tire

Abstract

Provided is a tire having excellent snow performance. A tire 10 has a tread surface 12. The tread surface 12 includes: a plurality of inclined grooves 14 arranged in the tire circumferential direction and inclined toward one side in the tire circumferential direction as the inclined grooves 14 extend from a ground-contact edge E toward a tire equatorial plane CP; and circumferential grooves 16 arranged on both sides in the tire width direction with respect to the tire equatorial plane CP and extending along the tire circumferential direction, the circumferential grooves 16 communicating the inclined grooves 14 with each other. The inclined grooves 14 include a branch groove portion 26 formed in a center land portion 54 partitioned and formed between the circumferential grooves 16. The branch groove portion 26 includes a first branch groove 28 and a second branch groove 30. The first branch groove 28 is inclined toward one side in the tire circumferential direction, and has a tip communicating with another inclined groove 14 adjacent on one side in the tire circumferential direction. The second branch groove 30 is inclined to the opposite side to the first branch groove 28 with respect to the tire circumferential direction, and has a tip terminating in the center land portion 54.

Description

tire

[0001] The present invention relates to a tire.

[0002] For example, Patent Document 1 discloses a winter tire having a tread portion provided with a plurality of first inclined grooves extending obliquely from a first tread edge on one side of the tire axial direction toward the tire equator, and the first inclined grooves include a main portion extending from the first tread edge and extending just short of the tire equator, and a branch portion branching from the main portion and crossing the tire equator, and the branch portion is discontinued without connecting to any grooves other than the first inclined grooves.

[0003] Japanese Patent Application Laid-Open No. 2018-193056

[0004] Winter tires are expected to have improved braking performance on icy and snowy roads.

[0005] An object of the present invention is to provide a tire with superior snow performance.

[0006] The tire of the present invention is a tire having a tread surface, wherein the tread surface comprises: a plurality of inclined grooves arranged in the tire circumferential direction, inclined from a ground contact edge toward the tire equatorial plane to one side in the tire circumferential direction; and circumferential grooves arranged on both sides in the tire width direction of the tire equatorial plane, extending along the tire circumferential direction and connecting the inclined grooves to each other, wherein the inclined grooves have branch groove portions formed in a center land portion defined between the circumferential grooves, the branch groove portion including a first branch groove and a second branch groove, wherein the first branch groove is inclined to one side in the tire circumferential direction and has a tip that connects to another inclined groove adjacent to the first branch groove on the one side in the tire circumferential direction, and the second branch groove is inclined to the opposite side of the first branch groove with respect to the tire circumferential direction, and has a tip that terminates within the center land portion.

[0007] According to the present invention, the snow performance is superior.

[0008] 1 is a plan view showing an example of a tread surface of a tire according to the present embodiment, an enlarged view of a portion II-II in FIG. 1, and an enlarged view of a portion III-III in FIG.

[0009] The tire of the present invention relates to the following aspects.

[0010] [Aspect 1] A tire having a tread surface, wherein the tread surface comprises: a plurality of inclined grooves arranged in the tire circumferential direction, inclined from a ground contact edge toward the tire equatorial plane to one side in the tire circumferential direction; and circumferential grooves arranged on both sides in the tire width direction of the tire equatorial plane, extending along the tire circumferential direction and connecting the inclined grooves to each other, wherein the inclined grooves have branch groove portions formed in a central land portion defined between the circumferential grooves, the branch groove portion including a first branch groove and a second branch groove, wherein the first branch groove is inclined to one side in the tire circumferential direction, and a tip end thereof is connected to another inclined groove adjacent to the first branch groove on the same side in the tire circumferential direction, and the second branch groove is inclined to the opposite side from the first branch groove with respect to the tire circumferential direction, and a tip end thereof terminates within the central land portion.

[0011] [Aspect 2] The tire according to Aspect 1, wherein the second branched grooves are arranged in a first center region centered on the tire equatorial plane, the length of the first center region in the tire width direction is 20% or less of the contact patch width, and the angle α between the extension direction of the second branched grooves and the tire circumferential direction is 45° or more and 60° or less.

