The tire of this disclosure is a tire having a land portion on a tread surface, wherein the land portion comprises a sipe unit consisting of a pair of sipes, each of the pair of sipes extends such that both ends in the extending direction of sipes terminate within the land portion, and the pair of sipes are opposed to each other in the tire circumferential direction only in part in the tire width direction.

TECHNICAL FIELD

This disclosure relates to a tire.

BACKGROUND

Conventionally, narrow grooves called sipes have been provided in the land portion of the tread of tires, particularly studless tires, in order to improve on-ice gripping performance of the tire. These sipes allow water that gushes out when the icy road surface melts on the contact patch of the tire to be discharged to the outside of the contact patch, thereby improving the on-ice gripping performance of the tire.

For example, Patent Document 1 proposes a technique that improves the on-ice gripping performance by densely arranging sipes while preventing a reduction in rigidity of the land portion.

CITATION LIST

Patent Literature

SUMMARY

Technical Problem

However, the compatibility between the rigidity of the land portion and the water drainage by the sipes in the prior art is not sufficient, and further improvement on the on-ice gripping performance of the tire is still required.

It is an object of the present disclosure, made in view of the above circumstances, to provide a tire with improved on-ice gripping performance.

Solution to Problem

The tire according to the present disclosure is a tire having a land portion on a tread surface, wherein the land portion comprises a sipe unit consisting of a pair of sipes, each of the pair of sipes extends such that both ends in the extending direction of sipes terminate within the land portion, and the pair of sipes are opposed to each other in the tire circumferential direction only in part in the tire width direction.

Advantageous Effect

According to the present disclosure, it is possible to provide a tire with improved on-ice gripping performance.

DETAILED DESCRIPTION

Hereinafter, embodiments of a tire according to the present disclosure will be described with reference to the drawings. Common members and parts in each figure are designated by the same reference numerals. However, it should be noted that the drawings are schematically drawn, and the ratio of each dimension may differ from the actual one.

As used herein, the “tire width direction” refers to the direction parallel to the tire rotation axis, and the “tire radial direction” refers to the direction perpendicular to the tire rotation axis. The “tire circumferential direction” refers to the direction in which the tire rotates around the tire rotation axis.

As used herein, the side closer to the tire rotation axis along the tire radial direction is referred to as the “inner side in the tire radial direction” and the side farther from the tire rotation axis along the tire radial direction is referred to as the “outer side in the tire radial direction”. At the same time, the side closer to the tire equatorial plane CL along the tire width direction is referred to as the “inner side in the tire width direction” and the side farther from the tire equatorial plane CL along the tire width direction is referred to as the “outer side in the tire width direction”.

As used herein, unless otherwise noted, the positional relationship of each element of the tire, etc., shall be measured in a reference condition. In this document, the “reference condition” refers to the condition in which the tire is mounted on a rim of a wheel, which is an applicable rim, filled with prescribed internal pressure, and unloaded.

As used herein, the “applicable rim” refers to the standard rim in the applicable size (Measuring Rim in ETRTO's STANDARDS MANUAL and Design Rim in TRA's YEAR BOOK) as described or as may be described in the future in the industrial standard, which is valid for the region in which the tire is produced and used, such as JATMA YEAR BOOK of JATMA (Japan Automobile Tyre Manufacturers Association) in Japan, STANDARDS MANUAL of ETRTO (The European Tyre and Rim Technical Organization) in Europe, and YEAR BOOK of TRA (The Tire and Rim Association, Inc.) in the United States. For sizes not listed in these industrial standards, the “applicable rim” refers to a rim with a width corresponding to the bead width of the tire. The “applicable rim” includes current sizes as well as future sizes to be listed in the aforementioned industrial standards. An example of the “size as described in the future” could be the sizes listed as “FUTURE DEVELOPMENTS” in the ETRTO 2013 edition.

As used herein, the “prescribed internal pressure” refers to the air pressure (maximum air pressure) corresponding to the maximum load capacity of a single wheel in the applicable size and ply rating, as described in the aforementioned JATMA YEAR BOOK and other industrial standards. In the case that the size is not listed in the aforementioned industrial standards, the “prescribed internal pressure” refers to the air pressure (maximum air pressure) corresponding to the maximum load capacity specified for each vehicle in which the tire is mounted. In addition, as used herein, the “prescribed load” refers to the load corresponding to the maximum load capacity of a single tire in the applicable size and ply rating described in the aforementioned industrial standards, or, for sizes not listed in the aforementioned industrial standards, the “prescribed load” refers to the load corresponding to the maximum load capacity specified for each vehicle in which the tire is mounted.

As used herein, the “tread surface” means the outer surface around the entire circumference of the tire that is in contact with the road surface when the tire is assembled on the applicable rim, filled with the prescribed internal pressure, and rolled under the prescribed load (hereinafter also referred to as the “maximum load condition”). In addition, the “tread edge” means the outer edge of the tread surface in the tire width direction.

As used herein, the “sipe” is defined as a sipe with a width of 1 mm or less in the area of 50% or more of the depth of the sipe in the above reference condition. Here, the “depth of sipe” shall be measured perpendicular to the tread surface in the above reference condition, and the “width of sipe” shall be measured in a cross section perpendicular to the extending direction of the sipes at the tread surface, parallel to the tread surface, in the above reference condition. In addition, the “length in the extending direction of the sipe” refers to the length of the centerline consisting of a series of sipe widthwise center points on the tread surface in the reference condition. The distance and length, etc. associated with the sipe shall also be measured, with respect to the above centerline, in the developed view of the tread surface, unless otherwise noted.

In this embodiment, unless otherwise noted, the internal structure, etc. of the tire can be the same as that of a conventional tire. As an example, the tire may have a pair of bead portions, a pair of sidewall portions connected to the pair of bead portions, and a tread portion disposed between the pair of sidewall portions. Also, the tire may have a carcass that straddles toroidally between the pair of bead portions, and a belt disposed on the outer side of the crown portion of the carcass in the tire radial direction.

In the following, the tire is described as one whose lumen is filled with air and mounted on a vehicle such as a passenger car. However, the tire lumen may be filled with a fluid other than air, and the tire may be mounted on a vehicle other than a passenger car.

Hereinafter, a tire1according to an embodiment of the present disclosure will be described with reference to the drawings.

