Patent Description:
The present invention relates to a tyre.

Patent Document <NUM> below has proposed a tyre that includes a crown land portion provided with a plurality of crown sipes. The tyre 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 <NUM>] <CIT> tyre in accordance with the preamble of claim <NUM> is known from <CIT>. Related tyres are described in <CIT> and <CIT>.

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

The object is solved by a tyre having the features of claims <NUM>. Sub-claims are directed to preferable embodiments of the invention.

In one aspect of the present invention, a tyre 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 tyre circumferential direction on a first tread edge side, a second longitudinal edge extending in the tyre 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.

According to an embodiment of the invention, the 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 tyre axial direction.

According to an embodiment of the invention, the opening width of each of the second crown sipes ranges from <NUM>% to <NUM>% of the opening width of each of the first crown sipes.

According to an embodiment of the invention, a maximum opening width of each of the third crown sipes is smaller than the opening width of each of the first crown sipe.

According to an embodiment of the invention, a length in a tyre axial direction of the third crown sipes is smaller than a length in the tyre axial direction of the first crown sipes.

According to an embodiment of the invention, the 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.

According to an embodiment of the invention, the 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, wherein the plurality of fourth crown sipes opens at the ground contact surface via chamfer portions, and each 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.

According to an embodiment of the invention, a maximum opening width of each of the fourth crown sipes is smaller than the opening width of each of the second crown sipes.

According to an embodiment of the invention, a length in a tyre axial direction of the fourth crown sipes is smaller than a length in the tyre axial direction of the second crown sipes.

According to an embodiment of the invention, the 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.

According to an embodiment of the invention, the 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, and a minimum distance in the tyre 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 <NUM>% of a circumferential arrangement pitch of the first crown sipes.

According to an embodiment of the invention, the 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.

According to an embodiment of the invention, a length in the tyre axial direction of the second crown sipes is greater than a length in the tyre axial direction of the first crown sipes.

According to an embodiment of the invention, the 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, wherein, 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, and a minimum distance in the tyre 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 <NUM>% of a circumferential arrangement pitch of the third crown sipes.

According to an embodiment of the invention, the third crown sipes and the fourth crown sipes are inclined with respect to a tyre axial direction in a same direction as with the first crown sipes and the second crown sipes.

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

<FIG> is a development view of a tread portion <NUM> of a tyre <NUM> showing an embodiment of the present invention. The tyre <NUM> according to the present embodiment of the invention, for example, is embodied as a winter tyre and may be suitably used as a pneumatic tyre for passenger cars. However, the present invention is not limited to such an embodiment, and may be applied to heavy-duty pneumatic tyres and non-pneumatic tyres in which the interior of the tyre is not filled with pressurized air.

As illustrated in <FIG>, the tread portion <NUM> according to the present invention includes a first tread edge T1, a second tread edge T2, a plurality of circumferential grooves <NUM> extending continuously in the tyre circumferential direction between the first tread edge T1 and the second tread edge T2, and a plurality of land portions <NUM> divided by the circumferential grooves <NUM>. As a preferred embodiment, the tyre <NUM> according to the present embodiment of the invention is configured as a so-called five-rib tyre in which the tread portion <NUM> is composed of four circumferential grooves <NUM> and five land portions <NUM>.

In the present embodiment of the invention, the tread portion <NUM>, for example, has a designated mounting direction on a vehicle. Thus, the first tread edge T1 is intended to be positioned outside the vehicle when installed, and the second tread edge T2 is 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 tyre <NUM>. However, the tyre <NUM> according to the present invention is not limited to such an embodiment and may be used without specifying the mounting direction on a vehicle.

The first tread edge T1 and the second tread edge T2 are the axial outermost edges of the ground contacting patch of the tyre <NUM> which occurs under the condition such that the tyre <NUM> under a normal state is grounded on a plane by zero camber angles with <NUM>% of a standard tyre load.

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

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

As used herein, when a tyre is a pneumatic tyre based on a standard, the "standard tyre load" is a tyre load officially approved for each tyre by the standards organization in which the tyre is based, wherein the standard tyre 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 tyres for which various standards are not specified, "standard tyre load" refers to the maximum load that can be applied when using the tyre according to the above-mentioned standards.

The circumferential grooves <NUM> include a first shoulder circumferential groove <NUM> and a second shoulder circumferential groove <NUM>. Further, the circumferential grooves <NUM> include a first crown circumferential groove <NUM> and a second crown circumferential groove <NUM>, which are arranged between the first and second shoulder circumferential grooves <NUM> and <NUM>. The first shoulder circumferential groove <NUM> is located nearest to the first tread edge T1 among the circumferential grooves <NUM>. The second shoulder circumferential groove <NUM> is located nearest to the second tread edge T2 among the circumferential grooves <NUM>. The first crown circumferential groove <NUM> is located between the first shoulder circumferential groove <NUM> and the tyre equator C. The second crown circumferential groove <NUM> is located between the second shoulder circumferential groove <NUM> and the tyre equator C.

