Tire

Abstract

To provide a tire with more excellent wet performance and snow performance while suppressing a decrease in a dry performance.SOLUTION: In a tire 10, a center land part 22 is partitioned and formed by two circumferential main grooves 16 and V-shape grooves 18 adjacent to each other in a tire circumferential direction, and a rotation direction is specified. The V-shape groove 18 includes a distal end portion 20 projecting in a V-shape to one side of the tire circumferential direction, extends from the distal end portion 20 to both sides of the tire width direction, and communicates with two circumferential main grooves 16. An inclined narrow groove 30 is inclined to a tire width direction outside toward one side of the tire circumferential direction and communicates with the adjacent V-shape groove 18 in the tire circumferential direction. In the distal end portion 20, a first branch groove and a second branch groove extending from the distal end portion 20 to one side of the tire circumferential direction are provided. The first branch groove terminates in the center land part 22. The second branch groove communicates with the adjacent V-shape groove 18 in one side of the tire circumferential direction.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a tire.

Background Art

[0002] As a tire capable of improving the wet performance and snow performance of a tire, for example, the tire described in Patent Document 1 is known. In the tire described in Patent Document 1, a plurality of first land portions are arranged adjacent to each other in the tire circumferential direction, a plurality of second land portions are arranged adjacent to each other in the tire circumferential direction, and the first land portions and the second land portions are arranged in a staggered manner along the tire equatorial plane. Further, each of the first land portion and the second land portion includes a plurality of through grooves that penetrate the land portion and open into the pair of inclined 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 among the blocks. Further, the edge portion of the innermost center block has a notch that opens to the connection portion of the inclined main groove.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

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

Means for Solving the Problems

[0005] A tire according to one aspect of the present invention includes, on a tread surface, two circumferential main grooves and a plurality of V-shaped grooves arranged inside the two circumferential main grooves in the tire width direction and spaced apart in the tire circumferential direction. The two circumferential main grooves and the V-shaped grooves adjacent to each other in the tire circumferential direction define a center land portion, and the tire has a specified rotation direction. The two circumferential main grooves are respectively provided on both sides in the tire width direction with the tire equatorial plane interposed therebetween, and extend in the tire circumferential direction. The V-shaped groove has a tip portion protruding in a V shape toward one side in the tire circumferential direction, and extends obliquely from the tip portion toward both sides in the tire width direction toward the other side in the tire circumferential direction, and communicates with the two circumferential main grooves. A plurality of inclined fine grooves are respectively provided between the tire equatorial plane and one circumferential main groove, and between the tire equatorial plane and the other circumferential main groove. The inclined fine grooves are inclined outward in the tire width direction toward one side in the tire circumferential direction, and communicate with the adjacent V-shaped grooves in the tire circumferential direction respectively. A first branch groove and a second branch groove, which extend from the tip portion toward one side in the tire circumferential direction, are provided at the tip portion. The first branch groove terminates within the center land portion. The second branch groove communicates with the V-shaped groove adjacent to one side in the tire circumferential direction.

Advantages of the Invention

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

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[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. Further, the constituent elements of the above embodiments include those that can be replaced by those skilled in the art and are easy to replace, or those that are substantially the same. Furthermore, various forms included in the above embodiments can be arbitrarily combined within the scope obvious to those skilled in the art.

[0009] In the following description, the tire radial direction refers to the direction orthogonal to the rotation axis of the tire, the inner side in the tire radial direction refers to the side facing the rotation axis in the tire radial direction, and the outer side in the tire radial direction refers to the side away from the rotation axis in the tire radial direction. Also, the tire circumferential direction refers to the circumferential direction around the rotation axis as the central axis. Furthermore, the tire width direction refers to the direction parallel to the rotation axis, the inner side in the tire width direction refers to the side facing the tire equatorial plane (tire equator line) in the tire width direction, and the outer side in the tire width direction 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 orthogonal to the rotation axis of the tire and passes through the center of the tire width. Note that "along" a certain direction includes not only the case of being parallel to a certain direction but also the case of being inclined at an angle of less than ±15° with respect to a certain direction. The kicking side and the stepping-in side in the tire circumferential direction are based on the forward movement.

