Patent Description:
<CIT> has proposed a tyre that includes a main groove extending continuously in the tyre circumferential direction with a groove bottom provided with a plurality of protrusions. The tyre is expected to improve traction performance and braking performance on snow by forming a snow column in the main groove and making the protrusions bite into the snow column when running on snow.

<CIT> discloses a tyre in accordance with the preamble of claim <NUM>. Other related tyres are disclosed, for example, in <CIT> and <CIT>.

In recent years, the performance required for tyres on snow has been increasing. On the other hand, it is necessary to consider steering stability of tyres on dry roads.

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

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, 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 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, 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. Further, in this specification, unless otherwise specified, known methods can be appropriately applied to the methods for measuring the dimensions and composition of materials.

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 "Tire 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 crown circumferential groove <NUM>. The first crown circumferential groove <NUM> is located on the first tread edge T1 side with respect to the tyre equator C. Further, in the present embodiment, the circumferential grooves <NUM> include a second crown circumferential groove <NUM>, a first shoulder circumferential groove <NUM> and a second shoulder circumferential groove <NUM>. The second crown circumferential groove <NUM> is located on the second tread edge T2 side with respect to the tyre equator C. The first shoulder circumferential groove <NUM> is located between the first crown circumferential groove <NUM> and the first tread edge T1. The second shoulder circumferential groove <NUM> is located between the second crown circumferential groove <NUM> and the second tread edge T2.

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, the first crown circumferential groove <NUM>, the second crown circumferential groove <NUM> and the second shoulder 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.

In the present embodiment, the land portions <NUM> include a crown land portion <NUM>. The crown land portion <NUM> is sectioned between the first crown circumferential groove <NUM> and the second crown circumferential groove <NUM> and is located on the tyre equator C. Thus, the first crown circumferential groove <NUM> is adjacent to the crown land portion <NUM> on the first tread edge T1 side. Further, the land portions <NUM> according to the present embodiment 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>, the first middle land portion <NUM> and the first crown circumferential groove <NUM>. <FIG> illustrates an enlarged perspective view of a groove bottom 7d of the first crown circumferential groove <NUM>. As illustrated in <FIG> and <FIG>, the groove bottom 7d of the first crown circumferential groove <NUM> is provided with a plurality of protrusions <NUM> projecting in the tyre radial direction. In <FIG>, the outlines of the protrusions <NUM> that can be observed in a tread plan view is conceptually shown as a solid line, but in <FIG>, these outlines are omitted. The specific configuration of the protrusions <NUM> will be described later.

As illustrated in <FIG>, no drainage grooves are provided on the crown land portion <NUM>. As used herein, "drainage groove" is a groove that can provide substantial drainage effect and whose opening width at the ground contact surface of the tread portion exceeds <NUM>. Further, "drainage groove" is a groove that has a depth (the length in the tyre radial direction) exceeds <NUM> of the area where the distance between two opposite groove walls exceeds <NUM>. On the other hand, the crown land portion <NUM> has a plurality of sipes <NUM>.

As used herein, "sipe" means a groove-shaped body (a longitudinal recess, including a groove and a sipe) having a small width, and a main body portion thereof has 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. In some preferred embodiments, the main body potion has a width, for example, in a range from <NUM> to <NUM>. As will be described later, the sipe may be provided with one or more chamfered portions. Alternatively, the sipe may have a so-called flask bottom with an increased width at the bottom.

The tyre according to the present invention can exhibit excellent on-snow performance while maintaining steering stability on dry roads (hereinafter, simply referred to as "steering stability") by adopting the above configuration. The following mechanism can be inferred as the reason for this.

The tyre <NUM> according to the present invention can exhibit a large reaction force by making the protrusions <NUM> bite into the snow column formed in the first crown circumferential groove <NUM> when driving on snow and can exhibits excellent traction performance and braking performance on snow.

On the other hand, the crown land portion <NUM> has no drainage grooves as mentioned above. This makes the crown land portion <NUM> have high rigidity, and when it is grounded on snow, the snow column in the first crown circumferential groove <NUM> adjacent to the crown land portion <NUM> can be strongly pressed and solidified, and the reaction force can be further increased. In addition, the crown land portion <NUM> can help to maintain the steering stability on dry roads. Furthermore, the crown land portion <NUM> is provided with sipes <NUM>, which can improve on-snow performance. By these mechanisms, the tyre <NUM> according to the present invention can maintain the steering stability and can exert excellent on-snow performance.

