Patent Description:
<CIT> describes a pneumatic tire in which sipes are formed on a ground-contacting part. On at least one surface of groove wall surfaces of the sipe, protrusions that come into contact with the other opposite surface are formed. It is said that this type of protrusion contacts the opposite wall surface when the ground-contacting part touches the road surface to suppress the displacement between the wall surfaces and suppresses uneven wear.

<CIT>, <CIT>, <CIT>, and <CIT> disclose sipes having hemispherical protrusions. <CIT> also discloses protrusions with cylindrical base parts and truncated cone-shaped tip parts.

<CIT> discloses conical protrusions with pointed ends. <CIT> discloses protrusions with a trapezoid shape. <CIT> discloses protrusions including portions with a cylindrical shape and ends with a truncated conical shape. <CIT> discloses protrusions with truncated cone-shaped taper parts and tip parts protruding from the taper parts in a cylindrical shape.

<CIT> discloses a tire as specified in the preamble of claim <NUM>. A protrusion has a truncated cone shape and protrudes at a taper angle of <NUM> to <NUM> degrees, preferably <NUM> to <NUM> degrees from one sipe wall toward the other sipe wall. An area of an upper surface of the protrusion is <NUM> to <NUM><NUM>, and a distance between the pair of sipe walls facing each other is <NUM> to <NUM>, preferably <NUM> to <NUM>.

<CIT> also discloses a tire as specified in the preamble of claim <NUM>. A sipe wall has a recess to be engaged with a protrusion. A base diameter of a truncated cone forming the recess is <NUM> to <NUM>, and a tip diameter is <NUM> to <NUM> but at least <NUM>% smaller than the base diameter.

For example, in order to improve on-ice performance, winter studless tires and the like are provided with a plurality of sipes in blocks divided by lateral grooves. Each of the sipes is arranged in the thickness direction thereof. In recent years, in such tires, it has been required to suppress wear of the blocks.

The invention has been made in view of the above circumstances, and provides a tire capable of improving the wear resistance without impairing the on-ice performance.

The invention provides a tire as specified in claim <NUM>.

In the tire according to the invention, the pair of sipe walls include a first sipe wall on one side in the thickness direction and a second sipe wall on the other side in the thickness direction, and the protrusion of each of the plurality of sipes protrudes from the first sipe wall toward the second sipe wall. A taper shape of the protrusion is a truncated cone shape. A maximum cross-sectional area of the protrusion is greater than or equal to <NUM><NUM> and is less than or equal to <NUM><NUM>. A ratio (Sb/Sa) of a minimum cross-sectional area Sb of the protrusion to the maximum cross-sectional area Sa of the protrusion is <NUM> to <NUM>.

In the tire according to the invention, the protrusion is provided on only one of the pair of sipe walls and no protrusion is provided on the other of the pair of sipe walls.

In the tire according to the invention, it is preferable that a cross section of the protrusion is circular.

In the tire according to the invention, it is preferable that the protrusion is one of a plurality of the protrusions provided on the one of the pair of sipe walls.

The tire of the invention is capable of improving the wear resistance without impairing the on-ice performance by adopting the above configurations.

Hereinafter, embodiments of the invention will be described with reference to the drawings. <FIG> is an enlarged plan view of a tread part <NUM> of a tire <NUM> showing an embodiment of the invention. The tire <NUM> of the embodiment is, for example, a pneumatic tire for a passenger vehicle, particularly for a passenger vehicle suitable for running in winter. However, the invention is also adopted for pneumatic tires for heavy loads and non-pneumatic tires in which compressed air is not filled.

As shown in <FIG>, the tread part <NUM> of the embodiment is provided with a ground-contacting part <NUM> and a lateral groove <NUM>. Further, the tread part <NUM> may be provided with, for example, a vertical groove <NUM>. The ground-contacting part <NUM> has a tread surface 3a in contact with the road surface. The lateral groove <NUM> extends in the tire axial direction. The vertical groove <NUM> extends in the tire circumferential direction. "Extending in the tire axial direction" means extending at an angle of less than or equal to <NUM> degrees with respect to the tire axial direction. Further, "extending in the tire circumferential direction" means extending at an angle of greater than <NUM> degrees with respect to the tire axial direction.