[0010] Similarly, in the following description, the standard rim refers to the "applicable rim" defined by JATMA, the "Design Rim" defined by TRA, or the "Measuring Rim" defined by ETRTO. Similarly, in the following description, the normal internal pressure refers to the "maximum air pressure" defined by JATMA, the maximum value described in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" defined by TRA, or "INFLATION PRESSURES" defined by ETRTO. Also, the normal load refers to the "maximum load capacity" defined by JATMA, the maximum value described in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" defined by TRA, or "LOAD CAPACITY" defined by ETRTO. Similarly, in the following description, the ground contact width refers to the maximum dimension in the tire width direction of the region in contact with the road surface in a state where the normal rim is incorporated, the normal internal pressure is applied, and a load of 80% of the normal load is applied.

[0011] <Basic form> The tire according to an embodiment of the present invention will be described below in its basic form. The tire 10 shown in FIG. 1 includes a tread portion 12 on the outer side in the tire radial direction. The rotation direction of the tire 10 is specified. One side in the tire circumferential direction is the lower side in FIG. 1 and is also referred to as the indentation side. The other side in the tire circumferential direction is the upper side in FIG. 1 and is also referred to as the kicking-out side.

[0012] The tread portion 12 is formed of a rubber material (tread rubber). The tread portion 12 has a tread surface 14 that contacts the road surface when the vehicle is running. The tread surface 14 is annular about the rotation axis of the tire 10, has a predetermined length in the tire width direction, and is continuous in the tire circumferential direction. A tread pattern of a predetermined pattern is engraved on the tread surface 14. The tread pattern is asymmetric with respect to the tire equatorial plane CL between both sides in the tire width direction of the tire equatorial plane CL. In FIG. 1, the symbol EL indicates the ground contact end line (a line connecting continuous ground contact ends in the tire circumferential direction).

[0013] As shown in FIG. 1, the tire 10 according to the present embodiment includes two circumferential main grooves 16 on the tread surface 14. The tire 10 includes a first circumferential main groove 16L on one side in the tire width direction and a second circumferential main groove 16R on the other side in the tire width direction with respect to the tire equatorial plane CL. 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 formed such that a virtual line parallel to the tire circumferential direction can pass through the groove. Therefore, at least a part of the water flowing 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, when the first circumferential main groove 16L and the second circumferential main groove 16R are not particularly distinguished, they are referred to as the circumferential main groove 16.

[0014] With the center lines of the first circumferential main groove 16L and the second circumferential main groove 16R as boundaries, 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 outside the first circumferential main groove 16L and the second circumferential main groove 16R in the tire width direction are called shoulder regions Sh, respectively.

[0015] The tire 10 includes a plurality of V-shaped grooves 18 on the tread surface 14. The V-shaped grooves 18 are arranged in the center region Ce and are provided at intervals in the tire circumferential direction. The V-shaped groove 18 has a tip portion 20 that protrudes in a V shape toward the indentation side, which is one side in the tire circumferential direction. The tip portion 20 is disposed in the vicinity of the tire equatorial plane CL, that is, 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 toward both sides in the tire width direction from the tip portion 20 toward the kicking-out side, 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, respectively.

[0017] The tire 10 has a center land portion 22 defined by a first circumferential main groove 16L, a second circumferential main groove 16R, and 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 with the V-shaped grooves 18 therebetween. The center land portion 22 may be provided with a plurality of sipes 24. The tire 10 has lug grooves 26 provided in the shoulder region Sh. The lug grooves 26 have openings respectively communicating with the first circumferential main groove 16L and the second circumferential main groove 16R, and are arranged at positions overlapping the openings of the V-shaped grooves 18 respectively communicating with the first circumferential main groove 16L and the second circumferential main groove 16R in the tire width direction. A plurality of lug grooves 26 are arranged at predetermined intervals in the tire circumferential direction, extend in the tire width direction, and define a shoulder land portion 28. The shoulder land portion 28 may be provided with a plurality of sipes 24. The lug grooves 26 may communicate with the ground contact end EL.

[0018] Under such a premise, the tire 10 according to the basic form includes, as shown in FIG. 2, inclined narrow grooves 30, and a first branch groove 32 and a second branch groove 34. The inclined narrow grooves 30, the first branch groove 32, and the second branch groove 34 are formed in each center land portion 22.

[0019] A plurality of inclined narrow grooves 30 are respectively provided 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. The inclined narrow grooves 30 have a smaller groove width than 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, and 10% or less of the first circumferential main groove 16L and the second circumferential main groove 16R.

[0020] In FIG. 1, two inclined narrow grooves 30 are respectively provided 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 within one center land portion 22, for a total of four. The inclined narrow grooves 30 are inclined outward in the tire width direction from the kick-out side to the indentation side in the tire circumferential direction. The inclined narrow grooves 30 communicate with the V-shaped grooves 18 adjacent to each other in the tire circumferential direction.