Hereinafter, a more detailed configuration of the present embodiment will be described. Note that each configuration described below shows a specific aspect of the present embodiment. Thus, the present 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.

As illustrated in <FIG>, the first crown circumferential groove <NUM> includes a first groove wall 7a and a second groove wall 7b. The first groove wall 7a is the groove wall on the crown land portion <NUM> side, and the second groove wall 7b is the groove wall on the first middle land portion <NUM> side. The protrusions <NUM> include a plurality of first protrusions <NUM> arranged on the first groove wall 7a side and a plurality of second protrusions <NUM> arranged on the second groove wall 7b side. The first protrusions <NUM> and the second protrusions <NUM> have substantially the same configuration, except that they are arranged in different directions. The first protrusions <NUM> are arranged at a constant pitch P1 in the tyre circumferential direction. Similarly, the second protrusions <NUM> are arranged at a constant pitch P1 in the tyre circumferential direction.

Each of the protrusions <NUM> has a longitudinally elongated shape with a maximum width W3 in the tyre axial direction and a length L3 in the tyre circumferential direction that is greater than the width W3. For example, in each protrusion <NUM>, the width W3 in the tyre axial direction ranges from <NUM>% to <NUM>% of the maximum groove width W2 of the first crown circumferential groove <NUM>. If, as in the present embodiment, the first crown circumferential groove <NUM> includes the first protrusions <NUM> and the second protrusions <NUM>, each protrusion <NUM> has a width W3 ranging from <NUM>% to <NUM>% of the groove width W2, preferably <NUM>% to <NUM>%.

For example, the length L3 of each protrusion <NUM> ranges from <NUM>% to <NUM>% of the circumferential pitch P1 of the protrusions <NUM>. Further, the circumferential length L3 of each protrusion <NUM> ranges from <NUM> to <NUM> times the width W3 of the protrusion <NUM>, for example. These protrusions <NUM> have sufficient rigidity in the tyre circumferential direction and can provide a large reaction force when shearing the snow column in the first crown circumferential groove <NUM> during driving on snow.

<FIG> illustrates an enlarged cross-sectional view of one protrusion <NUM> along a longitudinal direction of the first crown circumferential groove <NUM>. As illustrated in <FIG>, the maximum height h1 in the tyre radial direction of the protrusions <NUM> is, for example, equal to or less than <NUM>%, preferably from <NUM>% to <NUM>%, of the maximum groove depth d1 of the first crown circumferential groove <NUM>. The protrusions <NUM> as such can exert the above-mentioned effect while maintaining the drainage of the first crown circumferential groove <NUM>.

Each protrusion <NUM> includes a first surface <NUM> facing one side in the tyre circumferential direction and extending in the tyre radial direction, and a second surface <NUM> located on the opposite side of the first surface <NUM>. An angle θ1 of the first surface <NUM> with respect to the tyre radial direction is, for example, equal to or less than <NUM> degrees, preferably equal to or less than <NUM> degrees. The second surface <NUM> is connected to the first surface <NUM> by a ridge line <NUM>, for example, and extends from the ridge line <NUM> to the groove bottom 7d of the first crown circumferential groove <NUM> at a gradual slope. The second surface <NUM> in the present embodiment, for example, is slightly curved in the direction convex toward outwardly in the tyre radial direction, but it can also be a plane. As used herein, "ridge line" means a connection formed by two surfaces with different extension directions and having a longitudinal direction. Further, "ridge line" also includes those having a substantial width by constituting a micro-curved surface in its transverse section.

The second surface <NUM> has an angle with respect to the tyre radial direction larger than that of the first surface <NUM>. At an end of the second surface <NUM> on the groove bottom 7d side, an angle θ2 of the second surface <NUM> with respect to the tyre radial direction is, for example, equal to or more than <NUM> degrees, preferably from <NUM> to <NUM> degrees. The protrusions <NUM> including the first surfaces <NUM> and the second surfaces <NUM> can exert a large reaction force when the first surfaces <NUM> push the snow column away when driving on snow.

