tire

Abstract

A tire 10 includes, in a tread surface 14, two circumferential main grooves 16 and a plurality of V-shaped grooves 18 which are arranged on the inner side in the tire width direction of the two circumferential main grooves 16 and are provided at intervals in the tire circumferential direction. Center land parts 22 are formed demarcated by the two circumferential main grooves 16 and the V-shaped grooves 18 adjacent to one another in the tire circumferential direction. The V-shaped grooves 18 respectively have tip parts 20 projecting in a V-shape to one side in the tire circumferential direction, extend from the tip parts 20 to both sides in the tire width direction, and are connected to the two circumferential main grooves 16. A plurality of inclined narrow grooves 30 are provided between the tire center line CL and a circumferential main groove 16 on one side and between the tire center line CL and a circumferential main groove 16 on the other side. The inclined narrow grooves 30 are inclined outward in the tire width direction toward one side in the tire circumferential direction, and are connected to the V-shaped grooves 18 adjacent thereto in the tire circumferential direction. The tip parts 20 are each provided with a first branch groove 32 and a second branch groove 34. The first branch groove 32 is terminated in the corresponding center land part 22. The second branch groove 34 is connected to the corresponding V-shaped groove 18 adjacent thereto on the one side in the tire circumferential direction.

Description

tire

[0001] The present invention relates to a tire.

[0002] One example of a tire that can improve wet and snow performance is the tire described in Patent Document 1. The tire described in Patent Document 1 has a plurality of first land portions arranged adjacent to each other in the tire circumferential direction, a plurality of second land portions arranged adjacent to each other in the tire circumferential direction, and the first and second land portions arranged in a staggered pattern along the tire equatorial plane. Each of the first and second land portions includes a plurality of through grooves that penetrate the land portion and open into the pair of oblique main grooves, and a plurality of blocks defined by these through grooves. The innermost center block is defined as the block closest to the tire equatorial plane. The edge of the innermost center block has a notch that opens into the connection between the oblique main grooves.

[0003] Japanese Patent Application Laid-Open No. 2020-183128

[0004] In recent years, further improvements in wet and snow performance have been required for winter tires. An object of the present invention is to provide a tire that has excellent wet and snow performance while suppressing a decrease in dry performance.

[0005] A tire according to one aspect of the present invention comprises, on a tread surface, two circumferential main grooves and a plurality of V-shaped grooves disposed inward in the tire width direction from the two circumferential main grooves and spaced apart in the tire circumferential direction, a center land portion defined by the two circumferential main grooves and the V-shaped grooves adjacent in the tire circumferential direction, and the tire has a designated rotation direction, wherein the two circumferential main grooves are disposed on both sides in the tire width direction across the tire equatorial plane and extend in the tire circumferential direction, the V-shaped groove has a tip end portion projecting in a V shape to one side in the tire circumferential direction, and extends obliquely from the tip end toward the other side in the tire circumferential direction, and is connected to the two circumferential main grooves, and a plurality of oblique narrow grooves are provided between the tire equatorial plane and the circumferential main groove on one side, and between the tire equatorial plane and the circumferential main groove on the other side, The inclined narrow grooves are inclined outward in the tire width direction toward one side in the tire circumferential direction and are connected to the V-shaped grooves adjacent to each other in the tire circumferential direction, a first branch groove and a second branch groove are provided at the tip end portion and extend from the tip end portion to one side in the tire circumferential direction, the first branch groove terminates within the center land portion, and the second branch groove is connected to the V-shaped groove adjacent to the one side in the tire circumferential direction.

[0006] According to the present invention, the tire has excellent wet and snow performance while suppressing a decrease in dry performance.

[0007] Fig. 1 is a plan view showing an example of a tread surface of a tire according to the present embodiment. Fig. 2 is a partially enlarged view taken along line II-II in Fig. 1. Fig. 3 is a partially enlarged view taken along line III-III in Fig. 1. Fig. 4 is a partially enlarged cross-sectional view taken along line IV-IV in Fig. 2. Fig. 5 is a partially enlarged cross-sectional view taken along line V-V in Fig. 2.

[0008] Hereinafter, embodiments of the tire according to the present invention (basic embodiment and additional embodiments 2 to 9 shown below) will be described in detail with reference to the drawings. These embodiments do not limit the present invention. Furthermore, the components of the above embodiments include those that are easily replaceable by a person skilled in the art, or those that are substantially identical. Furthermore, the various embodiments included in the above embodiments can be combined in any way within the scope of what is obvious to a person skilled in the art.

[0009] In the following description, the tire radial direction refers to the direction perpendicular to the tire's rotation axis, the tire radially inner side refers to the side toward the rotation axis in the tire radial direction, and the tire radially outer side refers to the side away from the rotation axis in the tire radial direction. The tire circumferential direction refers to the direction around the rotation axis as the central axis. The tire width direction refers to the direction parallel to the rotation axis, the tire widthwise inner side refers to the side toward the tire equatorial plane (tire equator line) 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 CL is a plane that is perpendicular to the tire's rotation axis and passes through the center of the tire width. Note that "along" a certain direction does not necessarily mean a direction parallel to the certain direction, but also includes a case where the direction is inclined at an angle of less than ±15° relative to the certain direction. The trailing side and leading side in the tire circumferential direction are based on forward movement.