Preferably, a distance L1 in the tyre axial direction from the tyre equator C to the groove centerline of the first shoulder circumferential groove <NUM> or the second shoulder circumferential groove <NUM> is, for example, in a range from <NUM>% to <NUM>% of the tread width TW. Preferably, a distance L2 in the tyre axial direction from the tyre equator C to the groove centerline of the first crown circumferential groove <NUM> or the second crown circumferential groove <NUM> is, for example, in a range from <NUM>% to <NUM>% of the tread width TW. Note that the tread width TW is the distance from the first tread edge T1 to the second tread edge T2 in the tyre axial direction under the normal state.

In the present embodiment of the invention, the second shoulder circumferential groove <NUM>, the first crown circumferential groove <NUM>, and the second crown circumferential groove <NUM> each extend in a straight manner in parallel with the tyre circumferential direction. On the other hand, the first shoulder circumferential groove <NUM> has a zigzag groove edge on the tyre equator C side. However, each of the circumferential grooves <NUM> is not limited to such a shape.

The circumferential grooves <NUM> have a groove width W1 which is preferably equal to or more than <NUM>. In addition, the groove width W1 of the circumferential grooves <NUM>, for example, is preferably in a range from <NUM>% to <NUM>% of the tread width TW. A groove depth of the circumferential grooves <NUM> is in a range from <NUM> to <NUM> for passenger car tyres, for example.

The five land portions <NUM> according to the present embodiment of the invention include a crown land portion <NUM> located between the first tread edge T1 and the second tread edge T2. The crown land portion <NUM> is sectioned between the first crown circumferential groove <NUM> and the second crown circumferential groove <NUM> and thus is located on the tyre equator C. Further, the land portions <NUM> according to the present embodiment of the invention include a first middle land portion <NUM>, a second middle land portion <NUM>, a first shoulder land portion <NUM> and a second shoulder land portion <NUM>. The first middle land portion <NUM> is sectioned between the first shoulder circumferential groove <NUM> and the first crown circumferential groove <NUM>. The second middle land portion <NUM> is sectioned between the second shoulder circumferential groove <NUM> and the second crown circumferential groove <NUM>. The first shoulder land portion <NUM> includes the first tread edge T1 and is located outwardly in the tyre axial direction of the first shoulder circumferential groove <NUM>. The second shoulder land portion <NUM> includes the second tread edge T2 and is located outwardly in the tyre axial direction of the second shoulder circumferential groove <NUM>.

<FIG> illustrates an enlarged view of the crown land portion <NUM> of <FIG>. As illustrated in <FIG>, the crown land portion <NUM> includes a first longitudinal edge 15a extending in the tyre circumferential direction on a first tread edge T1 side, a second longitudinal edge 15b extending in the tyre circumferential direction on a second tread edge T2 side, and a ground contact surface <NUM> between the first longitudinal edge 15a and the second longitudinal edge 15b. In addition, the crown land portion <NUM> is provided with a plurality of first crown sipes <NUM>, a plurality of second crown sipes <NUM> and a plurality of third crown sipes <NUM>. Further, the crown land portion <NUM> according to the present embodiment of the invention is provided with a plurality of fourth crown sipes <NUM>.

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 <NUM> or less. Further, the main body portion means a portion in which two opposite inner walls extend substantially parallel to each other in the tyre radial direction. Here, "substantially parallel" means that the angle between two opposite inner walls is <NUM> 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> illustrates an enlarged view of one of the first crown sipes <NUM>, one of the second crown sipes <NUM>, one of the third crown sipes <NUM>, and one of the fourth crown sipes <NUM>. As illustrated in <FIG>, in the present invention, the first crown sipes <NUM> extend from the first longitudinal edge 15a and have closed end 41a in the ground contact surface <NUM>. The second crown sipes <NUM> extend from the second longitudinal edge 15b and have closed end 42a in the ground contact surface <NUM>. The third crown sipes <NUM> extend from the first longitudinal edge 15a and have closed end 43a in the ground contact surface <NUM>.

<FIG> illustrates a cross-sectional view taken along the line E-E of <FIG>, as an example of a sipe cross-sectional view. As illustrated in <FIG>, the first crown sipes <NUM>, the second crown sipes <NUM>, and the third crown sipes <NUM> open at the ground contact surface <NUM> via chamfer portions <NUM>. Each chamfer portion <NUM> includes an inclined surface <NUM> between the ground contact surface <NUM> and one of the sipe walls <NUM>. In the present embodiment of the invention, each of the sipes has two chamfer portions <NUM> which are inclined surfaces <NUM> connected to the respective sipe walls <NUM>. Each inclined surface <NUM> has a width Wb in a direction orthogonal to the longitudinal direction of the sipe. In the present embodiment of the invention, each inclined surface <NUM> is slightly curved in a direction convex outward in the tyre radial direction. The inclined surface <NUM> may, for example, be planar. In addition, each sipe has an opening width Wa at the ground contact surface <NUM>. 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 surfaces <NUM> on the ground contact surface <NUM> side to an end of the other one of the inclined surfaces <NUM> on the ground contact surface <NUM> side.

As illustrated in <FIG>, an opening width W6 at the ground contact surface <NUM> of each of the first crown sipes <NUM> is constant in the longitudinal direction of the sipe, and an opening width W7 at the ground contact surface <NUM> of each of the second crown sipes <NUM> is constant in the longitudinal direction of the sipe. On the other hand, an opening width at the ground contact surface <NUM> of each of the third crown sipes <NUM> decreases continuously from the first longitudinal edge 15a toward the closed end 43a. By adopting the above configuration, the tyre according to the present invention 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 tyre according to the present invention include the crown land portion <NUM> being 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 portion <NUM>. In addition, since these sipes open via the chamfer portions <NUM>, the ground pressure acting on the crown land portion <NUM> can be equalized by the chamfer portions <NUM>, which can be expected to improve the steering stability and on-snow performance.