As illustrated in <FIG> and <FIG>, each protrusion <NUM> includes a tapered portion <NUM> whose width in the tyre axial direction decreases in the tyre circumferential direction. Such tapered portions <NUM> can help to suppress the decrease in groove volume of the first crown circumferential groove <NUM> due to the protrusions <NUM>, maintaining wet performance. In addition, when driving on a dry road, the air passing through the first crown circumferential groove <NUM> may be disturbed by the first surfaces <NUM> and be encouraged to move in the circumferential direction by the tapered portions <NUM>. Such an action can suppress the generation of stationary waves in the first crown circumferential groove <NUM> and can help to reduce the air column resonance.

As illustrated in <FIG>, in a tread plan view, each tapered portion <NUM> is formed between a first side surface <NUM> extending along the tyre circumferential direction and a second side surface <NUM> inclined at a larger angle than that of the first side surface <NUM> with respect to the tyre circumferential direction. The first side surface <NUM> and the second side surface <NUM>, for example, are connected to the second surface <NUM> via respective ridge lines and extend in the tyre radial direction. Further, the first side surface <NUM> and the second side surface <NUM> are connected to the first surface <NUM> via respective ridge lines that extend in the tyre radial direction. In the present embodiment, the first side surface <NUM> is located on a groove centerline side of the first crown circumferential groove <NUM> with respect to the second side surface <NUM>. Thus, the region of the first surface <NUM> on the groove centerline side is less likely to deform in the tyre circumferential direction, and the above effects can be further improved.

In a tread plan view, an angle θ3 between the first side surface <NUM> and the second side surface <NUM> is, for example, equal to or less than <NUM> degrees, preferably ranging from <NUM> to <NUM> degrees. The first side surface <NUM> and the second side surface <NUM>, which are arranged at such an angle, can help to improve on-snow performance, as well as to improve wet performance and noise performance in a well-balanced manner. Note that the angle <NUM> is defined as the maximum angle between the ridge line formed between the first side surface <NUM> and the second surface <NUM> and the ridge line formed between the second side surface <NUM> and the second surface <NUM>.

As illustrated in <FIG> and <FIG>, in a tread plan view, the first protrusions <NUM> are oriented such that the second protrusions <NUM> are rotated by <NUM> degrees. The width of the tapered portion <NUM> of each first protrusion <NUM> becomes smaller toward a first direction R1 in the tyre circumferential direction to form a tip end. Further, the first surface <NUM> of each first protrusion <NUM> faces the second side R2 that is opposite to the first direction R1 in the tyre circumferential direction. The second surface <NUM> of each first protrusion <NUM> is connected to the first surface <NUM> on the first direction R1 side.

On the other hand, the width of the tapered portion <NUM> of each second protrusion <NUM> becomes smaller toward the second direction R2 to form a tip end. The first surface <NUM> of each second protrusion <NUM> faces the first direction R1. The second surface <NUM> of each second protrusion <NUM> is connected to the first surface <NUM> on the second direction R2 side. Further, in the present embodiment, tip ends of the tapered portions <NUM> of the plurality of first protrusions <NUM> are in contact with respective tip ends of the tapered portions <NUM> of the plurality of second protrusions <NUM>. By such an arrangement of the first protrusions <NUM> and the second protrusions <NUM>, in the case where the protrusions <NUM> shear the snow pillars compressed in the first crown circumferential groove <NUM> in the tyre circumferential direction when driving on snow, the first protrusions <NUM> can provide a large reaction force on one side in the tyre circumferential direction, and the second protrusions <NUM> can provide a large reaction force on the other side in the tyre circumferential direction. Thus, traction performance and braking performance on snow can be improved in a well-balanced manner.

In some preferred embodiments, the first protrusions <NUM> and the second protrusions <NUM> are staggered in the tyre circumferential direction. Specifically, in a tread plan view as illustrated in <FIG>, respective lengths of overlap between imaginary areas in which the first protrusions <NUM> are extended in parallel with the tyre axial direction and the respective second protrusions <NUM> are equal to or less than <NUM>% of the respective lengths of the second protrusions <NUM> in the tyre circumferential direction, more preferably equal to or less than <NUM>%. In some more preferred embodiments, the imaginary areas and the respective second protrusions <NUM> do not overlap with each other in the tyre circumferential direction. This arrangement of the protrusions <NUM> can prevent snow from clogging in the first crown circumferential groove <NUM> when driving on snow, and help to sustain excellent snow performance.

