A tire includes a tread part having main grooves and lands demarcated by the main grooves. A crown land between a pair of crown main grooves includes first crown lug grooves extending from one crown groove to tire axial direction inner side and terminated within the crown land, second crown lug grooves extending from the other crown groove to the tire axial inner side and terminated within the crown land, and first crown sipes formed at tire circumferential direction positions and connecting the crown grooves, each first crown sipe includes a first side crown sipe piece extending from one crown groove to the tire axial inner side, a second side crown sipe piece not positioned on an extension line of the first side piece and extending from the other crown groove to the tire axial inner side, and a connecting crown sipe piece connecting the first and second sipe pieces.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is based upon and claims the benefit of priority to Japanese Patent Application No. 2016-137932, filed Jul. 12, 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 that allows performance on snow and ice and steering stability to be improved in a well-balanced manner.

Description of Background Art

Japanese Patent Laid-Open Publication No. 2010-285035 describes a tire in which edges of main grooves are extending in a tire circumferential direction into zigzag shapes and a large number of sipes is 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 includes a tread part having main grooves each continuously extending in a tire circumferential direction, and land portions demarcated by the main grooves. The main grooves include a pair of crown main grooves, the land portions include a crown land portion demarcated between the pair of crown main grooves, the crown land portion includes first crown lug grooves each extending from one of the crown main grooves to a tire axial direction inner side and terminated within the crown land portion, second crown lug grooves each extending from the other one of the crown main grooves to the tire axial direction inner side and terminated within the crown land portion, and first crown sipes formed respectively at tire circumferential direction positions different from positions of the first and second crown lug grooves and each communicatively connecting the pair of crown main grooves, each of the first crown sipes includes a first side crown sipe piece extending from one of the crown main grooves to the tire axial direction inner side, a second side crown sipe piece not positioned on an extension line of the first side crown sipe piece and extending from the other one of the crown main grooves to the tire axial direction inner side, and a connecting crown sipe piece connecting the first side crown sipe piece and the second side crown sipe piece.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1is a developed view of a tread part2of a tire1of the present embodiment. As illustrated inFIG. 1, in the tread part2of the tire1of the present embodiment, multiple main grooves3that each continuously extend in a tire circumferential direction and multiple land portions4that are demarcated by the main grooves3are provided.

The main grooves3of the present embodiment include a pair of crown main grooves5and a pair of shoulder main grooves6that are each formed between a crown main groove5and a tread edge (Te). It is desirable that the crown main grooves5be respectively formed on both sides of a tire equator (C).

Here, the term “tread edge” (Te) refers to a tire axial direction outermost edge of a ground contact surface when a normal load is loaded to the tire1in a normal state and the tire1is grounded on a flat surface at a camber angle of 0 degree. A tire axial direction distance between the tread edges (Te) is defined as a tread ground contact width (TW).

The term “normal state” refers to a no-load state in which the tire1is mounted to a normal rim (not illustrated in the drawings) and is filled with air at a normal pressure. In the present specification, unless otherwise specified, values of dimensions of the parts of the tire1are values measured in the normal state. Further, unless otherwise specified, a groove width of each of the grooves is measured in a direction orthogonal to a longitudinal direction of the groove.

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 tire1is 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 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 tire1is 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 tire1is 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.

It is desirable that the crown main grooves5each have a substantially constant groove width (W1) and linearly extend. The groove width (W1) of each of the crown main grooves5is preferably 4%-6% of the tread ground contact width (TW).

It is desirable that the shoulder main grooves6each have a substantially constant groove width (W2) and linearly extend. The groove width (W2) of each of the shoulder main grooves6is preferably 5%-7% of the tread ground contact width (TW). It is desirable that a groove width (W2) of each of the shoulder main grooves6be larger than the groove width (W1) of each of the crown main grooves5.

FIG. 2is a cross-sectional view along an A-A line ofFIG. 1. As illustrated inFIG. 2, it is desirable that a groove depth (D1) of each of the crown main grooves5be substantially equal to or larger than a groove depth (D2) of each of the shoulder main grooves6.

As illustrated inFIG. 1, the land portions4of the present embodiment include a crown land portion7demarcated between the pair of the crown main grooves5, a pair of middle land portions8that are each demarcated by a crown main groove5and a shoulder main groove6, and a pair of shoulder land portions9that are each demarcated by a shoulder main groove6and a tread edge (Te).

It is desirable that the crown land portion7be formed on the tire equator (C). A tire axial direction width (W3) of the crown land portion7is preferably 10%-15% of the tread ground contact width (TW).

FIG. 3is a partial enlarged view of the crown land portion7. As illustrated inFIG. 3, the crown land portion7of the present embodiment has multiple first crown lug grooves (10A) that each extend from one crown main groove (5A) to a tire axial direction inner side and multiple second crown lug grooves (10B) that each extend from the other crown main groove (5B) to a tire axial direction inner side. Due to the first crown lug grooves (10A) and the second crown lug grooves (10B), the crown land portion7allows a high snow column shearing force to be obtained, and can improve the performance on snow and ice of the tire1.

It is desirable that the first crown lug grooves (10A) and the second crown lug grooves (10B) be each terminated within the crown land portion7. Such first crown lug grooves (10A) and second crown lug grooves (10B) can suppress a decrease in rigidity of the crown land portion7and allow excellent steering stability of the tire1on a dry road surface to be achieved.