Further, since the opening width at the ground contact surface <NUM> of each of the third crown sipes <NUM> decreases toward the closed end, an axial middle region of the crown land portion <NUM> has sufficient ground contact area, which can ensure the steering stability. By such a mechanism, the tyre <NUM> according to the present invention can exert excellent on-snow performance while maintaining the steering stability.

Hereinafter, a more detailed configuration of the present embodiment of the invention will be described. Note that each configuration described below shows a specific aspect of the present embodiment of the invention. Thus, the present invention can exert the above-mentioned effects even if the tyre does not include the configuration described below. Further, if any one of the configurations described below is applied independently to the tyre of the present invention 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 sipes <NUM> and the second crown sipes <NUM> are inclined with respect to the tyre axial direction in the same direction with each other. An angle of these sipes, for example, ranges from <NUM> to <NUM> degrees with respect to the tyre axial direction.

Preferably, the opening width W7 at the ground contact surface <NUM> of each of the second crown sipes <NUM> ranges from <NUM>% to <NUM>% of the opening width W6 at the ground contact surface <NUM> of each of the first crown sipes <NUM>, and in this embodiment of the invention, they are substantially the same with each other. Thus, uneven wear around the sipes can be suppressed.

The maximum opening width W8 at the ground contact surface <NUM> of each of the third crown sipes <NUM> is smaller than the opening width W6 at the ground contact surface <NUM> of each of the first crown sipes <NUM>. Specifically, the maximum opening width W8 of each of the third crown sipes <NUM> ranges from <NUM>% to <NUM>% of the opening width W6 of each of the first crown sipes <NUM>. In the third crown sipes <NUM> of the present embodiment of the invention, each chamfer portion is substantially eliminated at the closed end 43a, but each chamfer portion <NUM> is not limited to such an aspect, and one or more chamfer portions may have a chamfer width at the closed ends 43a. The same is true for the fourth crown sipes <NUM>.

The fourth crown sipes <NUM> extend from the second longitudinal edge 15b and have closed end 44a in the ground contact surface <NUM>. In a tread plan view, the fourth crown sipes <NUM> have a shape different from the first crown sipes <NUM> and the second crown sipes <NUM>. In the present embodiment of the invention, the fourth crown sipes <NUM> also open at the ground contact surface <NUM> via chamfer portions <NUM>. In addition, it is preferable that an opening width at the ground contact surface <NUM> of each of the fourth crown sipes <NUM> decreases continuously from the second longitudinal edge 15b toward the closed end 44a. This ensures sufficient ground contact area in a middle region of the crown land portion <NUM>, and thus the steering stability can be maintained.

An opening width W9 at the ground contact surface <NUM> of each of the fourth crown sipes <NUM> is smaller than the opening width W7 of each of the second crown sipes <NUM>. Specifically, the opening width W9 of the fourth crown sipes <NUM> ranges from <NUM>% to <NUM>% of the opening width W7 of the second crown sipes <NUM>. The fourth crown sipes <NUM> can help to enhance the balance between steering stability and on-snow performance.

As illustrated in <FIG>, in the present embodiment of the invention, a minimum distance L4 in the tyre circumferential direction between outer ends 41b on the first longitudinal edge 15a side of the first crown sipes <NUM> and outer ends 42b on the second longitudinal edge 15b side of the second crown sipes <NUM> is preferably equal to or less than <NUM>% of a circumferential arrangement pitch P1 (shown in <FIG>) of the first crown sipes <NUM>. 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 L6 in the tyre axial direction of the first crown sipes <NUM>, for example, ranges from <NUM>% to <NUM>% of a width W5 (shown in <FIG>) in the tyre axial direction of the ground contact surface <NUM> of the crown land portion <NUM>. Note that in this document, a length of a sipe is measured by the center line of the sipe.

Preferably, the second crown sipes <NUM> extend beyond the axial center in the tyre axial direction of the ground contact surface <NUM> of the crown land portion <NUM>. The second crown sipes <NUM> have closed ends 42a which are located on the first longitudinal edge 15a side with respect to the closed ends 41a of the first crown sipes <NUM>. Preferably, a length L7 in the tyre axial direction of the second crown sipes <NUM> is greater than a length L6 in the tyre axial direction of the first crown sipes <NUM>. Specifically, the length L7 of the second crown sipes <NUM> preferably ranges from <NUM>% to <NUM>% of the width W5 in the tyre axial direction of the ground contact surface <NUM> of the crown land portion <NUM>. The second crown sipes <NUM> as such can improve on-snow performance and wet performance while maintaining steering stability.

The third crown sipes <NUM> and the fourth crown sipes <NUM> are inclined with respect to the tyre axial direction in the same direction as the first crown sipes <NUM> and the second crown sipes <NUM>, and angles of these sipes range from <NUM> to <NUM> degrees with respect to the tyre axial direction, for example.

