Patent Description:
<CIT> describes a pneumatic tire having blocks provided in a tread portion. The blocks include constricted blocks each having recesses on side surfaces in the tire axial direction. Each of the recesses is defined by a V-shaped edge that protrudes toward the block center side. During running on snow, such a V-shaped recess traps snow therein, and compacts the trapped snow by compression deformation, to form a hard snow column. Therefore, the pneumatic tire of <CIT> is said to have excellent on-snow performance.

A pneumatic tire in accordance with the preamble of claim <NUM> is known from <CIT>. Related tires are known from <CIT> and <CIT>.

In recent years, further improvement of the snow road performance of tires has been desired. The inventors have conducted various experiments, and as a result, the inventors have found that snow road performance can be improved by modifying block corner portions of a tread portion.

The present invention has been made in view of the above circumstances, and a main object of the present invention is to provide a tire having improved snow road performance.

The present invention is directed to a tire including a tread portion, wherein: the tread portion is provided with a block having a tread surface; the block has a block corner portion including a top portion protruding toward an outer side of the block, in a tread plan view; the block corner portion has a stepped chamfered portion formed therein in which a block height decreases stepwise from the tread surface toward the top portion; the stepped chamfered portion includes a plurality of upper surfaces substantially parallel to the tread surface, a plurality of vertical surfaces extending in a block height direction, and a plurality of step corner portions each formed so as to protrude toward the outer side of the block as a result of the upper surface and the vertical surface or the vertical surface and the tread surface intersecting each other; and an angle between the tread surface and a virtual straight line connecting the plurality of step corner portions in a vertical cross-sectional view, of the block corner portion, passing through the top portion is <NUM> to <NUM> degrees.

In the tire according to the present invention, preferably, the block corner portion is formed at an intersection of the tread surface, a wall surface of a circumferential groove extending in a tire circumferential direction, and a wall surface of a lateral groove extending in a tire axial direction, and the stepped chamfered portion extends between the wall surface of the circumferential groove and the wall surface of the lateral groove.

In the tire according to the present invention, preferably, the stepped chamfered portion is provided with at least one rib extending in the block height direction.

In the tire according to the present invention, preferably, the rib extends in a zigzag manner.

In the tire according to the present invention, preferably, the rib has a plurality of zigzag corner portions, and each zigzag corner portion is located at the step corner portion.

In the tire according to the present invention, preferably, a ratio of a bending width of the zigzag of the rib to an inclination intercept of the stepped chamfered portion is <NUM> to <NUM>.

In the tire according to the present invention, preferably, the rib has a height of <NUM> to <NUM>, and the rib has a width of <NUM> to <NUM>.

In the tire according to the present invention, preferably, the rib has a pair of rising surfaces rising from the upper surface, and an angle between each of the rising surfaces and a virtual straight line connecting proximal ends of the pair of rising surfaces in a transverse cross-sectional view of the rib is <NUM> to <NUM> degrees.

In the tire according to the present invention, preferably, the stepped chamfered portion is provided with a plurality of ribs extending in the block height direction, and an interval between each rib gradually increases toward an outer side in the block height direction.

As a result of adopting the above configuration, the tire according to the present invention can have improved snow road performance.

<FIG> is a partial perspective view of a block <NUM> provided in a tread portion <NUM> of a tire <NUM> according to the present embodiment. <FIG> shows a block <NUM> of a pneumatic tire <NUM> for a passenger car as a preferable mode. However, the present invention can also be applied to, for example, a pneumatic tire for a heavy-duty vehicle and tires in the other categories.

As shown in <FIG>, in the present embodiment, the block <NUM> includes a tread surface 3a which comes into contact with a road surface, and a top portion 3b which protrudes toward the outer side of the block <NUM> in a tread plan view. The block <NUM> also includes a wall surface (first wall surface) 3c which extends from the top portion 3b toward one side, and a wall surface (second wall surface) 3d which extends from the top portion 3b toward the other side.