[0010] 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. Similarly, in the following description, the contact width refers to the maximum dimension in the tire width direction of the area that comes into contact with the road surface when the tire is fitted with a standard rim, the standard internal pressure is applied, and a load of 80% of the standard load is applied.

[0011] <Basic Configuration> A basic configuration of a tire according to an embodiment of the present invention will be described below. A tire 10 shown in Fig. 1 has a tread portion 12 on the outer side in the tire radial direction. The tire 10 has a specified rotation direction. One side in the tire circumferential direction is the lower side in Fig. 1, which is also referred to as the leading side. The other side in the tire circumferential direction is the upper side in Fig. 1, which is also referred to as the trailing side.

[0012] The tread portion 12 is formed of a rubber material (tread rubber). The tread portion 12 has a tread surface 14 that comes into contact with the road surface when the vehicle is traveling. The tread surface 14 is annular, centered on the rotational axis of the tire 10, 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 14. The tread pattern is asymmetric with respect to the tire equatorial plane CL between both sides of the tire equatorial plane CL in the tire width direction. In FIG. 1 , the symbol EL indicates a contact edge line (a line connecting consecutive contact edges in the tire circumferential direction).

[0013] As shown in FIG. 1 , a tire 10 according to this embodiment has two circumferential main grooves 16 on a tread surface 14. The tire 10 has a first circumferential main groove 16L on one side of the tire equatorial plane CL in the tire width direction and a second circumferential main groove 16R on the other side in the tire width direction. The first circumferential main groove 16L and the second circumferential main groove 16R extend in the tire circumferential direction. That is, the first circumferential main groove 16L and the second circumferential main groove 16R are each formed so that an imaginary line parallel to the tire circumferential direction can pass through the groove. Therefore, at least a portion of water that flows into the first circumferential main groove 16L and the second circumferential main groove 16R can move linearly in the tire circumferential direction through the first circumferential main groove 16L and the second circumferential main groove 16R. In the following description, unless otherwise distinguished, the first circumferential main groove 16L and the second circumferential main groove 16R will be referred to as the circumferential main groove 16.

[0014] The center lines of the first circumferential main groove 16L and the second circumferential main groove 16R are used as boundaries, and the region in the tire width direction from the first circumferential main groove 16L to the second circumferential main groove 16R is called the center region Ce, and the regions on the tire width direction outer side of the first circumferential main groove 16L and the second circumferential main groove 16R are called shoulder regions Sh.

[0015] The tire 10 has a plurality of V-shaped grooves 18 on the tread surface 14. The V-shaped grooves 18 are arranged in a center region Ce and are spaced apart in the tire circumferential direction. Each V-shaped groove 18 has a tip portion 20 that protrudes in a V-shape toward the leading side, which is one side in the tire circumferential direction. The tip portion 20 is arranged near the tire equatorial plane CL, i.e., within a range of 20%, preferably 10%, of the contact width W centered on the tire equatorial plane CL.

[0016] The V-shaped groove 18 extends obliquely from the tip end 20 to both sides in the tire width direction toward the trailing edge, which is the other side in the tire circumferential direction. The V-shaped groove 18 communicates with the first circumferential main groove 16L and the second circumferential main groove 16R.

[0017] In the tire 10, a center land portion 22 is defined by the first circumferential main groove 16L, the second circumferential main groove 16R, and the V-shaped grooves 18 adjacent to each other in the tire circumferential direction. A plurality of center land portions 22 are arranged in the tire circumferential direction, sandwiching the V-shaped groove 18 therebetween. The center land portion 22 may be provided with a plurality of sipes 24. The tire 10 is provided with lug grooves 26 in the shoulder regions Sh. The lug grooves 26 are arranged such that openings communicating with the first circumferential main groove 16L and the second circumferential main groove 16R overlap in the tire width direction with openings of the V-shaped grooves 18 communicating with the first circumferential main groove 16L and the second circumferential main groove 16R. The lug grooves 26 are arranged at predetermined intervals in the tire circumferential direction, extend in the tire width direction, and define shoulder land portions 28. The shoulder land portions 28 may be provided with a plurality of sipes 24. The lug groove 26 may communicate with the ground contact end EL.

[0018] Based on this premise, the tire 10 according to the basic embodiment includes an inclined narrow groove 30, a first branched groove 32, and a second branched groove 34, as shown in Fig. 2. The inclined narrow groove 30, the first branched groove 32, and the second branched groove 34 are formed in each center land portion 22.

[0019] A plurality of inclined narrow grooves 30 are provided between the tire equatorial plane CL and the first circumferential main groove 16L, and a plurality of inclined narrow grooves 30 are provided between the tire equatorial plane CL and the second circumferential main groove 16R. The inclined narrow grooves 30 have a groove width smaller than that of the first circumferential main groove 16L and the second circumferential main groove 16R. The groove width of the inclined narrow grooves 30 may be 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less of that of the first circumferential main groove 16L and the second circumferential main groove 16R.