A tire axial direction length (L1) of each of the first crown lug grooves (10A) is preferably 20%-45% of the width (W3) of the crown land portion7. A tire axial direction length (L2) of each of the second crown lug grooves (10B) is preferably 20%-45% of the width (W3) of the crown land portion7. It is desirable that the tire axial direction length (L1) of each of the first crown lug grooves (10A) and the tire axial direction length (L2) of each of the second crown lug grooves (10B) be substantially equal to each other.

The first crown lug grooves (10A) and the second crown lug grooves (10B) of the present embodiment each extend in an arc shape. It is desirable that each of the first crown lug grooves (10A) and each of the second crown lug grooves (10B) respectively have arcs that are convex in different directions from each other. Such first crown lug grooves (10A) and second crown lug grooves (10B) can suppress a localized decrease in rigidity of the crown land portion7.

A curvature radius (R1) of a groove center line of each of the first crown lug grooves (10A) is preferably 10-30 mm. A curvature radius (R2) of a groove center line of each of the second crown lug grooves (10B) is preferably 10-30 mm. It is desirable that the curvature radius (R1) of each of the first crown lug grooves (10A) and the curvature radius (R2) of each of the second crown lug grooves (10B) be substantially equal to each other.

The first crown lug grooves (10A) and the second crown lug grooves (10B) of the present embodiment are inclined in the same direction. Such first crown lug grooves (10A) and second crown lug grooves (10B) can efficiently disperse force acting on the crown land portion7.

An angle (θ1) of each of the first crown lug grooves (10A) with respect to the tire circumferential direction at a communicating part (10a) between the each of the first crown lug grooves (10A) and the crown main groove5is preferably 40-80 degrees. An angle (θ2) of each of the second crown lug grooves (10B) with respect to the tire circumferential direction at a communicating part (10b) between the each of the second crown lug grooves (10B) and the crown main groove5is preferably 40-80 degrees. It is desirable that the angle (θ1) of each of the first crown lug grooves (10A) and the angle (θ2) of each of the second crown lug grooves (10B) be substantially equal to each other.

As illustrated inFIG. 2, in the present embodiment, a groove depth (D3) of each of the first crown lug grooves (10A) and a groove depth (D4) of each of the second crown lug grooves (10B) are substantially equal to each other. It is desirable that the groove depth (D3) of each of the first crown lug grooves (10A) and the groove depth (D4) of each of the second crown lug grooves (10B) be smaller than the groove depth (D1) of each of the crown main grooves5. Such first crown lug grooves (10A) and second crown lug grooves (10B) suppress a decrease in the rigidity of the crown land portion7and allow a high snow column shearing force to be obtained.

As illustrated inFIG. 3, the crown land portion7of the present embodiment further has first crown sipes11each of which communicatively connects the pair of the crown main grooves5. It is desirable that the first crown sipes11be formed at tire circumferential direction positions different from those of the first crown lug grooves (10A) and the second crown lug grooves (10B). Such first crown sipes11can suppress a decrease in the rigidity of the crown land portion7and allow excellent steering stability of the tire1to be achieved. Further, the first crown sipes11can achieve an edge effect in both the tire circumferential direction and the tire axial direction and thus allow performance on snow and ice of the tire1in a front-rear direction and a left-right direction to be improved.

The first crown sipes11of the present embodiment each include a one-side crown sipe piece (11a) that extends from the crown main groove (5A) to a tire axial direction inner side and an other-side crown sipe piece (11b) that extends from the crown main groove (5B) to a tire axial direction inner side. The first crown sipes11further each include a connecting crown sipe piece (11c) that connects the one-side crown sipe piece (11a) and the other-side crown sipe piece (11b).

In the present embodiment, the other-side crown sipe piece (11b) is formed at a position that is not on an extension line of the one-side crown sipe piece (11a). It is desirable that the one-side crown sipe piece (11a) and the other-side crown sipe piece (11b) be each terminated within the crown land portion7. Such one-side crown sipe piece (11a) and other-side crown sipe piece (11b) allow each of the first crown sipes11to have inflection points and thereby can efficiently disperse force acting on the crown land portion7.

A tire axial direction length (L3) of the one-side crown sipe piece (11a) is preferably 30%-45% of the width (W3) of the crown land portion7. A tire axial direction length (L4) of the other-side crown sipe piece (11b) is preferably 30%-45% of the width (W3) of the crown land portion7. It is desirable that the tire axial direction length (L3) of the one-side crown sipe piece (11a) and the tire axial direction length (L4) of the other-side crown sipe piece (11b) be substantially equal to each other.

In the present embodiment, the one-side crown sipe piece (11a) and the other-side crown sipe piece (11b) each extend in an arc shape. Such one-side crown sipe piece (11a) and other-side crown sipe piece (11b) can suppress a localized decrease in the rigidity of the crown land portion7.

It is desirable that the one-side crown sipe piece (11a) and the other-side crown sipe piece (11b) respectively have arcs that are convex in different directions from each other. Further, it is desirable that the one-side crown sipe piece (11a) and each of the first crown lug grooves (10A) respectively have arcs that are convex in the same direction. Further, it is desirable that the other-side crown sipe piece (11b) and each of the second crown lug grooves (10B) respectively have arcs that are convex in the same direction.

A curvature radius (R3) of the one-side crown sipe piece (11a) is preferably 10-30 mm. A curvature radius (R4) of the other-side crown sipe piece (11b) is preferably 10-30 mm. It is desirable that the curvature radius (R3) of the one-side crown sipe piece (11a) and the curvature radius (R4) of the other-side crown sipe piece (11b) be substantially equal to each other.