The block <NUM> of the present embodiment has a block corner portion <NUM> which includes the top portion 3b. The block corner portion <NUM> has a stepped chamfered portion <NUM> formed therein in which the block height decreases stepwise from the tread surface 3a toward the top portion 3b. Such a stepped chamfered portion <NUM> treads snow and increases a snow column shearing force. The stepped chamfered portion <NUM> is formed, for example, in a triangular shape in a tread plan view.

<FIG> is a vertical cross-sectional view, of the block corner portion <NUM>, passing through the top portion 3b (a cross-sectional view taken along a line A-A in <FIG>). As shown in <FIG>, the stepped chamfered portion <NUM> includes a plurality of upper surfaces <NUM>, a plurality of vertical surfaces <NUM>, and a plurality of step corner portions <NUM> which project toward the block outer side. Each upper surface <NUM> is formed substantially parallel to the tread surface 3a. During running on snow, such an upper surface <NUM> can strongly compact snow to form a hard snow column. Each vertical surface <NUM> extends in the block height direction. Each step corner portion <NUM> is formed as a result of the upper surface <NUM> and the vertical surface <NUM> or the vertical surface <NUM> and the tread surface 3a intersecting each other.

The "substantially parallel" includes a mode in which an angle (not shown) between a virtual line n1 obtained by extending the tread surface 3a and a virtual line n2 obtained by extending the upper surface <NUM> is within <NUM> degrees in the vertical cross-sectional view, of the block corner portion <NUM>, passing through the top portion 3b. In addition, the "extending in the block height direction" includes a mode in which the vertical surface <NUM> extends at an angle (not shown) of <NUM> degrees or less with respect to the block height direction (orthogonal to the tread surface 3a), in addition to a mode in which the vertical surface <NUM> extends parallel to the block height direction.

In the present description, dimensions and the like of components of the tire <NUM> are values measured in a normal state where the tire <NUM> is fitted on a normal rim (not shown) and inflated to a normal internal pressure and no load is applied to the tire <NUM>. The "normal rim" is a rim that is defined, in a standard system including a standard on which the tire <NUM> is based, by the standard for each tire, and is, for example, the "standard rim" in the JATMA standard, the "Design Rim" in the TRA standard, or the "Measuring Rim" in the ETRTO standard.

The "normal internal pressure" is an air pressure that is defined, in a standard system including a standard on which the tire <NUM> is based, by the standard for each tire, and is the "maximum air pressure" in the JATMA standard, the maximum value indicated in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, or the "INFLATION PRESSURE" in the ETRTO standard. In the case where the tire is for a passenger car, the normal internal pressure is <NUM> kPa.

An angle θ1 between the tread surface 3a and a virtual straight line n3 obtained by connecting the plurality of step corner portions <NUM> is set to <NUM> to <NUM> degrees. When the angle θ1 is set in the range of <NUM> to <NUM> degrees, both the desired volume of a snow column formed by the stepped chamfered portion <NUM> and the effect of treading snow can be ensured to exert a large snow column shearing force. In particular, the above effect is effectively exhibited on a compressed snow road surface in which snow is compressed. From such a viewpoint, the angle θ1 is further preferably not less than <NUM> degrees and even more preferably not less than <NUM> degrees, and is more preferably not greater than <NUM> degrees and even more preferably not greater than <NUM> degrees. If the plurality of step corner portions <NUM> cannot be connected by a single straight line, a virtual straight line (linear function) obtained by the least squares method using each step corner portion <NUM> is adopted as the virtual straight line n3.

In the present embodiment, the stepped chamfered portion <NUM> further includes a plurality of step recesses <NUM> which are recessed on the block inner side as a result of the upper surface <NUM> and the vertical surface <NUM> intersecting each other. In the present embodiment, the step recesses <NUM> are formed alternately with the step corner portions <NUM>.

In the present embodiment, in the stepped chamfered portion <NUM>, the upper surfaces <NUM> and the vertical surfaces <NUM> are alternately formed. In the stepped chamfered portion <NUM>, for example, two to five upper surfaces <NUM> and two to five vertical surfaces <NUM> are formed. In the stepped chamfered portion <NUM> of the present embodiment, two upper surfaces <NUM> and three vertical surfaces <NUM> are formed. In the stepped chamfered portion <NUM>, for example, an innermost vertical surface 11b in the block height direction forms the top portion 3b.

