direction outermost side ground contact positions when the tire1in a normal state is loaded with a normal load and is grounded on a flat surface at a camber angle of 0 degree. The term “normal state” refers to a no-load state in which the tire is mounted to a normal rim and is filled with air at a normal internal pressure. In the present specification, unless otherwise specified, values of dimensions and the like of the parts of the tire are values measured in the normal state.

The term “normal rim” refers to a rim for which standards are set for each tire in a system of standards that includes standards on which the tire is based. For example, the term “normal rim” refers to a “Standard Rim” in the JATMA standards, a “Design Rim” in the TRA standards, or a “Measuring Rim” in the ETRTO standards.

The term “normal internal pressure” refers to an air pressure for which standards are set for each tire in a system of standards that includes the standards on which the tire is based, and refers to a “Highest Air Pressure” in the JATMA standards, a maximum value published in the table “Tire Load Limits at Various Cold Inflation Pressures” in the TRA standards, or an “Inflation Pressure” in the ETRTO standards.

The term “normal load” refers to a load for which standards are set for each tire in a system of standards that includes the standards on which the tire is based, and refers to a “Maximum Load Capacity” in the JATMA standards, a maximum value published in the table “Tire Load Limits at Various Cold Inflation Pressures” in the TRA standards, or a “Load Capacity” in the ETRTO standards.

The tread part2of the present embodiment has, for example, a directional pattern in which a rotation direction (R) is specified. The rotation direction (R) is displayed, for example, using a character or a symbol on a side wall part (not shown in the drawings).

Multiple inclined main grooves10are provided in the tread part2. The inclined main grooves10each obliquely extend from one of the first tread edge (Te1) and the second tread edge (Te2) toward a tire equator (C) side and are each terminated without reaching the other tread edge of the first tread edge (Te1) or the second tread edge (Te2).

The inclined main grooves10of the present embodiment include, for example, first inclined main grooves11and second inclined main grooves12. The first inclined main grooves11each obliquely extend from the first tread edge (Te1) toward the tire equator (C) side and are each terminated without reaching the second tread edge (Te2). The second inclined main grooves12each obliquely extend from the second tread edge (Te2) toward the tire equator (C) side and are each terminated without reaching the first tread edge (Te1).

The first inclined main grooves11and the second inclined main grooves12of the present embodiment have, for example, substantially line-symmetrical contours with respect to the tire equator (C).

InFIG. 2, as a drawing for describing a structure of each of the inclined main grooves10, an enlarged view of a contour of a first inclined main groove11is illustrated. The second inclined main grooves12can be understood in the same way by replacing first tread edge (Te1) with the second tread edge (Te2). As illustrated inFIG. 2, the inclined main grooves10each include an outer side portion15, an inner side portion16and a middle portion17.

The outer side portion15obliquely extends from the first tread edge (Te1). The outer side portion15of the present embodiment is inclined toward the rotation direction (R) side from the first tread edge (Te1) toward the tire equator (C) side. The outer side portion15extends, for example, from the first tread edge (Te1) to a point before the tire equator (C).

An angle of the outer side portion15of the present embodiment with respect to the tire axial direction, for example, gradually increases toward a tire axial direction inner side. The angle (θ1) of the outer side portion15with respect to the tire axial direction is preferably 5-45 degrees, and more preferably 5-30 degrees. Such an outer side portion15can also improve drainage performance during wet traveling while improving traction on snow.

The inner side portion16is provided on a tire axial direction inner side of the outer side portion15. The inner side portion16is inclined in the same direction as the outer side portion15. The inner side portion16of the present embodiment, for example, extends across the tire equator (C). However, it is also possible that the inner side portion16is terminated on the tire equator (C) or at a point before the tire equator (C).

An angle (θ2) of the inner side portion16with respect to the tire axial direction is desirably, for example, greater than the angle (θ1) of the outer side portion15. The angle (θ2) is, for example, preferably 40-80 degrees, and more preferably 45-60 degrees. Such an inner side portion16can provide a snow column shearing force also in the tire axial direction when traveling on snow.

The middle portion17is provided between the outer side portion15and the inner side portion16and extends so as to connect the outer side portion15and the inner side portion16. The middle portion17is inclined in an opposite direction to the outer side portion15and the inner side portion16.