In the present embodiment, the one-side crown sipe piece (11a) and the other-side crown sipe piece (11b) are inclined in the same direction. It is desirable that the one-side crown sipe piece (11a) and the other-side crown sipe piece (11b) be inclined in the same direction as the first crown lug grooves (10A) and the second crown lug grooves (10B). Such one-side crown sipe piece (11a) and other-side crown sipe piece (11b) can efficiently disperse force acting on the crown land portion7.

An angle (θ3) of the one-side crown sipe piece (11a) with respect to the tire circumferential direction at a communicating part (11d) between the one-side crown sipe piece (11a) and the crown main groove5is preferably 30-60 degrees. An angle (θ4) of the other-side crown sipe piece (11b) with respect to the tire circumferential direction at a communicating part (11e) between the other-side crown sipe piece (11b) and the crown main groove5is preferably 30-60 degrees. It is desirable that the angle (θ3) of the one-side crown sipe piece (11a) and the angle (θ4) of the other-side crown sipe piece (11b) be substantially equal to each other.

FIG. 4is a cross-sectional view along a B-B line ofFIG. 1. As illustrated inFIG. 4, the one-side crown sipe piece (11a) of the present embodiment has a 2-stage structure in which a depth (D5) on the crown main groove5side is smaller than a depth (D6) on the tire equator (C) side. The other-side crown sipe piece (11b) of the present embodiment also has a similar 2-stage structure. Such one-side crown sipe piece (11a) and other-side crown sipe piece (11b) respectively have inflection points at their bottoms and thereby can efficiently disperse force acting on the crown land portion7.

As illustrated inFIG. 3, it is desirable that the connecting crown sipe piece (11c) connect a termination point (11f) of the one-side crown sipe piece (11a) in the crown land portion7and a termination point (11g) of the other-side crown sipe piece (11b) in the crown land portion7. The connecting crown sipe piece (11c) of the present embodiment linearly extends. For example, the connecting crown sipe piece (11c) is formed so as to cross the tire equator (C).

The connecting crown sipe piece (11c) of the present embodiment is inclined in an opposite direction to that of the one-side crown sipe piece (11a) and the other-side crown sipe piece (11b). Such a connecting crown sipe piece (11c) can achieve an edge effect in a different direction from the one-side crown sipe piece (11a) and the other-side crown sipe piece (11b).

An angle (θ10) between the connecting crown sipe piece (11c) and the one-side crown sipe piece (11a) and an angle (θ11) between the connecting crown sipe piece (11c) and the other-side crown sipe piece (11b) are preferably each 90-150 degrees.

As illustrated inFIG. 4, in the present embodiment, a depth (D7) of the connecting crown sipe piece (11c) is smaller than the depth (D5) of the one-side crown sipe piece (11a) on the crown main groove5side. That is, the connecting crown sipe piece (11c) has a smaller depth (D7) than the one-side crown sipe piece (11a) and the other-side crown sipe piece (11b). Such a connecting crown sipe piece (11c) can suppress a decrease in the rigidity of the crown land portion7and improve the steering stability of the tire1, and, due to the edge effect thereof, can improve the performance on snow and ice of the tire1.

As illustrated inFIG. 3, the crown land portion7of the present embodiment further has second crown sipes (12A) that each extend from one crown main groove (5A) to a tire axial direction inner side and third crown sipes (12B) that each extend from the other crown main groove (5B) to a tire axial direction inner side.

It is desirable that the second crown sipes (12A) and the third crown sipes (12B) be each terminated within the crown land portion7. Further, it is desirable that the second crown sipes (12A) and the third crown sipes (12B) each extend in an arc shape and be inclined in the same direction as the one-side crown sipe piece (11a) and the other-side crown sipe piece (11b).

In the present embodiment, each of the second crown sipes (12A) and the one-side crown sipe piece (11a) have substantially the same tire axial direction length, curvature radius, arc orientation and inclination angle with respect to the tire circumferential direction. Similarly, each of the third crown sipes (12B) and the other-side crown sipe piece (11b) have substantially the same tire axial direction length, curvature radius, arc orientation and inclination angle with respect to the tire circumferential direction. On the other hand, although not illustrated in the drawings, it is desirable that the second crown sipes (12A) and the third crown sipes (12B) each have a substantially constant depth.

In the tire circumferential direction, each of the second crown sipes (12A) of the present embodiment is positioned on the other-side crown sipe piece (11b) side of the one-side crown sipe piece (11a). Similarly, each the third crown sipes (12B) of the present embodiment is positioned on the one-side crown sipe piece (11a) side of the other-side crown sipe piece (11b). Such second crown sipes (12A) and third crown sipes (12B) can achieve an edge effect while suppressing a decrease in the rigidity of the crown land portion7.

As illustrated inFIG. 1, it is desirable that the pair of the middle land portions8be respectively formed on tire axial direction outer sides of the crown land portion7. A tire axial direction width (W4) of each of the middle land portions8is preferably 11%-16% of the tread ground contact width (TW). It is desirable that the width (W4) of each of the middle land portions8be larger than the width (W3) of the crown land portion7.