The ground-contacting part <NUM> of the embodiment is provided with a plurality of blocks <NUM> divided by the lateral groove <NUM>. The blocks <NUM> are arranged, for example, in the tire circumferential direction. In addition, the blocks <NUM> may be arranged in the tire axial direction. In the embodiment, the block <NUM> is divided by a pair of lateral grooves <NUM> separated in the tire circumferential direction and a pair of vertical grooves <NUM> separated in the tire axial direction. In addition, the block <NUM> is not limited to such an implementation, and various implementations are adopted.

At least one of the plurality of blocks <NUM> is provided with a plurality of sipes <NUM>. The sipe <NUM> is a notched recess having a width w1 of less than or equal to <NUM>, and can be clearly distinguished from the lateral groove <NUM> and the vertical groove <NUM> having a groove width of greater than <NUM>. Further, the plurality of sipes <NUM> means two or more sipes <NUM>, and for example, about two to five sipes <NUM> are preferable.

Unless otherwise specified, the dimensions and the like of each part of the tire <NUM> are values measured in a regular state. The "regular state" is a no-load state in which the tire <NUM> is rim-assembled on a regular rim (not shown) and is filled with a regular internal pressure.

The "regular rim" is a rim defined for each tire in a standard system including a standard on which the tire <NUM> is based, and is, for example, a standard rim in the case of JATMA, a "Design Rim" in the case of TRA, and a "Measuring Rim" in the case of ETRTO.

The "regular internal pressure" is an air pressure defined for each tire in a standard system including a standard on which the tire <NUM> is based, and is the maximum air pressure in the case of JATMA, the maximum value described in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table in the case of TRA, and the "INFLATION PRESSURE" in the case of ETRTO.

The plurality of sipes <NUM> are arranged in a thickness direction (width direction) of the sipes <NUM>. As a result, the block <NUM> exhibits a high edge effect and has excellent on-ice performance. The "thickness direction" is a direction orthogonal to a center line 7c of the sipe <NUM>. Being "arranged in the thickness direction" means that other sipes <NUM> are arranged on a virtual straight line n orthogonal to the center line 7c of one sipe <NUM>.

Each sipe <NUM> has a pair of sipe walls <NUM> that are separated in the thickness direction. The pair of sipe walls <NUM> include a first sipe wall 8A on one side in the thickness direction (upper side in the drawing) and a second sipe wall 8B on the other side in the thickness direction (lower side in the drawing).

Each sipe <NUM> includes a protrusion <NUM> that protrudes in a taper shape from one toward the other of the pair of sipe walls <NUM>. Such a protrusion <NUM> is able to immediately contact the other sipe wall <NUM> when the block <NUM> touches the ground, suppress a block piece 6a between the sipes <NUM> from collapsing or slipping, and improve the wear resistance of the block <NUM> while exhibiting good on-ice performance. Further, since such a protrusion <NUM> alleviates the impact at the time of touching the ground and suppresses chipping and the like, the wear resistance is further improved. In the embodiment, each protrusion <NUM> of each sipe <NUM> protrudes from the first sipe wall 8A toward the second sipe wall 8B.

<FIG> is a cross-sectional perspective view taken along the line A-A of <FIG>. <FIG> is a cross-sectional view of the sipe <NUM>. As shown in <FIG>, in the embodiment, the protrusion <NUM> is provided on only one of the pair of sipe walls <NUM>. The protrusion <NUM> is provided on, for example, only the first sipe wall 8A. In addition, the protrusion <NUM> may be provided on only the second sipe wall 8B.

The cross-sectional area S of the protrusion <NUM> is greater than or equal to <NUM><NUM>. In this way, the effect of suppressing the collapse of the block <NUM> is well achieved. The cross-sectional area S of the protrusion <NUM> is less than or equal to <NUM><NUM>. If the cross-sectional area S of the protrusion <NUM> is greater than <NUM><NUM>, the suction amount of melted water on the ice road into the sipe <NUM> becomes small, and the on-ice performance may deteriorate. From this point of view, the cross-sectional area S of the protrusion <NUM> is preferably greater than or equal to <NUM><NUM>, and preferably less than or equal to <NUM><NUM>. The protrusion <NUM> is required to have a maximum cross-sectional area Sa of greater than or equal to <NUM><NUM>.