[0012] [Aspect 3] The tire according to aspect 1 or 2, wherein the second branched groove has a tapered shape.

[0013] [Aspect 4] The tire according to any one of Aspects 1 to 3, wherein the inclined groove has a widthwise groove portion extending along the tire width direction at a base end of the branched groove portion, the widthwise groove portion being disposed in a second center region centered on the tire equatorial plane, and the length of the second center region in the tire width direction is 5% to 10% of the contact width.

[0014] [Aspect 5] The tire according to any one of Aspects 1 to 4, wherein the inclined groove has a plurality of convex portions, and the plurality of convex portions are arranged outward in the tire width direction from the circumferential groove.

[0015] [Aspect 6] The tire according to any one of Aspects 1 to 5, wherein the angle β formed between the extending direction of the circumferential groove and the tire circumferential direction is 5° or more and 20° or less.

[0016] [Aspect 7] The tire according to any one of Aspects 1 to 6, wherein the one circumferential side of the tire is a leading side.

[0017] [Aspect 8] The tire according to aspect 5, wherein the protrusion is formed on the leading side.

[0018] [Aspect 9] The tire according to any one of Aspects 1 to 8, which is a studded tire.

[0019] (Tire Configuration) Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description, the tire radial direction refers to a direction perpendicular to the tire rotational axis, the tire radially inner side refers to the side toward the tire rotational axis in the tire radial direction, and the tire radially outer side refers to the side away from the tire rotational axis in the tire radial direction. The tire circumferential direction refers to the direction around the tire rotational axis as the central axis. Furthermore, the tire width direction refers to a direction parallel to the tire rotational axis, the tire widthwise inner side refers to the side toward the tire equatorial plane in the tire width direction, and the tire widthwise outer side refers to the side away from the tire equatorial plane in the tire width direction. The tire equatorial plane refers to a plane that is perpendicular to the tire rotational axis and passes through the center of the tire width. Unless otherwise specified, "along" a certain reference includes along a direction within a range of less than ±45° from the certain reference.

[0020] Similarly, in the following description, "regular rim" refers to the "applicable rim" specified by JATMA, the "design rim" specified by TRA, or the "measuring rim" specified by ETRTO. Similarly, in the following description, "regular internal pressure" refers to the "maximum air pressure" specified by JATMA, the maximum value specified in "tire load limits at variable cold inflation pressures" specified by TRA, or the "inflation pressures" specified by ETRTO. Furthermore, "regular load" refers to the "maximum load capacity" specified by JATMA, the maximum value specified in "tire load limits at variable cold inflation pressures" specified by TRA, or the "load capacity" specified by ETRTO.

[0021] 1 is a plan view showing a tread surface 12 of a tire 10 according to this embodiment. The figure shows the tire portion in a state where the tire is mounted on a rim, has a normal internal pressure applied, and is in an unloaded state.

[0022] The tire 10 shown in FIG. 1 has a tread surface 12 on the outer side in the tire radial direction. The tread surface 12 is formed of a rubber material (tread rubber). The tread surface 12 comes into contact with the road surface when the vehicle is traveling. The tread surface 12 is annular, has a predetermined length in the tire width direction, and is continuous in the tire circumferential direction. A predetermined tread pattern is engraved on the tread surface 12. The tread pattern is asymmetric with respect to the tire equatorial plane CP between both sides of the tire equatorial plane CP in the tire width direction.

[0023] In Fig. 1 , the symbol E indicates a contact edge (a line connecting consecutive contact edges in the tire circumferential direction). The contact edge E is the maximum position in the tire width direction of the contact surface between the tire 10 and a flat plate when the tire 10 is mounted on a specified rim, pressurized to a specified internal pressure, placed perpendicular to a flat plate in a stationary state, and subjected to a load corresponding to a specified load (80% of the maximum load capacity). The symbol R indicates the tire rotation direction, with the direction of the arrow (i.e., downward in Fig. 1 ) indicating the leading side, which is one side in the tire circumferential direction, and the side opposite the direction of the arrow indicating the trailing side, which is the opposite side. The leading side is the side that first contacts the ground when the tire rolls in a specified rotation direction, and the trailing side is the side opposite the leading side.