Preferably, a minimum distance L5 in the tyre circumferential direction between outer ends 43b on the first longitudinal edge 15a side of the third crown sipes <NUM> and outer ends 44b the second longitudinal edge 15b side of the fourth crown sipes <NUM> is equal to or less than <NUM>% of a circumferential arrangement pitch P2 (shown in <FIG>) of the third crown sipes <NUM>. This can improve wet performance further.

A length L8 in the tyre axial direction of the third crown sipes <NUM> is smaller than the length L7 of the second crown sipes <NUM> and the length L6 of the first crown sipes <NUM>. In addition, the closed ends 43a of the third crown sipes <NUM> are located on the first longitudinal edge 15a side with respect to the closed ends 44a of the fourth crown sipes <NUM>. In some more preferred embodiments of the invention, the closed ends 43a of the third crown sipes <NUM> are located on the second longitudinal edge 15b side with respect to the closed ends 42a of the second crown sipes <NUM>. The length L8 of the third crown sipes <NUM> ranges from <NUM>% to <NUM>% of the width W5 of the ground contact surface <NUM> of the crown land portion <NUM>. Such third crown sipes <NUM> can help to improve steering stability, on-snow performance, and wet performance in a well-balanced manner.

From a similar point of view, a length L9 in the tyre axial direction of the fourth crown sipes <NUM>, for example, is smaller than the length L7 of the second crown sipes <NUM> and the length L6 of the first crown sipes <NUM>. Specifically, the length L9 of the fourth crown sipes <NUM> preferably range from <NUM>% to <NUM>% of the width W5 of the ground contact surface <NUM> of the crown land portion <NUM>.

<FIG> illustrates an enlarged view of the first middle land portion <NUM>. As illustrated in <FIG>, the first middle land portion <NUM> includes a first longitudinal edge 13a extending in the tyre circumferential direction on the first tread edge T1 side, a second longitudinal edge 13b extending in the tyre circumferential direction on the second tread edge T2 side, and a ground contact surface <NUM> between the first longitudinal edge 13a and the second longitudinal edge 13b. In addition, the first middle land portion <NUM> is provided with a plurality of middle lateral grooves <NUM>. The middle lateral grooves <NUM>, for example, are inclined with respect to the tyre axial direction in the same direction as with the first crown sipes <NUM> (shown in <FIG>).

<FIG> illustrates an enlarged view of two middle lateral grooves <NUM>. Note that <FIG> is an enlarged view of a first middle lateral groove <NUM> and a second middle lateral groove <NUM>, which will be described later. As illustrated in <FIG>, at least one of the middle lateral grooves <NUM> includes a first groove portion <NUM> and a second groove portion <NUM>. The first groove portion <NUM> extends in the tyre axial direction from the first longitudinal edge 13a. The second groove portion <NUM> extends in the tyre axial direction from the second longitudinal edge 13b.

In the present embodiment of the invention, the first groove portion <NUM> and the second groove portion <NUM> are displaced in the tyre circumferential direction to form a pair of circumferential groove edges 28e extending in the tyre circumferential direction between groove edges 26e of the first groove portion <NUM> and groove edges 27e of the second groove portion <NUM>. In addition, the maximum groove depth of the first groove portion <NUM> is different from the maximum groove depth of the second groove portion <NUM>. When driving on snow, the middle lateral grooves <NUM> can 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 portion <NUM> and the second groove portion <NUM> are different, the shallower groove portion can maintain the rigidity of the first middle land portion <NUM> to 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 edges 28e described above can provides frictional force in the tyre axial direction and help to improve cornering performance on snow. Furthermore, the combination of the circumferential groove edges 28e, the first groove portions <NUM> and the second groove portions <NUM> allows snow entering the deeper groove portions to be pushed more strongly in the tyre axial direction and exerts greater snow-column shear force.

As illustrated in <FIG> and <FIG>, in the present embodiment of the invention, each of the middle lateral grooves <NUM> has the above-mentioned structure. In a tread plan view. the first groove portions <NUM> and the second groove portions <NUM> extend in the tyre axial direction with a constant groove width W3 (shown in <FIG>). The groove width W3 of the first groove portions <NUM> and the second groove portions <NUM>, for example, ranges from <NUM>% to <NUM>% of a width W2 (shown in <FIG>) in the tyre axial direction of the ground contact surface <NUM> of the first middle land portion <NUM>. An angle of the first groove portions <NUM> and the second groove portions <NUM> ranges from <NUM> to <NUM> degrees with respect to the tyre axial direction, for example.

The middle lateral grooves <NUM>, for example, include a plurality of the first middle lateral grooves <NUM> and a plurality of the second middle lateral grooves <NUM> which have different distribution of groove depths from one another. The first middle lateral grooves <NUM> and the second middle lateral grooves <NUM> are arranged alternately in the tyre circumferential direction.

<FIG> illustrates a cross-sectional view taken along the line A-A of <FIG>. <FIG> is a cross-sectional view of one of the first middle lateral grooves <NUM> along a groove longitudinal direction thereof. <FIG> illustrates a cross-sectional view taken along the line B-B of <FIG>. <FIG> is a cross-sectional view of one of the second middle lateral grooves <NUM> along a groove longitudinal direction thereof. As illustrated in <FIG> and <FIG>, in the present embodiment of the invention, the first groove portions <NUM> and the second groove portions <NUM> of the first middle lateral grooves <NUM> and the first groove portions <NUM> and the second groove portions <NUM> of the second middle lateral grooves <NUM> extend in the groove longitudinal direction with respective constant groove depths.