The ratio (Sb/Sa) of the minimum cross-sectional area Sb of the protrusion <NUM> to the maximum cross-sectional area Sa of the protrusion <NUM> is <NUM> to <NUM>. Since the ratio (Sb/Sa) is greater than or equal to <NUM>, the collapse of the block is suppressed. Since the ratio (Sb/Sa) is less than or equal to <NUM>, a high suction amount of the water is ensured. In the embodiment, the maximum cross-sectional area Sa is formed on the first sipe wall 8A. In other words, the maximum cross-sectional area Sa is formed at the base of the protrusion <NUM>. In the embodiment, the minimum cross-sectional area Sb is formed closest to the second sipe wall 8B side on the protrusion <NUM>. In other words, the minimum cross-sectional area Sb is formed at the tip of the protrusion <NUM>.

A plurality of the protrusions <NUM> are provided on, for example, one sipe wall <NUM>. In this way, the collapse of the block <NUM> may be further suppressed. In the embodiment, each protrusion <NUM> is provided on only the first sipe wall 8A. Two protrusions <NUM> are provided on the first sipe wall 8A.

The ratio (p/La) of the pitch p between the protrusions <NUM> to the length La of the protrusion <NUM> is preferably greater than or equal to <NUM>, more preferably greater than or equal to <NUM>, and preferably less than or equal to <NUM>, and more preferably less than or equal to <NUM>. In this way, the wear resistance and the on-ice performance are improved in a well-balanced manner. The length La of the protrusion <NUM> is the length along the longitudinal direction of the sipe <NUM>.

In the embodiment, the protrusion <NUM> has a substantially truncated cone shape. In this way, since the rigidity of the protrusion <NUM> can be maintained high, good wear resistance can be exhibited. The cross section of the protrusion <NUM> is, for example, circular. The term "circular" includes a circular shape or an elliptical shape. In the embodiment, the cross section of the protrusion <NUM> is formed in an elliptical shape. The cross section of the protrusion <NUM> is, for example, an elliptical shape whose major axis is arranged parallel to the longitudinal direction of the sipe <NUM>. In addition, the protrusion <NUM> may have an elliptical shape whose major axis is arranged parallel to the depth direction of the sipe <NUM> (not shown).

In the embodiment, the protrusion <NUM> is provided on the tread surface 3a side with respect to the bottom of the sipe <NUM>. In this way, when the block <NUM> touches the ground, the collapse or slippage of the block piece 6a may be firmly suppressed. From this point of view, it is preferable that the disposition position of the protrusion <NUM> is in a region R of <NUM>% of the depth d of the sipe <NUM> from the tread surface 3a to the bottom side of the sipe <NUM>.

In the embodiment, each sipe <NUM> extends in the tire axial direction. Each sipe <NUM> extends, for example, parallel to the lateral groove <NUM>. In each sipe <NUM>, for example, ends 7e on both sides are arranged within the block <NUM>. Each sipe <NUM> is not limited to such an implementation, and may cross the block <NUM>, or may have only one end 7e arranged within the block <NUM> (not shown).

<FIG> is a cross-sectional view of the block <NUM> of another embodiment. The same components as those of the above embodiment are denoted by the same reference numerals, and detailed descriptions thereof will be omitted. As shown in <FIG>, in this embodiment, the protrusions <NUM> provided on the sipes <NUM> adjacent to each other in the thickness direction are arranged in opposite directions. In other words, the protrusion <NUM> of one sipe <NUM> is provided on only the first sipe wall 8A, and the protrusion <NUM> of another sipe <NUM> adjacent to the one sipe is provided on only the second sipe wall 8B.

Next, a method for molding such a protrusion <NUM> will be described. (a) of <FIG> is a perspective view of a part of a vulcanization mold <NUM> for vulcanizing a raw tire 1a (shown in <FIG>), and (b) of <FIG> is a cross-sectional view taken along the line B-B of (a). The tire <NUM> is formed by vulcanizing the raw tire 1a by using the vulcanization mold <NUM>. As shown in <FIG>, the vulcanization mold <NUM> includes a tread molding surface 20a for molding the tread part <NUM> of the tire <NUM>. The tread molding surface 20a is provided with a thin plate-shaped knife blade <NUM> for molding the sipe <NUM>. The knife blade <NUM> protrudes outward from the tread molding surface 20a.