[0024] The tread surface 12 is formed with a plurality of inclined grooves 14 and a plurality of circumferential grooves 16. The tread surface 12 is defined by the plurality of inclined grooves 14 and the plurality of circumferential grooves 16, which define a plurality of land portions 18. Each land portion 18 is formed with a plurality of sipes 20. By forming the sipes 20 in the land portions 18, the rigidity of each land portion can be adjusted, and in particular, the contact area with an icy or snowy road surface can be increased to increase frictional force, thereby further improving braking performance on ice. This configuration is particularly effective in studded tires that have stud pins on the tread surface 12.

[0025] The multiple inclined grooves 14 are inclined from the ground contact edge E toward the tire equatorial plane CP toward the leading edge. The portion of the inclined groove 14 that is inclined from the ground contact edge E toward the tire equatorial plane CP toward the leading edge may be referred to as an inclined portion 15. The multiple inclined grooves 14 include multiple first inclined grooves 22 and multiple second inclined grooves 24. The first inclined grooves 22 are inclined from the ground contact edge E on one side of the tire width direction relative to the tire equatorial plane CP toward the leading edge toward the tire equatorial plane CP. The second inclined grooves 24 are inclined from the ground contact edge E on the opposite side of the tire width direction relative to the tire equatorial plane CP toward the leading edge toward the tire equatorial plane CP. The first inclined grooves 22 and the second inclined grooves 24 that are adjacent in the tire width direction are positioned at positions offset from each other in the tire circumferential direction. That is, the first inclined grooves 22 and the second inclined grooves 24 are positioned at positions offset from each other in the tire circumferential direction by ½ pitch. The groove width of the first inclined groove 22 and the second inclined groove 24 gradually decreases from the outer side in the tire width direction toward the tire equatorial plane. The first inclined groove 22 and the second inclined groove 24 have substantially the same configuration except for their orientation, and therefore will be collectively referred to as the inclined groove 14 in the following description unless otherwise specified.

[0026] The inclined groove 14 has a branch groove portion 26. That is, the tip of the inclined portion 15 of the inclined groove 14 is connected to the branch groove portion 26. The branch groove portion 26 has a first branch groove 28 and a second branch groove 30. The first branch groove 28 is inclined toward the leading side and is connected to another inclined groove 14 adjacent to the leading side. More specifically, the first branch groove 28 is connected to the inclined portion 15 of another inclined groove 14 adjacent to the leading side. That is, the first branch groove 28 provided in the first inclined groove 22 is connected to the inclined portion 15 of the second inclined groove 24 adjacent to the leading side. The first branch groove 28 provided in the second inclined groove 24 is connected to the inclined portion 15 of the first inclined groove 22 adjacent to the leading side.

[0027] As shown in FIG. 2 , the second branch groove 30 is inclined toward the trailing edge and terminates within the land portion 18. The second branch groove 30 may have a tapered tip 32 in which the groove width gradually decreases from the base end 33 to the tip 32. The tip 32 of the second branch groove 30 shown in FIG. 2 is formed by one inclined edge 36 inclined from one groove wall 34 to the other groove wall 34 of a pair of groove walls 34. The angle α between the extension direction of the second branch groove 30 and the tire circumferential direction may be 45° to 60°, or 45° to 55°. The angle α of the branch groove portion 26 shown in FIGS. 1 and 2 is 50°. The angle α refers to the angle between the tire circumferential direction and an imaginary line L1 connecting the midpoint C1 of the groove width at the base end of the branch groove portion 26 and the midpoint C2 of the groove width at the tip end. When the second branch groove 30 has a tapered shape, the angle α is the angle between the tire circumferential direction and an imaginary line L1 connecting the midpoint C1 of the groove width at the base end of the second branch groove 30 to the tip 32. The midpoint C1 is the intersection of two lines passing through the groove width center of the first branch groove 28 and the groove width center of each widthwise groove portion 38.