As illustrated in <FIG>, in each first middle lateral groove <NUM>, the maximum groove depth d1 of the first groove portion <NUM> is smaller than the maximum groove depth d2 of the second groove portion <NUM>. In each of the first middle lateral grooves <NUM>, the groove depth d2 of the second groove portion <NUM>, for example, ranges from <NUM>% to <NUM>% of a groove depth dc of the first crown circumferential groove <NUM>. Further, in each of the first middle lateral grooves <NUM>, the groove depth d1 of the first groove portion <NUM> ranges from <NUM>% to <NUM>% of the groove depth dc of the first crown circumferential groove <NUM>. Preferably, the groove depth d1 of the first groove portion <NUM> ranges from <NUM>% to <NUM>% of the groove depth d2 of the second groove portion <NUM>.

As illustrated in <FIG>, the second middle lateral groove <NUM> has substantially the inverted shape of the first middle lateral groove <NUM>. That is, in each of the second middle lateral grooves <NUM>, the maximum groove depth d1 of the first groove portion <NUM> is greater than the maximum groove depth d2 of the second groove portion <NUM>. In each of the second middle lateral grooves <NUM>, the groove depth d1 of the first groove portion <NUM>, for example, ranges from <NUM>% to <NUM>% of the groove depth dc of the first crown circumferential groove <NUM>. Further, in each of the second middle lateral grooves <NUM>, the groove depth d2 of the second groove portion <NUM> ranges from <NUM>% to <NUM>% of the groove depth dc of the first crown circumferential groove <NUM>. Preferably, the groove depth d2 of the second groove portion <NUM> ranges from <NUM>% to <NUM>% of the groove depth d1 of the first groove portion <NUM>.

In the present embodiment of the invention, since the first middle lateral grooves <NUM> and the second middle lateral grooves <NUM> are provided alternately in the tyre circumferential direction, the steering stability and on-snow performance can be improved in a well-balanced manner.

<FIG> illustrates a cross-sectional view taken along the line C-C of <FIG>. <FIG> is a cross-sectional view of the second groove portion <NUM> of each of the first middle lateral grooves <NUM>, or the first groove portion <NUM> of each of the second middle lateral grooves <NUM> (hereinafter, sometimes referred to collectively as deep groove portion <NUM>). <FIG> illustrates a cross-sectional view take along the line D-D of <FIG>. <FIG> is a cross-sectional view of the first groove portion <NUM> of each of the first middle lateral grooves <NUM>, or the second groove portion <NUM> of each of the second middle lateral grooves <NUM> (hereinafter, sometimes referred to collectively as shallow groove portion <NUM>).

As illustrated in <FIG>, the deep groove portion <NUM> and the shallow groove portion <NUM> preferably open at the ground contact surface via chamfer portions <NUM>. Each chamfer portion <NUM> includes an inclined surface <NUM> between the ground contact surface and one of the groove walls. In the present embodiment of the invention, each inclined surface <NUM> is slightly curved in a direction convex outward in the tyre radial direction. The inclined surface <NUM> may, for example, be planar. Such a chamfer portion <NUM> can help to equalize the ground pressure acting on the ground contact surface <NUM> to improve uneven wear resistance.

As illustrated in <FIG>, the deep groove portion <NUM>, for example, is configured to include a flat groove bottom 37d. On the other hand, as illustrated in <FIG>, the shallow groove portion <NUM> includes a groove bottom 36d which is provided with a groove bottom sipe <NUM> extending inwardly in the tyre radial direction. Such a groove bottom sipe <NUM> can facilitate the opening of the shallow groove portion <NUM> appropriately and help to improve on-snow performance. Note that the above-mentioned depths d1 and d2 of the first groove portion <NUM> of the first middle lateral grooves <NUM> and the second groove portion <NUM> of the second middle lateral grooves <NUM>, respectively, mean a depth without including the groove bottom sipe <NUM>. In addition, in <FIG> and <FIG>, the groove bottom sipes <NUM> are not illustrated. In some preferred embodiments of the invention, a total depth from the ground contact surface to a bottom of the groove bottom sipe <NUM> is smaller than a depth of the deep groove portion <NUM>. This can improve the balance between steering stability and on-snow performance.

In the present embodiment of the invention as illustrated in <FIG>, each of the pair of groove edges of each middle lateral groove <NUM> includes a circumferential groove edge 28e. Each circumferential groove edge 28e, for example, is located in the central area when the ground contact surface <NUM> of the first middle land portion <NUM> is divided into three equal portions in the tyre axial direction. In the present embodiment of the invention, a pair of circumferential groove edges 28e are positioned such that the axial center position of the ground contact surface <NUM> of the first middle land portion <NUM> is located therebetween. In addition, the pair of circumferential groove edges 28e extends along the tyre circumferential direction, preferably extending in parallel with the tyre circumferential direction. For example, an angle of the pair of circumferential groove edges 28e is preferably equal to or less than <NUM> degrees, more preferably equal to or less than <NUM> degrees with respect to the tyre circumferential direction. Preferably, a length L3 in the tyre circumferential direction of the pair of circumferential groove edges 28e is smaller than the maximum width of the first groove portion <NUM> and the second groove portion <NUM>. Specifically, the length L3 ranges from <NUM>% to <NUM>% of the maximum groove width. Such a pair of circumferential groove edges 28e can improve cornering performance when driving on snow, while suppressing uneven wear of the land portion.