In the present embodiment, the above-mentioned protrusions <NUM> are provided on only the first crown circumferential groove <NUM>. That is, the second crown circumferential crown groove <NUM> (shown in <FIG>) preferably has a flat groove bottom where no protrusions are provided. Similarly, the groove bottoms of the first shoulder circumferential groove <NUM> and the second shoulder circumferential groove <NUM> (shown in <FIG>) preferably have a flat shape without having the protrusions <NUM> described above. This structure may improve wet performance of the tyre. Alternatively, the present invention is not limited to such an embodiment, and from the viewpoint of further improving on-snow performance, the protrusions <NUM> described above may be provided in the circumferential grooves <NUM> other than the first crown circumferential groove <NUM> in order to further improve on-snow performance.

As illustrated in <FIG>, the sipes <NUM> (hereinafter may be referred to as crown sipes <NUM>) on the crown land portion <NUM> include, for example, first crown sipes <NUM>, second crown sipes <NUM>, third crown sipes <NUM> and fourth crown sipes <NUM>.

<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 of <FIG>. As illustrated in <FIG>, the first crown sipes <NUM> and the second crown sipes <NUM> have opening ends 26b and 27b, respectively, connected to the first crown circumferential groove <NUM> (shown in <FIG>) and closed ends 26a and 27a, respectively, in the ground contact surface of the crown land portion <NUM>. The third crown sipes <NUM> and the fourth crown sipes <NUM>, for example, have opening ends 28b and 29b, respectively, connected to the second crown circumferential groove <NUM> (shown in <FIG>) and closed ends 28a and 29a, respectively, in the ground contact surface of the crown land portion <NUM>. These crown sipes <NUM> can provide friction force on the snow surface while maintaining the rigidity of the crown land portion <NUM>. Thus, the balance between steering stability and on-snow performance can be improved.

As a figure showing a cross section of one crown sipe <NUM>, <FIG> illustrates a cross-sectional view taken along the line A-A of <FIG>. As illustrated in <FIG>, each crown sipe <NUM> is open at the ground contact surface <NUM> with one or more chamfer portions <NUM>. Each chamfer portion <NUM> includes an inclined surface <NUM> between the ground contact surface <NUM> and the sipe wall. In the present embodiment, the 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. The chamfer portion <NUM> can equalize the ground contact pressure acting on the ground contact surface of the land portion and help improve steering stability and uneven wear resistance.

As illustrated in <FIG>, it is preferable that the chamfer portion <NUM> of each first crown sipe <NUM> has a chamfer width decreasing toward a closed end 26a of the first crown sipe <NUM>. Similarly, the chamfer portion <NUM> of each third crown sipe <NUM> has a chamfer width decreasing toward a closed end 28a of the third crown sipe <NUM>. Thus, the first crown sipes <NUM> and the third crown sipes <NUM> can secure a sufficient ground contact area in the central area of the crown land portion <NUM>, and can reliably maintain steering stability. In the first crown sipes <NUM> of the present embodiment, each chamfer portion <NUM> is substantially eliminated at the closed end 26a, but each chamfer portion <NUM> is not limited to such an aspect, and one or more chamfer portions <NUM> may have a chamfer width at the closed ends 26a. The same is true for the third crown sipes <NUM>. As illustrated in <FIG> and <FIG>, a chamfer width W5 is the width measured perpendicular to the longitudinal direction of the sipe in a tread plan view.

Preferably, the second crown sipes <NUM> and the fourth crown sipes <NUM> are provided with chamfer portions <NUM> over the entyre respective sipe lengths. More preferably, a pair of chamfer portions <NUM> of each second crown sipe <NUM> has a constant chamfer width in the longitudinal direction of the second crown sipe <NUM>. Similarly, it is preferable that a pair of chamfer portions <NUM> of each fourth crown sipe <NUM> has a constant chamfer width in the longitudinal direction of the fourth crown sipe <NUM>. In addition, the chamfer width of the chamfer portions <NUM> of each fourth crown sipe <NUM> ranges <NUM>% to <NUM>% of the chamfer width of the chamfer portions <NUM> of each second crown sipe <NUM>, and in this embodiment, they are substantially the same with each other. The second crown sipes <NUM> and the fourth crown sipes <NUM> can help to suppress uneven wear of the crown land portion <NUM>.