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

[0022] Furthermore, the tire 10 may have a notch portion 36. The notch portion 36 is provided between the tip 20 of the V-shaped groove 18 and the inclined narrow groove 30. The notch portion 36 is on the extension line of the second branch groove 34 communicating with the kicking-out side with respect to the V-shaped groove 18, extends to the center land portion 22 on the recessed 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 a no-load state in which the tire is incorporated in a standard rim and filled with a specified internal pressure. In this state, for example, for a tire of size 205 / 55R16 91H, the groove widths of the first circumferential main groove 16L and the second circumferential main groove 16R are 4.0 mm to 6.0 mm, and their groove depths are 7.0 mm to 9.0 mm. The groove widths of the V-shaped grooves 18 are 4.0 mm to 8.0 mm, and their groove depths are 7.0 mm to 9.0 mm. The groove widths of the inclined narrow grooves 30 are 1.5 mm to 3.5 mm, and their groove depths are 5.0 mm to 9.0 mm. The groove widths of the first branch groove 32 and the second branch groove 34 are 1.5 mm to 3.5 mm, and their groove depths are 3.0 mm to 5.0 mm. Here, the groove width is the maximum dimension in a direction perpendicular to the extending direction of the groove, and the groove depth is the maximum dimension measured in the tire radial direction from the tire profile line (in the tire meridian cross-sectional view) when there is no groove to the bottom of the groove.

[0024] (Function) Since the tire 10 has circumferential main grooves 16 extending in the tire circumferential direction, water easily flows in the tire circumferential direction. Further, since the tire 10 has V-shaped grooves 18 that extend while inclining toward both sides in the tire width direction from the vicinity of the tire equatorial plane CL toward the kick-out side, water easily flows from the tire equatorial plane CL toward the outer side in the tire width direction. Furthermore, since the V-shaped grooves 18 of the tire 10 communicate with the circumferential main grooves 16 respectively, water is easily discharged in the tire circumferential direction. Therefore, the tire 10 is excellent in drainage performance.

[0025] The tire 10 has a plurality of inclined fine grooves 30 that communicate the V-shaped grooves 18 adjacent to each other in the tire circumferential direction, a first branch groove 32, and a second branch groove 34 provided at the tip portion 20. As a result, compared with conventional tires, the tire 10 has more edge components and thus is more excellent in snow performance. Further, since the tire 10 has a larger groove area than conventional tires by the amount of the plurality of inclined fine grooves 30, the tire 10 is more excellent in drainage performance.

[0026] As described above, the tire 10 can improve wet performance and snow performance as compared with the conventional ones. The circumferential main groove 16 of the tire 10 can improve wet performance as compared with conventional tires without changing the groove area only by changing the extending direction along the tire circumferential direction. Further, the tire 10 can increase the edge components and improve the snow performance by providing a plurality of inclined fine grooves 30. Since the groove width of the inclined fine grooves 30 is sufficiently smaller than that of the circumferential main groove 16, the ratio occupied in the whole tire is small, and the influence on the block rigidity is small. Therefore, although the groove area of the tire 10 increases by the amount of the additional inclined fine grooves 30 as compared with conventional tires, the ratio occupied by the inclined fine grooves 30 in the whole tire 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 is more excellent in wet performance and snow performance while suppressing a decrease in dry performance.

[0028] Further, by having the lug grooves 26 in the shoulder region Sh, the tire 10 can flow the water that has flowed from the V-shaped grooves 18 into the circumferential main grooves 16 outward in the tire width direction and discharge it from the grounding end to the outside of the tire 10. Furthermore, by having the notch portions 36, the tire 10 can further improve the snow performance by increasing the edge components more.

[0029] When the tire according to the basic form shown above is a pneumatic tire, although not shown, it has a meridian cross-sectional shape similar to that of a conventional tire. 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 form has, in a tire meridian cross-sectional view, a bead portion, a sidewall portion, a shoulder portion, and a tread portion from the inner side to the outer side in the tire radial direction. And the above tire includes, for example, in a tire meridian cross-sectional view, a carcass layer extending from the tread portion to the bead portions on both sides and wound around a pair of bead cores, and a belt layer and a belt reinforcing layer sequentially formed on the outer side in the tire radial direction of the carcass layer.