First Embodiment

FIG.1is a schematic developed view of the tread pattern of the tire1(1A) according to the first embodiment of this disclosure. InFIG.1, a part of the tread surface2of the tire1A is illustrated as a developed view from the outer side in the tire radial direction to a plane (as a developed view of the tread surface2).

As illustrated inFIG.1, the tire1A has, on the tread surface2, one or more (four in the illustrated example) circumferential main grooves3(3A,3B,3C,3D) extending in the tire circumferential direction; and a plurality (five in the illustrated example) of land portions4(4A,4B,4C,4D,4E) which are defined by the circumferential main grooves3adjacent to each other in the tire width direction of the one or more circumferential main grooves3, or by the circumferential main groove3(3A or3D) and the tread edge TE. In this embodiment, the circumferential main grooves3A and3B are located in one half of the tire widthwise position with the tire equatorial plane CL as a boundary, and the other circumferential main grooves3C and3D are located in the other half of the tire widthwise position with the tire equatorial plane CL as a boundary. Thus, in this embodiment, one land portion4(4C) is arranged on the tire equatorial plane CL and two land portions4(4A and4B,4D and4E) are arranged on each of the tire widthwise half.

The number of circumferential main grooves3in the tire1A may be any number other than four. Depending on the number of circumferential main grooves3, the number of land portions4in the tire1A may be any number other than five. Furthermore, the tire1A may be configured without circumferential main grooves3on the tread surface2. In such a case, the tire1A may have one land portion4on the tread surface2, which is defined by both tread edges TE in the tire width direction.

In the illustrated example, the circumferential main grooves3all extend along the tire circumferential direction. As used herein, “the straight line X extends along the direction Y” means that the straight line X extends parallel to the direction Y, or that the straight line X extends approximately parallel to the direction Y. The “extending direction of the straight line X is approximately parallel to the direction Y” means, for example, that the angle between the extending direction of the straight line X and the direction Y is within 5 degrees or less. However, at least one circumferential main groove3may extend at an angle greater than 5 degrees with respect to the tire circumferential direction. In the illustrated example, all of the circumferential main grooves3extend in a straight line along the tire circumferential direction, however at least one of the circumferential main grooves3may have a shape other than a straight line, such as zigzag or curved, either entirely or partially.

The width of the circumferential main grooves3is not limited, as it depends on the number of circumferential main grooves3, but may be 4 to 15 mm, for example. The width of the circumferential main groove3is measured as the opening width perpendicular to the extending direction of the groove in the reference condition, when viewed from the outer side in the tire radial direction and developed on a flat surface. Similarly, the depth (maximum depth) of the circumferential main groove3is not limited, but may be 6 to 20 mm, for example. The width of the circumferential main groove3does not have to be constant over the extending direction of the circumferential main groove3and may differ from each other depending on the location of the tread surface2where the circumferential main groove3is provided.

In the tire1A, each land portion4is divided into a plurality of block land portions6by one or more width direction grooves5that completely cross the land portion4and extend in the tire width direction.

In the illustrated example, all of the width direction grooves5completely cross the land portion4and extend in the tire width direction. For example, within the illustration, the land portion4C is divided into three block land portions6A,6B and6C adjacent to each other in the tire circumferential direction by two width direction grooves5A and5B adjacent to each other in the tire circumferential direction. As used herein, “the straight line X extends in the direction Y” means that the straight line X has at least a Y-direction component. That is, “the straight line X extends in the direction Y” means that the straight line X may extend along the direction Y, or the straight line X may extend at a predetermined angle with respect to the direction Y. The width direction groove5may extend in a straight line in the tire circumferential direction, or it may extend in a shape other than a straight line, such as zigzag or curved. The width direction groove5may extend along the tire width direction, or it may extend at an angle greater than 0° and less than 45° with respect to the tire width direction, as in the illustrated example.

The width (opening width) of the width direction groove5is not particularly limited, as it depends on the number of width direction grooves5, but may be 2 to 10 mm, for example. The width of the width direction groove5is measured as the opening width perpendicular to the extending direction of the groove in the reference condition, when viewed from the outer side in the tire radial direction and developed on a flat surface. Similarly, the depth (maximum depth) of the width direction groove5is not limited, but may be 5 to 20 mm, for example. However, the width of the width direction groove5is not limited in any way as long as it is large enough to prevent the block land portions adjacent in the tire circumferential direction from coming into contact with each other when the tire is grounded in the reference condition. In addition, the width of the width direction groove5does not have to be constant over the extending direction of the width direction groove5and may differ from each other depending on the location of the land portion4where the width direction groove5is provided.

The number of width direction grooves5across each of the land portions4may be any number. Depending on the number of width direction grooves5, the number of block land portions6included in the land portion4may be any number. Furthermore, the land portion4may be configured not to be crossed by the width direction groove5, i.e., the land portion4may be configured as a rib-shaped land portion that continues without interruption in the tire circumferential direction.

The land portion4comprises a sipe unit8consisting of a pair of sipes7. More specifically, a sipe unit8consisting of a pair of sipes7A and7B is arranged in the block land portion6included in the land portion4. Hereafter, when the sipes7A and7B are not specifically distinguished, they will be referred to collectively as simply sipe7.

Each of the pair of sipes7A and7B that constitutes the sipe unit8extends such that both ends in the extending direction of the sipe7terminate within the land portion4. More specifically, each of the pair of sipes7A and7B extends such that both ends in the extending direction of the sipe7terminate within the block land portion6. In other words, the sipe7does not have an open end that opens into the circumferential main groove3that defines the land portion4or the width direction groove5. In this way, since the sipe7does not have an open end and the block land portion6around the sipe7is connected, the block land portion6becomes difficult to collapse around the sipe7, and the rigidity of the block land portion6is improved.