During traveling on snow, snow in the inclined main grooves10tries to move to the first tread edge (Te1) side or the tire equator (C) side due to action of a ground contact pressure. The middle portion17that is inclined in an opposite direction to the outer side portion15and the inner side portion16prevents such movement of the snow and thus strongly presses the snow in the groove. Therefore, a tire according to an embodiment of the present invention can gain a large snow column shearing force and thus can increase traction on snow, in particular, traction during turning.

An angle (θ3) of the middle portion17with respect to the tire axial direction is desirably, for example, greater than the angle (θ1) of the outer side portion15. The angle (θ3) of the middle portion17is preferably 35 degrees or more and 65 degrees or less, and more preferably 45 degrees or more and 55 degrees or less. Such a middle portion17allows the above-described effect to be achieved while allowing the drainage performance of the inclined main grooves10during wet traveling to be maintained.

A length (L1) of the middle portion17is desirably, for example, greater than a groove width of each of the outer side portion15and the inner side portion16. Such a middle portion17can reliably prevent movement of snow in the groove during traveling on snow and thus can strongly press the snow. The length (L1) is a distance from a first intersection point21between a center line of the outer side portion15and a center line of the middle portion17to a second intersection point22between a center line of the inner side portion16and the center line of the middle portion17.

In the case of a winter tire for a passenger car, the length (L1) of the middle portion17is preferably 5-25 mm, and more preferably 10-20 mm. When the length (L1) is smaller than 5 mm, there is a risk that the above-described effect may be reduced. When the length (L1) is greater than 25 mm, there is a risk that the drainage performance of the inclined main grooves10may decrease and thus the hydroplaning phenomenon may be likely to occur.

A tire axial direction distance (L2) from the first tread edge (Te1) to the first intersection point21is desirably, for example, 0.25-0.40 times a tread width (TW). As illustrated inFIG. 1, the tread width (TW) is a tire axial direction distance from the first tread edge (Te1) to the second tread edge (Te2) in the normal state.

In the present embodiment, the inner side portion (16a) of a first inclined main groove11is connected to the middle portion (17b) of a second inclined main groove12. The inner side portion (16b) of a second inclined main groove12is connected to the middle portion (17a) of a first inclined main groove11. As a result, a large snow column can be generated at an intersecting portion of a first inclined main groove11and a second inclined main groove12and thus, excellent on-snow performance can be obtained.

Inclined sub-grooves30and longitudinal grooves40are further provided in the tread part2.

The inclined sub-grooves30, for example, are each provided between a pair of inclined main grooves (10,10) that are adjacent to each other in a tire circumferential direction, and are each adjacent to inclined main grooves10. The inclined sub-grooves30, for example, each extend from a tread edge toward the tire equator (C) side and are each terminated at a point before the tire equator (C). The inclined sub-grooves30of the present embodiment include first inclined sub-grooves31that each extend from the first tread edge (Te1) and second inclined sub-grooves32that each extend from the second tread edge (Te2). The first inclined sub-grooves31and the second inclined sub-grooves32of the present embodiment have, for example, substantially line-symmetrical contours with respect to the tire equator (C).

InFIG. 3, as a drawing for describing a structure of each of the inclined sub-grooves30, an enlarged view of a contour of a first inclined sub-groove31is illustrated. As illustrated inFIG. 3, the inclined sub-grooves30, for example, each include a first portion33and a second portion34.

The first portion33, for example, extends the outer side portion15of an adjacent inclined main groove10. An angle (θ4) of the first portion33with respect to the tire axial direction is preferably 5-30 degrees, and more preferably 10-20 degrees.

The second portion34, for example, extends inclined toward an opposite direction to the first portion33. An angle (θ5) of the second portion34with respect to the tire axial direction is desirably, for example, 30-45 degrees. Such inclined sub-grooves30can each generate a firm snow column at an intersecting portion between the first portion33and the second portion34.

The second portion34desirably has, for example, a smaller groove width than the first portion33. Specifically, a groove width (W2) of the second portion34is desirably 0.65-0.80 times a groove width (W1) of the first portion33. Such a second portion34helps to maintain rigidity of a land portion near the tire equator (C) and thus helps to maintain steering stability.