[0028] The inclined groove 14 has a width direction groove portion 38 on the base end side of the branch groove portion 26. That is, the inclined groove 14 has the width direction groove portion 38 between the inclined portion 15 and the branch groove portion 26. The base end of the width direction groove portion 38 is connected to the tip end of the inclined portion 15, and the tip end is connected to the base end of the branch groove portion 26. The width direction groove portion 38 extends along the tire width direction. The angle θ between the extension direction of the width direction groove portion 38 and the tire width direction is preferably 10° or less toward the trailing edge or leading edge, or 5° or less. The angle θ between the extension direction of the width direction groove portion 38 and the tire width direction shown in FIGS. 1 and 2 is 5°. The angle θ is the angle between the tire width direction and an imaginary line L2 connecting the midpoint C3 of the groove width at the base end of the width direction groove portion 38 and the midpoint C1 of the tip end. The midpoint C1 of the groove width at the tip of the widthwise groove portion 38 is the same as the midpoint C1 of the groove width at the base end of the branch groove portion 26. The inclined groove 14 inclines from the ground contact edge E toward the leading edge of the tire equatorial plane CP and is connected to the branch groove portion 26 via the widthwise groove portion 38 extending along the tire width direction. The midpoint C3 is the intersection of two lines passing through the groove width center of the inclined portion 15 and the groove width center of the widthwise groove portion 38.

[0029] The inclined groove 14 has protrusions 40 ( FIG. 1 ). The protrusions 40 are provided on the groove wall 42 on the leading side of the pair of groove walls 42 of the inclined groove 14. The protrusions 40 are formed by recessing the groove wall 42 on the leading side of the inclined groove 14. The protrusions 40 include those that are approximately trapezoidal in plan view. Recesses 44 are formed between the protrusions 40. One or more protrusions 40 shown in FIG. 1 are formed for each inclined groove 14.

[0030] The circumferential grooves 16 extend along the tire circumferential direction and connect adjacent first inclined grooves 22 or adjacent second inclined grooves 24 in the tire circumferential direction. The circumferential grooves 16 are inclined toward the tire equatorial plane CP from the leading side to the trailing side with respect to the tire circumferential direction. The angle β between the extension direction of the circumferential groove 16 and the tire circumferential direction may be 5° to 20°, or 10° to 20° ( FIG. 3 ). The angle β between the extension direction of the circumferential groove 16 and the tire circumferential direction shown in FIGS. 1 and 2 is 15°. The angle β refers to the angle between the tire circumferential direction and an imaginary line L3 connecting a midpoint C4 of the groove width at a base end 46 where the circumferential groove 16 intersects with the leading-side inclined groove 14 and a midpoint C5 of the groove width at a tip end 48 where the circumferential groove 16 intersects with the trailing-side inclined groove 14.

[0031] The circumferential groove 16 has connecting ends 50 and an intermediate portion 52. The connecting ends 50 are defined as ranges extending from the base end 46 and the tip end 48, which are connected to the inclined grooves 14, respectively, and each extending from the base end 46 and the tip end 48 to 15% or less of the longitudinal length of the circumferential groove 16. The intermediate portion 52 is located between the connecting ends 50. The circumferential groove 16 is formed in a crank shape by the connecting ends 50 and the intermediate portion 52. The pair of connecting ends 50 extend obliquely on the same side in the tire width direction, that is, in the case of Figure 3, extend obliquely toward the outer side in the tire width direction. The intermediate portion 52 is located between the connecting ends 50 and extends obliquely on the opposite side in the tire width direction from the connecting ends 50, that is, in the case of Figure 3, extend obliquely toward the inner side in the tire width direction.