Generally, as illustrated inFIG.2, when an external force such as frictional force is input from the road surface to the contact patch of the tread surface2that is in contact with the road surface, the block land portion6collapses into the void side of the sipe7. This causes to the block land portion6around the sipe7the lifting U from the road surface.FIG.2schematically illustrates the lifting U of the block land portion6around the sipe7.FIG.2illustrates a cross-sectional view in the tire circumferential direction of the tire1A, cut along the tire circumferential direction. When external force is applied to the tire1A in the direction indicated by the arrow inFIG.2, the lifting occurs in the block land portion6on the side where the external force is applied, with the sipe7as the boundary. In contrast, when the block land portion6around the sipe7is connected to each other, since the block land potion6around the sipe7restrains each other and can control the lifting U of the block land portion6around the sipe7caused by the input of external force from the road surface, thereby the footprint area of the tire1A at the time of the input of external force can be increased. This prevents the reduction in rigidity of the land portion of the tire1A due to the arrangement of the sipes7on the block land portion6, which in turn prevents the reduction in the footprint area of the tire1A. Therefore, the on-ice gripping performance of the tire1A is improved.

Referring again toFIG.1, each of the pair of sipes7A and7B that constitutes the sipe unit8extends in a straight line at an angle with respect to the tire width direction inFIG.1, i.e., in the developed view of the tread surface2.

The configuration of the sipe unit8is explained below with reference toFIGS.3and4.FIG.3schematically illustrates the arrangement of the sipe unit8depicted inFIG.1.FIG.4is a cross-sectional view illustrating the cross section (cross section perpendicular to the extending direction of the sipe7) by the line A-A′ indicated inFIG.3. InFIG.3, each of the pair of sipes7A and7B that constitute the sipe unit8extends in a straight line such that the angle φ with respect to the tire width direction satisfies 0°<φ<45°. In this way, the sipes7A and7B are inclined to the tire width direction, which allows the sipes7A and7B to contribute not only to the improvement of braking and driving force in the tire circumferential direction, but also to the improvement of lateral gripping performance (turning force) in the tire width direction. In particular, by setting φ<45°, the tire widthwise component of the sipe7is larger than the tire circumferential component thereof, and the sipe7can contribute to the improvement of braking and driving force in the tire circumferential direction, which is most important for safety. In this embodiment, the sipes7A and7B extend parallel to each other, however, the sipes7A and7B may extend at different angles with respect to the tire width direction.

InFIG.3, the length of the sipe7in the extending direction thereof is indicated by a. The length a of the sipe7in the extending direction thereof is, for example, between 3 and 15 mm. The length a of the sipe7in the extending direction thereof is preferably between 3 and 10 mm, and more preferably between 3 and 5 mm. The length a of the sipe7may be defined according to the depth (maximum depth) h of the sipe7. Specifically, the length a of the sipe7may be determined according to the depth h within the range where the length d of the sipe7in the tire width direction (d=a×cos φ) and the depth h of the sipe7satisfy d×h≤150 mm2. The length a of the sipe7is preferably defined within the range satisfying d×h≤100 mm2, and more preferably d×h≤50 mm2. The depth h of the sipe7may be, for example, 3 mm or more. The depth h of the sipe7may be 6.7 mm, for example.

Referring toFIG.4, the cross-sectional shape of the sipe7in a cross section perpendicular to the extending direction thereof at the tread surface2is described. In this embodiment, the cross-sectional shape of the sipe7in a cross section perpendicular to the extending direction thereof is approximately rectangular, as illustrated inFIG.4A. In the sipe7illustrated inFIG.4A, the width w of the sipe7is 1 mm or less as described above, and may be 0.4 mm, for example. However, the cross-sectional shape of the sipe7in a cross section perpendicular to the extending direction thereof may be other than rectangular. For example, the sipe7may be shaped with the groove bottom portion bulging in a cross section perpendicular to the extending direction of the sipe7, as illustrated inFIG.4B. In addition, for example, the sipe7may be rounded at the bottom in a cross section perpendicular to the extending direction of the sipe7. For example, in the cross section of the sipe7perpendicular to the extending direction thereof illustrated inFIG.4A, the bottom portion of the sipe7may be R-chamfered at both ends in the width direction of the sipe7, or the bottom portion of the sipe7may be semicircular. In the sipe7illustrated inFIG.4B, the width w of the sipe7may be 0.4 mm, for example, in the area of 50% or more of the depth of the sipe7.

Referring again toFIG.3, the sipe7B is displaced from the sipe7A by an offset s in the tire width direction and by an offset q in the tire circumferential direction. The offset s in the tire width direction of the sipes7A and7B may be defined, for example, in the range satisfying s≥1.5 mm.

The pair of sipes7A and7B that constitute the sipe unit8are opposed to each other in the tire circumferential direction only in part in the tire width direction. Here, “a line segment X and a line segment Y are opposed to each other in the direction Z” means that the line segment X and the line segment Y are separated from each other in the direction Z and that each of the ends of line segment Y is located on two straight lines extended along the direction Z from each end of the line segment X. However, “the sipes7A and7B are opposed to each other in the tire circumferential direction only in part in the tire width direction” shall include the case where only the end points of sipes7A and7B respectively are located on a straight line extending along the tire circumferential direction. In this embodiment, the sipes7A and7B are offset by s in the tire width direction. InFIG.3, the part7ain the tire width direction of the sipe7A and the part7bin the tire width direction of the sipe7B are opposed to each other in the tire circumferential direction. Here, the length d in the tire width direction of each of the sipes7A and7B (d=a×cos φ) and the offset s in the tire width direction of the sipes7A and7B satisfy d−s≥0. As a result, when the pair of sipes7A and7B in the sipe unit8are projected along the tire circumferential direction, at least one of the sipes7A and7B extends unbroken across the length of the sipe unit8in the tire width direction, as indicated by the shaded shading inFIG.3. Therefore, by increasing the length of the sipe unit8included in the tire width direction within the range where d−s≥0 is satisfied without changing the length of each of the sipes7A and7B that constitute the sipe unit8, the sipe unit8can provide edge effect and water removing effect in a wider range while maintaining the sipe density in the block land portion6. This improves the on-ice gripping performance of the tire1A.

Referring again toFIG.1, in the land portion4, a plurality of sipe units8are spaced apart from each other and repeatedly arranged in the tire circumferential direction to form a sipe unit row9. In the illustrated example, in one block land portion6, three sipe units8are arranged repeatedly in the tire circumferential direction to form a sipe unit row9. However, the number of sipe units8that constitute one sipe unit row9may be any number of two or more.

InFIG.3, the plurality of sipe units8that constitute the sipe unit row9are arranged repeatedly at a pitch p in the tire circumferential direction.