In order to improve steering stability on a dry road surface and on-snow performance in a well-balanced manner, a tire axial direction length (L5) of the first portion33is desirably, for example, 0.25-0.35 times the tread width (TW) (illustrated inFIG. 1; the same applies hereinafter). A tire axial direction length (L6) of the second portion34is desirably, for example, 0.10-0.15 times the tread width (TW). The length (L5) of the first portion33is a distance from the first tread edge (Te1) to a third intersection point23between a center line of the first portion33and a center line of the second portion34. The length (L6) of the second portion34is a distance from the third intersection point23to an inner end of the second portion34.

As illustrated inFIG. 1, the longitudinal grooves40, for example, are communicatively connected to the inclined main grooves10. The longitudinal grooves40include, for example, first longitudinal grooves41and second longitudinal grooves42. The first longitudinal grooves41are provided between the first tread edge (Te1) and the tire equator (C). The second longitudinal grooves42are provided between the second tread edge (Te2) and the tire equator (C). The first longitudinal grooves41and the second longitudinal grooves42of the present embodiment have, for example, substantially line-symmetrical contours with respect to the tire equator (C).

FIG. 4illustrates an enlarged view of a contour of a first longitudinal groove. As illustrated inFIG. 4, the first longitudinal grooves41include, for example, first outer side longitudinal grooves43and first inner side longitudinal grooves44.

The first outer side longitudinal grooves43, for example, each communicatively connect between the outer side portions15of a pair of inclined main grooves10that are adjacent to each other in the tire circumferential direction. The first outer side longitudinal grooves43of the present embodiment each intersect the first portion33of an inclined sub-groove30.

Each of the first outer side longitudinal grooves43is desirably, for example, inclined toward the tire equator (C) side as it extends toward the rotation direction (R). An angle (θ6) of each of the first outer side longitudinal grooves43with respect to the tire circumferential direction is preferably 5-45 degrees, and more preferably 10-25 degrees. Such first outer side longitudinal grooves43can smoothly guide water to the first tread edge (Te1) side during wet traveling.

A tire axial direction distance (L7) from a fourth intersection point24(between a center line of a first outer side longitudinal groove43and a center line of a inclined main groove10that is adjacent to the first outer side longitudinal groove43on one side (upper side inFIG. 4) in the tire circumferential direction) to the first tread edge (Te1) is desirably, for example, 0.15-0.25 times the tread width (TW). A tire axial direction distance (L8) from a fifth intersection point25(between the center line of the first outer side longitudinal groove43and a center line of a inclined main groove10that is adjacent to the first outer side longitudinal groove43on the other side (lower side inFIG. 4) in the tire circumferential direction) to the first tread edge (Te1) is desirably, for example, 0.20-0.30 times the tread width (TW).

The fourth intersection point24and a fifth intersection point25of an adjacent first outer side longitudinal grooves43on one side (upper side inFIG. 4) in the tire circumferential direction are desirably shifted from each other in the tire axial direction. A distance (L9) between the fourth intersection point24and the fifth intersection point25is desirably, for example, 10-25 mm. Such formation of the first outer side longitudinal grooves43helps to generate firm snow columns at intersecting portions with the inclined main grooves10.

A distance (L10) from a sixth intersection point26between a center line of a first outer side longitudinal groove43and a center line of an inclined sub-groove30to the third intersection point23between the first portion33and the second portion34of the inclined sub-groove30is preferably 5-25 mm, and more preferably 10-20 mm.

The first inner side longitudinal grooves44are respectively provided in tire axial direction inner sides of the first outer side longitudinal grooves43. The first inner side longitudinal grooves44, for example, each communicatively connect between the middle portion17of a first inclined main groove11and the inner side portion16of a second inclined main groove12. The first inner side longitudinal grooves44of the present embodiment each intersect the second portion34of an inclined sub-groove30.

The first inner side longitudinal grooves44are desirably inclined, for example, in the same direction as the first outer side longitudinal grooves43. An angle (θ7) of each of the first inner side longitudinal grooves44with respect to the tire circumferential direction is preferably 5-25 degrees, and more preferably 10-20 degrees. Such first inner side longitudinal grooves44have excellent drainage performance.