The middle land portions8of the present embodiment each have multiple first middle lug grooves (13A) that each extend from a crown main groove5to a tire axial direction outer side and multiple second middle lug grooves (13B) that each extend from a shoulder main groove6to a tire axial direction inner side. Due to the first middle lug grooves (13A) and second middle lug grooves (13B), the middle land portions8allow a high snow column shearing force to be obtained and can improve the performance on snow and ice of the tire1.

It is desirable that the first middle lug grooves (13A) and the second middle lug grooves (13B) be alternately provided in the tire circumferential direction. Therefore, a tire circumferential direction pitch (P2) of the first middle lug grooves (13A) is two times a tire circumferential direction pitch (P1) of the first crown lug grooves (10A) or the second crown lug grooves (10B). Similarly, a tire circumferential direction pitch (P3) of the second middle lug grooves (13B) is two times the tire circumferential direction pitch (P1) of the first crown lug grooves (10A) or the second crown lug grooves (10B).

It is desirable that each of the first middle lug grooves (13A) oppose a first crown lug groove (10A) or a second crown lug groove (10B) across a crown main groove5. Such first middle lug grooves (13A) cooperate with the first crown lug grooves (10A) or the second crown lug grooves (10B) to allow a higher snow column shearing force to be obtained.

It is desirable that the first middle lug grooves (13A) and the second middle lug grooves (13B) be each terminated within a middle land portion8. Such first middle lug grooves (13A) and second middle lug grooves (13B) suppress a decrease in rigidity of the middle land portions8and allow excellent steering stability of the tire1on a dry road surface to be achieved.

FIG. 5is a partial enlarged view of a middle land portion8. As illustrated inFIG. 5, a tire axial direction length (L5) of each of the first middle lug grooves (13A) is preferably 30%-70% of the width (W4) of each of the middle land portions8. A tire axial direction length (L6) of each of the second middle lug grooves (13B) is preferably 30%-70% of the width (W4) of each of the middle land portions8.

The first middle lug grooves (13A) and the second middle lug grooves (13B) of the present embodiment each extend in an arc shape. Such first middle lug grooves (13A) and second middle lug grooves (13B) can suppress a localized decrease in the rigidity of the middle land portions8.

As illustrated inFIG. 1, in each of the middle land portions8, it is desirable that each of the first middle lug grooves (13A) and each of the second middle lug grooves (13B) respectively have arcs that are convex in the same direction. On the other hand, it is desirable that each of the first middle lug grooves (13A) and the second middle lug grooves (13B) of a middle land portion (8A) on one side of the tire equator (C) and each of the first middle lug grooves (13A) and the second middle lug grooves (13B) of a middle land portion (8B) on the other side of the tire equator (C) respectively have arcs that are convex in different directions from each other.

Further, it is desirable that each of the first middle lug grooves (13A) and the second middle lug grooves (13B) of the middle land portion (8A) on one side and each of the first crown lug grooves (10A) respectively have arcs that are convex in the same direction. Further, it is desirable that each of the first middle lug grooves (13A) and the second middle lug grooves (13B) of the middle land portion (8B) on the other side and each of the second crown lug grooves (10B) respectively have arcs that are convex in the same direction.

As illustrated inFIG. 5, a curvature radius (R5) of each of the first middle lug grooves (13A) is preferably 80-110 mm. A curvature radius (R6) of each of the second middle lug grooves (13B) is preferably 80-110 mm. It is desirable that the curvature radius (R5) of each of the first middle lug grooves (13A) and the curvature radius (R6) of each of the second middle lug grooves (13B) be substantially equal to each other.

As illustrated inFIG. 1, in the present embodiment, the first middle lug grooves (13A) and the second middle lug grooves (13B) are inclined in an opposite direction to that of the first crown lug grooves (10A) and the second crown lug grooves (10B). Such first middle lug grooves (13A) and second middle lug grooves (13B) can cooperate with the first crown lug grooves (10A) and the second crown lug grooves (10B) to more efficiently disperse force acting on the tread part2.

As illustrated inFIG. 5, an angle (θ5) of each of the first middle lug grooves (13A) with respect to the tire circumferential direction at a communicating part (13a) between the each of the first middle lug grooves (13A) and the crown main groove5is preferably 40-70 degrees. An angle (θ6) of each of the second middle lug grooves (13B) with respect to the tire circumferential direction at a communicating part (13b) between the each of the second middle lug grooves (13B) and the shoulder main groove6is preferably 30-60 degrees.

As illustrated inFIG. 2, in the present embodiment, a groove depth (D8) of each of the first middle lug grooves (13A) and a groove depth (D9) of each of the second middle lug grooves (13B) are substantially equal to each other. It is desirable that the groove depth (D8) of each of the first middle lug grooves (13A) and the groove depth (D9) of each of the second middle lug grooves (13B) be substantially equal to the groove depth (D3) of each of the first crown lug grooves (10A) and the groove depth (D4) of each of the second crown lug grooves (10B). Such first middle lug grooves (13A) and second middle lug grooves (13B) suppress a decrease in the rigidity of the middle land portions8and allow a high snow column shearing force to be obtained.

As illustrated inFIG. 5, the middle land portions8of the present embodiment further each have first middle sipes14that each communicatively connect from a crown main groove5to a shoulder main groove6. It is desirable that the first middle sipes14be each provided between a first middle lug groove (13A) and a second middle lug groove (13B) in the tire circumferential direction. Such first middle sipes14suppress a decrease in the rigidity of the middle land portions8and allow excellent steering stability of the tire1to be achieved. Further, due to an edge effect, the first middle sipes14can improve the performance on snow and ice of the tire1.