In this embodiment, the plurality of sipes7arranged on the block land portion6extend parallel to each other in the developed view of the tread surface2. Here, when the distance in the tire circumferential direction between adjacent sipe units8in the tire circumferential direction in the sipe unit row9is denoted as the distance r between units, the distance r between units is indicated by r=p−q. In particular, when the pitch p of the sipe unit8that constitute the sipe unit row9and the offset q in the tire circumferential direction of the sipes that constitute the sipe unit8is q=p/2, r=q holds true, then all the sipes7in the sipe unit row9are equally spaced in the tire circumferential direction. Therefore, the sipe density in the tire circumferential direction in the block land portion6can be made uniform by setting q preferably in the range of (p/2)×0.8 to (p/2)×1.2, and more preferably to p/2. This allows the tread surface2to contact the road surface more uniformly and to equalize the distribution of the ground pressure applied to the ground contact patch of the tread surface2, thereby increasing the footprint area of the tire1A.

The plurality of sipe units8that constitute the sipe unit row9are preferably arranged so that both ends in the tire width direction of each sipe unit are aligned on a straight line extending along the tire circumferential direction, respectively. Specifically, inFIG.3, both ends E1and E2in the tire width direction of the plurality of sipe units8that constitute the sipe unit row9are aligned on a straight line extending along the tire circumferential direction, respectively. This reduces the blank area (the area enclosed by the dashed line in the figure) where no sipes7are provided within the area of the block land portion6where the sipe unit row9is arranged. As a comparison,FIG.5illustrates an arrangement of sipe units8, which is different from that illustrated inFIG.3. InFIG.5, both ends in the tire width direction of each of the plurality of sipe units8that constitute the sipe unit row9are not aligned on a straight line extending along the tire circumferential direction, respectively. ComparingFIGS.3and5, the area enclosed by the dashed line inFIG.3is smaller than the area enclosed by the dashed line inFIG.5. In this way, by arranging both ends in the tire width direction of the plurality of sipe units8that constitute the sipe unit row9on a straight line extending along the tire circumferential direction, the blank area where no sipes7are provided can be reduced within the area of the block land portion6where the sipe unit row9is arranged. However, the arrangement of the sipe units8may be as illustrated inFIG.5.

Referring again toFIG.1, the land portion4comprises a plurality of sipe unit rows9arranged side-by-side in the tire width direction. In the illustrated example, in each of the block land portions6of the land portions4A and4E respectively, two sipe unit rows9are arranged side by side in the tire width direction. Also, in each of the block land portions6of the block land portions4B,4C and4D respectively, four sipe unit rows9are arranged side by side in the tire width direction. However, the number of sipe unit rows9arranged in one block land portion6may be any number.

The arrangement of a plurality of sipe unit rows9in the first embodiment is described below with reference toFIG.6.FIG.6schematically illustrates the arrangement of a plurality of sipe unit rows9in the first embodiment. InFIG.6, two sipe unit rows9A and9B are arranged side by side in the tire width direction.

In the first embodiment illustrated inFIG.6, a plurality of sipes7in two adjacent sipe unit rows9A and9B in the tire width direction extend at an angle with respect to the tire width direction, in the same direction between the sipe unit rows9A and9B. Specifically, among the plurality of sipe unit rows9A and9B, the plurality of sipes7in the first sipe unit row9A extend toward one side in the tire width direction (right in the figure) while being inclined toward one side in the tire circumferential direction (up in the figure).

Furthermore, the plurality of sipes7in the second sipe unit row9B which is adjacent to the first sipe unit row9A extend, as well as the plurality of sipes7included in the first sipe unit row9A, toward the one side in the tire width direction (right in the figure) while being inclined toward the one side in the tire circumferential direction (up in the figure).

Thus, the plurality of sipes7included in the plurality of sipe unit rows9adjacent to each other in the tire width direction are arranged to extend in the same direction between the sipe unit rows9, which makes it easier to arrange the blades for forming the sipes7in the mold during tire manufacturing and facilitates the fabrication of molds for the tire1A.

InFIG.6, the tire widthwise spacing between the adjacent sipe unit rows9A and9B in the tire width direction is indicated by v. Also, the offset in the tire circumferential direction of the adjacent sipe unit rows9A and9B in the tire width direction is indicated by u. The tire widthwise spacing v and the offset in the tire circumferential direction u may each be set to any value.

The tire widthwise spacing v is preferably −s to s (s>0). Here, the s is the offset in the tire width direction between the pair of sipes7that constitute the sipe unit8. As illustrated inFIG.6, the positive value of the tire widthwise spacing v means that the area between the two ends in the tire width direction of the sipe unit row9A and the area between the two ends in the tire width direction of the sipe unit row9B adjacent to the sipe unit row9A in the tire width direction are spaced apart in the tire width direction by the spacing v in the tire width direction. On the other hand, the negative value of the tire widthwise spacing v means that the area between the two ends in the tire width direction of the sipe unit row9A and the area between the two ends in the tire width direction of the sipe unit row9B adjacent to the sipe unit row9A in the tire width direction overlap in the tire width direction by the absolute value of the spacing v. By defining the tire widthwise spacing v in this manner, the blank area (the area enclosed by the dashed line in the figure) where no sipes7are provided is reduced within the area of the block land portion6where the adjacent sipe unit rows9A and9B in the tire width direction are arranged.

More preferably, the tire widthwise spacing v is set to 0 and the offset in the tire circumferential direction u is (d+s)×tan φ. Here, φ is the angle between each of the pair of sipes7that constitute the sipe unit8and the tire width direction, d is the length of the sipe7in the tire width direction, and s is the offset in the tire width direction between the pair of sipes7that constitute the sipe unit8. The arrangement of the sipe unit rows9, when the tire widthwise spacing v is 0 and the offset in the tire circumferential direction u is (d+s)×tan φ, is schematically illustrated inFIG.7.

By setting the tire widthwise spacing v to 0, the tire widthwise components of the plurality of sipes7are continuously arranged without gaps in the tire width direction, when the plurality of sipes7aligned in the tire width direction are projected along the tire circumferential direction, as illustrated by the shaded shading inFIG.7. This allows the sipes7to be distributed evenly without gaps across the multiple sipe unit rows9, thereby improving the edge effect and water removal effect in the block land portion6. In addition, the sipe density in the block land portion6can be made uniform by distributing the sipes7evenly without gaps across the multiple sipe unit rows9. This allows the tread surface2to contact the road surface more uniformly and the distribution of the ground pressure applied to the contact patch of the tread surface2to be equalized, thereby increasing the footprint area of the tire1A.