<FIG> is a plan view of the block corner portion <NUM> in <FIG>. As shown in <FIG>, the angle θ1 of the stepped chamfered portion <NUM> is an angle on a bisector c1 of an angle θa formed between the first wall surface 3c and the second wall surface 3d about the top portion 3b in a tread plan view. In the block corner portion <NUM> of the present embodiment, the angle θ1 is <NUM> to <NUM> degrees in a vertical cross-section parallel to the bisector c1, for example, a vertical cross-section T.

In the block corner portion <NUM> having the stepped chamfered portion <NUM> formed therein, the angle θa is not particularly limited, but is preferably not less than <NUM> degrees and more preferably not less than <NUM> degrees, and is preferably not greater than <NUM> degrees and more preferably not greater than <NUM> degrees.

As shown in <FIG>, in the vertical cross-sectional view, for example, each of the upper surfaces <NUM> and the vertical surfaces <NUM> is formed in a straight shape. The upper surfaces <NUM> and the vertical surfaces <NUM> are not limited to such a mode, and, for example, may have an arc shape that is convex on the outer side of the block <NUM> or may have an arc shape that is concave on the inner side of the block <NUM>.

<FIG> is a plan view showing an embodiment of the tread portion <NUM>. As shown in <FIG>, the tread portion <NUM> is provided with circumferential grooves G1 extending in the tire circumferential direction and lateral grooves G2 extending in the tire axial direction. The circumferential grooves G1 and the lateral grooves G2 demarcate blocks <NUM>.

Each circumferential groove G1 is, for example, a groove extending at an angle of <NUM> degrees or more with respect to the tire axial direction. Each lateral groove G2 is, for example, a groove extending at an angle less than <NUM> degrees with respect to the tire axial direction. In the present description, the circumferential grooves G1 and the lateral grooves G2 are each a groove-like recess having a groove width w which is preferably not less than <NUM>, more preferably not less than <NUM>, and further preferably not less than <NUM>.

The blocks <NUM> include, for example, a crown block 3A disposed on a tire equator C, a pair of middle blocks 3B disposed on both sides in the tire axial direction of the crown block 3A, and a pair of shoulder blocks 3C disposed outward of the middle blocks 3B in the tire axial direction. The tread portion <NUM> is not limited to such a mode, and various shapes are adopted.

In the present embodiment, each of the blocks 3A to 3C has block corner portions <NUM> each located between the circumferential groove G1 and the lateral groove G2. In other words, in the present embodiment, each block corner portion <NUM> is formed at the intersection of the tread surface 3a, a wall surface Ga of the circumferential groove G1, and a wall surface Gb of the lateral groove G2.

In the present embodiment, the stepped chamfered portion <NUM> is provided to each of the blocks 3A to 3C. In other words, the stepped chamfered portion <NUM> of the present embodiment extends between the wall surface Ga of the circumferential groove G1 and the wall surface Gb of the lateral groove G2. Accordingly, during running on snow, a snow column formed by the stepped chamfered portion <NUM> of the present embodiment is smoothly removed via the circumferential groove G1 or the lateral groove G2. In the present embodiment, the wall surface Ga of the circumferential groove G1 forms the first wall surface 3c, and the wall surface Gb of the lateral groove G2 forms the second wall surface 3d. A height H (shown in <FIG>) of the stepped chamfered portion <NUM> is not particularly limited, but is preferably not less than <NUM>% and further preferably not less than <NUM>%, and is preferably not greater than <NUM>% and further preferably not greater than <NUM>%, of the groove depth (not shown) of the circumferential groove G1 which forms the first wall surface 3c or the second wall surface 3d.

In order to maintain the stiffness of each block <NUM> and exert a large snow column shearing force, a length L1 in the tire circumferential direction of the first wall surface 3c is preferably not less than <NUM>% and more preferably not less than <NUM>%, and is preferably not greater than <NUM>% and more preferably not greater than <NUM>%, of a length La in the tire circumferential direction of the block <NUM>.