[0030] The tire according to the basic form shown above is obtained through normal manufacturing processes, that is, a mixing process of tire materials, a processing process of tire materials, a molding process of a green tire, a vulcanization process, and an inspection process after vulcanization, etc. When manufacturing the tire of the basic form, convex portions and concave portions corresponding to the tread pattern shown in FIG. 1 are formed on the inner wall of the vulcanization mold, and vulcanization is performed using this mold.

[0031] The tire of the present basic form shown above is particularly preferably a pneumatic tire, but any tire having the tread pattern shown in FIG. 1 other than a pneumatic tire is also included in the scope of the present invention.

[0032] <Additional Forms> Next, additional forms 2 to 9 that can be optionally implemented with respect to the above basic form of the tire according to the present invention will be described.

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

[0034] As shown in FIG. 2, let the angle formed by the center line 16C of the circumferential main groove 16 with respect to the tire circumferential direction be α. The angle α is preferably within the range of ±5° centered on the tire circumferential direction, and more preferably within the range of ±3°. When the angle α is within the above range, water easily flows in the tire circumferential direction, so the drainage performance is more excellent.

[0035] Further, since the extending direction of the circumferential main groove 16 is within the range defined as above, the tire circumferential openings 16E of the circumferential main grooves 16 separated from each other by the V-shaped groove 18 penetrating the circumferential main groove 16 overlap more reliably in the tire width direction. That is, the two openings 16E of the circumferential main grooves 16 adjacent to each other in the tire circumferential direction across one V-shaped groove 18 overlap when viewed from the tire circumferential direction. Then, water flows more smoothly through the opening 16E from the circumferential main groove 16 on the stepping-in side through the V-shaped groove to the circumferential main groove 16 on the kicking-out side. Therefore, the tire 10 has excellent drainage performance during straight running.

[0036] From the viewpoint of drainage performance, it is preferable that the circumferential main grooves 16 are inclined to the same side in the tire width direction for each of the circumferential main grooves 16 separated from each other by the V-shaped groove 18 in the tire circumferential direction. Further, it is preferable that the circumferential main groove 16 is inclined outward in the tire width direction from the kicking-out side toward the stepping-in side. That is, it is preferable from the viewpoint of drainage performance that the two circumferential main grooves 16R and 16L are inclined in a substantially inverted V shape in 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 a part of the plurality of inclined fine grooves is a bent inclined fine groove including a bent portion having a shape convex outward in the tire width direction (Additional Form 3).

[0038] The plurality of inclined grooves 30 includes a substantially linear straight inclined groove 38 and a bent inclined groove 40. The straight inclined groove 38 linearly extends in a direction inclined outward in the tire width direction from the V-shaped groove 18 on the kicking-out side toward the stepping-in side, and communicates with the V-shaped grooves 18 adjacent to each other in the tire circumferential direction.

[0039] The bent inclined groove 40 has an inclined portion 42, a bent portion 44, and a circumferential portion 46. The inclined portion 42 linearly extends in a direction inclined outward in the tire width direction from the V-shaped groove 18 on the kicking-out side toward the stepping-in side. The bent portion 44 has a shape convex outward in the tire width direction and communicates the inclined portion 42 and the circumferential portion 46. The circumferential portion 46 linearly extends in a direction along the tire circumferential direction from the bent portion 44 and communicates with the V-shaped groove 18 adjacent to the stepping-in side in the tire circumferential direction.

[0040] The tire 10 shown in FIG. 1 is provided with a total of two inclined grooves 30, one straight inclined groove 38 and one bent inclined groove 40 each, between the tire equatorial plane CL and the first circumferential main groove 16L within one center land portion 22, and between the tire equatorial plane CL and the second circumferential main groove 16R. The tire 10 has, in order from the tire equatorial plane CL outward in the tire width direction, the straight inclined groove 38 and the bent inclined groove 40. That is, the straight inclined groove 38 is disposed between the tire equatorial plane CL and the bent inclined groove 40, and the bent inclined groove 40 is disposed between the straight inclined groove 38 and the circumferential main groove 16.

[0041] The bent inclined groove 40 forms an edge on the block partitioned and formed by the bent inclined groove 40 by having the bent portion 44. Therefore, by providing the bent inclined groove 40, the tire 10 has more edge components and thus has better snow performance.

[0042] The bent portion 44 has a shape that bulges 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 partitioned by the bent inclined groove 40 and the main groove in the tire circumferential direction from becoming too small. Therefore, the tire 10 can improve the 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 form obtained by adding at least any one of the additional forms 2 and 3 to the basic form, it is preferable that the inclined groove has a wider groove width on the kicking-out side than on the stepping-in side (Additional form 4).