[0032] The circumferential grooves 16 are arranged on both sides of the tire equatorial plane CP in the tire width direction. A set of circumferential grooves 16 that are connected to one inclined groove 14 and arranged in the tire circumferential direction may or may not communicate with each other. In Fig. 1, a set of circumferential grooves 16 that are connected to one inclined groove 14 in the tire circumferential direction communicate with each other, but do not communicate with another set of circumferential grooves 16 that communicates with another inclined groove 14 that is adjacent to the inclined groove 14 in the tire circumferential direction.

[0033] Using the circumferential grooves 16 arranged on both sides in the tire width direction with respect to the tire equatorial plane CP as a reference, the land portions 18 on the inner side of the circumferential grooves 16 in the tire width direction are referred to as center land portions 54, and the land portions 18 on the outer side of the circumferential grooves 16 in the tire width direction are referred to as shoulder land portions 56. The tread surface 12 shown in FIG. 1 does not have a circumferential groove in the center land portion 54.

[0034] The branched groove portions 26 and widthwise groove portions 38 are arranged in the center land portion 54 ( FIG. 1 ). The second branched grooves 30 are preferably arranged in the first center region AR1. The first center region AR1 is a region in the tire width direction centered on the tire equatorial plane CP. The tire width direction length of the first center region AR1 is 20% or 15% of the contact patch width. The contact patch width is the tire width direction length between the contact patch edges E on both sides in the tire width direction. The widthwise groove portions 38 are preferably arranged in the second center region AR2. The second center region AR2 is a region in the tire width direction centered on the tire equatorial plane CP. The tire width direction length of the second center region AR2 is 10% or 5% of the contact patch width. The tire width direction length of the widthwise groove portions 38 is preferably 5% or more of the contact patch width.

[0035] The inclined groove 14 has an inclined portion 15 in the center land portion 54. That is, the angle ω of the inclined groove 14 with respect to the tire circumferential direction in the center land portion 54 may be 35° or more and 55° or less, or 40° or more and 50° or less. In the tire 10 shown in FIG. 1 , the angle between the extension direction of the inclined groove 14, i.e., the inclined portion 15, in the center land portion 54 and the tire circumferential direction is 45°. The inclined groove 14 may extend in a direction along the tire width direction in the shoulder land portion 56. The angle ω refers to the angle between the tire circumferential direction and an imaginary line L4 connecting the midpoint C6 of the groove width of the inclined groove 14 at the position where it intersects with the circumferential groove 16 and the midpoint C3 of the groove width at the base end of the widthwise groove portion 38. The inclined groove 14 may extend in a direction less than ±10° with respect to the tire width direction in the shoulder land portion 56.

[0036] The convex portions 40 formed in the inclined groove 14 are arranged in the shoulder land portion 56. As shown in FIG. 1 , the convex portions 40 are formed on the groove wall 42 on the leading side of the inclined groove 14. Two or three convex portions 40 are arranged along the groove wall 42 of the inclined groove 14.

[0037] Although not shown in its entirety, the tire 10 of this embodiment has a meridian cross-sectional shape similar to that of a conventional pneumatic tire. That is, the tire 10 of this embodiment has, from the inner side to the outer side in the tire radial direction in a tire meridian cross-sectional view, a bead portion, a sidewall portion, a shoulder portion, and a tread portion. The tire 10 has, for example, a carcass layer extending from the tread portion to both bead portions and wound around a pair of bead cores in a tire meridian cross-sectional view, and a belt layer and, in some cases, a belt cover layer on the tire radial outer side of the carcass layer.

[0038] The tire 10 of this embodiment described above is obtained through each of the usual manufacturing steps, i.e., a tire material mixing step, a tire material processing step, a green tire molding step, a vulcanization step, and a post-vulcanization inspection step, etc. When manufacturing the tire of this embodiment, protrusions and recesses corresponding to a predetermined tread pattern are formed on the inner wall of a vulcanization mold, and vulcanization is carried out using this mold.