Each of the middle lateral grooves <NUM> includes a circumferential groove portion <NUM> arranged between the first groove portion <NUM> and the second groove portion <NUM>. In the present embodiment of the invention, the area between one of the pair of circumferential groove edges 28e and its imaginary extension line extending in the longitudinal direction and the other one of the pair of circumferential groove edges 28e and its imaginary extension line extending in the longitudinal direction is configured as the circumferential groove portion <NUM>, for example.

As illustrated in <FIG> and <FIG>, the maximum groove depth d3 of the circumferential groove portions <NUM> is smaller than the maximum groove depth d1 of the first groove portions <NUM> and the maximum groove depth d2 of the second groove portions <NUM>. Specifically, the maximum groove depth d3 of the circumferential groove portions <NUM> ranges from <NUM>% to <NUM>% of the groove depth dc of the first crown circumferential groove <NUM>. The circumferential groove portions <NUM> can increase the rigidity of a middle region of the first middle land portion <NUM> and improve uneven wear resistance.

As illustrated in <FIG>, it is preferable that the first middle land portion <NUM> is provided with at least one circumferential sipe <NUM> extending in the tyre circumferential direction. In the present embodiment of the invention, the first middle land portion <NUM> is provided with a plurality of circumferential sipes <NUM> spaced in the tyre circumferential direction. In addition, each circumferential sipe <NUM> according to the present embodiment of the invention extends from the ground contact surface <NUM> of the first middle land portion <NUM> to a bottom thereof with a constant sipe width. The circumferential sipes <NUM> can provide a large frictional force in the tyre axial direction when driving on wet or snow.

Preferably, each circumferential sipe <NUM>, for example, is located in the central area when the ground contact surface <NUM> of the first middle land portion <NUM> is divided into three equal portions in the tyre axial direction. An angle of each circumferential sipe <NUM> with respect to the tyre circumferential direction is, for example, equal to or less than <NUM> degrees, preferably equal to or less than <NUM> degrees. Such a circumferential sipe <NUM> can provide a large frictional force in the tyre axial direction when driving on snow.

The circumferential sipes <NUM>, for example, extend across some middle lateral grooves <NUM> in the tyre circumferential direction. In some preferred embodiments of the invention, the circumferential sipes <NUM> are arranged to extend across the respective first middle lateral grooves <NUM> but not to be communicated with the second middle lateral grooves <NUM>. More specifically, the circumferential sipes <NUM> extend across the respective circumferential groove portions <NUM> of the first middle lateral grooves <NUM>. Thus, at the groove bottoms of the circumferential groove portions <NUM>, the circumferential sipes <NUM> are formed as the groove bottom sipes. On the other hand, the second middle lateral grooves <NUM> do 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 in <FIG>, the first middle land portion <NUM> is further provided with a plurality of the first middle sipes <NUM> and a plurality of second middle sipes <NUM>. The first middle sipes <NUM> extend from the first longitudinal edge 13a and are in communication with the respective circumferential sipes <NUM>. The second middle sipes <NUM> extend from the second longitudinal edge 13b and are in communication with the respective circumferential sipes <NUM>. In some preferred embodiments of the invention, ends of the first middle sipes <NUM> in the ground contact surface <NUM> are connected to ends 31a on a first side in the tyre circumferential direction of the respective circumferential sipes <NUM>. Ends 32a of the second middle sipes <NUM> in the ground contact surface <NUM> are connected to ends on a second side in the tyre circumferential direction of the respective circumferential sipes <NUM>. The first middle sipes <NUM> and the second middle sipes <NUM> work together with the circumferential sipe <NUM> to provide multi-directional frictional force, further improving on-snow performance.

The first middle sipes <NUM> and the second middle sipes <NUM>, for example, are inclined with respect to the tyre axial direction in the same direction as the middle lateral grooves <NUM>. An angle of these sipes with respect to the tyre axial direction, for example, ranges from <NUM> to <NUM> degrees. In some preferred embodiments of the invention, an angle between the first middle sipes <NUM> and the circumferential sipes <NUM> is an acute angle. Similarly, an angle between the second middle sipes <NUM> and the circumferential sipes <NUM> is 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 sipes <NUM> and the second middle sipes <NUM> open at the ground contact surface <NUM> via chamfer portions <NUM>. The configuration of the chamfer portions <NUM> of crown sipes (shown in <FIG>) can be applied to the chamfer portions <NUM> of these sipes, and thus the details of the chamfer portions <NUM> will not be described here. The chamfer portions <NUM> can help to equalize the ground pressure acting on the ground contact surface <NUM> and to improve the steering and uneven wear resistance.

As illustrated in <FIG>, it is preferable that each of the first middle sipes <NUM> has an opening width at the ground contact surface <NUM>, and the opening width decreases toward the circumferential sipe <NUM>. Similarly, it is preferable that each of the second middle sipes <NUM> has an opening width at the ground contact surface <NUM>, and the opening width decrease toward the circumferential sipe <NUM>. This ensures the ground contact area in a middle region of the first middle land portion <NUM> and maintains the steering stability.