InFIG.7, each of the plurality of sipes7in the second sipe unit row9B extends over an extension line of any of the sipes7in the first sipe unit row9A. As a result, in the block land portion6, the plurality of sipes7are arranged in a straight line in the tire width direction. Because of this, by setting u preferably in the range of ((d+s)×tan φ)×0.8 to ((d+s)×tan φ)×1.2, and more preferably to (d+s)×tan φ, water captured in the voids of the sipes7is drained along the plurality of sipes7which are arranged in a straight line, toward the tire width direction, thereby improving the on-ice gripping performance on the land portion4. Furthermore, the plurality of sipes7in the adjacent sipe unit rows9A and9B are aligned in the same straight line, which facilitates the fabrication of molds with blades for forming the sipes7.

Referring again toFIG.1, twelve sipes7are arranged in each of the block land portions6of the land portions4A and4E respectively, and twenty-four sipes7are arranged in each of the block land portions6of the land portions4B,4C, and4D respectively. However, the number of sipes7arranged in one block land portion6may be any number.

For example, the number of sipes7arranged in the block land portion6may be determined based on the sipe density in the tire circumferential direction SD. The sipe density in the tire circumferential direction SD is a measure of the density in the tire circumferential direction of transverse sipes that completely cross the block land portion6. If the equivalent length in the tire circumferential direction of the block land portion6which is obtained by dividing the outer contour area of the block land portion6(mm2) by the maximum width BW is BL (mm), and the number of transverse sipes which are provided to completely cross the block land portion6is N′, the average sipe spacing in the tire circumferential direction is expressed as BL/(N′+1). The sipe density SD in the tire circumferential direction is expressed as the reciprocal of the average sipe spacing by the following formula (1).

The “outer contour area” of the block land portion6is the area enclosed by the outer contour of the block land portion6in the expanded view of the tread surface2. Therefore, even if non-grounded areas such as sipes, small holes, narrow grooves, etc. are arranged within the block land portion6, the area that does not exclude the area of the sipes, small holes, narrow grooves, etc. are considered.

The following is a description of the method used to calculate the sipe density SD in this embodiment. For example, assume a diamond-shaped block land portion6provided with multiple sipes7, as illustrated in the table providing sipe shapes inFIG.14. First, if the number of sipes7in the block land portion6is n, the length of sipes7in the tire width direction is d (mm), and the maximum width of the block land portion6in the tire width direction is BW (mm), the number of equivalent sipes N is expressed as d×n/BW. Here, the number of equivalent sipes N is the number of sipes when the sipes7in this embodiment are converted to transverse sipes (equivalent sipes) that are provided to completely cross the block land portion6. Furthermore, if the equivalent length in the tire circumferential direction of the block land portion6is BL (mm), the average sipe spacing in the tire circumferential direction is expressed as BL/(N+1). Here, the average sipe spacing in the tire circumferential direction is the spacing in the tire circumferential direction of the equivalent sipes in the block land portion6, when the sipes7in this embodiment are converted to the equivalent sipes. The sipe density SD in the tire circumferential direction is expressed as the reciprocal of the average sipe spacing by the following formula (2).

Note, that the number n of sipes7in the block land portion6, the length d in the tire width direction of the sipes7, the maximum width BW of the block land portion6in the tire width direction, and the outer contour area of the block land portion6are the values measured in the developed view of the tread surface2.

For example, a plurality of sipes7may be arranged in the block land portion6so that the sipe density SD is 0.15 (l/mm) or more. This improves the on-ice gripping performance of the tire1A.

A plurality of sipes7may be connected in the block land portion6by a shallow groove10.FIG.8schematically illustrates the arrangement of sipe units8in which the sipes7in the first embodiment are connected by the shallow grooves10. The block land portion6illustrated inFIG.8corresponds, for example, to the block land portion6B of the tire1A illustrated inFIG.1. InFIG.8, four of sipe unit rows9, aligned in the tire width direction, are arranged in the block land portion6. In each of the sipe unit rows9, three sipe units8are arranged repeatedly in the tire circumferential direction. InFIG.8, the sipes7, which are aligned in the tire width direction, are connected by the shallow groove10that completely crosses the block land portion6. A cross-section (B-B′ section) of the tire1A that is cut along the extending direction of the shallow groove10illustrated inFIG.8is illustrated inFIG.9. InFIG.9, the depth (maximum depth) H of the shallow groove10may be defined according to the depth h of the sipe7. For example, the depth H of the shallow groove10may be defined in the range of 5 to 60%, and preferably 5 to 20%, of the depth h of the sipe7. For example, the depth h of the sipe7may be 6.7 mm and the depth H of the shallow groove10may be 0.7 mm. With this configuration, water captured in the voids of the sipes7is drained through the shallow grooves10toward the tire width direction, thereby improving the on-ice gripping performance in the block land portion6.

Referring again toFIG.1, the block land portion6of the tire1A may be provided with sipes other than the sipe unit8described above. For example, in the illustrated example, the land portions4A and4E are provided with a plurality of zigzag-shaped sipes11extending in the tire width direction toward the tread edge TE. This improves drainage performance at the tread surface2, and thus the on-ice gripping performance of the tire1A.

Second Embodiment

Hereinafter, a tire1(1B) according to the second embodiment of the present disclosure will be described with reference toFIG.10.FIG.10is a schematic developed view of the tread pattern of the tire1B according to the second embodiment of this disclosure. Hereafter, tires1A and1B will be referred to collectively as simply tire1when no particular distinction is made between them.

As illustrated inFIG.10, the second embodiment differs from the first embodiment in that the plurality of sipes7in the two adjacent sipe unit rows9in the tire width direction are arranged to extend in different directions between the sipe unit rows9. The following is a description of the second embodiment, focusing on the points where it differs from the first embodiment. Note, that parts having the same configuration as those in the first embodiment are given the same reference numerals.