The knife blade <NUM> of the embodiment has a pair of longitudinal surfaces <NUM> separated in the width direction and a through hole <NUM> for forming the protrusion <NUM>. The through hole <NUM> extends, for example, between the pair of longitudinal surfaces <NUM>.

(a) of <FIG> is a cross-sectional view near the knife blade <NUM> of the raw tire 1a being vulcanized, and (b) of <FIG> is a cross-sectional view showing a state where the tire <NUM> has been detached from the vulcanization mold <NUM> after vulcanization is completed. As shown in <FIG>, when the raw tire 1a is put into such a vulcanization mold <NUM> and an internal pressure is applied, a rubber material <NUM> forming the block <NUM> enters the through hole <NUM>. When the vulcanization is completed and the vulcanized tire <NUM> is separated from the vulcanization mold <NUM>, the rubber material <NUM> that has entered the through hole <NUM> is cut by the knife blade <NUM> to form the protrusion <NUM>.

In order to form the protrusion <NUM> of the embodiment as shown in <FIG>, as shown in (b) of <FIG>, the through hole <NUM> has a continuously smaller cross-sectional area from one longitudinal surface 22A toward the other longitudinal surface 22B, and has a circular cross section. In other words, the through hole <NUM> is formed in a truncated cone shape. The ratio (Sd/Sc) of the opening area Sd of the through hole <NUM> on the other longitudinal surface 22B to the opening area Sc of the through hole <NUM> on the one longitudinal surface 22A is, for example, preferably greater than or equal to <NUM>, more preferably greater than or equal to <NUM>, and preferably less than or equal to <NUM>, and more preferably less than or equal to <NUM>.

Although the particularly preferable embodiments of the invention have been described in detail above, the invention is not limited to the illustrated embodiments, and may be modified into various implementations.

Sample tires having the block shown in <FIG> were manufactured. Then, the wear resistance and the on-ice performance of each sample tire were tested. The common specifications and test methods for each sample tire are as follows.

Each sample tire was mounted on all wheels of a passenger vehicle under the following conditions. Then, after the test driver actually ran the vehicle on a test course on a dry asphalt road surface, the wear condition of the block provided with the sipes was evaluated by senses. The results are shown with a score of <NUM> for the comparative example. The greater the value, the smaller the wear amount and the better the wear resistance.

Using the above test vehicle, the test driver actually ran the vehicle on a test course on an icy road surface, and evaluated the properties related to stability and ease of running at that time by senses. The results are shown with a score of <NUM> for the comparative example. The greater the value, the better the on-ice performance.

Claim 1:
A tire (<NUM>), comprising:
a tread part (<NUM>),
wherein the tread part (<NUM>) comprises a ground-contacting part (<NUM>),
the ground-contacting part (<NUM>) is provided with a plurality of blocks (<NUM>) divided by a lateral groove (<NUM>),
at least one of the plurality of blocks (<NUM>) is provided with a plurality of sipes (<NUM>),
the plurality of sipes (<NUM>) are arranged in a thickness direction of the sipes (<NUM>), meaning that other sipes (<NUM>) are arranged on a virtual straight line (n) orthogonal to a center line (7c) of one of the plurality of sipes (<NUM>), and
each of the plurality of sipes (<NUM>) comprises a pair of sipe walls (<NUM>) that are separated in the thickness direction, and comprises a protrusion (<NUM>) that protrudes in a taper shape from one toward the other of the pair of sipe walls (<NUM>), wherein
the taper shape of the protrusion (<NUM>) is a truncated cone shape,
characterized in that
the protrusion (<NUM>) is provided on only one of the pair of sipe walls (<NUM>) and no protrusion is provided on the other of the pair of sipe walls (<NUM>),
a maximum cross-sectional area of the protrusion (<NUM>) is greater than or equal to <NUM><NUM> and is less than or equal to <NUM><NUM>, and
a ratio (Sb/Sa) of a minimum cross-sectional area Sb of the protrusion (<NUM>) to the maximum cross-sectional area Sa of the protrusion (<NUM>) is <NUM> to <NUM>.