The first middle sipes14of the present embodiment each include a crown side middle sipe piece (14a) that extends from a crown main groove5to a tire axial direction outer side and a shoulder side middle sipe piece (14b) that extends from a shoulder main groove6to a tire axial direction inner side. The first middle sipes14further each include a connecting middle sipe piece (14c) that connects the crown side middle sipe piece (14a) and the shoulder side middle sipe piece (14b).

In the present embodiment, the shoulder side middle sipe piece (14b) is formed at a position that is not on an extension line of the crown side middle sipe piece (14a). It is desirable that the crown side middle sipe piece (14a) and the shoulder side middle sipe piece (14b) be each terminated within a middle land portion8. Such crown side middle sipe piece (14a) and shoulder side middle sipe piece (14b) allow each of the first middle sipes14to have inflection points and thereby can efficiently disperse force acting on the middle land portions8.

In the present embodiment, each of the crown side middle sipe piece (14a) and the shoulder side middle sipe piece (14b) extends in an arc shape. Such crown side middle sipe piece (14a) and shoulder side middle sipe piece (14b) can suppress a localized decrease in the rigidity of the middle land portions8.

In each of the middle land portions8, it is desirable that crown side middle sipe piece (14a) and the shoulder side middle sipe piece (14b) respectively have arcs that are convex in the same direction. Further, it is desirable that the crown side middle sipe piece (14a) and the shoulder side middle sipe piece (14b) and each of the first middle lug grooves (13A) and each of the second middle lug grooves (13B) respectively have arcs that are convex in the same direction.

A curvature radius (R7) of the crown side middle sipe piece (14a) is preferably 30-50 mm. A curvature radius (R8) of the shoulder side middle sipe piece (14b) is preferably 50-80 mm.

In the present embodiment, the crown side middle sipe piece (14a) and the shoulder side middle sipe piece (14b) are inclined in the same direction. Further, it is desirable that the crown side middle sipe piece (14a) and the shoulder side middle sipe piece (14b) be inclined in the same direction as the first middle lug grooves (13A) and the second middle lug grooves (13B). Such crown side middle sipe piece (14a) and shoulder side middle sipe piece (14b) can efficiently disperse force acting on the middle land portions8.

An angle (θ7) of the crown side middle sipe piece (14a) with respect to the tire circumferential direction at a communicating part (14d) between the crown side middle sipe piece (14a) and the crown main groove5is preferably 40-70 degrees. An angle (θ8) of the shoulder side middle sipe piece (14b) with respect to the tire circumferential direction at a communicating part (14e) between the shoulder side middle sipe piece (14b) and the shoulder main groove6is preferably 30-60 degrees.

As illustrated inFIG. 4, the crown side middle sipe piece (14a) of the present embodiment has a 2-stage structure in which a depth (D10) on the crown main groove5side is smaller than a depth (D11) on the shoulder main groove6side. The shoulder side middle sipe piece (14b) of the present embodiment also has a similar 2-stage structure. Such crown side middle sipe piece (14a) and shoulder side middle sipe piece (14b) respectively have inflection points at their bottoms and thereby can efficiently disperse force acting on the middle land portions8.

As illustrated inFIG. 5, it is desirable that the connecting middle sipe piece (14c) connect a termination point (14f) of the crown side middle sipe piece (14a) in the middle land portion8and a termination point (14g) of the shoulder side middle sipe piece (14b) in the middle land portion8.

The connecting middle sipe piece (14c) of the present embodiment linearly extends along the tire circumferential direction. A tire circumferential direction length (L7) of the connecting middle sipe piece (14c) is preferably 10%-40% of a tire circumferential direction pitch (P4) of the first middle sipes14. Such a connecting middle sipe piece (14c) can achieve an edge effect in a different direction from the crown side middle sipe piece (14a) and the shoulder side middle sipe piece (14b).

As illustrated inFIG. 4, in the present embodiment, a depth (D12) of the connecting middle sipe piece (14c) is smaller than the depth (D10) of the crown side middle sipe piece (14a) on the crown main groove5side. That is, the connecting middle sipe piece (14c) has a smaller depth (D12) than the crown side middle sipe piece (14a) and shoulder side middle sipe piece (14b). Such a connecting middle sipe piece (14c) can suppress a decrease in the rigidity of the middle land portions8and improve the steering stability of the tire1, and, due to the edge effect thereof, can improve the performance on snow and ice of the tire1.

As illustrated inFIG. 5, the middle land portions8of the present embodiment further each have second middle sipes (15A) that respectively connect the first middle lug grooves (13A) and a shoulder main groove6and third middle sipes (15B) that respectively connect the second middle lug grooves (13B) and a crown main groove5.

It is desirable that the second middle sipes (15A) be respectively formed at positions on extension lines of the first middle lug grooves (13A) and each have substantially the same curvature radius as that of each of the first middle lug grooves (13A). Further, it is desirable that the third middle sipes (15B) be respectively formed at positions on extension lines of the second middle lug grooves (13B) and each have substantially the same curvature radius as that of each of the second middle lug grooves (13B).

As illustrated inFIG. 2, in the present embodiment, a depth (D13) of each of the second middle sipes (15A) is smaller than the groove depth (D8) of each of the first middle lug grooves (13A). Further, in the present embodiment, a depth (D14) of each of the third middle sipes (15B) is smaller than the groove depth (D9) of each of the second middle lug grooves (13B). Such second middle sipes (15A) and third middle sipes (15B) can suppress a decrease in the rigidity of the middle land portions8and improve the steering stability of the tire1, and, due to an edge effect thereof, can improve the performance on snow and ice of the tire1.