[0020] 1 , a total of four inclined narrow grooves 30 are provided within one center land portion 22, two between the tire equatorial plane CL and the first circumferential main groove 16L and two between the tire equatorial plane CL and the second circumferential main groove 16R. The inclined narrow grooves 30 are inclined outward in the tire width direction from the trailing edge to the leading edge in the tire circumferential direction. Each inclined narrow groove 30 is connected to a V-shaped groove 18 adjacent to it in the tire circumferential direction.

[0021] The first branched groove 32 and the second branched groove 34 extend from the tip 20 of the V-shaped groove 18 toward the leading edge in the tire circumferential direction. The first branched groove 32 extends from the tip 20 toward the leading edge in the tire circumferential direction, obliquely extending to the other side in the tire width direction, and terminates within the center land portion 22. The second branched groove 34 extends from the tip 20 toward the leading edge in the tire circumferential direction, obliquely extending to one side in the tire width direction, and communicates with the V-shaped groove 18 adjacent to the leading edge in the tire circumferential direction.

[0022] Furthermore, the tire 10 may have a cutout portion 36. The cutout portion 36 is provided between the tip end portion 20 of the V-shaped groove 18 and the inclined narrow groove 30. The cutout portion 36 is on an extension line of a second branch groove 34 that communicates with the V-shaped groove 18 on the trailing-out side, extends to the center land portion 22 on the leading-out side of the V-shaped groove 18, and terminates within the center land portion 22.

[0023] FIG. 1 shows the shape of each groove in an unloaded state after the tire is mounted on a standard rim and inflated to the specified internal pressure. In this state, for example, for a tire with a size of 205 / 55R16 91H, the first circumferential main groove 16L and the second circumferential main groove 16R have a groove width of 4.0 mm to 6.0 mm and a groove depth of 7.0 mm to 9.0 mm. The V-shaped groove 18 has a groove width of 4.0 mm to 8.0 mm and a groove depth of 7.0 mm to 9.0 mm. The inclined narrow groove 30 has a groove width of 1.5 mm to 3.5 mm and a groove depth of 5.0 mm to 9.0 mm. The first branch groove 32 and the second branch groove 34 have a groove width of 1.5 mm to 3.5 mm and a groove depth of 3.0 mm to 5.0 mm. Here, the groove width is the maximum dimension in a direction perpendicular to the extension direction of the groove, and the groove depth is the maximum dimension measured in the tire radial direction from the tire profile line to the groove bottom (in a tire meridian cross section) in the absence of the groove.

[0024] (Operation) The tire 10 has circumferential main grooves 16 extending in the tire circumferential direction, so water easily flows in the tire circumferential direction. In addition, the tire 10 has V-shaped grooves 18 extending obliquely to both sides in the tire width direction from the vicinity of the tire equatorial plane CL toward the trailing edge, so water easily flows from the tire equatorial plane CL to the outside in the tire width direction. Furthermore, in the tire 10, the V-shaped grooves 18 are each connected to the circumferential main grooves 16, so water is easily discharged in the tire circumferential direction. Therefore, the tire 10 has excellent drainage properties.

[0025] The tire 10 has a plurality of inclined narrow grooves 30 that connect adjacent V-shaped grooves 18 in the tire circumferential direction, and a first branch groove 32 and a second branch groove 34 provided at the tip portion 20, which results in a larger edge component than conventional tires, resulting in superior snow performance. Furthermore, the tire 10 has a larger groove area than conventional tires due to the presence of the plurality of inclined narrow grooves 30, resulting in superior drainage.

[0026] As described above, the tire 10 can improve wet and snow performance compared to conventional tires. The circumferential main grooves 16 of the tire 10 can improve wet performance compared to conventional tires without changing the groove area by simply changing the extension direction to the tire circumferential direction. Furthermore, the tire 10 can improve snow performance by increasing the edge component by providing multiple inclined narrow grooves 30. Because the groove area of ​​the inclined narrow grooves 30 is sufficiently smaller than that of the circumferential main grooves 16, the proportion of the groove area to the entire tire is small, and the impact on block rigidity is small. Therefore, although the tire 10 has an increased groove area compared to conventional tires by the amount of the inclined narrow grooves 30, the proportion of the entire tire that the inclined narrow grooves 30 occupy is small, so the decrease in block rigidity is limited, and a decrease in dry performance can be suppressed.

[0027] As a result, the tire 10 has excellent wet and snow performance while suppressing deterioration in dry performance.

[0028] Furthermore, by providing the lug grooves 26 in the shoulder regions Sh, the tire 10 can direct water that has flowed from the V-shaped grooves 18 into the circumferential main grooves 16 outward in the tire width direction and be discharged from the contact edge to the outside of the tire 10. Furthermore, by providing the cutout portions 36, the tire 10 can further improve snow performance by increasing the edge component.