As in the first embodiment, the tire1B has, on the tread surface2, one or more (four in the illustrated example) circumferential main grooves3(3A,3B,3C,3D) extending in the tire circumferential direction; and a plurality (five in the illustrated example) of land portions4(4A,4B,4C,4D,4E) which are defined by the circumferential main grooves3adjacent to each other in the tire width direction of the one or more circumferential main grooves3, or by the circumferential main groove3(3A or3D) and the tread edge TE.

As in the first embodiment, in the tire1B, each land portion4is divided into a plurality of block land portions6by one or more width direction grooves5that completely cross the land portion4and extend in the tire width direction. For example, within the illustration, the land portion4C is divided into three block land portions6A,6B and6C adjacent to each other in the tire circumferential direction by two width direction grooves5A and5B adjacent to each other in the tire circumferential direction.

The land portion4comprises a sipe unit8consisting of a pair of sipes7, as in the first embodiment. More specifically, a sipe unit8, consisting of a pair of sipes7A and7B, is arranged in the block land portion6included in the land portion4.

As in the first embodiment, each of the pair of sipes7A and7B that constitutes the sipe unit8extends such that both ends in the extending direction of the sipe7terminate within the land portion4. More specifically, each of the pair of sipes7A and7B extends such that both ends in the extending direction of the sipe7terminate within the block land portion6.

As in the first embodiment, each of the pair of sipes7A and7B that constitutes the sipe unit8extends in a straight line at an angle with respect to the tire width direction in the developed view of the tread surface2. Each of the pair of sipes7A and7B that constitute the sipe unit8extends in a straight line such that the angle φ with respect to the tire width direction satisfies 0°<φ<45°.

As in the first embodiment, the pair of sipes7A and7B that constitute the sipe unit8are opposed to each other in the tire circumferential direction only in part in the tire width direction.

As in the first embodiment, in the land portion4, a plurality of sipe units8are repeatedly arranged in the tire circumferential direction to form a sipe unit row9. In the illustrated example, in one block land portion6, three sipe units8are arranged repeatedly in the tire circumferential direction to form a sipe unit row9. The plurality of sipe units8that constitute the sipe unit row9are preferably arranged so that both ends in the tire width direction of each sipe unit are aligned on a straight line extending along the tire circumferential direction, respectively.

In the land portion4, a plurality of sipe unit rows9are arranged side by side in the tire width direction. In the illustrated example, two sipe unit rows9are arranged side by side in the tire width direction in the block land portions6of the land portions4A and4E, respectively. Also, in the block land portions4B,4C and4D, four sipe unit rows9are arranged side by side in the tire width direction in the block land portions6of the land portions4B,4C and4D, respectively.

Hereinafter, referring toFIG.11, the arrangement of the plurality of sipe unit rows9in the second embodiment is described.FIG.11schematically illustrates the arrangement of the plurality of sipe unit rows in the second embodiment. InFIG.11, two sipe unit rows9A and9B are arranged side by side in the tire width direction.

In the second embodiment illustrated inFIG.11, unlike the first embodiment, a plurality of sipes7in two adjacent sipe unit rows9A and9B in the tire width direction extend at an angle with respect to the tire width direction, in a different direction between the sipe unit rows9A and9B. Specifically, among the plurality of the sipe unit rows9A and9B, the plurality of sipes7in the first sipe unit row9A extend toward one side in the tire width direction (right in the figure) while being inclined toward one side in the tire circumferential direction (up in the figure). On the other hand, the plurality of sipes7in the second sipe unit row9B which is adjacent to the first sipe unit row9A extend toward the one side in the tire width direction (right in the figure) while being inclined toward the other side in the tire circumferential direction (down in the figure).

This arrangement of the sipe unit rows9prevents the block land portion6from collapsing when external force is input to the tire1B, because the block land portion6is supported within the area where the adjacent sipe unit rows9A and9B are arranged. For example, when an external force is input in the direction indicated by the arrow inFIG.11, the block land portion6around the sipes7in the sipe unit row9A collapses toward the lower right in the drawing. On the other hand, the block land portion6around the sipes7in the sipe unit row9B collapses toward the lower left in the drawing. In this way, when an external force is input to the tire1B, the block land portion leans and collapses in different directions within the area where the adjacent sipe unit rows9A and9B in the tire width direction are arranged, so that the block land portion be supported within that area, and this makes the block land portion less likely to collapse. This increases the rigidity of the block land portion6. In addition, when an external force in the tire circumferential direction is applied to the tread surface2, the tire widthwise components of the external force applied to around the sipe unit rows9A and9B in the block land portion6cancel each other out, thereby preventing unexpected forces in the tire width direction from being applied to the tire1B and reducing the impact on the steering stability of a vehicle equipped with the tire1B.

InFIG.11, the length of sipe7in the extending direction thereof is indicated by a, and the angle between the sipe7and the tire width direction is indicated by φ. In this embodiment, the plurality of sipes7in one sipe unit row9extend parallel to each other in the developed view of the tread surface2. In the sipe unit8, a pair of sipes7A and7B is displaced each other by an offset s in the tire width direction and by an offset q in the tire circumferential direction. In addition, the plurality of sipe units8that constitute the sipe unit row9are arranged repeatedly at a pitch p in the tire circumferential direction. Here, when the distance in the tire circumferential direction between adjacent sipe units8in the sipe unit row9is denoted as the distance r between units, the distance r between units is indicated by r=p−q.

In particular, when the pitch p of the sipe unit8that constitute the sipe unit row9and the offset q in the tire circumferential direction of the sipes that constitute the sipe unit8is q=p/2, r=q holds true, then all the sipes7in the sipe unit row9are equally spaced in the tire circumferential direction. Therefore, the sipe density in the tire circumferential direction in the block land portion6can be made uniform by setting q preferably in the range of (p/2)×0.8 to (p/2)×1.2, and more preferably to p/2. This allows the tread surface2to contact the road surface more uniformly and to equalize the distribution of the ground pressure applied to the ground contact patch of the tread surface2, thereby increasing the footprint area of the tire1B.

InFIG.11, the tire widthwise spacing between the adjacent sipe unit rows9A and9B in the tire width direction is indicated by v. Also, the offset in the tire circumferential direction of the adjacent sipe unit rows9A and9B in the tire width direction is indicated by u.