As shown in <FIG>, the stepped chamfered portion <NUM> of the present embodiment is provided with at least one rib <NUM> extending in the block height direction. Such a rib <NUM> blocks snow on the stepped chamfered portion <NUM>, without releasing the snow, during running on snow, and thus serves to form a firm snow column. Therefore, the rib <NUM> further improves snow road performance.

For example, a plurality of ribs <NUM> are provided. In the present embodiment, three ribs <NUM> are provided. Accordingly, snow between adjacent ribs <NUM> is more blocked on the stepped chamfered portion <NUM>, so that the snow road performance is further improved.

Each rib <NUM> extends, for example, in a zigzag manner. Such a rib <NUM> has, for example, a length larger than that of a rib (not shown) extending in a straight manner, and thus can more effectively block snow. The rib <NUM> is not limited to such a mode, and may extend, for example, in a wavy or straight manner.

The rib <NUM> has a plurality of zigzag corner portions <NUM>. Each zigzag corner portion <NUM> is located at the step corner portion <NUM> or the step recess <NUM>. The rib <NUM> includes first inclined portions 15a which are inclined toward either the first wall surface 3c or the second wall surface 3d while extending toward the top portion 3b, and second inclined portions 15b which are connected to the first inclined portions 15a and which are inclined toward the side opposite to the side toward which the first inclined portions 15a are inclined, while extending toward the top portion 3b. Each zigzag corner portion <NUM> is formed at the position where the first inclined portion 15a and the second inclined portion 15b are connected to each other. Such a mode serves to smoothly remove snow on the upper surface <NUM> or the vertical surface <NUM>.

As shown in <FIG>, the ratio (α/β) of a bending width α of the zigzag of the rib <NUM> to an inclination intercept β of the stepped chamfered portion <NUM> in a tread plan view is preferably not less than <NUM>, and is preferably not greater than <NUM>. Since the ratio (α/β) is not less than <NUM>, the length of the rib <NUM> can be relatively long, so that the effect of blocking snow is exhibited. When the ratio (α/β) exceeds <NUM>, the effect of blocking snow is not enhanced, and the effect of removing snow may decrease. From such a viewpoint, the ratio (α/β) is further preferably not less than <NUM> and is further preferably not greater than <NUM>. The bending width α is the length between adjacent peaks of the zigzag in a direction orthogonal to a center line 15c of the amplitude of the rib <NUM>. The inclination intercept β is the length, on the first wall surface 3c or the second wall surface 3d, of the stepped chamfered portion <NUM>.

<FIG> shows a transverse cross-section of the rib <NUM>. As shown in <FIG>, a height h1 of the rib <NUM> is preferably not less than <NUM> and is preferably not greater than <NUM>. Since the height h1 of the rib <NUM> is not less than <NUM>, the effect of blocking snow is exhibited. Since the height h1 of the rib <NUM> is not greater than <NUM>, snow is easily separated from the stepped chamfered portion <NUM> during running on snow, so that snow clogging is suppressed. From such a viewpoint, the height h1 of the rib <NUM> is more preferably not less than <NUM> and is more preferably not greater than <NUM>.

A width w1 of the rib <NUM> is preferably not less than <NUM> and is preferably not greater than <NUM>. Since the width w1 of the rib <NUM> is not less than <NUM>, the stiffness of the rib <NUM> is maintained, and snow can be effectively blocked. Since the width w1 of the rib <NUM> is not greater than <NUM>, the areas of the upper surfaces <NUM> and the like are ensured in the stepped chamfered portion <NUM>, and a large snow column can be formed. From such a viewpoint, the width w1 of the rib <NUM> is more preferably not less than <NUM> and is more preferably not greater than <NUM>.