[0044] As shown in FIG. 3, when the groove width of the opening 48 of the inclined groove 30 in the V-shaped groove 18 on the stepping-in side is W1 and the groove width of the opening 50 of the inclined groove 30 in the V-shaped groove 18 on the kicking-out side is W2, it is preferable that W1 < W2. Further, W1 is preferably 95% or more and 70% or less of W2, and more preferably 90% or more and 75% or less.

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

[0046] Since the inclined groove 30 has W1 < W2, that is, the groove width W2 on the kicking-out side is wider, water can easily flow through the inclined groove 30 from the stepping-in side to the kicking-out side. Therefore, the tire 10 has excellent drainage performance during forward movement.

[0047] The groove widths W1 of the openings 48 of the straight inclined grooves 38 and the bent inclined 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 grooves 38 and the bent inclined 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 form 5) In the form in which the additional form 3 is added to the basic form, it is preferable that the groove depth on the indentation side of the bent inclined groove is shallower than the groove depth on the ejection side (additional form 5).

[0049] As shown in FIG. 4, when the groove depth on the indentation side of the bent inclined groove 40 is D1 and the groove depth on the ejection side is D2, it is preferable that D1 < D2. Further, D1 is preferably 95% or more and 70% or less of D2, and more preferably 90% or more and 75% or less.

[0050] When focusing on a certain center land portion 22, the groove depth of the bent inclined groove 40 may gradually increase with a predetermined change amount from D1 to D2 from the opening 48 of the bent inclined groove 40 in the V-shaped groove 18 on the indentation side to the opening 50 of the bent inclined groove 40 in the V-shaped groove 18 on the ejection side. Further, the bent inclined groove 40 may be formed such that the groove depth changes stepwise with the bent portion 44 as a boundary, with the groove depth of the circumferential direction portion 46 being D1 and the groove depth of the inclined portion 42 being D2.

[0051] The bent inclined groove 40 suppresses a decrease in the block rigidity on the indentation side by having D1 < D2, that is, by making the groove depth D1 on the indentation side shallower. 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 form 6) In a form in which additional form 3 is added to the basic form, it is preferable that the angle formed by the center line on the indentation side of the bent inclined fine groove with respect to the tire circumferential direction is within the range of ±5° (additional form 6).

[0053] As shown in FIG. 3, the indentation side of the bent inclined fine groove 40 is the circumferential portion 46. Let the angle formed by the center line 16D of the circumferential portion 46 with respect to the tire circumferential direction be β. The angle β is preferably within the range of ±5° centered on the tire circumferential direction, and more preferably within the range of ±3°. Since water easily flows in the tire circumferential direction when the angle β is within the above range, the tire 10 is excellent in drainage performance.

[0054] (Additional form 7) In the basic form or a form in which at least one of additional forms 2 to 6 is added to the basic form, it is preferable that at least a part of the second branch groove disposed within the range of 5% of the ground contact width from the tire equatorial plane has a raised bottom portion that makes the groove depth of the second branch groove shallower than the groove depths of the two circumferential main grooves (additional form 7).

[0055] As shown in FIG. 2, the second branch groove 34 extends while inclining toward one side in the tire width direction from the tip end 20 toward the indentation side in the tire circumferential direction, and communicates with the V-shaped groove 18 adjacent to the indentation side in the tire circumferential direction. That is, 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 the indentation side portion 52, which is a portion disposed within the range W5 of 5% of the ground contact width W from the tire equatorial plane, that is, in the range from approximately the center in the extending direction of the second branch groove 34 to the point where it communicates with the V-shaped groove 18 on the indentation side. 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 maximum ground contact pressure acts within the range of 5% of the ground contact width W from the tire equatorial plane CL.

[0057] In the vicinity of the tire equatorial plane CL where the largest ground pressure acts, by providing the bottom-raising portion 54 in the second branch groove 34, the block rigidity of the land portion 25 (Fig. 2) in the vicinity of the tire equatorial plane CL with a small surface area divided by the second branch groove 34 is increased. That is, while the tire 10 increases the edge component and the groove area by providing the second branch groove 34, it compensates for the reduced block rigidity by providing the bottom-raising portion 54. Therefore, the tire 10 has excellent dry performance.

[0058] Also, the tire 10 may be provided with a bottom-raising portion 54 in the first branch groove 32. Further, the tire 10 may be provided with a bottom-raising portion 54 in the notch portion 36. By having the bottom-raising portion 54 in at least one of the first branch groove 32 and the notch portion 36, the block rigidity of the land portion disposed between the inclined narrow grooves 30 respectively arranged in the tire width direction can be further increased.