[0029] When the tire according to the basic embodiment described above is a pneumatic tire, it has a meridian cross-sectional shape similar to that of a conventional tire, although not shown. Here, the meridian cross-sectional shape of the tire refers to the cross-sectional shape of the tire that appears on a plane perpendicular to the tire equatorial plane CL. The tire according to the basic embodiment has, from the inner side to the outer side in the tire radial direction, a bead portion, a sidewall portion, a shoulder portion, and a tread portion in the tire meridian cross-sectional view. The tire further includes, for example, a carcass layer that extends from the tread portion to both bead portions and is wound around a pair of bead cores in the tire meridian cross-sectional view, and a belt layer and a belt reinforcing layer that are sequentially formed on the outer side in the tire radial direction of the carcass layer.

[0030] The tire according to the basic configuration shown 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 a tire of the basic configuration, convex portions and concave portions corresponding to the tread pattern shown in Fig. 1 are formed on the inner wall of a vulcanization mold, and the tire is vulcanized using this mold.

[0031] The tire of this basic embodiment shown above is particularly suitable as a pneumatic tire, but tires other than pneumatic tires are also included in the scope of the present invention as long as they have the tread pattern shown in FIG.

[0032] <Additional Embodiments> Next, additional embodiments 2 to 9 that can be implemented optionally in addition to the basic embodiment of the tire according to the present invention will be described.

[0033] (Additional Embodiment 2) In the basic embodiment, it is preferable that the angle formed by each of the center lines of the two circumferential main grooves with respect to the tire circumferential direction is within a range of ±5° (Additional Embodiment 2).

[0034] As shown in Figure 2, the angle α of the center line 16C of the circumferential main groove 16 relative to the tire circumferential direction is preferably within a range of ±5° from the tire circumferential direction, and more preferably within a range of ±3°. When the angle α is within this range, water can easily flow in the tire circumferential direction, resulting in superior drainage.

[0035] Furthermore, by having the extension direction of the circumferential main grooves 16 within the range specified above, the tire circumferential openings 16E of the circumferential main grooves 16 separated in the tire circumferential direction by the V-shaped grooves 18 penetrating the circumferential main grooves 16 are more reliably overlapped in the tire width direction. That is, the two openings 16E of the circumferential main grooves 16 adjacent in the tire circumferential direction across one V-shaped groove 18 overlap when viewed from the tire circumferential direction. This allows water to flow more smoothly from the leading-side circumferential main groove 16 through the V-shaped groove to the trailing-side circumferential main groove 16 through the openings 16E. Therefore, the tire 10 has excellent drainage performance when traveling straight.

[0036] From the viewpoint of drainage, it is preferable that the circumferential main grooves 16, which are separated in the tire circumferential direction by the V-shaped grooves 18, are inclined toward the same side in the tire width direction. Also, it is preferable that the circumferential main grooves 16 are inclined outward in the tire width direction from the trailing edge to the leading edge. In other words, from the viewpoint of drainage, it is preferable that the two circumferential main grooves 16R, 16L are inclined in a substantially inverted V shape in a plan view.

[0037] (Additional Form 3) In the basic form or the form obtained by adding Additional Form 2 to the basic form, it is preferable that some of the plurality of inclined narrow grooves are curved inclined narrow grooves including a curved portion having a shape that is convex outward in the tire width direction (Additional Form 3).

[0038] The plurality of inclined narrow grooves 30 include linear inclined narrow grooves 38 that are substantially linear, and bent inclined narrow grooves 40. The linear inclined narrow grooves 38 extend linearly in a direction inclined outward in the tire width direction from the V-shaped groove 18 on the trailing-out side toward the leading-in side, and communicate with adjacent V-shaped grooves 18 in the tire circumferential direction.

[0039] The bent inclined narrow groove 40 has an inclined portion 42, a bent portion 44, and a circumferential portion 46. The inclined portion 42 extends linearly from the V-shaped groove 18 on the trailing edge side toward the leading edge side, inclining outward in the tire width direction. The bent portion 44 has a shape that convex outward in the tire width direction, and connects the inclined portion 42 and the circumferential portion 46. The circumferential portion 46 extends linearly from the bent portion 44 in the tire circumferential direction, and connects to the adjacent V-shaped groove 18 on the leading edge side in the tire circumferential direction.

[0040] 1 includes two inclined narrow grooves 30, one straight inclined narrow groove 38 and one bent inclined narrow groove 40, between the tire equatorial plane CL and the first circumferential main groove 16L and between the tire equatorial plane CL and the second circumferential main groove 16R in one center land portion 22. The tire 10 includes the straight inclined narrow groove 38 and the bent inclined narrow groove 40, in this order from the tire equatorial plane CL to the outer side in the tire width direction. That is, the straight inclined narrow groove 38 is disposed between the tire equatorial plane CL and the bent inclined narrow groove 40, and the bent inclined narrow groove 40 is disposed between the straight inclined narrow groove 38 and the circumferential main groove 16.

[0041] The bent oblique narrow grooves 40 have bent portions 44, thereby forming edges on the blocks defined by the bent oblique narrow grooves 40. Therefore, the tire 10 has more edge components due to the bent oblique narrow grooves 40, resulting in better snow performance.