As illustrated inFIG. 5, the middle land portions8of the present embodiment further each have fourth middle sipes (16A) that each extend from a crown main groove5to a tire axial direction outer side and fifth middle sipes (16B) that each extend from a shoulder main groove6to a tire axial direction inner side.

It is desirable that the fourth middle sipes (16A) and the fifth middle sipes (16B) be each terminated within a middle land portion8. Further, it is desirable that the fourth middle sipes (16A) and the fifth middle sipes (16B) each extend in an arc shape and be inclined in the same direction as the one-side crown sipe piece (11a) and the other-side crown sipe piece (11b).

In the present embodiment, each of the fourth middle sipes (16A) and the crown side middle sipe piece (14a) have substantially the same curvature radius, arc orientation and inclination angle with respect to the tire circumferential direction. Similarly, each of the fifth middle sipes (16B) and the shoulder side middle sipe piece (14b) have substantially the same curvature radius, arc orientation and inclination angle with respect to the tire circumferential direction.

On the other hand, it is desirable that a tire axial direction length of each of the fourth middle sipes (16A) and the fifth middle sipes (16B) be smaller than a tire axial direction length of each of the crown side middle sipe piece (14a) and the shoulder side middle sipe piece (14b). Further, it is desirable that the fourth middle sipes (16A) and the fifth middle sipes (16B) each have a constant depth.

In the tire circumferential direction, each of the fourth middle sipes (16A) of the present embodiment is positioned on the shoulder side middle sipe piece (14b) side of the crown side middle sipe piece (14a). Similarly, each of the fifth middle sipes (16B) of the present embodiment is positioned on the crown side middle sipe piece (14a) side of the shoulder side middle sipe piece (14b). Such fourth middle sipes (16A) and fifth middle sipes (16B) can achieve an edge effect while suppressing a decrease in the rigidity of the middle land portions8.

In the middle land portions8, further, first chamfered portions (17A) are each formed at a land portion edge between a first middle lug groove (13A) and a crown side middle sipe piece (14a); and second chamfered portions (17B) are each formed at a land portion edge between a second middle lug groove (13B) and a shoulder side middle sipe piece (14b). Such first chamfered portions (17A) and second chamfered portions (17B) can improve a snow column shearing force while suppressing a decrease in the rigidity of the middle land portions8.

As illustrated inFIG. 1, it is desirable that the pair of the shoulder land portions9be respectively formed on tire axial direction outer sides of the middle land portions8. A tire axial direction width (W5) of each of the shoulder land portions9is preferably 15%-23% of the tread ground contact width (TW). It is desirable that the width (W5) of each of the shoulder land portions9be larger than the width (W3) of the crown land portion7and the width (W4) of each of the middle land portions8.

The shoulder land portions9of the present embodiment each have multiple shoulder transverse grooves18that each communicatively connect from a shoulder main groove6to a tread edge (Te). Due to the shoulder transverse grooves18, the shoulder land portions9allow a high snow column shearing force to be obtained and can improve the performance on snow and ice of the tire1.

It is desirable that each of the shoulder transverse grooves18oppose a second middle lug groove (13B) or a second middle sipe (15A) across a shoulder main groove6. Each of the shoulder transverse grooves18, for example, has an arc that is convex in a direction different from the second middle lug groove (13B) or the second middle sipe (15A) to which the shoulder transverse groove18opposes.

It is desirable that a tire circumferential direction pitch (P5) of the shoulder transverse grooves18be substantially equal to a tire circumferential direction pitch (P6) between the first middle lug grooves (13A) and the second middle lug grooves (13B). Such shoulder transverse grooves18cooperate with the first crown lug grooves (10A) or second crown lug grooves (10B) to allow a higher snow column shearing force to be obtained and can improve the performance on snow and ice of the tire1.

FIG. 6is a partial enlarged view of a shoulder land portion9. As illustrated inFIG. 6, the shoulder transverse grooves18of the present embodiment each include a first shoulder transverse groove portion (18a) that extends in an arc shape on the shoulder main groove6side and a second shoulder transverse groove portion (18b) that linearly extends along the tire axial direction on the tread edge (Te) side. A curvature radius (R9) of the first shoulder transverse groove portion (18a) is preferably 30-50 mm.

In the present embodiment, the first shoulder transverse groove portion (18a) is inclined in the same direction as the first middle lug grooves (13A) and the second middle lug grooves (13B) (illustrated inFIG. 1). An angle (θ9) of the first shoulder transverse groove portion (18a) with respect to the tire circumferential direction at a communicating part (18c) between the shoulder transverse groove18and the shoulder main groove6is preferably 40-70 degrees. Such first shoulder transverse groove portions (18a) can cooperate with the first middle lug grooves (13A) and second middle lug grooves (13B) to more efficiently disperse a force acting on the tread part2.

As illustrated inFIG. 2, the shoulder transverse grooves18of the present embodiment each have a 2-stage structure in which a groove depth (D15) on the shoulder main groove6side is smaller than a groove depth (D16) on the tread edge (Te) side. Such shoulder transverse grooves18respectively have inflection points at their bottoms and thereby can efficiently disperse force acting on the shoulder land portions9.