The tire widthwise spacing v is preferably −s to s (s>0). Here, the s is the offset in the tire width direction between the pair of sipes7of the sipe unit8that constitute the sipe unit row9. As illustrated inFIG.11, the positive value of the tire widthwise spacing v means that the area between the two ends in the tire width direction of the sipe unit row9A and the area between the two ends in the tire width direction of the sipe unit row9B adjacent to the sipe unit row9A in the tire width direction are spaced apart in the tire width direction by the spacing v in the tire width direction. On the other hand, the negative value of the tire widthwise spacing v means that the area between the two ends in the tire width direction of the sipe unit row9A and the area between the two ends in the tire width direction of the sipe unit row9B adjacent to the sipe unit row9A in the tire width direction overlap in the tire width direction by the absolute value of the spacing v. By defining the tire widthwise spacing v in this manner, the blank area (the area enclosed by the dashed line in the figure) where no sipes7are provided is reduced within the area of the block land portion6where the adjacent sipe unit rows9A and9B in the tire width direction are arranged.

More preferably, the tire widthwise spacing v is set to 0 and the offset in the tire circumferential direction u is (d+s)×tan φ. Here, φ is the angle between each of the pair of sipes7that constitute the sipe unit8and the tire width direction, d is the length of the sipe7in the tire width direction, and s is the offset in the tire width direction between the pair of sipes7that constitute the sipe unit8. The arrangement of the sipe unit rows9when the tire widthwise spacing v is 0 and the offset in the tire circumferential direction u is (d+s)×tan φ is schematically illustrated inFIG.12.

By setting the tire widthwise spacing v to 0, the tire widthwise components of the plurality of sipes7are continuously arranged without gaps in the tire width direction, when the plurality of sipes7aligned in the tire width direction are projected along the tire circumferential direction, as illustrated by the shaded shading inFIG.12. This allows the sipes7to be distributed evenly without gaps across the multiple sipe unit rows9, thereby improving the edge effect and water removal effect in the block land portion6. In addition, the sipe density in the block land portion6can be made uniform by distributing the sipes7evenly without gaps across the multiple sipe unit rows9. This allows the tread surface2to contact the road surface more uniformly and the distribution of the ground pressure applied to the contact patch of the tread surface2to be equalized, thereby increasing the footprint area of the tire1B.

InFIG.12, each of the plurality of sipes7included in the second sipe unit row9B extends to intersect with an extension line of any of the sipes7included in the first sipe unit row9A. Therefore, when water captured in the void of one sipe7is drained from the sipe7along the extending direction of the sipe7, the water is captured again in another sipe7extending to intersect with the extension line of the sipe7, so that the on-ice gripping performance on the land portion4is less likely to be degraded.

In the tire1B, the number of sipes7arranged in the block land portion6may also be determined based on the sipe density SD, as described above in the first embodiment. For example, a plurality of sipes7may be arranged in the block land portion6so that the sipe density SD is 0.15 (l/mm) or more. This prevents the reduction in rigidity of the block land portion6of the tire1B due to the arrangement of the sipes7on the block land portion6, which in turn prevents the reduction in the footprint area of the tire1B. This improves the on-ice gripping performance of the tire1B.

In the tire1B, as in the first embodiment, a plurality of sipes7may also be connected in the block land portion6by a shallow groove10that crosses the block land portion6in the tire width direction.FIG.13schematically illustrates the arrangement of sipe units8in which the sipes7in the second embodiment are connected by the shallow grooves10. The block land portion6illustrated inFIG.13corresponds, for example, to the block land portion6B of the tire1B illustrated inFIG.10. InFIG.13, four rows of sipe unit rows9are arranged in the block land portion6, aligned in the tire width direction. In the sipe unit row9, three sipe units8are arranged repeatedly in the tire circumferential direction. Each of the sipes7(e.g.,7A inFIG.13) is connected to a sipe7(7C inFIG.13), one end of which is in an extension line along the extending direction of the sipe7(7A), by a shallow groove10that completely across the block land portion6. In other words, in the tire1B, a plurality of sipes7in the block land portion6are connected by the zigzag shallow grooves10that cross the block land portion6in the width direction groove. The depth H of the shallow groove10may be determined according to the depth h of the sipe7, as in the first embodiment. With this configuration, water captured in the voids of the sipes7is drained through the shallow grooves10toward the tire width direction, thereby improving the on-ice gripping performance in the block land portion6.

EXAMPLES

Examples of the tire1according to an embodiment of the present disclosure will be described below with reference toFIGS.14and15.FIG.14is a table providing Examples and Comparative Examples.FIG.15explains the block rigidity and footprint area in the Examples and Comparative Examples provided inFIG.14.

Finite Element Method (FEM) simulations were performed on the tires of Examples 1 to 2 and Comparative Examples 1 to 3 provided inFIG.14under the condition of applying a vertical load, which is obtained by multiplying the outer contour area of the block land portion by a standard ground pressure for passenger vehicle tires of 230 kPa, and thereby evaluating the block rigidity and the footprint area. In Examples 1 to 2 and Comparative Examples 1 to 3, the evaluation was performed as if the sipes provided in the sipe shapes inFIG.14were arranged in a diamond-shaped block land portion with a length in the tire circumferential direction of 45.6 mm and a length in the tire width direction of 27 mm, respectively.

As a result, as illustrated inFIG.15, both of the block rigidity Kx (N/mm) and the actual footprint area in shear Ar (mm2) were improved in Examples compared to Comparative Examples with the same sipe density. For example, Comparative Example 2 had an 11% increase in Kx and a 23% increase in Kx compared to Example 2. Here, the block rigidity Kx (N/mm) is the shear input value in the tire circumferential direction when the transverse displacement in the same direction is 1 mm, and the actual footprint area in shear Ar (mm2) is the remaining footprint area with partial lifting when the shear input in the tire circumferential direction is 0.3 times the above vertical load. Thus, in the tire1according to one embodiment of the present disclosure, the on-ice gripping performance can be improved by balancing sipe density and land rigidity (in other words, by improving land rigidity while maintaining sipe density, or by increasing sipe density while maintaining land stiffness).

From the above, it has been revealed that the tire1according to an embodiment of the present disclosure improves the on-ice gripping performance of the tire1.