[0059] (Additional Form 8) In the form obtained by adding Additional Form 7 to the basic form, a part of the plurality of inclined narrow grooves is a bent inclined narrow groove including a bent portion having a shape convex to the outer side in the tire width direction, and the groove depth of the second branch groove in the bottom-raising portion is in the range of 40% or more and 60% or less of the groove depths of the two circumferential main grooves, and it is preferable that it is shallower than the groove depth on the stepped-in side of the bent inclined narrow groove (Additional Form 8).

[0060] As shown in Fig. 5, when the groove depth of the second branch groove 34 in the bottom-raising portion 54 is D3 and the groove depths of the two circumferential main grooves 16R and 16L are DG respectively, it is preferable that D3 is 40% or more and 60% or less of DG, and more preferably 45% or more and 55% or less. Further, D3 is shallower than the groove depth D1 on the stepped-in side of the bent inclined narrow groove 40, that is, it has the relationship of D3 < D1. The groove depth D3 is not limited to the case where it is constant, and may gradually increase or decrease within the above range.

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

[0062] (Additional form 9) In the basic form or the form obtained by adding at least any one of additional forms 2 to 8 to the basic form, when a range of 20% of the contact width in the tire width direction centered on the tire equatorial plane is defined as the center portion, and a range of 20% of the contact width adjacent to the outside in the tire width direction of the center portion is defined as each middle portion, 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 belt-like region that is continuous in the tire circumferential direction within a range of 20% of the contact width W in the tire width direction centered on the tire equatorial plane CL. The groove area A1 included in the center portion 56 is the sum of the groove areas of the grooves existing in the center portion 56, in the case of FIG. 1, a part of the V-shaped groove 18 including the tip portion 20, the first branch groove 32, the second branch groove 34, and the notch portion 36.

[0064] The middle portion 58 is a belt-like region that is continuous in the tire circumferential direction within a range of 20% of the contact width W adjacent to the outside in the tire width direction of each center portion 56. The groove area A2 included in the middle portion 58 is the sum of the groove areas of the grooves existing in the middle portion 58L arranged on one side in the tire circumferential direction with respect to the center portion 56, or the sum of the groove areas of the grooves existing in the middle portion 58R arranged on the other side in the tire circumferential direction with respect to the center portion. The groove area A1 included in the middle portion 58 is the sum of the groove areas of a part of the V-shaped groove 18, the inclined fine groove 30, and a part of the circumferential main groove 16 in the case of FIG. 1.

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

[0066] The tire 10 has the groove area A1 of the center portion 56 close to the tire equatorial plane CL and the groove area A2 of the middle portion 58 satisfy the above relationship, that is, by setting A1 < A2, the block rigidity is maintained at a certain level or higher. Therefore, the tire 10 is more excellent in dry performance.

Example

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

[0068] Tires according to Examples 1 to 10 having a tire size of 205 / 55R16 91H and having the tread pattern shown in FIG. 1 (or a tread pattern approximated to the tread pattern shown in FIG. 1), and tires of comparative examples were manufactured. The detailed conditions of these tires are as shown in Table 1 below.

[0069] In the column of "Presence or absence of circumferential main groove", "Present" is indicated when the main groove extending in the tire circumferential direction is formed so that a straight line parallel to the tire circumferential direction can pass through, and "Absent" is indicated when the main groove is greatly inclined with respect to the tire circumferential direction and a straight line parallel to the tire circumferential direction cannot pass through. In the column of "Inclined fine groove", the number of inclined fine grooves provided in the same number in the first circumferential main groove and the second circumferential main groove from the tire equatorial plane is described. In the column of "Angle of circumferential main groove", the value of the angle α formed by the center line of the circumferential main groove with respect to the tire circumferential direction is described. In the column of "Presence or absence of bent portion", "Present" is indicated when the inclined fine groove includes a bent inclined fine groove having a bent portion, and "Absent" is indicated when it does not include a bent inclined fine groove. In the column of "Groove width of inclined fine groove", "Constant" is indicated when the groove width W1 on the indentation side and the groove width W2 on the kick-out side are the same, and "W1 < W2" is indicated when the groove width W2 on the kick-out side is wider than the groove width W1 on the indentation side. In the column of "Groove depth of inclined fine groove", "Constant" is indicated when the groove depth D1 on the indentation side and the groove depth D2 on the kick-out side are the same, and "D1 < D2" is indicated when the groove depth D1 on the indentation side is shallower than the groove depth D2 on the kick-out side. The column of "angle of the bending inclined groove" describes the value of the angle β formed by the center line of the circumferential portion with respect to the tire circumferential direction. The column of "presence or absence of the bottom raising portion" describes "present" when the second branch groove has a bottom raising portion, and "absent" when it does not have a bottom raising portion. The column of "groove depth (%) of the circumferential portion" describes the ratio (%) of D3 to DG when the groove depth of the second branch groove at the bottom raising portion is D3 and the groove depths of the two circumferential main grooves are DG. The column of "relationship between groove area A1 and groove area A2" describes the size relationship between the groove area A1 included in the center portion and the groove area A2 included in the middle portion.