[0039] (Functions and Effects) Next, the functions and effects of the tire 10 configured as described above will be described. When the tire 10 is on a snowy road surface, snow enters the inclined grooves 14 and is compacted within the inclined grooves 14 to form snow pillars. A snow pillar shear force acts on the snow pillar, which is generated between the tire 10 and the snow pillar, and the tire 10 obtains driving force and braking force.

[0040] The inclined grooves 14 are inclined from the ground contact edge E toward the tire equatorial plane CP, which provides snow column shear force during straight driving and cornering, resulting in excellent snow performance, i.e., braking performance on snow, traction performance on snow, and cornering performance on snow. In addition, the inclined grooves 14 have branch groove portions 26 in the center land portion 54 where ground pressure is high, which provides greater snow column shear force.

[0041] The branched groove portion 26 has a first branched groove 28 and a second branched groove 30 that terminates in the center land portion 54 and is inclined toward the trailing edge. The first branched groove 28 has a large groove area because it is connected to other inclined grooves 14 adjacent in the tire circumferential direction. The branched groove portion 26 is provided in the first center region AR1, where the ground contact pressure is higher. Therefore, the tire 10 can obtain a larger snow column shear force in proportion to the larger groove area. The second branched groove 30 terminates in the center land portion 54, thereby suppressing a decrease in block rigidity.

[0042] Because the second branched grooves 30 are inclined toward the trailing edge, after trailing edge, the tip 32 is lower from the road surface than the base 33. This makes it easier for snow packed inside the second branched grooves 30 to break down and fall from the tip 32 of the second branched grooves 30. In other words, the tire 10 can efficiently discharge snow from the second branched grooves 30 while driving, suppressing a decrease in snow column shear force due to snow clogging. Therefore, the tire 10 can maintain better traction on snow.

[0043] By setting the angle α between the extension direction of the second branch groove 30 and the tire circumferential direction to be between 45° and 60°, the tire 10 can obtain an appropriate edge effect and therefore has excellent braking performance on snow. Furthermore, by having the second branch groove 30 have a tapered shape, snow packed in the second branch groove 30 can easily be released from the second branch groove 30. Therefore, the tire can more efficiently discharge snow from the second branch groove 30, thereby maintaining better traction on snow.

[0044] The inclined grooves 14 have the widthwise groove portions 38 in the second center region AR2 where the ground pressure is greater, thereby providing greater driving force and braking force when traveling straight. Therefore, the tire 10 has excellent braking performance and traction on snow.

[0045] The inclined groove 14 has a protrusion 40, which allows it to obtain a large snow column shear force. Furthermore, since the protrusion 40 is provided in the shoulder land portion 56 on the leading side, it can exert an edge effect during braking. Therefore, the tire 10 has excellent braking performance and traction performance on snow. The protrusion 40 is formed by recessing the groove wall 42 on the leading side of the inclined groove 14, which increases the groove area and therefore obtains a correspondingly large snow column shear force.

[0046] The circumferential grooves 16 are inclined relative to the tire circumferential direction, which allows for greater snow column shear force when cornering on snowy roads. By setting the angle β between the extension direction of the circumferential grooves 16 and the tire circumferential direction to between 5° and 20°, an appropriate edge effect is obtained and snow can be more reliably discharged when traveling straight. Therefore, the tire can maintain excellent braking performance, traction performance, and cornering performance on snow.

[0047] The tire 10 is a studded tire with stud pins provided on the tread surface, thereby achieving better snow performance, i.e., braking performance on snow, traction performance on snow, and turning performance on snow.

[0048] (Modifications) The present invention is not limited to the above-described embodiment, and can be modified as appropriate within the scope of the invention.

[0049] For example, in the above embodiment, the multiple inclined grooves 14 are described as being inclined from the ground contact edge E toward the tire equatorial plane CP toward the leading side, but the present invention is not limited to this, and they may also be inclined toward the trailing side.