In a tread plan view as illustrated in <FIG>, it is preferable that at least one of the protrusions <NUM> (e.g., plural first protrusions <NUM>) overlaps, at least partially, either one of areas <NUM> (a dotted area <NUM> in <FIG>. ) in which the opening ends 26b with the chamfer portions <NUM> of the first crown sipes <NUM> are virtually extended in parallel with the tyre axial direction into the first crown circumferential groove <NUM>. As a more preferred embodiment, in the present embodiment, the first protrusions <NUM> overlap so as to straddle the respective areas <NUM> in a tread plan view. This structure allows the first protrusions <NUM> to increase the rigidity around the first crown sipes <NUM>, improving steering stability.

From the same point of view, it is also preferable that at least one of the protrusions <NUM> (e.g., plural second protrusions <NUM>) overlaps, at least partially, either one of areas <NUM> (a dotted area <NUM> in <FIG>. ) in which the opening ends with the chamfer portions <NUM> of the second crown sipes <NUM> are virtually extended in parallel with the tyre axial direction into the first crown circumferential groove <NUM>.

In the present embodiment, the first protrusions <NUM> and the second protrusions <NUM> are staggered in the tyre circumferential direction such that in a tread plan view, the areas <NUM> overlap with the respective first protrusions <NUM>, but does not overlap with the respective second protrusions <NUM>. Similarly, the areas <NUM> overlap with the respective second protrusions <NUM>, but not with the respective first protrusions <NUM>. This structure can improve steering stability of the tyre while maintaining wet performance.

As illustrated in <FIG>, these crown sipes <NUM> are inclined in the same direction with respect to the tyre axial direction. An angle of the crown sipes <NUM>, for example, ranges from <NUM> to <NUM> degrees, preferably from <NUM> to <NUM> degrees, with respect to the tyre axial direction. Note that an angle and a length of the sipes are measured at the centerline of the respective sipes.

A length L4 in the tyre axial direction of the first crown sipes <NUM> is smaller than a length L7 in the tyre axial direction of the fourth crown sipes <NUM> and smaller than a length L5 in the tyre axial direction of the second crown sipes <NUM>. In addition, the closed ends 26a of the first crown sipes <NUM> are located on the first crown circumferential groove <NUM> side (left side in <FIG>) with respect to the closed ends 28a of the third crown sipes <NUM>. In some more preferred embodiments, the closed ends 26a of the first crown sipes <NUM> are located on the second crown circumferential groove <NUM> side (right side in <FIG>) with respect to the closed ends 29a of the fourth crown sipes <NUM>. Preferably, the length L4 of the first crown sipes <NUM> ranges from <NUM>% to <NUM>% of a width W4 in the tyre axial direction of the ground contact surface <NUM> of the crown land portion <NUM>. The first crown sipes <NUM> as such can help to balance steering stability with on-snow performance and wet performance.

The length L5 in the tyre axial direction of the second crown sipes <NUM>, for example, ranges from <NUM>% to <NUM>% of the width W4 in the tyre axial direction of the ground contact surface <NUM> of the crown land portion <NUM>.

A length L6 in the tyre axial direction of the third crown sipes <NUM>, for example, is smaller than the length L7 of the fourth crown sipes <NUM> and smaller than the length L5 of the second crown sipes <NUM>. Specifically, the length L6 of the third crown sipes <NUM> preferably ranges from <NUM>% to <NUM>% of the width W4 in the tyre axial direction of the ground contact surface <NUM> of the crown land portion <NUM>.

Preferably, the fourth 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 fourth crown sipes <NUM> have closed ends 29a which are located on the first crown circumferential groove <NUM> side with respect to the closed ends 27a of the second crown sipes <NUM>. Preferably, the length L7 in the tyre axial direction of the fourth crown sipes <NUM> is greater than the length L5 in the tyre axial direction of the second crown sipes <NUM>. Specifically, the length L7 of the fourth crown sipes <NUM> preferably ranges from <NUM>% to <NUM>% of the width W4 in the tyre axial direction of the ground contact surface <NUM> of the crown land portion <NUM>. The fourth crown sipes <NUM> as such can improve on-snow performance and wet performance while maintaining steering stability.