[0070] The tires according to Examples 1 to 10 and the tires of the comparative example thus created were assembled on a 16×6.5J aluminum rim at 250 kPa, and each test tire was mounted on a test vehicle of the FF type (engine displacement: 1500 CC). Then, in accordance with the following procedures, in order to confirm the snow performance, wet performance, and dry performance, the handling stability on a snow-packed road surface, a wet road surface, and a dry road surface was evaluated.

[0071] (Handling stability on a snow-packed road surface) When the vehicle equipped with each test tire was driven on the test course of the snow-packed road surface, a sensory evaluation by the test driver was carried out. Then, based on this result, an index evaluation was performed with the comparative example as the reference (100). The evaluation results are also shown in Table 1. This evaluation indicates that the larger the index, the better the handling stability on the snow-packed road surface.

[0072] (Handling stability on a wet road surface) When the vehicle equipped with each test tire was driven on the test course of the wet road surface (water film: 1 mm), a sensory evaluation by the test driver was carried out. Then, based on this result, an index evaluation was performed with the comparative example as the reference (100). The evaluation results are also shown in Table 1. This evaluation indicates that the larger the index, the better the handling stability on the wet road surface.

[0073] (Handling stability on a dry road surface) A test course on a dry road surface with a flat circumferential groove was driven by a test vehicle at speeds ranging from 10 km / h to 180 km / h, and a sensory evaluation was conducted by a test driver on the steering performance during lane changes and cornering, and the stability during straight driving. Based on these results, an index evaluation was performed with the comparative example as the reference (100). The evaluation results are also shown in Table 1. This evaluation indicates that the larger the index, the better the handling stability on a dry road surface.

[0074]

Table 1

[0075] (Results) By comparing Examples 1 to 10 with Comparative Example 1, it was found that having a circumferential main groove and a plurality of inclined fine grooves improves drainage and increases the edge component, thus improving wet performance and snow performance. Note that although Examples 1 to 6 have two inclined fine grooves and are inferior in dry performance compared to Comparative Example 1, the impact on the actual performance is limited and thus within an acceptable range.

[0076] By comparing Example 1 and Example 2, it was found that when the angle α of the circumferential main groove is within the range of ±5°, drainage is improved and wet performance is enhanced.

[0077] By comparing Example 2 and Example 3, it was found that having a bent inclined fine groove increases the edge component and the groove area, thus improving snow performance and wet performance.

[0078] By comparing Example 3 and Example 4, it was found that for the inclined fine groove, the groove width W2 on the kicking side is wider than the groove width W1 on the stepping-in side, which improves drainage and wet performance.

[0079] By comparing Example 4 and Example 5, it was found that the drainage performance is improved by the fact that the groove depth D1 on the stepping side is shallower than the groove depth D2 on the kicking-out side in the bent inclined fine groove, and the decrease in the block rigidity on the stepping side is suppressed, and the wet performance and dry performance can be improved.

[0080] By comparing Example 5 and Example 6, it was found that the drainage performance is improved and the wet performance is improved by the fact that the angle formed by the center line on the stepping side of the bent inclined fine groove with respect to the tire circumferential direction is within the range of ±5°.

[0081] By comparing Example 6 and Example 7, it was found that at least a part of the second branch groove disposed within the range of 5% of the contact width from the tire equatorial plane has a raised bottom portion that makes the groove depth of the second branch groove shallower than the groove depths of the two circumferential main grooves, so that the block rigidity is increased and the dry performance can be maintained equivalent to that of the comparative example.

[0082] By comparing Example 7 and Example 8, it was found that the groove depth of the second branch groove in the raised bottom portion is in the range of 40% or more and 60% or less of the groove depths of the two circumferential main grooves, so that the block rigidity is increased and the dry performance can be improved.