[0050] In the above embodiment, the case where the plurality of protrusions 40 are provided on the groove wall 42 on the leading side of the inclined groove 14 has been described, but the present invention is not limited to this, and the protrusions 40 may be provided on the groove wall 42 on the trailing side. By providing the plurality of protrusions 40 on the groove wall 42 on the trailing side of the inclined groove 14, the groove area is increased, and the same effect as in the above embodiment can be obtained.

[0051] In the above embodiment, the second branched groove 30 has a tapered shape, but the present invention is not limited to this. The second branched groove 30 may have a groove width that changes by ±10% or less, ±5% or less, or be constant from the base end 33 to the tip end 32.

[0052] Although the tip 32 of the second branch groove 30 has been described as being formed by one inclined edge 36 that is inclined from one of the pair of groove walls 34 to the other, the present invention is not limited to this. The tip 32 of the second branch groove 30 may be formed by two inclined edges with the midpoint of the groove width as the vertex. The tip of the second branch groove 30 may also be elliptical.

[0053] Tires according to Examples 1 to 7 and a pneumatic tire according to Reference Example were manufactured, each having a tire size of 205 / 55R16 91H (specified by JATMA) and having inclined grooves and circumferential grooves with the shape shown in Fig. 1 when mounted on a rim. Detailed conditions of these tires are as shown in Table 1 below.

[0054] In Table 1, the inclined grooves, branched grooves, angle α (°), second branched grooves, widthwise grooves, convex portions, and angle β (°) all conform to the descriptions given in this specification.

[0055] In Table 1, "Present" in the "Inclined Groove" column indicates that the tire has the first inclined groove and the second inclined groove in FIG. 1 . "Present" in the "Presence or Absence of Branch Grooves" column and "20" in the "Angle α (°)" column indicates that the tire has branch grooves, but the angle α of the first branch groove is 20°. "Present" in the "Presence or Absence of Branch Grooves" column and "50" in the "Angle α (°)" column indicates that the tire has branch grooves, and the angle α of the first branch groove is 50°. In the "Second Branch Groove Tip Shape" column, "Parallel" indicates that the groove width of the second branch groove is constant from the base end to the tip, and "Tapered" indicates the tapered shape in FIGS. 1 and 2 . In the "Width Direction Groove" column, "Absent" indicates that the tire does not have width direction grooves, and "Present" indicates that the tire has width direction grooves that form an angle of 5° with the tire width direction.

[0056] The tires according to Examples 1 to 7 and the tire of the Reference Example thus prepared were mounted on a 16x6.5J aluminum rim at 250 kPa, and each test tire was mounted on a FF test vehicle (engine displacement: 1500 cc). Snow performance, i.e., braking performance on snow, traction performance on snow, and cornering performance on snow were evaluated according to the following procedures.

[0057] (Snow Braking Performance) A test vehicle was run on a packed snow road surface, and the braking distance was measured when braking at an initial speed of 40 km / h. The reciprocals of the results were calculated and the results are shown in the "Snow Braking Performance" column in Table 1 as an index, with the value of the Reference Example being 100. The larger the index, the shorter the braking distance and the better the tire.

[0058] (Drivability on Snow) The test vehicle was started from a stopped state on a packed snow road, and the time required to travel 15 m was measured. The reciprocals of the results were calculated and the results are shown in the "Drivability on Snow" column in Table 1 as an index with the value of the Reference Example being 100. The higher the index, the shorter the driving time and the better the performance.

[0059] (Snow turning performance) The test vehicle was measured for lateral acceleration when traveling at a speed of 30 km / h on a 30 m radius course on a snowy road surface at a snow road test site. The results of this measurement were used to calculate an index, with the value of the reference example being 100, and the results are shown in the "Snow turning performance" column of Table 1. The higher the index, the lower the acceleration and the better the snow turning performance.