[0042] The bent portion 44 has a shape that convex outward in the tire width direction, thereby preventing the surface area of ​​the outermost block 23 (FIG. 2) in the tire width direction in the center region Ce defined by the bent inclined narrow groove 40 and the tire circumferential main groove from becoming too small. Therefore, the tire 10 can improve snow performance while suppressing a decrease in the rigidity of the outermost block in the center region Ce.

[0043] (Additional Form 4) In the basic form or the basic form plus at least one of Additional Forms 2 and 3, it is preferable that the inclined narrow grooves have a wider groove width on the trailing side than on the leading side (Additional Form 4).

[0044] 3, when the groove width of the opening 48 of the inclined narrow groove 30 in the V-shaped groove 18 on the leading side is W1 and the groove width of the opening 50 of the inclined narrow groove 30 in the V-shaped groove 18 on the trailing side is W2, it is preferable that W1 < W2. Furthermore, W1 is preferably 70% to 95% of W2, and more preferably 75% to 90%.

[0045] When focusing on one center land portion 22, the groove width of the inclined narrow groove 30 may gradually increase from W1 to W2 by a predetermined amount from the opening 48 of the inclined narrow groove 30 in the V-shaped groove 18 on the leading side to the opening 50 of the inclined narrow groove 30 in the V-shaped groove 18 on the trailing side. Alternatively, the groove width of the inclined narrow groove 30 may change stepwise from W1 to W2 with the center in the extension direction as the boundary. In the case of the bent inclined narrow groove 40, the groove width of the circumferential portion 46 may be W1, and the groove width of the inclined portion 42 may be W2.

[0046] The narrow inclined grooves 30 have a width W1<W2, i.e., the groove width W2 on the trailing edge is wider, so that water flows more easily from the leading edge to the trailing edge in the narrow inclined grooves 30. Therefore, the tire 10 has superior drainage performance during forward movement.

[0047] The groove widths W1 of the openings 48 of the straight inclined narrow grooves 38 and the curved inclined narrow grooves 40 may be the same as or different from each other. Similarly, the groove widths W2 of the openings 50 of the straight inclined narrow grooves 38 and the curved inclined narrow grooves 40 may be the same as or different from each other. For example, the groove width W1 may be 1.5 mm to 2.5 mm, and the groove width W2 may be 1.6 mm to 3.3 mm.

[0048] (Additional Embodiment 5) In a configuration in which Additional Embodiment 3 is added to the basic configuration, it is preferable that the depth of the bent inclined narrow grooves on the leading side is shallower than the depth of the grooves on the trailing side (Additional Embodiment 5).

[0049] As shown in Fig. 4, when the groove depth of the bent inclined narrow groove 40 on the leading side is D1 and the groove depth on the trailing side is D2, it is preferable that D1 < D2. Furthermore, D1 is preferably 70% to 95% of D2, and more preferably 75% to 90%.

[0050] When focusing on one center land portion 22, the groove depth of the bent inclined narrow groove 40 may gradually increase from D1 to D2 by a predetermined amount from the opening 48 of the bent inclined narrow groove 40 in the leading-side V-shaped groove 18 to the opening 50 of the bent inclined narrow groove 40 in the trailing-side V-shaped groove 18. Alternatively, the bent inclined narrow groove 40 may be formed so that the groove depth changes stepwise, with the bent portion 44 as the boundary, with the groove depth of the circumferential portion 46 being D1 and the groove depth of the inclined portion 42 being D2.

[0051] The bent oblique narrow groove 40 has a depth D1<D2, i.e., the groove depth D1 on the leading side is shallower, thereby suppressing a decrease in block rigidity on the leading side. Therefore, the tire 10 can suppress a decrease in dry performance. For example, the groove depth D1 may be 4.0 mm to 6.0 mm, and the groove depth D2 may be 7.0 mm to 9.0 mm.

[0052] (Additional Embodiment 6) In an embodiment in which Additional Embodiment 3 is added to the basic embodiment, it is preferable that the angle of the center line of the bending inclined narrow groove on the leading side relative to the tire circumferential direction is within a range of ±5° (Additional Embodiment 6).

[0053] As shown in Figure 3, the leading side of the bent inclined narrow groove 40 is the circumferential portion 46. The angle β of the center line 16D of the circumferential portion 46 relative to the tire circumferential direction is defined as β. The angle β is preferably within a range of ±5° about the tire circumferential direction, and more preferably within a range of ±3°. When the angle β is within the above range, water can easily flow in the tire circumferential direction, and the tire 10 has excellent drainage properties.

[0054] (Additional Form 7) In the basic form or a form obtained by adding at least one of Additional Forms 2 to 6 to the basic form, it is preferable that at least a portion of the second branch grooves arranged within a range of 5% of the contact width from the tire equatorial plane have a bottom-up portion that makes the groove depth of the second branch groove shallower than the groove depth of the two circumferential main grooves (Additional Form 7).

[0055] 2, the second branch groove 34 extends from the tip end 20 toward the leading edge in the tire circumferential direction, inclining toward one side in the tire width direction, and communicates with the V-shaped groove 18 adjacent to the leading edge in the tire circumferential direction. In other words, the center land portion 22 is divided in the tire width direction by the second branch groove 34.