[0083] By comparing Example 8 and Example 9, when the groove depth of the second branch groove in the raised bottom portion is 30% of the groove depths of the two circumferential main grooves, the block rigidity is increased and the dry performance is improved, but the groove volume is reduced accordingly, so that the improved snow performance and wet performance are reduced.

[0084] By comparing Example 8 and Example 10, it was found that the block rigidity is maintained at a certain level or higher and the dry performance can be improved by the fact that the groove area A1 included in the center portion is smaller than the groove area A2 included in each middle portion.

Explanation of Signs

[0085] 10 Tire 12 Tread portion 14 Tread surface 16 Circumferential main groove Center line of the 16C circumferential main groove Opening of the 16E circumferential main groove 16L First circumferential main groove 16R Second circumferential main groove 18 V-shaped groove 20 Tip 22 Center land 24 Sipe 26 Lug groove 28 Shoulder land 30 Inclined fine groove 32 First branch groove 34 Second branch groove 36 Notch 38 Straight inclined fine groove 40 Bent inclined fine groove 42 Inclined part 44 Bent part 46 Circumferential part 48 Opening on the stepped-in side of the inclined fine groove 50 Opening on the kicked-out side of the inclined fine groove 52 Stepped-in side part 54 Raised bottom part 56 Center part 58 Middle part 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 on its tread surface two circumferential main grooves and a plurality of V-shaped grooves arranged inside the two circumferential main grooves in the tire width direction and spaced apart from each other in the tire circumferential direction, wherein a center land portion is defined by the two circumferential main grooves and the V-shaped grooves adjacent to each other in the tire circumferential direction, and the tire has a designated direction of rotation, the two circumferential main grooves are provided on both sides in the tire width direction with the tire equatorial plane interposed therebetween, and extend in the tire circumferential direction, the V-shaped grooves have tip portions protruding in a V-shape toward one side in the tire circumferential direction, and extend while inclining toward both sides in the tire width direction from the tip portions toward the other side in the tire circumferential direction, and communicate with the two circumferential main grooves, a plurality of inclined fine grooves are provided respectively between the tire equatorial plane and one circumferential main groove and between the tire equatorial plane and the other circumferential main groove, the inclined fine grooves incline outward in the tire width direction toward one side in the tire circumferential direction, and communicate with the adjacent V-shaped grooves in the tire circumferential direction respectively, the tip portions are provided with a first branch groove and a second branch groove extending from the tip portions toward one side in the tire circumferential direction, the first branch groove terminates within the center land portion, the second branch groove communicates with the V-shaped groove adjacent to one side in the tire circumferential direction. A tire.

2. The tire according to claim 1, wherein an angle formed by the center line of each of the two circumferential main grooves with respect to the tire circumferential direction is within a range of ±5°.

3. The tire according to claim 1, wherein a part of the plurality of inclined fine grooves is a bent inclined fine groove including a bent portion having a shape convex outward in the tire width direction.

4. The tire according to claim 1, wherein the groove width on the kicking-out side is wider than the groove width on the stepping-in side of the inclined fine groove.

5. The tire according to claim 3, wherein the groove depth on the stepping-in side of the bent inclined fine groove is shallower than the groove depth on the kicking-out side.

6. The tire according to claim 3, wherein an angle formed by the center line on the stepping-in side of the bent inclined fine groove with respect to the tire circumferential direction is within a range of ±5°.

7. With respect to the contact width in a state where a normal internal pressure is applied and a load of 80% of the normal load is applied, at least a part of the second branch groove disposed within a range of 5% of the contact width from the tire equatorial plane has a bottom-raising portion that makes the groove depth of the second branch groove shallower than the groove depth of the two circumferential main grooves. The tire according to claim 1.

8. Some of the plurality of the inclined grooves are bent inclined grooves including a bent portion having a shape convex to the outer side in the tire width direction. The groove depth of the second branch groove in the raised portion is in the range of 40% or more and 60% or less of the groove depth of the two circumferential main grooves, and is shallower than the groove depth on the indentation side of the bent inclined groove. The tire according to claim 7.

9. With respect to the contact width in a state where the normal internal pressure is applied and a load of 80% of the normal load is applied, a range of 20% of the contact width in the tire width direction centered on the tire equatorial plane is defined as the center portion, and the range of 20% of the contact width adjacent to the outside in the tire width direction of the center portion is defined as the middle portion respectively. The tire according to claim 1, wherein the groove area included in the center portion is smaller than the groove areas included in the respective middle portions.

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