A distance from a seventh intersection point27between a center line of a first inner side longitudinal groove44and a center line of an inclined main groove10to an eighth intersection point28between a center line of a first inner side longitudinal groove44and a center line of an inclined sub-groove30is desirably, for example, 10-25 mm.

As illustrated inFIG. 1, the second longitudinal grooves42include, for example, second outer side longitudinal grooves45and second inner side longitudinal grooves46. The second outer side longitudinal grooves45have substantially the same structure as the first outer side longitudinal grooves43. The second inner side longitudinal grooves46have substantially the same structure as the first inner side longitudinal grooves44.

Multiple blocks4partitioned by the above-described multiple grooves are provided in the tread part2. In the present embodiment, stud pins or stud pin holes5are respectively provided in some of the blocks4. In the present embodiment, the stud pins or the stud pin holes5are randomly positioned in the blocks. Such stud pins effectively improve on-ice performance. In the drawings of the present specification, the stud pins are omitted.

In each of the blocks4of the present embodiment, multiple sipes6each extending in the tire axial direction are provided. Such sipes6have an excellent edge effect and improve on-ice performance. In the present specification, the term “sipe” means a slit having a width of 1.5 mm or less, which is distinguished from a groove for drainage.

The blocks4include, for example, multiple center blocks51that are provided on the tire equator (C), multiple shoulder blocks52that are provided closest to the tread edges, and middle blocks53that are provided between the center blocks51and the shoulder blocks52.

FIG. 5illustrates an enlarged view of the middle blocks53. As illustrated inFIG. 5, the middle blocks53include, for example, first middle blocks (53A) and second middle blocks (53B). The second middle blocks (53B) are each adjacent to a first middle block (53A) on a trailing side in the tire rotation direction (R) across an inclined sub-groove30.

The first middle blocks (53A) of the present embodiment each include, for example, a convex portion55that projects toward the rotation direction (R) side, and a concave portion56that is provided on an opposite side of the convex portion55and is recessed toward rotation direction (R) side. As a result, the first middle blocks (53A) each have an arrow feather-like tread surface. Such first middle blocks (53A) are easy to partially deform and thus can promote discharge of snow in the grooves and improve on-snow performance.

An angle (θ8) between edges of the convex portion55is desirably smaller than an angle (θ9) between edges of the concave portion56. Such a convex portion55is easy to pierce on a road surface during traveling on snow and helps to improve on-snow performance. The angle (θ8) is desirably, for example, 90-100 degrees. The angle (θ9) is desirably, for example, 120-130 degrees.

An apex58of the concave portion56is desirably, for example, shifted from an apex57of the convex portion55. The apex58of the concave portion56of the present embodiment is positioned on a tire axial direction outer side of the apex57of the convex portion55. Such a formation of the convex portion55and the concave portion56can help to relax shear stress acting on the blocks and thus can improve durability of the blocks.

The second middle blocks (53B) each include, for example, a convex portion60that projects toward the rotation direction (R) side and an edge61that extends without bending on an opposite side of the convex portion60. As a result, the second middle blocks (53B) each have a substantially pentagonal tread surface. Such second middle blocks (53B) are harder to fall than the first middle blocks (53A) and thus snow can be strongly pressed in the grooves between the second middle blocks (53B).

An angle (θ10) between edges of the convex portion60of each of the second middle blocks (53B) is desirably, for example, greater than the angle (θ8) of the convex portion55of each of the first middle blocks (53A). Specifically, the angle (θ10) is desirably 120-130 degrees. Such second middle blocks (53B) deform in a different manner from the first middle blocks (53A) when grounded, and thus can promote discharge of snow in surrounding grooves.

In the above, a tire according to an embodiment of the present invention is described in detail. However, without being limited to the above-described specific embodiment, the present invention can also be embodied in various modified forms.

EXAMPLES

Tires for a passenger car each having a size of 205/60R16 and the basic pattern ofFIG. 1are prototyped based on specifications shown in Table 1. As a comparative example, a tire is prototyped in which inclined main grooves entirely obliquely extend in the same direction as illustrated inFIG. 6. On-snow performance and wet performance of the test tires are tested. Specifications and a test method of the test tires are as follows.