<FIG> illustrates an enlarged view of the second middle land portion <NUM>. As illustrated in <FIG>, the second middle land portion <NUM> is provided with third middle lateral grooves <NUM> and fourth middle lateral grooves <NUM> which are arranged alternately in the tyre circumferential direction. The third middle lateral grooves <NUM> and the fourth middle lateral grooves <NUM> have the same shape in a tread plan view, and extend across the second middle land portion <NUM> entirely in the tyre axial direction. In addition, the third middle lateral grooves <NUM> and the fourth middle lateral grooves <NUM> are inclined with respect to the tyre axial direction in the same direction as the middle lateral grooves <NUM> (shown in <FIG>). An angle of the third middle lateral grooves <NUM> and the fourth middle lateral grooves <NUM> with respect to the tyre axial direction is smaller than an angle of the middle lateral grooves <NUM> (shown in <FIG>) with respect to the tyre axial direction and an angle of the sipes provided on the crown land portion <NUM> (shown in <FIG>) with respect to the tyre axial direction. Specifically, an angle of the third middle lateral grooves <NUM> and the fourth middle lateral grooves <NUM> with respect to the tyre axial direction, for example, ranges from <NUM> to <NUM> degrees. On the other hand, the third middle lateral grooves <NUM> and the fourth middle lateral grooves <NUM> differ in their internal configuration.

<FIG> illustrates a cross-sectional view taken along the line F-F of <FIG>. As illustrated in <FIG>, the third middle lateral grooves <NUM> each have a shallow groove portion <NUM> on the second crown circumferential groove <NUM> side and a deep groove portion <NUM> on the second shoulder circumferential groove <NUM> side. <FIG> illustrates a cross-sectional view taken along the line G-G of <FIG>. As illustrated in <FIG>, the fourth middle lateral groove <NUM> have substantially the inverted shape of the third middle lateral grooves <NUM>. That is, the fourth middle lateral grooves <NUM> each have a deep groove portion <NUM> on the second crown circumferential groove <NUM> side and a shallow groove portion <NUM> on the second shoulder circumferential groove <NUM> side. In this embodiment of the invention, the third middle lateral grooves <NUM> and the fourth middle lateral grooves <NUM> are provided alternately in the tyre circumferential direction, which improve the uneven wear resistance and the steering stability.

For the shallow groove portions <NUM> of the third middle lateral grooves <NUM> and the fourth middle lateral grooves <NUM>, the shallow groove portions <NUM> of the middle lateral grooves <NUM> (shown in <FIG>) of the middle lateral grooves <NUM> described above can be applied to the shallow groove portions <NUM> of the third middle lateral grooves <NUM> and the fourth middle lateral grooves <NUM>. Similarly, for the deep groove portions <NUM> of the third middle lateral grooves <NUM> and the fourth middle lateral grooves <NUM>, the deep groove portions <NUM> of the middle lateral grooves <NUM> (shown in <FIG>) of the middle lateral grooves <NUM> described above can be applied to the deep groove portions <NUM> of the third middle lateral grooves <NUM> and the fourth middle lateral grooves <NUM>.

As illustrated in <FIG>, the second middle land portion <NUM> is provided with a plurality of middle sipe groups <NUM> each of which includes a plurality of bent sipes <NUM> arranged in the tyre axial direction. The middle sipe groups <NUM> are spaced in the tyre circumferential direction. In the present embodiment of the invention, each middle sipe group <NUM> is configured such that the plurality of bent sipes <NUM> is arranged so as to overlap partially in the tyre axial direction with each other. The bent sipes <NUM> each include a convex part on one side or the other in the tyre circumferential direction. The middle sipe groups <NUM> are 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.

The second middle land portion <NUM> is shown in <FIG>. <FIG> illustrates an enlarged view of the second middle land portion <NUM> in accordance with another embodiment of the present invention. As illustrated in <FIG>, the second middle land portion <NUM> is provided with a plurality of third middle sipes <NUM> and a plurality of fourth middle sipes <NUM> in addition to the above-mentioned third middle lateral grooves <NUM> and the fourth middle lateral grooves <NUM>. The third middle sipes <NUM> extend from the second crown circumferential groove <NUM> and have closed ends in the ground contact surface of the second middle land portion <NUM>. The fourth middle sipes <NUM> extend from the second shoulder circumferential grooves <NUM> and have closed end in the ground contact surface. The third middle sipes <NUM> and the fourth middle sipes <NUM>, for example, are inclined with respect to the tyre axial direction in the same direction as the third middle lateral grooves <NUM> and the fourth middle lateral grooves <NUM>. An angle of these sipes, for example, ranges from <NUM> to <NUM> degrees with respect to the tyre axial direction. The structure of the above-mentioned first middle sipes <NUM> and second middle sipes <NUM> can be applied to the third middle sipes <NUM> and the fourth middle sipes <NUM>.