As illustrated in <FIG>, a distance L9 in the tyre circumferential direction from center locations in the tyre axial direction of the first surfaces <NUM> of the first protrusions <NUM> to the respective closed ends 29a of the fourth crown sipes <NUM> (shown in <FIG>) preferably ranges from <NUM>% to <NUM>% of the circumferential pitch P1 of the protrusions <NUM>. Due to such an arrangement of the fourth crown sipes <NUM> in this way, a part of the land portion around the first surfaces <NUM> becomes moderately deformable. Thus, areas around the first surfaces <NUM> are less likely to be clogged with snow, and excellent on-snow performance can be maintained.

The first middle land portion <NUM> is provided with a plurality of middle lateral grooves <NUM>. The middle lateral grooves <NUM>, for example, extend to traverse the first middle land portion <NUM> completely in the tyre axial direction.

In a tread plan view, it is preferable that at least one of the plurality of protrusions <NUM> overlaps either one of areas in which the opening ends 40a of the middle lateral grooves <NUM> are virtually extended in parallel with the tyre axial direction into the first crown circumferential groove <NUM>. As a result, when driving on snow, the snow column formed at two least one connection between the first crown circumferential groove <NUM> and one of the middle lateral grooves <NUM> is sheared by the at least one protrusion <NUM>, generating a large reaction force and improving on-snow performance further.

Preferably, the opening ends 40a of the middle lateral grooves <NUM> are arranged close to the first surfaces <NUM> of the respective second protrusions <NUM>. Specifically, a distance L10 in the tyre circumferential direction from the groove centers of the opening ends 40a to the centers in the tyre axial direction of the respective first surfaces <NUM>, for example, is equal to or less than <NUM>%, preferably equal to or less than <NUM>%, of the pitch P1 of the protrusions <NUM>. As a result, uneven wear near the middle lateral grooves <NUM> can be suppressed. On the other hand, from the viewpoint of ensuring the drainage performance of the middle lateral grooves <NUM>, the distance L10 is preferably equal to or more than <NUM>% of the groove width at the opening ends 40a of the respective middle lateral grooves <NUM>.

Each of the middle lateral grooves <NUM> includes a first groove portion <NUM>, a second groove portion <NUM> and a circumferential groove portion <NUM>. The first groove portion <NUM> extends from the first shoulder circumferential groove <NUM> in the tyre axial direction. The second groove portion <NUM> extends from the first crown circumferential groove <NUM> in the tyre axial direction. An angle of the first groove portion <NUM> and an angle of the second groove portion <NUM> preferably range from <NUM> to <NUM> degrees, more preferably from <NUM> to <NUM> degrees, with respect to the tyre axial direction. The circumferential groove portion <NUM> extends in the tyre circumferential direction in communication with the first groove portion <NUM> and the second groove portion <NUM>. An angle of the circumferential groove portion <NUM>, for example, is equal to or less than <NUM> degrees, preferably equal to or less than <NUM> degrees, with respect to the tyre circumferential direction. Such middle lateral grooves <NUM> can help to improve traction performance and cornering performance on snow.

In the present embodiment, the cross-sectional shape of the first groove portion <NUM> differs from that of the second groove portion <NUM>. <FIG> illustrates a cross-sectional view taken along the line B-B of <FIG>, as a cross section of the first groove portion <NUM>. <FIG> is a cross-sectional view taken along the line C-C of <FIG> as a cross section of the second groove portion <NUM>. As illustrated in <FIG>, preferably, the first groove portion <NUM> and the second groove portion <NUM> are provided with chamfer portions <NUM>. Each chamfer portion <NUM> includes an inclined surface <NUM> between the ground contact surface <NUM> of the land potion and the groove wall. Each inclined surface <NUM> of the present embodiment is slightly curved in a direction convex outward in the tyre radial direction. Each inclined surface <NUM> may be plane, for example. The chamfered portions <NUM> can serve to equalize the ground contact pressure acting on the ground contact surface <NUM> and improve uneven wear resistance.