[0060]

[0061] According to Table 1, it was confirmed that the tires of Examples 1 to 7, which fall within the technical scope of the present invention, all had superior snow performance compared to the tires of Reference Examples, which do not fall within the technical scope of the present invention. In Example 2, the angle α between the second branch groove and the tire circumferential direction was 50°, thereby improving braking performance and turning performance on snow compared to Example 1. In Example 3, the tapered shape of the second branch grooves improved traction on snow compared to Example 2. In Example 4, the inclusion of widthwise grooves improved braking performance and turning performance on snow compared to Example 3. In Example 5, the inclined grooves had convex portions, thereby improving braking performance and turning performance on snow compared to Example 4. In Example 6, the angle β between the circumferential groove and the tire circumferential direction was 15°, thereby improving braking performance, turning performance, and turning performance on snow compared to Example 5. In Example 7, the stud pins were provided on the tread surface, and as a result, compared to Example 6, braking performance on snow, traction performance on snow, and cornering performance on snow were improved.

[0062] REFERENCE SIGNS 10 Tire 12 Tread surface 14 Inclined groove 15 Inclined portion 16 Circumferential groove 18 Land portion 20 Sipe 22 First inclined groove 24 Second inclined groove 26 Branched groove portion 28 First branched groove 30 Second branched groove 32 Tip end (second branched groove) 33 Base end (second branched groove) 34 Groove wall (second branched groove) 36 Inclined edge 38 Width direction groove portion 40 Convex portion 42 Groove wall (inclined groove) 44 Concave portion 46 Base end (circumferential groove) 48 Tip end (circumferential groove) 50 Connection end portion 52 Intermediate portion 54 Center land portion 56 Shoulder land portion C1 Midpoint of groove width at base end of second branched groove C2 Midpoint of groove width at tip end of second branched groove C3 Midpoint of groove width at base end of width direction groove portion C4 C5: Midpoint of groove width at base end of circumferential groove C1: Midpoint of groove width at tip end of circumferential groove L1: Virtual line L2: Virtual line (widthwise groove portion) L3: Virtual line (circumferential groove)

Claims

1. A tire having a tread surface, wherein the tread surface comprises: a plurality of inclined grooves arranged in the tire circumferential direction, the inclined grooves inclining from a ground contact edge toward the tire equatorial plane to one side in the tire circumferential direction; and circumferential grooves arranged on both sides in the tire width direction of the tire equatorial plane, the inclined grooves extending along the tire circumferential direction and connecting the inclined grooves to each other, wherein the inclined grooves have branch groove portions formed in a center land portion defined between the circumferential grooves, the branch groove portions including a first branch groove and a second branch groove, the first branch groove inclined to one side in the tire circumferential direction, and a tip end of the second branch groove inclined to the opposite side of the first branch groove with respect to the tire circumferential direction, and the tip end of the second branch groove terminates within the center land portion.

2. The tire described in claim 1, wherein the second branched grooves are arranged in a first center region centered on the tire equatorial plane, the length of the first center region in the tire width direction is 20% or less of the contact patch width, and the angle α between the extension direction of the second branched grooves and the tire circumferential direction is 45° or more and 60° or less.

3. The tire according to claim 1, wherein the second branch groove has a tapered shape.

4. The tire according to claim 1, wherein the inclined groove has a widthwise groove portion extending along the tire width direction at the base end of the branched groove portion, the widthwise groove portion being arranged in a second center region centered on the tire equatorial plane, and the length of the second center region in the tire width direction is 5% to 10% of the contact width.

5. The tire according to claim 1, wherein the inclined groove has a plurality of convex portions, and the plurality of convex portions are arranged outward in the tire width direction from the circumferential groove.

6. The tire according to claim 1, wherein the angle β formed between the extending direction of the circumferential groove and the tire circumferential direction is 5° or more and 20° or less.

7. The tire according to claim 1, wherein the one circumferential side of the tire is the leading side.

8. The tire according to claim 5, wherein the protrusion is formed on the leading side.

9. The tire of claim 1, which is a studded tire.

Images