In yet another embodiment of the invention of the second middle land portion <NUM>, for example, in a region between the third middle lateral groove <NUM> and the fourth middle lateral groove <NUM> which are adjacent to each other in the circumferential direction of the tyre, at least one middle sipe group <NUM> described above (shown in <FIG>), at least one third middle sipe <NUM> and at least one fourth middle sipe <NUM> shown in <FIG> may be arranged (not illustrated). Such a sipe arrangement can help to further enhance on-snow performance.

As illustrated in <FIG>, the first shoulder land portion <NUM> is provided with a plurality of first shoulder lateral grooves <NUM> and a plurality of first shoulder sipes <NUM>. The first shoulder lateral grooves <NUM> and the first shoulder sipes <NUM> extend, for example, from the first shoulder circumferential groove <NUM> to at least the first tread edge T1. In addition, the second shoulder land portion <NUM> is provided with a plurality of second shoulder lateral grooves <NUM> and a plurality of shoulder sipe groups <NUM> each of which includes a plurality of bent sipes <NUM> arranged in the tyre axial direction. The shoulder sipe groups <NUM> have substantially the same configuration as the middle sipe groups <NUM> described above. These grooves and sipes can help to further improve on-snow performance.

Although the tyre according to one or more embodiments of the present invention has been described in detail above, the present invention is not limited to the specific embodiments described above, and can be embodied in various ways within the scope of the appended claims.

As Example, pneumatic tyres of size <NUM>/40ZR18 with the basic pattern of <FIG> were prepared. As Comparative Example <NUM>, tyres each having the crown land portion "a" shown in <FIG> were 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 tyres of Comparative Example <NUM> have substantially the same configuration as the tyres 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 <NUM> and Example. The common specifications and test methods of each test tyre are as follows.

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 <NUM>, where the steering stability of Comparative Example <NUM> is set to <NUM>, 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 <NUM>, where the on-snow performance of Comparative Example <NUM> is set to <NUM>, and the higher the score, the better the on-snow performance.

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

Pneumatic tyres of size <NUM>/40ZR18 were prepared as Comparative Example <NUM>, Reference Example and Example. Reference Example has a crown land portion <NUM> shown in <FIG>. The crown land portion <NUM> shown in <FIG> includes features of the embodiment of the invention shown in <FIG>, and the minimum distance L4 in the tyre circumferential direction between the outer ends 41b of the first crown sipes <NUM> and the outer ends 42b of the second crown sipes <NUM> is about <NUM>% of the circumferential arrangement pitch of the first crown sipes. Each tyre of Example has the crown land portion <NUM> shown in <FIG>, and the distance is about <NUM>% of the circumferential arrangement pitch P1.

On the other hand, the tyres of Comparative Example <NUM> each has the crown land portion "d" shown in <FIG>. The crown land portion "d" is such that the minimum distance L4 in the tyre circumferential direction between the outer ends of the first crown sipes "e" and the outer ends of the second crown sipes "f" is about <NUM>% of the circumferential arrangement pitch P1. The crown land portion of Comparative Example <NUM> is substantially the same as the crown land portion <NUM> of Reference Example and Example, except for the items mentioned above. In addition, Comparative Example <NUM>, Reference Example and Example have the basic pattern shown in <FIG>, except for the configuration of the crown land portion described above, and have substantially the same configuration.

Comparative Example <NUM>, 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 tyre are described above.

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

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 <NUM> being <NUM>, and the larger the number, the better the wet performance.

Claim 1:
A tyre (<NUM>) comprising:
a tread portion (<NUM>) comprising a first tread edge (T1), a second tread edge (T2), and a crown land portion (<NUM>) arranged between the first tread edge (T1) and the second tread edge (T2), wherein
the crown land portion (<NUM>) comprises a first longitudinal edge (15a) extending in a tyre circumferential direction on a first tread edge (T1) side, a second longitudinal edge (15b) extending in the tyre circumferential direction on a second tread edge (T2) side, and a ground contact surface (<NUM>) between the first longitudinal edge (15a) and the second longitudinal edge (15b),
the crown land portion (<NUM>) is provided with a plurality of first crown sipes (<NUM>) and a plurality of second crown sipes (<NUM>),
the first crown sipes (<NUM>) and the second crown sipes (<NUM>) open at the ground contact surface (<NUM>) via chamfer portions (<NUM>),
the first crown sipes (<NUM>) extend from the first longitudinal edge (15a) and have closed ends (41a) in the ground contact surface (<NUM>),
the second crown sipes (<NUM>) extend from the second longitudinal edge (15b) and have closed ends (42a) in the ground contact surface (<NUM>),
characterized in that
the crown land portion (<NUM>) is furthermore provided with a plurality of third crown sipes (<NUM>), wherein
the third crown sipes (<NUM>) open at the ground contact surface (<NUM>) via chamfer portions (<NUM>),
the third crown sipes (<NUM>) extend from the first longitudinal edge (15a) and have closed ends (43a) in the ground contact surface (<NUM>),
each of the first crown sipes (<NUM>) has an opening width (W6) at the ground contact surface (<NUM>) which is constant in a longitudinal direction of the sipe (<NUM>),
each of the second crown sipes (<NUM>) has an opening width (W7) at the ground contact surface (<NUM>) which is constant in a longitudinal direction of the sipe (<NUM>), and
each of the third crown sipes (<NUM>) has an opening width (W8) which decreases continuously from the first longitudinal edge (15a) toward the closed end thereof.