Preferably, the first groove portion <NUM> has a depth d2 that excludes a groove bottom sipe <NUM> (described later) ranging from <NUM>% to <NUM>% of the maximum depth of the first crown circumferential groove <NUM>. Preferably, the second groove portion <NUM> has a depth d3, for example, ranging from <NUM>% to <NUM>% of the maximum depth of the first crown circumferential groove <NUM>. Each middle lateral groove <NUM> having the first groove portion <NUM> and the second groove portion <NUM> can serve to improve steering stability and on-snow performance in a well-balanced manner.

The first groove portion <NUM> has the groove bottom sipe <NUM> that opens at a groove bottom 46d and extends inwardly in the tyre radial direction. Such a groove bottom sipe <NUM> can facilitate the opening of the first groove portion <NUM> appropriately and help to improve on-snow performance.

As illustrated in <FIG>, in the present embodiment, the middle lateral grooves <NUM> include first middle lateral grooves <NUM> including the first groove portions <NUM> and the second groove portions <NUM> which have the above-mentioned shapes, and second middle lateral grooves <NUM> including the first groove portion <NUM> and the second groove portion <NUM> which have the different shape from those of the first middle lateral grooves <NUM>. The first groove portions <NUM> of the second middle lateral grooves <NUM> have a cross-sectional shape shown in <FIG>, and the second groove portions <NUM> of the second middle lateral grooves <NUM> have a cross-sectional shape shown in <FIG>. In addition, in the present embodiment, the first middle lateral grooves <NUM> and the second middle lateral grooves <NUM> are arranged alternately in the tyre circumferential direction. By arranging the middle lateral grooves <NUM> in this way, the rigidity of the first middle land portion <NUM> can be made uniform and uneven wear resistance can be improved.

As illustrated in <FIG>, the first middle land portion <NUM> is further provided with a plurality of first middle sipes <NUM>, a plurality of second middle sipes <NUM> and a plurality of circumferential sipes <NUM>. The first middle sipes <NUM> extend in the tyre axial direction from the first shoulder circumferential groove <NUM> and have respective terminal ends 51a on the ground contact surface of the first middle land portion <NUM>. The second middle sipes <NUM> extend in the tyre axial direction from the first crown circumferential groove <NUM> and have respective terminal ends 52a on the ground contact surface of the first middle land portion <NUM>. Each circumferential sipe <NUM> extends from one of the terminal ends 51a of the first middle sipes <NUM> to one of the terminal ends 52a of the second middle sipe <NUM> adjacent each other while passing the circumferential groove portion <NUM> of the first middle lateral groove <NUM> that is located between the adjacent terminal ends 51a and 52a. These various types of sipes can enhance traction and turning performance on snow while maintaining steering stability.

Each of the first and second middle sipes <NUM> and <NUM> is provided with one or more chamfer portions <NUM>. Preferably, a chamfer width of the chamfer portions <NUM> of the first and second middle sipes <NUM> and <NUM> decreases toward a circumferential sipe <NUM> side. This can ensure a ground contact area in the center of the first middle land portion <NUM> and can maintain steering stability.

Claim 1:
A tyre (<NUM>) comprising:
a tread portion (<NUM>) comprising a first tread edge (T1), a second tread edge (T2), a crown land portion (<NUM>) arranged between the first tread edge (T1) and the second tread edge (T2), and a first crown circumferential groove (<NUM>) extending continuously in a tyre circumferential direction adjacent to the crown land portion (<NUM>) on a first tread edge side, wherein
the first crown circumferential groove (<NUM>) comprises a groove bottom (7d) having a plurality of protrusions (<NUM>) projecting in a tyre radial direction,
each of the plurality of protrusions (<NUM>) has a longitudinally elongated shape with a width (W3) in a tyre axial direction and a length (L3) in the tyre circumferential direction that is greater than the width (W3),
the crown land portion (<NUM>) is not provided with drainage grooves that have an opening width exceeding <NUM> at a ground contact surface (<NUM>) of the crown land portion (<NUM>) and a depth exceeding <NUM> of an area where a distance between two opposite groove walls thereof exceeds <NUM>, and
the crown land portion (<NUM>) is provided with a plurality of sipes (<NUM>),
characterized in that each of the plurality of protrusions (<NUM>) comprises a tapered portion (<NUM>) whose width decreases toward a first side in the tyre circumferential direction.