As illustrated inFIG. 6, the shoulder land portions9of the present embodiment further each have a first shoulder sipe (19A) and a second shoulder sipe (19B) between each pair of shoulder transverse grooves18that are adjacent to each other in the tire circumferential direction.

It is desirable that the first shoulder sipes (19A) and the second shoulder sipes (19B) each extend from a shoulder main groove6to a tire axial direction outer side. Further, it is desirable that the first shoulder sipes (19A) and the second shoulder sipes (19B) be each terminated within a shoulder land portion9. Such first shoulder sipes (19A) and second shoulder sipes (19B) can suppress a decrease in the rigidity of the shoulder land portions9and improve the steering stability of the tire1, and, due to an edge effect thereof, can improve the performance on snow and ice of the tire1.

In the present embodiment, each of the first shoulder sipes (19A) and each of the second shoulder sipes (19B) have substantially the same shape. It is desirable that the first shoulder sipes (19A) and the second shoulder sipes (19B) each extend in an arc shape and be each inclined in the same direction as the first shoulder transverse groove portion (18a). In the present embodiment, each of the first shoulder sipes (19A) and each of the second shoulder sipes (19B) and the first shoulder transverse groove portion (18a) have substantially the same curvature radius, arc orientation and inclination angle with respect to the tire circumferential direction.

As illustrated inFIG. 4, the first shoulder sipes (19A) each have a 2-stage structure in which a depth (D17) on the shoulder main groove6side is smaller than a depth (D18) on the tread edge (Te) side. The second shoulder sipes (19B) (not illustrated inFIG. 4) of the present embodiment also each have a similar 2-stage structure. Such first shoulder sipes (19A) and second shoulder sipes (19B) respectively have inflection points at their bottoms and thereby can efficiently disperse force acting on the shoulder land portions9.

As illustrated inFIG. 6, the shoulder land portions9of the present embodiment further each have third shoulder sipes (19C) that communicatively connect between the first shoulder sipes (19A) and the second shoulder sipes (19B). It is desirable that the third shoulder sipes (19C) each communicatively connect between an arbitrary position of a first shoulder sipe (19A) and an arbitrary position of a second shoulder sipe (19B).

It is desirable that each of the third shoulder sipes (19C) linearly extends along the tire circumferential direction. Such third shoulder sipes (19C) can achieve an edge effect in a different direction from the first shoulder sipes (19A) and the second shoulder sipes (19B).

As illustrated inFIG. 4, in the present embodiment, a depth (D19) of each of the third shoulder sipes (19C) is smaller than the depth (D17) of each of the first shoulder sipes (19A) on the shoulder main groove6side. That is, the third shoulder sipes (19C) each have a smaller depth (D19) than each of the first shoulder sipes (19A) and the second shoulder sipes (19B). Such third shoulder sipes (19C) can suppress a decrease in the rigidity of the shoulder land portions9and improve the steering stability of the tire1, and, due to the edge effect thereof, can improve the performance on snow and ice of the tire1.

As illustrated inFIG. 6, the shoulder land portions9of the present embodiment further each have fourth shoulder sipes (19D) and fifth shoulder sipes (19E) that each extend from a tread edge (Te) to a tire axial direction inner side.

The fourth shoulder sipes (19D), for example, are respectively positioned on tire axial direction outer sides of the first shoulder sipes (19A) and each linearly extend along the tire axial direction. The fifth shoulder sipes (19E), for example, are respectively positioned on tire axial direction outer sides of the second shoulder sipes (19B) and each linearly extend along the tire axial direction. Such fourth shoulder sipes (19D) and fifth shoulder sipes (19E) can cooperate with the first shoulder sipes (19A) and second shoulder sipes (19B) to achieve an edge effect.

The shoulder land portions9of the present embodiment further each have third chamfered portions20that are respectively formed at land portion edges between the first shoulder sipes (19A) and the second shoulder sipes (19B). Such third chamfered portions20can improve a snow column shearing force while suppressing a decrease in the rigidity of the shoulder land portions9.

In the above, an embodiment of the present invention is described in detail. However, the present invention is not limited to the above-described embodiment illustrated in the drawings and can be embodied in various modified forms.

EXAMPLES

Tires each having a tread pattern ofFIG. 1are prototyped based on specifications shown in Table 1. The prototyped tires are mounted to a test vehicle, and performance on snow and ice and steering stability are tested. Common specifications and a test method of the test tires are as follows.

Performance on Snow and Ice

The test vehicle to which the prototyped tires are mounted is driven to travel on a test course having a snowy and icy road surface, and steering stability during testing is evaluated based on sensory evaluation by a test driver. The result is expressed as an index number with a result of Comparative Example 1 as 100. A larger index number indicates a better steering stability.

Steering Stability

The test vehicle to which the prototyped tires were mounted is driven to travel on a test course having a dry road surface, and steering stability during testing is evaluated based on sensory evaluation by a test driver. The result is expressed as an index number with a result of Comparative Example 1 as 100. A larger index number indicates a better steering stability.

The test results are shown in Table 1.

Based on the results of the tests, it can be confirmed that the tires of the examples allow performance on snow and ice and steering stability to be improved in a well-balanced manner as compared to the comparative examples.

A tire may have a large number of sipes in order to improve performance on snow and ice. In recent years, even for such a tire that has excellent performance on snow and ice, high steering stability on a dry road surface is demanded.