Tire mounting positions: all wheels

Angle (θ1) of the outer side portion: 25 degrees

Angle (θ2) of the inner side portion: 50 degrees

Driving characteristics related to traction performance, braking performance and turning performance when the test vehicle to which the test tires are mounted is driven on snow are evaluated by a driver based on sensory evaluation. The result is a score with a score of the comparative example as 100. A greater score indicates a better on-snow performance.

Wet Performance

The test vehicle is driven on an asphalt road surface having a radius of 100 m on which a puddle having a water depth of 5 mm and a length of 20 m is provided, and a lateral acceleration (lateral G) of front wheels of the test vehicle is measured. The result is an average lateral G of a speed of 50-80 km/h and is expressed as an index number with a value of the comparative example as 100. A greater index number indicates a better wet performance.

The test results are presented in Table 1.

As a result of the test, it can be confirmed that the tires of the examples have excellent on-snow performance. Further, it is confirmed that the tires of the examples also maintain good wet performance.

A tire according to an embodiment of the present invention has excellent on-snow performance based on improving a structure of the inclined main grooves.

A tire according to an embodiment of the present invention has a tread part demarcated by a first tread edge and a second tread edge. The tread part includes multiple inclined main grooves that each obliquely extend from one of the first tread edge and the second tread edge toward a tire equator side and are each terminated without reaching the other one of the first tread edge and the second tread edge. The inclined main grooves each include: a tire axial direction outer side portion that obliquely extends; a tire axial direction inner side portion that is inclined in the same direction as the outer side portion; and a middle portion that is provided between the outer side portion and the inner side portion and is inclined in an opposite direction to the outer side portion.

In a tire according to an embodiment of the present invention, it is desirable that the inclined main grooves each extend at least to the tire equator.

In a tire according to an embodiment of the present invention, it is desirable that the tread part further include inclined sub-grooves that are respectively adjacent to the inclined main grooves and each extend from one of the tread edges toward the tire equator side and are each terminated at a point before the tire equator, and the inclined sub-grooves each include a first portion that extends along the outer side portion of an adjacent inclined main groove, and a second portion that extends inclined toward an opposite direction to the first portion.

In a tire according to an embodiment of the present invention, it is desirable that the second portion has a smaller groove width than the first portion.

In a tire according to an embodiment of the present invention, it is desirable that the inclined main grooves include first inclined main grooves that each extend from the first tread edge, and second inclined main grooves that each extend from the second tread edge.

In a tire according to an embodiment of the present invention, it is desirable that the inner side portions of the first inclined main grooves are respectively connected to the middle portions of the second inclined main grooves, and the inner side portions of the second inclined main grooves are respectively connected to the middle portions of the first inclined main grooves.

The tread part according to an embodiment of the tire of the present invention includes the multiple inclined main grooves that each obliquely extend from one of the first tread edge and the second tread edge toward the tire equator side and are each terminated without reaching the other one of the first tread edge and the second tread edge. The inclined main grooves each include the tire axial direction outer side portion that obliquely extends, the tire axial direction inner side portion that is inclined in the same direction as the outer side portion, and the middle portion that is provided between the outer side portion and the inner side portion and is inclined in an opposite direction to the outer side portion.

When traveling on snow, due to action of a ground contact pressure, snow in the inclined main grooves tends to move to the tread edge sides or to the tire equator side. However, the middle portions prevent such movement of the snow and thus the snow can be strongly pressed in the grooves. Therefore, a tire according to an embodiment of the present invention can gain a large snow column shearing force and thus can increase traction on snow, in particular, traction during turning.

For example, Japanese Patent Laid-Open Publication No. 2016-016694 describes a tire in which inclined main grooves that each obliquely extend from a tread edge toward a tire equator are provided. The inclined main grooves of Japanese Patent Laid-Open Publication No. 2016-016694 are each entirely inclined in the same direction and each extend to a point near the tire equator. For such inclined main grooves, there is a problem that, when traveling on snow, snow in the grooves can easily move to the tread edge side or the tire equator side and it is difficult to strongly press the snow in the grooves.