[0056] The second branch groove 34 has a raised bottom portion 54 in a portion located within a range W5 of 5% of the contact width W from the tire equatorial plane, i.e., in a leading side portion 52 that is a range from approximately the center of the extension direction of the second branch groove 34 to where it connects to the leading-side V-shaped groove 18. As shown in FIG. 5 , the raised bottom portion 54 makes the groove depth of the second branch groove 34 shallower than the groove depth of the V-shaped groove 18. When the tire 10 is running, the greatest ground pressure acts within a range W5 of 5% of the contact width W from the tire equatorial plane CL.

[0057] By providing the raised bottom portion 54 in the second branch groove 34 near the tire equatorial plane CL where the greatest ground contact pressure acts, the block rigidity of the land portion 25 ( FIG. 2 ) near the tire equatorial plane CL, which has a small surface area and is separated by the second branch groove 34, is increased. That is, the tire 10 has an increased edge component and groove area by providing the second branch groove 34, while the lowered block rigidity is compensated for by providing the raised bottom portion 54. Therefore, the tire 10 has excellent dry performance.

[0058] The tire 10 may also have a bottom-raised portion 54 provided in the first branch groove 32. Furthermore, the tire 10 may have a bottom-raised portion 54 provided in the cutout portion 36. By providing the bottom-raised portion 54 in at least one of the first branch groove 32 and the cutout portion 36, the tire 10 can further increase the block rigidity of the land portions arranged between the inclined narrow grooves 30 arranged in the tire width direction.

[0059] (Additional Form 8) In a form obtained by adding Additional Form 7 to the basic form, some of the plurality of inclined narrow grooves are bent inclined narrow grooves including a bent portion having a shape that is convex outward in the tire width direction, and the groove depth of the second branch groove in the bottom-up portion is in the range of 40% to 60% of the groove depth of the two circumferential main grooves, and is preferably shallower than the groove depth on the leading side of the bent inclined narrow groove (Additional Form 8).

[0060] 5, if the groove depth of the second branch groove 34 in the bottom-raised portion 54 is D3 and the groove depth of each of the two circumferential main grooves 16R, 16L is DG, D3 is preferably 40% to 60% of DG, and more preferably 45% to 55%. Furthermore, D3 is shallower than the groove depth D1 on the leading edge of the bent inclined narrow groove 40, i.e., D3<D1. The groove depth D3 is not limited to being constant, and may gradually increase or decrease within the above range.

[0061] By setting the groove depth D3 of the bottom-raised portion 54 of the second branch groove 34 within a predetermined range, the tire 10 has excellent block rigidity while suppressing a decrease in drainage performance. Therefore, the tire 10 has better dry performance, snow performance, and wet performance.

[0062] (Additional Form 9) In the basic form or a form in which at least one of Additional Forms 2 to 8 is added to the basic form, when the center portion is defined as a range that accounts for 20% of the contact width in the tire width direction centered on the tire equatorial plane, and the middle portion is defined as a range that accounts for 20% of the contact width adjacent to the center portion on the outer side in the tire width direction, it is preferable that the groove area included in the center portion is smaller than the groove area included in each middle portion (Additional Form 9).

[0063] As shown in Fig. 1, the center portion 56 is a band-shaped region that is centered on the tire equatorial plane CL and that extends in the tire width direction and is continuous in the tire circumferential direction, covering an area that is 20% of the contact width W. The groove area A1 included in the center portion 56 is the sum of the groove areas of the grooves present in the center portion 56, i.e., in the case of Fig. 1, the part of the V-shaped groove 18 including the tip portion 20, the first branch groove 32, the second branch groove 34, and the cutout portion 36.

[0064] The middle portions 58 are circumferentially continuous band-shaped regions that are adjacent to the outer sides of the center portions 56 in the tire width direction and that cover 20% of the contact patch width W. The groove area A2 included in the middle portions 58 is the sum of the groove areas of the grooves that exist in the middle portions 58L that are located on one side of the center portions 56 in the tire circumferential direction, or the sum of the groove areas of the grooves that exist in the middle portions 58R that are located on the other side of the center portions in the tire circumferential direction. In the case of Figure 1, the groove area A1 included in the middle portions 58 is the sum of the groove areas of a portion of the V-shaped grooves 18, the inclined narrow grooves 30, and a portion of the circumferential main groove 16.

[0065] The belt-like region that is adjacent to the outer side of the middle portion 58 in the tire width direction and that is continuous in the tire circumferential direction and that is within 20% of the contact width W is called a shoulder portion 60 .

[0066] In the tire 10, the groove area A1 of the center portion 56 near the tire equatorial plane CL and the groove area A2 of the middle portion 58 satisfy the above relationship, i.e., A1 < A2, so that the block rigidity is maintained at a certain level or higher. Therefore, the tire 10 has excellent dry performance.

[0067] The following examples were evaluated using pneumatic tires.

[0068] Tires according to Examples 1 to 10 and a Comparative Example tire were manufactured with a tire size of 205 / 55R16 91H and a tread pattern shown in Fig. 1 (or a tread pattern similar to the tread pattern shown in Fig. 1). The detailed conditions of these tires are as shown in Table 1 below.