As described above, the tire1of each embodiment of this disclosure is a tire having a land portion4(block land portion6) on a tread surface2, wherein the land portion4(block land portion6) comprises a sipe unit8consisting of a pair of sipes7, each of the pair of sipes7extends such that both ends in the extending direction of the sipes7terminate within the land portion4(block land portion6), and the pair of sipes7are opposed to each other in the tire circumferential direction only in part in the tire width direction. According to such a configuration, the reduction in rigidity of the land portion4(block land portion6) of the tire1due to the arrangement of the sipes7on the land portion4(block land portion6) can be controlled, and thus the reduction in the footprint area of the tire1can be controlled. In addition, the sipe density in the land portion4(block land portion6) can be maintained while increasing the range in which the sipes7can exhibit edge effects and water removal effects. This improves the on-ice gripping performance of the tire1.

In the tire1of each embodiment of this disclosure, it is preferable that each of the pair of sipes7extends in a straight line such that the angle φ with respect to the tire width direction satisfies 0°<φ<45°. According to such a configuration, the sipes7can contribute not only to the improvement of braking and driving force in the tire circumferential direction, but also to the improvement of lateral grip performance (turning force) in the tire width direction.

In the tire1of each embodiment of this disclosure, it is preferable that a plurality of the sipe units8are repeatedly arranged in the tire circumferential direction to form a sipe unit row9in the land portion4(block land portion6), and the plurality of the sipe units8that constitute the sipe unit row9are arranged so that both ends in the tire width direction of each sipe unit are aligned on a straight line extending along the tire circumferential direction, respectively. According to such a configuration, in the range of land portion4(block land portion6) where the sipe unit row9is arranged, the blank areas where the sipes7are not provided can be reduced.

In the tire1A according to the first embodiment of this disclosure, it is preferable that the land portion4(block land portion6) comprises a plurality of the sipe unit rows9arranged side-by-side in the tire width direction, among the plurality of the sipe unit rows9, the plurality of sipes7in the first sipe unit row9A extend toward one side in the tire width direction while being inclined toward one side in the tire circumferential direction, and the plurality of sipes7in the second sipe unit row9B which is adjacent to the first sipe unit row9A extend toward the one side in the tire width direction while being inclined toward the one side in the tire circumferential direction. Such a configuration facilitates the arrangement of the blades for forming the sipes7in the mold during tire manufacturing, and facilitates the fabrication of molds for the tire1A.

In the tire1A according to the first embodiment of this disclosure, it is preferable that each of the plurality of sipes7in the second sipe unit row9B extends over an extension line of any of the sipes7in the first sipe unit row9A. According to this configuration, water captured in the voids of the sipes7is drained along the plurality of sipes7, which are arranged in a straight line, toward the tire width direction, thereby further improving the on-ice gripping performance of the tire1A.

In the tire1B according to the second embodiment of this disclosure, it is preferable that the land portion4(block land portion6) comprises a plurality of the sipe unit rows9arranged side-by-side in the tire width direction, among the plurality of the sipe unit rows, the plurality of sipes7in the first sipe unit row9A extend toward one side in the tire width direction while being inclined toward one side in the tire circumferential direction, and the plurality of sipes7in the second sipe unit row9B which is adjacent to the first sipe unit row9A extend toward the one side in the tire width direction while being inclined toward the other side in the tire circumferential direction. According to this configuration, the block land portion6is prevented from collapsing when external force is input to the tire1B, because the land portion4(block land portion6) is supported in the range where the adjacent sipe unit rows9are arranged. This increases the rigidity of the land portion4(block land portion6), which in turn increases the footprint area of the tire1B. This further improves the on-ice gripping performance of the tire1B.

In the tire1according to each embodiment of this disclosure, it is preferable that: when the length of the sipe7in the tire width direction is d (mm) and the depth of the sipe7is h (mm), d×h is 150 (mm2) or less, and when the number of the sipes7in the land portion4(block land portion6) is n, the maximum width of the land portion4(block land portion6) in the tire width direction is BW (mm), the equivalent length in the tire circumferential direction of the land portion4(block land portion6) which is obtained by dividing the outer contour area of the land portion4(block land portion6) (mm2) by the maximum width BW is BL (mm), the number of equivalent sipes N is expressed as d×n/BW, the average sipe spacing in the tire circumferential direction is expressed as BL/(N+1), and the sipe density SD in the tire circumferential direction is expressed as the reciprocal of the average sipe spacing as SD=(N+1)/BL=((d×n/BW)+1)/BL, SD is 0.15 (l/mm) or more. According to such a configuration, the sipe density can be increased while controlling the reduction in rigidity of the land portion4(block land portion6) of the tire1due to the arrangement of the sipes7on the land portion4(block land portion6). This improves the on-ice gripping performance of the tire1.

Although our tire has been described based on the drawings and embodiments, it should be noted that one skilled in the art can make various variations and modifications based on this disclosure. Therefore, it is noted that these variations and modifications are included in the scope of this disclosure. For example, the configuration or functions, etc. included in each embodiment can be rearranged so as not to be logically inconsistent. The configuration or functions, etc. included in each embodiment can be used in combination with other embodiments, and multiple configurations or functions, etc. can be combined into one, divided, or partially omitted.

REFERENCE SIGNS LIST

1,1A,1B Tire2Tread surface3,3A,3B,3C,3D Circumferential main groove4,4A,4B,4C,4D,4E) Land portion5,5A,5B Width direction groove6,6A,6B,6C Block land portion7,7A,7B,7C Sipe7a,7bPart of sipe8Sipe unit9,9A,9B Sipe unit row10Shallow groovea Length of sipeh Depth of sipeW Width of siped Length of sipe in the tire width directions Offset in the tire width directionq Offset in the tire circumferential directionφ Angle between the sipe and the tire width directionp Pitch of units in the tire circumferential directionr Distance between units in the tire circumferential directionv Tire widthwise spacing between adjacent sipe units in the tire width directionu Offset in the tire circumferential direction between adjacent sipe unit rows in the tire width directionSD Sipe densityN Number of equivalent sipesBW Maximum width of block land portion in the tire width directionBL Equivalent length in the tire circumferential direction of the block land portionA-A′, B-B′ Cutting surfaceE1, E2End of sipe unit in the tire width directionTE Tread edgeCL Tire equatorial planeAr Actual footprint area in shearKx Block rigidityH Depth of shallow groovesU Lifting