The rib <NUM> has a pair of rising surfaces <NUM> which rise from the upper surface <NUM>. In the transverse cross-sectional view of the rib <NUM>, an angle θ2 between each rising surface <NUM> and a virtual straight line n4 connecting proximal ends 18a of the pair of rising surfaces <NUM> is preferably <NUM> to <NUM> degrees. Since the angle θ2 is not less than <NUM> degrees, the effect of blocking snow is effectively exhibited. Since the angle θ2 is not greater than <NUM> degrees, a large volume of a snow column formed by the stepped chamfered portion <NUM> can be ensured.

The rib <NUM> is formed in a triangular shape in which distal ends 18b of the pair of rising surfaces <NUM> are connected to each other, in a transverse cross-section. Such a rib <NUM> forms a firm snow column, and can ensure a large volume of the snow column. The rib <NUM> may have, for example, a rectangular shape (not shown) in which the angle θ2 of each of the pair of rising surfaces <NUM> is <NUM> degrees, or a trapezoidal shape in which the distal ends 18b of the pair of rising surfaces <NUM> are connected by an outward surface <NUM> (shown in <FIG>) extending in the width direction of the rib <NUM>.

As shown in <FIG>, each rib <NUM> extends from an outermost vertical surface 11a in the block height direction to an innermost upper surface 10b in the block height direction. More specifically, the rib <NUM> extends from the step corner portion <NUM> of the vertical surface 11a to the step corner portion <NUM> of the upper surface 10b. Such a rib <NUM> has a relatively large length, and thus exhibits a great effect of blocking snow. In the present embodiment, the rib <NUM> is not formed on the innermost vertical surface <NUM>1b in the block height direction.

In the present embodiment, an interval L2 between each rib <NUM> gradually increases toward the outer side in the block height direction. A minimum gap Lb between the ribs <NUM> is not particularly limited, but is preferably not less than <NUM> and more preferably not less than <NUM>, and is preferably not greater than <NUM> and more preferably not greater than <NUM>. The minimum gap Lb between the ribs <NUM> is formed at the inner ends in the block height direction of the ribs <NUM>.

Although the tire according to the embodiment of the present invention has been described in detail above, the present invention is not limited to the above specific embodiment, and various modifications can be made to implement the present invention within the scope of the appended claims.

Tires with a size of <NUM>/60R16 having the basic pattern in <FIG> were produced as sample tires on the basis of specifications in Table <NUM>, and were tested for snow road performance. The common specifications and the test methods for the respective sample tires are as follows. The height H of the stepped chamfered portion is the same in all examples. Height H of stepped chamfered portion: <NUM>.

The respective sample tires were mounted to all the wheels of a front-wheel-drive passenger car having an engine displacement of <NUM> cc, under the following conditions, and a test driver drove the vehicle on a test course having a snow road surface. The test driver made sensory evaluation for running characteristics regarding steering responsiveness, traction, grip, and the like at that time. The results are indicated as scores with the result of Comparative Example <NUM> being regarded as <NUM>. The higher the value is, the better the result is.

Claim 1:
A tire (<NUM>) comprising a tread portion (<NUM>), wherein
the tread portion (<NUM>) is provided with a block (<NUM>) having a tread surface (3a),
the block (<NUM>) has a block corner portion (<NUM>) including a top portion (3b) protruding toward an outer side of the block (<NUM>), in a tread plan view,
the block corner portion (<NUM>) has a stepped chamfered portion (<NUM>) formed therein in which a block height decreases stepwise from the tread surface (3a) toward the top portion (3b), and
the stepped chamfered portion (<NUM>) includes
a plurality of vertical surfaces (<NUM>) extending in a block height direction,
characterized in that
the stepped chamfered portion (<NUM>) further includes a plurality of upper surfaces (<NUM>) substantially parallel to the tread surface (3a), and
a plurality of step corner portions (<NUM>) each formed so as to protrude toward the outer side of the block (<NUM>) as a result of the upper surface (<NUM>) and the vertical surface (<NUM>) or the vertical surface (<NUM>) and the tread surface (3a) intersecting each other, wherein
an angle (θ1) between the tread surface (3a) and a virtual straight line (n3) connecting the plurality of step corner portions (<NUM>) in a vertical cross-sectional view, of the block corner portion (<NUM>), passing through the top portion (3b) is <NUM> to <NUM> degrees.