[0069] The "presence or absence of circumferential main grooves" column indicates "present" if the main grooves extending in the tire circumferential direction are formed so that straight lines parallel to the tire circumferential direction can pass through them, and "absent" if they are so inclined with respect to the tire circumferential direction that straight lines parallel to the tire circumferential direction cannot pass through them. The "inclined narrow grooves" column indicates the number of inclined narrow grooves provided in the first circumferential main groove and the second circumferential main groove from the tire equatorial plane, with the same number. The "circumferential main groove angle" column indicates the value of the angle α formed by the center line of the circumferential main groove with respect to the tire circumferential direction. The "presence or absence of bends" column indicates "present" if the inclined narrow grooves include bent inclined narrow grooves with bends, and "absent" if they do not include bent inclined narrow grooves. The "groove width of inclined narrow grooves" column indicates "constant" if the groove width W1 on the leading side and the groove width W2 on the trailing side are the same, and indicates "W1 < W2" if the groove width W2 on the trailing side is wider than the groove width W1 on the leading side. The "Inclined Narrow Groove Depth" column indicates "Constant" when the groove depth D1 on the leading edge and the groove depth D2 on the trailing edge are the same, and indicates "D1 < D2" when the groove depth D1 on the leading edge is shallower than the groove depth D2 on the trailing edge. The "Angle of Circumferential Section" column indicates the value of the angle β formed by the center line of the circumferential section with respect to the tire circumferential direction. The "Presence or Absence of Bottom-Up Section" column indicates "Yes" when the second branch groove has a bottom-up section, and "Absent" when it does not have a bottom-up section. The "Circumferential Section Groove Depth (%)" column indicates the ratio (%) of D3 to DG, where D3 is the groove depth of the second branch groove in the bottom-up section and DG is the groove depth of the two circumferential main grooves. The "Relationship between Groove Area A1 and Groove Area A2" column indicates the relationship between the groove area A1 included in the center section and the groove area A2 included in the middle section.

[0070] The tires according to Examples 1 to 10 and the tire of the Comparative Example prepared in this manner were mounted on a 16x6.5J aluminum rim at 250 kPa, and each test tire was mounted on a FF test vehicle (displacement: 1500 cc). In order to confirm snow performance, wet performance, and dry performance, the handling stability on packed snow roads, wet roads, and dry roads was evaluated according to the following procedure.

[0071] (Steering stability on packed snow roads) A test driver performed a sensory evaluation when a vehicle equipped with each test tire was driven on a test course on packed snow roads. Based on the results, an index evaluation was performed with the comparative example set as the standard (100). The evaluation results are also shown in Table 1. In this evaluation, the higher the index, the better the steering stability on packed snow roads.

[0072] (Steering stability on wet roads) A test driver performed a sensory evaluation when a vehicle equipped with each test tire was driven on a test course on a wet road (water film 1 mm). Based on the results, an index evaluation was performed with the comparative example set as the standard (100). The evaluation results are also shown in Table 1. In this evaluation, the higher the index, the better the steering stability on wet roads.

[0073] (Dry road handling stability) The test vehicle was driven on a test course with a flat, circular, dry road surface at speeds of 10 km / h to 180 km / h, and the test driver performed a sensory evaluation of the steering performance during lane changes and cornering, and the stability during straight driving. Based on the results, an index evaluation was performed with the comparative example being assigned a standard index (100). The evaluation results are also shown in Table 1. In this evaluation, a higher index indicates better dry road handling stability.

[0074]

[0075] (Results) Comparing Examples 1 to 10 with Comparative Example 1, it was found that by having a circumferential main groove and multiple inclined narrow grooves, drainage performance is improved and edge components are increased, thereby improving wet and snow performance. Note that, although Examples 1 to 6 have inferior dry performance compared to Comparative Example 1 due to the inclusion of two inclined narrow grooves, the actual effect on performance is limited, and therefore within an acceptable range.

[0076] Comparing Example 1 and Example 2, it was found that by setting the angle α of the circumferential main groove within the range of ±5°, drainage performance was improved and wet performance was improved.

[0077] Comparing Example 2 with Example 3, it was found that the edge component and groove area are increased by having the bent inclined narrow grooves, thereby improving snow performance and wet performance.

[0078] Comparing Example 3 and Example 4, it was found that drainage was improved and wet performance was improved by having the inclined narrow grooves with a groove width W2 on the trailing side wider than the groove width W1 on the leading side.

[0079] Comparing Example 4 and Example 5, it was found that by having a shallower groove depth D1 on the leading-edge side of the curved inclined narrow groove compared to the groove depth D2 on the trailing-edge side, drainage is improved and the decrease in block rigidity on the leading-edge side is suppressed, resulting in improved wet and dry performance.

[0080] Comparing Example 5 and Example 6, it was found that drainage performance is improved and wet performance is improved when the angle β of the center line of the circumferential portion relative to the tire circumferential direction is within the range of ±5°.