In Japanese Patent Laid-Open Publication No. 2010-285035, a crown land portion is not formed in a block shape and thus high performance on snow and ice cannot be achieved. Therefore, further improvement is required for the tire of Japanese Patent Laid-Open Publication No. 2010-285035 in order to achieve both performance on snow and ice and steering stability.

A tire according to an embodiment of the present invention improves grooves and sipes of a crown land portion and improves performance on snow and ice and steering stability in a well-balanced manner.

A tire according to an embodiment of the present invention includes in a tread part: multiple main grooves that each continuously extend in a tire circumferential direction; and multiple land portions that are demarcated by the main grooves. The main grooves include a pair of crown main grooves. The land portions include a crown land portion that is demarcated between the pair of the crown main grooves. The crown land portion includes: first crown lug grooves that each extend from one of the crown main grooves to a tire axial direction inner side and are each terminated within the crown land portion; second crown lug grooves that each extend from the other one of the crown main grooves to a tire axial direction inner side and are each terminated within the crown land portion; and first crown sipes that are respectively formed at tire circumferential direction positions different from those of the first crown lug grooves and the second crown lug grooves and each communicatively connect the pair of the crown main grooves. The first crown sipes each include: a one-side crown sipe piece that extends from one of the crown main grooves to a tire axial direction inner side; an other-side crown sipe piece that is not positioned on an extension line of the one-side crown sipe piece and extends from the other one of the crown main grooves to a tire axial direction inner side; and a connecting crown sipe piece that connects the one-side crown sipe piece and the other-side crown sipe piece.

In a tire according to an embodiment of the present invention, it is desirable that the one-side crown sipe piece and the other-side crown sipe piece each extend in an arc shape, and the connecting crown sipe piece linearly extend.

In a tire according to an embodiment of the present invention, it is desirable that the connecting crown sipe piece have a depth smaller than those of the one-side crown sipe piece and the other-side crown sipe piece.

In a tire according to an embodiment of the present invention, it is desirable that the one-side crown sipe piece and the other-side crown sipe piece be inclined in the same direction, and the connecting crown sipe piece be inclined in an opposite direction to that of the one-side crown sipe piece and the other-side crown sipe piece.

In a tire according to an embodiment of the present invention, it is desirable that the first crown lug grooves and the second crown lug grooves each extend in an arc shape.

In a tire according to an embodiment of the present invention, it is desirable that the crown land portion further include: second crown sipes that each extend from one of the crown main grooves to a tire axial direction inner side and are each terminated within the crown land portion; and third crown sipes that each extend from the other one of the crown main grooves to a tire axial direction inner side and are each terminated within the crown land portion, and, in the tire circumferential direction, each of the second crown sipes be positioned on the other-side crown sipe piece side of the one-side crown sipe piece, and each of the third crown sipes be positioned on the one-side crown sipe piece side of the other-side crown sipe piece.

In a tire according to an embodiment of the present invention, it is desirable that the second crown sipes and the third crown sipes each extend in an arc shape.

In a tire according to an embodiment of the present invention, it is desirable that the main grooves further include shoulder main grooves that are each formed between a crown main groove and a tread edge, the land portions further include a pair of middle land portions that are each demarcated by a crown main groove and a shoulder main groove, each of the middle land portions have first middle lug grooves that each extend from a crown main groove to a tire axial direction outer side and are each terminated within the each of the middle land portions, and a tire circumferential direction pitch of the first middle lug grooves be two times a tire circumferential direction pitch of the first crown lug grooves or the second crown lug grooves.

In a tire according to an embodiment of the present invention, it is desirable that each of the first middle lug grooves oppose a first crown lug groove or a second crown lug groove across a crown main groove.

In a tire according to an embodiment of the present invention, it is desirable that the first crown lug grooves and the second crown lug grooves be inclined in the same direction, and the first middle lug grooves be inclined in an opposite direction to that of the first crown lug grooves and the second crown lug grooves.

In a tire according to an embodiment of the present invention, the crown land portion includes the first crown lug grooves that each extend from one of crown main grooves to a tire axial direction inner side and are each terminated within the crown land portion, the second crown lug grooves that each extend from the other one of the crown main grooves to a tire axial direction inner side and are each terminated within the crown land portion, and the first crown sipes that are respectively formed at tire circumferential direction positions different from those of the first crown lug grooves and the second crown lug grooves and each communicatively connect the pair of the crown main grooves.

Such first crown lug grooves and second crown lug grooves can suppress a decrease in rigidity of the crown land portion and allow excellent steering stability of the tire on a dry road surface to be achieved. Further, due to the first crown lug grooves and the second crown lug grooves, the crown land portion allows a high snow column shearing force to be obtained, and, due to an edge effect of the first crown sipes, the crown land portion can improve the performance on snow and ice of the tire.

In a tire according to an embodiment of the present invention, the first crown sipes each include the one-side crown sipe piece that extends from one of the crown main grooves to a tire axial direction inner side; the other-side crown sipe piece that is not positioned on an extension line of the one-side crown sipe piece and extends from the other one of the crown main grooves to a tire axial direction inner side; and the connecting crown sipe piece that connects the one-side crown sipe piece and the other-side crown sipe piece.

Such first crown sipes can suppress a decrease in the rigidity of the crown land portion and allow excellent steering stability of the tire to be achieved. Further, the first crown sipes can achieve an edge effect in both the tire circumferential direction and the tire axial direction and thus allow performance on snow and ice of the tire in a front-rear direction and a left-right direction to be improved.