[0081] Comparing Example 6 and Example 7, it was found that at least a portion of the second branch grooves located within 5% of the contact width from the tire equatorial plane have a bottom-raised portion that makes the groove depth of the second branch groove shallower than the groove depth of the two circumferential main grooves, thereby increasing block rigidity and maintaining dry performance equivalent to that of the comparative example.

[0082] Comparing Example 7 and Example 8, it was found that by setting the groove depth of the second branch groove in the bottom-raised portion to a range of 40% to 60% of the groove depth of the two circumferential main grooves, block rigidity can be increased and dry performance can be improved.

[0083] Comparing Example 8 and Example 9, when the groove depth of the second branch groove in the bottom-raised portion is set to 30% of the groove depth of the two circumferential main grooves, block rigidity is increased and dry performance is improved, but the groove volume is reduced accordingly, thereby reducing the improved snow performance and wet performance.

[0084] Comparing Example 8 and Example 10, it was found that by making the groove area A1 included in the center portion smaller than the groove area A2 included in each middle portion, block rigidity is maintained at a certain level or higher, thereby improving dry performance.

[0085] REFERENCE SIGNS LIST 10 Tire 12 Tread portion 14 Tread surface 16 Circumferential main groove 16C Center line of circumferential main groove 16E Opening of circumferential main groove 16L First circumferential main groove 16R Second circumferential main groove 18 V-shaped groove 20 Tip portion 22 Center land portion 24 Sipe 26 Lug groove 28 Shoulder land portion 30 Inclined narrow groove 32 First branch groove 34 Second branch groove 36 Cutout portion 38 Straight inclined narrow groove 40 Bend inclined narrow groove 42 Inclined portion 44 Bend portion 46 Circumferential portion 48 Opening on leading side of inclined narrow groove 50 Opening on trailing side of inclined narrow groove 52 Leading side portion 54 Bottom-raised portion 56 Center portion 58 Middle portion CL Tire equatorial plane Ce Center region Sh Shoulder region D1, D2, D3, DG Groove depth W1, W2 Groove width

Claims

1. A tire having a tread surface including two circumferential main grooves and a plurality of V-shaped grooves arranged at intervals in the tire width direction on the inner side of the two circumferential main grooves, the center land portion being defined and formed by the two circumferential main grooves and the V-shaped grooves adjacent in the tire circumferential direction, and the rotation direction of the tire is specified, the two circumferential main grooves being arranged on both sides in the tire width direction across the tire equatorial plane and extending in the tire circumferential direction, the V-shaped grooves having a tip end protruding in a V shape to one side in the tire circumferential direction, extending from the tip end to the other side in the tire circumferential direction at an incline to both sides in the tire width direction and communicating with the two circumferential main grooves, and a plurality of inclined narrow grooves being provided between the tire equatorial plane and the circumferential main groove on one side, and between the tire equatorial plane and the circumferential main groove on the other side, the inclined narrow groove is inclined outward in the tire width direction toward one side in the tire circumferential direction and is connected to each of the V-shaped grooves adjacent in the tire circumferential direction, the tip portion is provided with a first branch groove and a second branch groove extending from the tip portion to one side in the tire circumferential direction, the first branch groove terminates within the center land portion, and the second branch groove is connected to the V-shaped groove adjacent to one side in the tire circumferential direction.

2. The tire according to claim 1, wherein the angle between the center lines of the two circumferential main grooves and the tire circumferential direction is within a range of ±5°.

3. The tire according to claim 1, wherein some of the plurality of inclined narrow grooves are bent inclined narrow grooves including a bent portion having a shape that protrudes outward in the tire width direction.

4. The tire according to claim 1, wherein the inclined narrow groove has a groove width wider on the trailing side than on the leading side.

5. The tire according to claim 3, wherein the curved inclined narrow groove has a groove depth on the leading-out side that is shallower than the groove depth on the trailing-out side.

6. The tire according to claim 3, wherein the angle between the center line of the leading side of the bent inclined narrow groove and the tire circumferential direction is within a range of ±5°.

7. The tire as described in claim 1, wherein, with respect to a contact patch width when normal internal pressure is applied and a load of 80% of normal load is applied, at least a part of the second branch grooves arranged within a range of 5% of the contact patch width from the tire equatorial plane has a bottom-up portion that makes the groove depth of the second branch groove shallower than the groove depth of the two circumferential main grooves.

8. A tire as described in claim 7, wherein some of the plurality of inclined narrow grooves are bent inclined narrow grooves including a bent portion having a shape that is convex outward in the tire width direction, and the groove depth of the second branch groove in the bottom-up portion is in the range of 40% to 60% of the groove depth of the two circumferential main grooves and is shallower than the groove depth on the leading edge of the bent inclined narrow groove.

9. A tire as claimed in claim 1, in which, when the tire is pressurized under normal internal pressure and subjected to a load of 80% of the normal load, a center portion is defined as a range that is 20% of the contact width in the tire width direction centered on the tire equatorial plane, and middle portions are defined as ranges that are 20% of the contact width adjacent to the center portion on the outside in the tire width direction, and the groove area included in the center portion is smaller than the groove area included in each of the middle portions.

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